Fatigue Damage Evaluation of Epoxy Resin by Infrared Measurement

Resin materials are susceptible to degradation due to external factors such as heat, water, and ultraviolet (UV) radiation, depending on their usage environment. These degradations significantly affect the fatigue strength of the materials. To rapidly and quantitatively evaluate the decrease in fatigue strength caused by environmental degradation, this study proposes an evaluation method of fatigue damage by infrared measurement.
In previous studies, Shiozawa, et al. have proposed an estimation method of the fatigue limit by measuring heat generation caused by plastic deformation using infrared thermography and analyzing changes in heat generation. In the case of metallic materials, it has been clarified that the second harmonic component included in actual temperature variations corresponds to heat generation due to fatigue damage. However, it remains unclear whether resin materials exhibit the same heat generation mechanism as metallic materials.
Therefore, this study aims to propose an infrared measurement to evaluate the impact of UV-induced degradation on the fatigue strength of epoxy resin. By extracting the second harmonic component from actual temperature variations, similar to the approach used for metallic materials, we investigated whether evaluation of fatigue damage is feasible for epoxy resin itself and for UV-induced degradation.
The second harmonic component of the epoxy resin exhibited a trend similar to the change in dissipated energy observed in metallic materials. Furthermore, this component was presumed to reflect degradation due to UV exposure and the resulting changes in fatigue strength. In UV-degraded materials, a decrease in the estimated fatigue limit was observed, suggesting that the decrease in fatigue limit can be captured using the second harmonic component.