Suleyman Tasgetiren

Identification of delamination failure of boride layer on common Cr-based steels

Adhesion is an important aspect in the reliability of coated components. With low-adhesion of interfaces, different crack paths may develop depending on the local stress field at the interface and the fracture toughness of the coating, substrate, and interface. In the current study, an attempt has been made to identify the delamination failure of coated Cr-based steels by boronizing. For this reason, two commonly used steels (AISI H13, AISI 304) are considered. The steels contain 5.3 and 18.3 wt.% Cr, respectively. Boriding treatment is carried out in a slurry salt bath consisting of borax, boric acid, and ferrosilicon at a temperature range of 800–950 °C for 3, 5, and 7 h. The general properties of the boron coating are obtained by mechanical and metallographic characterization tests. For identification of coating layer failure, some fracture toughness tests and the Daimler-Benz Rockwell-C adhesion test are used.

Biomechanical evaluation of syndesmotic screw position: a finite-element analysis.

Objectives: To evaluate the stresses in syndesmotic screws and widening of syndesmosis under loading after placement of the screws at different levels from the ankle joint line and to determine the optimal level. Methods: From a set of computed tomographic data of an ankle, a 3-dimensional finite-element model was reconstructed. Six fixation configurations of the syndesmosis with placement of 3.5 or 4.5 mm single tricortical screws at 20–45 mm from the tibiotalar joint were performed on this model. Physiological loads approximating those during both midstance and heel-off states of stance phase of normal walking were applied to evaluate the stress in the screw and widening of the syndesmosis. Results: Among the 6 fixation configurations, the lowest von Mises stress was found in the screws placed 30–40 mm above the joint line (373.31–380.17 MPa for 3.5 mm cortical screw and 284.06–327.31 MPa for 4.5 mm cortical screw in midstance phases), whereas the least syndesmosis widening was determined when the screw was placed 30 mm above the tibial plafond (0.005 mm) for 3.5 mm cortical screw and 20, 25, and 30 mm above the tibial plafond (0.004 mm for each, respectively) for 4.5 mm cortical screw during midstance phases. Conclusions: This study showed that syndesmosis fixation at the level of 30–40 mm above the tibiotalar joint has advantages with regard to stress in screws in comparison with the other evaluated levels.

A numerical study of the behaviour of surface cracks under dry-sliding conditions

Abstract The shape and amount of the surface roughness of a machine part is based on the manufacturing processes. The irregularities cause serious stress concentrations due to the loads acting on the surface. When the loads effect on the surface repeatedly, the irregularities penetrate to turn into a crack. The load may act as normal and/or fractional forces. The latter is caused in general due to friction under rolling–sliding contact conditions. In this study, the behaviour of surface cracks under the normal and tangential loads were analysed. Three angular location for the crack is considered (i.e. −π/4, π/2 and π/4) The problem is considered under condition of linear elastic fracture mechanics and the finite element method was used for numerical solution. The intensity factors at crack tip, K I and K II , were calculated using displacement correlation method. Maximum principal stress theory was used to determine the direction of crack propagation. Effect of the friction coefficient on the stress intensity factors K I and K II and crack growth direction was also investigated.

Anatomical evaluation and stress distribution of intact canine femur.

In the biomedical field, three‐dimensional (3D) modeling and analysis of bones and tissues has steadily gained in importance. The aim of this study was to produce more accurate 3D models of the canine femur derived from computed tomography (CT) data by using several modeling software programs and two different methods.

Anatomical comparison and evaluation of human proximal femurs modeling via different devices and FEM analysis

Breuckmann optical scanning, Metris laser scanning and CT are general devices used for modeling hard or soft tissues in the biomedical field. Whereas the CT device is able to model internal and external structures of hard tissues, Breuckmann and Metris devices can only model the exterior portions of tissues. In this study, a human proximal femur was modeled using these devices, and the matching accuracy thereof is presented.

Alterations in pituitary gland volume in Polycystic Ovary Syndrome: A structural magnetic resonance imaging study.

The purpose of this prospectively designed cross-sectional observational study was to evaluate the effect of polycystic ovary syndrome (PCOS) on pituitary gland volume (PGV) under the hypothesis that endocrinologic changes may lead to morphologic changes of the pituitary gland. Twenty-six PCOS patients and 31 control subjects underwent magnetic resonance imaging (MRI) of the pituitary. Informed consent was obtained from all subjects. PGV was significantly larger in PCOS patients than in control subjects. Luteinizing hormone/follicle-stimulating hormone ratio was the only predictor of PGV. The association between pituitary gland enlargement and PCOS should be kept in mind when pituitary hypertrophy is detected on MRI.

