| 1. |
- Boelhouwers, Jan, et al.
(författare)
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Observations on a blockstream in the vicinity of Sani Pass, Lesotho Highlands, southern Africa
- 2002
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Ingår i: Permafrost and Periglacial Processes. - : Wiley. - 1045-6740 .- 1099-1530. ; 13:4, s. 251-257
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Tidskriftsartikel (refereegranskat)abstract
- Coarse slope deposits, frequently grading into blockstreams, are common throughout the Lesotho highlands, southern Africa. This paper describes one such blockstream. It is interpreted as a typical lag deposit derived from valley-wide colluvial mantles, which contains superimposed and incorporated Late-Pleistocene blocky material. Blocks are largely derived from local scarps but may contain a component of corestones from mobilized regolith. The widespread mantle argues against landscape-scale glaciation in the Lesotho highlands in the Late Pleistocene. Rather, the environment appears to have been conducive to deep seasonal frost during the period of block production. No unequivocal evidence for permafrost is found.
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| 2. |
- Christiansen, H. H., et al.
(författare)
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The Thermal State of Permafrost in the Nordic Area during the International Polar Year 2007-2009
- 2010
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Ingår i: Permafrost and Periglacial Processes. - : Wiley. - 1099-1530 .- 1045-6740. ; 21:2, s. 156-181
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Tidskriftsartikel (refereegranskat)abstract
- This paper provides a snapshot of the permafrost thermal state in the Nordic area obtained during the International Polar Year (IPY) 2007-2009. Several intensive research campaigns were undertaken within a variety of projects in the Nordic countries to obtain this snapshot. We demonstrate for Scandinavia that both lowland permafrost in palsas and peat plateaus, and large areas of permafrost in the mountains are at temperatures close to 0 degrees C, which makes them sensitive to climatic changes. In Svalbard and northeast Greenland, and also in the highest parts of the mountains in the rest of the Nordic area, the permafrost is somewhat colder, but still only a few degrees below the freezing point. The observations presented from the network of boreholes, more than half of which were established during the IPY, provide an important baseline to assess how future predicted climatic changes may affect the permafrost thermal state in the Nordic area. Time series of active-layer thickness and permafrost temperature conditions in the Nordic area, which are generally only 10 years in length, show generally increasing active-layer depths and risings permafrost temperatures. Copyright (C) 2010 John Wiley & Sons, Ltd.
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| 3. |
- Gisnås, Kjersti, et al.
(författare)
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Permafrost Map for Norway, Sweden and Finland
- 2017
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Ingår i: Permafrost and Periglacial Processes. - : Wiley. - 1045-6740 .- 1099-1530. ; 28:2, s. 359-378
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Tidskriftsartikel (refereegranskat)abstract
- A research-based understanding of permafrost distribution at a sufficient spatial resolution is important to meet the demands of science, education and society. We present a new permafrost map for Norway, Sweden and Finland that provides a more detailed and updated description of permafrost distribution in this area than previously available. We implemented the CryoGRID1 model at 1km(2) resolution, forced by a new operationally gridded data-set of daily air temperature and snow cover for Finland, Norway and Sweden. Hundred model realisations were run for each grid cell, based on statistical snow distributions, allowing for the representation of sub-grid variability of ground temperature. The new map indicates a total permafrost area (excluding palsas) of 23 400km(2) in equilibrium with the average 1981-2010 climate, corresponding to 2.2 per cent of the total land area. About 56 per cent of the area is in Norway, 35 per cent in Sweden and 9 per cent in Finland. The model results are thoroughly evaluated, both quantitatively and qualitatively, as a collaboration project including permafrost experts in the three countries. Observed ground temperatures from 25 boreholes are within +/- 2 degrees C of the average modelled grid cell ground temperature, and all are within the range of the modelled ground temperature for the corresponding grid cell. Qualitative model evaluation by field investigators within the three countries shows that the map reproduces the observed lower altitudinal limits of mountain permafrost and the distribution of lowland permafrost.
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| 4. |
- Hugelius, Gustaf, et al.
(författare)
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Soil Organic Carbon Pools in a Periglacial Landscape; a Case Study from the Central Canadian Arctic
- 2010
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Ingår i: Permafrost and Periglacial Processes. - : Wiley. - 1045-6740 .- 1099-1530. ; 21:1, s. 16-29
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Tidskriftsartikel (refereegranskat)abstract
- We investigated total storage and landscape partitioning of soil organic carbon (SOC) in continuous permafrost terrain, central Canadian Arctic. The study is based on soil chemical analyses of pedons sampled to 1-m depth at 35 individual sites along three transects. Radiocarbon dating of cryoturbated soil pockets, basal peat and fossil wood shows that cryoturbation processes have been occurring since the Middle Holocene and that peat deposits started to accumulate in a forest-tundra environment where spruce was present (∼6000 cal yrs BP). Detailed partitioning of SOC into surface organic horizons, cryoturbated soil pockets and non-cryoturbated mineral soil horizons is calculated (with storage in active layer and permafrost calculated separately) and explored using principal component analysis. The detailed partitioning and mean storage of SOC in the landscape are estimated from transect vegetation inventories and a land cover classification based on a Landsat satellite image. Mean SOC storage in the 0–100-cm depth interval is 33.8 kg C m−2, of which 11.8 kg C m−2 is in permafrost. Fifty-six per cent of the total SOC mass is stored in peatlands (mainly bogs), but cryoturbated soil pockets in Turbic Cryosols also contribute significantly (17%). Elemental C/N ratios indicate that this cryoturbated soil organic matter (SOM) decomposes more slowly than SOM in surface O-horizons.
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| 5. |
- Jelinski, Nicolas A., et al.
(författare)
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Utilising a suite of isotopic and elemental tracers to constrain cryoturbation rates and patterns in a non-sorted circle
- 2017
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Ingår i: Permafrost and Periglacial Processes. - : John Wiley & Sons. - 1045-6740 .- 1099-1530. ; 28:4, s. 634-648
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Tidskriftsartikel (refereegranskat)abstract
- The empirical quantification of rates of material movement in cryoturbated soils has lagged behind the physical and chemical characterisation of these materials. We applied a novel suite of elemental (C, Hg), stable isotope (C-13) and radioisotope (Cs-137, Pb-210, C-14, Be-10) tracers in conjunction with analytical and numerical models to constrain the rates and patterns of soil movement due to cryoturbation in a non-sorted circle (NSC) near Abisko, Sweden. We present the first observations of the variability of Be-10 across a patterned-ground feature, which facilitate the interpretation of subsurface peaks in soil organic carbon, Hg and C-13 and provide constraints on the surficial histories of cryoturbated materials. Apparent rates of surficial lateral movement across the NSC estimated from Cs-137 and Pb-210 (0-2.55cm year(-1)) decreased with distance from its centre and were an order of magnitude greater than rates of subduction and subsurface movement estimated from C-14 (0.04-0.27cm year(-1)). Novel estimates of the original surficial residence times of cryoturbated parcels based on excess Be-10 and Hg inventories ranged from 238 to 3940years. Our results demonstrate the utility of the spatially explicit application of elemental and radioisotopic tracer suites to constrain cryoturbation rates in Arctic patterned ground.
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| 6. |
- Klaminder, Jonatan, 1976-, et al.
