DIC investigation of the failure behavior in CuCrZr1/CFRP joints exploiting different joint concepts

Kurzfassung

Space propulsion for large carriers such as the Ariane vehicles relies on complex engine designs consisting, amongst others, of turbo-pumps, injectors, the combustion chamber and a nozzle extension. The combustion chamber normally consists of an inner copper liner that incorporates the cooling channels and is covered by a heavy load jacket made of galvanized nickel. The load jacket adds substantial mass to the engine and, thus, reduced available payload mass. Hence, hybrid lightweight concepts based on carbon fiber-reinforced polymers (CFRP) have gained interest as disruptive alternatives that can potentially replace the nickel load jackets. For these concepts, the joining of the CFRP components to a copper liner, which can be additively manufactured, is essential. Adhesive joints between CFRP and metals can be enhanced through surface treatments like laser pretreatment, while the integration of pins transforms the failure behavior from sudden to progressive. This enables residual load-bearing capacity, improves safety, and allows for damage detection—critical factors for the reliability of space structures. We investigated both the design of different concepts of load-jackets for copper liners and the adhesive bonding of the copper alloy CuCrZr1 (CCZ) with CFRP. We focusing on two interface modification strategies: laser surface pretreatment and the integration of additively manufactured metal pins. Through a combination of mechanical testing and Digital Image Correlation (DIC) analysis the failure behavior of the different joint types was investigated. Laser surface treatment alone significantly increased single lap-shear strengths compared to untreated surfaces. While the incorporation of pins did not increase lap-shear strength, it succeeded in transforming failure into more controllable, stepwise failure mode, contrasting the abrupt, catastrophic failure typical of joints without pins. This progressive failure behavior is highly valuable for predictability, improving structural safety and enabling early damage detection. Further investigations are being carried out to improve the manufacturability of the joints and their reliability on the coupon level before transferring the technology to a full combustion chamber demonstrator.