Abstract
The decohesion of coatings, thin films, or layers used to protect or strengthen technological and structural components causes the loss of their functions. In this paper, analytical, computational, and semi-analytical 2D solutions are derived for the energy release rate and mode-mixity phase angle of an edge-delamination crack between a thin layer and an infinitely deep substrate. The thin layer is subjected to general edge loading: axial and shear forces and bending moment. The solutions are presented in terms of elementary crack tip loads and apply to a wide range of material combinations, with a large mismatch of the elastic constants (isotropic materials with Dundurs’ parameters − 1 ≤ α ≤ 1 and − 0.4 ≤ β ≤ 0.4 ). Results show that for stiff layers over soft substrates ( α → 1 ), the effects of material compressibility are weak, and the assumption of substrate incompressibility is accurate; for other combinations, including soft layers over stiff substrates ( α → − 1 ), the effects may be relevant and problem specific. The solutions are applicable to edge- and buckling-delamination of thin layers bonded to thick substrates, to mixed-mode fracture characterization test methods, and as benchmark cases.
Highlights
The decohesion of thin layers from thicker substrates is a well-known failure mechanism which may occur at very different scales in structural and technological components due to various loading conditions, and is controlled by the interfacial fracture toughness, a material property which depends on the relative magnitude of shear and normal tractions on the interface [1,2,3,4]
The finite element model, Appendix B, and the Crack Surface Displacement Extrapolation (CSDE) technique implemented in ANSYS are first applied to define the energy release rate, stress intensity factors, and mode mixity angles associated with the elementary loads in Figure 1b for a bi-material interface with Dundurs’ parameter β = 0
The absolute error between the finite element based CSDE results and the analytical results is always below 0.04◦ on the phase angle, and below 0.001 on the dimensionless stress intensity factors for −0.8 ≤ α ≤ 0.8; errors are slightly larger for −0.99 ≤ α ≤ −0.9 and 0.9 ≤ α ≤ 0.99, but always below 0.2◦ and 0.01
Summary
The decohesion of thin layers from thicker substrates is a well-known failure mechanism which may occur at very different scales in structural and technological components due to various loading conditions, and is controlled by the interfacial fracture toughness, a material property which depends on the relative magnitude of shear and normal tractions on the interface [1,2,3,4]. Delamination (or debonding) of the face sheets from the core is one of the dominant failure mechanisms of thick sandwich structures used in naval, aeronautical, automotive, and wind energy applications, and can be due to direct loadings, stress waves, or internal pressure cycles [4,5,6,7,8]. In these systems, the face sheets are typically laminate composite materials, and the core is made up of cellular foams, honeycomb or balsa; exemplary applications are naval bulkheads and deck panels, primary aerostructures, e.g., wing leading edges and rudders, and wind turbine blades. The cracking of thin films used in electronic packages or of metal alloy coatings on elastomers, used in soft electronics, is often driven
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