Reliability of Thermomechanical Fatigue in Polymer Matrix Composites

摘要

A methodology to compute probabilistic fatigue life of polymer matrix laminated composites has been developed and demonstrated. Matrix degradation effects due to long term environmental exposure and mechanical/thermal cyclic loads are accounted for in the simulation process. Sensitivity of fatigue life reliability to uncertainties in the primitive random variables e.g. constituent properties, fiber volume ratio, void volume ratio, ply thickness, etc. are computed and their significance in the reliability based design for maximum life is discussed. A graphite/epoxy (0/+-45/90) deg_s laminate with ply thickness 0.127 mm, is used to demonstrate the methodology. The results show that at low mechanical cyclic loads and low thermal cyclic amplitudes, fatigue life for 0.999 reliability is most sensitive to matrix compressive strength, matrix modulus, thermal expansion coefficient and ply thickness. Whereas at high mechanical cyclic loads and high thermal cyclic amplitudes, fatigue life at 0.999 reliability is more sensitive to the shear strength of matrix, longitudinal fiber modulus, matrix modulus and ply thickness.