The Work of Fracture of Epoxide Resins at Temperatures to 4K

Abstract

Epoxide resins are frequently employed as bonding/insulating materials in cryogenic structures and thermal stresses, resulting from differential contraction, may be induced in the resin. While this stress is likely to be below the failure stress of the resin and is independent of the volume of resin that is cooled, the total stored strain energy is volume related and if this stored energy exceeds the work of fracture, failure will result. The work of fracture of a number of epoxide resins has been measured at room temperature, 77K and at 4K and the results used to explain the observed thermal shock resistance of these materials. For semiflexible resins at room temperature, the geometry dependent elastic/plastic contribution to the work of fracture is discussed. The paper indicates how the work of fracture and the Tg of the resin may be used to guide developments of resins for low temperature applications and possibly to derive a numerical term as a “Cracking Index”. The relationship of the plane strain critical stress intensity factor (K _IC ) with the work of fracture is also considered.