Mechanical behavior and failure mechanisms of boron carbide based three-layered laminates with weak interfaces

摘要

The effect of weak interfaces on failure mechanisms of a three-layered composite was studied. Three-layered B_4C/B_4C-C_(nanofibers) laminates have been produced using a hot pressing technique. The laminates were designed with thick (～2.6 mm) outer layers of B_4C and a thin (～90 μm) center layer of B_4C-70 wt.% C_(nanofibers). Based on the difference in coefficients of thermal expansion and Young's moduli of the pure B_4C and B_4C-70 wt.% C_(nanofibers) layers, it was estimated that low tensile thermal residual stress with a magnitude of 11.3 ± 2.5 MPa was developed in the thick B_4C outer layers, and compressive residual stress with a magnitude of 455.7 ± 5 MPa was developed in the thin central B_4C-70 wt.% C_(nanofibers) layer. The apparent fracture toughness of laminates was measured and based on the estimated fracture toughness values, a threshold stress was calculated.