| 1. |
- Eppanapelli, Lavan Kumar, 1988-, et al.
(författare)
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Estimation of Liquid Water Content of Snow Surface by Spectral Reflectance
- 2018
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Ingår i: Journal of cold regions engineering. - : American Society of Civil Engineers (ASCE). - 0887-381X .- 1943-5495. ; 32:1
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Tidskriftsartikel (refereegranskat)abstract
- This study measures the spectral reflectance from snow with known liquid water content (LWC) in a climate chamber using two optical sensors, a near-infrared (NIR) spectrometer and a Road eye sensor. The spectrometer measures the backscattered radiation in the wavelength range of 920–1,650 nm. The Road eye sensor was developed to monitor and classify winter roads based on reflected intensity measurements at wavelengths of 980, 1,310, and 1,550 nm. Results of the study suggest that the spectral reflectance from snow is inversely proportional to the LWC in snow. Based on the effect of LWC on the spectral reflectance, three optimum wavelength bands are selected in which snow with different LWCs is clearly distinguishable. A widely used remote sensing index known as the normalized difference water index (NDWI) is used to develop a method to estimate the surface LWC for a given snow pack. The derived NDWI values with respect to the known LWC in snow show that the NDWI is sensitive to the LWC in snow and that the NDWI and LWC are directly proportional. Based on this information, the NDWI is used to estimate the surface LWC in snow from measurements on a ski track using the Road eye sensor. The findings suggest that the presented method can be applied to estimate the surface LWC in order to classify snow conditions potentially for ski track and piste applications.
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| 2. |
- Hanaeus, Jörgen, et al.
(författare)
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Seasonal Operation of Ponds for Chemical Precipitation of Wastewater
- 2010
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Ingår i: Journal of cold regions engineering. - : ASCE. - 0887-381X .- 1943-5495. ; 24:4, s. 98-111
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Tidskriftsartikel (refereegranskat)abstract
- Wastewaterprecipitation ponds (fellingsdams) are conventional stabilization ponds adapted to coldclimate by the use of chemical precipitation to attain sufficientremoval efficiency of impurities, primarily phosphorus. The objective with thisinvestigation was to study the influence of an interruption ofthe dosage of coagulant during summer periods at two fellingsdamsystems (Orrviken and Lockne) in the middle of Sweden. Theinvestigation took place over two years characterized by unusual precipitationconditions; 2001 was intense in precipitation whereas summer 2002 representeda dry season. The results showed that there is apotential to utilize the summer biological activity in fellingsdams. AtOrrviken the effluent quality measured as organic matter and phosphorusin the effluent was just slightly above the values thatwere reached by chemical precipitation. At Lockne the performance waslower. The organic matter reduction at Orrviken in the summersof 2001 and 2002 were 71 and 67%, respectively, comparedto previous years using precipitant when the average was 78%.At Lockne, however, the values in the summers of 2001and 2002 were 36 and 18%, respectively, compared to previousyears using precipitant when the average was 55%. The phosphorousreduction at Orrviken in the summers of 2001 and 2002were 85 and 89%, respectively, compared to previous years usingprecipitant when the average was 95%; at the Lockne plant,the phosphorous reduction during the summers of 2001 and 2002were 60 and 66%, respectively, compared to the previous years'average of 86%. The nitrogen reduction varied considerably over thetwo summer periods. The reduction at Orrviken was 13% in2001 and 58% in 2002; the reduction at Lockne was13% in 2001 and 33% in 2002. Reference values ofnitrogen reduction during normal operations were not available.
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| 3. |
- Lintzén, Nina, 1978-, et al.
(författare)
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Laboratory Investigation of Different Insulating Materials Used for Snow Storage
- 2019
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Ingår i: Journal of cold regions engineering. - : American Society of Civil Engineers (ASCE). - 0887-381X .- 1943-5495. ; 33:4
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Tidskriftsartikel (refereegranskat)abstract
- Storage of snow has become of increasing interest for the winter business industry. Covering a pile of snow with an insulating material protects the snow from heat transfer from the surroundings and reduces the melting. Storing snow enables ski resorts to set an opening date, and it can also be used to secure winter sports events that are dependent on snow. Cover materials that are commonly used as insulation are wood-based materials, such as sawdust, and textile materials and sheets. How efficiently a cover material functions as thermal insulation depends on the material characteristics and thickness of the insulating layer. In this study, results from a laboratory experiment are presented, which aimed at comparing different commonly used cover materials, as well as some other materials that have not previously been used as thermal insulation on snow. Different layer thicknesses were also investigated. The results show that the insulating capacity of sawdust is reduced with time. Despite degrading insulating properties with time, sawdust is still considered one of the best materials to use as insulation on snow, and it is also more efficient than the textile materials investigated in this study. Doubling the textile layers or adding a three-dimensional (3D) spacer textile, which implies adding a layer of air between the textile and the snow, reduces the snow melting. Water absorption, water transport, and evaporation of water affect the melting. In this work, evaporative cooling did not prove to reduce melting; therefore, it was not evident whether a textile material should be permeable. An interesting material used in the study was Quartzene, which absorbed all the melt water and protected the snow most efficiently of the materials tested.
