Combined shear-compression tests and simulations were performed on a closed-cell aluminum foam over a wide range of loading angles in order to probe their yield behaviors under biaxial loading conditions.Combined shea...Combined shear-compression tests and simulations were performed on a closed-cell aluminum foam over a wide range of loading angles in order to probe their yield behaviors under biaxial loading conditions.Combined shear-compression tests were carried out by using a pair of cylindrical bars with beveled ends.The yield surfaces were experimentally measured and compared with various theoretical yield surface models.The cellular structures of closed-cell aluminum foams were modeled as tetrakaidecahedrons and their biaxial crushing behaviors were simulated by the finite element method.The results show that,yield initiates from the stress-concentrated corners in the specimens under combined shear-compression loading and the stress distribution is no longer uniform at the specimen/bar interfaces.In the range of cell sizes studied,the larger the foam cell size is,the higher the yield stress is.Aluminum foam density is found to be the dominant factor on its mechanical properties compared with the cell size and is much more significant in engineering practice.展开更多
Metal foams are typically subjected to quasi-static or dynamic shear-compression combined loading in applications such as energy absorbers and structure protectors. The yield behavior of a metal foam under dynamic and...Metal foams are typically subjected to quasi-static or dynamic shear-compression combined loading in applications such as energy absorbers and structure protectors. The yield behavior of a metal foam under dynamic and quasi-static shear-compression combined loadings is investigated in this study. First, quasi-static and dynamic compression-shear combined tests at different loading angles are conducted using a universal testing machine and a rotatable Hopkinson bar system, respectively. Shear deformation reduces the plateau stress as the loading angle increases. Subsequently, the yield modes of the metal foam under combined loadings are investigated. Only one yield band occurs under a combined loading with large loading angles(mode I),whereas several yield bands occur under a combined loading with small loading angles(mode II). Finally, the yield surface plot of metal foam indicates significant enhancement in terms of normal stress and shear stress under dynamic loading. Quasi-static and dynamic phenomenological yield criteria for a shear-normal stress space are established to provide a brief and precise prediction of the behavior of metal foam under quasi-static and dynamic combined loadings.展开更多
An analytical expression for the prediction of shear-compressive fracture process zone(SCFPZ) is derived by using a proposed local strain energy density criterion, in which the strain energy density is separated into ...An analytical expression for the prediction of shear-compressive fracture process zone(SCFPZ) is derived by using a proposed local strain energy density criterion, in which the strain energy density is separated into the dilatational and distortional strain energy density, only the former is considered to contribute to the brittle fracture of rock in different loading cases. The theoretical prediction by this criterion shows that the SCFPZ is of asymmetric mulberry leaf in shape, which forms a shear-compression fracture kern. Dilatational strain energy density along the boundary of SCFPZ reaches its maximum value. The dimension of SCFPZ is governed by the ratio of K_Ⅱ to (K_Ⅰ.) The analytical results are then compared with those from literatures and the tests conducted on double edge cracked Brazilian disk subjected to diametrical compression. The obtained results are useful to the prediction of crack extension and to nonlinear analysis of shear-compressive fracture of brittle rock.展开更多
利用偶极横波声波成像(Dipole Shear Sonic Imager,DSI)测井资料计算了纵、横波衰减和纵、横波品质因子QP和QS.对纵、横波在碳酸盐岩含气层和非含气层中的衰减特征研究表明,碳酸盐岩含气层中的纵波衰减比非含气层中的纵波衰减强;横波衰...利用偶极横波声波成像(Dipole Shear Sonic Imager,DSI)测井资料计算了纵、横波衰减和纵、横波品质因子QP和QS.对纵、横波在碳酸盐岩含气层和非含气层中的衰减特征研究表明,碳酸盐岩含气层中的纵波衰减比非含气层中的纵波衰减强;横波衰减和横波品质因子在碳酸盐岩含气层和非含气层中的变化不大。根据DSI测井资料计算出的纵、横波衰减和纵、横波品质因子在碳酸盐岩含气层和非含气层中的这些差异,给出了一种利用纵、横波品质因子比值QP/QS识别碳酸盐岩含气层的方法。展开更多
基金Project(2017JJ3359)supported by the Natural Science Foundation of Hunan Province,ChinaProject(KFJJ13-11M)supported by the Opening Project of State Key Laboratory of Explosion Science and Technology(Beijing Institute of Technology),China.
