Piezospectroscopic measurement of the stress field around an indentation crack tip in ruby using SEM cathodoluminescence

Piezospectroscopy using stress-sensitive lines in the cathodoluminescence (CL) spectrum generated in response to excitation by the electron beam of an SEM has recently been shown to be a promising technique for submicron resolution stress measurements in alumina and other ceramics. This paper develops and applies the technique by mapping the wavelength shifts of the R1 CL line around the tip of an indentation crack in a ruby single crystal. Accounting for crystallographic anisotropy, the shifts observed were quantitatively consistent with the classical crack tip stress field for all polar angles ahead of the crack tip and indicated a crack tip stress intensity factor of 1.0 MPa m1/2. This is significantly lower than the fracture toughness of the crack plane (4.5 MPa m1/2), and indicates the post-indentation development of lateral cracks and slow crack growth. The spatial resolution of the stress measurements was measured as 550 nm and the effects of specimen heating by the electron beam were shown to be negligible.