{"title":"Issue Information","authors":"","doi":"10.1111/str.12323","DOIUrl":"https://doi.org/10.1111/str.12323","url":null,"abstract":"No abstract is available for this article.","PeriodicalId":51176,"journal":{"name":"Strain","volume":" ","pages":""},"PeriodicalIF":2.1,"publicationDate":"2020-09-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1111/str.12323","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49626427","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}
Full‐field optical measurements like digital image correlation or the grid method have brought a paradigm shift in the experimental mechanics community. While inverse identification techniques like finite element model updating or the virtual fields method have been the object of significant developments, current test methods, inherited from the age of strain gauges or linear variable displacement transducers, are generally not well adapted to the rich information provided by these new measurement tools. This paper provides a review of the research dealing with the design and optimization of heterogeneous mechanical tests for the identification of material parameters from full‐field measurements, christened here Material Testing 2.0 (MT2.0).
{"title":"Towards Material Testing 2.0. A review of test design for identification of constitutive parameters from full‐field measurements","authors":"F. Pierron, M. Grédiac","doi":"10.1111/str.12370","DOIUrl":"https://doi.org/10.1111/str.12370","url":null,"abstract":"Full‐field optical measurements like digital image correlation or the grid method have brought a paradigm shift in the experimental mechanics community. While inverse identification techniques like finite element model updating or the virtual fields method have been the object of significant developments, current test methods, inherited from the age of strain gauges or linear variable displacement transducers, are generally not well adapted to the rich information provided by these new measurement tools. This paper provides a review of the research dealing with the design and optimization of heterogeneous mechanical tests for the identification of material parameters from full‐field measurements, christened here Material Testing 2.0 (MT2.0).","PeriodicalId":51176,"journal":{"name":"Strain","volume":"57 1","pages":""},"PeriodicalIF":2.1,"publicationDate":"2020-09-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1111/str.12370","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42148183","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}
Response of dry stack stone masonry walls under mechanical loading is complex and difficult to determine, mainly due to heterogeneous and discrete nature of the components of the stone wall. In this paper, reflection photoelasticity is used on scaled down models of stone masonry wall under uniaxial compression. Two walls are tested, and the methods to obtain near perfect dry stack masonry for reflection photoelastic studies are presented. Five‐step phase‐shifting methods are employed with TFP/RGB photoelasticity to quantitatively analyse the mechanical behaviour of the dry stack masonry walls. Isochromatics and isoclinic data are processed to obtain other whole field experimental stress data. Highly stressed zones are observed resulting in distinctive localised vertical failure in some of the stone units. In dry stack masonry construction, the failure mechanism is found to be dictated by the contact mechanics, which are governed by the non‐uniformity of block geometry even in very regular dry stack masonry.
{"title":"Experimental study of dry stone masonry walls using digital reflection photoelasticity","authors":"Pankaj Kumar, M. Hariprasad, A. Menon, K. Ramesh","doi":"10.1111/str.12372","DOIUrl":"https://doi.org/10.1111/str.12372","url":null,"abstract":"Response of dry stack stone masonry walls under mechanical loading is complex and difficult to determine, mainly due to heterogeneous and discrete nature of the components of the stone wall. In this paper, reflection photoelasticity is used on scaled down models of stone masonry wall under uniaxial compression. Two walls are tested, and the methods to obtain near perfect dry stack masonry for reflection photoelastic studies are presented. Five‐step phase‐shifting methods are employed with TFP/RGB photoelasticity to quantitatively analyse the mechanical behaviour of the dry stack masonry walls. Isochromatics and isoclinic data are processed to obtain other whole field experimental stress data. Highly stressed zones are observed resulting in distinctive localised vertical failure in some of the stone units. In dry stack masonry construction, the failure mechanism is found to be dictated by the contact mechanics, which are governed by the non‐uniformity of block geometry even in very regular dry stack masonry.","PeriodicalId":51176,"journal":{"name":"Strain","volume":" ","pages":""},"PeriodicalIF":2.1,"publicationDate":"2020-09-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1111/str.12372","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41874387","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 ability to characterise residual stress distribution accurately and over different length scales, particularly deep into an engineering part, plays a significant role in assessing structural integrity. Two most commonly used techniques to measure residual stress fields deep into engineering components include neutron diffraction (ND) and deep‐hole drilling (DHD). As the measurements depend on several physical quantities, they are susceptible to error. The error or uncertainties may turn substantial and compromise the suitability of the results. Although noninvasive, the neutron diffraction technique is neither readily available nor portable and is limited to approximately 60‐mm‐thick specimen; errors associated with results become unacceptable at greater flight paths. Moreover, a mock‐up representing the engineering component is normally used in the ND technique. In contrast, the DHD technique is portable and measures residual stresses with high spatial resolution. An error propagation technique was applied to develop an error analysis procedure taking into consideration various stages of the DHD method and successfully applied to different DHD measurements. An essential feature comprising the effect of plasticity due to the creation of reference hole in the DHD procedure has not yet been taken into account in the error analysis procedure. This paper briefly describes how the uncertainties due to the creation of the initial reference hole can be determined. The effect of plasticity in the drilling procedure is quantified in this study. This error is combined with other sources of error and formulated to determine the total error. An incremental DHD technique was used to measure the complex triaxial residual stress field in an as‐welded circular disc, and the measured data were used to illustrate the total error using the error analysis method developed in the study.