文摘Combined shear-compression tests and simulations were performed on a closed-cell aluminum foam over a wide range of loading angles in order to probe their yield behaviors under biaxial loading conditions.Combined shear-compression tests were carried out by using a pair of cylindrical bars with beveled ends.The yield surfaces were experimentally measured and compared with various theoretical yield surface models.The cellular structures of closed-cell aluminum foams were modeled as tetrakaidecahedrons and their biaxial crushing behaviors were simulated by the finite element method.The results show that,yield initiates from the stress-concentrated corners in the specimens under combined shear-compression loading and the stress distribution is no longer uniform at the specimen/bar interfaces.In the range of cell sizes studied,the larger the foam cell size is,the higher the yield stress is.Aluminum foam density is found to be the dominant factor on its mechanical properties compared with the cell size and is much more significant in engineering practice.
基金supported by the National Natural Science Foundation of China (Grant Nos. 11672248 and 12072288)the Innovation Foundation for Doctor Dissertation of Northwestern Polytechnical Universitythe Fundamental Research Funds for the Central Universities, CHD。
文摘Metal foams are typically subjected to quasi-static or dynamic shear-compression combined loading in applications such as energy absorbers and structure protectors. The yield behavior of a metal foam under dynamic and quasi-static shear-compression combined loadings is investigated in this study. First, quasi-static and dynamic compression-shear combined tests at different loading angles are conducted using a universal testing machine and a rotatable Hopkinson bar system, respectively. Shear deformation reduces the plateau stress as the loading angle increases. Subsequently, the yield modes of the metal foam under combined loadings are investigated. Only one yield band occurs under a combined loading with large loading angles(mode I),whereas several yield bands occur under a combined loading with small loading angles(mode II). Finally, the yield surface plot of metal foam indicates significant enhancement in terms of normal stress and shear stress under dynamic loading. Quasi-static and dynamic phenomenological yield criteria for a shear-normal stress space are established to provide a brief and precise prediction of the behavior of metal foam under quasi-static and dynamic combined loadings.
基金Project(50274074) supported by the National Natural Science Foundation of China project(04JJ6030) supported by theNatural Science Foundation of Hunan Province
文摘An analytical expression for the prediction of shear-compressive fracture process zone(SCFPZ) is derived by using a proposed local strain energy density criterion, in which the strain energy density is separated into the dilatational and distortional strain energy density, only the former is considered to contribute to the brittle fracture of rock in different loading cases. The theoretical prediction by this criterion shows that the SCFPZ is of asymmetric mulberry leaf in shape, which forms a shear-compression fracture kern. Dilatational strain energy density along the boundary of SCFPZ reaches its maximum value. The dimension of SCFPZ is governed by the ratio of K_Ⅱ to (K_Ⅰ.) The analytical results are then compared with those from literatures and the tests conducted on double edge cracked Brazilian disk subjected to diametrical compression. The obtained results are useful to the prediction of crack extension and to nonlinear analysis of shear-compressive fracture of brittle rock.
文摘利用偶极横波声波成像(Dipole Shear Sonic Imager,DSI)测井资料计算了纵、横波衰减和纵、横波品质因子QP和QS.对纵、横波在碳酸盐岩含气层和非含气层中的衰减特征研究表明,碳酸盐岩含气层中的纵波衰减比非含气层中的纵波衰减强;横波衰减和横波品质因子在碳酸盐岩含气层和非含气层中的变化不大。根据DSI测井资料计算出的纵、横波衰减和纵、横波品质因子在碳酸盐岩含气层和非含气层中的这些差异,给出了一种利用纵、横波品质因子比值QP/QS识别碳酸盐岩含气层的方法。
