Constitutive modeling of damaged unidirectional composite laminae

Analysis of composite laminates is a multi-faceted problem due to the inherent characteristic features such as anisotropy, heterogeneity, multiple failure modes, etc. Due to a lack of an accurate analysis methodology that accounts for all of these features, applications of composite materials are often limited or poorly optimized. One of the key aspects of failure analysis that can be improved for better predictions of the mechanical behavior is the representation of the damage state in composite materials. In this research, degradation models for damaged unidirectional composite laminae were studied.; A thorough literature review of the available degradation models in progressive failure analysis of composite materials was conducted. The degradation models were grouped into sudden degradation models and gradual degradation models and several aspects of damage modeling in composite laminates were investigated.; Gradual degradation behavior was studied for two matrix damage modes. The first of which is matrix normal cracking characterized by matrix cracks oriented perpendicular to the fibers. The residual properties of a lamina with matrix normal cracks were estimated using volume-averaged stresses and strains obtained from a finite element unit cell model. The influence of various parameters on the residual properties of a lamina with matrix normal cracks was also examined using the finite element model.; Matrix ply cracking, characterized by through lamina cracks running parallel to the fibers, was studied using a finite element unit cell model. The residual properties of the cracked lamina were estimated using the volume-averaged stresses and strains from the finite element model. The influence of the thickness, material properties, and the position of the cracked lamina and the thickness, fiber angle, and the material properties of adjacent plies on the residual properties of the cracked lamina was investigated.; Damage in a lamina generally originates as damage of the constituents. Therefore, utilizing Multi-continuum technology and a reverse engineering method, an approach was developed for estimating the reduced properties of a lamina in terms of reduced properties of the constituents. This may enable future progressive failure modeling of composites using Multicontinuum technology.