Failure analysis of scarf adhesive joints modified with SiC-nanoparticles under fatigue loading at room temperature

Abstract

Adhesive joints were fabricated by joining two woven carbon fiber composite adherends with scarf angle of 5° using Epocast adhesive system of 50-A1/946 modified with optimum weight percent of 1.5 wt% SiC-nanoparticles. The scarf adhesive joints (SAJs) were characterized through static tensile as well as tension-tension fatigue loading. The stress-number of cycles to failure curves are useful in determining the fatigue life, but they do not give any indication about the fatigue damage development during the joint's lifetime. In consideration of early detecting damage development in the SAJs, many dynamic parameters were estimated from the analysis of the stress-local strain cycles, with the aim to obtain more accurate predictions. These parameters include loss and storage moduli, potential and dissipated energies, and damping factor. It has been found that the tensile strength and fatigue limit of the SiC-SAJ were increased by 9.6% and 55% respectively with decreasing the bondline thickness from 0.25 mm to 0.17 mm. Incorporation of SiC-nanoparticles into the adhesive layer improves the tensile strength and the fatigue limit of the SAJs with bondline thickness of 0.17 mm by 26.1% and 22% respectively compared to the unmodified joint. At higher stress levels, the storage modulus and potential energy can be modeled for early prediction of the joint life and thereby, help in preventing their catastrophic failure. Zhang model showed good agreement with the measured potential energy compared to the storage modulus.