Study on Strain Release Coefficients and Its Plasticity Correction for Four Typical Ductile Iron
The blind hole method is the most common method for measuring residual stresses in engineering,in which the strain release coefficient of the material is the key parameter in the method,and there are relatively few studies on the strain release coefficient of ductile iron at home and abroad.In this paper,the strain release coefficients of four commonly used ductile iron QT450-10,QT550-6,QT600-3 and QT700-4 were calibrated by the blind hole method,and the relationship curves between strain release coefficients and stresses were obtained.It was found that the lower grades of ductile iron are more sensitive to stress concentration due to the high ferrite content,and are prone to local plastic deformation in the calibration test.The strain release coefficients of the four ductile irons were corrected using a correction method based on the shape change ratio S.It was found that,unlike other homogeneous metallic materials,there was a good linear relationship between the strain release coefficients and √S for ductile irons,so the correction formula for the strain release coefficients of ductile irons with respect to √S was proposed,which can be directly applied to the measurement of residual stresses in ductile irons by the blind hole method.
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