216 Table 1  Design 1: Lot A  Design 1: Lot C Design 2   Baseline Construction / design  1: Lot A initial build & lot of materials, no performance affecting damage observed Construction / Design 1 same as Lot A, different build date and lot of materials; Cold Welding and damage observed in multiple layers along length of cable Design 2 incorporated intermediate layer, multiple Design 2 cables tested, Sporadic Cold Welding between Outer Conductor layer observed with minimal damage.   Life Tests Successful   (2 of 2 cables passed) Life Tests Failed  (2 of 2 cables failed) Life Test Successful  (6 of 6 cables passed)  Design 2 cables went through multiple tests, multiple permutations of profiles, and various other stress  and fatigue tests in addition to the same level of testing of Design 1. Design 2 cable outperformed Design 1 cable. Two key features differentiate Design 2 Cable from the Design 1 cable: the intermediate non-silver coated copper layer between the outer conductor and the braided shield; and alloyed center conductor strands with a thicker outer silver coating. The failed Design 1 cable incorporated relatively pure copper strands coated with a thinner layer of silver within the center conductor strands.  In regard to cold welding, the intermediate layer prevents cold welding between the outer conductor and  the braid by inserting a different material between the silver coated copper layers. This intermediate layer  feature is believed to be the key difference preventing the most damaging occurrences of cold welds : cold  welds that form between two separate layers in the outer portion of the cable. When the cable is put in  bending, the outer layers are forced to move/slide relative to each other (more than the inner layers); if cold welds are present, instead of moving relative to each other by sliding, local yielding or pushing of surface materials occurs. Referring back to Figure 5, it is evident that braid to outer conductor cold welds initiated tearing and yielding in both layers through motion / bending of the cable.   The alloyed center conductor mitigates some level of the similar metal interaction required for cold  welding, has better metal fatigue properties, and with a thicker layer of silver on each strand the silver is likely to transfer between strands acting as a lube or additional wear layer through plowing and compliance.   To mitigate the effects of cold welding in coaxial cables, the design and material of the cable for flexing  applications should incorporate the two features mentioned:   1. Incorporate an intermediate layer between the outer conductor and braid of a different  preferably non-metallic material. It will act as both a wear buffer and will prevent cold welding between the two outer most metallic layers of the cable. It also has the potential to mitigate insertion loss instability within cables (where the outer conductor loosens up  over time developing a radial gap between adjacent wraps).  2. Ensure the center conductor is a higher strength alloyed copper and that the silver coating  on the strands has a well controlled thickness (thicker likely is better based on the test observations).  Because of the many variables involved, a life test must be performed for each new design of cable even with the recommended features incorporated. In addition to design verification, an important lesson-learned was that coax cable construction and implementation can vary in subtle ways between production lots that can affect cold welding and fatigue capability, and therefore a life test should be performed for each production lot regardless of design similarity.