The effect of temperature on fatigue crack growth in FM94 epoxy adhesive bonds investigated by means of energy dissipation

The effect of temperature on fatigue crack growth in epoxy adhesive bonds was investigated for a range of temperatures from −55 to 80 °C. The fatigue crack growth behaviour was characterised using both strain energy release rate (SERR) and by measurements of energy dissipation. It was found that for a given maximum SERR, or a given energy dissipation per cycle, crack growth rate was higher at higher temperatures. The resistance to crack growth (in terms of energy dissipation per unit crack growth) was linearly related to the maximum SERR, and this relationship was not affected by temperature. A number of tests did show anomalous behaviour, which could be linked to differences on the fracture surfaces. Previous work had found a power-law relationship between the amount of available energy and the applied cyclic work. This relationship was found to be insensitive to temperature changes in the range of 0 °C to 40 °C, but at −55 °C and −20 °C, as well as at 60 °C and 80 °C, the behaviour was affected by temperature. This could again be linked to differences on the fracture surfaces. It was concluded that temperature does not affect crack growth by directly affecting the failure mechanisms themselves, but rather by affecting which mechanisms are active