Fracture analysis and geometrical parameter optimization of bolted composite joints

Composite materials are commonly used in structures that demand a high level of mechanical performance. Due to high strength and safety requirements, these applications require joining composites either to composites or to metals. Composite joints create highly localized stress concentration around the joints that cause failure in the substrates. The fracture toughness is the critical aspect that influence on the failure of the substrates. In this work, fracture toughness is determined for a center crack developed on the surface of the substrate of the composite joints. In FEM analysis, Stress intensity factor (K) and J integral are used to find out the fracture toughness value. The influence of various parameters such as fiber orientation angle, crack length, applied load and bolt hole diameter on fracture toughness is determined with the use of LEFM in finite element analysis. Stress intensity factor and J integral are validated with the theoretical data available. Geometrical parameters which affect fracture toughness are optimized by using Taguchi analysis and design of experiments. The result shows that the crack length is the most significant parameter which affects the fracture toughness substantially. Elasto plastic region (dog bone shape) near the crack tip is also analyzed in this work.