To aid in the design of future wearable health devices (WHDs), contact pressure between the distal forearm (wrist) and two different wrist-worn devices was investigated in this work. The first device included eight force sensors arranged in series along the length of a wristband to measure the pressure profile. The band also included a tensioner device for manually tightening the band while on a wrist. Testing was done on dummy wrists and the results were statistically significant supporting the hypothesis that areas of the wrist with lower radius of curvature will experience higher contact pressures generally and a faster rate of change in pressure as the band is tightened. The second band included a controller, actuator, and force sensors for actively controlling the contact pressure of a photoplethysmography (PPG) sensor on the wrist during user motion. A total of eight tests were performed on six human subjects to estimate previously unknown design parameters related to contact pressure control of a wrist-worn device. Participants were asked to perform several actions including tapping their finger at different rates, tossing a ball, wrist flexion and extension, and making a fist. The design parameters investigated were system stiffness, range in contact pressure caused by motion, range of motion in the radial direction required to maintain a desired pressure, arterial pulse pressure amplitude and its relation to pressure tolerance, and system response time required to maintain a constant pressure. System stiffness was observed to be greater during motion (dynamic) than during rest (static) and to increase with increasing contact pressure. The change in contact pressure caused by motion was around 18 kPa in some cases and the maximum range of motion to maintain a contact pressure was about 7 mm. The arterial pulse pressure amplitude ranged between 0.05 to 0.3 kPa. It was estimated that a maximum sensor platform speed of 30 mm/s or greater is required to maintain a constant contact pressure during large motion actions such as flexing the wrist up and down. Finally, no significant differences were observed in the PPG signal between states in which the contact pressure was controlled vs. not controlled.

After Total Knee Arthroplasty, contact stresses at the surface and stresses at the implant-cement-bone interface are directly related to the joint contact forces. These stresses are a major factor in wear and fatigue, aseptic loosening, stress shielding and osteoporosis. Implant contact stresses influence the wear and fatigue damage of the Ultra High Molecular Weight Polyethylene (UHMWPE) articulating surface, decreasing the longevity of the implant. The contact stresses are influenced by the kinematics, the bearing congruency of the articulating surfaces and insert thickness. Thus, various studies have focused on the prediction and optimization of kinematics at the joint interface, contact areas, and stresses in different knee implant designs. As a result, the successful total knee replacement designs depend on joint kinematics and the contact stresses. The objective of this study was to perform contact stress analysis on a newly designed surface guided knee implant, in order to evaluate the design with respect to the potential of polyethylene wear. In order to test the performance of this design, Finite Element Modeling (FEM) was used as a good medium to analyze the design’s specifications, and to evaluate the results of the stress analysis of the design. For validation and also comparison with previous studies, results of this study were compared with those of related work with similar loading and constraints. Based on the gathered data from FE analysis of the design, it can be concluded that the new surface guided knee implant shows lower peak contact pressure than other previously evaluated implants. / October 2015

no / Given that most of the working life of a brake pad life is spent in the bedded condition, it is important to examine the conditions of a fully bedded contact interface. An experimental and a numerical method are combined. Contact pressure and its effects (heat generation/partition and temperature rise) for the drag braking process with and without bedding are compared. The real contact area is also measured and found to be increased for the bedded interface. This results to the contact pressure being ¿more¿ evenly distributed than before. Spreading the contact pressure also results in increasing the total heat transfer between the disc and pad since now more heat can be transferred from the pad (where it is generated) to the disc. It is concluded that in order to have a reliable simulation it is recommended that the bedding-in effects are introduced in the simulations. / IMechE, RAE Travel Grant

Nowadays FE-simulations for sheet metal forming process are used to reduce the tryout phase in automotive industries. But the complex forming simulation processes are very challenging. One of the challenges is to create an FE-model which can be used to analyze the effects of cushion motion on the forming process. This thesis is focused on creating an FE model for two dies single cushion sheet metal forming press which can be used to analyze the effects of cushion motion on the contact pressure between the stamping tools and blanks. Using LS-PrePost a model with rigid stamping tools and cushion was created where the two blanks were of different thicknesses. After the model creation LS-DYNA was used for the simulations. The results showed that the cushion is moving in all DOFs and due to this movements, uneven contact pressure distribution is seen on the blanks and stamping tools.

