Cyclic Contact Stresses Research Articles

Analysis of fatigue damage of hot rolling work rolls coupled with wear effect

During the hot rolling process, the work roll experiences cyclic contact stress due to the deformation of the strip steel, as well as thermal stress from periodic heating and cooling. The surface failure of the work roll results from the combined effects of wear and fatigue damage. This study proposes a comprehensive approach to analyzing coupled wear and fatigue damage using a method based on the Manson-Coffin equation, modified slope formula, and the Miner criterion. Finite element models were developed to simulate simplified heat transfer and thermal coupling, taking into account the actual rolling parameters and high-temperature material properties of the work roll. The evolution of the physical field of the work roll during the rolling process was analyzed. The analysis of these models revealed that the maximum strain on the work roll occurred at the rolling exit and was predominantly influenced by temperature. The effects of rolling speed and temperature on work roll strain varied, with fatigue damage being significantly reduced when wear was considered compared to scenarios where wear was not accounted for, under the same number of cycles.

Comparative study on fretting friction and wear characteristics of different impregnated graphite for sealing application

Impregnated graphite has attracted considerable attention and has been widely used as an ideal sealing material in many fields. However, the service environment often contains vibrations, which can easily lead to severe fretting wear and leakage. In this study, the fretting friction and wear properties of resin-impregnated graphite and antimony-impregnated graphite were investigated. The results revealed that only gross slipping regime (GSR) occurred for two impregnated graphite. For resin-impregnated graphite, both abrasive and adhesive wear were discovered. Yet slight fatigue wear occurred on the worn surface of antimony-impregnated graphite at higher cyclic contact stress. The significant properties of the impregnated graphite can be attributed to a transfer film, which uniformly and stably adsorbs on the contact interfaces. This study provides an important basis for matching the industrial applicability of graphite-based modified sealing materials.

Surface Integrity of 20MnCr5 Laser Powder Bed Fusion parts subject to contact fatigue test

Additive Manufacturing (AM) is vital for industrial innovation, offering high potential for groundbreaking solutions. However, its successful implementation still depends on overcoming several challenges. Particularly, the assessment of surface integrity in AM-generated components, and its degradation when subjected to contact stresses presents an ongoing endeavor. Within this context, the current work delves into the study of the surface integrity of 20MnCr5 case-hardened samples manufactured through laser powder bed fusion (L-PBF), as well as delves into the investigation of surface failure progression when the samples are subjected to cyclic contact stresses. This study encompasses the analysis of residual stresses, hardness, and roughness of specimens manufactured through both additive and conventional production routes. The study’s findings show that it is feasible to attain analogous surface quality when proper finishing is applied to L-PBF samples. Although, despite the comparable surface quality, the contact fatigue performance was significative lower on the AM sample when compared to the conventionally manufactured. Additionally, additive manufacturing brings up new challenges to performance by presenting a heterogeneous stress distribution and sub-superficial porosity. In conclusion, to attain a desirable surface integrity for additive manufactured parts, further research should not only focus on improving the process parametrization but should also developing finishing routes especially oriented to additive manufacturing, considering therefore how the interaction between the manufacturing processes will evolve into a desirable surface integrity state.

Microstructure characteristics and formation mechanisms of white etching layer (WEL) and brown etching layer (BEL) on martensite bearing raceway

White Etching Layer (WEL) and Brown Etching Layer (BEL) always form on the surface of rails and bearings subjected to rolling cyclic contact stress. Because of the different properties between WEL/BEL and matrix, the cracks initiate and propagate easily, leading to failure ultimately. The WEL and BEL found on pearlite rail, have been widely investigated, but WEL and BEL on bainite rail and martensite bearing have not been further studied. Especially the BEL on martensite bearing raceways has rarely been reported. This study investigates the features of WEL and BEL found on martensite bearing raceway. The BEL locates in the middle of WEL and matrix, but its hardness values are the highest, which is different from the general results reported: WEL > BEL > matrix. The WEL is mainly consisted of austenite with coarse grains, ferrite and retained tempered martensite. The mainly composition of BEL is quenched martensite. Thermal effect is the main formation mechanism of the WEL and BEL in this study. BEL forms because the surface temperature exceeds Acm point, and then rapidly decreases. The formation of WEL may originate from two processes: (1) The austenitizing and slowly cooling process again of BEL; (2) The austenitizing and slowly cooling process of the matrix. WEL and BEL forming processes are closely related to the diffusion and redistribution of carbon. The contributory heat conduction and diffusion mechanism in the confined spaces of grease lubricated bearings have been also discussed in this study.

