Fatigue crack growth analysis in composite bonded joints by back face distributed strain sensing and comparison with X-ray microtomography

Fatigue crack growth in composite, single lap bonded joints is analysed by back face distributed strain sensing, using optical backscatter reflectometry. Crack growth is inferred from the back-face strain profile measured with high spatial resolution along optical fibres bonded on the joints. The indications about the position of the crack front are compared with micro computed tomography scans conducted on specimens at suitable interruptions of the fatigue tests. By the proposed technique, crack initiation can be clearly detected, and measurements of crack growth are in good agreement with observations, with decreasing error with increasing crack length.