On the Analysis and Design of the End Notched Flexure (ENF) Specimen for Mode II Testing

Abstract

The end notched flexure (ENF) specimen is examined as a candidate for measuring interlaminar fracture toughness in skew symmetric loading. A simple design study for sizing the ENF specimen to minimize geometric nonlinear response and to avoid nonlinear material behavior or flexural failure is presented. Results indicate that inter laminar shear effects may be significant for tough resin systems requiring large thickness-to-length geometries. The influences of interlaminar shear deformation and fric tion between the crack surfaces on the strain energy release rate are examined.

A phantom node formulation with mixed mode cohesive law for splitting in laminates

“…With beam theory and the assumption that the fracture energy is constant, the force and displacement during crack propagation for each value of crack length a can be obtained. We have used relations concatenated by Reeder and Crews (1990) composed from the work of Kanninen (1973); Whitney et al (1982) and Carlsson et al (1986). The theoretical solutions to the pure mode cases of the DCB and ENF tests will be presented first, followed by the theoretical solution for the MMB tests.…”

“…63, the force corresponding with a certain fracture energy G c = G I and crack length a is computed. Subsequently, the corresponding displacement u e is computed with: For the ENF test, the following relations, including shear deformation (Carlsson et al 1986), are used…”

On the calculation of energy release rates for cracked laminates with residual stresses

“…This contact raises the concern that frictional effects may influence the results. 8 When the beams are heterogeneous and there are residual stresses, most experimental conditions will still have contact, but the contact will only be at the loading point (see Fig. 3).…”

Study of Asymmetric Glass Reinforced Plastic Beams in Off-Axis Four-Point Bending

“…Since there is a need for reliable data, a testing procedure for determining interlaminar shear properties has already been developed [6]. The interlaminar fracture toughness in end notched flexure specimens [7] and the interlaminar shear fracture of interleaved graphite/epoxy composites [8] have been examined. The fracture of sandwich beams in three point bending has also been considered [9,10].…”