A Combined Mode Fatigue Model for Glass Reinforced Nylon as applied to Molded Engine Cooling Fans

The use of glass reinforced nylon in fatigue inducing environments calls for a new method of stress analysis.

With an engine cooling fan, both mean and vibratory stresses need to be examined. Speed cycling can cause tensile fatigue, while vibration can cause flexural fatigue. Since tensile and flexural stresses exist in the fan simultaneously, a combined mode fatigue model is needed.

The proposed model is based on high cycle flexural and tensile fatigue strengths, and tensile strength. It relates measurable strain to stress using temperature dependent flexural and tensile moduli, and treats underhood temperature and desired product life as variables.