Experimental and numerical studies on filled-hole compression of FRP laminates considering different countersunk hole configurations

The present paper investigates the load-bearing properties of composite laminates featuring filled circularfrustum-shaped countersunk holes under compression loads. A sophisticated three-dimensional model based on the continuum damage mechanism (CDM) is employed in finite element analysis (FEA). This model integrates both the fiber-kinking and modified characteristic length sub-models and is implemented through a user subroutine. The FEA results exhibit a strong correlation with experimental findings, highlighting that delamination tends to occur before other failure modes such as fiber breakage and matrix cracking. Following validation, the FEM is utilized to explore the relationships between the bevel depths of countersunk holes and the strength of laminates. Regarding the effects of hole configurations, when the bevel depths are below 1.25 mm, composite laminates demonstrate a converging load-bearing capability with increasing bevel depth. However, for bevel depths ranging from 1.25 to 2.75 mm and exceeding 2.75 mm, the load-bearing capacities exhibit fluctuating decline and a monotonic decreasing trend, respectively, as the bevel depth increases. The developed model, coupled with the obtained results, can serve as a valuable tool for guiding the design and optimization of connection mechanisms in composite structures across various sectors, including constructions and buildings.