ABSTRACT
Contact mechanics has been an important subject in engineering as it is related to force or moment transition, rolling and sliding between bodies and with many friction and lubrication problems. Analytical, experimental and numerical methods are three techniques for analysing the stress and deformation of two solid bodies into contact. Many analytical solutions, such as Hertz’ theory for the contact between two elastic bodies with parabolic profiles [1], Boussinesq’s solution for small area contact on semi-infinite space, etc [2], form the basis of contact mechanics. Among the experimental methods for solving contact problems, optical techniques are useful for determining contact deformation and stresses. In fact, just from Newton’s experiments on interference fringes in a gap between two glass lenses, in 1882 Heinrich Hertz developed his theory for classical contact thus laying the earliest foundation of contact mechanics [3]. With the development of modern optics, other optical techniques have been applied to contact problems. For instance, a combination of the isochromatic fringes of photoelasticity, that show the difference of the principal stress, and the isopathic fringes from holographic photoelasticity, which presents the sum of principal stresses, can be used to separate the normal contact stresses by data subtraction in the near region of the contact surface [4]. The shadow optical method of caustics indicates the stress concentration or singularity by simple caustic curves and the contact force of the in-plane concentrated touch can be easily determined by measuring the maximum diameter of the caustic shadows beneath the contact location [5].
