B. Aksakal

Influence of orthopaedic drilling parameters on temperature and histopathology of bovine tibia: An in vitro study

Orthopaedic drilling operations without optimum operating parameters by surgeons may cause bone defects such as bone fracture, cracks, osteolysis and tissue loss around the drilling zone. For the sake of optimum drilling parameters, an in vitro study was performed by considering the bone mineral density, bone sex, drill tip angle, drill speed, drill force and feed-rate. The specimens were taken from the drilled sites of fresh male and female calf tibias. The temperature changes at the drill site were investigated throughout the statistical and histopathological analysis. It was observed that the temperature increased with an increasing drill speed and decreased with high feed-rates and applied drill forces. The drilling temperatures of the female bovine tibias were found to be higher than that of the male tibias and the drill speed was found to be a significant parameter on the maximum temperature. Moreover, the maximum temperature increased with an increasing drill tip angle and bone mineral density. Therefore the bone quality around the drill site was found to be worse than the bone samples exposed to low temperatures.

Production and indentation analysis of WC/Fe–Mn as an alternative to cobalt-bonded hardmetals

Abstract An iron–manganese (Fe–Mn) alloy-bonded tungsten carbide hardmetal, WC/Fe–13.5 wt.% Mn, was produced in various combinations of binder phase by using powder metallurgical routes. This was done in order to provide lower-cost hardmetals and to offer a nontoxic alternative to cobalt (Co)-based materials. The outcome of this effort has been the preparation, at acceptable sintering temperatures, of a Fe–Mn bonded WC with a fully austenitic binder phase. Vickers indentations on the hardmetal substrates produced Palmqvist-type cracks. The variation of Vickers hardness with sintering temperature was investigated for WC bonded with 15 and 25 wt.% Fe–Mn alloys. Mechanical property evaluations showed that the alloys possess higher hardness and slightly lower fracture toughness values than the equivalent of Co-bonded grades. This fact could lead to the use of such hardmetal alloys in mining and wear-resistant applications with better reliability.

Transient and residual thermal stresses in quenched cylindrical bodies

To predict residual and thermal stresses which occur during water quenching of solid cylindrical rod and ring cross-sectioned steel tubes, a finite element technique has been used. The variations of residual stresses on different surfaces and cross-sections, e.g. in the radial, axial and tangential directions have been examined, and the effect of internal diameter of tubes on residual stress was investigated. The results show that the residual stresses act as a compressive force along the cooling surface and then by moving away from the surface begin to decrease and reverse their sign, near the centre of the cylinder are subjected to tensile stresses. Because of the reversal of the sign of stress, the effective stress goes to a minimum at some distance from the frontal surface and this may be vital since lower plastic deformation may cause cracking failure. As in solid cylinder, in cylindrical tubes also, the frontal and the upper cooling surface has significant effect on the stress distribution. From the comparison of the residual stress distributions of solid cylinder and cylindrical tubes and using their individual stress maps it was seen that they vary considerably along different cooling surfaces, especially at the frontal surface.

Hydroxyapatite dip coated and uncoated titanium poly-axial pedicle screws: an in vivo bovine model.

Study Design. A 1-year-old calf was implanted with titanium pedicle screws either uncoated (n = 7) or coated with hydroxyapatite (n = 7) by the dipping method on the pedicles of vertebrae (t10–l3). Objective. To evaluate biomechanical and histomorphologic responses to titanium pedicle screws uncoated and coated with hydroxyapatite. Summary of Background Data. Failure of fixation caused by loosening of pedicle screws is a problem in spinal surgery. Enhancement of the fixation ability of screws by coating with biocompatible materials may improve prognosis of surgery. Methods. The calf was euthanized 4 months after implantation for determination of insertion and extraction torques for screws, and histologic and scanning electron microscopic examinations of areas screw embedded. Results. Insertion torques did not differ by the kind of screws (99 ± 5.7 Ncm). However, extraction torques for screws coated with hydroxyapatite were higher than for screws uncoated (249 vs. 133 Ncm, P < 0.01). As compared with uncoated screws, implanted areas for hydroxyapatite-coated screws were denser, had more cracks, and provided better bonding. Fibrous tissue and new bone formation were observed around the areas of uncoated and hydroxyapatite-coated screws embedded, respectively. Conclusions. Hydroxyapatite coating of titanium pedicle screws by the dipping method improved fixation and vertebral bone-implant interface, suggesting a decreased risk of a screw-loosening problem.

A finite-element analysis of the indentation of an elastic-work hardening layered half-space by an elastic sphere

Abstract An elastic–plastic contact problem in elastic-work hardening layered half-space indented by an elastic sphere was solved numerically using the finite element method. The case of a surface layer stiffer than the substrate is considered, and general solutions for the subsurface stresses and deformation fields are presented for a relatively thin elastic layer. Differences between the elastic and elastic–plastic solutions for the contact pressure distribution have been investigated for various layer thicknesses. Crack initiation and decohesion of the layer was also discussed with reference to the growth of the plastic zone.

