An Experimental Investigation of the Effect of Tooth Asymmetry and Tooth Root Shape on Root Stresses and Single Tooth Bending Fatigue Life of Gear Teeth

2011 ◽  
Author(s):  
Aaron Sanders ◽  
Donald R. Houser ◽  
Ahmet Kahraman ◽  
Jonny Harianto ◽  
Sam Shon
Keyword(s):  
Stress Reduction ◽  
Fatigue Tests ◽  
Analysis Model ◽  
Bending Fatigue ◽  
Single Tooth ◽  
Dimensional Measurements ◽  
Bending Stresses ◽  
Significant Life ◽  
Maximum Root ◽  
The Right

In this paper, effects of root fillet geometry and tooth asymmetry on tooth bending stresses and fatigue lives of spur gears are investigated. For this purpose, an existing gear analysis model, the Load Distribution Program (LDP), is employed to define four basic tooth geometry variations. These four variations are (i) symmetric tooth profiles (i.e. identical loaded and unloaded flanks) with full circular root geometry (at the maximum radius possible), (ii) symmetric tooth profiles with an elliptical root geometry, (iii) asymmetric tooth profiles (i.e. loaded and unloaded flanks at different pressure angles) with full circular root geometries, and (iv) asymmetric tooth profiles with an elliptical root geometry on the right (loaded) flank and a circular root geometry on the left flank. Under these conditions, variations (ii), (iii), and (iv) are predicted to have maximum root stresses that are 7.6%, 22.4%, and 24.3% less than that of the baseline case (i). Actual test articles representing these four variations were qualified through dimensional measurements of the profiles and the root fillet regions. The roots of several of the teeth of each gear type were instrumented and strain measurements under various tooth load levels are compared with the predictions. Single tooth bending fatigue tests were also performed to obtain fatigue data for each variation of the test gears. The resultant tooth bending fatigue performance of each gear variation is shown to correlate with the level of root stress reduction achieved. Experiments indicate that the most significant life increases compared to the baseline conditions are achieved with the last variation (asymmetric tooth profiles and an elliptical root shape), where the mean life is increased by more than 30 times. It is also shown through examination of the broken teeth that the critical locations where the cracks initiated agree well with the predicted locations of the maximum root stresses.

Gear root bending strength: a comparison between Single Tooth Bending Fatigue Tests and meshing gears

2021 ◽  
pp. 1-17
Author(s):  
Luca Bonaiti ◽  
Ahmed Bayoumi Mahmoud Bayoumi ◽  
Franco Concli ◽  
Francesco Rosa ◽  
Carlo Gorla
Keyword(s):  
Failure Modes ◽  
Bending Strength ◽  
Gear Tooth ◽  
Fatigue Tests ◽  
Bending Fatigue ◽  
Gear Design ◽  
Single Tooth ◽  
Actual Strength ◽  
Meshing Gears ◽  
Definition Of

Abstract Gear tooth breakage due to bending fatigue is one of the most dangerous failure modes of gears. Therefore, the precise definition of tooth bending strength is of utmost importance in gear design. Single Tooth Bending Fatigue (STBF) tests are usually used to study this failure mode, since they allow to test gears, realized and finished with the actual industrial processes. Nevertheless, STBF tests do not reproduce exactly the loading conditions of meshing gears. The load is applied in a pre-determined position, while in meshing gears it moves along the active flank; all the teeth can be tested and have the same importance, while the actual strength of a meshing gear, practically, is strongly influenced by the strength of the weakest tooth of the gear. These differences have to be (and obviously are) taken into account when using the results of STBF tests to design gear sets. The aim of this paper is to investigate in detail the first aspect, i.e. the role of the differences between two tooth root stress histories. In particular, this paper presents a methodology based on high-cycle multi-axial fatigue criteria in order to translate STBF test data to the real working condition; residual stresses are also taken into account

scholarly journals Pitting and Bending Fatigue Evaluations of a New Case-Carburized Gear Steel

2007 ◽  
Author(s):  
Timothy Krantz ◽  
Brian Tufts
Keyword(s):  
Power Density ◽  
Fatigue Testing ◽  
Surface Hardness ◽  
Fatigue Tests ◽  
Bending Fatigue ◽  
Surface Fatigue ◽  
Gear Steel ◽  
Single Tooth ◽  
Carburized Gear ◽  
Gear Steels

The power density of a gearbox is an important consideration for many applications and is especially important for gearboxes used on aircraft. One approach to improving power density of gearing is to improve the steel properties by design of the alloy. The alloy tested in this work was designed to be case-carburized with surface hardness of Rockwell C66 after hardening. Test gear performance was evaluated using surface fatigue tests and single-tooth bending fatigue tests. The performance of gears made from the new alloy was compared to the performance of gears made from two alloys currently used for aviation gearing. The new alloy exhibited significantly better performance in surface fatigue testing, demonstrating the value of the improved properties in the case layer. However, the alloy exhibited lesser performance in single-tooth bending fatigue testing. The fracture toughness of the tested gears was insufficient for use in aircraft applications as judged by the behavior exhibited during the single tooth bending tests. This study quantified the performance of the new alloy and has provided guidance for the design and development of next generation gear steels.

