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 Model for Junction Growth of a Spherical Contact Under Full Stick Condition

Abstract: The evolution of the contact area (junction growth) of an elastic-plastic preloaded spherical contact subjected to an additional tangential loading is investigated theoretically. The normal preloading, under full stick condition, leads to the formation of a junction that can support additional tangential load. A gradual increase of this tangential load, while the normal preload remains constant, can incept plasticity of the contact zone in case the initial normal preload was elastic or enhance an existing one, thus lowering the tangential stiffness of the junction. Finally, the tangential stiffness approaches zero, which corresponds to sliding inception (i.e., loss of stability). The evolution of the contact area during the tangential loading prior to sliding inception reveals an essential junction growth which depends on the magnitude of the normal preload. The mechanism causing this junction growth seems to be new points of the sphere surface, which originally lay outside of the initial contact area that are coming into contact with the rigid flat during the tangential loading. The theoretical results for the junction growth obtained in the present work correlate well with some limited experiments.

A model of the interfacial heat-transfer coefficient during unidirectional solidification of an aluminum alloy

Abstract: A model is presented for the prediction of the interfacial heat-transfer coefficient during the unidirectional solidification vertically upward of an Al-7 wt pct Si alloy cast onto a water cooled copper chill. It has been experimentally determined that the casting surfaces were convex toward the chill, probably due to the deformation of the initial solidified skin of the casting. The model was, therefore, based upon a determination of the (macroscopic) nominal contact area between the respective rough surfaces and, within this region, the actual (microscopic) contact between the casting and the chill surfaces. The model produced approximate agreement with both experimentally determined values of the heat-transfer coefficient and the measured curvature of the casting surface and showed a reasonable agreement with measured temperatures in the casting and the chill also. A common experimental technique for the experimental determination of the heat-transfer coeffcient involves the assumption of one-dimensional heat transfer only. An implication of the approach adopted in this model is that the heat transfer in the region of the casting-chill interface may be two-dimensional, and the subsequent error in the experimentally determined values is discussed.

Quantitative determination of contact depth during spherical indentation of metallic materials- : A FEM study

Abstract: The continuous indentation technique, because it is fast, precise and nondestructive, has been widely used to determine such mechanical properties as flow properties, residual stress, fracture properties, viscoelastic properties and hardness of materials and structural units. In particular, continuous indentation by a spherical indenter can provide hardness and flow properties, such as yield strength, tensile strength and work-hardening exponent, using the characteristic that strain from the loaded indenter changes with indentation depth. Since the stress and strain values on the flow properties are defined based on the contact area between the indenter and material in the loaded state, accurate determination of the contact area is essential. Determination of the contact area is closely connected with the pile-up/sink-in behavior. In this study, the pile-up/sink-in phenomenon is considered as two independent behaviors, elastic deflection and plastic pile-up, which can be respectively described by a formula. The formulas can be obtained from FE simulation with conditions reflecting real indentation tests for materials used for various purposes and with a wide range of material properties. By analyzing indentation morphology from the FE simulation, the two phenomena were quantified as formulas. In particular, plastic pile-up behavior was formulated in terms of work-hardening exponent and indentation ratio.

A Model for Contact and Static Friction of Nominally Flat Rough Surfaces Under Full Stick Contact Condition

Abstract: A model for elastic-plastic nominally flat contacting rough surfaces under combined normal and tangential loading with full stick contact condition is presented. The model incorporates an accurate finite element analysis for contact and sliding inception of a single elastic-plastic asperity in a statistical representation of surface roughness. It includes the effect of junction growth and treats the sliding inception as a failure mechanism, which is characterized by loss of tangential stiffness. A comparison between the present model and a previously published friction model shows that the latter severely underestimates the maximum friction force by up to three orders of magnitude. Strong effects of the normal load, nominal contact area, mechanical properties, and surface roughness on the static friction coefficient are found, in breach of the classical laws of friction. Empirical equations for the maximum friction force, static friction coefficient, real contact area due to the normal load alone and at sliding inception as functions of the normal load, material properties, and surface roughness are presented and compared with some limited available experimental results.