Siclanic is a copper alloy, CuNiSi, which is extensively used for JET components both inside and outside the vacuum vessel, in particular, the divertor cryopump, the water cooled baffles and the Lower Current Hybrid Drive (LHCD) cryopump.

A series of material tests was undertaken at of Imperial College to determine the mechanical behaviour of this alloy. The material was provided by MSX-CLAL, France, in a form of a 3 mm thick sheet and in a TB-Trempe condition, meaning that after the rolling process the sheet was annealed at 800 deg C and subsequently quenched in water for 15 min. Tensile and Compact Tension (CT) specimens were extracted from the supplied sheet and subjected to a special precipitation hardening process to match the condition of the material used for the construction of the above components.

The effect of the heat treatment on the mechanical properties of Siclanic was determined by a series of tensile tests at room temperature. Since the main interest is in the precipitation hardened material operating at low temperatures, further tests were performed at -80 deg C. These low temperatures were achieved by testing the specimens in a chamber, cooled by gaseous nitrogen. Stress strain curves, the associated static properties, as well as the fracture mode were obtained during these tests.

The fracture toughness properties of Siclanic were also determined by a number of JIC tests using CT specimens and following the requirements of the relevant ASME standards. Tests were performed at room temperature, at -80 deg C, and at liquid nitrogen temperature, using a liquid nitrogen bath. The failure mode was observed to be by a ductile rupture mechanism in all cases and the fracture toughness was observed to be only weakly dependent on temperature over the range examined, in contrast to other structural materials such as carbon steel.

Based on the measurements, a further investigation was carried out to construct a Failure Assessment Diagram (FAD), according to the so called R6 procedure, a method already incorporated in a British Standard Published Document and an ASME Code Case. This diagram associates critical crack lengths to applied stresses and provides the means for assessing the integrity of structures containing defects. The latter analysis resulted in the determination of the largest allowable crack length to avoid failure for a component made from Siclanic, under different load conditions.