Study on surface fatigue and metamorphic layer of raceway of hybrid ceramic ball bearing in high-speed spindle for machine tool

Performance degradation of the precision bearing originates from the surface fatigue damage, which results in the premature failure of precision bearings in high-end spindle for machine tool. A metamorphic layer forms on the upper surface of the bearing raceway under the cyclic contact stress. The microstructure of the metamorphic layer is consisted of the nanocrystalline layers paralleled to the surface of the raceway. Stress-induced effect plays an important role in the transformation from the common martensite structure to the metamorphic layer, i.e., the grain refinement. Under the cyclic contact stress, the dislocation pile-up groups form in carbide particles, and the carbide particles can even be elongated and crushed. The cracks initiate and propagate near the metamorphic layer, which lead to the peeling band, the surface fatigue damage and premature failure of the precision bearings. This finding indicates that one solution to mitigating the surface fatigue in bearing might be the surface technology application.

A general mathematical modeling and finite element analysis of a strain wave gear possessing a double-circular-arc-with-a-common-tangent profile

In this study, the characteristics of a strain wave gear (SWG) with a double-circular-arc with a common tangent (DCACT) profile were simulated using two-dimensional (2D) and three-dimensional (3D) finite element analysis (FEA). First, theoretically generated tooth profiles for the flexible spline (FS) and circular spline (CS) of an SWG were developed according to the theory of gearing. An automated mesh-generating computer program was developed in Visual C++ to establish 2D and 3D finite element models of the SWG based on its derived geometry. An FEA was then performed to explore the meshing characteristics, including the stress distribution, torsional angle, torsional stiffness, and number of engaged teeth, of the SWG. Continuous meshing of multiple tooth pairs between the FS and CS from the 2D FEA verified the conjugation of tooth profiles. The coning effect on the FS during assembly of the SWG was also predicted and discussed from the 3D FEA results. The 3D FEA produced more accurate and practical results than the 2D FEA did. Additionally, 3D FEAs of a modified (with longitudinal crowning) and unmodified (without longitudinal crowning) FS were performed and compared. Finally, a 3D FEA of a modified FS was successfully conducted to predict cyclic contact stress, root stress, and transmission error.

Performance of selective laser sintered polyamide spur gear under dry and lubricated conditions

The durability of a selective laser sintered (SLS) polyamide gear was evaluated using an in-house gear test rig under dry and oil-lubricated conditions. The lubricated SLS gear exhibited inferior contact fatigue performance at lower torques than that under dry conditions. Cyclic contact stress coupled with sliding motion diffuses the lubricating oil into the porous subsurface and reduces the contact fatigue strength of the gear tooth. The failure of the SLS gear under dry conditions exhibited the polishing effect, thermal softening with surface cracks, and thermal bending at 1.8, 2.5, and 3.5 Nm, respectively, whereas failure of the SLS gear under the oil-lubricated condition was only pitting for all the considered conditions. The lubricated gear exhibited superior performance at a higher torque than the gears in the dry-running condition, owing to its improved thermal stability.

