Evaluation of residual stress in cast iron by an ultrasonic technique

An ultrasonic technique using critically refracted longitudinal wave (L{dollar}sb{lcub}rm CR{rcub}{dollar}) was employed for determining the magnitude and distribution of residual stresses in gray and ductile cast iron bars. When they are not properly accounted for, residual stresses can prove to be disastrous. The problem of measuring these hidden stresses is usually difficult and requires careful attention being paid to the reliability and accuracy of the results. The L{dollar}sb{lcub}rm CR{rcub}{dollar} technique has proved to be one of the leading candidates for realistic residual stress measurement.; Two sets of samples were prepared from gray cast iron cylinder liners: one set was machined and the other unmachined. Longitudinal ultrasonic wave velocity measurements were then made on all the samples before and after stress relief. The experimental set-up included the standard equipment along with Plexiglas probes, accurately machined for both sets of samples. Metallographic examination was then carried out on small polished pieces of samples that were cut from all these samples including the measurement of the eutectic cell count.; Ultrasonic velocity measurements were also carried out on two austempered ductile cast iron samples and the results were then compared with those of gray iron, to study the effect of parameters like effect of graphite shape on L{dollar}sb{lcub}rm CR{rcub}{dollar} velocity and overall range of L{dollar}sb{lcub}rm CR{rcub}{dollar} speed. Information on residual stress in the samples was derived from this data and the use of this ultrasonic technique as an important diagnostic and quality control tool was established.