Experimental studies of embroidery for the local reinforcement of composites structures: 1. Stress concentrations

Abstract

Embroidery techniques were investigated for the manufacture and modification of engineered preforms. Flat 0° fabric specimens were produced by Cornely embroidery and their tensile properties compared to commercial fabric alternatives. Similarly, the effects of through-thickness stitching via Barudan embroidery were assessed for both 0° and quasi-isotropic laminates. Specimens containing a central cut-out were tested by using a variety of in-plane and through thickness fibre architectures to study ways of suppressing damage in the vicinity of stress concentrations. The elastic properties and the accumulation of damage were monitored by measurements of the instantaneous stiffness and the results were compared with conventional, fabric specimens. Cornely embroidery was shown to produce in-plane properties comparable with commercial fabrics. For the hole-in-a plate specimens no significant improvements in performance were achieved for unidirectional laminates but through-thickness stitching effectively doubled the load at which the onset of damage occurred in the quasi-isotropic specimens.