Rolling Contact Fatigue Machine Research Articles

Effect of dynamic windblown sand environments on the wear and damage of wheel-rail under different slip ratios

Although the railways in windblown sand areas has been continuously developed in recent years, the effect of dynamic windblown sand environment on the wear and damage of wheel-rail under different slip ratios is still unclear. This work focused on the effect of Gobi and desert dynamic windblown sand environments on the wear and damage behaviors of wheel-rail under different slip ratios using a twin-disc rolling contact fatigue machine. The corresponding experiments in dry condition (without wind and sand) were also performed for comparison. The results indicated that in these three conditions (Gobi, desert and dry), their trends of adhesion coefficient with slip ratio were not exactly the same. The wear rate of wheel and rail in these three conditions could be ranked as: dry > desert > Gobi. As the slip ratio increased, the fatigue wear of wheel and rail gradually aggravated. Furthermore, the oxidative wear of wheel also gradually exacerbated, especially in Gobi dynamic windblown sand environment. Based on the results of experiments and finite element simulations, the interaction mechanism between sand and wheel-rail interface was proposed and the reasons for wear reduction in dynamic windblown sand environments were summarized.

Crack observation and subsurface stress evaluation in carburized steel (SCM415) using one-point rolling contact fatigue machine

Crack observation and subsurface stress evaluation in carburized steel (SCM415) using one-point rolling contact fatigue machine

Understanding microstructure-evolution-dependent fracture behaviors in pearlitic steels

Microstructure evolution or degradation has been well recognized to be closely related to the formation of microcracks in pearlitic rails and wheels. The rolling contact fatigue machine was employed to simulate the rail–wheel contact, and the microstructure evolution and crack formation of pearlitic steels subjected to rolling–sliding contact loading were then experimentally characterized. To further quantitatively predict the fracture behaviors, a phase-field model was herein established to investigate the cyclic loading-driven microstructure evolution and the microstructure-dependent fracture resistance in pearlite. The coupling of microstructure evolution and crack propagation was realized through the introduction of two-set order parameters, i.e., the crack field and the microstructure field, and the microstructure-dependent fracture toughness. The proposed model can predict the fracture resistance of microstructure at different depths from the contact surface, after different rolling cycles and with different initial pearlitic microstructures, which can shed light on the design of damage-resistant microstructure of pearlitic steels.

Observation of Subsurface Crack of Carburized Steel (SCM415) under Single-Ball Rolling Contact Fatigue over 10<sup>7</sup> Cycles

Bearing fails due to the flaking failure which is caused by the subsurface cracks. The observation of the subsurface cracks is not easy beacause the cracks propagate inside the material. In order to observe the whole subsurface cracks, we performed rolling contact fatigue (RCF) tests of carburized SCM415 until over 107 cycles with the single-ball RCF machine. After the RCF tests, we directly observed the subsurface cracks.

Influence of a WC/a-C:H tribological coating on micropitting wear of bearing steel

The focus of this work was to evaluate the use of a WC/a-C:H coating, specifically designed to withstand rolling contact fatigue, to mitigate micropitting damage on through-hardened AISI 52100 bearing steel. This was accomplished by conducting experiments with various combinations of coated discs and rollers using a three-disc-on-roller rolling contact fatigue machine. In addition to testing coated and uncoated contacts, discs and rollers with three hardness levels and different surface roughness values were also evaluated. Upon the completion of this work, it was observed that the onset of micropitting damage was affected by the hardness of the asperities on the mated roller and disc samples. It was also observed that the coated surface can cause abrasive wear damage on an uncoated surface if the coating is applied to a surface that has a roughness Rq≥0.5μm. If the coating is applied to a smoother roller surface (Rq≤0.26μm), the coating is able to mitigate micropitting damage on the roller surface without causing high abrasive wear rates on the disc surfaces.

Observation of Crack Initiation from Inclusions in Rolling Contact Fatigue Tested Specimens, Using a Newly Developed Single-Ball Testing Device

In order to obtain experimental data to investigate the mechanism of crack initiation and propagation, an innovative rolling contact fatigue (RCF) machine was developed. Compared to the conventional thrust type RCF machine the new device enables more efficient RCF testing and observation of subsurface cracks. Experimental data and information on inclusions and micro-cracks were obtained through observation by a laser confocal microscope and comparison with stress analysis. The depth of detected crack initiation is strongly correlated with the stress distribution.

Coating of Ti64 Bearings in Air by Using a Q-Sw Laser

The influence of surface oxidizing using a Q-sw laser on the wear loss of titanium-4Al-6V (Ti64) alloy during rolling contact fatigue is investigated. Titanium components are widely appreciated for their superb biocompatibility, high strength to weight ratio and corrosion resistance. Due to the above mentioned advantages titanium bearings are a popular choice in applications requiring high strength, light weight, and minimum maintenance (for example, aerospace and defence industries). In these rolling contact applications however issues such as fretting and wear related problems are a common occurrence as the tribological properties of titanium alloys are inferior to those of other metal alloys, such as steel. In an attempt to tackle this problem, a Q-sw laser was used in this work to coat Ti64 bearings with complex titanium oxide layers in a closed chamber without any protective gas. Non-coated and coated samples were tested under water by using a thrust-type rolling contact fatigue machine. The morphology and crystallographic texture of the layers were observed by laser confocal microscope, scanning electron microscope and X-ray diffraction. The wear loss of the coated samples was at least fifty-fold lower than that of the non-coated bearings and a 3-fold increase in the maximum load capacity compared with TiN layers was achieved.

