Using Spiral Notch Torsional Test to Investigate Fracture of Unidirectional Fiber Reinforced Composites

Wind turbine blades are essential to the harnessing of wind energy, which are subjected to a complex combination of bending and torsion during service. The mechanical performance of unidirectional fiber-reinforced composites under mixed mode I (bending) and III (torsion) is critical to the durability of wind turbine blades. In this work, Spiral Notch Torsion Test (SNTT) was used to probe the fracture of epoxies and fiber-reinforced composites used in wind turbine blades, including glass and carbon fiber-reinforced composites. Three types (A, B and C) of composite specimens with different fiber and notch orientations were tested using torsion tests. Finite element analyses were performed to probe the fracture resistance of different types of specimens. Results showed that type A and C specimens fractured into halves, whereas type B specimen remained connected with circular cracks propagated alternatively between fiber-matrix interface and resin matrices. The mathematical findings showed that fracture resistance was affected by the fiber and notch orientations.