Papers by Keyword: Strain Softening

Abstract: There are many constitutive models that have been used to model the mechanical behavior of soils. Some of these models are either unable to represent important features such as the strain softening of dense sand or required many parameters that can be hard to obtain by standard laboratory tests. Because of that, a more reliable constitutive model, which is capable to capture the main features of the soil behavior with easily obtained parameters, is required. The Hypoplasticity model is considered as a promising constitutive model in this respect. It is considered as a particular class of rate non-linear constitutive model at which the stress increment is expressed in a tensorial equation as a function of strain increment, actual stress, and void ratio. The hypoplastic model required only eight material parameters (critical friction angle critical, maximum and minimum void ratio respectively), granular stiffness h_s and the model constants n, α, β). The appealing feature of the hypoplastic model is that the material parameters are separated from the state variables (void ratio and the initial stresses). This feature enables the model to simulate the soil behavior under a wide range of stresses and densities with the same set of material parameters. In this research, a brief description of the Hypoplasticity model is presented. Detailed discussions regarding the measurement and calibration of the model parameters of an Iraqi soil are then exposed. It is concluded that only Consolidated Drained (CD) triaxial test, oedometer test, and the well-known limit density tests are needed to get all the parameters of the hypoplasticity model.

Abstract: The spectrum of stresses at a hazardous point on bearing metal structures of mining, road-building and transporting machines, as a rule, is random by nature. Objective complexity of the fatigue process and variety of fatigue crack nucleation mechanisms are the main causes of errors in prediction of their lifespan, along with an experimentally untestable hypothesis of linear summation of damages. The method of complete stress-strain diagrams uses a representative parameter of the fatigue process, selected in accordance with the results of testing, carried out on trained thin specimens of a specific material. The summation of fatigue damages is based on experimental kinematic curves, whose intersection with a load vector is used as a criterion of fatigue failure. It is shown that the approach proposed to calculate the lifespan gives certain advantages, as far as individual properties of the material are concerned, and when it comes to describing the kinetics of the fatigue process and determining the limiting state of the material in a structure.

Abstract: A biaxial test model was established based on the discrete element method to simulate the microscopic evolution of non-viscous soil upon loading. The shear strain, deviator stress and volumetric strain of the samples at different time steps were recorded, the evolution process of the force chain in the samples was observed, and the average degree (coordination number), 3-cycle and average clustering coefficient over force-chain particles were also analyzed respectively from the perspective of complex network. The following analysis results are obtained. The larger the value of inter-particle friction coefficient, the higher the peak value of shear stress, and the more obvious the strain softening phenomenon. The force chains in the samples with higher inter-particle friction coefficient tend to be more vulnerable to damage during loading. In the loading process, the average degree first increases, then decreases and finally tends to be stable. The value of average degree increases with the increase of confining pressure, and decreases with the increase of friction coefficient. The clustering coefficient of the particles within the force-chain particles is linearly related to the average length of the force chains at critical state.

Abstract: The issue of material and construction fracture is one of unresolved problems in mechanics. The phenomenological approach used by mechanics of softening materials is taken by the authors for the purposes of solving that problem. Deformation of the “machine – model specimen” system is analyzed in the article using catastrophe theory for various boundary conditions. Computer simulations using a material’s calculation model allowed to establish nonlocal character of fracture criteria and correlation between static and cyclic properties of the model material. It is shown that the fracture scenario for a mechanical system depends on the degree of structural inhomogeneity of the material and the loading conditions. Regarding the fracture as a loss of deformation stability leads to a new understanding of the mechanical system’s ultimate state. The obtained results could be used to improve methodologies for calculating life and durability of constructions.

Abstract: We study the effects of two scaling exponents on the mechanical properties of swollen elastomers under equibiaxial and planar extensions. Two scaling exponents are introduced to extend the Flory-Rehner free energy function, and are adjusted based on the previous study. Results show that swelling-induced strain softening is apt to occur under equibiaxial extension compared to uniaxial extension. The additional tensile stress in a lateral direction enables it to occur in relatively poor solvents, and accelerates the onset point. Planar extension shows more complicated responses because the stress in the constrained direction changes dramatically depending on the combination of two scaling exponents and the Flory-Huggins interaction parameter.

Abstract: In this study, a planar spring lattice model is used to study the evolution of damage variable d_L in disordered media. An elastoplastic softening damage constitutive law is implemented which introduces a cohesive length scale in addition to the disorder-induced one. The cohesive length scale affects the macroscopic response of the lattice with the limiting cases of perfectly brittle and perfectly plastic responses. The cohesive length scale is shown to affect the strength-size scaling such that the strength increases with increasing cohesive length scale for a given size. The formation and interaction of the microcracks is easily captured by the inherent discrete nature of the model and governs the evolution of d_L . The proposed method provides a way to extract a mesoscale dependent damage evolution rule that is linked directly to the microstructural disorder.

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: Quantities Mg-12Gd-5Y-3Zn-0.6Zr magnesium alloy billets were compressed with true strain 0.7 on hot process simulator at 350,400,450,480^°C under strain rates of 0.001, 0.01, 0.1 and 0.5s^-1. A constitutive model with a few parameters is used to characterize the dynamic recrystallization strain softening of Mg-12Gd-5Y-3Zn-0.6Zr alloy, which comprehensively reflect the effects of the deformation temperature, strain and strain rate on flow stress.

Abstract: In the sphere of the consolidating technique of the engineering structure the new and developing theory of the steel adhered reinforcement has gradually applied to the practical engineering. Reinforcement steel structural adhesive is a method using steel plate pasting on the component surface to improve bearing capacity of the structure, which is widely used in reinforced concrete bending, eccentric compression and tension reinforcement. In this paper, based on continuum damage theory and statistical strength theory, Starting from each phase of the concrete, medium micro softening plasticity and strain of non-uniform, Numerical simulation of steel bonded reinforcement bending failure of concrete beam was carried out and Analysis of the crack propagation and failure form were put forward. Based on FEM analysis, the size of material and binder were selected reasonably, ensuring the safety and durability of concrete beams, provide technical support for the practical engineering as well.

Abstract: Mechanical behaviors and thermoforming features of plastic material PMMA-IRK-304 used in-mold decoration are studied in this paper. Dynamic mechanical analysis experiments, uniaxial tension tests at several high temperatures and different stretching velocity were carried out to analysis and explain the phenomenon of yielding, strain softening and strain hardening. Results showed that the glass transition temperature range of PMMA-IRK-304 films was suitable for thermoforming of in-mold decoration.