Mode II Interlaminar Fracture of the Center Notch Flexural Specimen under Impact Loading

Abstract

The Mode II interlaminar fracture of unidirectional graphite/epoxy (AS4/2220-3) and graphite/polyetheretherketone (APC-2) composite laminates subjected to impact loading is investigated using the Center Notch Flexural (CNF) test specimen. Experimentally, instrumented impact testing of the CNF specimen enables the impact force history and the absorbed energy during delamination propagation to be estimated. Scanning electron microscopic examination is conducted to assess the influence of impact loading on fracture morphology in the crack initiation and propagation regions of the frac ture surface. Data reduction for evaluating the Mode II interlaminar initiation toughness is based upon beam theory that includes kinetic energy effects and dynamic finite element analysis of the specimen in conjunction with virtual crack closure techniques. The initia tion toughness under impact loading was approximately 20 and 28% lower than the static values for AS4/2220-3 and APC-2, respectively. Data reduction for evaluating the Mode II interlaminar propagation toughness is based upon the area method and a 24 and 44% reduction in fracture toughness is measured for the AS4/2220-3 and APC-2 composite materials, respectively.