Deformation mechanisms of 3D LTL woven preforms in hemisphere forming tests

Abstract

Three dimensional layer-to-layer interlock (3D LTL) woven composites have better integrity and higher inter-layer performance than 2D composites for the existence of binder yarns which connect the neighboring weft layers. The deformation mechanisms of 3D LTL preforms are complicated in the forming process due to their large thickness. In particular, when the forming geometry is double curved, deformation of the preform is composed of several meso-scale deformation modes, including the compression, in-plane and inter-layer shear of the unit cell structures. This paper investigates the hemisphere forming of 3D LTL preforms. Effect of structural parameters on the forming process is analyzed. The results indicate that the reaction load, macro-scale deformation and microstructure variations of 3D LTL preform in forming process are closely related to the weaving structure of the yarns. This study would provide valuable information for the formability analysis of 3D LTL preforms and design of complex-shaped composite parts.