Crack Growth Study of Fibre Metal Laminates Using Thermoelastic Stress Analysis

The behaviour of crack growth in fibre metal laminates (FML) was investigated using Thermoelastic Stress Analysis (TSA). Fatigue tests were performed on Single Edge Notch Tension (SENT) specimens and thermoelastic data recorded. A Newton–Raphson iteration combined with a least-squares approach was used to fit equations describing the stress field around the fatigue crack tip to the thermoelastic data. The stress intensity factor range was thus determined at intervals of fatigue crack growth. By correlating the experimental results with a phenomenological crack growth prediction model, it was shown that our thermoelastic methodology which had been used previously for crack studies in monolithic metal specimens is capable of determining accurately fracture parameters in hybrid materials. The thermoelastic technique also allows identification of the crack tip in the metal layer, thus fatigue crack growth rate was determined easily. The experimental results agreed with the general trend reported elsewhere, of decreasing crack growth rate in FMLs. Delamination between the metal and fibre layers in the crack wake was investigated by comparing thermoelastic data with ultrasound measurements. It was found that the out-of-phase thermoelastic signal gave an accurate representation of the delamination in the crack wake. TSA, therefore, shows great potential for several aspects of fracture study in FMLs.