Jamari

Experimental Investigation of Fully Plastic Contact of a Sphere Against a Hard Flat

In this paper we report the experimental investigation to evaluate the published models for the contact of a deformable sphere against a hard flat in the fully plastic contact regime. A new measurement method has been used to measure the contact area. The behavior of the mean contact pressure and the contact area as a function of the contact load are presented. Substantial differences are found between the measurements and the model predictions. A constant value of the mean contact pressure as the load increases is observed, however, the value is lower than the hardness, as often reported. The contact area is found to be a simple truncation of the sphere by a hard flat.

Numerical study of the load-carrying capacity of lubricated parallel sliding textured surfaces including wall slip

This article analyzes the combined effect of surface texturing and wall slip on the load-carrying capacity of parallel sliding systems. A new modified Reynolds equation with slip is proposed, based on the critical shear stress model, to reveal the hydrodynamic load-carrying capacity. A range of parameters such as texturing zone, texture cell aspect ratio, critical shear stress, and slip length are analyzed. It is shown that the optimal texturing zone length oscillates around 75% of the slider length. A slight shift of the optimized texturing zone toward the inlet of the contact is observed when the critical shear stress is increased. The numerical analysis also shows that there is a unique threshold value of the critical shear stress for every texture cell aspect ratio. When this ratio is increased, the threshold value increases, thus influencing the slip considerably. Slip has a positive effect on the load-carrying capacity for critical shear stress lower than the threshold value, whereas it has no effect on higher values. It is also found that in comparison with a solely textured surface, the load-carrying capacity of the combined textured/wall slip pattern can be increased by around 300% using the optimized slip parameters.

Numerical Study of Salat Movements for Total Hip Replacement Patient

Salat as a daily Muslim activitiy in praying contains several movements which are not suggested by orthopaedic doctor to be conducted by patient with total hip replacement (THR). Sujud and sitting are two movements in Salat which is recommended to be done above the chair for THR patients. There are lacks of scientific discussions about the consequences of the normal salat movement for Muslim THR patients. This paper observes the effect of these movements to the artificial hip joint in THR patient body. A three-dimensional finite element simulation is used to investigate the resisting moment, the contact pressure and the von Mises stress. An artificial hip joint model proposed by previous researcher is used in the simulations. The results show that sujud induces the impingement and plastic deformation whereas sitting is relatively safe to be conducted by THR patients. Some suggestions are also discussed with respect to the design of new artificial hip joint model which allows THR patients to conduct Salat in a normal way. The reduction of inset at the liner, the new profile at circumferential edge inner liner and the increase in the femoral head diameter can be considered as a guideline for new design of the artificial hip joint for Muslim.

The Effect of Repeated Impingement on UHMWPE Material in Artificial Hip Joint during Salat Activities

In Indonesia, a country with largest Muslim population in the world, the necessity to study the artificial hip joint which allows Muslim patients with total hip replacement to have normal Salat becomes important issues. This paper discusses the effect of impingement which occurs during one of the Salat movements. i.e. last tashahhud sitting motion. An artificial hip joint model, proposed by previous researcher from developed country, is simulated using finite element analysis to perform last tashahhud sitting motion. The result shows that impingement occurs and causes the plastic deformations and plastic strains in the acetabular liner component which is manufactured from UHMWPE material. The repetition of Salat movement induces repeated impingements and higher plastic deformation. It experiences dimensional change in the liner lip and has a potency to cause clinical failure of total hip replacement. A new design of the artificial hip joint is required to be proposed to avoid the repeated impingement and deformations.

Modeling of Repeated Rolling Contact on Rough Surface: Surface Topographical Change

An finite element analysis (FEA) of a repeated rolling contact over an elastic-plastic deforming rough surface is performed. The surface topographical change is calculated to determine the running-in phase to the steady-state rolling contact situation. A rigid hemisphere is repeatedly rolled over a rough flat aluminum surface and the effect of the contact load and the number of overrollings is studied. It is found that the change in surface topography due to the repeated rolling contact results in smoothening of the rough surface due to the flattening of the highest asperities. The result shows that the running-in of the repeated rolling contact takes place within the first few overrollings.

