Contact Fatigue Characteristics Research Articles

An Investigation of the Contact Fatigue Characteristics of an RV Reducer Crankshaft, Considering the Hardness Gradients and Initial Residual Stress.

The crankshaft is one of the core components of a Rotate Vector (RV) reducer. The fatigue life of the RV reducer is severely hindered by fatigue failure on the eccentric cylindrical surface of the crankshaft. The hardness gradients and residual stress in the crankshaft, associated with machining operations, exert an enormous impact on the rolling contact fatigue (RCF). In this work, a finite element method (FEM)-based three-dimensional elasto-plastic contact model is established to calculate the stress-strain field by taking hardness gradients and initial residual stress into account. The RCF characteristics of an RV reducer crankshaft is investigated by applying modified Fatemi-Socie (FS) multiaxial fatigue criterion. The results indicate that initial residual stress plays an influential role in the fatigue damage by altering the distribution of the maximum normal stress near the contact surface. The modified FS fatigue criterion could better consider the effect of initial residual stress and the shear stress, which significantly improves the prediction accuracy of the contact fatigue life model. The contact fatigue performance could be considerably improved by designing appropriate shot peening parameters to obtain optimized residual stress distribution. Therefore, the technique presented may serve as an important guideline for the anti-fatigue design of an RV reducer crankshaft.

Effect of deposition material and heat treatment on wear and rolling contact fatigue of laser cladded rails

To develop a laser cladding technique for repairing rail surface damages due to rolling contact, wear and rolling contact fatigue characteristics of a set of laser cladded rails were investigated using a roller-on-disc test machine. Three deposition materials 410L, SS420 and Stellite 6, were chosen to clad a premium hypereutectoid steel rail under two different heat treatment processes. In the first heat treatment, only preheating at 350 °C was conducted and in the second heat treatment, preheating at 350 °C, post-heating at 350 °C (1 h) then slow-cooling to room temperature was conducted. Preheating the substrate was insufficient to prevent martensite formation resulting from the rapid cooling rate, whereas post heat treatment was beneficial for refining the lamellar spacing and eliminating martensite formation in the clad layer and heat affected zone. Following the roller-on-disc tests, wear loss was calculated from wear track profiles using a laser optical profilometer. The level of surface degradation, surface cracking and spalling was investigated using an optical microscope. Experimental results revealed that SS420 cladding had the highest wear resistant behaviour but severe surface cracks and spalling were found in the worn area. Stellite 6 cladding showed similar wear resistance as the parent substrate rail and the best fatigue resistance behaviour among the three cladded rail samples. Based on this research, Stellite 6 is the most promising deposition material for repairing rails by laser cladding.

Experimental investigation on the effect of shot peening on contact fatigue strength for carburized and quenched gears

Contact fatigue is one of the main failure modes of the gear. The contact fatigue test of gear is not only an important way to understand the capacity of gear, but also the data base in product design. In order to obtain the contact fatigue characteristics of 20CrMnMo carburized and hardened gears with or without shot peening, this paper presents a method combined with up-down test method and the grouping test method for contact fatigue test of gears. The optimal configuration scheme of gears is also given to obtain experimental data with the least specimens. The R-S-N curves considered confidence level is fitted by the lognormal distribution, to obtain the fatigue limiting stress values under different reliability, which provides the basic test data for the finite life design and high reliability design of the contact fatigue of the gears. The experimental results show that the shot peening treatment can significantly improve the contact fatigue strength of the gear, thus improving the service life.

A Subscale Experimental Investigation on the Influence of Sanding on Adhesion and Rolling Contact Fatigue of Wheel/Rail Under Water Condition

With a subscale rolling-sliding apparatus, the objective of this study is to explore the adhesion and rolling contact fatigue characteristics of wheel/rail rollers with sanding under water condition. Sanding improves adhesion coefficient but aggravates the surface damage of wheel and rail materials. With the particle diameter and feed rate increasing, the adhesion coefficient is further improved. However, the surface damage (spalling and pits) becomes severer as well as the surface roughness. Note that pitting is a special damage type when sanding is used to improve the adhesion. Big pits and fatigue cracks appear on subsurface under larger particle diameter and feed rate conditions. Severe cracks initiate from big pits and develop into material to a depth, which results in bulk material breaking.

