Micro/macro damage evaluation of flat braided composites with a circular hole

Abstract

In this study, attention is paid to braided fabrics as the form of reinforcing fiber in composite materials and the influence of a circular hole on the mechanical properties of a flat braided composite is investigated. Two types of specimens are prepared; a flat braided bar with a braided hole in which the fiber bundle is continuous around the hole, and one with a machined hole. The effects of a circular hole on fracture behavior in the braided flat bar is examined by static tensile and fatigue testing. Moreover, specimens with a pin inserted at the circular hole are also examined under static tensile loading. In order to evaluate damage, macro and micro damage observations are carried out. From the results of static tensile and fatigue testing, the flat bar with a braided hole had higher performance than the flat braided bar with the machined hole. Furthermore, difference of damage propagation and dominant factor of fracture in the two types of flat braided composites with a circular hole was confirmed by macro and micro observation. Damage at the composite with a hole by machining work depends on the interface between fiber bundles and was confirmed to concentrate around a hole. Beside, damage at the composite with a hole by application of braiding technique depends on continuously oriented fiber in the longitudinal direction. Consequently, it is considered that a performance of the reinforcing fiber properly works in the case that reinforcement configuration is braided fabric.