M. Toparli

Fracture toughness determination of composite resin and dentin/composite resin adhesive interfaces by laboratory testing and finite element models

OBJECTIVES The reliability and validity of the adhesive bond toughness of dentin/composite resin interfaces were studied from the standpoint of fracture mechanics. METHODS The fracture toughness (KIC) and fracture energy (JIC) values of two different composite resins (Brilliant Dentin and P50) were determined by using single edge notch (SEN) specimens loaded in three point bending and the results were analyzed by the t-test method (p < 0.1). The fracture loads of dentin/composite resin interface with different initial crack lengths were obtained experimentally. The adhesive fracture energy (J(adh)), residual fracture energy (J(res)) and effective (total) fracture energy (J(eff)) for the symmetrical bimaterial (SBM) joint specimen for dentin/composite resin interfaces were calculated and the applied fracture energy (J(appl)) values under the mastication force were obtained for the axisymmetric tooth models. All numerical calculations were carried out by the finite element method and software programs were prepared according to fortran 77. RESULTS The fracture toughness and energy values obtained experimentally for Brilliant Dentin were found to be higher than those for P50. It was seen that, calculated J values (J(adh) and J(res)++) changed with the crack length; but the effective fracture energy (J(eff)++) was independent of the crack length, as expected. The applied fracture energy (J(appl)) and effective fracture energy (J(eff)) are considerably smaller than the experimentally determined JIC values of composite resins. SIGNIFICANCE The bonded interface tends to produce microscopic flaws which could act as critical stress risers promoting interfacial failures. The initiation and propagation of such flaws under the mastication forces can be followed by fracture toughness (KIC) or fracture energy (JIC) in linear elastic fracture mechanics (LEFM).

Hardness and yield strength of dentin from simulated nano-indentation tests

The finite element method (FEM) is applied for studying the hardness (H) and yield strength (Y) of dentin subjected to a nano-indentation process. The nano-indentation experiments were simulated with the ABAQUS finite element software package. This test, performed with a spherical indenter, was simulated by axisymmetric finite element analysis. The load versus displacement was calculated during loading-unloading sequence for different elastic modulus (E) and yield strength. Hardness and maximum principal compressive and tensile stresses were plotted for different elastic modulus depending on yield strength. The dentin was assumed to be isotropic, homogenous and elasto-plastic. The theoretical results outlined in this study were compared with the experimental works reported in the literature and then hardness and yield strength of dentin was estimated.

An investigation of temperature and stress distribution on a restored maxillary second premolar tooth using a three-dimensional finite element method

This paper presents the stress analysis of the maxillary second premolar tooth under thermal loading as a result of hot/cold liquid in the mouth using the three-dimensional (3D) finite element method (FEM). The tooth was considered to be in a restored state with composite resin and amalgam on glass-ionomer as the base material. In the first step of the study, the temperature changes as a result of hot/cold liquid in the mouth were calculated. The thermal stress distributions owing to the temperature changes were then obtained. All calculation programs were prepared by the authors using FORTRAN 77. The tooth was assumed to be isotropic, homogeneous, elastic and unsymmetric. The distribution of temperature and stress were plotted for some critical points.

Residual thermal stress analysis in cylindrical steel bars using finite element method and artificial neural networks

Abstract In this study, it was proposed that the residual stresses within steel bars after quenching in water from 600 °C could be calculated by using the finite element method (FEM) and an artificial neural network (ANN) algorithm. Three modelled cylindrical specimens of AISI 1020 steel were heated and then quenched in water. Using FEM, temperature distribution with time and thermal residual stress values in the samples were calculated after cooling. The analysis was extended to elastic–plastic deformation during the quenching of steel cylinders of various diameters. The calculated temperature and thermal residual stress values were used in training a multi-layer, feed forward, back propagation ANN algorithm. The results obtained via the ANN algorithm method have been compared with the FEM results. Comparison showed good agreement.

Modelled and measured residual stresses in a bimaterial joint

Abstract A finite element technique has been used to predict residual and thermal stresses due to welding. For this purpose, a steel–brass material couple was chosen and thin plates of the materials were hard brazed. The finite element study was carried out using two-dimensional models. After the temperature distributions as a result of welding were calculated, thermal and residual stress values obtained. Thermo-elasto-plastic formulations using a von-Mises yield criterion with linear isotropic-hardening were employed. For this deformation, the initial stress method was used and the kinematical Bauschinger effect was considered. The authors prepared all calculation programs using FORTRAN 77. To obtain residual stresses that occur during the welding, the hole-drilling strain-gage method was chosen and conducted in accordance with the ASTM Standard E 837-99. The agreement between the calculated results and the experimental data shows that the finite element analysis method is reliable.

