TESTING MECHANICAL PROPERTIES OF HIGHLY IRRADIATED ADHESIVE MATERIALS

The Large Hadron Collider (LHC) High-Luminosity Upgrade will expose the ATLAS particle detector to levels of radiation dosage never before experienced. The innermost detector layers will see integrated doses of up to 11 MGy (1.1 Grad). This extreme environment is known to change both the strength and modulus of adhesives and composites. A qualification program of thermal adhesives (Dow Corning Dowsil SE4445 [1], a silicone based thermal compound) was conducted to determine changes in material properties versus radiation exposure. The detector design consists of delicate silicon sensors mounted on ultra-high modulus carbon fiber, thus both the shear modulus and strength of several adhesives were measured at doses of 0, 5, 10 and 15 MGy, in 2cm single lap shear specimens of polyimide and silicon sandwich. Rigid epoxies like Hysol 9394 [4] were found to experience modest hardening under irradiation, while the Dowsil was found to undergo a qualitative change from viscoelastic behavior to a modestly rigid adhesive. These results suggest a significant extension of what has until now been considered safe operating exposures for adhesives of these kinds.