On the determination of crack tip opening angle, CTOA, using light microscopy and δ5 measurement technique

The crack tip opening angle (CTOA) of growing cracks in 3 mm thick Al5083 sheet material was determined using two different experimental techniques such as optical measurements via light microscopy and δ5 clip gauge technique. It was found that both methods provide similar CTOA-data but their practicability and accuracy are different. CTOA-data obtained from optical measurements exhibited large scatter. Moreover, optical CTOA determination requires extensive practical knowledge and its application is costly. In case of using the δ5 clip gauge technique, it was found that the slope of the experimentally determined δ5 R-curve is reflecting CTOA. Compared to optical measurements, the technique provides CTOA-data with less scatter. In addition, the δ5 technique has the advantage of a straightforward application to all kinds of thin wall structures and specimens.