Recent unpublished work has established chemical recipes for joining stainless steel and E-glass composite surfaces for composite shipbuilding application. Combination of self-assembled monolayer (silane) coverings on steel surfaces, and epoxy has led to remarkable joint sections that fail through the substrate (composite delamination), when loaded using the double cantilever beam test geometry. Figure 1 summarizes the data. As expected, exposure to moisture and seawater dramatically reduces the joint toughness. In these samples, the failure was observed at the steel/epoxy interface, indicating its susceptibility to moisture segregation and degradation. This is the main reason why epoxy joints have historically been ruled out in the design of crashworthy joints in automobiles and aerospace structures.

One of the accomplishments of our work is to show (see Fig. 1 with silanes) that the long-term reliability of the joint to moisture degradation can be dramatically improved by using a self-assembled monolayer on steel surfaces. Because of its rather ordered structure, it acts as a diffusion barrier to water molecules and leads to a much higher long-term joint toughness value. Silane B optimizes the joint as joint failure occurs from failure within the composite.

Figure 1. Moisture degradation of composite joints

We believe that this can have a major impact in designing of crashworthy joints.