Papers by Keyword: Contact Fatigue

Abstract: This paper presents the influences of quenching technologies (classical, with cooling in magnetic field, cryogenic, with cooling in the ultrasonic field) on the dimensional stability in time and the contact fatigue behaviour of some elements of ball bearings made from 100Cr6 (RUL 1) steel. From the analysis of the experimental data obtained it has resulted that the use of ultrasound for martensitic quenching of these steels ensures changes to the properties favorable to elements of ball bearings and may represent an effective way of increasing the quality of bearings; the technology is relatively simple, it does not require substantial constructive changes in the quenching machines and no further investment of large values.

Abstract: The paper deals with an investigation of surface laser hardening characteristics on contact and bending fatigue resistance of a 42CrMo4 steel, being often used for manufacture of gear wheels. The aim of the experimental programme was to simulate the complex service loading of fairly large gears by two separate investigations, namely contact fatigue performed on a special, so called analogon machine and bending fatigue performed on high cycle fatigue resonance machines using three-point-bend (3PB) fairly large specimens. It was shown that after optimising the methodology and parameters of the laser hardening technology, contact fatigue resistance is very good, comparable with very expensive and time consuming thermochemical high-depth surface treatments. Bending endurance limit can be increased. The role of residual stresses resulting from the laser treatment was shown as decisive.

Abstract: Failure analysis on the GCr15 bearing steel and the 20CrMo carburized steel nuts was performed after two sets of fatigue tests of GD8020×1100 ball screw pair. By means of scanning electron microscopy observation, energy dispersive analysis and microhardness testing, it is found that there is an obvious indentation, slight pitting and microcracks on the raceway of the GCr15 bearing steel nut and shows the characteristics of contact fatigue failure. The nonuniformity of microstructure and the lower carbon and chromium content in the indentation, leading to local lower hardness, account for the nut failure. While the raceway of the 20CrMo carburized steel nut is more rough with scratches caused by the damaged steel balls so as to show the characteristics of wear failure. Therefore there are different failure ways for the different nuts made by different steels and heat treatments under the same fatigue testing condition.

Abstract: By means of chemical composition testing, scanning electron microscopy observation, metallographic observation and hardness gradient detection etc, analysis of the typical failure samples from a well-known brand GD8020×1100 ball screw unit in the fatigue test was carried on. Results show that there is no obvious surface wear of the ball screw, showing the normal contact fatigue failure. But severe surface wear happens on the raceway of nut A with obvious flaking and many local cracks; which is the main reason leading to the failure of ball screw unit. So effective measures to avoid earlier failure of the ball screw unit can be put forward by controlling the steel quality strictly and improving the hardness and depth of the hardened layer on the raceway of nut A.

Abstract: Rolling contact fatigue is a very complex process. The mechanism can only be described by speculative considerations. Because the loading conditions during the elastic- hydro- dynamical contact are not clearly described. The loading cycle runs within extremely short rates and structural alterations occur under high hydrostatic pressure. Widely unknown is therefore, how the materials conditions are influenced by these processes. But by means of simplified considerations an approach to the rolling contact fatigue process can be obtained. Following these conceptions simplifying quasi-static conditions are drawn. A lubricant film inhibits the metallic contact of the revolved bearing components. A HERTZian load stress will be accumulated over an elliptical contact area and within and beneath this contact area three dimensional stresses are acting. The materials strengthening can be described by the hypothesis of alteration of shape. During the fatigue period, the microstructure will be changed by micro- and macro- plastically deformation. By this residual stresses occur. These are superimposed to the operational -loading –stresses which change the distressing conditions of the material. The progressive plastically deformations accompanying the growing fatigue procedure cause perpetually alterations in the distress- conditions of the material. Structural alterations of the rolling contact fatigue process are shown by means of metallography as followed: by dark etching areas (DEA), and by white etching areas (WEA) showing bands, which are positioned beneath the contact area at an angle of 30° (30°WEB) and for instance at 80° (80°WEB), and furthermore by so called butterfly structures (butterflies with “white etched” flanks). All these white etching areas, regarding their morphological structure and the etching conditions, are commonly originated by two axial distressing. The three dimensional materials distressing within the roller-bearing component on the one hand and the two dimensionally originating of the WEA on the other seem to be an antagonism. But when the changes of residual stresses during the contact rolling fatigue process are to be analyzed, it is clear that this antagonism rises only virtually because there exists a real tri-axial stress condition, which tolerates a two axial distressing of the material. By the concept, that the growing plastically deformations cause residual stresses superposing the operational load stresses, the temporary cycle of the structural alterations and the local and angular positions of the 30° WEB can be explained.

Abstract: The article presents the research results referring to the analysis of the influence of finish treatment ( lathing, grinding, burnishing) on the contact fatigue of steel applied to marine pump shafts. The research was performed on a roller 40 mm in diameter made of 304L stainless steel. Within the research, the optimalization of burnishing technological parameters was conducted on account of the minimalization of Ra surface roughness coefficient as well as the maximalization of S_U degree of surface layer relative hardness [. The multi criteria optimalization conducted by min-max method [ with regard to minimum surface roughness as well as maximum degree of surface layer hardness demonstrated that burnishing process should be carried out at the following technological parameters: burnishing force 1.1 kN, burnishing speed 35 m/min, feed 0.13 mm/rev. In addition, the influence of the burnisher passes number on the surface layer quality was determined [.The paper will present the research results of contact fatigue examination of samples after finish machining.

Abstract: A model of gear contact has been established based on Hertz theory in this thesis, Analysis of non-standard gear contact fatigue life test process . For ha* take 1,1.15,1.25 and c* take 0.25,0.5 respectively ,the gear generates contact fatigue failure, then calculate the meshing ratio under different tooth high coefficients, and gear pairs state with fatigue testing time by the finite element method and orthogonal test. These data are compared with the results of specific experiments verified. They description that tooth height coefficients and headspace coefficients change have a great impact on gear contact fatigue life.

Abstract: A general method for calculating contact fatigue strength of Mine helical cylindrical gear was studied in this paper. Both the Solid model and finite element model were created in ANSYS. Based on the fatigue analysis module of the ANSYS Workbench, The contact fatigue strengths of the helical cylindrical gear pair were calculated, and corresponding contact fatigue lives and safety factors of two gears in any meshing position were obtained and shown in contour map. A simulation calculation for a pair of mine helical cylindrical gears was carried out. Simulation results show that calculation of the contact fatigue strength of helical cylindrical gear by this method is more scientific and reasonable than traditional empirical method.

Abstract: Based on the dynamic balance principle and contact fatigue properties of cylindrical gear pair, the influence factors of dynamics are researched and the meshing location for the maximum contact stress is accurately determined. Loading spectrum of contact stress is obtained by transient dynamic analysis. At the same time, the corresponding S-N curve for contact fatigue is described in a double logarithmic coordinate system. Then the finite element analysis on the contact fatigue life is carried out by ANSYS Workbench and safety factor for both gears are obtained. It has great significance for evaluating the reliability of the cylindrical gear pair.

Abstract: This paper deals with calculation procedure for lifetime determination of a large three-row roller slewing bearing. First, the contact force distribution between the rollers and the bearing raceway is determined both analytically and numerically. Then, the position and the magnitude of the maximum contact force are identified. In a separate numerical model finite element analyses are performed to determine the subsurface stress distribution as the result of contact between the raceway and different rollers. These stress fields serve as an input for the fatigue lifetime calculation, which is done in accordance with the stress-life approach (S-N). At the end the influence of roller geometry on the calculated fatigue life is presented.