Papers by Keyword: Shear Band

Abstract: Damp Newton algorithm based on FEPG system is developed for calculating strain softening problem. The algorithm can solve displacement and yield surface equation simultaneously. Soften modulus is introduced into D-P yield function. The example result shows that, the algorithm with damp factor can be used to solve softening problems. The plastic theory described by finite element weak form has no requirement of continuity, so appropriate outcome can be obtained by first-order element. Descent segment of stress-strain curve and cloud picture of finite shear band are presented.

Abstract: Based on the triaxial test of coarse grained soil, using the discrete element method to simulate the biaxial test by using PFC2D as the discrete element method (DEM) tools, and generate particles by a gradation which is similar with that in laboratory. Through self-programming, depends on the macro-reaction in lab to find out the mesoscopic parameters and deformation characteristics of coarse grained soil, then calibrate the value of friction coefficient correspond to that in laboratory, and at last find out the shear bands. The results show that the value of sample volumetric increment ratio (VIR) dεv/dε is positive (shear shrinkage) at first and then negative (shear dilation) when confining stress is 300kPa, when the confining pressure is greater than 300kPa, samples have been on the shear shrinkage.

Abstract: The dynamic double-notched experiments by using Split Hopkinson Pressure Bars (SHPB) and high-speed camera were performed on bulk metallic glass. In the double-notched experiment, shear crack propagating process was captured with the high temporal resolution of high-speed camera and the crack front propagating velocity was estimated to be 1137m/s. the shear strain/shear stress curve of BMG under dynamic loading was also obtained. Static in-situ SEM tensile experiments were included to study the multiple shear bands propagating behavior on a glassy ribbon. It was found that shear bands propagates progressively in an intermittent and discontinuous manner, and the choice of which shear bands to propagate and which ones to keep still among multiple shear bands is quite stochastic. This is explained qualitatively from the view point of energy.

Abstract: The deformation characteristic of granular material is important. It is important factor to analysis the bearing capacity and the thickness of granular material footings. There are many factors influence the deformation of granular material, such as material characteristic, content of water, degree of compaction, test method, etc. For analyzing size effect on the deformation characteristic of granular material, hypoplastic constitutive model considering void ratio is introduced. The influence of an initial void ratio, pressure and a mean grain diameter on the deformation is investigated by polar quantities: rotations, curvatures, couple stresses and a characteristic length. Thus, the influence of density and pressure on the initiation of shear bands can be investigated with a single set of constitutive constants.

Abstract: Shape multiformity and formation mechanism of shear band in normal consolidated soil were analyzed based on Modified Cam-Clay model under plane strain condition. The results proved that shear band forms because of impact action caused by strain energy releasing. End restraint and initial defect can induce and control the formation process and shape of shear band. The interaction of different boundary and initial defect settings was analyzed in order to obtain the mechanism and deformation process of shear band.

Abstract: This paper describes recent experimental results on the strain distributions developed during bending of AA6xxx sheet for automotive applications, together with a new model for the mechanics and metallurgy of strain localization during bending. A detailed microscopic study (optical and SEM/EBSD) shows that damage development during bending to strains of order unity is controlled by through-thickness shear banding at the grain scale. A new finite element microstructure-based model is introduced to predict this strain localization during practical bending. The sheet metal is modelled as a grain aggregate, each grain having its own flow stress. After validation, the model is applied to the experimental results through an analysis of the critical plastic strain at the outer surface during bending of AA6016 sheet alloys. It correctly describes the respective influences of sheet thickness, grain size and shape, and work hardening. In particular the model brings out the primary importance of large-strain hardening and the spread of the flow stress distribution.

Abstract: Al-Mg-Si alloys are usually applied a T4 temper as the plate material for automobile bodies due to the necessity of a high bake hardening property. Many reports about the improvement in the bendability of Al-Mg-Si alloys applied a T4 temper have been published, because they easily crack during the hemming process. On the other hand, Al-Mg-Si alloys applied T6 and T7 tempers are used as the material of wiring plates and heat radiation devices. A high electrical conductivity and good bendability are necessary for these devices. In this study, the effect of the aging conditions on the bendability was investigated. As a result, the bendability at the T6 temper significantly decreased. The bendability under the aging temper, and over the aging temper was better than that at the T6 temper. Samples treated by natural-aging at high temperature before the T6 temper easily cracked during the bending test. It was postulated that the formation of shear bands was significant and the bendability decreased during the bending test under the high density and fine β phase precipitate conditions.

Abstract: Rolling texture evolution of pure nickel, and nickel – cobalt alloys containing 20wt.%, 40wt.%, 60wt.% cobalt content has been studied to very large true strain (ε ~ 4). The texture evolution in pure nickel and Ni-20Co was very similar, and resulted in typical Cu-type rolling texture. Microstructural analyses showed that the deformation was mostly slip dominated up to 95% beyond which it shear bands. Deformation twinning was a major deformation mechanism up to 50% reduction, and at higher strains, microstructure showed extensive shear banding. The evolution of final Goss texture in low SFE Ni-Co alloys could be explained based on the twin fraction and shear band volumes which showed grains preferably oriented towards Goss.

Abstract: Equal-channel angular pressing (ECAP) was applied to 16mass%Cr steel sheets for one pass prior to cold rolling in order to improve formability and alleviate ridging of the sheets. Effect of channel angle of ECAP (90° and 120°) on the deformation microstructure and the subsequent recrystallization was focused. One-pass ECAP indeed modified the cold-rolled microstructures, texture and subsequent recrystallization as compared with that in cold rolling alone. In particular, grain-scale shear bands were introduced during ECAP in otherwise hard-to-recrystallize <001>//ND grains by ECAP, and they facilitated the recrystallization. However, the effect of reducing the channel angle from 120°to 90°on the recrystallization and the formability was limited in spite of higher shear strain imposed on the sheets.

Abstract: In recent years, bulk metallic glasses (BMGs) have received considerable attention due to their unique mechanical properties. However, the deformation of BMGs is highly localized in a few shear bands so that many of them exhibit poor plasticity. As such, more and more researchers have focused on improving the plasticity by in-situ or ex-situ introducing of nanoor micro-scale crystalline phases into the metallic glassy matrix in order to formation of multiple shear bands.