Stress transfer mechanism and interfacial debonding behavior of composites with axially graded interphase

In this paper, we explore the stress distributions of the composites with axially graded interphase, a newly proposed configuration. A three-phase shear-lag model considering the modulus gradient in the axial direction is developed and its validity in resolving the stress distributions is carefully verified with the help of finite element method. The results suggest that the shear stress concentration at the interphase/matrix interface can be significantly alleviated by introducing the functionally graded interphase. The parameter analysis indicates that longer length of functionally graded part, thicker interphase, smaller end modulus of the interphase, and lower convexity of interphase modulus profile, can enhance the effect on reducing the shear stress concentration. In addition, the introduction of functionally graded interphase also changes the debonding behavior of the composites: the onset of the debonding is postponed and the process of debonding is altered. Besides, we find that debonding on the two interfaces of the composites generally follow different trends when varying the geometrical and mechanical parameters of the interphase, which means that, by properly designing these parameters, one can easily modulate the failure modes of the composites.