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| 2. |
- Bergström, Lena, et al.
(author)
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Coastal fish indicators response to natural and anthropogenic drivers-variability at temporal and different spatial scales
- 2016
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In: Estuarine, Coastal and Shelf Science. - : Elsevier BV. - 0272-7714 .- 1096-0015. ; 183, s. 62-72
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Journal article (peer-reviewed)abstract
- Ecological indicators are increasingly used in marine and freshwater management but only few are developed towards full operationalization with known patterns of variability and documented responses to natural and anthropogenic environmental drivers. Here, we evaluate potential sources of indicator variability at two different spatial scales in three coastal fish-based indicators of environmental status in the Baltic Sea; abundance of cyprinids, abundance of perch and the proportion of larger perch. The study was performed on a data set covering 41 monitoring areas subject to different levels of anthropogenic impact, at a latitudinal range of 56-66 degrees N and a salinity range of 2-8. Interannual variation was clearly minor relative to spatial variation. Small-scale spatial variation was related to water depth, wave exposure and water temperature. The remaining variation was assessed in relation to differences in natural and anthropogenic drivers between monitoring areas. Cyprinids showed a clear inverse relationship to water transparency, which was used as a proxy for eutrophication, indicating increased abundances in nutrient enriched areas. None of the indicators showed an expected negative relationship to the level of coastal commercial fisheries catches. Rather, a positive relationship for Perch suggested that the coastal fisheries were concentrated to areas with strong perch populations in the studied areas. The effect of salinity and climate (temperature during the growth season) among monitoring areas were small. The results emphasize the importance of assigning area-specific boundary levels to define good environmental status in the coastal fish indicators, in order to account for natural sources of variability. Further, although long-term monitoring in reference areas is crucial for obtaining a historical baseline, our results suggest that the status assessment of coastal fish would generally gain precision by increasingly including spatially based assessments. We propose that similar analytical approaches could be applied to other ecosystem components, especially in naturally heterogenic environments, in order to separate indicator variability attributed to potential anthropogenic impact. (C) 2016 The Authors. Published by Elsevier Ltd.
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| 3. |
- Bergström, Stig M., et al.
(author)
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Maurits Lindström - A renaissance geoscientist
- 2007
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In: GFF. - : the Geological Society of Sweden. - 1103-5897. ; 129:2, s. 65-69
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Journal article (other academic/artistic)abstract
- This issue of the GFF is dedicated to Professor Maurits Lindström on the occasion of his 75th birthday by students, colleagues, and friends in recognition of his profound impact on the Science of Geology as researcher and teacher during more than half a century.
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| 5. |
- Ekengren, Jens, 1976-, et al.
(author)
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Assessment of strength and inclusions of tool steels in very high cycle fatigue
- 2009
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In: Proceedings of the 8th International Tooling Conference, Vol 1. - Aachen : Verlag Mainz, Wissenschaftsverlag. - 9783810793058
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Conference paper (peer-reviewed)abstract
- Fatigue strength is an important material property for many tooling applications, particularly in high performance applications. The research in Very High Cycle Fatigue (VHCF) has demonstrated that the traditional fatigue limit may not be valid for many materials subjected to 107 or more load cycles. Presently, both materials data and mechanism knowledge is missing on VHCF applications, even though many components are run at these life lengths. The fatigue strength is commonly controlled by different defects initiating failure, as in well controlled laboratory experiments may be internal inclusions. In this paper VHCF experimental testing was accomplished by the use of ultrasonic fatigue testing run at 20 kHz allowing long life evaluation within reasonably short test time. Fatigue strength, failure mechanisms and inclusion content were accordingly assessed. Fatigue strength data on H13 tool steel are presented, as well as a statistical approach considering available defect distribution and load distribution in the critically stressed volume, important to both steel supplier and end-user.
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| 6. |
- Ekengren, Jens, 1976-, et al.