Effect of cooling liquids on cutting process using diamond segmented disc of natural stones

In this study, various cooling liquids considered as alternatives to water were investigated for cutting performance of diamond sawing disc utilized in cutting process of natural stones. In experiments, four various cooling liquids such as water, Ace-Cool, boron oil and liquid soap and two different natural stones (Blue Pearl and Nero Zimbabwe) were used. Down-cutting mode was selected for cutting experiments. In experiments, power consumption, cutting forces, specific energy, diamond segment wear and diamond crystal failures were determined. Power consumption of diamond sawing disc was measured through an energy analyzer and cutting forces through a three-directional dynamometer (ESIT). Specific energy values were calculated through an analytical method on the basis of the resulting power consumption and cutting forces. Besides, diamond segment wear was measured through a laser device (KEYENCE) and diamond crystal failure in cutting process was analyzed through scanning electron microscopy on the basis of cooling liquids. Results of the study show that various cooling liquids proposed as alternatives to water increase significantly cutting performance of the diamond sawing disc. While maximum cutting performance was achieved with a mixture of water and boron oil, minimum performance was achieved through use of water.

Biomechanical Evaluation of Syndesmotic Screw Design via Finite Element Analysis and Taguchi's Method

BACKGROUNDnScrew fixation of syndesmotic injuries facilitates ligament healing and restoration of ankle stability, but failure of the screw might threaten the success of the treatment. Screw design parameters, such as outer diameter, inner diameter, thread pitch, leading edge radius, trailing edge radius, leading edge angle, and trailing edge angle, might have effects on the stresses that occur in the screws. This is the first study, to our knowledge, to investigate which geometric screw parameters play key roles in stresses that occur in screws used for syndesmotic fixation.nnnMETHODSnA three-dimensional finite element model of an ankle was reconstructed. Four different types of titanium screws—4.5-mm malleolar, 4-mm cancellous, 4-mm machine, and 3.5-mm cortical—were placed on this model. Physiologic load was applied to evaluate the stress in the screw. Then the contribution of each design factor to stress in the screws was analyzed systematically by Taguchis robust design method.nnnRESULTSnThe maximum equivalent ductile failure (von Mises equivalent stress) value was found in the 4-mm cancellous screw (402 MPa). Taguchis analysis showed that the descending order of contribution of the design factors to stress emerging on the screw is inner diameter, leading edge angle, thread pitch, outer diameter, and trailing edge angle.nnnCONCLUSIONSnStress that occurs in syndesmotic screws is closely related to their geometry and dimensions. According to the results, a 3.5-mm cortical screw with the ideal screw design regarding optimal parameters to resist against stresses in the syndesmosis seems more reasonable to choose in syndesmotic fixation.

Three-dimensional finite element analysis used to compare six different methods of syndesmosis fixation with 3.5- or 4.5-mm titanium screws: a biomechanical study.

BACKGROUNDnUse of thicker and longer (four cortices) screws or of multiple screws seems to be more stable and efficient for syndesmosis fixation.nnnMETHODSnA three-dimensional finite element model of an ankle was constructed from serial axial sections from an existing two-dimensional computed tomographic image. Constructions of syndesmosis fixation with 3.5-mm single tricortical, 3.5-mm single quadricortical, 3.5-mm double tricortical, 3.5-mm double quadricortical, 4.5-mm single tricortical, and 4.5-mm single quadricortical screws were performed on this model. Physiologic loads approximating those during stance phase normal walking were applied to this ankle system. Stress values on the screws using the six fixation methods were compared.nnnRESULTSnThe highest maximum stress was determined over 3.5-mm cortical screws applied as single quadricortical, and the lowest maximum stress was determined over the 4.5-mm cortical screw applied as single quadricortical. Stress on the 3.5-mm single screw with quadricortical application was found to be higher than that with tricortical application and also compared with the 4.5-mm quadricortical screw application. Differences between the 4.5-mm single tricortical and quadricortical screws and between the 3.5-mm single tricortical and 3.5-mm double tricortical screw applications were not significant.nnnCONCLUSIONSnQuadricortical application of 3.5-mm single screws and tricortical application of 3.5-mm double cortical screws are not good choices for syndesmosis fixation. If the plan is tricortical application, a 3.5-mm single cortical screw is adequate. If quadricortical application of syndesmosis fixation is planned, a 4.5-mm cortical screw should be used.

Experimental investigation of aluminum matrix functionally graded material: Microstructural and hardness analyses, fretting, fatigue, and mechanical properties:

This study investigated the mechanical properties of aluminum matrix functionally graded material (FGM) reinforced by integration of aluminum 2014 alloy (AlCu4SiMg) and 15 vol% SiC. The specimens were obtained by centrifugal casting technique, followed by aging treatment. The variations that occurred in microstructure, hardness, Young’s modulus, tensile strength, yield strength, elongation, fatigue, and fretting fatigue behaviors were analyzed. In both cast and aged conditions, it was observed that hardness values and mechanical properties changed between SiC-rich and aluminum-rich regions. Fatigue and fretting fatigue data were similar. It was determined that greater wear was occurring on the pad surfaces compared to that occurring on the sample surfaces.