Contact stress in lenses is caused by axial forces exerted within small areas of the lens surfaces. This stress is proportional to the square root of the applied force (preload) and also depends on the surface radii, the geometry of the glass-to-metal interface, and the elastic properties of the contacting materials. In this chapter, we summarize a theory for approximating the magnitude of the contact stress for any of several commonly used mounting designs. Equations useful in estimating the rate of change of axial preload with temperature for single- and multiple-component designs are presented. Given the preload applied at assembly, these equations allow the contact stress to be estimated at any temperature. The chapter closes with brief considerations of stress effects resulting from unsymmetrical application of forces on opposite sides of lenses.
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