Effects of aging 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 to 0×, 1×, 2×, and 3× the out life (28 days) in an environmental chamber at 23∘C and 50%RH. From 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 unaged 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 fracture tests on geometrically-scaled Single Edge Notch Tension (SENT) specimens. 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 number of platelets through the thickness with aging due to increase in resin viscosity, and 2) the plasticization of the matrix with aging. The results of this study suggest that the mechanical performance of Discontinuous Fiber Composites (DFCs) made from reused materials is not negatively affected by aging of the starting material. On the contrary, repurposed DFCs can exhibit equal, if not better, performance than unaged DFCs. The results of this work further corroborate the feasibility of using DFCs as a mean to mitigate the environmental impact of thermoset composite waste. 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.