Development of Novel Compact Compression Specimen for Matrix Compression Damage Initiation and Propagation Behavior in Fiber Reinforced Composites

Robust design and analysis of carbon fiber reinforced polymers (CFRP) mandates a thorough understanding of the onset and propagation of damaging mechanisms. Damage can manifest from fiber tension, fiber compression, matrix tension, and matrix compression. Of these damage forms, matrix compression has seen the least attention. Previous work has developed experimental specimens that enabled characterization of the onset and propagation of matrix compression damage. However, if high performance composite materials are used complications can arise when the matrix compression strength (σMC) exceeds the matrix tension strength (σMT). When the σMC/σMT ratio is greater than 2, compact compression (CC) specimens can exhibit matrix tension damage before the onset of matrix compression damage. The onset of matrix tension damage prevents proper characterization of matrix compression damage mechanisms. This paper presents the development of a novel stepped compact compression specimen. The reduced thickness of the stepped region allows significant matrix-compression damage to occur prior to tensile failure. Specimens comprised of 90° plies were fabricated using either a machined taper or a layering process. Both methods were successful however variability in machining generated substantial inconsistency and layering was found to be superior.