Contact area

About: Contact area is a research topic. Over the lifetime, 12358 publications have been published within this topic receiving 256401 citations. The topic is also known as: contact patch & contact region.

A comparison of contact pressures in tibial and patellar total knee components before and after service in vivo

Abstract: Laboratory testing of total knee components indicates that many designs produce contact stresses that exceed the yield strength of ultra-high molecular weight polyethylenes (UHMWPEs). It is often assumed that the polyethylene component will creep and wear to become more conforming over time, thus reducing these stresses. To test this theory, retrieved polyethylene tibial and patellar components, which showed signs of increased contact area through in vivo deformation, were tested for contact stress against matching components using Fuji Prescale pressure-sensitive film. The results showed an inverse relationship between initial conformity and in vivo changes in contact stress

Modeling and experimental validation of the force–surface roughness relation for smoothing burnishing with a spherical tool

Abstract: The effect of a smoothing-burnishing process strongly depends on the initial roughness of a workpiece. This factor has not been considered by existing classical models of the processes. In this paper, assuming a model of burnishing with a spherical tool, in the form of wedges of surface roughness deformed with a force normal to the base line, expressions describing the relation between burnishing force and displacement of the tops of surface asperities is derived. The expression includes the effect of mechanical properties of the workpiece material, geometry of contact of the tool with the workpiece and the roughness of the burnished surface. Using the derived expressions it is possible to determine an optimum burnishing force. This has been verified experimentally. The experiment made it possible to demonstrate that the optimum burnishing force of the ground 42CrMo4 steel samples was 11–15 daN and that the burnishing effect depends a lot not only on the mechanical properties of the machined workpiece and the geometry of the contact area between the tool and the workpiece but also on the initial surface roughness. The applied optimum burnishing force, calculated on the basis of the theoretical, assumed model-derived dependences, is 12–13 daN. The above proves the validity of the adopted assumptions and the formulas worked out.

Discrete dislocation plasticity analysis of the wedge indentation of films

Abstract: The plane strain indentation of single crystal films on a rigid substrate by a rigid wedge indenter is analyzed using discrete dislocation plasticity. The crystals have three slip systems at ± 35 . 3 ∘ and 90 ∘ with respect to the indentation direction. The analyses are carried out for three values of the film thickness, 2 , 10 and 50 μ m , and with the dislocations all of edge character modeled as line singularities in a linear elastic material. The lattice resistance to dislocation motion, dislocation nucleation, dislocation interaction with obstacles and dislocation annihilation are incorporated through a set of constitutive rules. Over the range of indentation depths considered, the indentation pressure for the 10 and 50 μ m thick films decreases with increasing contact size and attains a contact size-independent value for contact lengths A > 4 μ m . On the other hand, for the 2 μ m films, the indentation pressure first decreases with increasing contact size and subsequently increases as the plastic zone reaches the rigid substrate. For the 10 and 50 μ m thick films sink-in occurs around the indenter, while pile-up occurs in the 2 μ m film when the plastic zone reaches the substrate. Comparisons are made with predictions obtained from other formulations: (i) the contact size-independent indentation pressure is compared with that given by continuum crystal plasticity; (ii) the scaling of the indentation pressure with indentation depth is compared with the relation proposed by Nix and Gao [1998. Indentation size effects in crystalline materials: a law for strain gradient plasticity. J. Mech. Phys. Solids 43, 411–423]; and (iii) the computed contact area is compared with that obtained from the estimation procedure of Oliver and Pharr [1992. An improved technique for determining hardness and elastic-modulus using load and displacement sensing indentation experiments, J. Mater. Res. 7, 1564–1583].