Utku Ahmet Özden

Stability of zygomatic plate-screw orthodontic anchorage system: a finite element analysis.

OBJECTIVE To evaluate the biomechanical properties of a standard and a newly designed plate-screw orthodontic anchorage system. MATERIALS AND METHODS A three-dimensional model of the posterior maxilla, including the zygomatic buttress region, was prepared. Insertion of standard and newly designed plates was simulated on the three-dimensional model. The effect of 200 g of orthodontic force on the plate, screws, and zygomatic bone was evaluated in three-dimensional models by finite element analysis. To determine the force distribution, Von Mises stress, principal maximum and minimum stress, and principal maximum and minimum elastic strain values were evaluated. RESULTS In all plate models the highest stresses occurred on the threaded bone site where the force application unit was attached. CONCLUSION Changing the plate configuration did not affect the stress distribution in the newly designed plates. To equalize the force distribution, new plate designs that change the location of the force application unit are required.

On the Statistical Determination of Yield Strength, Ultimate Strength, and Endurance Limit of a Particle Reinforced Metal Matrix Composite (PRMMC)

In this paper we present a numerical methodology to determine the load bearing capacity of a random heterogeneous material. It is applied to a particulate reinforced metal matrix composite (PRMMC), WC-30 Wt.% Co, to predict its strength against both monotonic and cyclic loads. In this approach, limit and shakedown analysis based on Melan’s static theorem [30] is performed on representative volume element (RVE) models generated from real material microstructure and the obtained results are converted to macroscopic load domains through homogenization. To evaluate microstructure’s impact on the overall material strength, the relationship between strength and composite structure is investigated by means of statistics. Meanwhile, several numerical issues, e.g. the impact of RVE’s size, mesh density, as well as the discrepancy between 2D and 3D models, are studied.

The comparison of angular and curvilinear marginal mandibulectomy on force distribution with three dimensional finite element analysis

AIM The purpose of this study was to analyse and compare right angled and curved osteotomy design on stress distribution and to determine an osteotomy design which decreases the risk of pathologic fracture. PATIENTS AND METHODS Solid mathematical model of the mandible was created by three dimensional finite element analysis and two different osteotomy, right angled and curvilinear osteotomy was performed on model. 150 N incisal force vertically and 250 N molar force to the angulus area oblically were applied. The effects of osteotomy types to the stress formation and risk of fracture between models were evaluated. RESULTS Right angled osteotomy causes much more stress in the posteroinferior quadrant and mainly localized on the horizontal and vertical osteotomy intersection area. On the other hand, the distribution of the stress on curvilinear formed osteotomy shows posteroinferior localization and stress spreads wider area. Furthermore the amount of stress was less than right-angled one. CONCLUSION In this study, curved osteotomy denominated less stress distribution. The shape of osteotomy might be a factor to decrease the risk of postoperative atrophic mandible fracture.

A model for predicting crack initiation in forged M3:2 tool steel under high cycle fatigue

AISI type M3 class 2 tool steel (or in German designation DIN: HS6-5-3 tool steel) is most commonly used in tooling industry, and also in some engine parts. Those components are usually subjected to cyclic stresses and mostly fail by fatigue. Fatigue crack initiation in this material occupies large fraction of total lifetime and strongly depends on microstructural features of primary and eutectic carbides, such as shape, shape ratio, volume fraction, the distribution of carbides as well as load ratio. To model fatigue initiation mechanisms of forged M3:2 tool steel, McDowell’s model was modified and developed for different length-scales. For fatigue crack formation and short crack growth, a hierarchical approach was used and the life time of these stages were estimated based on the local cyclic plasticity. Through this relation the effect of microstructural features on both fatigue crack formation and short crack growth in the material were identified. The results of the proposed model have explicitly reflected the influence of microstructural features on both fatigue crack formation and propagation in forged M3:2 tool steel. Moreover, the model can be used for improving the fatigue resistance of a tool steel component.