Papers by Keyword: Hertzian Contact

Abstract: A finite element model with functionally graded materials is established. Furthermore, the distributions of the maximum contact stresses on monolithic substrates under Hertz contact conditions have been analyzed. The effect of the coating thickness is obtained by single-layer coating systems. With increasing the coating thickness, the distribution of maximum radial stress is moved from the coating surface to coating/substrate interface. Meanwhile, the depth of maximum shear stress is moved away from the interface. The location of the maximum shear stress within the multilayer coating systems is not changed. The deformation of the model is more serious with the increase of the applied load.The results can provide some insights regarding the design of the graded coatings in the engineering application.

Abstract: Tribological failure of machine components, such as wear and flaking failure is caused by contact stress concentration. However, observation of stress under contact load is a difficult task. Non-destructive methods that can be related to contact conditions are necessary to study and understand the phenomena caused by the contact stresses. In the present work, a scanning Hall probe microscope (SHPM) equipped with a GaAs film sensor was used to observe the three-dimensional magnetic fields in a long square bar specimen (JIS-SUJ2) before and after contact tests at 196N. It was found that the changes in the three-dimensional magnetic fields caused by spherical Hertzian contact are not affected by the location of the magnetization point on the specimen's surface.

Abstract: In order to understand the phenomena caused by the contact stresses occurring within surface, non-destructive methods that can be related to contact conditions are necessary. The main purpose of this work is to study the relationship between magnetization location and direction, spherical Hertzian contact and changes in the magnetic field asymmetry. In the present work, we used a newly developed GaAs film sensor-equipped scanning Hall probe microscope (SHPM) and observed magnetic fields in tool steel plates before and after contact tests under 196N load, at room temperature in air. Medium carbon low alloy steels specimens (JIS S45C) were used in the experiments. Around the contact test area, changes in ‘S’ and ‘N’ poles generated by magnetization using a square magnet block were investigated.

Abstract: Flaking failure of bearings is caused by crack growth and stress concentration. The contact conditions between ball, retainer and race affect the durability of the bearings. Non-destructive methods that can be related to contact conditions are necessary to study and understand the phenomena caused by the contact stresses. In the present work, a scanning Hall probe microscope (SHPM) equipped with a GaAs film sensor was used to observe the asymmetric distribution of three-dimensional magnetic fields in bearing steel plates (JIS-SUJ2) before and after light load contact tests of 19.6N. It was found that only vertical components of the magnetic fields are slightly affected by the spherical Hertzian contact. Furthermore, the change in the three-dimensional magnetic fields is asymmetric to the contact center and magnetization center.

Abstract: Failure of dies and molds is caused by wear and deformation during the metal sheet forming process. Die wear takes various forms, and the contact conditions in die-parts affect the strength of the components. Non-destructive methods that can be related to contact conditions are necessary to study and understand the phenomena caused by the contact stresses. In the present work, a newly developed scanning Hall probe microscope (SHPM) equipped with a GaAs film sensor was used to observe the three-dimensional magnetic fields in tool steel plates before and after contact tests at room temperature in air. It was found that the intensity of three-dimensional magnetic fields is only slightly affected by the spherical Hertzian contact. However, all of the three-dimensional components of the magnetic fields change significantly. The extent of the changes depends not on the distribution of stress under spherical Hertzian contact but on the initial distribution of the magnetic fields.

Abstract: This paper reports on an investigation of the relationship between the polishing force and the contact characteristics as the polishing tool approaches the boundary of a part surface during polishing. It was previous established that, for fixed abrasives, when the polishing tool is on the inner surface, the relationship between the polishing force and the pressure at the contact is approximately Hertzian and the contact is a full ellipse. The contact cannot be a full ellipse as the tool touches the boundary. The same polishing force could yield rather different pressure distribution, and thus rate of material removal, within the contact region. A model is proposed to relate the force and the pressure distribution as the tool is close to the edge of a part surface. The model takes into account changes of the contact near the edge. Experimental results are also presented to validate the proposed method.

Abstract: This paper reports on an investigation of the relationship between the polishing force and the contact characteristics as the polishing tool approaches the boundary of a part surface during polishing. It was previous established that, for fixed abrasives, when the polishing tool is on the inner surface, the relationship between the polishing force and the pressure at the contact is approximately Hertzian and the contact is a full ellipse. The contact cannot be a full ellipse as the tool touches the boundary. The same polishing force could yield rather different pressure distribution, and thus rate of material removal, within the contact region. A model is proposed to relate the force and the pressure distribution as the tool is close to the edge of a part surface. The model takes into account changes of the contact near the edge. Experimental results are also presented to validate the proposed method.

Abstract: The advanced actuator is a kind of swaying mechanism specially developed for certain aircraft, having low rotational speed and great torque. Utilizing criterions of mass equivalent and bending stiffness equivalent, this paper firstly applies simplification to the actuator, getting a piece of continuous beam with varying circular sections. According to the mounting condition of actuator, then establishes the finite element dynamic analyzing model, using I-DEAS software, selecting method of synchronous vector iteration, finishes normal modal analyzing. Next, carries Hertzian contact resonance analyses to ball straight-rotary pair, ball spline pair and ball unload pair, calculates contact resonance frequencies. Considering the resistance torque being moving still concludes formulae of quantity of contact resonance frequencies. Lastly, based on load spectra, makes a conclusion that antiresonance behavior of the actuator is well, showing that the design plan is feasible. Experimentation of prototype indicates that the above theoretical analyses are correct.

Abstract: Rolling contact fatigue initiated defects such as surface corrugation, head check, squat, are one of growing problems in high speed railway line. A squat is generally developed below the rail surface and grows parallel to surface until it turns down into rail. Estimation of critical crack size and crack growth rate is an essential to prevent rail from failure and develop cost effective railway maintenance strategy. In this study, we predict crack growth rate of a rail with a squat defect. For this purpose, a rail model with a squat defect is developed. Timoshenko’s beam theory is applied to calculate the global bending stress at the crack tip and Hertzian contact model is applied to calculate the local contact stresses at the surface of rail by simulating rolling over a railway wheel on a rail. Stress intensity factors are calculated from the total stress at the crack tip. Fatigue crack growth curve of 60kg rail steel is applied to calculated crack growth rate. Software to predict crack growth life through whole life cycle is developed. We expect that we can make a more cost effective rail maintenance strategy by considering the crack growth analysis for a defective rail.

Abstract: In this paper the formation of shear bands in columnar EB-PVD thermal barriers coatings is studied. In particular, critical parameters of nucleation of shear bands, such as contact pressure and initiation of cracks in the columns, are extracted from the experimental results. The pertinence of these parameters is discussed respecting to the stress field induced in the material during the indentation.