Study of the compressive properties of adhesively bonded carbon fiber laminates at different strain rates

The characteristics of bond line thickness, and joint type of adhesively joined composites have been studied under variable mechanical loading conditions. However, the high strain rate (HSR) response of adhesively bonded composites is lacking and has been the subject of recent interest. The compressive properties of adhesively bonded carbon fiber laminates are studied under low and high strain rates. The investigation includes butt joints of two different bond line thicknesses of an epoxy-based adhesive that are subjected to longitudinal and transverse loading. The strength of butt joint that is subjected to longitudinal loading is 17% and 30% lower compared to the values of butt joints subjected to transverse loading at 0.44 and 0.77 mm thicknesses. For the same bond line thickness, the effective modulus of butt joint that is subjected to longitudinal loading is found to be 17% and 25% lower than that of butt joints subjected to transverse loading. HSR compression tests are conducted using a SHPB in the strain rate range 510 to 925 s−1. The strength of butt joints subjected to longitudinal loading did not show any measurable dependence on the strain rate, while strength of butt joints subjected to transverse loading decreased by ~20%. In addition, the energy absorption decreased by ~75% compared to the quasi-static values because of lower failure strain. Microscopy on the failed specimens revealed that failure mode was due to crack propagation in the adhesive bond line.