Fatih Karpat

Computer Aided Analysis of Bending Strength of Involute Spur Gears with Asymmetric Profile

This paper presents a method for the determination of bending stress minimization of involute spur gears. A computer program has been developed to investigate the variation of bending stress and contact ratio depending on the pressure angle on the drive side. Since asymmetric tooth is not standard, the tooth model, which was introduced by DIN 3990/Method C and ISO/TC 60, has been adjusted for asymmetric tooth by the authors. The determination of the tooth form and stress concentration factors for asymmetric tooth has been accomplished for each different parameter (pressure angles, tool radius, rack shift, etc.). The sample results, which were obtained by using a developed computer program, are illustrated with numerical examples.

Influence of Tip Relief Modification on the Wear of Spur Gears with Asymmetric Teeth

Recently, spur gears with asymmetric teeth have been considered a way of increasing performance while maintaining the gearbox dimensions. Asymmetric teeth have different pressure angles on drive and coast sides. They provide, among other advantages, a high bending strength and low vibration. In spur gears with asymmetric teeth, wear has been observed to be a major failure mode. In this study, the impact of tip relief modification and pressure angle on the wear of spur gears with asymmetric teeth is numerically investigated. Here, the focus is on sliding wear. A wear model based on Archards equation is employed to predict wear depth. The pressure angle and the tip relief are parameterized. In the analysis, instantaneous contact loads and Hertz pressures are used in wear depth calculations. It is shown that as the amount of the tip relief increases, the wear depth, particularly at the beginning and end of the mesh, decreases. As the number of wear cycles increases, the effect of the tip relief modification on wear depths decreases slightly. It was also shown that with an increase in tip relief, the dynamic load decreases. However, if the amount of tip relief modification increases excessively, the maximum dynamic load also increases. Therefore, an excessive increase in tip relief modification should be avoided, whereby the level of excessive increase depends on the tip relief configuration.

Wear of Involute Spur Gears With Asymmetric Teeth Under Dynamic Loading

Spur gears with asymmetric teeth have a significant potential for some applications requiring extreme performance like in the aerospace industry. In this study, the influence of tooth wear on the dynamic behavior of involute spur gears with asymmetric teeth is analyzed. The Archards wear model was adopted in formulating and accounting for wear. Effects of gear parameters such as gear contact ratio, tooth height, mesh stiffness, and pressure angles on tooth wear are considered. These parameters are used to describe the relationship between dynamic tooth load and tooth wear. A comparison of symmetric and asymmetric teeth is also presented with respect to tooth wear. Sample simulation results, which were obtained by using an in-house developed computer program, are illustrated with numerical examples. The numerical results match well with the practical and analytical results which are available in literature. For asymmetric teeth, it was shown that the wear depth decreased with increasing pressure angle on drive side.© 2006 ASME

The Investigation of Stress Distribution on the Tractor Clutch Finger Mechanism by Using Finite Element Method

In recent years, there has been an increasing demand for tractor usage for agricultural activities in the world. Tractors are an integral part of mechanization and have a crucial role to play to enhance agricultural productivity. They are used for many kinds of farm work, under various soil and field conditions. It provides agricultural activities in challenging conditions by using several farming equipment. During the operations, tractors have to efficiently transfer power from the engine to the drive wheels and PTO through a transmission. Tractor clutch is the essential element in this system. During the torque transmission, loads which occur on the clutch components cause damages. In many cases, especially PTO clutch finger mechanism is fractured under the torque transmission.In this study, finger mechanism, which used in tractor clutch PTO disc, is investigated. Finite element analyses were performed for two different thicknesses (3.5 and 4 mm) of the finger mechanism. Stress and deformation values which occur during the transfer of power in a safe manner are investigated for these thicknesses. The finger mechanism CAD models were created using CATIA V5 and then imported into ANSYS for static finite element analyses. As a result of the analyses, approximately 13% stress decreasing was observed with the increment of the 0.5 mm for the finger thicknesses. Results from the analyses provide an accurate prediction of the material yielding and load path distribution on the PTO clutch finger. To verify the analyses results prototype PTO finger mechanism was manufactured and was conducted bench tests. Consequently, a good correlation was achieved between finite element model and test results.Copyright

Effect of Rim Thickness on Tooth Root Stress and Mesh Stiffness of Internal Gears

In recent years, internal gears are used commonly in a number of automotive and aerospace applications especially in planetary gear drives. Planetary gears have many advantages such as compactness, large torque-to-weight ratio, large transmission ratios, reduced noise and vibrations. Although internal gears have many advantages, there are not enough studies on it. Designing an internal gear mechanism includes two important parameters. The gear mesh stiffness which is the main excitation source of the system. In this paper, 2D gear models are developed in order to compute gear mesh stiffness for various rim thicknesses and different rim shapes of the internal gear design. Effects of root stress with varying rim thickness and some tooth parameters are investigated by using 2D gear models. The stress calculated according to ISO 6336 and the stresses calculated against FEM are compared. These results are well-matched. It is observed that when the rim thicknesses are increased, both the maximum bending stresses and gear mesh stiffness are decreased considerably.Copyright