(författare)
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Using Short-lived Radionuclides to Estimate Rates of Soil Motion in Frost Boils
- 2014
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Ingår i: Permafrost and Periglacial Processes. - : Wiley. - 1099-1530 .- 1045-6740. ; 25:3, s. 184-193
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Tidskriftsartikel (refereegranskat)abstract
- Cryoturbation in high-latitude soils is crucial for the long-term cycling of elements, but the rates of soil motion are poorly constrained. Here, we test whether the rate of frost creep, soil erosion and vertical soil mixing in frost boils can be estimated using short-lived radionuclides (Cs-137 and Pb-210). We find a small-scale variation in Cs-137 and Pb-210 inventories in the lower levels of the eroding regions of frost boils in comparison to the expected depositional sites; hence, the distribution of the radionuclides appears to reflect a lateral transport of atmospheric fallout from the centre of the boil (inner domain) towards the surrounding soil (outer domain). C-14 dating of the soil indicates that fallout of Cs-137 was mobile in the soil and that Pb-210 moved with the soil matrix. A soil creep model and a surface soil erosion model are derived and applied to the lateral and vertical distributions of Pb-210 in the frost boil. Both models predict the expected trajectories of soil motion and provide rates of creep, erosion and mixing at a mm yr(-1) to cm yr(-1) scale. The distribution of Pb-210 provides new insights about the processes and rates of soil mass movement in frost boils, if sound mass-balance models are applied.
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| 7. |
- Klaus, Marcus, et al.
(författare)
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Cryogenic Soil Activity along Bioclimatic Gradients in Northern Sweden : Insights from Eight Different Proxies
- 2013
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Ingår i: Permafrost and Periglacial Processes. - : John Wiley & Sons. - 1045-6740 .- 1099-1530. ; 24:3, s. 210-223
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Tidskriftsartikel (refereegranskat)abstract
- Cryogenic soil activity caused by differential soil movements during freeze-thaw cycles is of fundamental importance for Arctic ecosystem functioning, but its response to climate warming is uncertain. Eight proxies of cryogenic soil activity (including measurements of soil surface motion, vegetation and grey values of aerial photographs) were examined at eight study sites where non-sorted patterned ground spans an elevation gradient (400-1150 m asl) and a precipitation gradient (300-1000 mm yr(-1)) near Abisko, northern Sweden. Six proxies were significantly correlated with each other (mean |r|=0.5). Soil surface motion increased by three to five times along the precipitation gradient and was two to four times greater at intermediate elevations than at low and high elevations, a pattern reflected by vegetation assemblages. The results suggest that inferences about how cryogenic soil activity changes with climate are independent of the choice of the proxy, although some proxies should be applied carefully. Four preferred proxies indicate that cryogenic soil activity may respond differently to climate warming along the elevation gradient and could be greatly modified by precipitation. This underlines the strong but spatially complex response of cryogenic processes to climate change in the Arctic. Copyright (c) 2013 John Wiley & Sons, Ltd.
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| 8. |
- Kuhry, Peter, et al.
(författare)
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Characterisation of the Permafrost Carbon Pool
- 2013
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Ingår i: Permafrost and Periglacial Processes. - : Wiley. - 1045-6740 .- 1099-1530. ; 24:2, s. 146-155
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Tidskriftsartikel (refereegranskat)abstract
- The current estimate of the soil organic carbon (SOC) pool in the northern permafrost region of 1672 Petagrams (Pg) C is much larger than previously reported and needs to be incorporated in global soil carbon (C) inventories. The Northern Circumpolar Soil Carbon Database (NCSCD), extended to include the range 0-300cm, is now available online for wider use by the scientific community. An important future aim is to provide quantitative uncertainty ranges for C pool estimates. Recent studies have greatly improved understanding of the regional patterns, landscape distribution and vertical (soil horizon) partitioning of the permafrost C pool in the upper 3m of soils. However, the deeper C pools in unconsolidated Quaternary deposits need to be better constrained. A general lability classification of the permafrost C pool should be developed to address potential C release upon thaw. The permafrost C pool and its dynamics are beginning to be incorporated into Earth System models, although key periglacial processes such as thermokarst still need to be properly represented to obtain a better quantification of the full permafrost C feedback on global climate change.
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| 9. |
- Kuhry, P., et al.
(författare)
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Potential Remobilization of Belowground Permafrost Carbon under Future Global Warming
- 2010
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Ingår i: Permafrost and Periglacial Processes. - : Wiley. - 1045-6740 .- 1099-1530. ; 21:2, s. 208-214
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Tidskriftsartikel (refereegranskat)abstract
- Research on permafrost carbon has dramatically increased in the past few years. A new estimate of 1672 Pg C of belowground organic carbon in the northern circumpolar permafrost region more than doubles the previous value and highlights the potential role of permafrost carbon in the Earth System. Uncertainties in this new estimate remain due to relatively few available pedon data for certain geographic sectors and the deeper cryoturbated soil horizons, and the large polygon size in the soil maps used for upscaling. The large permafrost carbon pool is not equally distributed across the landscape: peat deposits, cryoturbated soils and the loess-like deposits of the yedoma complex contain disproportionately large amounts of soil organic matter, often exhibiting a low degree of decomposition. Recent findings in Alaska and northern Sweden provide strong evidence that the deeper soil carbon in permafrost terrain is starting to be released, supporting previous reports from Siberia. The permafrost carbon pool is not yet fully integrated in climate and ecosystem models and an important objective should be to define typical pedons appropriate for model setups. The thawing permafrost carbon feedback needs to be included in model projections of future climate change.
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| 10. |
- Lindgren, Amelie, et al.
(författare)
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GIS-based Maps and Area Estimates of Northern Hemisphere Permafrost Extent during the Last Glacial Maximum
- 2016
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Ingår i: Permafrost and Periglacial Processes. - : Wiley. - 1045-6740 .- 1099-1530. ; 27:1, s. 6-16
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Tidskriftsartikel (refereegranskat)abstract
- This study presents GIS-based estimates of permafrost extent in the northern circumpolar region during the Last Glacial Maximum (LGM), based on a review of previously published maps and compilations of field evidence in the form of ice-wedge pseudomorphs and relict sand wedges. We focus on field evidence localities in areas thought to have been located along the past southern border of permafrost. We present different reconstructions of permafrost extent, with areal estimates of exposed sea shelf, ice sheets and glaciers, to assess areas of minimum, likely and maximum permafrost extents. The GIS-based mapping of these empirical reconstructions allows us to estimate the likely area of northern permafrost during the LGM as 34.5 million km(2) (which includes 4.7 million km(2) of permafrost on exposed coastal sea shelves). The minimum estimate is 32.7 million km(2) and the maximum estimate is 35.3 million km(2). The extent of LGM permafrost is estimated to have been between c. 9.1 to 11.7 million km(2) larger than its current extent on land (23.6 million km(2)). However, 2.4 million km(2) of the lost land area currently remains as subsea permafrost on the submerged coastal shelves. The LGM permafrost extent in the northern circumpolar region during the LGM was therefore about 33 percent larger than at present. The net loss of northern permafrost since the LGM is due to its disappearance in large parts of Eurasia, which is not compensated for by gains in North America in areas formerly covered by the Laurentide ice sheet.
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| 11. |
- Nieuwendam, Alexandre, et al.
(författare)
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Reconstructing cold climate paleoenvironments from micromorphological analysis of relict slope deposits (Serra da Estrela, Central Portugal)
- 2020
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Ingår i: Permafrost and Periglacial Processes. - : Wiley. - 1099-1530 .- 1045-6740. ; 31:4, s. 567-586
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Tidskriftsartikel (refereegranskat)abstract
- The paper focuses on analysis of macro‐ and micromorphological characteristics of relict slope deposits in Serra da Estrela (Portugal) to understand the significance of different slope processes and paleoenvironmental settings. Micromorphology is a useful sedimentology technique allowing significant advances compared to macroscopic techniques. Results show that different processes are involved in the development of the slope deposits, reflecting different environmental conditions. The main processes responsible for the emplacement of the relict slope deposits are solifluction, debris‐flow and runoff, but postdepositional changes are also present. Solifluction was identified in slope deposits between 650 and 1500 m a.s.l. The common microfeatures identified are circular arrangement of grains with a core grain, rounded vesicles, vertical grains, matrix deformations and fine‐grained deposits. Slope deposits above 1300 m a.s.l have a platy microstructure and coincide with the altitudinal range of the relict rock glaciers, indicating the elevation limit of permafrost. Below this altitude platy microstructures are less frequent. Slope deposits in north‐facing slopes were affected by frost‐induced processes in a seasonal frost regime, followed by a postdeposition illuvial phase. Debris‐flow and runoff were identified in slope deposits between 680 and 1260 m a.s.l. The common microfeatures are oblique grains, grain dumps, and coarse and fine grain lineations, and banded microstructures were identified in runoff processes. Debris‐flow deposits have a circular arrangement of grains without a core grain, identified in sediments in paraglacial and periglacial environments. The slope deposits show evidence of past periods of enhanced periglacial activity since the last glaciation until the Younger Dryas.
