Mechanical Tests on Reduced Scale Mock-Ups of ITER Pre-compression Rings

The ITER Pre-Compression Ring (PCR) system consists of two sets of 3 rings each, located on the top and the bottom inner region of the Toroidal Field (TF) coils providing a centripetal load and a radial constraint with beneficial effects on the force distribution in the TF magnet system. PCRs are large and thick rings with a diameter of 5 m manufactured by winding and bonding a flat pultruded tape made of fiberglass in epoxy matrix. Due to the particular composite material and to the innovative process an overall qualification phase has been planned including a dedicated testing campaign on reduced scale ring mock-ups with the aim to characterize their mechanical properties and to verify the compliance to requirements. The mock-ups were procured by F4E with a diameter of 1 m (1/5 of the full scale) and the tests were performed at ENEA Frascati by using a dedicated hydraulic testing facility consisting of 18 radial pulling actuators aiming at reproducing the loads and displacements occurring to the rings. The testing campaign consisted in a detailed sequence of Stress Relaxation (SR) tests performed at different stress levels/durations and followed by final ultimate tensile strength (UTS) tests at room temperature. Acoustic emission (AE) monitoring was also performed during testing of one ring mock-up. This paper describes the testing programme, the ring mock-ups, the test equipment and reports the main results of the testing campaign.