Stress Analysis of Bonded-interface Technique on Subsurface Damage Observations of Brittle Porcelains

摘要

In the subsurface damage observations on the wear behavior of brittle dental porcelains, it still remains unsolved that how to distinguish the cracks that develops accidentally during the preparing sample process from those actually produced in the tests. In the sliding friction tests, the bonded-interface technique (BIT) was successfully used for subsurface damage evaluations. The profile of wear scar was easily observed on the cemented section of the blocks without inducing any cracks. The stresses on the surface and internal of dental porcelains were calculated with the contact element method (CEM) by ABAQUS software. The model of rectangular dental porcelain and Si_3N_4 ball were developed based on sliding friction tests. The Si_3N_4 ball modeled in this study was of the diameter of 4mm and 12 mm. The size of Vita VMK 95 porcelain blocks was 5 mm wide, 2 mm thick and 15 mm long. The glue layer thickness values are 10 μm, 20 μm and 30 μm. The loading of the Si_3N_4 ball was modeled as a constant distributed vertical load applied across the bonding line of the porcelain. Stresses and displacements of all nodes of the model, especially at the bonding interface, were analyzed and compared. The results of the study indicated that stress values correlated strongly to the applied loads. Stress distribution was symmetric about the bonded-interface plane. The maximum occurred in surface layer and the minimum on the bottom line in the porcelain blocks. Along the interface, stresses decreased with the distance from the surface of porcelain. On the other hand, high stresses focus on the surface part and go sharply down in the internal region along the depth direction. Among the parameters of sliding test on the stresses, the load effect is prominent. The BIT model experiences a different, non-axisymmetric stress field than that of real work-piece. So the BIT should not be considered as a reliable source of quantitative analysis but as a qualitative method for observing the form of the damage modes with more visible information than the conventional tools.