RELAK500 Series Tensile Stress Relaxation Testing Machine is used to determine stress-relaxation of metal, such as Pre-stressed concrete strand, Pre-stressed concrete bar, steel rope and so on., the specimen is deformed a given amount and decrease in stress is recorded over prolonged period of exposure at constant elevated temperature. The product accords with the relevant requirements of ISO 15630-3 Steel for the reinforcement and pre-stressing of concrete. Test methods-Pre-stressing steel, ASTM E328 Standard Test Methods for Stress Relaxation Tests for Materials and Structures, BS 5896 Specification for High tensile steel wire and strand for the pre-stressing of concrete.