SHEAR-WAVES IN FIBER-REINFORCED COMPOSITES WITH INTERFACIAL CRACKS

An ensemble-average statistical method is used to calculate the overal l effective mechanical properties of fiber-reinforced composites with interfacial cracks. The cracks here are specifically the fiber-matrix interfacial cracks which occur during the manufacturing process or are from inherent material defects. The problem starts with the establish ment of the Helmholtz equations and boundary conditions followed by a full scale solution of the multiple scattering equations. Then by cons idering the low frequencies limit and the statistics of randomly spati al distribution of the fibers, a manageable homogeneous linear matrix equation is obtained. In a homogenized point of view the macroscopic m echanical properties of the composite system are derived. The calculat ed average mechanical properties include the overall effective shear m odulus mu, the average shear wave phase speed B, and the average speci fic damping capacity Psi of the composite system. The shear modulus co rresponds to the elasticity of the static state, while the shear wave phase speed and damping capacity correspond to the viscoelasticity of the dynamic state of the composite. The results show that, among other s: 1. the fiber-reinforced composites with interfacial cracks are tran sversely anisotropic material systems possessing viscoelastic behavior 2. the axially shear modulus of the composite, as the half crack leng th (delta) increases, is in a 'decreasing steps' fashion for which fin ite numerical jumps exist between those steps 3. for a fiber-reinforce d composite with interfacial cracks, the composite system with 1/2 pi half crack length is the least attenuated and is nearly transversely i sotropic 4. the composite is a non-dispersed material system in low fr equency ranges. (C) 1998 Elsevier Science Ltd.