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| 12. |
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| 13. |
- Palmtag, Juri, et al.
(författare)
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Grain size controls on cryoturbation and soil organic carbon density in permafrost-affected soils
- 2018
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Ingår i: Permafrost and Periglacial Processes. - : Wiley. - 1045-6740 .- 1099-1530. ; 29:2, s. 112-120
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Tidskriftsartikel (refereegranskat)abstract
- This meta-analysis aims to describe the relationship between grain size distributions and soil organic carbon (SOC) storage in mineral subsoil and SOC-enriched cryoturbated pockets in five areas of continuous permafrost that differ in glaciation history and soil parent materials. Our results show a positive relationship between the proportion of soil particles in fine-grained fractions (colloid to medium silt) and SOC storage. Finer textured soils had significantly higher SOC storage in mineral subsoil samples (not SOC-enriched through cryoturbation) than coarser textured soils. However, the process of SOC enrichment through cryoturbation was most pronounced in soils with coarser grain sizes in the range of coarse silt and very fine sand. Although fine-grained textures provide better physical and biochemical protection for soil organic matter, their strong cohesion reduces the mixing of soil horizons and the effectiveness of cryoturbation. A higher ratio of coarse silt to clay in samples was a good predictor of SOC enrichment through cryoturbation across soil samples, soil profiles and study areas.
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| 14. |
- Ridefelt, Hanna, et al.
(författare)
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Observations on Regional Variation in Solifluction Landform Morphology and Environment in the Abisko, northern Sweden
- 2006
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Ingår i: Permafrost and Periglacial Processes. - : Wiley. - 1045-6740 .- 1099-1530. ; 17:3, s. 253-266
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Tidskriftsartikel (refereegranskat)abstract
- Turf-banked lobes and terraces on the valley slopes and stone-banked or non-sorted lobes at summits show a distinct regional trend of decreasing size from west to east in the Abisko region, northern Sweden. Significant correlations with environmental parameters exist between morphometry and elevation, soil moisture and soil texture. At a regional scale, high soil moisture environments can be associated with larger dimensions. The turf-banked forms in the valleys are associated with deep seasonal snow cover and therefore saturated conditions are believed to enhance gelifluction at these locations. The smaller forms on the vegetation- and snow-free summit sites are believed to be dominated by frost creep.
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| 15. |
- Ridefelt, Hanna, 1977-, et al.
(författare)
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Spatial analysis of solifluction landforms and process rates in the Abisko Mountains, northern Sweden
- 2010
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Ingår i: Permafrost and Periglacial Processes. - : Wiley. - 1045-6740 .- 1099-1530. ; 21:3, s. 241-255
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Tidskriftsartikel (refereegranskat)abstract
- The occurrence of turf-banked solifluction landforms in the Abisko region was analysed using a grid-based approach and statistical modelling through logistic regression. Significant parameters in the model were the vegetation index NDVI, annual incoming potential radiation, wetness index, slope gradient and elevation. The model had an acceptable discrimination capacity and rather low model-fit values, but clearly showed the importance of vegetation patterns for the occurrence of solifluction at a regional scale. Solifluction movement rates measured at eight sites were combined with model parameters and the annual duration of sun hours to regionalise solifluction movement rates through an unsupervised terrain classification. For comparison, the linear relationship between the probability of solifluction occurrence and variations in movement rates was also used to regionalise movement rates. Potential geomorphic work was calculated for six different areas within the region, with the greatest being for Ka " rkevagge, the area with the highest precipitation. The combination of a logistic regression model of mapped landforms and field measurements of solifluction rates represents a promising methodology to assess the occurrence and activity of the process at a regional scale.
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| 16. |
- Sanchez-Garcia, Laura, et al.
(författare)
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Characterisation of Three Regimes of Collapsing Arctic Ice Complex Deposits on the SE Laptev Sea Coast using Biomarkers and Dual Carbon Isotopes
- 2014
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Ingår i: Permafrost and Periglacial Processes. - : Wiley. - 1045-6740 .- 1099-1530. ; 25:3, s. 172-183
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Tidskriftsartikel (refereegranskat)abstract
- Arctic amplification of climate warming is intensifying the thaw and coastal erosion of the widespread and carbon-rich Siberian Ice Complex Deposits (ICD). Despite the potential for altering long-term carbon dynamics in the Arctic, the susceptibility of organic carbon (OC) to degradation as the ICD thaw is poorly characterised. This study identifies signs of OC degradation in three Siberian ICD regimes of coastal erosion through elemental, isotopic and molecular analyses. The degree of erosion appears to determine the extent of degradation. The moisture-limited and beach-protected ICD bluff near Buor-Khaya Cape, characterised by thermokarst mounds (baydzherakhs), represents a dormant regime with limited ongoing degradation. Conversely, the more exposed ICD scarps on eroding riverbanks (Olenek Channel, Lena Delta) and coastal slopes (Muostakh Island) showed more pronounced signs of ongoing OC decay. Different parameters suggest that degradation can partially explain the shift of the OC signature with C-14 age in the thawing ICD. Exposure time, degree of erosion, slope gradient and moisture conditions appear to be key factors determining the degradation propensity of OC in exposed ICD. These field results document the lability of OC in ICD upon thaw and illustrate the potential for transferring old OC into the rapidly cycling atmosphere-biosphere carbon pools.
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| 17. |
- Sannel, A. Britta K.
(författare)
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Ground temperature and snow depth variability within a subarctic peat plateau landscape
- 2020
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Ingår i: Permafrost and Periglacial Processes. - : Wiley. - 1045-6740 .- 1099-1530. ; 31:2, s. 255-263
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Tidskriftsartikel (refereegranskat)abstract
- Subarctic permafrost peatlands cover extensive areas and store large amounts of soil organic carbon that can be remobilized as active layer deepening and thermokarst formation increase in a future warmer climate. Better knowledge of ground thermal variability within these ecosystems is important for understanding future landscape development and permafrost carbon feedbacks. In a peat plateau complex in Tavvavuoma, northern Sweden, ground temperatures and snow depth have been monitored in six different landscape units: on a peat plateau, in a depression within a peat plateau, along a peat plateau edge (close to a thermokarst lake), at a thermokarst lake shoreline, in a thermokarst lake and in a fen. Permafrost is present in all three peat plateau landscape units, and mean annual ground temperature (MAGT) in the central parts of the peat plateau is -0.3 degrees C at 2 m depth. In the three low-lying wetter or saturated landscape units (along the thermokarst lake shoreline, in the lake and the fen) taliks are present and MAGT at 1 m depth is 1.0-2.7 degrees C. Topographical differences between the elevated and low-lying units affect both local snow depth and soil moisture, and are important for ground thermal patterns in this landscape. Permafrost exists in landscape units with a shallow mean December-April snow depth (<20 cm) whereas snow depths >40 cm mostly result in absence of permafrost.
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| 18. |
- Sannel, A. Britta K., et al.
(författare)
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Permafrost Warming in a Subarctic Peatland - Which Meteorological Controls are Most Important?
