Life Prediction of High Temperature Polymer Matrix Composites for Aircraft Engine and Airframe Applications

摘要

Dynamic experiments were conducted to evaluate the effects of oxidation on the mechanical properties of both 5250-4 resin and its composite under high strain rates. A long split Hopkinson pressure bar was used in experiments. For the resin oxidized at 245 deg C for 1500 hrs its mechanical properties, such as Young's modulus and compressive strength, show only slight reduction at high strain rates. For composites oxidized at 195 deg C for 1500 hrs, near the service temperature, the changes of mechanical properties are negligible. For composites oxidized at 245 deg C for 1500 hrs, when loaded along the fiber direction, the mechanical properties decreases by 1/3, when loaded in other two directions the properties show even more drastic reduction, maintaining only about 1/3 of the stiffness and strength compared with pristine composites. Results indicate that when the composites are subject to a temperature slightly higher than the service temperature, the property degradation is extremely significant. In the modeling task, the micromechanical model was extended to predict progressive failure of a laminate in the presence of nonlinear effects, such as, matrix cracking, fiber/matrix debond, delaminations, and viscoelasticity using fundamental principles of continuum damage mechanics.