221 Aside from cables, the risks may be obvious, but it is worth mentioning that similar metal to metal contact  interfaces requiring motion within mechanisms are at risk.   If two surfaces are required to move relative to each other and there is no (non-metallic) barrier  between them (lube, coating or otherwise) then cold welding can lead to failure (seizure / increased force to slide, move or separate; or low cycle fatigue) at that joint / interface.   Any critical surface contact and motion between critical interfaces should be tested in as flight like  manner as possible (Test Like You Fly). Recall cold welding is exacerbated by clean surfaces, time, and contact pressure, so ensure testing incorporates / encompasses these critical parameters.   Dithering motion and vibration can exacerbate cold welds by abrading the surfaces and exposing  the atomically clean metallic surfaces underneath. A space vacuum environment also contributes to maintaining clean surfaces (no oxidation, sulfides, water vapor, etc) – Test like you fly considerations should be validated.   Pausing, idle periods and non-operation between operation / motion cycles can exacerbate cold  welds by allowing the two adjacent surfaces time to molecularly bond to one another and form stronger cold welds. Sequence of initialization, deployments, and storage periods should be given consideration during a qualification of critical contact surfaces.    A higher contact pressure and softer metallic interface contribute to a larger contact surface area  and more energy at the interface to encourage the metals to share molecules, i.e., the higher the likelihood of cold welding. Reference 5 goes into further detail about the contribution of surface micro hardness of the constituents as it relates to cold welding.    Material Lot Changes: Hardness, contamination/cleanliness, alloy/material difference, subtle  construction differences/ machine and assembly setups all make a difference and should be considered when making a decision on whether cold welding is a concern in your system. Complete a life test on every lot of material for critical surfaces whether or not you have completed a life test in one version or design. 

Conclusion  Moving cables are sensitive to changes in material lot and test parameters including vacuum, strain / motion, speed, and other test like you fly assumptions much like other components within moving mechanical assemblies. This was the conclusion after a multiple year investigation completed on coaxial cable for an aerospace Moving Mechanical Assembly. Fatigue has been widely discussed as the primary failure mode of flexing wire; however, other phenomena need to be considered when designing a cable to move over life. Cold welding, a condition in which welds occurs between similar metals in the absence of heat, can occur on cable layers if precautions are not put in place when choosing a cable design to use for a moving application. For coax cable it has been shown that cold welding between the outer braid and  the outer conductor can lead to degradation in RF performance. Three key points were discussed during the course of this paper:  1. Life Test Programs are not usually driven by lot/date code changes, however, life testing for coax  cable from each production lot is recommended   2. Coax Cable Designs to be used in life critical MMA’s should incorporate a non-metallic  intermediate layer to prevent multi-layer cold welding between any metal to metal layers. Additional attention should be paid to the lot construction of the individual metal constituents