- 2016
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Ingår i: Permafrost and Periglacial Processes. - : Wiley. - 1045-6740 .- 1099-1530. ; 27:2, s. 177-188
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Tidskriftsartikel (refereegranskat)abstract
- Because climate change can affect the carbon balance and hydrology in permafrost peatlands, a better understanding of their sensitivity to changes in temperature and precipitation is needed. In Tavvavuoma, northernmost Sweden, meteorological parameters and ground thermal properties have been monitored in a peat plateau from 2006 to 2013. During this time period, the air temperature record shows no warming trend, and the late-season thaw depth has been relatively stable at around 55-60cm. Meanwhile, the mean annual ground temperature at 1m depth has increased by 0.06 degrees C/yr and at 2-5m depth the permafrost is currently warmer than -0.3 degrees C. Statistical analyses suggest that interannual changes in thaw depth and ground temperatures are affected by different meteorological factors. Summer air temperatures and annual thawing degree-days control thaw depth (p0.05), whereas winter precipitation/snow depth affects ground temperatures (p0.1). The permafrost in this peat plateau is likely relict and not in equilibrium with current climatic conditions. Since the early 20(th) century, there has been a regional increase in air temperature and snow depth. If the ongoing permafrost warming in Tavvavuoma is a result of these long-term trends, short-term variability in meteorological parameters can still have an impact on the rate of permafrost degradation, but unless pronounced climate cooling occurs, thawing of the peat plateau is inevitable.
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| 19. |
- Sjöberg, Ylva, et al.
(författare)
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Hot trends and impact in permafrost science
- 2020
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Ingår i: Permafrost and Periglacial Processes. - : John Wiley & Sons. - 1045-6740 .- 1099-1530. ; 31:4, s. 461-471
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Tidskriftsartikel (refereegranskat)abstract
- An increased interest in Arctic environments, mainly due to climate change, has changed the conditions for permafrost research in recent years. This change has been accompanied by a global increase in scientific publications, as well as a trend towards open access publications. We have analyzed abstracts, titles and keywords for publications on permafrost from 1998 to 2017 to identify developments (topics, impact and collaboration) in the field of permafrost research in light of these changes. Furthermore, to understand how scientists build on and are inspired by each other's work, we have (a) developed citation networks from scientific publications on permafrost and (b) conducted an online survey on inspiration in permafrost science. Our results show an almost 400% increase in publications containing the word permafrost in the title, keywords or abstract over the study period, and a strong increase in climate-change-related research in terms of publications and citations. Survey respondents (n = 122) find inspiration not only in scientific journal publications, but to a large extent in books and public outreach materials. We argue that this increase in global-scope issues (i.e., climate change) complementing core permafrost research has provided new incentives for international collaborations and wider communication efforts.
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| 20. |
- Sjöberg, Ylva, et al.
(författare)
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Thermokarst Lake Morphometry and Erosion Features in Two Peat Plateau Areas of Northeast European Russia
- 2013
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Ingår i: Permafrost and Periglacial Processes. - : Wiley. - 1045-6740 .- 1099-1530. ; 24:1, s. 75-81
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Tidskriftsartikel (refereegranskat)abstract
- High-resolution satellite remote sensing analysis (n=637 lakes) and field measurements (n=29 lakes) of two peat plateau areas in northeast European Russia were carried out to investigate lake morphology, map shoreline erosion indicators and assess possible orientation patterns in lake and shore morphology. The study includes the first detailed characterisation of the shape and size of thermokarst lakes in organic terrain. The area covered by lakes is 7.0 per cent and 13.6 per cent, and median lake size is 184m2 and 265m2, respectively, for the two study areas. In both areas, most lakes have a similar northwest to southeast orientation, and shores most commonly face northeast or southwest. The shores are generally steeper and have more cracks and lake depths are greater along shores facing northeast or southeast, and along the shorelines of larger lakes. Shores with a peat substrate are more heterogeneous than those with a mineral substrate in terms of steepness, cracks and water depths. Since the lakes are generally small, the shoreline/area ratio is high and a large part of the peat plateau areas can potentially be affected by shoreline erosion.
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| 21. |
- Stammler, Melanie, et al.
(författare)
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Geographic object‐based image analysis (GEOBIA) of the distribution and characteristics of aeolian sand dunes in Arctic Sweden
- 2023
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Ingår i: Permafrost and Periglacial Processes. - : John Wiley & Sons. - 1045-6740 .- 1099-1530. ; 34:1, s. 22-36
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Tidskriftsartikel (refereegranskat)abstract
- Current climate change in the Arctic is unprecedented in the instrumental record, with profound consequences for the environment and landscape. In Arctic Sweden, aeolian sand dunes have been impacted by climatic changes since their initial formation after the retreat of the last glacial ice sheet. Dune type, location and orientation can therefore be used to explore past wind patterns and landscape destabilisation in this sensitive area. However, knowledge of the full spatial extent and characteristics of these dunes is limited by their inaccessibility and dense vegetation cover. Geographic object-based image analysis (GEOBIA) permits the semi-automatic creation of reproducible parameter-based objects and can be an appropriate means to systematically and spatially map these dunes remotely. Here, a digital elevation model (DEM) and its derivatives, such as slope and curvature, were segmented in a GEOBIA context, enabling the identification and mapping of aeolian sand dunes in Arctic Sweden. Analysis of the GEOBIA-derived and expert-accepted polygons affirms the prevalence of parabolic dune type and reveals the coexistence of simple dunes with large coalesced systems. Furthermore, mapped dune orientations and relationships to other geomorphological features were used to explore past wind directions and to identify sediment sources as well as the reasons for sand availability. The results indicate that most dune systems in Arctic Sweden were initially supplied by glaciofluvial and fluvial disturbances of sandy esker systems. Topographic control of wind direction is the dominant influence on dune orientation. Further, our approach shows that analysing the GEOBIA-derived dune objects in their geomorphological context paves the way for successfully investigating aeolian sand dune location, type and orientation in Arctic Sweden, thereby facilitating the understanding of post-glacial landscape (in)stability and evolution in the area.
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| 22. |
- Stiegler, Christian, et al.
(författare)
-
An Undercooled Scree Slope Detected by Geophysical Investigations in Sporadic Permafrost below 1000 M ASL, Central Austria
- 2014
-
Ingår i: Permafrost and Periglacial Processes. - : Wiley. - 1099-1530 .- 1045-6740. ; 25:3, s. 194-207
-
Tidskriftsartikel (refereegranskat)abstract
- Multi-method geophysical investigations, accompanied by microclimatic measurements and vegetation mapping, were performed at an undercooled scree slope near Schladming (Austria) in the eastern Alps in order to detect, map and monitor mountain permafrost. The study site, at an elevation of 990m asl, is one of the lowest-lying examples of a cold, undercooled scree slope in the Alps. Geophysical measurements with electrical resistivity tomography, ground-penetrating radar and seismic refraction indicate the presence of several isolated areas of frozen ground over a full year, far below the regional lower limit of mountain permafrost. Frozen sediments identified at shallow depths (beneath 1-3m) were 5-20m thick and ice-rich. Near-surface temperatures at the foot of the scree slope were strongly influenced by pronounced cooling. Vegetation mapping showed a dominance of cryophilic plant species. The results suggest that the scree slope is strongly influenced by the interplay of vegetation cover, ground thermal regime and the distribution of frozen sediments. Copyright (C) 2014 John Wiley & Sons, Ltd.
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| 23. |
- Strand, Sarah, et al.
(författare)
-
Active layer thickening and controls on interannual variability in the Nordic Arctic compared to the circum-Arctic.
