Damage Initiation of Continuous Fiber Laminated Thermoplastic Composites

Abstract

The use of advanced thermoplastic composites (TPC) for structural applications in the aerospace and automotive industries has grown increasingly popular due to their high performance, high manufactured part output, and sustainability. Advanced manufacturing processes of thermoplastic composites allow for the building of complex optimized structural geometries with both continuous and discontinuous fibers. With more complex parts and processes comes the need for established qualification methodologies. Characterization of damage evolution from different manufacturing processes needs to be further explored to better understand the behavior of TPC for aerospace environments. Investigation into the differences in the damage behavior of continuous and discontinuous laminated TPC in tension and compression is important for aerospace applications where impact and crush damage is likely. Experiments using continuous fiber laminated IM7/PEKK TPC, [±45]4s specimens loaded in tension and [90/0]3s specimens loaded in compression, are performed to obtain stress vs strain curves with Digital Image Correlation (DIC) and acoustic emission (AE) transducers to monitor damage initiation and evolution. Next, interrupted low-cycle mechanical tests are performed on [±45]4s laminates with optical microscopy in between cycles to support characterization and understanding of the relevant damage mechanisms needed for material models. The damage mechanisms in laminated composites are of interest to better understand the effects of different fiber architectures on the laminate scale behavior, which can be used to calibrate continuum damage mechanics models.