Joining of CFRP and low-CTE glass-ceramics for aerospace applications

Joining of dissimilar materials is a crucial point in aerospace applications; in particular CFRP and low-CTE glass-ceramics that are widely employed in space structures. The main challenge in this context is manufacture light and stable joints able to withstand aerospace conditions. Joining materials for this purpose, in order to be used in aerospace atmosphere, need to be lightweight, with low coefficient of thermal expansion, low moisture absorption, mechanical strength to sustain the component weight and low curing temperature to avoid damage of the composite polymeric matrix. For these reasons use of organic joining materials is limited by their moisture absorption and relatively high CTE values. In this study several inorganic joining materials, such as inorganic cements and pre-ceramic adhesives, were selected and tested. Inorganic cements have the advantage of room temperature curing and low CTE, but the disadvantage of relatively low mechanical properties. For this reason addition of fibers (e.g. glass fibers) to these materials was performed to improve mechanical strength. For ceramic adhesives, curing temperature might damage the polymeric matrix of CFRP, therefore the treatment was modified to preserve the matrix and at the same time ensure sufficient mechanical strength. Joints have been manufactured using the selected inorganic materials and mechanical strength was evaluated with tensile and shear strength tests. Most promising materials were also tested after ageing cycles developed to simulate aerospace conditions. Furthermore surface modification of CFRP was also studied, with different techniques, to improve the adhesion of inorganic materials. Each joining technique and joining material has been studied in order to offer an innovative approach in the field of CFRP/low-CTE glass-ceramic joining. Moreover, selected joining solutions take into account scalability and the possibility to transfer the process to larger structures. This activity was developed in the frame of the H2020-SMS (Sandwich Material and Structure) project.