- 2020
-
Ingår i: Permafrost and Periglacial Processes. - : Wiley. - 1099-1530 .- 1045-6740. ; 32:1, s. 47-58
-
Tidskriftsartikel (refereegranskat)abstract
- Active layer probing in northern Sweden, northeast Greenland, and central Svalbard indicates active layer thickening has occurred at Circumpolar Active Layer Monitoring (CALM) sites with long‐term, continuous observations, since the sites were established at these locations in 1978, 1996, and 2000, respectively. The study areas exhibit a reverse latitudinal gradient in average active layer thickness (ALT), which is explained by site geomorphology and climate. Specifically, Svalbard has a more maritime climate and thus the thickest active layer of the study areas (average ALT = 99 cm, 2000–2018). The active layer is thinnest at the northern Sweden sites because it is primarily confined to superficial peat. Interannual variability in ALT is not synchronous across this Nordic Arctic region, but study sites in the same area respond similarly to local meteorology. ALT correlates positively with thawing degree days in Sweden and Greenland, as has been observed in other Arctic regions. However, ALT in Svalbard correlates with freezing degree days, where the maritime Arctic climate results in relatively high and variable winter air temperatures. The difference in annual ALT at adjacent sites is attributed to differences in snow cover and geomorphology. From 2000 to 2018, the average rate of active layer thickening at the Nordic Arctic CALM probing sites was 0.5 cm/yr. The average rate was 1 cm/yr for Nordic Arctic CALM database sites with significant trends, which includes a borehole in addition to probing sites. This range is in line with the circum‐Arctic average of 0.8 cm/yr from 2000 to 2018.
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| 24. |
- Vieira, Goncalo, et al.
(författare)
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Thermal State of Permafrost and Active-layer Monitoring in the Antarctic : Advances During the International Polar Year 2007–2009
- 2010
-
Ingår i: Permafrost and Periglacial Processes. - : Wiley. - 1045-6740 .- 1099-1530. ; 21:2, s. 182-197
-
Tidskriftsartikel (refereegranskat)abstract
- Results obtained during the International Polar Year (IPY) on the thermal state of permafrost and the active layer in the Antarctic are presented, forming part of ANTPAS (‘Antarctic Permafrost and Soils’), which was one of the key projects developed by the International Permafrost Association and the Scientific Committee for Antarctic Research for the IPY. The number of boreholes for permafrost and active-layer monitoring was increased from 21 to 73 during the IPY, while CALM-S sites to monitor the active layer were increased from 18 to 28. Permafrost temperatures during the IPY were slightly below 0°C in the South Shetlands near sea-level, showing that this area is near the climatic boundary of permafrost and has the highest sensitivity to climate change in the region. Permafrost temperatures were much lower in continental Antarctica: from the coast to the interior and with increasing elevation they ranged between −13.3°C and −18.6°C in Northern Victoria Land, from −17.4°C to −22.5°C in the McMurdo Dry Valleys, and down to −23.6°C at high elevation on Mount Fleming (Ross Island). Other monitored regions in continental Antarctica also showed cold permafrost: Queen Maud Land exhibited values down to −17.8°C on nunataks, while in Novolazarevskaya (Schirmacher Oasis) at 80 m a.s.l. the permafrost temperature was −8.3°C. The coastal stations of Molodeznaya at Enderby Land showed permafrost temperatures of −9.8°C, Larsemann Hills – Progress Station in the Vestfold Hills region – recorded −8.5°C, and Russkaya in Marie Byrd Land, −10.4°C. This snapshot obtained during the IPY shows that the range of ground temperatures in the Antarctic is greater than in the Arctic. Copyright © 2010 John Wiley & Sons, Ltd.
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| 25. |
- Åkerman, Jonas, et al.
(författare)
-
Thawing permafrost and thicker active layers in sub-arctic Sweden
- 2008
-
Ingår i: Permafrost and Periglacial Processes. - : Wiley. - 1099-1530 .- 1045-6740. ; 19:3, s. 279-292
-
Tidskriftsartikel (refereegranskat)abstract
- Observations of active-layer thickness from nine sites with up to 29 years of gridded measurements located in the Tornetrask region, northernmost Sweden, were examined in relation to climatic trends. Mean annual air temperatures in this area have warmed and recently rose above 0 degrees C. Active layers at all sites have become thicker, at rates ranging from 0.7 to 1.3 cm per year. This trend has accelerated in the past decade, especially in the westernmost site where rates have reached 2 cm per year and permafrost has disappeared at 81 per cent of the sampling points. Increased active-layer thicknesses are correlated with increases in mean summer air temperature, thawing degree-days and, in five of the nine sites, with increases in snow depth. Copyright (C) 2008 John Wiley & Sons, Ltd.
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| 26. |
- Backstöm, Daniel, et al.
(författare)
-
Modeling flexural vibration of a sandwich beam using modified fourth-order theory
- 2006
-
Ingår i: Journal of Sandwich Structures and Materials. - : SAGE Publications. - 1099-6362 .- 1530-7972. ; 8:6, s. 465-476
-
Tidskriftsartikel (refereegranskat)abstract
- The purpose of this study is to evaluate the possibility of using modified lower order methods - such as the Bernoulli-Euler or Timoshenko beam theories with frequency dependent parameters - to calculate the response of sandwich beams subject to different end conditions. The models have been verified by measurements on a freely suspended asymmetric sandwich beam with aluminum laminates and a plastic foam core, indicating good agreement.
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| 27. |
- Battley, Mark, et al.
(författare)
-
Characterization of Ductile Core Materials
- 2010
-
Ingår i: Journal of Sandwich Structures and Materials. - : SAGE Publications. - 1099-6362 .- 1530-7972. ; 12:2, s. 237-252
-
Tidskriftsartikel (refereegranskat)abstract
- This article describes an experimental investigation of characterization methods for ductile core materials. Full-field optical strain measurement methods are used to determine the strain distributions in standard testing methods such as block shear and four-point beam testing, particularly for highly ductile cores subjected to large deformations. The results show that the stress and strain fields in both block shear and sandwich beam tests are very different to those assumed by the testing standards. The test methods result in complex post yield states of stress in the core materials, meaning the core shear strength and ultimate shear strain should not be calculated by classical methods in the post yield region.
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| 28. |
- Bull, Peter Hoaas, et al.
(författare)
-
Curved sandwich beams with face-core debond subjected to bending moment
- 2004
-
Ingår i: Journal of Sandwich Structures and Materials. - : SAGE Publications. - 1099-6362 .- 1530-7972. ; 6:2, s. 115-127
-
Tidskriftsartikel (refereegranskat)abstract
- Curved sandwich beams subjected to opening bending moment are studied. Face-core debonds of varying size are introduced at the compressively loaded face sheet and the structural integrity is investigated. Analytical and finite element models are compared in order to identify the governing failure modes of the beams. A simple expression is presented as a tool for getting a quick estimate of the severity of an interface crack in a curved sandwich beam. Five different configurations of beams are tested experimentally in a custom made bending rig.
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| 29. |
- Bull, Peter Hoaas, et al.
(författare)
-
High-velocity and quasi-static impact of large sandwich panels
- 2004
-
Ingår i: Journal of Sandwich Structures and Materials. - : Sage Publications. - 1099-6362 .- 1530-7972. ; 6:2, s. 97-113
-
Tidskriftsartikel (refereegranskat)abstract
- An investigation of the response of sandwich structures subjected to impact velocities of virtually 0 m/s and approximately 1000 m/s is conducted. The higher velocity exceeds both the longitudinal and the transverse wave propagation velocities of the core material in the sandwich panels. The objective is to investigate the possibility to simulate the damage from ballistic impact of sandwich panels through quasi-static experiments. Panels are impacted using a 40 mm Bofors AA gun and, using a similar projectile, other panels are indented quasi-statically. Energy absorption is measured in both test series. After impact, the panels are tested in in-plane compression together with one undamaged panel for reference. Residual strength of impacted panels is analyzed by finite element analysis. It is shown that the damage from high-velocity impact is limited, and it is possible to regain most of the undamaged strength by repair.
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| 30. |
- Burman, Magnus, 1966-, et al.
