Amplitude-Dependent Internal Friction Study of Fatigue Deterioration in Carbon Fiber Reinforced Plastic Laminates

Abstract

The amplitude-dependent internal friction in carbon fiber reinforced plastic (CFRP) laminates subjected to fatigue cycling has been measured and analyzed to convert into the plastic strain of the order of 10-8 as a function of effective stress. The microplastic flow indeed occurs in the stress range three orders of magnitude lower than the failure stress, and the stress-strain curves tend to shift to a lower stress as the number of cycles increases, thus indicating a decrease in the CFRP strength. The microflow stress at the plastic strain of 1×10-8 keeps a constant value of about 0.4 MPa in the range less than 10 3 cycles but then decreases gradually, whereas the Young's modulus evaluated from the resonant frequency is almost constant up to 10 4 cycles where only transverse cracks are found. Thus we can successfully detect the onset of fatigue deterioration by means of the amplitude-dependent internal friction.