Experimental investigations into damage mechanism in the low-velocity impact and tension-after-impact testing of z-pin reinforced curved CFRP composite

This paper studies the influence of z-pins on the impact resistance and residual tensile properties of composite large curvature components through low velocity impact and tension-after-impact tests to explore the damage mechanism. Unpinned and z-pinned specimens with different diameters (0.3 and 0.5 mm) and spacing (3, 4, and 5 mm) were impacted at energies of 28 J and 14 J + 14 J and were stretched until failure. The theoretical models were used to predict impact dent depth and tensile strength, and the effectiveness of z-pins and damage patterns were characterized by force-time/displacement curves and through visual observation. The agreement between the experiments and predictions can thus validate the presented approach. Through the low-velocity impact test, it is found that z-pins with higher density and smaller diameter make the impact dent shallower and the surface damage less, thus showing better performance. Later, the impacted specimens mainly show delamination, explosion, breakage, and splitting after tension. During the first stage of the force-displacement curves, since z-pins mitigate the delamination, tensile strength shows a 29.58%-59.17% increase while in the third stage, a decrease of 3.95%-15.12% occurs due to initial damage caused by z-pins. Highlights center dot Different impact energies are implemented on large curved CFRP laminates of z-pins with different diameters and spacing to explore the damage mechanism.center dot Low-velocity impact and tension-after-impact (TAI) tests are used to simulate the centrifugal force of the blade subjected to impact and rotation after impact.center dot Z-pinned group with a small diameter and high density causes less damage and tensile strength in the first stage increases while decreasing in the third stage compared with the unpinned group.