Boundary element analysis of orthotropic delamination specimens with interface cracks

Abstract

The boundary element method (BEM) with special crack-tip elements is used to obtain the stress intensity factors, K 1 and K 2, and the strain energy release rates of interface cracks in bilayer double cantilever beam (DCB) and end-loaded-split (ELS) specimens. The material system considered is one in which an orthotropic, transversely isotropic layer is bonded to another layer of equal thickness and made of the same material, but the latter being in the plane of transverse isotropy. The effects of the mechanical properties of the orthotropic material are characterized by the parameters, η 1 and η 2, which correspond to the purely imaginary roots of the characteristic equation for the material. Calibration results showing the variations of the normalized strain energy release rates with the geometry of the specimens are presented for a range of values of these material parameters. They show the same qualitative trends as for a completely homogeneous beam specimen. To provide a complete characterization of the near-tip fields of the interface crack, the phase angle ψ = tan −1 ( K 2/ K 1), which denotes the degree of the mode mixity there, is also obtained for each case. The results show that ψ generally attains a constant value when the ratio of the crack length to the layer thickness reaches a value of less than eight.