Fibreglass unidirectional composite to be used for ITER pre-compression rings

The ITER magnet system will be kept in place by a system of pre-compression rings, which have stringent material requirements. The best solution, at the present level of knowledge, is to use a composite material consisting of unidirectional glass fibres in a resin matrix. To study the characteristics of the composite, ENEA performed a series of impregnations using S-2 glass and an epoxy resin matrix. Standard and non-standard specimens were tested both at room and at liquid nitrogen (77 K) temperature. The mechanical strength values were as high as 2200 MPa and the behaviour remained linear practically until failure. A set of specimens will be tested at room temperature with 70-80% of the collapse load in order to verify the creep behaviour of the material. A facility is under construction to test the rings on a scale of 1/5 of the final ITER rings in operating conditions and up to stresses leading to rupture. The test results will supply the information on the behaviour of massive structures in unidirectional fibreglass composite required for the design of the ITER rings.