서강대학교

초록/요약

This research work aims at findings the fracture toughness of brittle materials by spherical indentation. Fracture toughness KIC is a very important material property for explaining the cracking behavior of a material. Spherical indentation can be used to measure the fracture toughness by characterizing the indentation damages such as ring and cone-cracks, and then relating the indention variables i.e (i) critical load, (ii) ring crack radius, (iii) cone-crack length and angle with fracture toughness. However, the spherical indentation technique needs a better understating of the complex stress distribution and cone-crack formation in the material beneath the indenter. Here, we use the extended finite element method (XFEM) to simulate spherical indentation cone-cracking in brittle materials. Compared with conventional FE techniques such as re-meshing or cohesive zone model, XFEM requires no re-meshing, no pre-existing cracks, nor a pre-defined crack path to allow the crack initiation and propagation. The crack path is determined by the evolution of the stress field in the damaged specimen. An axisymmetric XFE model with a rigid spherical indenter is used to simulate the cone-cracking in Abaqus / Standard. Convergence issues associated with XFEM are discussed for spherical indentation. We investigate the effects of material and contact properties (Young’s modulus, Poisson’s ratio, damage initiation stress, fracture energy, friction) on cone-crack formation. Spherical indentation tests are conducted on soda-lime glass specimens to confirm the cone-cracks observed in XFEM. Based on XFEM and experimental observations, a method to evaluate fracture toughness is presented by considering kinked-cone-crack, which forms in the material beneath the indenter. This research provides a database of saturated normalized energy release rate values, which is generated by using XFE analyses, to evaluate the brittle fracture toughness.