The evaluation of contact fatigue strength for 20MnCr5 carburized gear

A FZG test rig for determining the contact fatigue characteristics of gear teeth was used in this paper. Under the range of operating conditions, experiments were performed by using standard spur gear test specimens which were made from 20MnCr5 gear alloy steel. Test rig, spur gear test specimens, the properties of the gear material were also introduced as well as the method to determine the stress levels. After the test, a small spalling pitting phenomenon was observed in the vicinity of the test pinion pitch line which is close to the gear tooth root portion. The tooth is subjected to the highest load due to the single tooth pair contact. The test data was analyzed and processed by statistical methods, and the equation parameters of gear contact fatigue and the contact fatigue limit were obtained. The analyzed results showed that the three-parameter Weibull distribution was best to fit the given stress for the contact fatigue life of 20MnCr5 carburized gear with better precision and adaptability. Finally, the P-S-N (Probability-Stress-Life) curves for the contact fatigue strength had been obtained by the reliability theory. It would provide a reliable basis for the reliability design for 20MnCr5 carburized gear fatigue life.

On microstructure and properties of Si modified 100Cr6 bearing steels

As an alloying element to increase the resistance to softening during tempering, silicon content was modified to investigate its effect on the microstructure and properties of 100Cr6 bearing steel. It turned out that increasing the silicon content brought about two difficulties in the manufacturing process, promoting the decarburisation during heating and/or hot rolling and retarding the spheroidisation of cementite. The maximum size of non-metallic inclusions was predicted to reduce evidently with increasing silicon content, although the total oxygen content in steels was nearly the same. There has been no fine carbide precipitation during tempering that can be attributed to the increasing silicon content, leading to the stabilisation of retained austenite due to the diffusion of carbon atoms from martensite. As a result, the new Si modified high carbon chromium bearing steel showed superior rolling contact fatigue characteristics to conventional steel.

ROLLING CONTACT FATIGUE CHARACTERISTICS OF SAE52100 BY ULTRASONIC NANOCRYSTAL SURFACE MODIFICATION TECHNOLOGY

UNSM(Ultrasonic Nanocrystal Surface Modification) technology has been applied to test specimens of bearing rings and rollers made of SAE52100. Mechanical properties, especially rolling contact fatigue characteristics, are analyzed using two-roller test and 6-ball test before and after UNSM treatment. The main effects to improve rolling contact fatigue characteristics by UNSM treatment are explained in the view points of residual stress, hardness and surface topology.

Influence of shot peening on the surface durability of thermomechanically treated En 24 steel spur gears

En steel, in untreated and thermal treated conditions, with and without shot peening, were tested in a back-to-back gear test rig. Their contact fatigue characteristics were studied and S–N curves have been established. Contact fatigue strength of shot peened gears for a given life showed an improvement in relation to unpeened gears.

Bending fatigue and contact fatigue characteristics of carburized gears

In order to assure reliability, the manufacture of gears for power transmission in high load bearing applications requires precise control of a wide range of processing parameters during manufacture, aimed at achieving specific material properties. Process selection and control in forming and heat treatment operations plays a crucial role in gear production, and must start at the design stage. Material selection, choice of forming processes, thermochemical and heat treatment operations, surface finish and condition will ultimately determine the integrity and performance limits of the gears. An ongoing research programme by Birrana Engineering, Adelaide, and the University of South Australia involves the evaluation of materials, process route and process control used in the manufacture of a range of gears and relates these factors to fatigue resistance, with the aim to reduce production costs and improve gear quality and reliability. The results of single tooth bending fatigue, and contact fatigue tests on production gears manufactured from EN39B steel (steel A), and experimental steels B, C and D (heat treatment details restricted for commercial reasons) are presented and discussed.