Contact Mechanics UW Courses Web Server接触力学 威斯康星大学课程的Web服务器.pdf

Contact Mechanics Handout Contact Mechanics Introduction While Classical Mechanics deals solely with bulk material properties Contact Mechanics deals with bulk properties that consider surface and geometrical constraints. It is in the nature of many rheological tools to probe the materials from outside. For instance, a probe in the form of a pin in a pin-on-disk tester is brought into contact with the material of interest, measuring properties such as hardness, wear rates, etc. Geometrical effects on local elastic deformation properties have been considered as early as 1880 with the Hertzian Theory of Elastic Deformation.1 This theory relates the circular contact area of a sphere with a plane (or more general between two spheres) to the elastic deformation properties of the materials. In the theory any surface interactions such as near contact Van der Waals interactions, or contact Adhesive interactions are neglected. An improvement over the Hertzian theory was provided by Johnson et al. (around 1970) with the JKR (Johnson, Kendall, Roberts) Theory.1 In the JKR-Theory the contact is considered to be adhesive. Hence the theory correlates the contact area to the elastic material properties plus the interfacial interaction strength. Due to the adhesive contact, contacts can be formed during the unloading cycle also in the negative loading (pulling) regime. Such as the Hertzian theory, the JKR solution is also restricted to elastic sphere- sphere contacts. A more involved theory (the DMT theory) also considers Van der Waals interactions outside the elastic contact regime, which give rise to an additional load. The theory simplifies to Bradleys Van der Waals model if the two sur