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Unified instability criterion for quasibrittle material in uniaxial tension, direct shear and uniaxial compression subjected to shear failure
Published in Günther Meschke, René de Borst, Herbert Mang, Nenad Bićanić, Computational Modelling of Concrete Structures, 2020
It is assumed that the failure of material is governed by shear stress acting on shear band. The normal stress acting on shear band does not remain a constant in uniaxial compression, as is different from direct shear test with a constant confining pressure. Herein, the effect of the normal stress on the failure is neglected.
Numerical simulation of granular materials flow in silo by modified distinct element method
Published in Heinz Konietzky, Numerical Modeling in Micromechanics via Particle Methods, 2017
Figures 5a, b show flow patterns in a free rolling test and a rolling resistance test at time t = 0, 2, 4, 6 sec. In both tests, the particles near the vertical walls move slower than the particles in the central region. A high velocity gradient is observed along a boundary layer near the vertical walls. In all the simulations, this high velocity gradient is commonly observed, except in a test in which the friction coefficient between wall and particle is set to zero. The high velocity gradient means that shear strain is localized within a shear band. In Figure 5b, in addition to the shear bands along the vertical walls, other shear bands are generated, which extended from a vertical wall to the central region in silo.
Measuring stiffness of soils in situ
Published in Fusao Oka, Akira Murakami, Ryosuke Uzuoka, Sayuri Kimoto, Computer Methods and Recent Advances in Geomechanics, 2014
Fusao Oka, Akira Murakami, Ryosuke Uzuoka, Sayuri Kimoto
The dissipation of the excess pore pressures leads to a gradual reduction of the effective stress normal to the shear band both inside and ahead of the plastic zone. As a consequence, the shear stresses decrease inside the shear band and, in order to satisfy equilibrium, increase ahead of the tip of the shear band, thus causing failure propagation. This stress redistribution process continues until the shear band has progressed through the entire system. Afterwards, the system collapses. This happens earlier or later depending on the propagation speed of the shear band. The stand-up time increases with the element size. The finer the FE mesh, the earlier the system will fail, the reason being that a fine discretization captures yielding sooner than a coarse discretization.
Numerical analysis of bifurcation and shear band measurement in geomaterials
Published in European Journal of Environmental and Civil Engineering, 2023
Jiangfang Chang, Wei Wang, Qinghe Niu, Lei Wen, Wei Yuan
The failure analysis of geomaterials in constitutive level generally consists of two different types, the diffuse mode and the localization mode (Rizzi et al., 1995, Lu et al., 2014). The former is due to the singularity of the tangent stiffness operator and also can be described by the vanish of the second-order work. The latter is ascribed to the singularity of the acoustic or localization tensor which is obtained by contracting the tangent stiffness with the normal vector of the singular surface in a shear band. By contrast, the strain localization phenomenon is more common seen in geoengineering, such as slope, foundations, embankments and so on (Wei et al., 2020, Shahin et al., 2019, Yuan et al., 2020). The typical character of strain localization is that severe deformation is concentrated in a narrow band (the so-called shear band) (Rice, 1976). The onset of the shear band is regarded as the precursor of the failure of the geostructures and the development of the shear band may result in the final failure even engineering disaster (Houdoux et al., 2019).
Effect of temperature variation on the behaviour of Bushveld rocks: comparison of laboratory test and numerical modelling results
Published in Mining Technology, 2021
G. O. Oniyide, H. Yilmaz, E. Nordlund
In the laboratory experiment, some of the rocks tested displayed the transition from Class I to Class II due to changes in temperature and confining pressure. The results of preliminary tests conducted on the selected rocks for this research showed that spontaneous and violent post-peak failure commenced at confining pressure of 40 MPa. The dominant mode of failure in triaxial testing is shear failure through the formation of shear plane or band. Röchter et al. (2011) defined shear band (Figure 8) as thin zones of localized deformation with a discontinuity of the strain field at its boundaries. Charalampidou et al. (2011) also described shear band as a zone of cracked and sheared grains, a few grains wide, in which the predominant displacement of grain pieces is parallel to the band’s long axis. Figures 8–11 show the results of FLAC and laboratory tests for norite with specimen superimposed for comparison of the shear bands. In the FLAC plots, the units of stress and strain are MPa and mm/mm respectively, as it is the case with the laboratory results.
A study of the dynamic impact behaviour of IN 718 and ATI 718Plus® superalloys
Published in Philosophical Magazine, 2019
G. Asala, J. Andersson, O. A. Ojo
Under impact loading and high strain rates deformation, materials tend to deform in-homogeneously leading to the formation of the adiabatic shear band (ASB). The evolution of ASB, owing to intense shear localisation, is the major precursor to brittle failure of metals/alloys during dynamic deformation [8]. It is known that the dynamic impact behaviour of materials and their tendency to fail due to ASB is strongly influenced by the materials properties and microstructure. The microstructure of precipitation strengthened alloys, in particular, have been shown to possess disparate effect on the impact behaviour depending on the presence of precipitates, the precipitate sizes and operational strengthening mechanism in the alloy [9–11]. In IN 718, DeMange et al. [12] found the solution heat treated alloy to absorb impact energy more readily and resist strain localisation under ballistic impact than the precipitates-bearing microstructure in comparison. Similarly, in a recent shear localisation study of IN 718 by Johansson et al. [13], it was observed that although the precipitation hardening increases the flow stress of the alloy, strain localisation leading to the formation of deleterious shear bands is promoted.