Determining specimen thickness limit in fracture toughness tests applied to dental ceramics and metal alloy interfaces

The aims of the current study are to present computational simulations based on the finite element method in order to determine the lowest viable thickness of materials used to make ceramic samples based on the interface of groups of materials (Ni-Cr/ceramics, alumina/ceramics), and samples made of each of these materials, alone; as well as to report the effect of variation in the stress intensity factor of these interfaces (beta). Test conditions were simulated in Abaqus CAE software and mesh features focused the crack tip. Fracture toughness analysis was carried out by simulating the three-point bending test (SEVNB specimen of the Fracture Mechanic standards). Based on the present results, the lowest material thickness necessary to meet the stress intensity requirement at the crack tip was 8 mm of each material, under symmetry condition, for sandwich composition. Such a thickness included fracture process zone (FPZ) size and plastic zone (PZ). Sandwich thickness was enough to maintain the test conditions established for the standards. Samples produced in the present study met the requirements of the fracture toughness test, based on the ASTM E-399 standard -specimens with the lowest possible sandwich thickness were obtained and they met the stress intensity requirements of the crack tip. This finding pointed towards a sample based on using a reduced amount of test materials -such as those used for dental restoration. The lowest material thickness in the sandwich was 8 mm, for all groups of materials, under symmetry conditions. This thickness includes fracture process zone size and plastic zone size. The herein proposed sandwich thickness was enough to maintain the test conditions established by fracture mechanic standards.