International Journal of Damage Mechanics

Delamination along the 0°/90° interface following transverse cracking in the 90° plies of a cross-ply composite laminate is analyzed based on the principle of minimum potential energy. The laminate is subjected to longitudinal applied tensile loading and internal residual thermal stresses. The strain energy release rate criterion has been employed to evaluate the critical applied stresses for transverse cracking and interface delamination. The effect of delamination along the 0°/90° interface on laminate stiffness and thermal property is presented for E-glass/epoxy and graphite/epoxy composite laminates. The longitudinal tensile stress in the 90° plies decreases gradually as the transverse crack density increases and thereby decreasing the tendency for transverse crack multiplication. For a given laminate configuration there exists a saturation (limit) crack density. Continued loading beyond this limit, delamination at the 0°/90° interface would occur. The analytical results are compared with the available experimental data.

The purpose of this paper is to show that shortcomings exist in the plasticity induced damage theories. Existing phenomenological thermodynamic approaches used for describing elasto-plasticity coupled with damage are therefore evaluated. Within the concept of effective stress both the postulate of strain equivalence and the postulate of (complementary) energy equivalence, as well as extensions of the postulates, are considered.

As a prototype model the von Mises plasticity model coupled with isotropic damage is considered. Simulations of a strain-controlled uniaxial model are also performed. The results reveal that a mapping, similar to that of the stress, of both the kinematic and isotropic hardening variables is to be preferred. More interesting is that, irrespective of the postulate employed, the elastic strain will not equal zero when failure takes place, i.e. the interpretation of elastic strain is lost. From the results it is also concluded that (complementary) energy equivalence have some undesirable properties.

In this paper, a micro-macromechanical approach is used to establish the macroscopic constitutive model with anisotropic damage in continuous fiber reinforced ceramic matrix composites (CFCC). For microlevel analysis of unit cell, the homogenization method based on double-scale asymptotic expansion is used to derive the material properties of composites. The macrolevel analysis is conducted to compute the macrostresses and strains with anisotropic damage. The two analyses are conducted by using Finite Element Method (FEM). An overall anisotropic damage tensor for the whole composite is used to describe all types of damage that composite undergoes, such as matrix cracking, fiber breakage, and interfacial damage between matrix and fiber. The damage evolution equation is obtained by using thermodynamic theory. The numerical calculation is carried out to investigate and to predict the onset and evolution of anisotropic damage for composites with different types of laminate. The damage material parameters are determined by fitting the numerical results to the experimental data, and some results are compared well with experimental results in the literature [Wang, S.W. and Parvizi-Majidi, A. (1992). Experimental Characterization of the Tensile Behavior of Nicalon Fiber-Reinforced Calcium Aluminosilicate Composites, Journal of Materials Science, 27: 5483-5496.]. By using the proposed model, the stiffness and nonlinear stress-strain response of brittle composite materials are predicted, and the macroscopic elastic brittle anisotropic damage behavior is also described

Based on the wave propagation theory on the jointed media, a dynamic damage model of the jointed medium is developed based on theoretical analyses and model tests to describe the wave propagation behavior on the jointed rock mass under the blasting pulse. The presented model is capable of describing the behavior of dynamic response of the microjoints and its interaction with wave propagation properties, as well as the consideration of the degradation of the material stiffness and strength, which cannot be described by the classical continuum damage mechanics theory. Comparisons between the proposed model and the test results are also discussed.