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| 4. |
- Lintzén, Nina, et al.
(författare)
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Uniaxial Strength and Deformation Properties of Machine-Made Snow
- 2015
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Ingår i: Journal of cold regions engineering. - 0887-381X .- 1943-5495. ; 29:4
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Tidskriftsartikel (refereegranskat)abstract
- Snow as a construction material has been used for centuries, with igloos among the first examples. Each winter, snow and ice villages, buildings, and artwork are built in many places around the world. Machine-made snow manufactured by snow guns is commonly used for constructions made of snow. However, only a few basic studies on machine-made snow have been published. Knowledge based on experience and studies on natural snow constitute the basis for constructions made using snow and ice. Through material tests on machine-made snow used for construction, data on important physical and mechanical properties have been established that aim to improve and optimize safe constructions made from snow. Strength tests have been performed using two different qualities of machine-made snow. Specimens used for testing were cut out from one block of snow that had a coarse-grained structure with clusters of ice in the snow and from one block of snow with a fine-grained and homogeneous structure. The density for each tested snow sample was measured and strength tests were performed at different deformation rates to investigate the relationship between mechanical properties and deformation rate or strain rate. The load response curves achieved from the strength tests were used to evaluate compressive strength, Young’s modulus, and the residual modulus. The results show that compressive strength increases with increasing density. Increasing compressive strength with an increasing strain rate was also observed for fine-grained snow quality specimens, whereas no similar tendency was observed for coarse-grained snow. The residual modulus increased with an increasing strain rate up to a certain critical value for the fine-grained machine-made snow specimens. Regression analysis was used to investigate whether any dependence was observed between the calculated mechanical properties; no further relationship between the mechanical and the physical properties was noticed
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| 5. |
- Mattsson, Jonathan, et al.
(författare)
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Impacts on rural wastewater systems in subarctic regions due to changes in inputs from households
- 2018
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Ingår i: Journal of cold regions engineering. - : American Society of Civil Engineers (ASCE). - 0887-381X .- 1943-5495. ; 32:1
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Tidskriftsartikel (refereegranskat)abstract
- The use of water-saving appliances and heat exchangers is becoming increasingly popular to decrease water consumption and recover energy from preheated water. However, such in-household changes can bring particular implications for subarctic rural areas, in terms of solids deposition in sewers and drops in performance of wastewater treatment plants (WWTPs), because these are already experiencing diminishing wastewater flows due to depopulation and seasonal dips in wastewater temperature resulting from infiltration into sewers. Hence, this study has considered two communities in Sweden, postulating three different cases with various scales of retrofitting and usage. The results indicate that the decrease in in-pipe velocities when all households are retrofitted with water-saving appliances could be counteracted by sewer relining, but not by the inclusion of a conventional estimate of infiltration. However, for the case in which retrofitting was combined with decreased usage of the appliances, the decrease in self-cleansing capacity could not be counteracted. The retrofitting of heat exchangers under shower trays in all households did not have a significant effect on treatment processes at the WWTP.
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| 6. |
- Moghadas, Shahab, et al.
