An experimental dynamic analysis of Z-pinned unidirectional CFRP beams

The application of composites in mechanical components has been growing gradually over the years. In general, laminated composite material have excellent mechanical resistance to in-plane loads, however, for out-of-plane loads this resistance decreases considerably due the weakness of matrix, that is responsible to keep layers mechanically connected. This may lead the structure to present a high vulnerability to delamination between the layers. The delamination is a common problem in composite materials and frequently occurs due the appearance of interlaminar shear stresses or loads under impact spreading damage along the matrix area of composite. To increase the resistance to delamination in composite laminates, different techniques for inserting reinforcements through thickness are applied including stitching, z-anchoring, tufting and z-pinning. This work aims to evaluate the influence of z-pinning on the modal responses. The z-pinning process was made considering machined rectangular carbon fiber/epoxy z-pins with different dimensions at different insertion spacing densities on the structure. Both the insertion density and the dimensions of the pin were obtained by RSM analysis to evaluate the influence on the mechanical modal properties (natural frequency, loss factor and vibration amplitude) and to obtain an ideal value of insertion area density and pin width. Experimental results have shown that the pin has a statistically significant influence on modal responses, allowing a reduction of up to 110% in vibration levels.