Influences of complex loading and margin geometry: failure of curved brittle layer structures

Abstract

This study investigates the influences of off-axis loading and of margin geometry on "margins failure" observed in loaded curved bi-layer structures, away from the contact loading point. Specimens of hemispherical bi-layer model consist of glass shells with varying margins geometry, and filled with epoxy resin substrate are prepared. These specimens are loaded with compliant PTFE Teflon cylindrical indenters, with a modulus of several orders of magnitude lower than the indented materials. Load is applied normally; axisymmetric to the dome apex, and at 45 • from the axis of symmetry. In this fashion, the effect of offaxis loading and the influence of margin geometry on "margins failure" are studied. The onset of fracture is observed in situ using a video camera system. Finite element analysis is applied to determine basic stress distribution within the dome structures, and to confirm a shift in maximum tensile stress from the near-contact area to the dome sides with the use of more compliant indenters. Critical loads to initiate radial cracks and damage evolution are presented, and interpreted with the results of FEA.

Effect of different loading pistons on stress distribution of a CAD/CAM silica-based ceramic: CAD-FEA modeling and fatigue survival analysis

“…The last two decades have witnessed the development of new ceramics for dental reconstructions capable of embracing greater loads and surviving longer under masticatory function (Qasim, 2007;Oilo et al, 2014).…”

“…Currently, computer-aided design/computer-aided manufacturing (CAD/CAM) using ceramic block milling system allows for (Qasim, 2007;Lin et al, 2012) fabrication of prefabricated ceramic blocks with improved mechanical properties owing to the standard process of fabrication and thereby obtaining more homogeneous material (Aurélio et al, 2015;Figueiredo-Pina et al, 2016). In order to ensure favorable mechanical behavior and to estimate clinical performance, materials are initially evaluated under laboratory conditions (Kelly, 1999;Basso et al, 2016;Homai et al, 2016).…”

“…Laboratory tests used for ceramics generate stresses and modes of failures that differ from those observed clinically (Kelly et al, 2010) since the behavior of a ceramic material is very susceptible to the testing conditions (Yang et al, 2014), such as thickness and geometry of the specimen (Kelly, 1999;Oilo et al, 2014;Ramos et al, 2015;Basso et al, 2016), type of loading piston (Qasim, 2007), frequency of the load application (Borba et al, 2013), humidity (Kelly et al, 2010), and type of piston movement (Basso et al, 2016;Qasim et al, 2006).…”

“…The simulation of the opposing tooth or restoration acting forces upon ceramics could be simulated using pistons made of different materials that influences the maximum stress distributed throughout the specimen Qasim, 2007;Kelly et al, 2010). Traditionally, the piston is made of tungsten but in limited number of studies piston materials were changed to steel, epoxy resin, or wood (Qasim, 2007;Kelly et al, 2010. On the other hand, Finite Element Analysis (FEA) of low modulus piston materials loaded against ceramic substrates showed a tendency for higher fracture loads on feldspathic porcelain that was validated by a single-load to failure mechanical test (Weber et al, 2018). Therefore, more information is needed on the effect of poston materials and their possible effects of survival of ceramic materials.…”

Cracks Interaction due to Sequential Indentation in Curved Brittle Coating: Effect of Relative Orientation

“…It is confirmed that the radial cracks can initiate and propagate anywhere in the tensile region either from flaws in the material or from pre-existing cracks (defects) in the form of large flaws. The methodology used for specimen fabrication and testing by hard and soft indenters in the previous studies [5,6] is well suited and applied in this study, to ensure continuity in the procedures and for comparative reasons.…”