Impact of yielding material upsets on cold pressure welded C101 joint strength for potential use in the space environment

Abstract

Abstract Cold Welding (CW) is a solid-state metal joining process associated with the unintended bonding of metal surfaces in space. The bond can be classified as a weld (joint strength = σ yield ) or partial weld (< σ yield ). CW is closely related to Cold Pressure Welding (CPW) but occurs in ambient environment, relies on high plastic deformation and multi-upsetting actions to disrupt surface oxides. This action enables virgin metal-to-metal contact for bond formation. This research aims to quantify the determining factors (forces, metal candidates, surface conditions and oxidation factors) and their relative contributions in CPW so it may be adopted for in-situ CW of spacecraft hulls after micrometeoroid/debris perforation. A commercial CPW machine was adapted to investigate the effect of applied forces and number of upsets using Copper C101 rods (Ø 3 mm, N6), a material which is commonly used in electrical cables and gaskets. Two fixed force conditions were tested, F_1 = 2228 N (3.7 × σ yieldC101 ) and F_2 = 1794 N (3 × σ yieldC101 ). No weld was observed with less than three upsets under these loading conditions. Results show that higher force initiates bond formation, but it is weak (47% σ yield ) and the number of subsequent upsets will achieve full joint strength. Lower force requires more upsets, but initial bonds are stronger (66% σ yield ). Future work will assess the effect of chemical etching (oxide removal) on the force requirements for joint initiation and weld formation. This research aims to guide the development of CW for spacecraft hull repair methods.