Coating of Ti64 Bearings in Air by Using a Q-Sw Laser

The influence of surface oxidizing using a Q-sw laser on the wear loss of titanium-4Al-6V (Ti64) alloy during rolling contact fatigue is investigated. Titanium components are widely appreciated for their superb biocompatibility, high strength to weight ratio and corrosion resistance. Due to the above mentioned advantages titanium bearings are a popular choice in applications requiring high strength, light weight, and minimum maintenance (for example, aerospace and defence industries). In these rolling contact applications however issues such as fretting and wear related problems are a common occurrence as the tribological properties of titanium alloys are inferior to those of other metal alloys, such as steel. In an attempt to tackle this problem, a Q-sw laser was used in this work to coat Ti64 bearings with complex titanium oxide layers in a closed chamber without any protective gas. Non-coated and coated samples were tested under water by using a thrust-type rolling contact fatigue machine. The morphology and crystallographic texture of the layers were observed by laser confocal microscope, scanning electron microscope and X-ray diffraction. The wear loss of the coated samples was at least fifty-fold lower than that of the non-coated bearings and a 3-fold increase in the maximum load capacity compared with TiN layers was achieved.

Rolling Contact Fatigue of Titanium Alloys Coated by Gas Nitriding Using a Q-Sw Laser

The influence of gas nitriding of commercial pure titanium and Ti-6Al-4V (Ti64) alloy by using a Q-sw laser on the wear loss during rolling contact fatigue is investigated. Despite very good biocompatibility, high strength to weight ratio and corrosion resistance, the tribological properties of titanium alloys are inferior to those of other metal alloys, such as steel. Fretting and wear related aspects become important issues when titanium alloys are used in rolling contact applications. Titanium bearings are employed in applications requiring high strength, light weight, and minimum maintenance (for example, aerospace and defense industries). In this work, a Q-sw laser was used to coat pure commercial titanium and Ti-6Al-4V bearings with TiN in a closed chamber in nitrogen atmosphere. The samples were tested under water by using a thrust-type rolling contact fatigue machine. The microstructure, morphology and crystallographic texture of the layers were observed by laser confocal microscope, scanning electron microscope and electron backscatter diffraction (EBSD). By optimizing the laser processing parameters, such as laser scanning speed, power and beam diameter, thin TiN coats of 1 to 3 mm were produced. The wear loss of the coated samples was at least ten times lower than that of the uncoated bearings.

Wear Resistance Improvement of Titanium Bearings by Laser Gas Nitriding

The influence of gas nitriding of commercial pure titanium and Ti-6Al-4V (Ti64) alloy by using a Q-sw laser on the wear loss during rolling contact fatigue is investigated. Despite very good biocompatibility, high strength to weight ratio and corrosion resistance, the tribological properties of titanium alloys are inferior to those of other metal alloys, such as steel. Fretting and wear related aspects become important issues when titanium alloys are used in rolling contact applications. Titanium bearings are employed in applications requiring high strength, light weight, and minimum maintenance (for example, aerospace and defense industries). In this work, a Q-sw laser was used to coat pure commercial titanium and Ti-6Al-4V bearings with TiN in a closed chamber in nitrogen atmosphere. The samples were tested under water by using a thrust-type rolling contact fatigue machine. The microstructure, morphology and crystallographic texture of the layers were observed by laser confocal microscope, scanning electron microscope and electron backscatter diffraction (EBSD). By optimizing the laser processing parameters, such as laser scanning speed, power and beam diameter, thin TiN coats of 1 to 3 m were produced. The wear loss of the coated samples was at least ten times lower than that of the uncoated bearings.

Residual stresses and retained austenite evolution in SAE 52100 steel under non-ideal rolling contact loading

Residual stresses are introduced and modified during manufacturing as well as by normal use under rolling contact loading. Operations such as heat treatments, shot peening, grinding, etc., are known to alter the magnitude and distribution of residual stresses. Our work revolves around the changes in magnitude and distribution of residual stresses, as they relate to deformation and the strain induced transformation of retained austenite. The residual stresses and retained austenite measurements were carried out using X-ray diffraction techniques. The rolling contact fatigue lives of different variants of SAE 52100 bearing steel were evaluated in a 5-ball-rod rolling contact fatigue machine under testing conditions leading to surface nucleated failure, i.e. non-ideal rolling contact. The tests were accelerated by applying well controlled micro-indentations on the wear track. The contribution of the residual stresses and amount of retained austenite to the rolling contact fatigue life were analyzed.