ELASTIC COMPLIANCE OF THE COMPACT TENSION SPECIMEN COMPRISING 2 LINEAR-ELASTIC MATERIALS BONDED WITH A THIN-LAYER

Although the compact-tension C(T) specimen is widely used in conventio nal fracture mechanics testing, its application to the fracture behavi or of layered structures, in the assessment of the toughness and fatig ue crack growth behavior of bimaterial interfaces, for example, has be en limited due to problems in identifying the crack length. Accordingl y, to provide a basis for crack-length monitoring in the sandwich C(T) specimen, comprising two materials bonded with a thin layer under lin ear-elastic conditions, the linear-elastic compliance based on back-fa ce strain, crack-opening displacement and load-line displacement has b een determined for a wide range of substrate/layer material combinatio ns using finite-element analyses. Calculations for sandwich systems, w ith 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 c rack sizes between 0.25 to 0.75 of the specimen width, the compliance is significantly different from that of the bulk substrates, except wh en the layer is very thin and the modulus ratio approaches unity. It i s concluded that crack-opening displacements are preferable for the mo nitoring and detection of interfacial and near-interfacial cracks in t his specimen geometry, as the compliance based on these displacements is the least sensitive to errors from either measurement site or crack location.