The three-dimensional finite element analysis of fixed bridge restoration supported by the combination of teeth and osseointegrated implants.

This study investigated the designs of osseointegrated prostheses in cases of free-end partial edentulism using comparative stress interpreted with the three-dimensional finite element method. Three free-end fixed osseointegrated prostheses models with various connection designs (ie, rigidly connected to an abutment tooth and an implant, rigidly connected to an implant and two abutment teeth, and rigidly connected to an implant and three abut- ment teeth) were studied. The stress values of the three models loaded with vertical, buccolingual, and linguobuccal directions at 30° angled to vertical axis forces were analyzed. When the fixed partial denture was connected to the three natural abutment teeth and an implant, the lowest levels of stress in the bone were noted.

Evaluation of the adhesion of TiN films using nanoindentation and scratch testing

Abstract The scratch test method is applied to the coated sample using a diamond indenter. This sample is displaced at a constant speed and certain load damage occurs along the scratch path. Using a nanoindentation and nanoscratch technique, the mechanical properties of physically vapour-deposited films were investigated experimentally and numerically. In order to evaluate the microhardness and adhesive properties of thin films, we applied a nanoindentation and scratch test experimentally. The TiN films were deposited on silicon wafers at a thickness of about 1.2 μm by physical vapour deposition. The elastic stress distribution was calculated on the coating material for different loads, friction coefficients and directions using three-dimensional finite-element models. A FORTRAN computer program was developed for the study. The coating material was assumed to be a homogeneous, isotropic and infinite body. This paper compares the measured critical load and calculated critical load for different directions using the scratch test and finite-element method respectively. It has been seen that agreement is reasonably good.

Enhancement of the mechanical properties of hydroxyapatite by SiC addition.

Improvements of mechanical and anticorrosive properties, as well as superior osseointegration of the hydroxyapatite coated titanium alloy were reported in the last years by the addition of different elements (Si or Ti) into hydroxyapatite structure. The aim of this work was to prepare and to investigate the hydroxyapatite (HAP) coatings enriched with SiC in order to enhance the mechanical properties of HAP films. The coatings were deposited on Ti6Al4V alloy substrates by co-sputtering of HAP and SiC targets, using a magnetron sputtering system. The films were characterized in terms of elemental and phase composition, chemical binding, morphology and mechanical properties by EDS, XRD, FTIR, SEM, AFM, and nanoindentation. Overall, improved mechanical properties were found by adding SiC to the basic HAP structure.

An Investigation of Al-SiCp Composites Under Thermal Cycling

The effect of thermal cycling on the behavior of the aluminum-silicon matrix alloy Al-7%Si-0.7%Mg (AlSi7) reinforced with 10% volume SiC particles has been investigated experimentally and theoretically. Cast ingots of the matrix alloy and composite samples were extruded at 773 K at an extrusion ratio of 10:1. The extruded microstructures exhibit a more uniform distribution of the SiC particles. In this study, for determining the thermal stress and deformation on the composite materials ABAQUS finite element software package was used. Thermal residual stresses developed during and after thermal cycling were also investigated. Thermal cycling tests were performed between 373 and 703 K under a constant tensile load (150 N) and without external load. The stress distributions in the composite during heating and cooling were revealed. The axial displacement under constant external load after one thermal cycling was 0.01672 mm and kept increasing considerably. The maximum residual stresses were generated at the interfacial region during thermal cycling. SEM micrographs showed that cracks were present in the composite structure under repeated action of thermal cycling process (100 cycles).

Recrystallization and particle growth in Al-based SiC particle-reinforced composites

Abstract The recrytallization behaviour of Al—Si—Mg matrix composites reinforced with SiC particles of 10 and 20 vol.% and unreinforced matrix alloy have been studied. Also, the effect of annealing temperature and time on grain growth and particle coarsening has been evaluated. Cast ingots of the matrix alloy and composites were extruded at 500°C at an extrusion ratio of 10: 1. The microstructures and hardness of the composite samples have been investigated. It has been found that particle volume fraction and size affect the recrystallization temperature of the materials.