Experimental study of silicone-epoxy dual adhesive joints for high temperature aerospace applications

Adhesive bonding is extensively used in aerospace applications. Some of the most important aerospace applications are in heat shields intended to protect metallic structures from extreme heat. Many heat shields are bonded with RTV silicone based adhesives, which have excellent resistance to high temperature but very low strength. This work proposes and studies three alternative configurations to these adhesive layers. One configuration with RTV silicone only (RTV106), one with only a high temperature epoxy (XN1244) and finally another configuration introducing both adhesives in the same joint (mixed joint). Experimental specimens and a testing device intended to simulate the loads on an actual heat shield were manufactured. These specimens were subjected to loading and tested until failure at both low and high temperatures. It was demonstrated that while the RTV silicone joints lose strength at 100 degrees C, the epoxy and mixed joints are able to retain most of their strength. The mixed joint is also able to withstand large values of displacement at relatively high forces, indicating excellent capabilities at absorbing directed energy. The improvements and advantages deriving from the use of these alternative configurations are described and compared.