Computational Modeling of Damage Growth in Composite Laminates

Abstract

A progressive damage growth model is developed for composite laminates under compression. The mechanics of damage initiation and growth in a single lamina is modeled in a two-dimensional plane stress setting, using a system of orthotropic nonlinear elastic relations and a set of internal state variables. The latter are associated with different damage mechanisms that are unique to a e ber-reinforced lamina. A thermodynamically consistent set of equations is developed for the evolution of damage growth. The formulation is numerically implemented using the commercially available e nite element package ABAQUS. The present method is applied to analyze the problem of damage growth in a compressively loaded notched laminate. Predictions of the model compared against available experimental observations are promising. EVELOPMENT of computational methodologies for the prediction of progressive damage growth in continuous e ber composite laminates is presently an active area of research. Available predictive methods are based on dee ning strength-based criteria at the lamina level. Based on critical values for tensile, compressive and shear “ strengths,” these methods compute predee ned damage indices that are expressed in functional form in terms of the current stress state. When any of these indices exceeds a predee ned critical value, the material is said to have failed. 1 Beyond initial failure, a consistent and rigorous methodology to account for progressive material deterioration has not been investigated thoroughly. An exception to this is the work by Schapery and Sicking, 2 who carried out lamina-level tests and validated the test results by developing a thermodynamically based progressive damage formation and growth model. In these studies Schapery and Sicking assumed that the e ber-direction response is essentially linear (slight elastic nonlinearity in the e ber direction was accounted for), but damage (microcracking and transverse cracking) formation affected the response in the transverse direction. Consequently, internal state variables that are related to the damage mechanisms in the transverse direction were identie ed, and evolution laws that specify the growth of damage and hence its ine uence on the transverse direction response were prescribed. In contrast to the transverse direction, in which damage accumulation results in progressively decreasing but smooth variations in instantaneous tangent moduli, damage accumulation in the e ber direction leads to nonsmooth abrupt changes in the corresponding moduli. These changes must be properly captured if progressive damage growth in composite laminates is to be modeled accurately. In the present paper Schapery’ s theory (ST) is extended to account for e ber-direction damage (both, in tension and compression) by identifying an additional internal state variable associated with the e ber-direction response. By doing this, we have shown that it is