Upper-bound analysis for the automation of open-die forging

Abstract The automation of open-die forging systems can be attractive for small batch manufacture of medium-size parts where they can compete against a number of machining processes. The introduction of new manufacturing systems and the associated work-in-progress minimization technique prompts a consideration of the use of open-die forging for incremental profiling and shaping processes. In order to develop an automated open-die forging process it is essential to be able to predict the shape changes occurring at each step. Therefore a general computerized methodology is proposed for small batch manufacture via a theoretical model, producing rapid predictions of metal flow for continuing incremental deformation. This paper reviews the open-die forging process in this context as a part of a computer-controlled robotics flexible forging system for the economic production of small-batch quantities. The metal flow in open-die forging is analyzed through a number of upper-bound solutions and the basis of an on-line analytical modeling system, together with experimental correlation and a planning system, is presented to produce bar profile features.

Reactive sintering of electroless nickel-plated aluminum powders

Fine (about 2 mm) particle size aluminum powders were produced in a plasma reactor, in a flow of argon gas, and the particle size distribution analyzed. A uniformly thick nickel film was deposited on the aluminum powder particles by electroless nickel plating, thus providing more efficient surface contact than can be obtained using conventional methods such as mechanical mixing of nickel and aluminum powder. Nickel-plated aluminum compacts were subsequently sintered at various temperatures in argon and in vacuum, and Ni3Al intermetallic alloys produced. Differential thermal analyses, scanning electron microscopy, and X-ray diffraction analyses of the sintered samples were carried out. Satisfactory densities of 99.8% were achieved by sintering in vacuum at temperatures as low as 680� C. D 2001 Elsevier Science Inc. All rights reserved.

Diffractaic acid, a novel proapoptotic agent, induces with olive oil both apoptosis and antioxidative systems in Ti-implanted rabbits☆

Usnea longissima Ach., a lichen species, is a traditional herbal medicine with anti-detrimental effects. We evaluated the in vivo effects of a major constituent of U. longissima, diffractaic acid, and the main fatty component of the Mediterranean diet, olive oil, against apoptosis, including various caspase activations and oxidative injury in surrounding tissues after titanium implantation in rabbit femurs. Furthermore, we evaluated the underlying molecular mechanisms. In this study, this lichen metabolite and olive oil activated caspase-dependent cell death with apoptotic morphology, which is distinctly different from necrosis. Both orally and locally administered olive oil and diffractaic acid exerted pro-apoptotic induction in tissues surrounding the implants in titanium-implanted rabbits through the activation of initiator caspases (Cas-2, -8 and -9) and executioner caspase (Cas-3). In addition, they displayed strong myeloperoxidase and inducible nitric oxide synthase activities, providing an alleviating effect. Furthermore, administrations of diffractaic acid and olive oil attenuated the Ti-alloy implantation, and decreased superoxide dismutase activity and total glutathione level in peri-implant tissues. These results demonstrate that diffractaic acid and olive oil are involved in the induction of apoptotic cell death both through caspase-dependent cell death and as an antioxidant. Thus, the data suggest that both diffractaic acid and olive oil could be developed as effective proapoptotic agents in various disorders treatments.

Analysis for the Automation of Small Batch Manufacturing Using Open Die Forging

Abstract Open die forging is a long established process which can be used to produce a wide range of shapes. Its characteristics features in relationship to other types of forming processes are that it requires low forming loads and only a small range of simple tools to make a wide variety of shapes. Whilst the process is generally associated with the production of large forgings, an automated version could be attractive for small batch manufacturing of low weight forgings. Such a system could compete effectively against machining process. This paper examines the process of pressing small size pans by open die forging, reviews existing literature and presents an upper bound based solution for single step and incremental open die forging. The validity of the theoretical analysis is assessed by comparison with experiments and found to be ill a good agreement.

Effect of Die Radius on Blank Holder Force and Drawing Ratio: A Model and Experimental Investigation

A numerical model for a newly designed deep drawing process has been built up and analyzed using the finite element method (FEM) in comparison with performed experiments using the DIN 10130-99-DC05 sheet material. It was aimed to increase the limiting drawing ratio (β) and decrease the blank holder forces (BHFs). To predict the deformation behavior of the process, the parameters are analyzed using FEM. The effects of the die radius, blank holder and punch forces, friction, cup wall, and blank thickness in the process were investigated. A deep drawing die set was designed and manufactured, and the validity of the design was demonstrated through the theoretical and experimental analysis. The results showed that the blank holder die radii and friction have the greatest effect on the thickness of deformed steel cups. The drawing ratio of β has an influence on the BHFs and it decreased with increasing die angle (α). The β was considerably increased by 26% compared with dies having no angle (α = 0°). The current design and analyses can help the optimization of the control scheme of drawing processes rather than using the conventional designs. A comparison of the predicted and experimental results showed good agreement.