Damage and Degradation of Unidirectional Composites under Quasi-Static and Fatigue Loading - A Continuum Damage Micro Mechanics Approach

This work proposes an analytically based approach to assessment of the fatigue behavior of composites on the micro-mechanical level of constituents fiber and matrix. It implies adequate transferring functions for stresses from ply level to constituent material level. The stress-exposure e of the constituent materials can be assessed utilizing an equivalent stress approach for isotropic materials. Furthermore, a continuum damage description for matrix and fiber that relates constituent moduli to their stress-exposure and damage is of vital importance. Resulting damages are accumulated and lead to further degradation. As a next step, strainenergy based functions for assessment of load carrying capacity of constituents of different plies within the composite are applied and compared to identify the residual load carrying capacity of the laminate in comparison to applied loading in each load cycle. Thereby, not only damage initiation and degradation but as well failure of the laminate can be predicted. The combination of the above modules is referred to as Continuum Damage Micro Mechanics (CDMM) framework.