Clustering effect on mechanical properties and failure mechanism of open hole high modulus carbon fiber reinforced composite laminates under compression

The clustering effect of open hole high modulus carbon fiber (M40J) reinforced composite laminates under compressive load is studied with digital image correction (DIC), acoustic emission (AE) and high-resolution digital camera. Three types of quasi-isotropic laminates [45 _m/0_m/−45 _m/90 _m]_ns (m × n = 4) with different clustering levels (m = 1, 2 and 4) are manufactured and tested to investigate their mechanical properties and failure mechanism. The experimental results indicate that as clustering levels increases, the open hole compressive strength gradually decreases accompanied by failure mode transferring from brittle fracture to delamination. Four types of sub-critical damages are found in the progressive failure process: splitting, delamination, layers buckling and layers compressive damage. The layers buckling and layers compressive damage can result in final failure of laminates yielding failure mode of delamination and brittle fracture, respectively. Besides, the effect of sub-critical damages and layer thickness on both mechanical properties and failure mode are discussed consequently obtaining the qualitative relationships between open hole compressive strength and material mechanical properties. The ratio of inter-fiber strength to layer longitudinal compressive strength is the crucial factor affecting the mechanical properties, and it should be controlled within the range where the push-in failure mode occurs for better properties.