Stress-wave induced fracture of unidirectional composites: an experimental study using digital image correlation method

Abstract

Fracture behavior of unidirectional graphite/epoxy composite materials is investigated. Single-edge notched coupons are studied under geometrically symmetric impact loading. The notch orientation parallel to or at an angle relative to the fiber orientation is considered to produce mode-I as well as mixed-mode fracture. Stress-wave induced crack initiation and rapid crack growth events are studied using the digital correlation technique and high-speed photography. Surface deformations histories in the crack-tip vicinity are obtained by analyzing speckle image recordings. Measured deformation fields are used to extract mixedmode fracture parameters and examine the effect of fiber orientation on crack initiation and growth behaviors. The maximum crack speed observed is the highest for mode-I dominant conditions and decreases with increasing fiber orientation angle. With increasing fiber orientation angle, crack takes longer to attain the maximum speed upon initiation. The crack initiation toughness values decrease with increasing degree-of-anisotropy.