{"title":"Advances in analysis of total uncertainties in a semi‐invasive residual stress measurement method","authors":"S. Hossain, G. Zheng, D. Goudar","doi":"10.1111/str.12368","DOIUrl":"https://doi.org/10.1111/str.12368","url":null,"abstract":"The ability to characterise residual stress distribution accurately and over different length scales, particularly deep into an engineering part, plays a significant role in assessing structural integrity. Two most commonly used techniques to measure residual stress fields deep into engineering components include neutron diffraction (ND) and deep‐hole drilling (DHD). As the measurements depend on several physical quantities, they are susceptible to error. The error or uncertainties may turn substantial and compromise the suitability of the results. Although noninvasive, the neutron diffraction technique is neither readily available nor portable and is limited to approximately 60‐mm‐thick specimen; errors associated with results become unacceptable at greater flight paths. Moreover, a mock‐up representing the engineering component is normally used in the ND technique. In contrast, the DHD technique is portable and measures residual stresses with high spatial resolution. An error propagation technique was applied to develop an error analysis procedure taking into consideration various stages of the DHD method and successfully applied to different DHD measurements. An essential feature comprising the effect of plasticity due to the creation of reference hole in the DHD procedure has not yet been taken into account in the error analysis procedure. This paper briefly describes how the uncertainties due to the creation of the initial reference hole can be determined. The effect of plasticity in the drilling procedure is quantified in this study. This error is combined with other sources of error and formulated to determine the total error. An incremental DHD technique was used to measure the complex triaxial residual stress field in an as‐welded circular disc, and the measured data were used to illustrate the total error using the error analysis method developed in the study.","PeriodicalId":51176,"journal":{"name":"Strain","volume":" ","pages":""},"PeriodicalIF":2.1,"publicationDate":"2020-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1111/str.12368","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43885476","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.12322","DOIUrl":"https://doi.org/10.1111/str.12322","url":null,"abstract":"No abstract is available for this article.","PeriodicalId":51176,"journal":{"name":"Strain","volume":" ","pages":""},"PeriodicalIF":2.1,"publicationDate":"2020-07-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1111/str.12322","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49312636","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 this paper, the use of the virtual fields method for the identification of a strongly asymmetric compression–tension response of rock‐like materials under dynamic tensile loading is investigated. The photomechanical spalling set‐up is used, which induces an indirect tensile load in a non‐balanced sample, and the inertial component of the test is directly related to the measured dynamic stress with no previous assumption on the material behaviour. This experimental method provides a direct route to identifying the material asymmetric constitutive response in compression and tension under a uniaxial stress state as well as the material non‐linear response after tensile strength is reached. To validate this approach, the entire measurement chain for the case of a post‐peak response is investigated through simulated experiments that incorporate a damage model and synthetic grid images. Finally, the method is applied to the case of granite rock, namely, a Bohus granite, as to directly measure the material asymmetric compression–tension and the softening response after peak tensile stress.
{"title":"Validation of the photomechanical spalling test in the case of non‐linear dynamic response: Application to a granite rock","authors":"B. Lukić, D. Saletti, P. Forquin","doi":"10.1111/str.12363","DOIUrl":"https://doi.org/10.1111/str.12363","url":null,"abstract":"In this paper, the use of the virtual fields method for the identification of a strongly asymmetric compression–tension response of rock‐like materials under dynamic tensile loading is investigated. The photomechanical spalling set‐up is used, which induces an indirect tensile load in a non‐balanced sample, and the inertial component of the test is directly related to the measured dynamic stress with no previous assumption on the material behaviour. This experimental method provides a direct route to identifying the material asymmetric constitutive response in compression and tension under a uniaxial stress state as well as the material non‐linear response after tensile strength is reached. To validate this approach, the entire measurement chain for the case of a post‐peak response is investigated through simulated experiments that incorporate a damage model and synthetic grid images. Finally, the method is applied to the case of granite rock, namely, a Bohus granite, as to directly measure the material asymmetric compression–tension and the softening response after peak tensile stress.","PeriodicalId":51176,"journal":{"name":"Strain","volume":" ","pages":""},"PeriodicalIF":2.1,"publicationDate":"2020-07-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1111/str.12363","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43412564","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}
R. Vargas, A. Tsitova, F. Bernachy-Barbe, Benoit Bary, R. B. Canto, François Hild
This paper proposes an approach to defining the path of a curved crack in a single‐edge notched specimen with gray level residuals extracted from digital image correlation, followed by the calibration of the parameters of a cohesive zone model. Only the experimental force is used in the cost function minimized via finite element model updating. The displacement and gray level residual fields allow for the validation of the calibrated parameters. Last, the results are confronted with those given by a straight crack to highlight the benefits of accounting for the actual crack path.
