Quasistatic delamination of sandwich-like Kirchhoff-Love plates

A quasistatic rate-independent adhesive delamination problem of laminated plates with a finite thickness is considered. By letting the thickness of the plates go to zero, a rate-independent delamination model for a laminated Kirchhoff-Love plate is obtained as limit of these quasistatic processes. The same dimension reduction procedure is eventually applied to processes which are sensitive to delamination modes, namely opening vs. shearing is distinguishe

Theory of Martensitic Phase Transitions in Elastoplastic Materials

The conditions of nucleation, nondisappearance of nucleus and interface propagation are derived for noncoherent and coherent phase transitions (PT) in elastoplastic materials. Extremum principles for determination of all unknown parameters are derived based on the postulate of realizability. Two model problems are solved. The predicted effect of shear stresses and plastic strains on PT pressure and hysteresis is in qualitative agreement with experiments

Phase Transitions in Inelastic Materials at Finite Strains: A Local Description

A general theory of phase transitions (PT) in the material point of simple inelastic materials with arbitrary constitutive equations is developed. The standard thermodynamical approach can be applied only after averaging of thermodynamical parameters, related to PT, over a PT duration. A PT criterion for the material point is derived, taking into account the temperature variation and dissipation due to PT, as well as internal variables. Temperature variation in the course of PT is determined with the help of the entropy balance equation under the assumption that the process is adiabatic. Based on results for the material point, new nucleation and interface propagation criteria are derived. A postulate of realizability is applied to determine all unknown parameters in PT criteria. A model problem is solved

Conditions of Nucleation and Interface Propagation in Thermoplastic Materials

Nucleation and interface propagation criteria are derived with account for temperature variation in the course of phase transition (PT) and internal variables. A model problem concerning the nucleation of thin inclined infinite layer in a rigid-plastic half-space under prescribed normal and shear stresses is solved. Nontrivial effect of shear stress on the PT pressure is shown

Shape memory alloys: Micromechanical modeling and numerical analysis of structures

Multiscale modeling of structures made from shape memory alloys (SMA) is presented. Starting with consideration of a single transformation event at the micro-level and averaging over the representative volume, micromechanically-based macroscopic constitutive equations are derived, which are used in Finite Element Method (FEM) code to model the behaviour of structures. Using the thermodynamic theory of phase transformations (PT) in elastic materials on the micro-level, the macroscopic associated transformation flow rule, the corresponding extremum principle and the nonconcavity of the transformation surface are derived for transformational micromechanisms of inelastic deformation due to phase transformation, twinning and reorientation of martensitic variants. A simple three-dimensional micromechanically-based model for thermoelastic martensitic PT is presented. The model is transformed to the fashion similar to that for J2-plasticity theory. It allows one to modify the FEM for elastoplasticity (including the radial return algorithm for numerical integration of the constitutive equations and calculation of the consistent tangent moduli) in order to model PT in SMA. Some axisymmetric problems for PT in SMA tubes are solved. In particular, PT regularities of a tube assembly with a SMA cylinder element are investigated at different external conditions

A simple micromechanical model for pseudoelastic behavior of CuZnAl alloy

A simple micromechanical model for thermoelastic martensitic phase transitions (PT) is developed. It is deduced from the local description of PT in transforming particles with subsequent usage of average procedure, based on a model for elastic three-phase materials (austenite, martensite and new infinitesimal nucleus) under assumption of homogeneity of stresses in each phase. In contrast to known approaches, a new local PT criterion and a corresponding extremum principle for PT with dissipation are used. The macroscopic PT criterion obtained is split into two different equations for description of temperature-induced PT and stress-induced PT. To identify the material parameters of the model and to check its validity, simple one-dimensional experiments were carried out for CuZnAl alloy. The experimental values of martensite start and finish temperatures and austenite finish temperature for temperature-induced PT and the stress-strain diagram for stress-induced direct PT at any fixed temperature have allowed to determine six material parameters of the model for the simplest one-dimensional case. Then model prediction is compared with other independent tests. A good agreement is obtained of the calculated stress-strain curves for reverse PT (martensite-austenite) at θ,1 = 20°C and for direct PT at temperature range of 30-80°C with experimental data. Finally, the formula for determination of the transformation heat during temperature-induced PT for the given model is derived. It is shown that the predicted transformation heat is close to the experimental one. © 1999 Technomic Publishing: Co., Inc