(författare)
-
Blister propagation in sandwich panels
- 2019
-
Ingår i: Journal of Sandwich Structures and Materials. - : SAGE Publications Ltd. - 1099-6362 .- 1530-7972. ; 21:5, s. 1683-1699
-
Tidskriftsartikel (refereegranskat)abstract
- This paper deals with the problem of face/core interfacial disbonds in sandwich panels that are pressurised, i.e. the disbond has an initial fluid pressure that causes the disbond to deform. The problem is often referred to as a blister. The panel with a blister is then subjected to an in-plane compressive load. Four different panels are analysed and tested, having different size disbonds and different initial internal pressure. The cases are analysed using a finite element approach where the blister is modelled using fluid elements enabling the pressure inside the blister to vary as the in-plane load is applied. The analysis uses non-linear kinematics, and in each load step, the energy release rate is calculated along the disbond crack front. This model is used for failure load predictions. The four cases are then tested experimentally by filling a pre-manufactured disbond cavity with a prescribed volume of air. This air volume is then entrapped, and the panel is subjected to an in-plane compressive load. The load and blister pressures are measured throughout the test and compared with the finite element analysis. Surface strains and blister deformations are also measured using digital correlation measurements. The predicted failure loads compare well with the experimental results, and so does the blister pressures, the latter at least qualitatively. © The Author(s) 2019.
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| 31. |
- Cameron, Christopher John, et al.
(författare)
-
Structural-acoustic Design of a Multi-functional Sandwich Panel in an Automotive Context
- 2010
-
Ingår i: Journal of Sandwich Structures and Materials. - : SAGE Publications. - 1099-6362 .- 1530-7972. ; 12:6, s. 684-708
-
Tidskriftsartikel (refereegranskat)abstract
- This article deals with the design and weight optimization of a multi-functional vehicle body panel in an automotive context. An existing vehicle design has provided functional design requirements regarding static, dynamic, and acoustic behavior of the components of a car roof. A novel, multifunctional panel is proposed which integrates the component requirements present in a traditional roof system within a single module. The acoustic properties of two configurations of the novel panel are examined using numerical methods including advanced poro-elastic modeling tools compatible with Nastran, and compared with numerical results of a finite element model of the existing construction.
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| 32. |
- Fagerberg, Linus, et al.
(författare)
-
Effects of anisotropy and multiaxial loading on the wrinkling of sandwich panels
- 2005
-
Ingår i: Journal of Sandwich Structures and Materials. - : Sage Publications. - 1099-6362 .- 1530-7972. ; 7:3, s. 177-194
-
Tidskriftsartikel (refereegranskat)abstract
- The works that have been already published on sandwich face wrinkling consider isotropic or almost isotropic sandwich configurations. Hence, only the critical wrinkling load needs to be evaluated in the principal compressive stress direction. This is insufficient for a sandwich panel with a higher degree of anisotropy. This paper presents a method for estimating the wrinkling behavior of highly anisotropic sandwich panels under biaxial loading. The method is based on the assumption that wrinkling occurs at the angle where the ratio of applied load to sustainable wrinkling loads reaches a global maximum. In addition to the description of the analytical theories, the paper presents comparisons with finite element calculations and testing of real sandwich configurations. The results indicate that the derived model works excellently both for uni- and biaxial loadings, though a small factor of safety is required as with all other standard wrinkling theories.
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| 33. |
- Fagerberg, Linus, et al.
(författare)
-
Imperfection-induced wrinkling material failure in sandwich panels
- 2005
-
Ingår i: Journal of Sandwich Structures and Materials. - : Sage Publications. - 1099-6362 .- 1530-7972. ; 7:3, s. 195-219
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, sandwich wrinkling or local face sheet instability is treated in the context of material failure. Traditionally, test results rarely complied well with the predicted failure load and a knock down factor often had to be used. The reason for this is often referred as the effect of initial geometric imperfections. In this paper, imperfections are included in the natural waveform given by the linear stability analysis, i.e., a short wavelength sinusoidal buckling shape. These initial imperfections lead to increased displacements during loading giving rise to both, an in-plane compressive strain and a varying bending strain. These strains can then be related to material failure criteria, one for the face sheet compressive strain and one for the core normal strain. An analytical model is derived and compared with experimental results and several issues are revealed. The panel strength measured using a realistic initial imperfection amplitude agrees very well with the derived model, giving a prediction somewhat below the values obtained from the traditional approach. This verifies that the actual wrinkling failure is below the theoretical instability load. The model is able to distinguish between different failure modes, face sheet compression failure or core-adhesive joint tensile failure, giving good correlation with the experimental findings. Thus, it appears that using initial imperfections as a basis for wrinkling analysis provides a better foundation for the failure analysis than the ordinary stability analysis, and it also allows to determine which failure mode is predominant. Finally, it is shown that the choice of the core material can be made based on the theory presented to obtain a more efficient sandwich panel.
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| 34. |
- Fagerberg, Linus
(författare)
-
Wrinkling and compression failure transition in sandwich panels
- 2004
-
Ingår i: Journal of Sandwich Structures and Materials. - : SAGE Publications. - 1099-6362 .- 1530-7972. ; 6:2, s. 129-144
-
Tidskriftsartikel (refereegranskat)abstract
- This paper investigates the transition from face wrinkling failure to face sheet compression failure, the latter induced by local buckling at fibre level, so called face sheet microbuckling. An experimental series is performed on small sandwich panels subjected to uni-axial compression. Two different face sheet lay-ups are used in conjunction with a range of PVC core material densities. The results are compared to analytical wrinkling formulae and the correlation is found to be very good. The experimental results also clearly show the transition from wrinkling failure to face sheet microbuckling failure when the core modulus exceeds a certain value. The localised failure surfaces are inspected by microscope and some different characteristics of the failure modes are indicated.
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| 35. |
- Galos, Joel, et al.
(författare)
-
Multifunctional sandwich panel design with lithium-ion polymer batteries
- 2021
-
Ingår i: Journal of Sandwich Structures and Materials. - : SAGE Publications. - 1099-6362 .- 1530-7972. ; 23:8, s. 3794-3813
-
Tidskriftsartikel (refereegranskat)abstract
- This paper investigates the mechanical properties of lithium-ion polymer (LiPo) batteries and their subsequent use in the design of multifunctional sandwich panels for automotive applications. Shear properties, flexural properties and compression properties of prismatic pouch LiPo batteries are determined experimentally through a hole-punch test, a three-point bending test and an in-plane compression test, respectively. This study is the first to characterize the shear properties of a lithium-ion battery, which are critical in sandwich panel design. The mechanical properties of the batteries obtained are then applied to existing analytical models of multifunctional sandwich panels consisting of carbon fibre composite facesheets and LiPo battery cores, which are currently being considered for use in automotive panel design. A material selection procedure for a stiffness-limited automotive car door panel subjected to bending shows that a trade-off between mechanical performance and cost can be achieved by using a composite sandwich panel with thin LiPo battery cores or by embedding larger LiPo batteries in lower-density polymer foam cores. The practicality and implementation aspects of using sandwich composites with LiPo battery cores in automotive design are also discussed.
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| 36. |
- Hägglund, Rickard, et al.
(författare)
-
Measuring thickness changes of edge-wise compression loaded corrugated board panels using digital image correlation
- 2012
-
Ingår i: Journal of Sandwich Structures and Materials. - : SAGE Publications. - 1099-6362 .- 1530-7972. ; 14:1, s. 75-94
-
Tidskriftsartikel (refereegranskat)abstract
- This study examines thickness changes in web-core sandwich panels under edgewise compressive loading. Both undamaged and damaged panels were examined. Three-dimensional full-field digital image correlation systems were used to determine deflections on both sides of loaded panels. The change in thickness at any given point in the panel was obtained as the difference between the two displacement fields. It was observed that the thickness was reduced in the post-buckling regime. Damage introduced into the corrugated core by lateral compression proved to significantly reduce the load-carrying capability panels and elevate the thickness reduction of the panels.
