Effect of Cyclic Heat, Humidity, and Joining Method on the Static and Dynamic Performance of Lightweight Multimaterial Single-Lap Joints

This experimental study investigates the effect of environmental loading and joining methods on the static and dynamic performance of lightweight multimaterial single-lap joints (SLJ). Joint adherend material combinations are divided into two groups; namely, composite-based and steel-based materials that include glass fiber reinforced polymer (GFRP), steel (St), aluminum (Al), and magnesium (Mg). A commercially available adhesive is selected for the study. Investigated joining methods include bonding-only, bolting-only, and hybrid bonding-and-bolting. Static performance is assessed by the load transfer capacity (LTC) of SLJ after they have been subjected to heat cycling at ambient level of relative humidity, or after heat cycling at high relative humidity. Dynamic performance is measured by durability life (in cycles) of SLJ test samples under a fixed dynamic load ratio in a tensile–tensile fatigue test, after they have been subjected to heat cycling and humidity. The cyclic test load fluctuated between 67.5% and 75% of the static LTC at ambient condition. Sample finding includes the significant effect of heat cycling at an ambient humidity level; it has tripled the LTC of bonded-only composite-to-composite SLJ, relative to their baseline LTC at ambient conditions. Detailed discussion of the results, observations, and conclusions are presented in this paper.