• Title, Summary, Keyword: strain softening model

Search Result 142, Processing Time 0.045 seconds

A softening hyperelastic model and simulation of the failure of granular materials

  • Chang, Jiangfang;Chu, Xihua;Xu, Yuanjie
    • Geomechanics and Engineering
    • /
    • v.7 no.4
    • /
    • pp.335-353
    • /
    • 2014
  • The softening hyperelastic model based on the strain energy limitation is of clear concepts and simple forms to describe the failure of materials. In this study, a linear and a nonlinear softening hyperelastic model are proposed to characterize the deformation and the failure in granular materials by introducing a softening function into the shear part of the strain energy. A method to determine material parameters introduced in the models is suggested. Based on the proposed models the numerical examples focus on bearing capacity and strain localization of granular materials. Compared with Volokh softening hyperelasticity and classical Mohr-Coulomb plasticity, our proposed models are able to capture the typical characters of granular materials such as the strain softening and the critical state. In addition, the issue of mesh dependency of the proposed models is investigated.

Development of Strain-softening Modeling for Interfaces between Geosynthetics (토목섬유 interface의 변형율 연화 모델 개발)

  • Seo, Min-Woo;Park, Jun-Boum;Park, Inn-Joon;Cho, Nam-Jun
    • Journal of the Korean Geosynthetics Society
    • /
    • v.2 no.1
    • /
    • pp.57-68
    • /
    • 2003
  • Strain-softening model is developed to characterize the interface behavior of geomembrane with geotextile and geosynthetic clay liner(GCL). The model proposed in this research is calibrated by using data from direct shear tests conducted on smooth and textured geomembrane. The research is divided into two regions, pre-peak and post-peak, to take into account of strain-softening effect. Although slight difference between measured and back calculated data is observed under high normal stress, good agreements, in general, are found from back calculations. Especially, good consistency is observed in the case of low normal stress. Based on the results, it can be concluded that the proposed model can be a reasonable constitutive law to figure out the behavior of strain-softening between interfaces of geomembrane. In addition, DSC(Disturbed State Concept) model is also presented for further application in geosynthetic interfaces.

  • PDF

Localized failure in damage dynamics

  • Do, Xuan Nam;Ibrahimbegovic, Adnan;Brancherie, Delphine
    • Coupled systems mechanics
    • /
    • v.4 no.3
    • /
    • pp.211-235
    • /
    • 2015
  • In this work we present a one-dimensional damage model capable of representing the dynamic fracture for elastodamage bar with combined hardening in fracture process zone - FPZ and softening with embedded strong discontinuities. This model is compared with another one we recently introduced (Do et al. 2015) and it shows a good agreement between two models. Namely, it is indicated that strain-softening leads to a sensitivity of results on the mesh discretization. Strain tends to localization in a single element which is the smallest possible area in the finite element simulations. The strain-softening element in the middle of the bar undergoes intense deformation. Strain increases with increasing mesh refinement. Strain in elements outside the strain-softening element gradually decreases to zero.

Combined hardening and localized failure with softening plasticity in dynamics

  • Do, Xuan Nam;Ibrahimbegovic, Adnan;Brancherie, Delphine
    • Coupled systems mechanics
    • /
    • v.4 no.2
    • /
    • pp.115-136
    • /
    • 2015
  • We present for one-dimensional model for elastoplastic bar with combined hardening in FPZ - fracture process zone and softening with embedded strong discontinuities. The simplified version of the model without FPZ is directly compared and validated against analytical solution of Bazant and Belytschko (1985). It is shown that deformation localizes in an area which is governed by the chosen element size and therefore causes mesh sensitivity and that the length of the strain-softening region tends to localize into a point, which also agrees with results obtained by stability analysis for static case. Strain increases in the softening domain with a simultaneous decrease of stress. The problem unloads elastically outside the strain-softening region. The more general case with FPZ leads to more interesting results that also account for induced strain heterogeneities.

Tunnel Deformation in Shallow Unconsolidated Ground by Using Strain-Softening Model (변형연화모델을 이용한 미고결 지반의 터널변형)

  • Seo, In-Shik;Kim, Byung-Tak
    • Journal of the Korean Society of Industry Convergence
    • /
    • v.10 no.2
    • /
    • pp.81-88
    • /
    • 2007
  • In case of an urban tunnel, the displacement of ground base controls the tunnel design because it is built on shallow and unconsolidated ground many times. There are more insufficiency to describe the ground movement which coincides in the measured result of the situ because the design of an urban tunnel is dependent on the method of numerical analysis used to the existing elastic and elasto-plastic models. We studied about the prediction for the ground movement of a shallow tunnel in unconsolidated ground, mechanism of collapse, and settlement. Also this paper shows comparison with the existing elastic and elasto-plastic model using the unlinear analysis of the strain-softening model. We can model the real ground movement as the increasement of ground surface inclination or occurrence of shear band by using strain-softening model for the result of ground movement of an urban NATM tunnel.