{"title":"On the identification of cohesive zone model for curved crack in mortar","authors":"R. Vargas, A. Tsitova, F. Bernachy-Barbe, Benoit Bary, R. B. Canto, François Hild","doi":"10.1111/str.12364","DOIUrl":"https://doi.org/10.1111/str.12364","url":null,"abstract":"This paper proposes an approach to defining the path of a curved crack in a single‐edge notched specimen with gray level residuals extracted from digital image correlation, followed by the calibration of the parameters of a cohesive zone model. Only the experimental force is used in the cost function minimized via finite element model updating. The displacement and gray level residual fields allow for the validation of the calibrated parameters. Last, the results are confronted with those given by a straight crack to highlight the benefits of accounting for the actual crack path.","PeriodicalId":51176,"journal":{"name":"Strain","volume":" ","pages":""},"PeriodicalIF":2.1,"publicationDate":"2020-07-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1111/str.12364","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48757803","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}
S. R. Akanda, R. Wheeler, K. Rozman, Jessica Rider, Ö. Doğan, M. L. Young, J. Hawk
Deformation of a weldment is governed by the mechanical properties of its base metals and fusion zone. In a weldment, the base metals and fusion zone exhibit changing microstructural features with various phases present along the weldment. Specifically, the heat affected zone of a base metal exhibits a heterogeneous microstructure generated during weld thermal cycles and by post‐weld heat treatment. As a result, the mechanical properties in a weldment are often non‐uniformly distributed. In this study, tensile tests combined with digital image correlation were performed to obtain the non‐uniform distributions of the mechanical properties of a weldment composed of P91 and 347H steels. From the experimental tensile tests, it was found that the 347H base metal had significantly distinct mechanical properties compared to the other zones of the weldment. Furthermore, the 347H base metal had the lowest yield stress but the highest strain hardening exponent. Because of its lowest yield stress, the 347H base metal had the highest plastic strain accumulation at any stage of global deformation. However, the strain hardening rate of the P91 base metal enabled it to accumulate the necessary plastic strain to activate its necking first. Therefore, the failure location of the P91‐347H weldment was expected to occur at the P91 base metal. A 3D finite element simulation of the tensile deformation of P91‐347H weldment also suggested the same. However, from the present experimental observations, one weldment out of three was found to fail unexpectedly at the heat affected zone of the P91 base metal. The reason for this unexpected failure was determined by microscopic analysis to be the presence of a large defect.
{"title":"Tensile deformation behaviour of a dissimilar metal weldment of P91 and 347H steels","authors":"S. R. Akanda, R. Wheeler, K. Rozman, Jessica Rider, Ö. Doğan, M. L. Young, J. Hawk","doi":"10.1111/str.12366","DOIUrl":"https://doi.org/10.1111/str.12366","url":null,"abstract":"Deformation of a weldment is governed by the mechanical properties of its base metals and fusion zone. In a weldment, the base metals and fusion zone exhibit changing microstructural features with various phases present along the weldment. Specifically, the heat affected zone of a base metal exhibits a heterogeneous microstructure generated during weld thermal cycles and by post‐weld heat treatment. As a result, the mechanical properties in a weldment are often non‐uniformly distributed. In this study, tensile tests combined with digital image correlation were performed to obtain the non‐uniform distributions of the mechanical properties of a weldment composed of P91 and 347H steels. From the experimental tensile tests, it was found that the 347H base metal had significantly distinct mechanical properties compared to the other zones of the weldment. Furthermore, the 347H base metal had the lowest yield stress but the highest strain hardening exponent. Because of its lowest yield stress, the 347H base metal had the highest plastic strain accumulation at any stage of global deformation. However, the strain hardening rate of the P91 base metal enabled it to accumulate the necessary plastic strain to activate its necking first. Therefore, the failure location of the P91‐347H weldment was expected to occur at the P91 base metal. A 3D finite element simulation of the tensile deformation of P91‐347H weldment also suggested the same. However, from the present experimental observations, one weldment out of three was found to fail unexpectedly at the heat affected zone of the P91 base metal. The reason for this unexpected failure was determined by microscopic analysis to be the presence of a large defect.","PeriodicalId":51176,"journal":{"name":"Strain","volume":" ","pages":""},"PeriodicalIF":2.1,"publicationDate":"2020-06-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1111/str.12366","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45740578","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}
We present a new approach to assess the two‐dimensional motion of rigid bodies in granular materials. Although it was adapted from digital image correlation technique, the heart of the presented technique relies on specific treatments related to the discrete nature of grain‐displacement fields. The code called Tracker has been developed to process the digital images and measure the in‐plane displacement and rotation of each individual grain from one image to another. A remarkable feature is the use of a specific strategy that allows tracking all particles, without losing any of them (which is a typical problem when tracking assemblies of discrete particles over many images). This is achieved by a two‐step procedure, where, in case of problematic tracking of a grain, the size of the search zone is increased in an adaptive manner, that is, taking into account the results of tracking in the neighbourhood of the particle. The accuracy of the measured displacements and rotations was tested on both perfect synthetic images and digital photographs of a sheared assembly of grains. An automatic procedure that corrects the lens distortion further improves the quality of the measurements. The accurate assessment of the grain kinematics opens very interesting perspectives, especially in the study of displacement fluctuations in granular media.
