Elastic Compliance of the Compact Tension Specimen Comprising Two Linear-Elastic Materials Bonded with a Thin Layer

Although the compact-tension C(T) specimen is widely used in conventional fracture mechanics testing, its application to the fracture behavior of layered structures, in the assessment of the toughness and fatigue crack growth behavior of bimaterial interfaces, for example, has been limited due to problems in identifying the crack length. Accordingly, to provide a basis for crack-length monitoring in the sandwich C(T) specimen, comprising two materials bonded with a thin layer under linear-elastic conditions, the linear-elastic compliance based on back-face strain, crack-opening displacement and load-line displacement has been determined for a wide range of substrate/layer material combinations using finite-element analyses. Calculations for sandwich systems, with elastic moduli ratios varying from 0.2 to 5 and with joining layer thicknesses between 0.4 and 2% of the specimen width, show that for crack sizes between 0.25 to 0.75 of the specimen width, the compliance is significantly different from that of the bulk substrates, except when the layer is very thin and the modulus ratio approaches unity. It is concluded that crack-opening displacements are preferable for the monitoring and detection of interfacial and near-interfacial cracks in this specimen geometry, as the compliance based on these displacements is the least sensitive to errors from either measurement site or crack location.