A wiring harness in an aircraft engine, and in aircraft systems, has the vital function of conveying sensor information and carrying power to various components. Some harnesses, especially in the vicinity of a broad-spectrum high vibration and high temperature environment, can experience unexpected internal damage and cause faulty readings. This can happen despite following the best industry practices developed for such wire harnesses. A series of investigations have been conducted at the Raytheon Technologies Research Center (RTRC) Structural Dynamics Laboratory to understand the underlying reason for the vibration induced harness failures. When subject to the operational vibration spectrum, we were able to capture the first two bending modes of the suspect harness with a high-speed camera. From the mode shapes, we can extract the harness bending distribution. In addition, the temperature distribution of the harness resonating at its modal frequencies is measured with an infrared camera, and several hot spots are identified. These hot spots coincide with the locations with highest bend locations. The accelerated endurance test was then conducted, in which the harness is excited at the mode of interest. The resistance of the harness shield is monitored in real time to assess the damage severity. Towards the end of the endurance test, the resistance increases exponentially. The tear down confirmed that the failure mechanism is the wire fretting induced by the first harness bending mode. The evaluation procedure of the fretting risk is described, and the mitigation method is proposed at the end.
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Harness failure, vibration induced failure
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