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| 37. |
- Juntikka, Rickard, et al.
(författare)
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Shear characterization of sandwich core materials using four-point bending
- 2007
-
Ingår i: Journal of Sandwich Structures and Materials. - : SAGE Publications. - 1099-6362 .- 1530-7972. ; 9:1, s. 67-94
-
Tidskriftsartikel (refereegranskat)abstract
- A new shear test method for sandwich core materials is proposed and evaluated. Sandwich beams are loaded in four-point bending, and the shear deformation is measured with two rotary sensors. Conditions of idealized sandwich theory are assumed to prevail, and the accuracy of the proposed methodology is thus dependent on a few mechanical and geometric relations between the sandwich constituents. The stress-strain responses for two polymer foam core materials, one relatively brittle and one relatively ductile, are extracted and compared with results from single-block shear tests of the same material batch. The new method provides several benefits with respect to the block shear test. It does not suffer from extreme stress concentrations and the specimens are tested under in-service conditions. Problems arise, however, for the ductile material, predominantly related to large deformations during the test eventually resulting in bending failure of the face sheet instead of shear failure of the core.
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| 38. |
- Kalińska-Nartiša, Edyta, et al.
(författare)
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Microtextural Inheritance on Quartz Sand Grains from Pleistocene Periglacial Environments of the Mazovian Lowland, Central Poland
- 2017
-
Ingår i: Permafrost and Periglacial Processes. - : Wiley. - 1045-6740. ; 28:4, s. 741-756
-
Tidskriftsartikel (refereegranskat)abstract
- Sand grains from Quaternary glacial, aeolian and fluvial deposits in the Mazovian Lowland, central Poland, were examined to characterize the effects of different Quaternary processes on sand-grain surfaces that experienced repeated cycles of intense polar-desert-like conditions during the Middle and Late Pleistocene. A cold, dry and windy periglacial environment prevailed here at least twice between the Saalian (Marine Isotope Stage (MIS) 6) and Holocene (MIS 1) stages. Because the surface characteristics of quartz sand grains can provide important palaeoenvironmental information, we examined grains extracted from sediment samples in different landforms to determine their surficial features from scanning electron microscope images. The grain surfaces were dominated by microtextures characteristic of aeolian-induced grain transformation, indicated by a high percentage of well-rounded, low-relief-worn grains with dish-shaped depressions, bulbous edges and upturned plates. Although remnants of previous sedimentary cycles were occasionally observed, aeolian effects were dominant even in glacial and fluvial settings. Quartz microtextures indicated that none of the examined grains represented their original setting, but rather suggested remobilisation under periglacial conditions.
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| 39. |
- Koissin, Vitaly, et al.
(författare)
-
Deformation of foam cores in uniaxial compression-tension cycle
- 2006
-
Ingår i: Journal of Sandwich Structures and Materials. - : SAGE Publications. - 1099-6362 .- 1530-7972. ; 8:5, s. 395-406
-
Tidskriftsartikel (refereegranskat)abstract
- This article deals with experimental and analytical analysis of the mechanical behavior of crushed foam cores. Three rigid cellular core materials are tested in a uniaxial compression-tension cycle. An analytical model is proposed describing the stress-strain curve in tension and secondary compression. A special emphasis is laid on the relaxation behavior of a crushed foam core in tension.
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| 40. |
- Koissin, Vitaly, et al.
(författare)
-
Residual In-plane Mechanical Properties of Transversely Crushed Structural Foams
- 2009
-
Ingår i: Journal of Sandwich Structures and Materials. - : SAGE Publications. - 1099-6362 .- 1530-7972. ; 11:2-3, s. 199-211
-
Tidskriftsartikel (refereegranskat)abstract
- The mechanical properties of structural polymer foams are investigated after crushing in the rise direction (out-of-plane axis of a foam material block). The crushed foams are loaded in uniaxial compression, tension, or shear. All tests are performed in the plane of the foam block, i.e., perpendicular to the crushing direction. For comparison, virgin foams are also characterized. The results are discussed featuring the properties of crushed foams, which can be important for the damage tolerance analysis of a foam core sandwich structure.
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| 41. |
- Koissin, Vitaly, et al.
(författare)
-
Wrinkling in sandwich panels - an analytical approach
- 2011
-
Ingår i: Journal of Sandwich Structures and Materials. - : SAGE Publications. - 1099-6362 .- 1530-7972. ; 13:6, s. 705-730
-
Tidskriftsartikel (refereegranskat)abstract
- This article deals with theoretical modeling of the local buckling in foam-core sandwich panels. This phenomenon is considered mainly in the periodic (unbounded wrinkle wave) and linearly elastic formulation. The analytical solutions are in agreement with results of finite element analysis and can be applied with a good precision for many finite-size panels, as well as for many sandwiches having honeycomb cores.
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| 42. |
- Larsson, Johan, et al.
(författare)
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A sequential mixed-integer programming method for concurrent optimization of core topology and face sheet thickness of a sandwich beam
- 2023
-
Ingår i: Journal of Sandwich Structures and Materials. - : SAGE Publications. - 1099-6362 .- 1530-7972. ; 25:6, s. 666-686
-
Tidskriftsartikel (refereegranskat)abstract
- A method is proposed that allows for the concurrent optimization of core topology and face sheet thickness of a sandwich beam under compliance constraints. The problem is solved using a novel mixed-linear extension of the Topology Optimization of Binary Structure (TOBS) topology optimization method aiming to minimize the total mass of the beam. The method has been demonstrated on a clamped beam example and the results have been compared to results from topology optimization of the core with a range of a priori fixed face sheet thicknesses. It is shown that the new method, starting from a fully populated core, finds a minimum mass that is lower than but in the neighbourhood of the best results from the topology optimization with fixed face sheet thicknesses. By varying the compliance constraint it is shown that the core topology approaches an ideal corrugated geometry as the compliance constraint is relaxed. The trends observed in the results are compared to analytical models for an idealized core.
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| 43. |
- Niu, Kangmin, et al.
(författare)
-
Buckling of a thin face layer on Winkler foundation with debonds
- 1999
-
Ingår i: Journal of Sandwich Structures and Materials. - : SAGE Publications. - 1099-6362 .- 1530-7972. ; 1:4, s. 259-278
-
Tidskriftsartikel (refereegranskat)abstract
- The buckling behavior of a face layer debonded locally from the core of a sandwich panel is analyzed by considering a Euler beam on Winkler foundation with debonds subjected to in-plane compression. Exact closed form solutions of the buckling load and mode shape are obtained, and corresponding numerical results are given to illustrate the solution. Results indicate that the wrinkling wavelength of the perfectly bonded face layer can be used as an appropriate characteristic length for normalizing the debond length of a relatively long face layer. The effects of length and location of debonds and the end constraints of the face layer on the load carrying capacity are discussed. Interactive effects due to two debonds and the overlapping of debond faces are also studied. A master curve based on a classical solution is developed by employing the new normalization of the debond length. A modification to the usual Winkler foundation constants is made for an isotropic core, and it agrees very well with published results of a finite element analysis.
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| 44. |
- Rajput, Moeen S, et al.
(författare)
-
Compression of structural foam materials : Experimental and numerical assessment of test procedure and specimen size effects
- 2017
-
Ingår i: Journal of Sandwich Structures and Materials. - : Sage Publications. - 1099-6362 .- 1530-7972.
-
Tidskriftsartikel (refereegranskat)abstract
- This study was initiated based on the observation that standardized test for flatwise compression of foam materials, give significantly different test results for the measured moduli, and that these standards to date lack adequate instructions on how the strain should be measured and what specimen size should be used. A brief review of previous work shows that existing test methodologies provide significantly different results for the compressive moduli of foams depending on how the strains are measured. A thorough experimental study of the out-of-plane compressive properties is conducted on three different closed-cell foam materials, where strains measured with two different extensometer placements, and with digital image correlation, come out significantly differently. A parametric study is also performed showing that the results vary considerably with in-plane specimen dimensions, indicating effects of finite size and localized strain at edges. Both stochastic amorphous and homogenized finite element models of foam back the experimental observations by illustrating the effects of finite size and various boundary conditions on the measured properties.
