On internal cone cracks induced by conical indentation in brittle materials

On radial crack and half-penny crack induced by Vickers indentation

“…For RCs and HPCs, the polar coordinates are q and j, respectively-it is expected that along the circular crack front, the SIF is a function of q or j. For brittle materials upon indentation, elasticperfectly plastic model is often used to describe its constitutive property, which could effective describe the permanent penetration (Sun et al 1995;Care & Fischer-Cripps 1997;Chen et al 2004bChen et al , 2005Yan et al 2007b). Indeed, compression tests on many brittle ceramic-like materials show that these materials can be approximated by the ideal elastic perfectly-plastic behaviour (Francois et al 1988;Rabier & Demenet 2000;Gei et al 2004;Jiang et al 2006;Yao et al 2006).…”

“…Most brittle ceramics and glasses can be assumed isotropic and homogeneous and, in this paper, the material's Young's modulus is E and the yield stress is s y ; the plastic behaviour is characterized by the von Mises yield criterion and with the elastic-perfectly plastic behaviour. The Poisson ratio n, which is a minor factor during indentation cracking Yan et al 2007b), is set to be 0.2, a typical value for brittle materials. We do not consider residual stress in the specimen prior to indentation although that could affect the indentation behaviour Zhao et al 2006b).…”

“…The commonly used superposition technique (Anderson 1995;Chen et al 2005;Yan et al 2007b) is employed to determine the stress intensity of the system, which is suitable when the cracktip plasticity can be ignored (e.g. for brittle material).…”

“…and on the properties of the material. Among them, the lateral and cone cracks have been studied using both experimental and theoretical approaches (Lawn & Evans 1977;Chen et al 2005;Yan et al 2007b). Various forms of cone cracks were observed in brittle materials when an axisymmetric indenter was used.…”

“…Lawn and co-workers have investigated cone cracks developed from the free surface in spherical indentation (Lawn & Fuller 1975;Lawn 1993Lawn , 1998, and the inner cone cracks developed in brittle solids submerged in water (Chai & Lawn 2005). Cone cracks induced by conical indentation were studied in Yan et al (2007b). The elastic recovery during unloading leads to stress redistribution, which is responsible for lateral cracking (Marshall et al 1982;Chen et al 2005).…”