Post-peak Stress Drop Research Articles

A Plastic-Damage Model for Stress-Strain Behavior of Soils

This paper presents a constitutive model for soil, which combines elements of plasticity with damage mechanics to simulate the stress-strain behavior. The model is primarily suitable for soil types that exhibit a postpeak strain-softening behavior, such as dense sand and stiff clay. The postpeak stress drop is captured by the elasto-damage formulation, while the plasticity is superimposed beyond the elastic range. The total strain increment is composed of an elasto-damage strain increment and a plastic strain increment. The elasto-damage strain increment is found using the elasto-damage formulation, while the plastic strain increment is found using either the Drucker-Prager classical plasticity model or as a function of damage strain. To implement this model, an experimental program was conducted on local cohesive and cohesionless soils. Various physical and mechanical properties of these soils were determined. Both triaxial tests and hydrostatic tests were performed under different confining pressures, in order to obtain the model parameters. These parameters were used to calibrate the model, which was coded in computer programs to simulate the stress-strain behavior of soils. The model was verified and found to be a good predictor of the geomaterial response for the selected stress path.

Three-Dimensional Micromechanical Model for Quasi-Brittle Solids with Residual Strains under Tension

Presented in this paper is a three-dimensional micromechanical model that enables the simulation of microcrack-weakened quasi-brittle materials with permanent residual strains subjected to tension. The microcracking damage of such a material is described by the concept of domain of microcrack growth. It is thought that the occurrence of residual strains is attributable to two reasons, namely, the release of microscopic residual stresses due to microcracking and the microscopic plastic deformation along microcrack front edges. By introducing the analytical results of the two physical mechanisms into the constitutive relation, a micromechanical damage model is established to describe the effective response of microcrack-weakened quasi-brittle materials such as ceramics and concrete under complex loading/unloading paths. The response of such a material is divided into four stages, namely, the stages of linear elasticity, pre-peak nonlinearity, post-peak stress drop, and strain softening before macroscopic fracture.