Reliability Analysis of the Static Bending Strength of Cylindrical Hardened Gears

Öz

The target of this study is to investigate the static bending strength of teeth in cylindrical hardened gears based on reliability analysis. The effect of hardness on the static bending strength of the tooth of the cylindrical gear was investigated in the static loading conditions. The gears were carburized with low-pressure in a 4 mbar acetylene atmosphere and cooled with gas. In order to obtain different hardness values, different cooling rates were applied using different gases and gas-pressures. For this objective, shot-peened and unshot-peened gears having different core and surface hardness values are tested on a pulsator test machine providing a quasi-static loading condition.  Shot peening treatment was performed according to Atmen A and Atmen N method. Material used for gear samples is 20MnCr5 steel and samples have the same geometry. The quasi-static load for tooth fracture is monitored and measured. The bending stresses for applied load which causes fracture is calculated. Tooth-root failures starting from the surface are experimentally observed. The shot-peening treatment is found to have no positive effect on the bending strength of the tooth under static loading conditions, although the shot peening treatment is effective in improving the dynamic bending strength of the gears. The increase in the hardness value results in an increase in the static bending strength of the gears. A high static bending strength value was obtained for high-rigidity gears heat-treated in a 20 bar Helium (He) atmosphere. The hardness of the core has been shown to have no significant effect on the determination of the static bending strength of the gears since the damage occurred from the surface. The appearance of the damage surfaces for gears is typical static loading damage from the surface, depending on the maximum tensile stress of the crack. Reliability involves the damage behavior of a product and is therefore an important criterion for product assessment. Gears are the most important machine elements in many mechanical power transmission systems and therefore the reliability of the gears is very important. Reliability analysis is required to determine the possible strength values ​​of the gears to meet the strength values ​​foreseen in the literature. Reliability analyses of the static bending strength of the tooth in cylindrical hardened gears are conducted. The mean values, standard deviations and standard variables of the static bending strength are calculated. It is concluded that the reliability levels of the static bending strength satisfy the required strength values given in the literature.

Anahtar Kelimeler

• Hardened gears,Shot-peening,Bending strength,Reliability

Sertleştirilmiş Silindirik Düz Dişli Çarkın Statik Eğilme Dayanımının Güvenirlik Analizi

Öz

Özet

Bu çalışmanın amacı sertleştirilmiş silindirik düz dişli çarkın statik eğilme dayanımını güvenirlik analizi temelinde incelemektir. Bu amaç için, bilya-püskürtülmüş ve bilya-püskürtülmemiş farklı yüzey sertliği değerlerine sahip dişli çarklar bir yarı-statik yükleme koşulu sağlayan bir pulsator test makinasında test edilmiştir. Test edilen tüm dişli çark numunesi malzemeleri 20MnCr5 çeliğidir ve aynı geometriye sahiptir. Diş kırılması için yarı-statik yükleme durumu gözlemlenmiş ve ölçülmüştür. Hasara sebep olan uygulanan yük için eğilme gerilmeleri hesaplanmıştır. Yüzeyden başlayan diş-dibi hasarları deneysel olarak gözlemlenmiştir. Bilya-püskürtme işleminin statik yükleme koşullarında dişin eğilme dayanımı üzerinde hiç olumlu etkisinin olmadığı belirlenmiştir. Sertleştirilmiş silindirik düz dişli çarkın statik eğilme dayanımı güvenirlik analizi gerçekleştirilmiştir. Statik eğilme dayanımının ortalama değerleri, standart sapmalar ve standart değişkenleri hesaplanmıştır. Statik eğilme dayanımının güvenirlik seviyelerinin literatürde verilen istenilen dayanımı sağladığı sonucuna varılmıştır.

Anahtar Kelimeler

• Sertleştirilmiş dişli çark,Bilya-püskürtme,Eğilme dayanımı,Güvenilirlik

Kaynakça

1. [1] Mehmet Bozca, Influence of core hardness on bending strength of tooth in cylindrical gears under quasistatic loading conditions, Fatigue & Fracture of Engineering Materials & Structures, Blachwell Publishing Ltd. 31, pp.902-910, 2008.
2. [2] William D. Callister, Jr., Materials Science and Engineering, An Introduction, John Wiley & Sohns, Inc. 2007.
3. [3] Karin Björkeborn, Uta Klement, Hans-Börje Oskarson, Study of microstructureal influences on machinability of case hardening steel, Int. J. of Advanced Manufacturing Technology, 49, pp.441-446, 2010.
4. [4] S. B. Mahagaonkar, P. K. Brahmankar, C. Y. Seemikeri, Effect of shot peening parameters on microhardness of AISI 1045 and 316L material: an analysis using design of experiment, Int. J. of Advanced Manufacturing Technology, 38, pp.563-564, 2008.
5. [5] VDI Guidelines 4001.
6. [6] ISO 6336-5, Calculation of load capacity of spur and helical gears-Part 5: Strength and quality of materials.
7. [7] ISO 6336-3, Calculation of load capacity of spur and helical gears-Part 3: Calculation of tooth bending strength.
8. [8] Bernd Bertsche, “Reliability in Automotive and Mechanical Engineering”, Springer, 2008.