TENSILE-STRESS RELAXATION IN HIGH-STRENGTH SPRING STEEL WIRE

Stress relaxation data were obtained in tension tests using the vibrating string technique (measuring the resonance frequency) in spring steel wire of ASTM Grade A 228 (also known as music wire). The steel wire of 0.56 mm diameter had a 0.20% offset tensile yield strength of 1689 MPa. Tests were conducted at low temperatures in the range of 23 to 140-degrees-C, and at initial stress levels of up to 75% of the 0.20% offset yield strength of the wire. The test duration was to 4000 h at 23-degrees-C and to 100 h at temperatures to 140-degrees-C. The test results indicate a faster rate of stress relaxation during the early stage of stress relaxation, and subsequently a slower rate of stress relaxation rate with increasing time, as is usually observed. An empirical equation has been determined that fits the experimental data very well under the given test conditions.