Experimental assessment of Fully-Uncoupled Multi-Directional specimens for mode I delamination tests

This paper proposes an experimental study whose goal is to validate the concept of Fully-Uncoupled Multi-Directional (FUMD) specimens for delamination tests. In order to reduce the likelihood of delamination jump, a glass/epoxy UD-fabric composite was used to fabricate double cantilever beam specimens. Mode I tests were performed with standard UD specimens and with FUMD specimens having the following delamination interfaces: 0 °//0 °, 0°// 15°, 0 °//30 °, 0 °//45 ° and −45 °//45 °. Delamination fronts after the tests were observed by means of ultrasonic C-scans. By comparison with the UD specimens, it is shown that FUMD sequences are able to promote a fairly symmetric and flat delamination front. Analysis of the rotations of such specimens during the test confirms that they do exhibit an uncoupled mechanical behaviour. Critical energy release rate is found to be dependent on interface plies mismatch angle, but not on global stiffness of the specimens.