Performance of non-linear seabed interaction models for steel catenary risers, part II: global response

Fatigue response of steel catenary risers (SCR) in the touchdown zone (TDZ) is significantly affected by riser-seabed interaction. Non-linear hysteretic riser-seabed interaction models have been recently developed to simulate the SCR cyclic embedment into the seabed. Despite the advancements achieved in the prediction of non-linear hysteretic riser-seabed interaction, several inconsistencies have been recently identified in the nodal performance of some of the popular models. These limitations need to be resolved by proposing new models or improving the existing models. However, it is necessary to evaluate the influence of the identified shortcomings of the existing models on the global performance of the riser. In this paper, the influence of nodal inconsistencies observed in a popular riser-seabed interaction model on the global performance of the riser was comprehensively examined in the TDZ. The riser embedment profile, cyclic contact stress, contact stress envelop, mean shear force, cyclic bending moment, and consequently the cumulative fatigue damage was investigated. The study showed that the soil model overestimates the riser embedment and other global responses. Recommendations were made to overcome the identified shortcomings of the existing models in future developments.

A new damage-mechanics-based model for rolling contact fatigue analysis of cylindrical roller bearing

Abstract The cyclic contact stresses in cylindrical roller bearings are evaluated through the explicit finite element analysis with rolling the roller instead of moving a constant contact pressure in the computational domain. A new damage evolution equation in terms of the amplitude of octahedral shear stress is proposed, which considers the non-proportional variation of stress, and the material parameters in which are easily obtained from torsion fatigue testing data. Numerical simulations of crack initiation, crack propagation, and spalling are performed. The simulation results are consistent with the previous experimental results. Furthermore, the coupling effect between the contact stresses and fatigue damage is investigated, and the effects of contact loading on the fatigue life are studied.

Diffusion of Carbon in Steel Grippers Due to Cyclic Contact Stress

The stress-assisted diffusion of carbon atoms due to high-stress cyclic loading of serrations on a case-hardened steel gripper, leading to the redistribution of carbon near the surface of the serrations is explored in this paper. An elastic plastic finite element model coupled with simulation of stress-assisted diffusion of carbon is employed for the study. Kinematic hardening rule is used to estimate the dissipated plastic strain energy due to the contact stress and these results are transferred to the nodes of a very fine square grid. Potential gradient due to dissipated plastic strain energy coupled with modified Fick’s law are employed to simulate the stress-assisted diffusion of carbon near the surface of a serration on the gripper jaw. Measures for quantifying the redistribution of carbon are introduced, and the effect of the number of cycles and loading condition on the redistribution of carbon in steel are explored.

풍력발전시스템의 주 베어링용 0.18C-3.5Ni-1.5Cr-0.2Mo강의 침탄 표면특성

Characteristics of carburized surface layers in 0.18C-3.5Ni-1.5Cr-0.2Mo steels for main shaft bearings of wind turbines have been analyzed and evaluated before and after rolling contact fatigue tests. Mixed microstructure consisting of retained austenite and tempered martensite has been formed with compressive residual stresses in the surface hardened layers of the specimens showing uniform hardness distribution with value about Hv700 after vacuum carburizing and tempering. It has been found on the raceway of the layers of the specimens after rolling contact fatigue tests that the amount of retained austenite decreased and compressive residual stresses increased, resulting from cyclic contact stresses applied during the tests. It has been also revealed that higher durability of the bearings can be obtained through controlling the amount of the retained austenite in the surface of the bearing steels to be lower in this study.

Wear mechanisms experienced by a work roll grade high speed steel under different environmental conditions

High speed steels are used for the manufacture of hot mill work rolls. The rolls suffer a variety of degradation mechanisms, of which abrasive wear and thermal fatigue are the most understood. However, what is less well characterised is the role that oxidation contributes to the deterioration of the roll surface. In particular, the roll surface undergoes rapid thermal cycles (possibly up to 650 °C in one roll rotation), and is subjected to a high humidity environment, and of course, significant cyclic contact stresses. In this work, the relationship between the friction and wear of a work roll grade high speed steel (1.55% C, 7.70% Cr, 4.90% V, 2.00% Mo) and oxidation was investigated at 400, 500 and 600 °C for two different environmental conditions (water, both gaseous and liquid, and laboratory dry air). A rolling-sliding disc on disc configuration was employed with a 25 N load for a sliding distance of 111 km. The specific wear rate of the high speed steel discs was greater for the tests conducted in laboratory dry air compared to the tests with the presence of water. However, the specific wear rate of the dry tests was strongly temperature dependent, while for the wet tests, the wear rate was insensitive to temperature. The dry tests exhibited a combination of metallic and oxidational wear, while the wet tests were almost entirely oxidational, with a different oxide phase constitution to the dry tests. Surprisingly, the wet tests exhibited higher friction compared to the wet tests. The reasons for this and the difference in wear rates are discussed and related to the phase constitution of the oxide layer and the amount of oxide formed in each experimental condition.

