Assessment of process-induced microcracks in 3D woven composites using meso-scale model simulations

One of the advantages of 3D woven composites is the ability to create unique fiber architectures in which tows can be individually arranged to optimize performance to meet specific structural requirements. This flexibility may lead to a design with unintended mismatch of thermal properties in areas of the composite, creating the potential for manufacturing issues such as process-induced microcracking. This paper presents results of a case study in which various architectures were analyzed, including some that led to intra-tow microcracks in the molded composite and others that did not. The objective was to develop an approach using meso-scale finite element modeling at the unit cell level to evaluate the propensity of these architectures to microcrack. Analysis results showed that the transverse principal stresses which developed in tow elements during cooling from cure to room temperature were significantly different in the various architectures. Comparison to the micro-computed tomography scans of the molded composites established strong correlation between regions with microcracks and areas of high predicted transverse principal stresses in the simulations. This study suggests that meso-scale finite element modeling of 3D woven architectures can be used in the design cycle to reduce or eliminate microcracking in the finished composite parts.