Bonding force determination at AFB~? interfaces of single crystal sapphire composites

摘要

We report on the bond strength at the interfaces of Adhesive-Free-Bonded (AFB~?) single crystal sapphire composite bars as deduced from the fracture toughness. Fracture toughness (K_(IC)) characterizes the resistance of a bulk brittle material to fractural failure caused by unstable crack propagation. Correlation between the well-defined initial flaw size and the apparent failure strength gives the fracture toughness that is a function of the average bond strength at the fractured interfaces. To ensure that the fracture interface coincides with the AFB~? interface, we make a pre-notch at the AFB~? interface to be the initial surface flaw using a 532 nm wavelength marking laser. The measured failure strength yields the fracture toughness of the AFB~? composites. We have found in this study that the average fracture toughness of AFB composite samples is 2.51 MPa~*√m and that of non-composite control samples is 2.39 MPa~*√m. The correlating fracture energy is 13.1 J/m~2 and 11.9 J/m~2, respectively. The apparently greater fracture toughness of composite samples compared to that of non-composite samples conforms with the hypothesis that attributes the origin of the bonding forces at the AFB interfaces to the Lodon-Van der Waals interaction between two solid bodies.