Finite element study of contact pressure distribution on inner and outer liner in the bipolar hip prosthesis

Wear in the hip prosthesis due to sliding contact as a product of human activity is a phenomenon which cannot be avoided. In general, there are two modelof hip prostheses which are widely used in total hip replacement, i.e. unipolar and bipolar models. Wear in the bipolar model is more complex than the unipolar model due to its contact motion. The bipolar model has two contact mechanisms while the unipolar model has only one contact mechanism. It means that the bipolar model has two wear positions, i.e. wear on inner and outer liner surface. Fortunately, wear phenomena in the hip prosthesis can be predicted by analytical or numerical method. Wear on the inner and outer liner surface in the bipolar model itself can be early predicted by contact pressure distribution that is obtained from contact mechanic analysis.The contact pressure distribution itself is an essential variable in wear equations. This paper is aimed to studythe difference of the contact pressure distribution on the inner and outer liner surface in the bipolar model. To obtain the contact pressure distribution at each surface, contact mechanic analysis on the inner and outer liner surface by analytical and numerical method were performed. Results showedthat there was significant difference of the contact pressure distribution on the inner and outer liner surface in the bipolar model. Therefore, it is expected that there is significant wear difference on the inner and outer liner in the bipolar model.

Closure to "Discussion of 'Experimental Investigation of Fully Plastic Contact of a Sphere Against a Hard Flat' " (2007, ASME J. Tribol., 129, p. 700)

The authors thank the reviewers’ Dr. Jackson and Dr. Green interest in the paper arising several issues for discussion. We agree with the reviewers that even in the fully plastic regime there will be some elastic recovery. However, this elastic recovery is very small relatively compared to the total deformation, which in turn, the effect to the contact area is very small as well. The measurement method used has a lateral resolution of 1 mo r about 0.1% of the measured plastic contact area. We have been investigating the effect of the roughness to the contact area and mean contact pressure, see 1. We concluded that in our experiments the effect of the roughness is negligible. We assume that no strain hardening occurred in our experiments. This assumption is based on hardness tests performed. A small increase in the hardness value of 1.15 to 1.2 GPa for copper was measured in the plastic contact area. Due to this small devia

Theoretical investigation of boundary slip on the hydrodynamic lubrication performance in pocketed bearings including cavitation

Boundary slip in bearings is becoming more and more popular to improve the hydrodynamic performance (pressure and shear stress). However, most of previously published works regarding textured bearings neglected the cavitation effect and make their results questionable. The main aim of this paper is to investigate the hydrodynamic performance of slip pocketed bearings considering cavitation by a theoretical approach. Cavitation was of particular interest with respect to pressure generation and shear stress. One main result presented here was that slip over the whole surface could retard the presence of cavitation and therefore the generated pressure and shear stress could be optimal. The work presented here leads to a design reference guideline that could be used by the designer/engineer to design slip pocketed bearings for improving the hydrodynamic performance.

Study the effect of wear rate on impingement failure of an acetabular liner surface based on finite element analysis

In this study, correlation of wear inside of an acetabular liner surface (ALS) and damage on an acetabular liner rim (ALR) due to impingement effect are investigated. The analysis included evaluation of the macrostructure of the damage based on visual investigation and computer simulation analysis. A commercial finite element method ABAQUS software package is used to simulate local impingement on the ALR due to wear depth variations (wear rates) inside the ALS. Here, the wear depth is based on the data of wear experiment from literature. The von Mises stress and contact deformation on the ALR at impingement is presented. In addition, the initial impingement angle is also presented to show the correlation between the wear inside of the ALS and the angle of impingement occurrence. The results show that the existence of wear inside of the ALS can increase the damage of the ALR due to impingement effect.

Finite element analysis of the impingement on the acetabular liner rim due to wear of the acetabular liner surface

This workstudies the impingement on the rim of acetabular liner due to wear on the surface of acetabular liner using finite element simulation. A three dimensional contact model between a femoral head and an acetabular liner was developed. There are three steps in this simulation, i.e. creating the virtualwear on the surface of acetabular liner, applying the load at the femoral head, and rotating the femoral head from neutral position till the impingement occurrence. The virtualwear is created based on the data of wear depth which was obtained from literature. Results showed that the wear on the acetabular liner surface wouldaffected the impingement occurrence, in which the impingement angle becomes narrow. In addition, the failure possibility of the acetabular liner rimwould become higher.