ENERGY-RELEASE RATES FOR THE ENF SPECIMEN USING A BEAM ON AN ELASTIC-FOUNDATION

A new modified beam theory analysis is presented for the ENF specimen, which is used to evaluate the mode II delamination fracture toughness of fiber reinforced composite materials. The analysis combines the solution of a beam on a generalized elastic foundation to incorporate the effect of crack tip deformation, and a Timoshenko Beam Theory solution of the ENF to incorporate transverse shear on the predicted energy release rates. A distinctive feature of this approach is that crack tip deformation and shear deformations are treated separately and explicitly in accounting for deviations from simple beam theory. Two unknown parameters are introduced, however, that must be determined by comparison with finite element solutions. The resulting solution nevertheless demonstrates considerable accuracy over a wide range of material properties (e.g., axial to shear modulus ratios) and crack lengths. In addition, the current analysis compares very favorably with other analyses of the ENF that incorporate the effect of crack tip deformations on the energy release rate.