Shear strength and yield surface of a partially saturated sandy silt under generalized stress states

This paper studies the hydromechanical behavior of a slightly compacted mixture of sand and clayey silt (30%/70%) under a generalized stress state. The experimental study focused on analyzing the yielding response and shear strength behavior at different stress states (characterized by the intermediate principal stress parameter b, or Lode angle) and at different initial total suctions (as-compacted state). For the investigation, a hollow cylinder apparatus was used. The shear strength results allowed defining the variation of the critical state line with the Lode angle and the suction. Different models were proposed for isotropic and anisotropic yield surfaces, and their shape and rotation were calibrated with experimental results. The modeled yield surfaces fitted reasonably well the experimental results, considering their inclination and dependence on the suction, mean and deviatoric stresses and Lode angle. In addition, some relationships between the stresses and the model parameters were proposed to normalize the yield surface equation.

Investigation on Plastic Flow Behaviors of FCC Polycrystalline Aluminum under Pre-Cyclic Tension-Compression Loading: Experiments and Crystal Plasticity Modeling

The plastic flow behaviors of FCC polycrystalline aluminum after pre-cyclic tension-compression deformation are mainly investigated in tension–torsion stress space by the physically based crystal plasticity model introducing a back-stress. A global finite element model (GFEM) constructed of sufficient grains was established to simulate the same-size thin-walled tube specimen constrained and loaded as the experiments of yield surfaces. The computational results showed that the shape of subsequent yield surfaces and the plastic flow directions directly depended on the given offset strain levels and the applied re-loading paths under different pre-cyclic deformations. The angle deviation between the plastic flow direction and the theoretical orthogonal direction further indicated that there was a large difference between them in the inverse pre-straining direction, but the difference was negligible in the pre-straining direction. From the influence of the anisotropic evolution of the subsequent yield surfaces on plastic flow, we found that the plastic normality rule followed the smooth yield locus; conversely, the significant non-associated flow was attributed to the distorted yield locus. Furthermore, it was also demonstrated that the anisotropic evolution and the plastic flow trend of the subsequent yield surfaces obtained by experiments can be better reproduced by the crystal plasticity model.

Overview of an Experimental Program for Development of Yield Surfaces Tracing Method

This paper develops an experimental technique to evaluate the initial yield surfaces of metallic materials, as well as to study their evolution during plastic flow. The experimental tracing of yield surfaces is necessary for deriving and calibrating more robust phenomenological models of directional distortional hardening. Such models can be used to characterize the behavior of structures experiencing complicated and demanding loading modes, such as multiaxial ratcheting. The experimental technique developed in this work uses thin-walled tubular specimens, along with a servo-hydraulic machine, under various modes of tension/compression and torque. Identification of the onset of plastic flow is based on a small proof equivalent plastic strain evaluated from the outputs of a contact biaxial extensometer firmly attached to a specimen surface. This allows for evaluation of both the initial yield surface, as well as theevolved yield surface after a plastic prestrain. Throughout a test, continuous and fully automatized evaluation of elastic moduli and proof plastic strain is assured through algorithms written in C# language. The current technique is shown to provide promising results to effectively capture the yield surfaces of conventional metallic materials.

Geometrically exact elastoplastic rods: determination of yield surface in terms of stress resultants

This work addresses the determination of yield surfaces for geometrically exact elastoplastic rods. Use is made of a formulation where the rod is subjected to an uniform strain field along its arc length, thereby reducing the elastoplastic problem of the full rod to just its cross-section. By integrating the plastic work and the stresses over the rod’s cross-section, one then obtains discrete points of the yield surface in terms of stress resultants. Eventually, Lamé curves in their most general form are fitted to the discrete points by an appropriate optimisation method. The resulting continuous yield surfaces are examined for their scalability with respect to cross-section dimensions and also compared with existing analytical forms of yield surfaces.

A Piecewise Yield Failure Criterion including the Critical State for Brittle Rock

The critical state of rock is an important index for measuring the changes in rock characteristics. However, this state is not unique because of the different researcher assumptions. Based on the theory of the partial differential equation proposed by Vutukuri, according to Mohr’s envelope, a piecewise yield failure criterion (referred to as the Mohr–Wedge criterion), including the critical state for brittle rock, is obtained by introducing the wedge model to solve this equation. The Mohr–Wedge (M–W) criterion consisting of nonlinear and linear components includes the critical state for brittle rock. When the minimum principal stress σ3 is lower than the confining pressure σk, the maximum principal stress σ1 varies nonlinearly with σ3; otherwise, σ1 varies linearly with σ3. This variation conforms to rock deformation features under triaxial compression. In this study, we investigate the rationality of this critical state by an analogy method and illustrate that the critical state mentioned in this criterion is related to the microcracks in the potential failure zone of the rock. Alternatively, the primary object of this study is to reveal the applicability of predicting the yield state for this criterion. The method used in our study is compared to the Mohr–Coulomb (M-C) criterion, the Hoek–Brown (H-B) criterion, and the Exponential (Exp.) criterion by the yield surfaces on the deviatoric plane. Notably, there is a vertex consistent region for the four criteria, but except for this region, the yield state of rock predicted by the four criteria is quite different, depending on the extent of the parameters for the criteria and the magnitude of the slopes of the yield surfaces. The results show that the M-W criterion has certain applicability for predicting the rock yield state by using the multiple data of rock triaxial compression tests in the published literature.