Selective laser illumination method for enhanced damage monitoring of micro cracking and delamination in GFRP laminates

Transmitted light photography, microscopy and transmitted light scanning are well-established methods of optical damage characterization in glass fiber-reinforced composites. Subsequent damage evaluation such as determination of crack density and delaminated areas can either be done by hand or by means of image analysis software. Digital image analysis, however, is rather sensitive to damage illumination and contrast. Results tend to be inaccurate when damage states are complex, showing overlapping cracks and delamination. Therefore, a new laser-based illumination method capable of separately illuminating transverse cracks and interfacial delamination is presented. An exemplary [90/0]s cross-ply laminate tested in the very high cycle fatigue range was evaluated using transmitted light photography as well as the new method.