13th International Conference on Fracture June 16–21, 2013, Beijing, China -1- Fracture toughness measurements on bovine enamel by indentation techniques J. Rodríguez1*, M.A. Garrido1, L. Ceballos2 1 Departamento de Tecnología Mecánica, Universidad Rey Juan Carlos, 28933 Madrid, Spain 2 Departamento de Estomatología, Universidad Rey Juan Carlos, 28933 Madrid, Spain * Corresponding author: jesus.rodriguez.perez@urjc.es Abstract. Many works have attempted to estimate the fracture toughness of enamel by indentation techniques. Most of these works have in common the use of equations whose success in determining the actual value of fracture toughness depends on the particular three-dimensional pattern of cracks. Although microscopic techniques are usually employed, only a superficial image of the cracks is provided, and no information about the propagation within the enamel is given. Therefore, there is some uncertainty about the applicability of this type of equations. More recently, an alternative methodology based on an energetic approach has been developed to estimate the fracture toughness by depth sensing indentation that is not so affected by the cracks pattern generated. In this work, the energetic approach to indentation fracture toughness of bovine enamel is presented and compared with those toughness values obtained using the most common expressions reported in the literature. The results showed that some modifications in the energetic methodology should be performed in order to apply it successfully. Keywords indentation fracture toughness, enamel 1. Introduction Enamel is the hardest and stiffest tissue of mammals. It forms the outer layer of the tooth and shows a characteristic hierarchical microstructure. At large scale, the enamel consists of rods encapsulated by thin protein rich sheaths that are arranged parallel in a direction perpendicular to the dentino-enamel junction (DEJ) from dentin to the outer enamel surface [1]. The enamel microstructure of all mammals appears to be very similar on a histochemical and anatomic basis [2]. Numerous methods have been employed to experimentally measure the fracture toughness (KC) of the enamel. The determination of KC by indentation technique is based on measuring the size of cracks induced in a material during indentation. Several expressions are available to determine KC by this technique, depending on the indenter geometry and crack morphology. One of the most widely used expressions for radial cracks is the relationship proposed by Lawn, Evans and Marshall [3]: 3 2 n C c P H E K k = (1)
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