Effects of Out Time on the Mechanical and Fracture Properties of Chopped Fiber Composites Made From Repurposed Aerospace Prepreg Scrap and Waste

In this study, the effects of prepreg out time on the mechanical and fracture properties of Discontinuous Fiber Composites (DFCs) are investigated. Carbon fiber prepregs are aged at 0x, 1x, 2x, and 3x the out life in an environmental chamber at constant temperature and humidity. Degree of cure is measured via Differential Scanning Calorimetry (DSC) while tension, compression, and shear tests are performed to investigate the effects that aging has on these mechanical properties. For the first time, Mode I intra-laminar fracture and its size effect are also investigated by means of fracture tests on geometrically-scaled Single Edge Notch Tension (SENT) specimens. From the tension, compression, and shear experiments it is seen that the out time has no effect on the elastic moduli. However, the strength increases with increasing age of the specimens for all the loading conditions. The percent increase compared to the non-aged material ranges from 15% to 33%. This is likely caused by plasticization of the matrix with age, allowing for higher energy absorption. More complex trends are reported for the SENT specimens for all the sizes. It is found that the fracture energy and characteristic length initially decrease with age, and then finally increase for the longest out time. This trend is owed to two factors with countering effects on the fracture behavior: 1) the increase of the average number of platelets with increasing aging due to increase in resin viscosity, and 2) the plasticization of the matrix with aging. The results from this study suggest that Discontinuous Fiber Composites (DFCs) made from reused materials can have equal, if not better, performance than non-aged DFCs. The experimental data presented in this work can be used as a baseline to design DFC composite components made from repurposed prepreg scrap and waste.