This book presents the proceedings of the American Society for Composites 39th Technical Conference. This volume, the third of six volumes, gathers studies and findings related to testing with ASTM standards, assessment of the effects of defects, aspects of Nondestructive Evaluation (NDE) of composites, and processes toward sustainable composites. The content includes experimental and computational approaches that contribute to advancing knowledge in the characterization of composite behavior, assessment of manufacturing defects and damage growth on mechanical properties and failure, nondestructive characterization of the material and its process, diagnostics & prognostics, imaging, and the development of recycled and sustainable practices for composite materials.