Short-term tests on unidirectional fiberglass for ITER pre-compression rings

The unidirectional fiberglass unidirectional composite has been proposed as one of the candidate materials for ITER pre-compression rings. Material samples have been produced and tested for ITER pre-compression ring manufacturing and testing. In 2003, an initial batch was produced, giving interesting results, but presenting a lower limit for the mechanical characteristics of the material. Therefore, a grip system has been developed and tested, which requires longer samples (650 mm) for obtaining reproducible results which meet the standard. This development led to a grip system using 45 deg. fiberglass for grips and INCONEL compression rings for keeping the grips in place. In 2006, in short-term test, the fourth batch resulted in an ultimate tensile strength of about 2200 MPa (room temperature) and a very limited dispersion of results. Tests at a temperature of 77 K resulted in a mean value greater than 2750 MPa with a similar dispersion. From the above results, an allowable stress value of 1000 MPa can be envisaged at the operating temperature. Stress relaxation tests are presently in progress