Failure Analysis of the Electric Crimp Joint on a Harness in an Automotive Environment

This paper describes the process by which the failure modes of the crimp joint from field returned electric harnesses were identified. To record the transient behavior of the contact resistance, an oscilloscope was used to display the resistance variation over time. The crimp showed that, as received, its contact resistance could change to a few Ohms, and would remain at that level if undisturbed. When the tested sample was baked at 85°C in an oven for a few days, it would usually restore the high resistance. This was repeated many times. After being documented with high contact resistance intermittence, a crimp was cross-sectioned to expose its compactness. Visual inspection showed that the crimp was reasonably ‘good’ by conventional criteria but the contact between the strands and the barrel in the serration locations might not be tight enough. It might be further inferred that the slight looseness in the crimp must have allowed some micro-motion, which caused fretting corrosion under the vibration from vehicles. Examination of the surfaces in contact between the tin-plated crimp barrel and the strands of bare copper revealed the evidence of fretting corrosion that the oxides of insulative nature on these surfaces must have caused the consequent high resistance intermittence in the crimp joint.