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| 45. |
- Rajput, Moeen S, et al.
(författare)
-
Evaluation of test methods and face-sheet thickness effects in damage tolerance assessment of composite sandwich plates
- 2022
-
Ingår i: Journal of Sandwich Structures and Materials. - : SAGE Publications. - 1099-6362 .- 1530-7972. ; 24:2, s. 1340-1366
-
Tidskriftsartikel (refereegranskat)abstract
- Composite sandwich materials provide high bending performance-to-weight ratios. However, these materials are vulnerable to impact damages which can drastically reduce their load-bearing capability. Presently there is a lack of standardised test methods for impact assessment. This study compares three different test methods for impact assessment; single skin compression after impact (CAI-SS), sandwich compression after impact (CAI-SW) and four-point bending-after-impact (BAI). The CAI-SS test method shows high compressive strength and strain at failure and the tesr is relatively easy to evaluate. For finite size plates with significant impact damage, the CAI-SS test method is recommended for post impact strength assessment. For large sandwich panels with relatively small impact damages the CAI-SW test method could be more relevant since it includes effects of panel asymmetry generated from the impact damage. The BAI test method may be recommended as an alternative to CAI but quite long specimens are required in order to assure compressive failure in the tested face-sheet, making the test both demanding and expensive. On the other hand, lower load levels are required to break the specimens and there is less need for precise machining during specimen manufacturing. A finite element model including progressive damage evolution was used to estimate the post impact strength. The simulations showed generally good agreement with the experiments.
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| 46. |
- Rajput, Moeen S
(författare)
-
Experimental and numerical study of the response to various impact energy levels for composite sandwich plates with different face thicknesses
- 2019
-
Ingår i: Journal of Sandwich Structures and Materials. - : SAGE Publications. - 1099-6362 .- 1530-7972. ; , s. 1654-1682
-
Tidskriftsartikel (refereegranskat)abstract
- Composite sandwich structures find wide application in the aerospace sector thanks to their lightweight characteristics. However, composite structures are highly susceptible to low velocity impact damage and therefore thorough characterization of the impact response and damage process for the used material configurations is necessary. The present study investigates the effect of face-sheet thickness on the impact response and damage mechanisms, experimentally and numerically. A uni-directional, non-crimp fabric is used as reinforcement in the face-sheets, and a closed cell Rohacell 200 Hero polymer foam is used as core material. Low-velocity impact tests are performed in a novel instrumented drop-weight rig that is able to capture the true impact response. A range of impact energies are initially utilized in order to identify when low level damage (LLD), barely visible impact damage (BVID) and visible impact damage (VID) occur. A thorough fractography investigation is performed to characterize the impact damage using both destructive and non-destructive testing. The damage from the impacts in terms of dent depth, peak contact force, deflection and absorbed energy is measured. The results show bilinear responses in dent depth vs. impact energy and absorbed energy vs. impact energy. It is found than the BVID energy works well as an indication for the onset of excessive damage. Fractography reveals that there is a failure mode shift between the LLD and the VID energy levels, and that delaminations predominantly grow along the fiber direction and rotate in a spiral pattern through the thickness, following the laminate ply orientations. Finally, a progressive damage finite element model is developed to simulate both the impact response and the delamination extent, incorporating both intra- laminar and inter-laminar damage modes. The simulation shows good agreement with the experiments.
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| 47. |
- Shipsha, Andrey, et al.
(författare)
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Failure mechanisms and modelling of impact damage in sandwich beams - A 2D approach : Part II - Analysis and modelling
- 2003
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Ingår i: Journal of Sandwich Structures and Materials. - : SAGE Publications. - 1099-6362 .- 1530-7972. ; 5:1, s. 33-51
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Tidskriftsartikel (refereegranskat)abstract
- This study addresses the effect of low velocity impact damage on the post-impact residual strength and failure mechanisms of sandwich beams with Rohacell WF51 foam core. The considered impact damage has a form of a sub-interface cavity surrounded by crushed core while the face sheet remains virtually undamaged. Part I of this study deals with experimental investigation of impact-damaged beams tested in transverse shear, bending and edgewise compression. It is shown that the crushed core and the bridging condition in the peripheral regions of the impact damage exert a significant effect on the post-impact critical loads and failure mechanisms. In this paper, parameterised finite element (FE) models of impact damage with implemented crushed core properties are developed for numerical analyses of post-impact failure. In the analysis of the shear case, a model for II bridging condition in the peripheral regions of impact damage is introduced. A point-stress criterion is applied for predictions of failure loads and crack kink angle. Geometrically non-linear FE analysis is employed for evaluation of critical loads for local buckling in the beams with impact damage. The FE analyses demonstrate good agreement with experimental results.
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| 48. |
- Shipsha, Andrey, et al.
(författare)
-
Failure mechanisms and modelling of impact damage in sandwich beams - A 2D approach : Part I - Experimental investigation
- 2003
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Ingår i: Journal of Sandwich Structures and Materials. - : SAGE Publications. - 1099-6362 .- 1530-7972. ; 5:1, s. 7-31
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Tidskriftsartikel (refereegranskat)abstract
- This paper addresses the effect of low velocity impact damage on post-impact failure mechanisms and structural integrity of foam core sandwich beams subjected to edgewise compression, shear and bending load cases. The study deals with a 2D configuration, where a sandwich beam is impacted by a steel cylinder across the whole width of the specimen. The impact damage is characterised as indentation of the core with sub-interface damage seen as a cavity while the GFRP faces remain virtually unaffected by the impact. Digital speckle photography (DSP) analysis is employed for in situ monitoring of crushing behaviour in the foam core during static indentation of sandwich specimens. The static shear strength of impact-damaged sandwich beams is compared with specimens with fabricated sub-interface cracks of the same length. DSP analysis reveals that the face-core interface in the peripheral regions of 2D impact damage is not entirely separated. The crack analogy is thus not fully representable since the surfaces remain bridged resulting in higher strength, when compared with fabricated cracks. The post-impact resistance to compressive loads is lower than for the specimens with fabricated cracks due to the presence of the cavity and the crushed core with reduced foundation stiffness support. The properties of crushed foam core are experimentally determined as they appear to be important for accurate modelling and analysis of the residual strength of sandwich beams. Modelling and post-impact analysis of the specimens with impact damage is elaborated in detail in part 11 of this study.
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| 49. |
- Shipsha, A., et al.
(författare)
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Fatigue behavior of foam core sandwich beams with sub-interface impact damage
- 2003
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Ingår i: Journal of Sandwich Structures and Materials. - : SAGE Publications. - 1099-6362 .- 1530-7972. ; 5:2, s. 147-160
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Tidskriftsartikel (refereegranskat)abstract
- The fatigue life of impact-damaged foam core sandwich beams with GFRP faces is investigated for constant load-amplitude cyclic loading. The damage produced by the low velocity/energy impact is characterised as a sub-interface cavity with surrounding crushed core whereas the face sheet is undamaged. The effect of bridging owing to the crushed core in the peripheral regions of impact damage, revealed in the preceding static study Shipsha et al. [1,2] is assessed under cyclic loading. The fatigue test results are analysed in a stress-life S-N diagram and compared with published data from undamaged beams. The effect of two load ratios R = 0.1 and -1 is investigated. The fatigue threshold load levels are experimentally quantified from the S-N curves. Furthermore, a modified point-stress criterion based on the threshold stress intensity factor, K-th, is proposed to estimate the no-crack growth limit loads. The results show good agreement with performed experiments.
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| 50. |
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