Constitutive modeling of static and cyclic behavior of interfaces and implementation in boundary value problems.

Abstract

A constitutive model based on elasto-plasticity theory is proposed here to describe the behavior of interfaces subjected to static and cyclic loading conditions. The proposed model is developed in a hierarchical manner wherein a basic model describing simplified characteristics of the interfaces is modified by introducing different features, to model increasingly complex behavior of the interfaces. The proposed model can simulate associative, nonassociative, and strain-softening behavior during monotonic as well as cyclic loading. The parameters influencing interface behavior are identified using data from laboratory simple shear tests on sand-steel and sand-concrete interfaces. A parameter called "interface roughness ratio, R" is defined in order to model the interface behavior under different interface roughnesses. Similarly, a cyclic parameter Ω is introduced to simulate the cyclic volumetric behavior of the interfaces. Proposed model is verified with respect to comprehensive test data on interfaces with different roughnesses, normal loads, initial densities and type of sand, and quasi-static and cyclic loading. A new and highly efficient algorithm is developed to perform drift correction under constraint condition. This algorithm is used for the integration of constitutive relation for interfaces to perform back prediction. Performance of the algorithm is compared with various existing algorithms. Using Lyapunov's Stability Theorem, it is proved that the proposed algorithm is stable. The proposed model for the interfaces is used in the context of the thin-layer element approach and is implemented in a nonlinear dynamic finite element code to solve a boundary value problem involving dynamics of an axially loaded pile. It is shown here that the use of the interface model can allow proper modeling of shear transfer, volumetric behavior and localized relative slip in the interface zone. The effect on shear transfer from pile to soil due to the coupling between normal behavior and shear behavior of interface is established here for soil-structure interaction problems. The findings of this research have contributed to the understanding of the interface behavior in soil-structure interaction problems. The proposed model can simulate a number of important behavioral aspects of the interfaces.