(author)
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Detecting large inclusions in steels : evaluating methods
- 2009
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In: Steel Research International. - : Wiley-VCH Verlagsgesellschaft. - 1611-3683 .- 1869-344X. ; 80:11, s. 854-858
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Journal article (peer-reviewed)abstract
- The distributions of large non-metallic inclusions in two steel grades have been investigated using light optical microscopy, scanning electron microscopy and ultrasonic fatigue testing in the gigacycle range. The different methods have inherently different capabilities for finding inclusions in different size ranges. A measure of the distribution of large inclusions is proposed as the size S at which half of the fatigue specimens are expected to contain at least one inclusion of size S or larger, corresponding to 50% failure probability. Values of S are obtained using the volume distribution estimated by the three methods. Extrapolation from microscopy measurements on surfaces agree with fatigue fractography results regarding density of large inclusions, as measured by the proposed ranking variable S
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| 7. |
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| 8. |
- Ekengren, Jens, 1976-, et al.
(author)
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Detecting large inclusions in steels : evaluating methods
- 2009
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In: Steel Research International. - Weinheim, Germany : Wiley-VCH Verlagsgesellschaft. - 1611-3683 .- 1869-344X. ; 80:11, s. 854-858
-
Journal article (peer-reviewed)abstract
- The distributions of large non-metallic inclusions in two steel grades have been investigated using light optical microscopy, scanning electron microscopy and ultrasonic fatigue testing in the gigacycle range. The different methods have inherently different capabilities for finding inclusions in different size ranges. A measure of the distribution of large inclusions is proposed as the size S at which half of the fatigue specimens are expected to contain at least one inclusion of size S or larger, corresponding to 50% failure probability. Values of S are obtained using the volume distribution estimated by the three methods. Extrapolation from microscopy measurements on surfaces agree with fatigue fractography results regarding density of large inclusions, as measured by the proposed ranking variable S.
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| 9. |
- Ekengren, Jens, 1976-
(author)
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Estimating inclusion content in high performance steels
- 2008
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Licentiate thesis (other academic/artistic)abstract
- Non-metallic inclusions in steel pose a major problem for the fatigue resistance, especially regarding fatigue at very long lives corresponding to low cyclic stress levels, as well as being detrimental to material toughness and polishability.The largest inclusions are quite rare, which makes conventional detection methods timeconsuming if reliable results are to be obtained. Based on surface scanning using light or electron microscopes, these methods provide results that have to be converted to reflect the statistical volume distribution of inclusions.Very high cycle fatigue (in the order of 109 cycles or more) using ultrasonic fatigue at 20 kHz has been found efficient at finding the largest inclusions in volumes of about 300 mm3 per specimen. The inclusions found at the fatigue initiation site can then been used to estimate the distribution of large inclusions using extreme value statistics.In this work, a new method for estimating the volume distribution of large inclusions is presented as well as a suggested ranking variable based on the volume distribution.Results from fatigue fractography and area scanning methods are compared to the endurance limit at 109 cycles for a number of batches from two high performance steels.In addition, the extreme value distributions of fatigue initiating inclusions in six high performace steels, produced by different routes, are presented. It is shown that all modes of the Generalized Extreme Values distribution can be found in different materials. This result shows that the assumption of mode I distribution, also known as Gumbel or Largest Extreme Value distribution, must be substantiated.
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| 10. |
- Ekengren, Jens, 1976-, et al.
(author)
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Estimating the volume distribution of large defects using Generalized Extreme Values
- 2011
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In: Extremes. - 1386-1999 .- 1572-915X.
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Other publication (other academic/artistic)abstract
- The presence of defects, such as oxides and other non-metallic inclusions, is an important factor in determining the properties of steels. Due to improvements in the manufacturing of high-quality steels, the amount of large defects has decreased and therefore it has become increasingly difficult to accurately determine their distribution using conventional methods. Previously, a method for estimating the distribution of large defects using a conversion from the Gumbel distribution has been presented. However, it has been shown that the Gumbel distribution is not always appropriate for modelling the sizes of the largest defects and that the Generalized Extreme Values (GEV) distribution should be used instead. In this work a more general method for the estimation of the total volume distribution of large defects isproposed, showing how the volume distribution may be calculated from the estimated parameters for the GEV distribution. The new method is applied to the results of a series of specimens made from high-quality tool steel tested in ultrasonic resonance fatigue. Possible methods for obtaining the confidence limits of thevolume distribution are also discussed.
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