Contact and bending fatigue behaviour of austempered ductile iron gears

2017 ◽  
Vol 232 (6) ◽  
pp. 998-1008 ◽  
Author(s):  
Carlo Gorla ◽  
Edoardo Conrado ◽  
Francesco Rosa ◽  
Franco Concli
Keyword(s):  
Ductile Iron ◽  
Contact Fatigue ◽  
Research Programme ◽  
Fatigue Behaviour ◽  
Fatigue Tests ◽  
Austempered Ductile Iron ◽  
Fatigue Properties ◽  
Bending Fatigue ◽  
Metallurgical Analysis ◽  
Single Tooth

In the present paper a research programme aimed at investigating both the bending and contact fatigue properties of an austempered ductile iron applied to gears is presented, in order to determine reliable values of the limits, which take into account the influence of the production process, to be applied in the design of gearboxes. The bending fatigue tests are performed according to the single tooth fatigue approach and the pitting tests are performed with a back-to-back rig. Metallurgical analysis is performed on the failed specimens, in order to understand the origin and the propagation of the failures and to appreciate the influence of the micro-structure on the performances obtained.

scholarly journals Gear Root Bending Strength: A New Multiaxial Approach to Translate the Results of Single Tooth Bending Fatigue Tests to Meshing Gears

Metals ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 863
Author(s):  
Franco Concli ◽  
Lorenzo Fraccaroli ◽  
Lorenzo Maccioni
Keyword(s):  
Material Properties ◽  
Bending Strength ◽  
Load Ratio ◽  
Fatigue Tests ◽  
Multiaxial Fatigue ◽  
Design Data ◽  
Bending Fatigue ◽  
Relevant Effect ◽  
Accurate Design ◽  
Single Tooth

Developing accurate design data to enable the effective use of new materials is undoubtedly an essential goal in the gear industry. To speed up this process, Single Tooth Bending Fatigue (STBF) tests can be conducted. However, STBF tests tend to overestimate the material properties with respect to tests conducted on Running Gears (RG). Therefore, it is common practice to use a constant correction factor fkorr, of value 0.9 to exploit STBF results to design actual gears, e.g., through ISO 6336. In this paper, the assumption that this coefficient can be considered independent from the gear material, geometry, and loading condition was questioned, and through the combination of numerical simulations with a multiaxial fatigue criterion, a method for the calculation of fkorr was proposed. The implementation of this method using different gear geometries and material properties shows that fkorr varies with the gears geometrical characteristics, the material fatigue strength, and the load ratio (R) set in STBF tests. In particular, by applying the Findley criterion, it was found that, for the same gear geometry, fkorr depends on the material as well. Specifically, fkorr increases with the ratio between the bending and torsional fatigue limits. Moreover, through this method it was shown that the characteristics related to the material and the geometry have a relevant effect in determining the critical point (at the tooth root) where the fracture nucleates.

An analysis of the effect of pressure angle change on bending fatigue performance in asymmetrical spur gears

2021 ◽  
pp. 146442072110266
Author(s):  
Seyit M Demet ◽  
Ali S Ersoyoğlu
Keyword(s):  
Fatigue Tests ◽  
Fatigue Performance ◽  
Spur Gears ◽  
Bending Fatigue ◽  
Pressure Angle ◽  
Angle Change ◽  
Single Tooth ◽  
Aisi 4140 ◽  
Tooth Flank ◽  
Torque Values

In this study, the fatigue performances of symmetrical and asymmetrical spur gears were analyzed by performing single tooth bending fatigue tests. The gears tested were determined to be symmetrical spur gears with a 20°/20° pressure angle, asymmetrical spur gears with a 20°/22° pressure angle, and asymmetrical spur gears with a 20°/25° pressure angle. These gears were made of AISI 4140 material. Single tooth bending fatigue tests were performed under variable loads. Considering the tests performed at the same torque values in asymmetrical spur gears with a 20°/22° pressure angle compared to symmetrical spur gears with a 20°/20° pressure angle, a statistically significant increase in performance was achieved at close to 90%. While gears with 20°/20° and 20°/22° pressure angles break at the tooth root, tooth flank fracture was observed in relatively high numbers of cycles in asymmetric spur gears with a 20°/25° pressure angle. It was observed that the formation of tooth flank damage negatively affected the fatigue performance.