Competition between wear and rolling contact fatigue at the wheel—rail interface: some experimental evidence on rail steel

Recent studies of the rail—wheel interface have shown that wear and rolling contact fatigue (RCF) are competitive phenomena. Wear, by removing the material from the contact surface, tends to limit the propagation of cracks formed by cyclic contact stresses. Several parameters influence these phenomena. This article studies the effects of various working conditions on the surface damage of railway steels. The competition between wear and RCF is particularly strong in dry rolling—sliding contacts, in which the damage severity of our test cases can be adequately predicted using the shakedown map. In wet contacts, RCF is prevalent: cracks rapidly propagate into the subsurface layer in response to hydraulic pressure penetration and then branch towards the surface causing severe damage (macroscopic pitting). The severity of this phenomenon depends strongly on the applied load and cannot be inhibited by wear due to the low friction. On the basis of these results, a general procedure is proposed to the structural integrity of rails.

Experimental and Numerical Characterization of a Rail Steel Behavior under Cyclic Contact Stresses

Wear and rolling contact fatigue interaction in rolling/sliding contact is an important topic in the research on structural integrity of rails and railway wheels. Wear is in competition with rolling contact fatigue, as it removes surface material layers, reducing cracks length and hindering their propagation. Cracks nucleate by accumulation of cyclic unidirectional plastic strain (ratcheting). In this paper a model for ratcheting assessment is discussed and applied to the UIC 900A steel, after a calibration based on experimental results. The experimental tests allow also a characterization of the crack formation condition for this material. By this model, a computer program is developed in order to simulate in a very short time the effect of a large number of load cycles, providing a tool for predicting crack formation and propagation rates.

The combined effects of crosslinking and high crystallinity on the microstructural and mechanical properties of ultra high molecular weight polyethylene

Ultra high molecular weight polyethylene (PE) has been used for more than forty years as the bearing surface in total joint replacements. In recent years, there have been numerous advances in processing conditions that have improved the wear resistance of this material. In particular, crosslinking has been shown to dramatically improve the wear behavior of this orthopedic polymer in simulator studies. This benefit to wear resistance, however, is accompanied by a decrease in mechanical properties such as ultimate tensile strength, ductility, toughness and fatigue resistance. This degradation to mechanical properties may have serious implications for devices with high stress concentrations or large cyclic contact stresses. Tailoring microstructure for improved structural performance is essential for implant design. In this work we examined the role of crystallinity and crosslinking on the microstructure and mechanical properties of PE. Crystallinity was increased with a high pressure process and crosslinking was obtained with gamma irradiation. Crystallinity was beneficial to fatigue crack propagation resistance and when coupled with crosslinking a polymer with both wear and fatigue resistance was obtained.

Inclined standing contact fatigue

ABSTRACTAn experimental method is presented, in which a sphere is repeatedly pressed against a surface with an inclined contact load. The method is a development of the normally loaded standing contact fatigue test. Experiments are performed for three inclination angles below the angle of friction and the results are compared to those of the normally loaded standing contact fatigue test. The influence of tangential load on endurance limit load, number of cycles to crack initiation, contact mark appearance and crack behaviour in the surface as well as in cut views are evaluated. The surface crack behaviour outside the contact mark is analysed based on the cyclic contact stresses in the test specimen. The trajectories of the largest principal stresses are followed in both the surface view and in the cut view on the symmetry plane. These stress trajectories are compared to the experimental crack results. The connection between the inclined standing contact fatigue cracks and surface distress micro‐cracks is also discussed.

