X-ray tomographic microscopy investigation of the ductile rupture of an aluminum foil bonded between sapphire blocks

Ultrahigh vacuum diffusion bonding has been used to make model specimens in the Al/sapphire system. The geometry of a thin, ductile foil sandwiched between strong, elastic ceramic blocks is identical to that modeled by several investigators. The micromechanics of failure for this system were observed by XTM. The primary findings are that (i) damage ahead of the notch initiates by interface debonding at a location coinciding with maxima in triaxiality and tensile traction at the interface, (ii) debonding occurs at the most early stages in the observation of plasticity, (iii) the debond expands for a limited distance, likely arresting due to crack tip blunting, (iv) this lenticular debond then becomes spherical with further strain and (v) intergrowth of the spherical voids leads to the typical ductile rupture fracture surfaces observed in this system. Future efforts to model this effect will need to include the debonds at the interface which alter the state of stress.