Prototyping a New Lightweight Passenger Seat

Profitability is the key concern for transport companies. Costs are increased due to the rising fuel prices and technological investments. As well as new legal restrictions on the emission rates have forced the sector different fuel efficient technologies. Reducing weight is one of the most important methods of improving fuel efficiency and cutting CO2 emissions. Accordingly lighter, more fuel efficient, environmentally sustainable and safety vehicles are in the priority list of European authorities. And also the future of hybrid and electric vehicles depends on the lightweighting. The seat structure was chosen as the area for study which presented the best opportunity for weight reduction by the use of new materials. A seat provides comfort and safety of an occupant’s while travelling. In the event of crash, the passenger seat is exposed many different forces. For this reason it should be designed sufficient strength and stiffness. Therefore an optimized seat design should be aesthetically pleasing, ergonomic, light and meet the safety requirements. Seats play an important role in mass of buses and coaches due to number of seats per vehicle. In this project, finite element analysis, together with topology and free-size optimization is used to design a lightweight passenger seat for new generation commercial vehicles.The seat CAD models were created with CATIA V5 and then imported into HyperMesh for finite element model creation and analysis. Results from the nonlinear analysis provide an accurate prediction of the material yielding and load path distribution on the seat structural frame components. In the end, the verification tests which were determined by ECE are applied the new seat and results were compared with the FEA results.In this study, the lightweight passenger seat prototypes have developed. High strength steel and fiber-reinforced plastic parts are used. An overall 20% weight reduction is achieved including the structural frame, cushion, armrest, and pillar. And also the new passenger seat provides ECE safety norms.Copyright

A Weibull Failure Theory for Contact Loading in Gears With Asymmetric Teeth

Meshing gear pairs have regions of high stress gradients due to contact loading. In other applications, high stress gradients can also be generated due to geometric irregularities, material mismatch, or thermal mismatch. In meshing gear pairs, the extent of the region with a high stress gradient depends on the material and the geometric properties. It is common that failure, through crack initiation, will occur in the region of high stress and strain gradients. The conventional Weibull failure theory fails to accurately predict the probability of failure of components with high stress gradients. In this research, the contact loading in a gear pair, with asymmetric teeth, is analyzed. Thus, the objective of this work is to develop a Weibull failure theory to handle the high stress gradients due to contact loading in gear pairs with asymmetric teeth. The modified Weibull failure theory developed uses the weight function approach to account for the variation of the critical stress along the face of natural flaws. For contacting gear teeth, it is demonstrated that the modified Weibull failure theory generates monotonous trends for the probability of failure with respect to increasing Weibull modulus.Copyright

DYNAMIC ANALYSIS OF HIGH-CONTACT-RATIO SPUR GEARS WITH ASYMMETRIC TEETH

In this research, a numerical technique is used to study the performance of high-contact-ratio (HCR) spur gears with asymmetric teeth. Asymmetric teeth have been shown to minimize dynamic loads and to increase the load carrying capacity. This is due to the fact that these teeth have a larger pressure angle on the drive side compared to the coast side. In literature, symmetric gear teeth with HCR have been shown to also yield low dynamic loads and high load capacities. HCR gears have these positive attributes because for gears in a mesh, the number of tooth pairs sharing the transmitted load alternates between two and three. In this study, the separate benefits of an HCR gear and asymmetric teeth are unified into a spur gear with asymmetric teeth. In this case, the effect of the gear contact ratio, addendum factor, mesh stiffness, pressure angles, and operation speeds on dynamic tooth loads are considered. The influences of these parameters on dynamic response are presented and discussed. A comparison between standard and non standard gear pairs in literature is also presented, with respect to dynamic tooth loads. Sample simulation results, which were obtained by using an in-house computer program, are discussed. The results obtained are shown to match well with some related analytical and experimental results in literature. It is further demonstrated that HCR spur gears with asymmetric teeth do provide a marked advantage compared to the conventional spur gears with symmetric teeth.Copyright

Probabilistic Analysis of MEMS Asymmetric Gear Tooth

Asymmetric gear teeth are used to improve the performance of gears by increasing the load capacity or by reducing vibrations. Recently these types of gears have found application in MEMS devices where the use of gears is on the rise. In this research a probabilistic computer program, in conjunction with a commercially available finite element program, is developed and the reliability of the asymmetric gear tooth is studied. Specifically, the probability of failure of the asymmetric gear is extracted for various parameters. The parameters considered included pressure angle, tooth height, and contact ratio. The efficacy of using asymmetric gear tooth is shown in this study.Copyright

Effects of Heat Input in Laser Welding of Dissimilar Galvanized Steel to Aluminium Alloy

The hybrid structures of aluminum-steel have been increasingly used for body-in-white constructions in order to reduce weight and cost. Obtaining acceptable joints between steel and aluminum required a better understanding of welding metallurgy and their effects on the resultant mechanical properties as well as the microstructure of the joints. In this research, laser welding of galvanized steel and aluminum alloy in an overlapped configuration was carried out. The influence of heat input on the weld bead dimension, microstructural and mechanical properties of the joints was studied. The experimental results showed that the penetration depth and weld width increased with the increase of heat input level. However, in order to limit IMC layer thickness and hardness at the surface of the weld seam and aluminum alloy, iron to aluminum dilution should be restricted by limiting the penetration depth. At lower heat input levels, less brittle IMC formation was formed. Consequently, with limited penetration depths at low heat input levels, tensile shear load increased, with failures located in the interface of the joints.