The characteristics of super-elastic Ni-Ti wires in three-point bending. Part II: Intra-batch variation.

Intra-batch variation in the load-deflection characteristics of 13 superalloy nickel-titanium wires has been examined at nominal mouth temperature (35 degrees C). The results indicate that although most of the superalloy nickel-titanium wires were undersized, the variation in diameter within a batch was of the same order as that reported for 18/8 stainless steel wire. The largest coefficients of variation for the intra-batch variation for the initial slope and the unloading plateau values were found to be approximately 7.5 and 10 per cent, respectively. A high degree of correlation was found between the mean slopes of the initial load-deflection curve in three-point bending at 35 degrees C and the mean wire diameter raised to the fourth power for the 13 superalloys wires, from which a value for Young's modulus (E) of 55.4 GPa was deduced on the basis that at this temperature the wires will have an austenitic structure and virtually identical compositions.