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1.
The rheological nature of paper or board is usually treated either as elasto-plastic or as viscoelastic depending on the studied paper making process or behavior in converting and end use. In this paper we study several stress–strain curve models and the determination of material parameters from an elasto-plastic point of view. Finally, a suitable approach for all stress–strain curves measured from 180 strips is constructed using a linear function for an elastic region and a nonlinear function for a strain hardening region. This model determines a proportional limit (elastic limit) and gives fairly elegant dependencies between material/fitting parameters and two important factors of mechanical properties of paper: dry solids content and anisotropy. In this paper the dependency of a plastic strain on dry solids content and anisotropy is estimated using the introduced stress–strain curve model. Correspondingly, the model can be used to estimate many other mechanical behaviors, for example, the tension differences arising from non-uniform moisture content of the paper web profile. However, the main target of this study is to produce competent parameters based on modeled stress–strain curves for further construction of a material model. This elasto-plastic material model will be utilized in out-of-plane deformation and fracture models.  相似文献   
2.
The paper presents quasi-static FE-simulations of the crack formation in a reinforced concrete bar without stirrups subject to tension. The material was modeled with a continuum smeared crack model using an elasto-plastic constitutive law. A linear Rankine criterion with isotropic softening and associated flow rule was adopted in a tensile regime. To ensure the mesh-independency, the softening parameter was enhanced by a characteristic length of micro-structure by means of a non-local theory. Attention was laid to the effect of a different characteristic length of micro-structure and initial bond-slip stiffness on the spacing of localized zones.  相似文献   
3.
We develop a constitutive model of paper's in-plane biaxial tensile response accounting for the elastic–plastic hardening behavior, and its orthotropic character. The latter aspect is motivated by machine-made papers, which, in contrast to isotropic laboratory handsheets, are strongly oriented. We focus on modeling paper's response under monotonic loading, this restriction allowing us to treat the elastic-plastic response as a physically nonlinear elastic one. A strain energy function of a hyperbolic tangent form is developed so as to fit the entire range of biaxial and uniaxial experiments on a commercial grade paper. This function may then be introduced as the free energy function into a model based on thermomechanics with internal variables.  相似文献   
4.
5.
This work is devoted to establishing a regularity result for the stress tensor in quasi-static planar isotropic linearly elastic – perfectly plastic materials obeying a Drucker–Prager or Mohr–Coulomb yield criterion. Under suitable assumptions on the data, it is proved that the stress tensor has a spatial gradient that is locally squared integrable. As a corollary, the usual measure theoretical flow rule is expressed in a strong form using the quasi-continuous representative of the stress.  相似文献   
6.
In this paper, the incremental formulation for the mean-field homogenization (MFH) of elasto-plastic composites is enriched by including second statistical moments of per-phase strain increment fields, thus combining two advantages. The first one is to handle non-monotonic loading histories and the second is to better account for the heterogeneity of microscopic fields. The proposal is currently restricted to elasto-plasticity with J2 flow theory in each phase, under the small perturbation hypothesis. The formulation crucially exploits the return mapping algorithm for the J2 model, with its two steps: elastic predictor, and plastic corrections. It is shown that the second-moment measure of the average von Mises stress in each phase at the elastic predictor step plays a major role in the computation of both the average stress and the comparison tangent operator. The proposal is implemented for an extended Mori-Tanaka scheme. Predictions are compared to results provided by full-field, finite element computations of representative volume elements or unit cells, for various composite materials, with polymer or metal matrices. There are cases where the predictions of the proposed modeling improve significantly over those of a first-order incremental formulation.  相似文献   
7.
In this paper, the effect of confining pressure on the mechanical behavior of rock-like materials, such as concrete, is studied by using a coupled elastoplastic damage model. Damage mechanism is coupled, in different manners, with two plastic flow mechanisms: plastic shear mechanism developed under low confining pressure and plastic pore collapse mechanism observed under high confinement. The proposed model is applied to study a series of laboratory tests performed under extremely low to very high confining pressure, up to 650 MPa. The numerical predictions of proposed model are in good agreement with the experimental results.  相似文献   
8.
A constitutive theory for large elastic–plastic deformations is presented by employing F=FpFe decomposition of the total deformation gradient. A duality in constitutive formulation based on this and the well-known Lee's decomposition F=FeFp is established for isotropic polycrystalline and single crystal plasticity.  相似文献   
9.
Experiments have shown that magnesium alloy sheet a common hexagonal close-packed metal, exhibits mechanical behavior unlike that of sheets made of cubic metals (X.Y. Lou et al., 2007, Int. J. Plasticity, 24, 44). The unique stress–strain response includes a strong asymmetry in the initial yield and subsequent plastic hardening. In other words, the stress–strain curves in tension and compression are significantly different. A proper representation of the constitutive relationships is crucial for the accurate evaluation of springback, which occurs due to the residual moment distribution through the sheet thickness after bending. In this paper, we propose an analytical model for asymmetric elasto-plastic bending under tension followed by elastic unloading in order to evaluate the bending moment, which is equivalent to the springback amount. To simplify the calculations, the experimentally measured stress–strain curve of the magnesium alloy sheet was approximated with discrete linear hardening in each deformation region, and the material properties were characterized according to several simplifying assumptions. The bending moment was calculated analytically using the approximate asymmetric stress–strain relationship up to the prescribed curvature corresponding to the radius of the tool in sheet metal forming operations. A numerical example showed an unusual springback increase, even with an increase in the applied force; this is an unexpected result for conventional symmetric materials. We also compared the calculated springback amounts with the results of physical measurements. This showed that the proposed model predicts the main trends of the springback in magnesium alloy sheets reasonably well considering the simplicity of the analytical approach.  相似文献   
10.
以灌注桩桩土相互作用的原位试验为基础, 结合西安土层结构、性质; 采用有限单元法对黄土地区的砼灌注桩桩—土相互作用进行仿真模拟, 研究了桩土相互作用、荷载的传递规律、桩土相对位移与桩侧摩阻力的关系。通过桩载试验资料对比, 得出三维有限单元法的模拟结果与实测值相近, 该研究进一步揭示了桩土相互作用的实质, 为最优桩长的选取和单桩承载力的确定奠定了基础。  相似文献   
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