Moiré Analysis of Planar Elastic Contact for Understanding Wheel-Rail Traction
Author(s): Matic, P. and S. Kumar Corporate Author: Illinois Institute of Technology, Department of Mechanics, Mechanical and Aerospace Engineering Corporate Report Number: IIT-TRANS-77-1 Date of Publication: 1977-04 Pages: 37 Contract: DOT-OS-40103
Abstract: The nature of adhesion and creep in the contact region between two planar surfaces with normal and tangential loads is experimentally investigated with moiré analysis. This study is aimed at advancing the understanding of adhesion and creep in the contact zone between a steel wheel and rail. The contact region between a silicon block (width 2.4", length 2.4", and height 1.6") and a thick plexiglass plate was investigated. Loads of 0.33 lbs to 5.01 lbs were applied at angles of 0° to 11.1° from the vertical. Gratings of 300 and 302 lines/inch were placed on the contacting surfaces of the plate and block respectively. Movement of the moiré fringes yielded the displacement fields. Analysis of the displacement fields for four loads at four different inclination angles show that the adhesion zone appears as a region of restrained displacements. It is believed that ideal adhesion (i.e. zero displacements) is possible only for optically flat surfaces, and that surface roughness, as was present in this investigation, is responsible for restrained displacements in the adhesion zone. For only vertical loads, the adhesion zone was in the middle of the contact surface and the adhesion zone decreases in size. This is as predicted by theory and the finite element method. Underinclined loads, the adhesion zone moves opposite the direction of horizontal components of loading. The adhesion zone will eventually move to the edge of the contact zone when there is a large enough tangential load. The experimental results were compared with a finite element analysis conducted at I.I.T. earlier and showed good agreement.
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