Partial Slip Contact Research Articles

Analysis of the Size Effect in Partial-Slip Contact Fatigue

A size effect has been observed in cylinder-on-flat partial slip contact fatigue experiments (Hills et al., 1988 and 1990). The size effect in this case is defined as a discontinuous drop in the fatigue life beyond some critical value of the width of the contact region. New analysis that directly accounts for the finite substrate thickness used in the original experiments shows that both the maximum local bulk stress and maximum local bulk cyclic stress range increased systematically with contact width in the original cylinder-on-flat experiments, rather than remaining approximately constant as intended in the original experimental design.

A method based on asymptotics for the refined solution of almost complete partial slip contact problems

A refined semi-infinite contact solution, for a punch possessing a rounded edge and under conditions of partial slip is derived. This is applied, as an example, to the D-shaped punch. It permits the addition of a lot of detail to a sharp, locally adhered solution, and the technique is of general applicability.

Numerical analysis of fretting contacts of dissimilar isotropic and anisotropic materials

A numerical method is presented to obtain the contact tractions when two dissimilar isotropic or anisotropic bodies are in partial slip contact. The solution to the governing coupled singular integral equations (SIEs) is obtained by incorporating the appropriate singular behaviour for the contact pressure and the shear traction. The edges of the contact zone and the stick zone are determined by iteration such that the constant multipliers of the singular functions vanish. For anisotropic materials the out-of-plane shear traction is assumed to be very small and hence neglected. The solution method has been successfully verified by comparing its results to solutions available in the literature and to the results obtained by the finite element method (FEM). By modifying the slip function to take into account the remote stress on the half-space, the SIE method can be used to analyse fretting contact problems. The resulting technique efficiently accounts for the effect of load history on the contact tractions and the contact and stick zone sizes. The pronounced effect that load history has on the stick zone size is illustrated.

Wear in Partial Slip Contact

An analytical method that evaluates the evolution of stress and surface profile in fretting under the partial slip conditions is presented. The repeated slip occurring near the edges of contact generates wear that changes the contact geometry and contact stresses. The method is based on two scales of time: time for one cycle of the oscillating tangential force and time corresponding to the number of cycles. Archard’s wear law is used to evaluate wear and gap variation within the slip zones during one cycle. The governing integral equations are reduced to calculate the contact pressure after each cycle. Evolution of the contact characteristics (contact pressure and shear stress, contact width, gap and slip functions) in fretting is calculated using a stepwise procedure. It is shown that the size of stick zone does not change in wear process of bodies with similar elastic properties under the constant amplitude load conditions, and that an asymptotic solution corresponding to the number of cycles approaching to infinity exists. Analytical expressions for the asymptotic contact pressure, shear and tensile stress, and the gap function are presented. It is proved that the asymptotic contact pressure and shear stress are singular at the ends of stick zone. Detailed results are given for two initial shapes of elastic indenter contacting with an elastic half-space: for the parabolic cylinder and for the indenter having a flat base with rounded edges.

Identification of the characteristic length scale for fatigue cracking in fretting contacts

Fretting damage consisting in cracking and wear generated by debris formation is induced by very small alternated displacements between contacting surfaces. It is often considered through the drastic drop in the fretting fatigue limit which is very detrimental for industrial applications. This paper focuses on the quantification of the fretting crack nucleation appearance by comparing fretting experiments obtained on well defined quenched 30NCD16 steel and a multiaxial fatigue approach. The plane/sphere configuration was studied under partial slip situations characterised by a central stick domain surrounded by an external sliding zone. Validated for classical fatigue conditions, the Dang Van's fatigue prediction is compared to fretting cracking mechanisms (10 6 cycles). The correlation is achieved according to some conditions: - the local friction coefficient operating in the annular partial slip contact has to be identified. It permits a more accurate estimation of the stress loading path evolution during the fretting cycle. - the loading states which are computed to determine the crack nucleation risk must be averaged on an elementary volume representative of the microstructure of the steel. It allows a convenient size effect consideration regarding the very small material volume stressed below the contact.