Reliability Analysis of the Static Bending Strength of Cylindrical Hardened Gears

Yıl 2018, Cilt: 30 Sayı: 4, 388 - 397, 31.12.2018

Mehmet Bozca

https://doi.org/10.7240/marufbd.411425

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] 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] William D. Callister, Jr., Materials Science and Engineering, An Introduction, John Wiley & Sohns, Inc. 2007.
• [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] 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] VDI Guidelines 4001.
• [6] ISO 6336-5, Calculation of load capacity of spur and helical gears-Part 5: Strength and quality of materials.
• [7] ISO 6336-3, Calculation of load capacity of spur and helical gears-Part 3: Calculation of tooth bending strength.
• [8] Bernd Bertsche, “Reliability in Automotive and Mechanical Engineering”, Springer, 2008.