{"title":"Issue Information","authors":"","doi":"10.1111/str.12390","DOIUrl":"https://doi.org/10.1111/str.12390","url":null,"abstract":"No abstract is available for this article.","PeriodicalId":51176,"journal":{"name":"Strain","volume":" ","pages":""},"PeriodicalIF":2.1,"publicationDate":"2022-01-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45816065","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This study is a combination of constant amplitude fatigue experimental tests with strain control technique and staircase method to assess the fatigue strain limit (FSL). The strain control provides a dwell‐fatigue test to the failure by a strain gauge bonded to the reduced section center of the specimen. A staircase test procedure with a vibration bending bench is detailed in this work, including parameters selection. The result analysis is based on kernel density estimation, used to access the FSL on non‐parameter distribution. Low‐carbon steel specimens with fatigue zone were selected to evaluate the FSL statistical features. The results highlight the efficiency of the strain‐controlled staircase method to reach the FSL.
{"title":"Experimental strain‐based vibration control to obtain the fatigue strain limit by the staircase method","authors":"Lu Shi, L. Khalij, C. Gautrelet","doi":"10.1111/str.12408","DOIUrl":"https://doi.org/10.1111/str.12408","url":null,"abstract":"This study is a combination of constant amplitude fatigue experimental tests with strain control technique and staircase method to assess the fatigue strain limit (FSL). The strain control provides a dwell‐fatigue test to the failure by a strain gauge bonded to the reduced section center of the specimen. A staircase test procedure with a vibration bending bench is detailed in this work, including parameters selection. The result analysis is based on kernel density estimation, used to access the FSL on non‐parameter distribution. Low‐carbon steel specimens with fatigue zone were selected to evaluate the FSL statistical features. The results highlight the efficiency of the strain‐controlled staircase method to reach the FSL.","PeriodicalId":51176,"journal":{"name":"Strain","volume":" ","pages":""},"PeriodicalIF":2.1,"publicationDate":"2022-01-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44156812","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pierre A. Faucheux, H. Miao, M. Lévesque, F. Gosselin
Aluminium skins on the lower wings of most commercial aircraft are shaped using shot peen forming. This process, which involves bombarding the skins with hard shot, uses nonuniform plastic flow to induce curvatures—in the same way that differential expansion makes metal bilayers bend when heated. Here, we investigate experimentally how constraining conditions affect the final shape of peen formed parts. We report peen forming experiments for 4.9‐mm‐thick rectangular 2024–T3 aluminium sheets of different aspect ratios uniformly shot peened on one face with a low intensity saturation treatment. Some specimens were free to deform during peening while others were elastically prestressed in a four‐point bending jig. For each aspect ratio and prestress condition, residual stresses were measured near the peened surface with the hole drilling method. Additional residual stress profiles were also obtained with the slitting method. The residual stress measurements show that the progressive deformation of unconstrained specimens had the same effect as an externally applied prestress. For the peening conditions investigated, this progressive deformation caused unconstrained strips to exhibit curvatures 33% larger than identical strips held flat during peening. Furthermore, we found that the relative importance of material anisotropy and geometric effects did determine the bending direction of unconstrained specimens.
