On mode I/II interlaminar fracture toughness of double-sided-loop 2D woven laminated composites

Two-dimensional (2D) plain fabric is prone to delamination when subjected to bending, shear, impact loads. To enhance the interlayer properties of 2D plain fabrics, standing up loops is added. In this paper, specimens of the double-sided-loop 2D woven laminated composites (DWLC) and general 2D woven laminated composites (GWLC) are made for double cantilever beam (DCB) tests and end-notch flexure (ENF) tests to study their toughening mechanism. Test results show that the values of model I and mode II interlaminar fracture toughness are increased by 870% and 250% for the DWLC compared with the GWLC. Based on the three-linear cohesive zone model (CZM), finite element (FE) models of composite laminates specimens of DCB and ENF considering the phenomenon of interlaminar bridging are established, and numerical results are in good agreement with the experimental data, that verifies the accuracy of the FE models. Using the verified FE models, model I and mode II fracture properties of the DWLC specimens of DCB and ENF with different initial crack lengths are investigated, and the results show that the stress is redistributed and the load gradually decreases as the length of the prefabricated cracks increases. The obtained fracture toughness of the DWLC provides a reference for the toughening methods and the engineering applications of DWLC.