(författare)
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Modeling Urban Runoff from Rain-on-Snow Events with the U.S. EPA SWMM Model for Current and Future Climate Scenarios
- 2018
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Ingår i: Journal of cold regions engineering. - : American Society of Civil Engineers (ASCE). - 0887-381X .- 1943-5495. ; 32:1
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Tidskriftsartikel (refereegranskat)abstract
- A methodological study of modeling runoff from rain-on-snow events was conducted using the northern Swedish city of Kiruna as a test case, with respect to physiographic, drainage system, and the current and projected future climate data. Runoff simulations were carried out with the PCSWMM, which is a geographic information system (GIS) supported version of the U.S. EPA Storm Water Management Model (U.S. EPA SWMM5) developed by Computational Hydraulics International (CHI). In total, 177 simulations were run covering four scenario categories: eight rain events, three climates (the current and two projected), three soil infiltration rates, and five snow water equivalent (SWE) values. Simulation results were analyzed with respect to influential rainfall/snowmelt/runoff factors and the noted differences were statistically tested for significance. Result analysis revealed new findings concerning the differences between runoff generated by rain-on-snow and summer thunderstorm events. In particular, it was noted that a relatively frequent rain-on-snow event, with a return period of 1.4 year, caused fewer flooded nodes and surcharged pipes in the catchment sewer system, but almost five times greater runoff volume, when compared to the same drainage system performance indicators corresponding to a 10-year event occurring in the summer. Depending on the physical characteristics of the snow cover, among which the depth appears the most important, rainwater and snowmelt may be retained in, or released from, the snowpack, which acts as a dynamic reservoir controlling the generation and release of runoff. Smaller snow depths produce smaller volumes of melt, smaller storage capacity and less effective insulation of soils, which may freeze to greater depths and become practically impervious, until the process of soil thawing has been completed. The impacts of climate change in the study area, described by increases in precipitation and air temperatures, are likely to cause more frequent runoff problems attributed to the future rain-on-snow events. Even though the runoff tendencies reported here reflect the characteristics of the study area and climate, they suggest the need to consider rain-on-snow events in sewer design and storm water management in regions with seasonal snow covers, certainly with respect to runoff volumes.
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| 7. |
- Patil, Aniket, et al.
(författare)
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Simulation of Brash Ice Behavior in the Gulf of Bothnia Using Smoothed Particle Hydrodynamics Formulation
- 2021
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Ingår i: Journal of cold regions engineering. - : American Society of Civil Engineers (ASCE). - 0887-381X .- 1943-5495. ; 35:2
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Tidskriftsartikel (refereegranskat)abstract
- The repeated passage of ships through ice-infested waters create a field of broken ice pieces. The typical size of the broken ice pieces is generally <2.0 m. This area might be referred to as a brash ice field. The movement of ships and vessels leads to the transportation and accumulation of broken ice pieces in a brash ice field. A better understanding of the properties and behavior of brash ice could improve the estimates of ice load that are associated with shipping in a brash ice field. An in situ test referred to in this study as a pull up test will be performed in Luleå harbor, Luleå, Sweden. An attempt will be made to estimate the mechanical and physical properties of a brash ice field based on the in situ test results. The test setup, procedure, and test results will be described in detail. Furthermore, the test will be simulated using the smoothed particle hydrodynamics (SPH) formulation. The numerical simulations will calibrate the numerical and material model of brash ice using the pull up test measurements. In this numerical model, a discrete mass-spring-dashpot model will be used to simulate buoyancy and drag. The continuous surface cap model (CSCM) will be used as a material model for the brash ice. The elastic modulus and the fracture energy of brash ice as a material model input will be estimated by an ad hoc scaling formula. The parameters, such as void fraction (Vf), cohesion (c), and angle of internal friction (φ) will be altered to assess their influence on the test data. The analysis of the in situ test results and the simulation results provide a preliminary approach to understand the brash ice failure process that could be further developed into modeling techniques for marine design and operations.
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| 8. |
- Savin, Andrej, et al.
(författare)
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Full-Scale Measurement of Reaction Force Caused by Level Ice Interaction on a Buoy Connected to a Wave Energy Converter
- 2019
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Ingår i: Journal of cold regions engineering. - : ASCE-AMER SOC CIVIL ENGINEERS. - 0887-381X .- 1943-5495. ; 33:2
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Tidskriftsartikel (refereegranskat)abstract
- Wave energy is an attractive source of renewable energy. In regions with a cold climate, for example, in the Baltic Sea, a good understanding of ice loads is vital for developing a reliable and cost-effective buoy for a wave energy converter (WEC). The first full-scale attempt was made to measure the vertical reaction force on a floating buoy connected to the WEC under the ice level interaction process. The force equation for a buoy connected to the WEC during the ice level interaction process is presented. It provides essential information on forces from the floating level of ice, which is very important for the design and construction of a buoy in regions with a cold climate.
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| 9. |
- Sollén, Sofia, et al.
