In-Situ Characterization of Polymer Matrix Composites and Progressive Damage Analysis of Virtually Reconstructed Microstructures

Abstract

Process-induced variabilities in fiber-reinforced polymer composite (FRPC) microstructures result in large scatters in the experimentally measured composite properties which lead to conservative designs and unnecessary manufacturing cost. Processing conditions such as cure temperature and time combined with low thermal conductivity impose spatially varying thermal histories that influence cure evolution and property development in composite during manufacturing. Additionally, irregular and off-axial fiber architectures introduce thermo-mechanical constraints which lead to residual stress generation, damage accumulation during curing, and in-situ matrix properties. Complete understanding of the process-induced variation in the fiber and matrix at the microscale is necessary to identify sources of scatter in bulk composite mechanical properties and eventually optimize the manufacturing process. The objective of the proposed study is to establish the processing-microstructure-property correlation to improve predictions and reduce processing times of FRPCs using experimental techniques and computational modeling. Statistical descriptors are developed to study process-induced variation in the fiber microstructures. Micro-CT scans of aerospace- and automotive-grade laminates are analyzed. The effect of processing conditions on the two microstructures is investigated; qualitative and quantitative comparisons of the statistical metrics are made. Micro-Raman spectroscopy is successfully employed to generate a 3D map of the degree of cure variation in a partially cured epoxy sample. This technique will be further explored to quantify the process-induced degree of cure variation in a composite laminate. Finally, a finite element (FE) based process modeling computational framework is developed to virtually study the process-induced variations in the composite microstructure. The process-induced variability in fiber and matrix will be correlated to residual stress generation, damage accumulation during cure, and bulk composite properties through process modeling simulations of virtually reconstructed microstructures.