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With the rapid advances in electronic control within automobiles, the junction block (J/B), primarily used for electrical transmission and electrical wiring, has begun to house electronic control units. It is evolving into an active component with smart functions that also controls vehicle devices, at the core of the wiring harness. We have developed a method using CAE to predict the fatigue failure life of J/B brackets for use as a design-assist tool in the early stage of J/B development. Failure of J/B brackets starts with the repetitive stress generated in the brackets during resonance. This stress is maximum at primary natural vibration which is the lowest frequency during resonance. By accurately estimating the above-mentioned stresses using CAE, we established a method to determine the number of vibrations at which fatigue failure of the J/B bracket would occur (fatigue failure life) from the fatigue failure life characteristics of the material.

We developed a method to simulate the bending reliability with the aim of shortening the development time of wiring harnesses and achieving reliability in the initial stages of development. PVC-insulated wires are generally used in automobiles. Wire breakage due to repeated bending occurs easier at low temperature than at room temperature. Research showed us that we can estimate the number of bends until wire breakage at low temperature (bending life) from the amount of change in the strain in the wire insulation. Further, by using CAE analysis technology, it is possible to estimate the bending life of complex wire harnesses. This has greatly reduced the time and effort needed to perform evaluation compared with conventional evaluation tests.

Using tin-plated terminals generally used for vehicle connectors, we studied the variation in thickness of the oxide film on the terminal surface, progress of copper diffusion to the tin-plated layer, and terminal stress remaining rate against the ambient conditions of temperature, humidity, and oxygen concentration. As well, we collected terminals from aged vehicles for actual field data, and tested them in the same way. We analyzed the obtained data using the regression analysis technique and obtained an expression for the relationship between the environmental factors and the transition of the terminal state as time elapses. This paper describes the accelerated test method that produces the same results as actual products used for ten years, by making calculations with the said expression.