(författare)
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Experimental Investigation of an Infrared Deicing System for Wind Power Application in a Cold Climate
- 2022
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Ingår i: Journal of cold regions engineering. - : American Society of Civil Engineers (ASCE). - 0887-381X .- 1943-5495. ; 36:4
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Tidskriftsartikel (refereegranskat)abstract
- Icing of wind turbine blades poses a great challenge for wind farms in cold climates, this challenge is addressed by implementing various deicing practices that require significant cost to operate. Thus, alternative and potential solutions are needed to improve wind power production in cold climate. The present study is investigates the effectiveness of a new deicing system consisting of infrared heaters. Two types of heaters were selected based on wavelength, input power, and investment cost. The heaters were tested on blades covered with soft rime ice. A thermal camera was used to image the deicing procedure together with a load cell to measure the weight of the ice melted. It was found that a combination of two different types of heaters provides effective deicing at a distance of 1.5 m compared with multiple units of the same type of heaters. It was observed that the infrared deicing system has a larger area of heat distribution, which is one of the major advantages compared with traditional systems. © 2022 American Society of Civil Engineers.
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| 10. |
- Bahaloo, Hassan, et al.
(författare)
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Capillary Bridge in Contact with Ice Particles Can Be Related to the Thin Liquid Film on Ice
- 2024
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Ingår i: Journal of cold regions engineering. - : American Society of Civil Engineers (ASCE). - 0887-381X .- 1943-5495. ; 38:1
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Tidskriftsartikel (refereegranskat)abstract
- We experimentally demonstrate the presence of a capillary bridge in the contact between an ice particle and a smooth aluminum surface at a relative humidity of approximately 50% and temperatures below the melting point. We conduct the experiments in a freezer with a controlled temperature and consider the mechanical instability of the bridge upon separation of the ice particle from the aluminum surface at a constant speed. We observe that a liquid bridge forms, and this formation becomes more pronounced as the temperature approaches the melting point. We also show that the separation distance is proportional to the cube root of the volume of the bridge. We hypothesize that the volume of the liquid bridge can be used to provide a rough estimate of the thickness of the liquid layer on the ice particle since in the absence of other driving mechanisms, some of the liquid on the surface must have been pulled to the bridge area. We show that the estimated value lies within the range previously reported in the literature. With these assumptions, the estimated thickness of the liquid layer decreases from nearly 56 nm at T = −1.7°C to 0.2 nm at T = −12.7°C. The dependence can be approximated with a power law, proportional to (TM − T)−β, where β < 2.6 and TM is the melting temperature. We further observe that for a rough surface, the capillary bridge formation in the considered experimental conditions vanishes.
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| 11. |
- Bergstrom, A, et al.
(författare)
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Friction measurement on cycleways using a portable friction tester
- 2003
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Ingår i: Journal of cold regions engineering. - 0887-381X .- 1943-5495. ; 17:1, s. 37-57
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Tidskriftsartikel (refereegranskat)abstract
- In seeking to promote cycling in wintertime, it is desirable to understand how important the winter maintenance service level is in people's decision to cycle or not,, and methods to compare different road conditions on cycleways are therefore needed. By measuring friction, an assessment of the service level can be achieved, but methods available often involve the use of large vehicles, which can lead to overloading damage on cycleways, and constitute a safety risk for cyclists and pedestrians. A portable friction tester (PFT), originally designed to measure friction on road markings, was thought to be an appropriate instrument for cycleways and was, therefore, tested on different winter road conditions, and on different cycleway pavement materials. In this study, it was found that the PFT is a valuable tool for measuring friction on cycleways. Different winter road conditions, as well as different pavement materials, can be distinguished from each other through PFT measurements. The PFT provides a good complement to visual inspections of cycleways in. winter maintenance evaluation and can, for example, be used to determine if desired service levels have been achieved.
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| 12. |
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| 13. |
- Domaschuk, L., et al.
(författare)
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Reactive soil pressures along pile in frozen sand
- 1991
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Ingår i: Journal of cold regions engineering. - 0887-381X .- 1943-5495. ; 5:4, s. 174-194
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Tidskriftsartikel (refereegranskat)abstract
- A multistage, lateral, pile-load creep test is carried out in a frozen sand maintained at -3° C. The pile is a tubular pipe, 150 mm square and 1,800 mm long. A series of plate load cells is mounted along the primary bearing face of the pile. Application of lateral loads of 35, 65, and 115 kN result in attenuating creep, whereas a lateral load of 145 kN leads to accelerating creep. The immediate components of pile displacement increase approximately linearly with applied load, while the creep components increase exponentially. Generally, the soil reaction forces near the ground surface decrease as the result of pile creep, and those further down the pile increase. Moduli of horizontal subgrade reaction computed on the basis of the measured soil reaction forces and the pile displacement are found to vary with applied pressure and creep. Magnitudes based on immediate displacements range from 1 to 7.5 GN/m3, while those based on total displacements range from 0.3 to 2 GN/m3.
