A thermographic and energy based approach to define high cycle fatigue strength of flax fiber reinforced thermoset composites

In order to explore the long-term reliability of flax fiber reinforced composites under fluctuating loads through high cycle fatigue strength (HCFS), fatigue tests were conducted on unidirectional flax fiber reinforced thermoset composites at different percentages load of ultimate tensile strength (UTS) with a loading frequency of 5 Hz. The change in temperature of the sample during cyclic loading was captured using an IR camera. Initially, the temperature increase was rapid, but after a certain period of time it stabilized. A Mathematical model was developed to predict the fatigue life from the data of stabilized temperature. Stabilized temperature and dissipated energy per cycle were compared with applied stress. Both of them exhibited a bilinear behavior and the intersection point of those two curves was used to determine HCFS. HCFS for unidirectional flax fiber reinforced composites was about 45% of UTS for a loading frequency of 5 Hz. Unlike fatigue life, stabilized temperature and dissipated energy-based models are convenient to define HCFS as they are timesaving and have little variation from sample to sample.