Mechanical-Property Changes of Polymeric and Composite Materials after Low-Temperature Proton Irradiation

Abstract

The mechanical properties of polymeric and composite materials are known to be sensitive to ionizing radiation. Most of the existing data, however, is the result of near-room-temperature irradiations, most commonly with 60Co gamma irradiation. For use of these materials in applications such as for magnetic fusion magnets, where operation will be at cryogenic temperatures in sometimes severe radiation fields, knowledge of the materials’ radiation response to low-temperature irradiations is required. This paper reports the results of mechanical-property-change measurements made at 4.2K on a number of potential magnet materials following 200-MeV-proton irradiation at temperatures below 20K. Standard three-point bend tests were performed at 4.2K for short-beam shear determinations in the laminate materials and for shear strength in the remainder of the specimens. Specimens were warmed to room temperature for one week prior to the mechanical testing in order to emulate the expected mechanical state of the material assuming room-temperature cycling in the expected magnet applications. Data are presented in the form of yield stresses before and after irradiations with percentages of change. There were five specimens per test dose for each material. Data are presented for exposures ranging from nominally 10 7 to 10 9 rad. Results of the mechanical tests range from complete delamination and distortion of the specimens at 10 9 rad to an increase in the yield stress of 63% after 10 9 rad. The latter specimen did, however, evidence significant embrittlement. The phenomenon of irradiation-induced strengthening due to enhanced cross linking in undercured polymers was observed in some cases.