{"title":"The particle image tracking technique: An accurate optical method for measuring individual kinematics of rigid particles","authors":"V. Richefeu, G. Combe","doi":"10.1111/str.12362","DOIUrl":"https://doi.org/10.1111/str.12362","url":null,"abstract":"We present a new approach to assess the two‐dimensional motion of rigid bodies in granular materials. Although it was adapted from digital image correlation technique, the heart of the presented technique relies on specific treatments related to the discrete nature of grain‐displacement fields. The code called Tracker has been developed to process the digital images and measure the in‐plane displacement and rotation of each individual grain from one image to another. A remarkable feature is the use of a specific strategy that allows tracking all particles, without losing any of them (which is a typical problem when tracking assemblies of discrete particles over many images). This is achieved by a two‐step procedure, where, in case of problematic tracking of a grain, the size of the search zone is increased in an adaptive manner, that is, taking into account the results of tracking in the neighbourhood of the particle. The accuracy of the measured displacements and rotations was tested on both perfect synthetic images and digital photographs of a sheared assembly of grains. An automatic procedure that corrects the lens distortion further improves the quality of the measurements. The accurate assessment of the grain kinematics opens very interesting perspectives, especially in the study of displacement fluctuations in granular media.","PeriodicalId":51176,"journal":{"name":"Strain","volume":" ","pages":""},"PeriodicalIF":2.1,"publicationDate":"2020-06-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1111/str.12362","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49158994","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 study the residual stress induced by foreign object damage (FOD), the distribution of residual stress caused by the impact of a hard spherical body was measured via the sin2ψ technique, using synchrotron X‐ray. A steel sphere was impacted onto a flat surface of a Ti‐6Al‐4V alloy from an angle of either 90° or 45°, at a velocity of 180 m/s. The same sphere was also quasi‐statically pressed into the surface. In the cases of right‐angled impact and quasi‐static indentation, a compressive residual stress was extensively distributed inside the generated crater. No remarkable difference in residual stress distribution was noted between the dynamic case and the quasi‐static case. However, at an impact angle of 45°, a tensile residual stress that is more detrimental to fatigue strength was widely distributed inside the crater. Outside of the craters, tensile stress was generally observed in all cases.
{"title":"Effect of impact velocity and impact angle on residual stress fields caused by foreign object damage","authors":"H. Matsunaga","doi":"10.1111/str.12367","DOIUrl":"https://doi.org/10.1111/str.12367","url":null,"abstract":"In order to study the residual stress induced by foreign object damage (FOD), the distribution of residual stress caused by the impact of a hard spherical body was measured via the sin2ψ technique, using synchrotron X‐ray. A steel sphere was impacted onto a flat surface of a Ti‐6Al‐4V alloy from an angle of either 90° or 45°, at a velocity of 180 m/s. The same sphere was also quasi‐statically pressed into the surface. In the cases of right‐angled impact and quasi‐static indentation, a compressive residual stress was extensively distributed inside the generated crater. No remarkable difference in residual stress distribution was noted between the dynamic case and the quasi‐static case. However, at an impact angle of 45°, a tensile residual stress that is more detrimental to fatigue strength was widely distributed inside the crater. Outside of the craters, tensile stress was generally observed in all cases.","PeriodicalId":51176,"journal":{"name":"Strain","volume":" ","pages":""},"PeriodicalIF":2.1,"publicationDate":"2020-06-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1111/str.12367","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44766265","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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