Clint Morrow

A JKR?DMT transition solution for adhesive rough surface contact

Utilizing Maugis–Dugdale transition theory and a procedure demonstrated by Fuller and Tabor, a solution is given for adhesive rough surface contact. The resulting solution includes adhesive forces of asperities that are in intimate contact and asperities that are not in contact but within the range of adhesion. This work further illustrates that adhesive overload can significantly increase frictional forces.

Numerical contact analysis of transversely isotropic coatings

Abstract Solid lubricant coatings are commonly used to reduce friction and wear in contacting surfaces. In this work, the contact characteristics of transversely isotropic coatings are investigated using the finite element method. A two-dimensional finite element model is presented for determining the maximum surface pressure, contact area, and approach distance for the line contact of coated cylinders. Using the model, contact behavior is evaluated over a diverse range of transversely isotropic coating materials and thicknesses. Verified numerical results are obtained at 297 distinct operating conditions by varying coating material (SiC, NbSe 2 , Graphite, Al 2 O 3 , Cadnium, Cobalt, GaS, GaSe 2 , InSe 2 , MoS 2 ), coating thickness (10–100 μm), normal load (200–20,000 N/m), and cylinder radii (0.005–0.015 m). Based on the finite element results, numerical expressions are derived as a function of a transversely isotropic coating parameter, ζ , for the maximum surface pressure, contact length, and approach distance. The importance of these expressions, as related to design and the selection of materials for reducing wear in contacting surfaces, is subsequently discussed.

A Solution for Lightly Loaded Adhesive Rough Surfaces With Application to MEMS

The stiction forces that exist in microelectromechanical systems (MEMS) are characterized by surface energy and surface roughness. To simulate this contact condition, a three-dimensional fractal surface geometry and an adhesive contact model for a single asperity are used together to create a numerical adhesive rough surface solution methodology. This novel method of solution determines the characteristic adhesive contact type for each individual asperity uniquely at the time of load and area integration. Such a simulation more accurately represents the physics of the asperity-based contact. Numerical results for the adherence force are presented as a function of surface topography, interface compliance, and the work of adhesion for a MEMS interface. The magnitude of the force required to separate an adhesive rough surface interface is given in relation to a polysilicon system.

Anisotropic Strength Approach for Wear Analysis of Unidirectional Continuous FRP Composites

Based on the anisotropic strength failure criteria, a model is introduced to predict the wear behavior of unidirectional continuous fiber reinforced polymer composites (FRP) for arbitrary fiber orientations. This approach, which includes the influence of the friction on the failure strength, is initially validated by comparison to experimental data for T300/ Epoxy. The benefits of the model and trends for variation of wear with fiber orientations are subsequently ascertained and discussed.

Numerical Contact Analysis of Transversely Isotropic Coatings: A Cylinder Within a Circumferential Groove

The contact characteristics of transversely isotropic coatings are investigated for a cylinder within a circumferential groove using a two-dimensional finite element model. With the model, contact behavior is evaluated at more than 400 operating conditions by varying coating material, coating thickness, normal load, and cylinder/groove radii. Based on the finite element results, numerical expressions are derived for the maximum surface pressure, contact length, and approach distance as a function of a transversely isotropic coating parameter, ζ. The importance of these expressions, as related to design and the selection of materials for reducing wear in contacting surfaces, is subsequently discussed.

Contact Analysis of Anisotropic Coatings with Application to Ball Bearings

Anisotropic coatings represent an important class of tribological materials that are used to reduce friction and wear in mating surfaces. In the present investigation, a three-dimensional finite element model was utilized to analyze the contact behavior of a spherical indentor normally loaded between two transversely isotropic coated surfaces. After initially being validated via comparison to theoretical results available in the literature, the numerical model was used to determine the stress and displacement fields for a diverse range of coating materials and thicknesses, indentor radii and materials, and loading conditions. By curve-fitting the numerical data, expressions were generated for predicting the contact behavior in the posed problem. The relevance of these expressions, as related to the optimization of engineering components, was subsequently ascertained and discussed. Presented at the STLE Annual Meeting in Toronto, Ontario, Canada Review led by Bob Fusaro

An Extension to a Cohesive Zone Solution for Adhesive Cylinders

When adhesive forces are taken into consideration, contacting asperities can still interact after intimate contact is broken. Current theories that predict the contact behavior of adhesive cylindrical asperities fail to capture the forces in this regime. In the present investigation, prior solutions for adhesive cylindrical asperities will be extended to include the condition where the asperities are not in physical contact but are still interacting through adhesive forces. In the extended results, relationships between the adhesive contact radius and the applied normal load will be developed and discussed with respect to the design of micro-scale components.

Determination of a Critical Forming Parameter for the Cross-Wedge Rolling of Tubes

An explicit dynamic finite element model is used to analyze the tribological behavior of the cross-wedge rolling (CWR) of tubular structures. Cross-wedge rolling is a manufacturing process used to form axisymmetric parts by the relative motion of two opposing hardened dies. To date, the CWR process has been used to form only solid parts. In the present investigation, results are presented for the counteraction of flat dies that are used to deform tubular structures. By combining, numerical and experimental evidence, a critical forming parameter is developed which predicts the critical rolling conditions for the CWR forming of tubular structures. This parameter combines the effects of friction, wall thickness to radius reduction, and tube hardness.Copyright