{"title":"Peen forming and stress peen forming of rectangular 2024–T3 aluminium sheets: Curvatures, natural curvatures and residual stresses","authors":"Pierre A. Faucheux, H. Miao, M. Lévesque, F. Gosselin","doi":"10.1111/str.12405","DOIUrl":"https://doi.org/10.1111/str.12405","url":null,"abstract":"Aluminium skins on the lower wings of most commercial aircraft are shaped using shot peen forming. This process, which involves bombarding the skins with hard shot, uses nonuniform plastic flow to induce curvatures—in the same way that differential expansion makes metal bilayers bend when heated. Here, we investigate experimentally how constraining conditions affect the final shape of peen formed parts. We report peen forming experiments for 4.9‐mm‐thick rectangular 2024–T3 aluminium sheets of different aspect ratios uniformly shot peened on one face with a low intensity saturation treatment. Some specimens were free to deform during peening while others were elastically prestressed in a four‐point bending jig. For each aspect ratio and prestress condition, residual stresses were measured near the peened surface with the hole drilling method. Additional residual stress profiles were also obtained with the slitting method. The residual stress measurements show that the progressive deformation of unconstrained specimens had the same effect as an externally applied prestress. For the peening conditions investigated, this progressive deformation caused unconstrained strips to exhibit curvatures 33% larger than identical strips held flat during peening. Furthermore, we found that the relative importance of material anisotropy and geometric effects did determine the bending direction of unconstrained specimens.","PeriodicalId":51176,"journal":{"name":"Strain","volume":" ","pages":""},"PeriodicalIF":2.1,"publicationDate":"2021-12-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45564291","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Palaniappan Jaya Seelan, F. Pierron, J. Dulieu‐Barton
During a material deformation process, part of the mechanical energy is dissipated as heat due to thermodynamically irreversible processes occurring at the microscale of the material. In particular, part of the plastic deformation energy is transformed into heat and is referred to as ‘intrinsic dissipation’ as it is intrinsic to the material behaviour. The intrinsic dissipation is a heat source that is sensitive to microstructural states which can be used to identify different microstructural regions resulting from material processing such as welding. To determine the heat source in a full‐field manner, it is necessary to use an infrared camera to measure any temperature rise in a specimen undergoing elastic cyclic loading. Unlike the intrinsic dissipative heat source, the temperature change is sensitive to thermal exchanges with the surroundings. Hence, the thermomechanical heat diffusion equation is used to determine the full‐field dissipative heat from the thermographic temperature measurement by implementing an image processing procedure based on least squares fitting enabled by specially devised experimental approach. The procedure is verified by deriving both the thermoelastic and dissipative heat sources from a ‘hole‐in‐plate’ specimen manufactured from 316L stainless steel, that is, a specimen with a known stress distribution. The approach is then applied to a 316L laser welded specimen, and it is demonstrated that the different microstructures resulting from the welding process can be identified with the procedure. The heterogeneous microstructure is confirmed using micrographs and further verified by the different stress–strain behaviour obtained for each microstructural region using digital image correlation (DIC).
{"title":"Assessment of the heterogeneous microstructure in the vicinity of a weld using thermographic measurements of the full‐field dissipative heat source","authors":"Palaniappan Jaya Seelan, F. Pierron, J. Dulieu‐Barton","doi":"10.1111/str.12406","DOIUrl":"https://doi.org/10.1111/str.12406","url":null,"abstract":"During a material deformation process, part of the mechanical energy is dissipated as heat due to thermodynamically irreversible processes occurring at the microscale of the material. In particular, part of the plastic deformation energy is transformed into heat and is referred to as ‘intrinsic dissipation’ as it is intrinsic to the material behaviour. The intrinsic dissipation is a heat source that is sensitive to microstructural states which can be used to identify different microstructural regions resulting from material processing such as welding. To determine the heat source in a full‐field manner, it is necessary to use an infrared camera to measure any temperature rise in a specimen undergoing elastic cyclic loading. Unlike the intrinsic dissipative heat source, the temperature change is sensitive to thermal exchanges with the surroundings. Hence, the thermomechanical heat diffusion equation is used to determine the full‐field dissipative heat from the thermographic temperature measurement by implementing an image processing procedure based on least squares fitting enabled by specially devised experimental approach. The procedure is verified by deriving both the thermoelastic and dissipative heat sources from a ‘hole‐in‐plate’ specimen manufactured from 316L stainless steel, that is, a specimen with a known stress distribution. The approach is then applied to a 316L laser welded specimen, and it is demonstrated that the different microstructures resulting from the welding process can be identified with the procedure. The heterogeneous microstructure is confirmed using micrographs and further verified by the different stress–strain behaviour obtained for each microstructural region using digital image correlation (DIC).","PeriodicalId":51176,"journal":{"name":"Strain","volume":" ","pages":""},"PeriodicalIF":2.1,"publicationDate":"2021-12-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47357795","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The checkerboard constitutes the best pattern for in‐plane displacement and strain measurement because it maximizes image gradient. The use of laser marking to deposit such a pattern on flat surfaces is investigated in this paper. Optimal settings for the parameters influencing the quality of the pattern are given. This pattern being periodic, the images are processed with the localized spectrum analysis, which is one of the spectral techniques used to process such images. It is shown that the metrological performance in terms of measurement resolution is equivalent to the one obtained with transferred checkerboards. Compared to the classic transfer technique generally used to deposit such patterns, the benefit of using laser marking is its ease of use, a much higher print speed and the fact that a thin coat of white paint instead of a thicker layer of white adhesive is employed to ensure a good contrast in the images. Various examples of strain measurements are given, in particular the measurement of the strain field around a knot embedded in a wood specimen subjected to a tensile test.
