Papers by Author: Jeffery Loughran

Abstract: Natural human tooth consists of multiple layered quasi-brittle biomaterials, which make dental restorations experience a complex stress state under masticatory contact loading. As such, many restorations are prone to failure and a constant effort is made to improve the mechanical characteristics of the restorative materials. Clinical observations have shown that improved strengths and fracture toughness in ceramic materials do not necessarily lead to an anticipated higher functional longevity of the restoration. While substantial experimental investigations have been carried out to identify the contact induced fracture in such multi-layer material systems, numerical modelling of this event was largely unexplored. This paper presents a new numerical method to account for micro-damage driven fracture in various multi-layered biomaterial structures. In this study, a Rankine constitutive model is adopted and the crack initiation and propagation are automatically implemented in an explicit finite element (FE) framework. The effects of indenter radius, surface curvature and thickness of layered biomaterials on the cracking patterns are investigated. The results show good agreement with the experimental studies in literature.

Abstract: Wear is often of definite influence in the service life of mechanical components and has been recognised as one of the major causes of failure in engineering practice. It is noted that although extensive attention has been paid to phenomenological studies like surface morphology analysis for wear assessment, the physical mechanism of wear particle formation remains unclear. This paper proposes a micro damage and fracture model to simulate the process of wear particle generation. An explicit finite element (FE) formulation is employed to capture the nonlinearities involved. Unlike existing FE analysis (FEA), any initial sub-fractures underlying the wear surface are no longer required. Crack initiation and propagation as well as the corresponding mesh updating are implemented in an automatic fashion associated with the explicit FE framework. The results presented are in good agreement with experimental observation and the reports in existing literature.

Abstract: Ceramics have rapidly emerged as one of the major dental biomaterials in prosthodontics due to exceptional aesthetics and outstanding biocompatibility. However, a challenging aspect remaining is its higher failure rate due to brittleness, which has to a certain extent prevented the ceramics from fully replacing metals in such major dental restorations as multi-unit bridges. This paper aims at simulating the crack initiation and propagation in dental bridge. Unlike the existing studies with prescriptions of initial cracks, the numerical model presented herein will predict the progressive damage in the bridge structure which precedes crack initiation. This will then be followed by automatic crack insertion and subsequent crack growth within a continuum to discrete framework. It is found that the numerical simulation correlates well to the clinical and laboratory observations.