Experimental and numerical investigation of the bending fatigue performance of symmetric and asymmetric polymer gears

2020 ◽  
Vol 234 (6) ◽  
pp. 819-834
Author(s):  
A Karthik Pandian ◽  
Sachin Singh Gautam ◽  
S Senthilvelan
Keyword(s):  
Form Factor ◽  
Correction Factor ◽  
High Stress ◽  
Fatigue Tests ◽  
Multiple Cracks ◽  
Bending Stress ◽  
Element Analysis ◽  
Bending Fatigue ◽  
High Stress Concentration ◽  
Bending Stresses

In this work, the bending fatigue strengths of injection-molded symmetric and asymmetric nylon 66 gears were evaluated experimentally, and the results were substantiated using numerical studies. The symmetric (20°/20°) and asymmetric (34°/20° and 20°/34°) configurations were subjected to bending fatigue tests under a load controlled mode. The bending stresses of the symmetric and asymmetric gears were predicted by quasi-static simulations using a commercial finite element analysis software. The form factor ([Formula: see text]) and the stress correction factor ([Formula: see text]) were computed using an adapted ISO method. The 34°/20° configuration exhibited the lowest bending stress and highest bending fatigue life among the tested configurations. The form factor exerted a decisive influence on the magnitude of the bending stress compared to the stress correction factor. For the considered loading conditions, deflection-induced load sharing occurred in the 20°/20° and 20°/34° configurations but was absent in the 34°/20° configuration. Failure analysis indicated that a high stress concentration caused multiple cracks in the fillets of asymmetric gears.

Gear root bending strength: statistical treatment of Single Tooth Bending Fatigue tests results

2021 ◽  
Author(s):  
Luca Bonaiti ◽  
Francesco Rosa ◽  
Prasad Mahendra Rao ◽  
Franco Concli ◽  
Carlo Gorla
Keyword(s):  
Bending Strength ◽  
Statistical Treatment ◽  
Fatigue Tests ◽  
Bending Fatigue ◽  
Single Tooth

Stress Calculation of Fillet Rolled Crankshaft in Bending Fatigue Tests

2010 ◽  
Vol 44-47 ◽  
pp. 2798-2804 ◽  
Author(s):  
Ke Bao ◽  
Ri Dong Liao ◽  
Zheng Xing Zuo
Keyword(s):  
Residual Stresses ◽  
Fatigue Test ◽  
Three Dimensional ◽  
Rolling Process ◽  
Fatigue Tests ◽  
Superposition Method ◽  
Bending Fatigue ◽  
Bending Fatigue Test ◽  
Bending Stresses ◽  
Three Dimensional Finite Element

The stresses around the fillet of fillet rolled crankshaft section in bending fatigue test are quite complicated, which include the residual stresses induced by fillet rolling process and bending stresses caused by bending fatigue test loads. In this paper, the corresponding three dimensional finite element models of roller- shaft are created and the residual stresses near the fillet of crankshaft section are obtained by flexible-flexible contact computation. Then the transient analysis of bending fatigue test based on modal superposition method is carried out and the bending stresses are got. The results of stress can be used to the bending fatigue design of crankshafts.

A Testing Device for Fatigue Crack Propagation Experiments on Bevel and Face Gears

2003 ◽  
Author(s):  
Mauro Filippini ◽  
Carlo Gorla
Keyword(s):  
Fatigue Crack ◽  
Crack Propagation ◽  
Fatigue Crack Propagation ◽  
Fatigue Testing ◽  
Testing Machine ◽  
Gear Wheel ◽  
Fatigue Tests ◽  
Testing Device ◽  
Bending Fatigue ◽  
Single Tooth

A testing device for performing single tooth bending fatigue tests on bevel and face gears is presented. Basically, it works as a normal gearbox in which the pinion acts as loading element while the gear wheel is kept fixed to the frame. The entire rig is installed in a servo-hydraulic torsion fatigue testing machine, so that torque amplitudes up 2200 Nm may be applied with convenient loading frequencies. Torque amplitude is measured by connecting the testing rig to the load cell of the testing machine. It’s possible to rotate the gearwheel at fixed positions so that a large number of teeth of the same wheel may be tested. If the tests are performed on teeth weakened by pre cracking, no special pinion is requested. The proposed testing rig may be employed for testing both bevel and face gears, by simply adapting the parts that keep the gearwheel fixed with the frame and by choosing the proper meshing pinion.

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