A strength criterion for frozen clay considering the influence of stress Lode angle

To investigate the influence of stress Lode angle on frozen soil, a series of directional shear tests was conducted on artificial frozen clay at three temperatures (–6, –10, and –15 °C) and five stress Lode angles (θσ = –30°, –16.1°, 0°, 16.1°, and 30°) using a hollow cylindrical apparatus. An elliptical function was proposed according to the strength envelope evaluation with the mean principal stress (p) in the p–q plane. In addition, generalized nonlinear strength theory (GNST) was introduced in the π plane to describe the evolution of the strength envelope with increasing mean principal stress. Then a strength criterion for frozen clay in three-dimensional principal stress space was proposed by combining strength functions in the p–q and π planes. The temperature effect was also introduced into the strength criterion. The proposed strength criterion can predict the multi-axial strength characteristics of frozen clay and reveal the influence of the stress Lode angle.

Lower Bound Axisymmetric Limit Analysis Using Drucker–Prager Yield Cone and Simulation with Mohr–Coulomb Pyramid

This paper presents a lower bound limit analysis approach for solving an axisymmetric stability problem by using the Drucker–Prager (D–P) yield cone in conjunction with finite elements and nonlinear optimization. In principal stress space, the tip of the yield cone has been smoothened by applying the hyperbolic approximation. The nonlinear optimization has been performed by employing an interior point method based on the logarithmic barrier function. A new proposal has also been given to simulate the D–P yield cone with the Mohr–Coulomb hexagonal yield pyramid. For the sake of illustration, bearing capacity factors Nc, Nq and Nγ have been computed, as a function of ϕ, both for smooth and rough circular foundations. The results obtained from the analysis compare quite well with the solutions reported from literature.

The ‘ I 3 ’ generalization of the Galileo–Rankine tension criterion

The paper presents a new tension failure criterion which generalizes the so-called Galileo–Rankine formulation. The criterion can be used as a component of the so-called perfectly no-tension model for masonry and cements as well as for establishing a tension cut-off in complex constitutive models for soils, granular materials and powders. The criterion is described by means of a very concise equation based on the third invariant of the stress tensor, approximating the boundaries of the compressive octant of the principal stress space. This sheds new light on the physical significance of the third invariant of the stress tensor. The new criterion has been validated against two known analytical solutions for no-tension materials and also effectively applied for solving two geotechnical and structural engineering problems. The proposed formulation allows for an efficient implementation in finite-element programmes, removing some of the numerical difficulties associated with the Galileo–Rankine criterion.

Modeling of Strength Differential Effects in HCP Sheet Materials

A simple approach is proposed to employ symmetric yield functions for modeling the tension-compression asymmetry commonly observed in hcp materials. In this work, the strength differential (SD) effect is modeled by choosing separate symmetric plane stress Barlat Yld 2000 yield functions for the tension i.e., in the first quadrant of principal stress space, and compression i.e., third quadrant of principal stress space. In the second and fourth quadrants, the yield locus is constructed by adopting Bézier interpolating functions between uniaxial tensile and compressive stress states. The main advantage of this proposed approach is that the yield locus parameters are deterministic and relatively easy to identify when compared to the Cazacu-Plunkett-Barlat (CPB) family of yield functions commonly used for modeling the SD effect observed in hcp materials. The proposed yield function is implemented as a user material subroutine (UMAT) within the commercial finite element software, LS-DYNA. The predictions of the developed material model are compared with the measured load-displacement and strain distributions from a three-point bend experiment on AZ31B sheet.

Evolution Model of Concrete Failure Surface under the Action of Load and Frezee-Thaw Cycles

Concrete failure surface is the most important tool to predict concrete strength under complicated load. Most concrete structures in cold regions are subjected to both external loads and freezing-thawing, while now most researchers focused on the freeze-thaw durability of concrete without external loads. To make up the deficiency, the degradation of compressive strength of concrete under the simultaneous action of external loads and freezing-thawing are experimentally investigated in this research. Finally, a concrete failure criterion is adopted to establish an applicable failure surface in principal stress space for concrete.

Strength Hypothesis Applied to Hard Foams

The analysis of well-known strength hypotheses leads to the derivation of a generalized model, which contains a number of known hypotheses as special cases and could be used for the description of the 3D-failure of hard foams. This model in the case of the strength hypothesis for hard foams is characterized by a closed surface in the principal stress space. In order to fit the model to the experimental data certain objective functions are formulated. The optimization results are shown in the Pareto-diagram (optimal solutions for several targets). The results of the fitting are plotted in the Burzyński-plane. It can be seen that reliable modeling requires the knowledge of the material behavior under hydrostatic tension and compression.