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| 14. |
- Eigenbrod, K. Dieter, et al.
(författare)
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Pore-water pressures in freezing and thawing fine-grained soils
- 1996
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Ingår i: Journal of cold regions engineering. - 0887-381X .- 1943-5495. ; 10:2, s. 77-92
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Tidskriftsartikel (refereegranskat)abstract
- Laboratory freezing tests were performed on laterally confined samples of lightly overconsolidated fine-grained soil exposed to one-dimensional freezing at a constant temperature gradient. Pore-water pressures and temperatures were measured at the perimeter of the specimens at various points along their height during freezing and thawing. Vertical heave and water inflow and outflow were also recorded in the sample. X-ray pictures were taken in order to correlate ice lens formation to the measured data. Of particular interest were occurrences of high pore-water pressures shortly after the freezing front had stabilized. Pore-water pressure peaks coincided typically with temperature peaks. Maximum negative pore-water pressures measured during freezing can be correlated to the compression observed in soft clay specimens subsequent to freezing and thawing, which is often called freeze-thaw consolidation. During early freezing, no heave was indicated in soft clay specimens even though numerous ice lenses had formed. No freeze-thaw-consolidation was recorded for stiff clay specimens with initial water contents near the plastic limit.
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| 15. |
- Eppanapelli, Lavan Kumar, 1988-, et al.
(författare)
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Estimation of specific surface area of snow based on density and multispectral infrared reflectance
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Ingår i: Journal of cold regions engineering. - 0887-381X .- 1943-5495.
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a multiple regression method for predicting snow SSA based on multispectral reflectance and snow density. Multispectral near-IR reflectance from snow was measured at wavelengths 980 nm, 1,310 nm and 1,550 nm. In total, 16 different artificially prepared snow samples were investigated using two optical sensors, a spectrometer and a Road eye sensor. Both the sensors measured backscattered radiance from snow and measurements were carried out in a climate chamber. Snow types with variations in physical properties such as grain distribution, surface texture, SSA, density and depth are considered. Variations in snow density were obtained through compaction and aging process. Correlation between the snow density and reflectance is investigated and influence of snow density and multispectral reflectance on snow SSA is also investigated. A generalized linear model is developed to predict the snow SSA with a coefficient of determination equal to 98\%. The preliminary validation of results show that the SSA can be accurately estimated from the density and multispectral reflectance. The model results indicate that the snow density has minor effect on the variations in snow SSA. Results suggest that snow with varying physical properties can be qualitatively characterized based on the presented approach, which is of interest for applications such as winter roads classification and pistes classification.
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| 16. |
- Hedström, Annelie, et al.
(författare)
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Natural freezing, drying, and composting for treatment of septic sludge
- 1999
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Ingår i: Journal of cold regions engineering. - 0887-381X .- 1943-5495. ; 13:4, s. 167-179
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Tidskriftsartikel (refereegranskat)abstract
- A full-scale experimental plant intended for local treatment of septic sludge, situated in northern Sweden, is presented in this paper. The concept investigated included natural freezing, thawing, and drying in combination with composting. The experimental plant consisted of an undrained freezing-thawing-drying bed and a heat-insulated composter. About 500 L of fresh sludge, with a dry matter (DM) content of 4–5%, collected from a septic tank employed by one family, was transferred to the freezing-thawing-drying bed in the beginning of November 1996. During the winter months, the sludge froze and then thawed in the middle of May 1997. During a drying period of three weeks, the DM content increased from 10.6–21.3 to 25–95%. The final sludge volume and weight were 180 L and 54 kg, respectively. Approximate concentrations of nitrogen, phosphorus and total organic carbon of the dried sludge were determined to be 23, 5.9, and 346 g/kg DM. From June until the end of August, the sludge was cocomposted with kitchen refuse. Within two weeks, the composting temperature exceeded 65°C. The measured composting temperature indicated a high pathogen die-off, but before this concept can be suggested as an alternative to conventional septic sludge treatment, further studies should be conducted, including direct measurements of pathogens. The concept, however, has proved to be of interest in cold regions due to its simple construction and operation
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| 17. |
- Hellgren, Rikard, 1988-, et al.
