Investigation of laminate debonding in horizontal axis water turbine composite blades

Carbon fiber reinforced polymer (CFRP) composites are becoming popular due to their superior strength to weight ratio and stiffness properties. This study highlights the interlaminar debonding growth, which is considered one of the most frequent problems with composite materials. A three-blade horizontal axis water turbine (HAWT) was manufactured using IM7/Cycom5320-1 carbon/epoxy prepreg. During the process of manufacturing, a specific number of Teflon sheets were placed between the composite layers in two locations to create a separation between the layers and to investigate the delamination growth. Three different laminate stacking sequences were selected to be tested: [0°]₄, [0°/90°]_S, and [45°/−45°]_S. The composite blades were placed in a water tunnel and run for 3 million revolutions. A thermography analysis was carried out to evaluate the propagation and growth of the delamination. A one-way fluid–structure interaction (FSI) model was created and implemented to obtain the stress values along the blade. The results showed the influence of the composite lay-up orientation on the growth of the delamination. The unidirectional blades ([0°]₄) showed the lowest amount of propagation, while the cross-ply ([0°/90°]_S) showed the most delamination growth. The bottom location (near the root) showed the maximum delamination. Both sides of the blades showed significant delamination growth. However, the back side showed more interlaminar debonding growth than the front side. After three million revolutions, the percentage of debonding growth for the bottom/back side of the blades was 6.58%, 36.25%, and 27.63% for [0°]₄, [0°/90°]_S, and [45°/−45°]_S, respectively.