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 simplified model of wheel/rail contact mechanics for non-Hertzian problems and its application in rail vehicle dynamic simulations

Abstract: The presented model assumes semi-elliptical normal pressure distribution in the direction of rolling. The contact area is found by virtual penetration of wheel and rail. The normal pressure is calculated by satisfying contact conditions at the geometrical point of contact. The calculation is non-iterative, fast and completely reliable. It may be carried out on-line in MultiBody Systems (MBS) computer codes. The tests using the programme CONTACT by Kalker and experience from application in MBS codes show that the model is suitable for technical applications. The creep forces have been calculated with the FASTSIM algorithm, adapted for a non-elliptical contact area. Some applications in rail vehicle dynamics and wear simulation have been outlined.

The indentation modulus of elastically anisotropic materials for indenters of arbitrary shape

Abstract: The contact of an indenter of arbitrary shape on an elastically anisotropic half space is considered. It is demonstrated in a theorem that the solution of the contact problem is the one that maximizes the load on the indenter for a given indentation depth. The theorem can be used to derive the best approximate solution in the Rayleigh–Ritz sense if the contact area is a priori assumed to have a certain shape. This approach is used to analyze the contact of a sphere and an axisymmetric cone on an anisotropic half space. The contact area is assumed to be elliptical, which is exact for the sphere and an approximation for the cone. It is further shown that the contact area is exactly elliptical even for conical indenters when a limited class of Green's functions is considered. If only the first term of the surface Green's function Fourier expansion is retained in the solution of the axisymmetric contact problem, a simpler solution is obtained, referred to as the equivalent isotropic solution. For most anisotropic materials, the contact stiffness determined using this approach is very close to the value obtained for both conical and spherical indenters by means of the theorem. Therefore, it is suggested that the equivalent isotropic solution provides a quick and efficient estimate for quantities such as the elastic compliance or stiffness of the contact. The “equivalent indentation modulus”, which depends on material and orientation, is computed for sapphire and diamond single crystals.

Shear strength of rock joints based on quantified surface description

Abstract: One of the primary objectives of this work is to better understand the frictional behavior of joints under shear loads, including the creation of damage zones. Discontinuities have an important influence on the deformational behavior of rock systems. The choice of a general criterion to determine the shear strength of rough rock joints is a general problem that has been investigated for many years. Numerous shear models have been proposed in the last decades to relate shear-strength to measurable joint parameters, but their limitations have to be recognized. The problem is how to measure and then to express the roughness with a number (e.g. JRC) or a mathematical expression in order to introduce the morphology of the joint into a shear strength criterion. In the frame of this work it has been pointed out that the geometry of roughness influences the size and distribution of contact areas during shearing. In order to locate and estimate the contact area during the shearing, it was argued that only the zones of the surface faced to the shear direction, and steeper than a threshold inclination are involved in the shearing. An empirical relation between the potential contact area and the minimal apparent dip inclination of the surface is proposed. The close agreement between this empirical description of the potential contact area, and experimental points permits to predict the real contact area involved in the phenomena. A new constitutive law, relating stress and displacements, is proposed to model the shear resistance of joints under constant normal load conditions. It is based on the empirical surface description, and on the results from more than fifty constant-normal-load direct-shear tests performed on both replicas of tensile joints, and induced tensile fractures for seven rock types. It is shown that this constitutive model is able to describe experimental shear tests realized in laboratory. Moreover, the parameters required in the model can be easily obtained through standard laboratory tests. The proposed model was also used to estimate the JRC value. The expression obtained to evaluate the joint roughness coefficient is capable of predicting the JRC. It was successfully compared with JRC values obtained by back analysis of shear tests. In the current research no attention was paid to investigate the influence of the scale on the shearing. The results have been validated only in the range of the samples tested in laboratory. Further studies are needed to explore the applicability of the proposed model in field conditions.