Analysis of surface and subsurface of sliding electrical contact steel/steel in magnetic field

This paper reports the analysis of the surface and subsurface after the friction tests of a steel/steel sliding couple. Experiments were carried out on a pin-on-disc tribometer in ambient environment with a 10-mm-diameter pin under a normal load N=63 N and sliding linear speed v=0.38 m/s. During sliding, a DC electric current was passed through the contact. Simultaneously, an AC magnetic field was applied perpendicularly to the friction area. Experimental results showed that the presence of electric current and magnetic field around the tribocontact modifies the mechanical properties of the surface and subsurface. The mean friction coefficient changes from μ≈0.16 without electric current and magnetic field to μ≈0.26 with them, and its variation reduces considerably. The worn surfaces were smoother with magnetic field application than that without it, and the modification of subsurface structure was observed. The magnetic field and the electric current modify the mechanical and chemical properties of this ferromagnetic material in the sliding contact by interaction with cyclic contact stresses and increasing the temperature on the contact surface. We have characterized this interaction by an increase of the microhardness, the activation of oxidation on the surfaces, the difference of contact noise level and the changes induced in subsurface structure.

A Theoretical Study of Residual Stress Effects on Fatigue Life Prediction

Recently, the trend has been toward the use of the full subsurface stress field in rolling element bearing fatigue life prediction (stress field-based life models). By using the stress field-based bearing life models, more accurate assessments of such things as fitting practice and thermal treatments on the bearing performance are achieved. However, one aspect missing in most models has been the consideration of the changing residual stress during operation of the bearing. This study was conducted to investigate the time dependent residual stress on contact fatigue life predictions. This study concluded that the changes in residual stress during operation were most likely a fatigue reaction of the material to the pre-fatigue residual stress and cyclic contact stress fields. The materials fatigue response changes the instantaneous values of the material constants in most stress field-based life equations, thus making them in-calculable. As such, the pre-fatigue residual stress field should be used in the stress field-based models. Presented as a Society of Tribologists and Lubrication Engineers Paper at the STLE/ASME Tribology Conference in San Francisco, CA October 21–24, 2001

Experimental Tools for Characterizing Fretting Contacts.

The severe near-surface conditions associated with partial slip or fretting contact of interacting surfaces have been linked to premature and often catastrophic failure of a myriad of mechanical systems and components, including riveted aircraft structures, power generation systems and jet engines. Developing a mechanics-based characterization of these conditions through combined modeling and experimental efforts is a challenging task, confounded by factors such as an evolution of friction driven by interfacial wear and the multiaxial, non-proportional nature of the cyclic contact stress field. This paper presents results from the recent successful application of infrared thermal imaging techniques to measure near-surface temperature fields in a way that clearly discerns this change in friction coefficient. These thermal images illustrate the transition from sliding to partial slip conditions related to wear-induced increases in friction coefficient. The experimental temperature fields have also been juxtaposed with recorded histories of the requisite fretting fatigue loads and a finite element analysis of the fully coupled thermoelastic and heat conduction problems to obtain a validated model of the near-surface conditions responsible for fretting wear and fretting fatigue damage. The observed interfacial conditions have been combined with results from three-dimensional finite element modeling to assess the applicability of two-dimensional modeling approaches to contacting mechanical components of finite dimensionality. As an example, the thermography/FEM approach has been exercised to understand the influence of fretting on the fatigue failure of riveted aircraft structures.

Tribological characteristics of various surface coatings for rotary compressor vane

In developing rotary compressors that will use HFC refrigerants, the biggest challenge is overcoming wear of the various components. In particular, severe wear between the vane and roller sliding pair is a persistent problem. In this study several hard coatings were applied on vane surfaces in order to improve the tribological characteristics, and their performances were evaluated experimentally. Coatings with very high hardness, namely TiAlN and DLC, produced high friction and severe wear on the roller, and thus seem unsuitable for this application. Softer WC/C (tungsten carbide carbon) coatings formed durable tribo-films on the mating surface and showed good tribological properties. TiN coated vanes showed good wear resistance properties but produced high friction. Ion nitriding is not suitable for this application since the durability of ion nitride layer appeared to be insufficient to sustain the cyclic contact stress encountered in the vane–roller system.