Enhancing the fracture toughness of laminated composites through loop warp yarns

The delamination tendency is a key factor affecting the practical use of laminated composites. How to improve the interlaminar strength and interlaminar fracture toughness of laminated composite is a focus of research on composite materials. A three-dimensional (3D) weaving technique is employed to weave loop warp yarns (loops) with 3D fiber bundles instead of warp yarns on the basis of plain fabrics. The contribution of loops to the interlayer performance is revealed by double cantilever beam (DCB) tests, end-notch flexure (ENF) tests, flexural tests, and double notch shear (DNS) tests. Test results show that the mode I and mode II interlaminar fracture toughness values of the single-sided-loop two-dimensional (2D) woven laminated composite (SWLC) are 77% and 58.2% higher than the interlaminar fracture toughness values of the general 2D woven laminated composite (GWLC). As companied with the ones of GWLC, flexural strength and modulus of SWLC increase by 73% and 69.1%, and the interlaminar shear strength of SWLC increases by 45.7%. The loop yarns act as a link between the interlaminar matrix and the reinforcing fiber fabric and thus improve the poor interlaminar performance of GWLC. The reported information may provide a reference for the application of the SWLC in practice.