{"title":"Using laser marking to engrave optimal patterns for in‐plane displacement and strain measurement","authors":"Quentin Bouyra, B. Blaysat, H. Chanal, M. Grédiac","doi":"10.1111/str.12404","DOIUrl":"https://doi.org/10.1111/str.12404","url":null,"abstract":"The checkerboard constitutes the best pattern for in‐plane displacement and strain measurement because it maximizes image gradient. The use of laser marking to deposit such a pattern on flat surfaces is investigated in this paper. Optimal settings for the parameters influencing the quality of the pattern are given. This pattern being periodic, the images are processed with the localized spectrum analysis, which is one of the spectral techniques used to process such images. It is shown that the metrological performance in terms of measurement resolution is equivalent to the one obtained with transferred checkerboards. Compared to the classic transfer technique generally used to deposit such patterns, the benefit of using laser marking is its ease of use, a much higher print speed and the fact that a thin coat of white paint instead of a thicker layer of white adhesive is employed to ensure a good contrast in the images. Various examples of strain measurements are given, in particular the measurement of the strain field around a knot embedded in a wood specimen subjected to a tensile test.","PeriodicalId":51176,"journal":{"name":"Strain","volume":"58 1","pages":""},"PeriodicalIF":2.1,"publicationDate":"2021-12-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41777409","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Issue Information","authors":"","doi":"10.1111/str.12360","DOIUrl":"https://doi.org/10.1111/str.12360","url":null,"abstract":"No abstract is available for this article.","PeriodicalId":51176,"journal":{"name":"Strain","volume":" ","pages":""},"PeriodicalIF":2.1,"publicationDate":"2021-11-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41591048","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This paper proposes to measure true stress–strain curves at the necking region of cylindrical bar samples by using an advanced mirror‐assisted multi‐view digital image correlation (MV–DIC) technique. The mirror‐assisted MV–DIC can measure the panoramic shape and deformation fields of a cylindrical bar sample with only a single two‐camera stereo‐DIC system and two planar mirrors. The measured panoramic shape enables accurate determination of the cross‐section area and radius of curvature at the necking region by using cylindrical or torus fitting. The retrieved cross‐section area and radius of curvature at the necking region further enable the measurement of the true stress–strain curves and even the Bridgman's correction of the true stress.
{"title":"Measuring true stress–strain curves of cylindrical bar samples with mirror‐assisted multi‐view digital image correlation","authors":"Bin Chen, B. Pan","doi":"10.1111/str.12403","DOIUrl":"https://doi.org/10.1111/str.12403","url":null,"abstract":"This paper proposes to measure true stress–strain curves at the necking region of cylindrical bar samples by using an advanced mirror‐assisted multi‐view digital image correlation (MV–DIC) technique. The mirror‐assisted MV–DIC can measure the panoramic shape and deformation fields of a cylindrical bar sample with only a single two‐camera stereo‐DIC system and two planar mirrors. The measured panoramic shape enables accurate determination of the cross‐section area and radius of curvature at the necking region by using cylindrical or torus fitting. The retrieved cross‐section area and radius of curvature at the necking region further enable the measurement of the true stress–strain curves and even the Bridgman's correction of the true stress.","PeriodicalId":51176,"journal":{"name":"Strain","volume":" ","pages":""},"PeriodicalIF":2.1,"publicationDate":"2021-11-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46833358","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In order to advance the understanding of fracture failure mechanisms in concrete, a series of three‐point bend tests of pre‐notched specimens were conducted to study the characteristics of the fracture process zone. Electronic speckle pattern interferometry (ESPI) was used to determine the location and size of the cracks. The experimental results have shown that crack in the pre‐notched concrete beams will initiate when the load increases to 40% of the peak load (Pmax) and expands unstably after reaching the peak load. When the load drops to about 25% Pmax in the load drop section, a complete fracture process zone (FPZ) was developed, and the corresponding crack tip opening displacement is about 7.1 times to the critical crack tip opening displacement. The analysis of surface strain of concrete specimen showed that microcracks will initiate when the surface tensile strain of concrete reaches about 2 × 10−4; when the surface tensile strain value of concrete reaches 4 × 10−2, the FPZ will move forward; the length of the FPZ of concrete essentially remains the same in the entire fracture process, which is about 71% of the ligament height. The analysis of experimental data also shows that the size of the FPZ is not significantly affected by the cubic compressive strength of concrete. In addition, the tension‐softening curves of the specimens were finally determined by using the incremental displacement collocation method, and it is concluded that the critical width of the FPZ is related to the cubic compressive strength of the concrete.