No description available.

This thesis deals with the experimental description of friction between steel and wood materials, specifically laminated veneer lumber (LVL) and pine wood with two types of annual rings. It studies the influence of a number of different parameters on the coefficient of friction such as contact pressure, moisture content, fiber orientation in relation to the load direction, steel surface roughness, and horizontal load rate. First, the theoretical mechanical and physical properties as well as the coefficient of friction itself are described. This is followed by the description of the test setup including the test method and how the obtained data is exported, handled and processed and how the coefficient of friction is determined. The results study the influence of different parameters and show that the coefficients of friction for the smooth sliding plate tests vary in between 0.1 and 0.3, whereas tests with the rough sliding plate vary around 0.7. Factors influencing the coefficient of friction were found to be the different moisture content under all tested pressures, the different fiber direction under low contact pressure, the contact pressure itself, though under higher pressures the influence was found to be low, and the horizontal load rate under low pressures. The outcomes are further discussed in the discussion chapter.

In recent years, the interest in the design, construction and utilization of rubber tracks for agriculture and earth moving machinery has increased considerably. The development of such types of tracks was initiated by the efforts to invent a more environmentally friendly vehicle-terrain system. These tracks are also the result of the continuous effort to develop more cost-effective traction systems. A rubber-surfaced and friction-based prototype track was developed and mounted on the patented modification of a new Allis Chalmers four wheel drive tractor. The track is propelled by smooth pneumatic tyres by means of rubber-rubber friction and the tractive effort of the track is mainly generated by soil-rubber friction between the rubber surface of the track elements and terrain. The experimental track layer tractor, based on an Allis Chalmers 8070 tractor (141 kW) was tested on concrete and on cultivated sandy loam soil at 7.8%; 13% and 21% soil water content. The contact pressure and the tangential force on an instrumented track element, as well as the total torque input to one track, was simultaneously recorded during the drawbar pull-slip tests. Soil characteristics for pressure-sinkage and friction-displacement were obtained from the field tests by using an instrumented linear shear and soil sinkage device. By applying the approach based on the classical bevameter technique, analytical methods were implemented for modelling the traction performance of the prototype track system. Different possible pressure distribution profiles under the tracks were considered and compared to the recorded data. Two possible traction models were proposed, one constant pressure model, for minimal inward track deflection and the other a flexible track model with inward deflection and a higher contact pressure at both the front free-wheeling and rear driving tyres. For both models, the traction force was mainly generated by rubber-soil friction and adhesion with limited influence by soil shear. For individual track elements, close agreement between the measured and predicted contact pressure and traction force was observed based on the flexible track model. The recorded and calculated values of the coefficient of traction based on the summation of the traction force for the series of track elements were comparable to the values predicted from modelling. However, the measured values of drawbar pull coefficient were considerably lower than the predicted values, largely caused by internal track friction in addition to energy dissipated by soil compaction. The tractive efficiency for soft surface was also unacceptably low, probably due to the high internal track friction and the low travel speeds applied for the tests. The research undertaken identified and confirmed a model to be used to predict contact pressure and tangential stresses for a single track element. It was capable of predicting the tractive performance for different possible contact pressure values. / Thesis (PhD (Argricultural Engineering))--University of Pretoria, 2007. / Civil Engineering / Unrestricted

No description available.

Master’s thesis deals with development of software application to calculate contact pressure in eleastohydrodynamic lubricated contact in order to use previously obtained data of the lubricating film thickness. The introduction contains a short overview of methods used for the study of film thickness and contact pressure. Custom work includes a contact pressure solution derived from a film thickness, a description of the developed software and analysis of algorithms used for its compilation. The last part deals with the verification of algorithm, application of software for calculating the contact pressure on the rough surface and analysis of the results. The conclusion includes a summary and possible application of software in practice.

Diploma thesis includes design of bearings of steering joints of tandem vibratory pivot-steering roller Ammann AV 95-2, design of bearings of steering joints of tandem vibratory with new type of steering kinematics and calculation and comparison of contact pressures between drum and soil for different angles of turn of front and rear drum for different types of tandem vibratory rollers. Comparison of contact pressures is realised for pivot steering roller AV 95-2, articulated tandem roller AV 80 X, articulated tandem roller with modified configuration of steering-joints and tandem roller with new type of steering kinematics.