(författare)
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Systematic Literature Search and Meta Regression of Measured Static Ice Loads on Concrete Dams
- 2024
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Ingår i: Journal of cold regions engineering. - : American Society of Civil Engineers (ASCE). - 0887-381X .- 1943-5495. ; 38:2
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Tidskriftsartikel (refereegranskat)abstract
- This study presents a systematic literature review of ice load measurements on dams. Several hypotheses about the relationship between the maximum ice load and external variables are tested using regression analysis on the data collected from the literature. The performed tests show that ice thickness, water level change category, and dam height are factors that have a significant and relevant relationship with the magnitude of all measured ice loads. The ice thickness is the only tested variable that also shows a significant and relevant relationship with differences in ice load between winters at one dam. The variation in recorded ice load from several sensor positions at one dam during the same winter is considerable. Generally, the difference between the sensor area and the structure–ice interaction area is large, resulting in extensive extrapolation and uncertainties regarding the representativeness of the measured results.
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| 18. |
- Hellström, Daniel, et al.
(författare)
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Natural sludge dewatering. I : Combination of freezing, thawing, and drying as dewatering methods
- 1997
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Ingår i: Journal of cold regions engineering. - 0887-381X .- 1943-5495. ; 11:1, s. 1-14
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Tidskriftsartikel (refereegranskat)abstract
- A Swedish full-scale pilot plant employing all-year-round natural sewage sludge dewatering is presented in this paper. The treatment includes three different types of outdoor ditches: a freezing ditch for the winter months, a drying ditch for the early summer months, and a combined drying-freezing-thawing-drying (DFTD) ditch for sludge produced in late summer and early autumn. The test period included two consecutive winters. Complete freezing of the sludge was achieved in the first winter in contrast to the second when incomplete freezing of the sludge occurred due to an unusually warm winter. The dry matter content for the freezing ditch was, at the harvest in August, 30–70 of the first test year. The second test year yielded a sludge with a dry matter content of 20–40 in the freezing ditch. The final dry matter result for the DFTD ditch was 20–40. The summers included were similar to the extent that both late summers were unusually warm, helping to produce sludge of high final dry matter content. The first summer, being somewhat warmer and with a lower sludge loading, yielded a sludge of 60–90 dry matter in the drying ditch. The second summer, when the sludge load was approximately double the preceding year, resulted in a sludge of 20–60 dry matter.
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| 19. |
- Hellström, Daniel
(författare)
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Natural sludge dewatering. II : Thawing-drying process in full-scale sludge freezing ditches
- 1997
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Ingår i: Journal of cold regions engineering. - 0887-381X .- 1943-5495. ; 11:1, s. 15-29
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Tidskriftsartikel (refereegranskat)abstract
- The thawing and drying process in full-scale sludge freezing ditches was studied. The ditches are located in northern Sweden. The treated sludge derived from a small wastewater-treatment plant with mechanical and chemical treatment. Due to the relatively warm winter of 1994–1995, it became possible to study the effect of incomplete freezing. The results show that frozen and thawed sludge has a porous and humus-like structure, whereas unfrozen sludge has a compact and smeary consistency. The study also shows that incomplete freezing decreases the dewaterability of the sludge, but that the result measured as solid content is satisfactory even if all the sludge is not well frozen. Moreover, the study indicates that the thawing depth could be estimated by a simple equation based on the number of positive degree-days.
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| 20. |
- Lindhagen, Johan, et al.
(författare)
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Low Temperature Strength and Notch Sensitivity of Glass Mat Polypropylene
- 1997
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Ingår i: Journal of cold regions engineering. - 0887-381X .- 1943-5495. ; 11:3, s. 180-197
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Tidskriftsartikel (refereegranskat)abstract
- Literature on the effects of lowered temperature on the toughness of random short fiber composites have neither offered a clear trend nor explained the mechanisms of failure. In this work, unnotched and notched strengths at room temperature and -30°C of two glass mat polypropylenes with different fiber architectures are investigated. Observations are explained based on models for Young's modulus and notch sensitivity. Increases in strength and stiffness with lowered temperature are caused by increased matrix modulus and yield stress. Fiber bridging operating in a damage zone of substantial length was the major toughening mechanism and forms the basis for the modeling approach for notch sensitivity. Increased notch toughness at low temperature is caused by increased work of fracture in the damage zone. The increased matrix modulus and yield stress lead to an increased toughening efficiency of short fibers.
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