Tooth bending strength of gears with a progressive curved path of contact

Zorko Damijan,Duhovnik Jože,Tavčar Jože 한국CDE학회 2021 Journal of computational design and engineering Vol.8 No.4

The article presents a comprehensive study on the tooth bending strength of spur gears with a progressive curved path of contact, or so-called S-gears. Systematic gear meshing simulations were conducted to study the effects of S-gear geometry parameters on tooth bending strength. Different S-gear geometries were analysed in a systematically organized manner, and a comparison was made against a standard 20° pressure angle involute shape. Furthermore, different material combinations, e.g. polymer/polymer, steel/polymer, and steel/steel, of both drive and driven gear were analysed within a meaningful range of loads. The gear profile shape, material combination of the drive and the driven gear, and the transmitted load were found as the main parameters affecting gear tooth bending stress. Complex, non-linear relations between the recognized effects and the corresponding root stress were observed. Based on the numerical results, a shape factor, which considers the above-mentioned effects, was introduced, and a model for root strength control of S-gears was proposed and verified employing the finite element method (FEM).

The effect of gear-manufacturing quality on the mechanical and thermal responses of a polymer-gear pair

Zorko Damijan,Wei Peitang,Vukašinović Nikola 한국CDE학회 2024 Journal of computational design and engineering Vol.11 No.1

Gear-manufacturing quality affects the load sharing between the meshing gears as well as the load distribution along the width of the tooth. This study aims to investigate the effect of gear-manufacturing quality on the mechanical and thermal states of polymer-gear pairs and consequently on their lifetime. The deviations of the geometric quality parameters, i.e., the lead profile and pitch, were found to have a substantial effect on the stress (root and flank) state of the gear. The effect of the lead deviation was found to be most pronounced for the quality grades Q12 to Q10, where depending on the load, a 30–80% stress reduction was observed when improving the gear quality from Q12 to Q10. Improving the quality from Q10 to Q8 did not lead to a substantial improvement in the load distribution and the observed stress reduction was in range of 5–20%. Similar trends were found for the pitch deviation, where again the most pronounced stress reduction was seen when improving the quality grade from Q12 to Q10. The study reveals where the most effective changes, leading to an increased gear-life, can be achieved. Improving the gear quality grade from Q12 to Q11 proved to have a much more substantial effect than improving the gear quality from Q9 to Q8. Considering that improving the gear quality from Q12 to Q11 or even Q10 can be achieved by a proper tool design and corrective iterations with the right process parameters, while improving the quality from Q9 to Q8 is by far more challenging. A novel methodology is proposed to assess the effect of the gear’s quality on the generation of heat and the resulting operational temperature. The proposed methodology enables more accurate prediction of the gear pair’s operating temperature.

Fast fabrication of mesoporous SiC with high and highly ordered porosity from ordered silica templates

Milena Zorko,Saša Novak,Miran Gaberscek 한양대학교 세라믹연구소 2011 Journal of Ceramic Processing Research Vol.12 No.6

Three-dimensional (3D) mesoporous SiC samples with highly ordered porosity were prepared using three different routes. The essential difference was in the first step in which sacrificial uniform silica spheres were packed into ordered three-dimensional arrays using: i) sedimentation, ii) centrifugation and iii) electrophoretic deposition (EPD) methods. Regardless of the method used, the quality of arrays was quite high and reproducible. The prepared silica arrays were infiltrated with a pre-ceramic polymer precursor. The infiltration step was followed by a thermal curing step, a pyrolysis step at 850 oC in an Ar atmosphere and, finally, removal of the silica templates by etching with a 3M NaOH solution. The final products were porous 3D SiC samples with typical volumes around 1 cm3 and a pore size of 240 or 650 nm. The synthesized porous SiC was characterized using SEM, TEM and XRD methods.

A multicriteria function for polymer gear design optimization

Jozˇe Tavcˇar,Borut Cˇerne,Jozˇe Duhovnik,Damijan Zorko 한국CDE학회 2021 Journal of computational design and engineering Vol.8 No.2

A reliable method of optimization of polymer gears remains, to date, an open challenge, due to the lack of specific material characterization of polymers and to the complex nonlinear relations between different geometric and operating parameters. For spur and helical gears, the authors herein have developed the optimization algorithm, which primarily enables variation of geometry according to various criteria: the number of teeth (z1, z2), face width (b), helix angle (β), and normal module (mn). The method enables a better insight into how design parameters influence the target criteria. The main paper contribution is a newly developed multicriteria function that enables a simultaneous consideration of different criteria such as root/flank stress, gear bulk/flank temperature, wear, deformation, quality, cost, and volume.

Experimental and numerical analysis of laminated carbon fibre-reinforced polymer gears with implicit model for coefficient-of-friction evaluation

Černe B,Bergant Z,Šturm R,Tavčar J,Zorko D 한국CDE학회 2022 Journal of computational design and engineering Vol.9 No.1

Laminated composites have so far received little attention as a potential material for gear drive applications. In the presented study, the thermomechanical performance of a newly developed type of epoxy impregnated, autoclave-cured carbon fibre-reinforced polymer gear—running in pair with a steel pinion—was analysed, using a combination of experimental and numerical approaches. The employed methods enabled the identification of the composite’s mechanical, thermal, and tribological characteristics, as related to the studied gear pair application. A newly proposed, finite-element-analysis-based iterative procedure enabled an implicit evaluation of the analysed material pair’s coefficient of friction (COF), which is a key parameter in determining the gear pair’s thermomechanical characteristics. For the considered material pair, a value of 0.34 was identified for the coefficient in the quasi-steady region. As the coefficient is strongly correlated with frictional heat generation and significantly affects the surface shear stress, it can consequently have a meaningful influence on the composite’s wear rate. The developed COF identification procedure was validated using a reciprocating cylinder-on-flat tribological test method. The composite gear’s service life was additionally tested at various running loads, resulting in pitch contact pressures ranging between 400 and 540 MPa. Lifetime gear test results showed a markedly superior performance compared to the high-temperature thermoplastic polyether ether ketone, which is typically employed in the most demanding polymer gear applications. Several methods are additionally proposed that could further improve the developed composite gears’ performance.

A comparative study of fatigue behavior between S-shaped and involute POM gears

Wu Ruo,Wei Peitang,Lu Zehua,Liu Huaiju,Zorko Damijan,Xie Huaijie 한국CDE학회 2022 Journal of computational design and engineering Vol.9 No.6

Applications of polymer gears have been gradually expanding from motion transmission to power transmission fields. Design of new gear teeth profiles plays a crucial role in meeting the requirement of replacing metallic gears with polymer ones. This work develops a computational framework consisting of tooth profile generation and fatigue life prediction of S-shaped and involute POM gears. The contact and bending fatigue performances of S-shaped and involute POM gears under oil lubrication are comparatively studied. It is found that the S-shaped profile reduces the tooth root stress by 25% and significantly improves the bending fatigue life by 10 times compared with the involute profile, especially under medium or high loading levels. Furthermore, the S-shaped gear with a single circular-filleted root curve benefits a 20% reduction of tooth root stress and a 30% increase in bending fatigue life compared to a double circular-filleted root curve S-shaped gear.