Fusion Engineering and Design 87 (2012) 608–612 Contents lists available at SciVerse ScienceDirect Fusion Engineering and Design journal homepage: www.elsevier.com/locate/fusengdes Overview of the testing activities on ITER sub-scale pre-compression rings Paolo Rossi a,∗ , Mario Capobianchi a , Fabio Crescenzi a , Alberto Massimi a , Giampiero Mugnaini a , Aldo Pizzuto a , Juan Knaster b , Hannu Rajainmaki c a Associazione EURATOM-ENEA sulla Fusione, C.R. Frascati, C.P. 65, 00044 Frascati, Rome, Italy b ITER Organisation, Route de Vinon sur Verdon, 13115, St. Paul lez Durance, France c FUSION FOR ENERGY, Josep Pla no. 2, Torres Diagonal Litoral Edificio B3, 08019 Barcelona, Spain article info Article history: Available online 20 March 2012 Keywords: Composite Epoxy resin Fiber glass ITER TF coils pre-compression rings Ultimate tensile strength (UTS) abstract After a first R&D and testing activity to develop and characterize by tensile and creep tests a high strength glass fiber-epoxy composite as reference material for the manufacture of ITER pre-compression rings, ENEA designed and manufactured a dedicated testing facility and different sub-scale composite ring mock-ups in order to characterize their mechanical properties. The paper reports the results of the overall testing activities performed during the last years on a total number of eleven sub-scale pre-compression ring mock-ups manufactured by winding S2 glass fibers on a diameter of 1 m (1/5 of the full scale) both by vacuum pressure epoxy impregnation (VPI) and filament wet winding techniques (WW). The first three rings were manufactured by ENEA Frascati thanks to a particular VPI technique; one of them was used as base composite material to manufacture different sets of specimens for shear, compression and non destructive tests (NDT). Then, five other mock-ups were manufactured following ENEA VPI process and three using WW technique by two different industrial companies. The rings were tested in ENEA Frascati in a dedicated hydraulic testing machine consisting of 18 radial actuators working in position control with a total load capability of 1000 tons. The complete testing campaign consisted of six ultimate tensile strength (UTS) tests and four stress relaxation (SR) tests. The tests demonstrated that the composite (S2 glass-epoxy) is a valid and viable solution for the ITER pre-compression rings (non conductive, non magnetic, capable to work at high stress level without relaxation). UTS tests showed an overall average ultimate strength of 1550 MPa (mean hoop stress in the cross section) and a constant hoop modulus to failure of all the mock-ups. Stress relaxation tests did not show any significant relaxation at different stress levels and durations. © 2012 EURATOM ENEA Association. Published by Elsevier B.V. All rights reserved. 1. Introduction ENEA has developed and characterized a high strength glass fiber-epoxy composite (non conductive, non magnetic) as struc- tural material for manufacturing the ITER pre-compression rings. These rings are pre-tensioned on top and bottom of the inner straight leg region of the ITER magnet system providing a cen- tripetal radial force of about 70 MN/coil under cryogenic conditions (35 MN at the top and 35 MN at the bottom) and pulling the toroidal field coils into contact reducing the toroidal tension in the four outer intercoil structures and the loss of shear key pre-load at the inner intercoil structures [1]. ∗ Corresponding author. Tel.: +39 0694005338; fax: +39 0694005492. E-mail address: paolo.rossi@enea.it (P. Rossi). The composite material was developed by dry winding pre- tensioned unidirectional glass fibers and then impregnating with epoxy resin under vacuum. Tensile tests on linear specimens with glass content of about 2/3 in volume gave an UTS of 2200 MPa at room temperature (RT) [2], very promising for the high strength ITER hoop stress requirement of about 400 MPa at RT [2,3]. Then ENEA manufactured the first three composite ring mock- ups with a diameter of 1 m (1/5 of the ITER rings) by means of a dedicated mould for glass winding and Vacuum Pressure Impregna- tion (VPI) with epoxy resin and realized a hydraulic testing machine consisting of 18 radial pulling actuators for mechanical testing of the ring mock-ups. Later other ring mockups were manufactured both by VPI pro- cess and also by the more conventional filament Wet Winding (WW) technique. The testing campaign on ring mock-ups was based on Ultimate Tensile Strength (UTS) tests and Stress Relaxation (SR) tests and in 0920-3796/$ – see front matter © 2012 EURATOM ENEA Association. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.fusengdes.2012.01.035