Investigation of running-in process based on surface roughness parameters, real contact area ratio and tribological properties

The running-in process is the initial process for the new moving parts wearing against each other to establish the shape adjustment that will regulate them into a stable relationship for the rest of their working life. The objective of this research is to investigate and evaluate the running-in process by using disk-on-block line contact device. Due to its empirical nature and well-ploughed analysis, an asperity micro-contact model is considered. The experiment is performed by varying the surface roughness of the block with rigid smooth sphere surface under specific condition. The effects of surface roughness, load, speed, and lubrication on the running-in behaviour is studied. The running-in process encourage plastic deformation of asperities and created microstructural changes on contact surfaces. The theoretical and experiment result shows that the plasticity index ps, surface roughness parameter b, real contact area ratio * A0 and specific film thickness l is influenced by the running-in process.

An Effect of Bearing Surface Angle at Bolt Head on the Nut Factor and Contact Area Ratio in Tightening Bolted Joints

Bolted joints are used in many industrial products such as mechanical structures, automobiles, airplanes, chemical plants, and so on. In designing bolted joints, the bolt preload in the joints should be determined appropriately and rationally for preventing accidents due to bolt loosening and fracture. Also, in actual bolt tightening, it is important that the bolts should be fastened with a designed bolt preload range. Several methods for tightening bolts are well known, one of which is the torque clamping method. In this method, the designed bolt preload can be obtained by a controlled tightening torque. The relationship between the tightening torque and bolt preload is assumed to be linear in the elastic range, and the bolt preload is often calculated from the tightening torque using the nut factor. However, in some cases, where the relationship between the tightening torque and the bolt preload is not linear. One of the reasons is the effect of bearing surface angle at bolt head. In this study, the effect of the bearing surface angle at the bolt head on the nut factor is examined experimentally. Also, it is known that the bearing surface angle at the bolt head affects the contact stress at the bearing surface of the joint member. The contact area ratio is newly proposed and obtained. As a result, a method to obtain an appropriate bearing surface angle at the bolt head and tightening torque range is proposed, taking the effect of contact area ratio factor into account.

Fluid wetting infiltration mechanism at the micro-contact zone boundary of rubber–glass interfaces

Purpose This paper aims to clarify the fluid infiltration mechanism at the micro-contact zone boundary of rubber-glass interfaces. Design/methodology/approach An in situ observation instrument was putted up; then the fluid infiltration process was recorded. Experimental results indicated that the fluid infiltration was more likely to occur in a high-contact-area-ratio zone, and the path order of fluid infiltration was first inner normal to the boundary of micro-contact area, and then along the boundary, at last external normal to the direction of boundary. Findings By analysis, capillary pressure is the driven force of fluid at interfaces. The micro-channel size at higher-contact-area-ratio zone is smaller, and the capillary pressure is bigger. Moreover, along different section directions of wedge-shaped region, the horizontal driving force of fluid is different due to difference of conical angle. Originality/value The main contribution of this study is proposing a new wedge-shaped model for better understanding the phenomena of fluid infiltration at rubber contact interfaces. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-10-2019-0453

Dynamic contact area ratio in shoulder instability: an innovative diagnostic technique measuring interplay of bony lesions

Purpose The hypothesis of this study is that Dynamic Contact Area Ratio of the humerus and glenoid, measured with CT scans, is significantly reduced in patients with anterior shoulder instability compared to the Dynamic Contact Area Ratio in a control group of people without shoulder instability. Methods Preoperative CT scans of patients who underwent surgery for anterior shoulder instability were collected. Additionally, the radiologic database was searched for control subjects. Using a validated software tool (Articulis) the CT scans were converted into 3-dimensional models and the amount the joint contact surface during simulated motion was calculated. Results CT scans of 18 patients and 21 controls were available. The mean Dynamic Contact Area Ratio of patients was 25.2 ± 6.7 compared to 30.1 ± 5.1 in healthy subjects (p = 0.014). Conclusion Dynamic Contact Area Ratio was significantly lower in patients with anterior shoulder instability compared to controls, confirming the hypothesis of the study. The findings of this study indicate that calculating the Dynamic Contact Area Ratio based on CT scan images may help surgeons in diagnosing anterior shoulder instability. Level of evidence III.

Critical shoe contact area ratio for sliding on a tennis hard court

Dimples have been used in the design of some modern tennis shoe outsoles to enhance sliding ability on hard courts. Experiments were performed with bespoke rubber samples possessing various numbers of holes, which served to simulate dimples in tennis shoe treads. The aim of the research was to assess the effect of contact area on sliding friction. As the ratio of holes to solid rubber increased, a critical ratio was reached whereby the static friction coefficient decreased by more than 11% for tread-to-court pressures comparable to real tennis play. Although this study analyzed bespoke rubber samples and not actual tennis shoe treads, shoe manufacturers should be interested in the existence of a critical dimple ratio that could aid them in the creation of tennis shoes suited for sliding on hard courts.

Finite-Temperature Multiscale Simulations for 3D Nanoscale Contacts

A finite-temperature analysis of a multiscale model, which couples finite element and molecular dynamics, is presented in this paper. The model is evaluated by the patch test and demonstrates its capacity. Then, the multiscale scheme is used to study 3D nanoscale contacts. The linear relationship between the contact area ratio and load is observed at small loads, but the temperature effect is small. However, the change in the root mean square (RMS) of heights depends on the temperature at high loads.

The Surface Parameters Analysis of Magnesium Alloys Sheet during Warm Isothermal Forming

This study uses the finite element method (FEM) to predict the workpiece surface parameters, including contact area ratio and surface roughness, of asperity flattening in indentation and sliding contact for magnesium alloys sheet during warm isothermal forming. Contact area ratio and surface roughness are investigated for different process and material parameters, such as sliding distance, temperature, normal pressure and bulk strain rate by finite element analysis. The predicted results of the surface parameters from the finite element analysis are in good agreement with the results obtained from experiments.