{"title":"Experimental investigation on the concrete fracture process zone using electronic speckle pattern interferometry","authors":"Xingzhen Huang, Hongniao Chen, Bin Sun","doi":"10.1111/str.12402","DOIUrl":"https://doi.org/10.1111/str.12402","url":null,"abstract":"In order to advance the understanding of fracture failure mechanisms in concrete, a series of three‐point bend tests of pre‐notched specimens were conducted to study the characteristics of the fracture process zone. Electronic speckle pattern interferometry (ESPI) was used to determine the location and size of the cracks. The experimental results have shown that crack in the pre‐notched concrete beams will initiate when the load increases to 40% of the peak load (Pmax) and expands unstably after reaching the peak load. When the load drops to about 25% Pmax in the load drop section, a complete fracture process zone (FPZ) was developed, and the corresponding crack tip opening displacement is about 7.1 times to the critical crack tip opening displacement. The analysis of surface strain of concrete specimen showed that microcracks will initiate when the surface tensile strain of concrete reaches about 2 × 10−4; when the surface tensile strain value of concrete reaches 4 × 10−2, the FPZ will move forward; the length of the FPZ of concrete essentially remains the same in the entire fracture process, which is about 71% of the ligament height. The analysis of experimental data also shows that the size of the FPZ is not significantly affected by the cubic compressive strength of concrete. In addition, the tension‐softening curves of the specimens were finally determined by using the incremental displacement collocation method, and it is concluded that the critical width of the FPZ is related to the cubic compressive strength of the concrete.","PeriodicalId":51176,"journal":{"name":"Strain","volume":" ","pages":""},"PeriodicalIF":2.1,"publicationDate":"2021-10-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43719932","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Issue Information","authors":"","doi":"10.1111/str.12359","DOIUrl":"https://doi.org/10.1111/str.12359","url":null,"abstract":"No abstract is available for this article.","PeriodicalId":51176,"journal":{"name":"Strain","volume":" ","pages":""},"PeriodicalIF":2.1,"publicationDate":"2021-09-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1111/str.12359","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41770099","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Finite element generated synthetic image deformation is used to assess factors affecting the reliability and accuracy of strain fields measured by the DIC technique, when using the inherent historical tapestry image to track deformations. Compared with direct correlation with the reference image, incremental correlation is found to introduce accumulated error and is less suitable for DIC analysis under low strains. Image quality, for example, variation in resolution, is demonstrated to strongly affect DIC performance. Finally, it is recommended that an iterative approach is required to determine the optimum subset and strain filter size for effective DIC analysis using inherent tapestry patterns, especially at low strain levels.
{"title":"Investigating the accuracy of digital image correlation in monitoring strain fields across historical tapestries","authors":"K. Nwanoro, P. Harrison, F. Lennard","doi":"10.1111/str.12401","DOIUrl":"https://doi.org/10.1111/str.12401","url":null,"abstract":"Finite element generated synthetic image deformation is used to assess factors affecting the reliability and accuracy of strain fields measured by the DIC technique, when using the inherent historical tapestry image to track deformations. Compared with direct correlation with the reference image, incremental correlation is found to introduce accumulated error and is less suitable for DIC analysis under low strains. Image quality, for example, variation in resolution, is demonstrated to strongly affect DIC performance. Finally, it is recommended that an iterative approach is required to determine the optimum subset and strain filter size for effective DIC analysis using inherent tapestry patterns, especially at low strain levels.","PeriodicalId":51176,"journal":{"name":"Strain","volume":" ","pages":""},"PeriodicalIF":2.1,"publicationDate":"2021-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1111/str.12401","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46874339","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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