Analysis of Composite End Notch Flexure Specimen using13; Various Plate Theories

Abstract: Mathematical formulation for the stress analysis of symmetric multidirectional end notch flexure (ENF) specimen, using classical plate theory, first,second, 13; and third-order shear deformation plate theories under generalized plane stress and cylindrical bending conditions, is developed to determine the mode II interlaminar fracture toughness of symmetric 13; multidirectional composites. In the present formulation,13; appropriate matching conditions are applied at the crack tip and these matching conditions at the crack tip are derived by enforcing the displacement continuity at the13; crack tip in conjunction with the variational equation. Compliance approach is used to calculate strain energy release rate (SERR). Generalized plane stress model 13; and cylindrical bending model are applicable and close 13; to each other for unidirectional and cross-ply composite 13; ENF specimens. For multidirectional ENF specimens, the13; appropriate compliance/SERR values, obtained from the combination of compliance/SERR values of generalized 13; plane stress and cylindrical bending models,appear to be 13; reasonable and encouraging. For unidirectional and cross-ply composite ENF specimens, classical and first order 13; plate theories give similar SERR under generalized plane 13; stress and cylindrical bending conditions where as for multidirectional ENF specimen they give similar SERR 13; only under generalized plane stress condition. In general, 13; second and third order plate models of ENF specimen are found to be good for unidirectional, cross-ply composite 13; ENF specimens and reasonably good for multidirectional composite ENF specimens in determining the interlaminar 13; fracture toughness (or SERR) and interlaminar shear 13; stress distribution ahead of the crack tip