Hydrodynamic modelling of hydrostatic magnesium extrusion

Wilson’s hydrodynamic model of the hydrostatic extrusion process is extended to meet the geometry found on residual billets. The transition from inlet\ud to work zone of the process is not considered sharp as in the model of Wilson but as a rounded edge, modelled by a parabolic function. It is shown that\ud this rounded edge has a considerable influence on the predicted film thickness. Furthermore, it is shown that for hydrostatic extrusion of magnesium with castor oil as pressure medium, it is not possible to generate full film lubrication in the work zone of the hydrostatic extrusion process

The effect of highly elongated micro-contacts on rolling contact stress field

This study presents a boundary element model to analyze contact pressure distribution and the subsurface stress field in rough rolling elements. The methodology is demonstrated by the stress field of the backup roll and work roll in the cold/temper rolling process and characterized by a parallel orientation of roughness lay with rolling direction, resulting in a cluster of highly elongated elliptical micro-contacts. The numerical outcomes revealed that the amplitude of in-plane and out-of-plane shear stress components are strongly dependent on the ellipticity of the micro-contacts. Comparison with experimental results shows that the crack plane is oriented transversal to the rolling direction and the crack initiation location corresponds to the location where the shear stress components are maximum

Deterministic Model for Rubber-Metal Contact Including the Interaction Between Asperities

Rubber-metal contact involves relatively large deformations and large real contact areas compared to metal-metal contact. Here, a deterministic model is proposed for the contact between rubber and metal surfaces, which takes into account the interaction between neighboring asperities. In this model, a description of the actual micro-contact is used instead of a summit which is a local maximum at the surface. Linear viscoelastic behavior, modeled by a three-element mechanical model, is assumed for the rubber. In the present model, the equations regarding the deformation due to a Hertzian pressure inside and outside the contact area have been modified for the viscoelastic case. The deterministic case is compared with the statistical one. Besides this, the deformation of the bulk material beneath the asperities is taken into account. The results reveal that the bulk deformation has a significant effect at higher nominal pressures

On the Transition from Bulk to Ordered Form of Water: A Theoretical Model to Calculate Adhesion Force Due to Capillary and van der Waals Interaction

The adhesion force due to capillary interaction between two hydrophilic surfaces is strongly dependent on the partial pressure of water and is often calculated using the Kelvin equation. The validity of the Kelvin equation is questionable at low relative humidity (RH) of water, like in high vacuum and dry nitrogen environments, where water is only present as layers of several molecules thick at the surfaces. A model from ordered to bulk form of water has been developed using the Brunauer, Emmett, and Teller adsorption model. The results show that the adhesion force calculated using the Young–Laplace and Kelvin equations at low (5–30 %) RH is underestimated. The total adhesion force shows changes when the RH is changed from 0 to 100 %. In dry conditions, at RH below 10 %, the total adhesion force is contributed by the van der Waals interaction due to solid–solid contact. The total adhesion force then increases and remains constant being equal to the superposition of van der Waals interaction due to solid–solid contact and van der Waals interaction due to adsorbed water layers on the surfaces. The total adhesion force further increases slowly with the increase in RH incorporating capillary forces and then decreases at very high RH due to screening of van der Waals forces. This change in adhesion force occurs from solid–solid interaction to ordered form of water at low RH and from ordered form to bulk form of water at high RH along with the screening effect of van der Waals interaction. The results have been compared with the experiments and it has been seen that at small length scales, the model is in agreement with the existing experimental data. However, at large length scales roughness of the surfaces should be taken into account