Thermal stress in a glass/metal bond with PR 1578 adhesive

Abstract

PR 1578 adhesive is often used for bonding a glass mirror to its mounting flexures (Invar or Aluminum) when the mirror assembly is designed to operate in a low temperature environment PR 1578 is used because it has high strength and remains elastic at low temperature. Several tests conducted at Itek, however, show that the thermal stress induced in the bond may cause fracture of the glass near the bond at cryogenic temperawre. This paper examines the reason of fracture and the effects of flexure material, adhesive thickness, and size of bonding. A finite element model is developed for simulating the bonding of flexure, adhesive, and glass. Temperature dependent material properties are used in the analysis. Good correlation between the analysis and the test is obtained.