Evaluation of the strain energy release rate for the fracture of titanium—porcelain interfacial bonding

An attempt has been made to measure the critical strain energy release rate or interfacial toughness between an oxide coating and metal layer in the present study. Twelve pure titanium cast plates veneered with transparent incisal porcelain were subjected to four-point bending after introducing a precrack through a controlled notch on the ceramic veneer. Cycles of loading and unloading at crosshead speed of 0.1 mm min−1 were repeated and extension of the crack along the interfacial oxide layer was observed through the transparent porcelain. Parallelled extension with the initial notch at each loading was observed and multiple loading was possible until the crack reached the inner loading points. Fracture resistance was calculated by dividing the energy value determined from a force-displacement curve by the corresponding fracture area. A theoretical calculation of the fracture resistance using a formula developed by Charalambides et al. (J. Appl. Mech., 1989, 56, 77–82) was also estimated. The result from the two methods agreed well (R2 = 0.75) but the theoretical calculation (16.06 ± 4.53 J m2) gave lower average value than the other value (18.29 ± 4.23 J m2), (p < 0.05). These preliminary results indicate that this novel technique is a suitable means for quantifying interfacial toughness of porcelain—metallic bonding.