  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.
