Tensile strength of composite bonded scarf joint in various thermal environmental conditions

Abstract

This study analyzed variations of tensile strength and the failure mode of composite bonded scarf joint in various thermal environments. A total of 70 scarf bonded joints were manufactured using secondary bonding and co-bonding methods, in which a number of 10 scarf joints were additionally attached to an external ply over the joint area to examine its effect. Six different environmental temperatures ranged from 25 degrees C to 150 degrees C were chosen and tested. A pure laminate having the same stacking sequence as the parent laminate was prepared and tested at the six temperatures for references. Experimental results revealed that tensile strengths of the secondary bonded (SB) and co-bonded (CB) joints at 75 degrees C reduced by 9.3% and 10.5% in comparison with strengths of the corresponding joints at 25 degrees C, respectively. Particularly, at 125 degrees C, which is higher than the resin glass transition temperature, significant reductions of 57.1% and 53.6% in strength were found for SB and CB joints, respectively. In terms of the manufacturing methods, the strengths of the SB joints were higher than those of the CB at 25 degrees C, 50 degrees C, and 75 degrees C by 6.5%, 7.6%, and 8.0%, respectively. However, at high temperatures (100 degrees C, 125 degrees C, and 150 degrees C) these differences were negligible. Strengths of SB joints attached external ply increased by 5.9% and 37.5% compared to those of SB joints without the external ply at 25 degrees C and 100 degrees C, respectively.