Visualization of fractures in alumina ceramics by mechanoluminescence

The use of a mechanoluminescent (ML) paint enables a propagating crack and bridging stress distribution to be visualized. This technique was used to examine the mechanism of fracture in alumina ceramics. The mechanism appears to be inconsistent with currently accepted R-curve concepts. The magnitude and shape of the bridging stress distribution changes with the advancing crack. It continues to change as the applied load changes, even after the cessation of crack propagation. The measured R-curve increased dramatically up to 120 MPa(square root)m. ML technology provides not only a versatile tool for the study of fracture mechanism, but also has the potential for use in the low-cost safety diagnosis of structural components or the visualization of microelectromechanical systems operations.