  • PDF

A Constitutive Model for Polymer-Bonded Explosive Simulants Considering Stress Softening and Residual Strain (응력연화와 잔류변형을 고려한 복합화약 시뮬런트의 구성방정식연구)

  • Yeom, KeeSun;Huh, Hoon;Park, Jungsu
    • Journal of the Korea Institute of Military Science and Technology
    • /
    • v.17 no.6
    • /
    • pp.844-852
    • /
    • 2014
  • PBX simulant is known to exhibit highly nonlinear behaviors of deformation such as the stress softening, hysteresis under cyclic loading, residual strain after unloading, and aging. This paper proposes a new pseudo-elastic model for PBX simulant considering stress softening and residual strain. Uniaxial loading and unloading tests at quasi-static states were carried out in order to obtain the mechanical properties of the PBX simulants. And then the Dorfmann-Ogden model is modified to make it consistent with the test result of PBX simulants. Prediction with the new model shows a good correspondence to the experimental data demonstrating that the model properly describes stress softening and residual strain of PBX simulants.

Shearing characteristics of slip zone soils and strain localization analysis of a landslide

  • Liu, Dong;Chen, Xiaoping
    • Geomechanics and Engineering
    • /
    • v.8 no.1
    • /
    • pp.33-52
    • /
    • 2015
  • Based on the Mohr-Coulomb failure criterion, a gradient-dependent plastic model that considers the strain-softening behavior is presented in this study. Both triaxial shear tests on conventional specimen and precut-specimen, which were obtained from an ancient landslide, are performed to plot the post-peak stress-strain entire-process curves. According to the test results of the soil strength, which reduces from peak to residual strength, the Mohr-Coulomb criterion that considers strain-softening under gradient plastic theory is deduced, where strength reduction depends on the hardening parameter and the Laplacian thereof. The validity of the model is evaluated by the simulation of the results of triaxial shear test, and the computed and measured curves are consistent and independent of the adopted mesh. Finally, a progressive failure of the ancient landslide, which was triggered by slide of the toe, is simulated using this model, and the effects of the strain-softening process on the landslide stability are discussed.

Determination of representative volume element in concrete under tensile deformation

  • Skarzyski, L.;Tejchman, J.
    • Computers and Concrete
    • /
    • v.9 no.1
    • /
    • pp.35-50
    • /
    • 2012
  • The 2D representative volume element (RVE) for softening quasi-brittle materials like concrete is determined. Two alternative methods are presented to determine a size of RVE in concrete subjected to uniaxial tension by taking into account strain localization. Concrete is described as a heterogeneous three-phase material composed of aggregate, cement matrix and bond. The plane strain FE calculations of strain localization at meso-scale are carried out with an isotropic damage model with non-local softening.

Experimental and numerical investigations on the ratcheting characteristics of cylindrical shell under cyclic axial loading

  • Shariati, M.;Hatami, H.;Torabi, H.;Epakchi, H.R.
    • Structural Engineering and Mechanics
    • /
    • v.44 no.6
    • /
    • pp.753-762
    • /
    • 2012
  • The ratcheting characteristics of cylindrical shell under cyclic axial loading are investigated. The specimens are subjected to stress-controlled cycling with non-zero mean stress, which causes the accumulation of plastic strain or ratcheting behavior in continuous cycles. Also, cylindrical shell shows softening behavior under symmetric axial strain-controlled loading and due to the localized buckling, which occurs in the compressive stress-strain curve of the shell; it has more residual plastic strain in comparison to the tensile stress-strain hysteresis curve. The numerical analysis was carried out by ABAQUS software using hardening models. The nonlinear isotropic/kinematic hardening model accurately simulates the ratcheting behavior of shell. Although hardening models are incapable of simulating the softening behavior of the shell, this model analyzes the softening behavior well. Moreover, the model calculates the residual plastic strain close to the experimental data. Experimental tests were performed using an INSTRON 8802 servo-hydraulic machine. Simulations show good agreement between numerical and experimental results. The results reveal that the rate of plastic strain accumulation increases for the first few cycles and then reduces in the subsequent cycles. This reduction is more rapid for numerical results in comparison to experiments.

A numerical stepwise approach for cavity expansion problem in strain-softening rock or soil mass

  • Zou, Jin-Feng;Yang, Tao;Ling, Wang;Guo, Wujun;Huang, Faling
    • Geomechanics and Engineering
    • /
    • v.18 no.3
    • /
    • pp.225-234
    • /
    • 2019
  • A numerical stepwise approach for cavity expansion problem in strain-softening rock or soil mass is investigated, which is compatible with Mohr-Coulomb and generalized Hoek-Brown failure criteria. Based on finite difference method, plastic region is divided into a finite number of concentric rings whose thicknesses are determined internally to satisfy the equilibrium and compatibility equations, the material parameters of the rock or soil mass are assumed to be the same in each ring. For the strain-softening behavior, the strength parameters are assumed to be a linear function of deviatoric plastic strain (${\gamma}p^*$) for each ring. Increments of stress and strain for each ring are calculated with the finite difference method. Assumptions of large-strain for soil mass and small-strain for rock mass are adopted, respectively. A new numerical stepwise approach for limited pressure and plastic radius are obtained. Comparisons are conducted to validate the correctness of the proposed approach with Vesic's solution (1972). The results show that the perfectly elasto-plastic model may underestimate the displacement and stresses in cavity expansion than strain-softening coefficient considered. The results of limit expansion pressure based on the generalised H-B failure criterion are less than those obtained based on the M-C failure criterion.