Study Of Residual Stress Measurement Technique In Metallic Strip Using Crack Compliance Method

High accurate copper-alloy strips are fundamental material in the production of electrical component. Strict allowance on strip buckling and residual stress controlling were introduced to manufacture process of copper-alloy strip with thickness between 0.1mm and 0.4mm. One of preconditions for buckling controlling is gotten to know residual stress distribution in strip accurately. However, in residual stress measurement, common techniques could not satisfy the demands of strip buckling controlling accurately and effectively. It is worthwhile to study residual stress measurement technique on metallic strip.In residual stress measurement based on crack compliance method (CCM), the key points in strain measurement are sensitivity and error reducing, and in calculating process are accuracy and model stability that would be extensively discussed in present work, respectively.Major sources of uncertainty in strain measuring and stress modeling were analyzed and a corresponding method to minimize error factors was established in modified CCM. The results of convergence and endpoint stability from different interpolations were compared. The Error propagation formulation for Legendre polynomials including covariance was established in order to determine optimum expansion order. The function of strain caused by complex-crack ofⅠandⅡtype was employed to find the way in suit with copper-alloy strip measurement. The relation between residual stress and microstructure with different deformation in aged copper-alloy was concluded. Modified rotating structure was employed to detect residual stress in metallic plate. With the principle of minimum potential energy, the strip deflection function was constructed.The results show that the abnormal strain data near crack end was mainly caused by specimen gravity in CCM and a weight function could reduce the influences efficiently. The flat-smooth regularization could improve end-point stability and reduce the random strain error effects. In the way of above data treatment, the uncertainty in residual stress detecting had been greatly reduced form±4MPato±1.89MPa in bent beam validity test. Compared with normal methods, the multi-point- symmetry strain measurement could achieve as high as double sensitivity compared with common methods, in other hand; the strain effect caused by shear stress could be eliminated. Both crack machining process and measuring condition could largely be improved by air-cooling instead of liquid. The results from validity test in bent beam were well consistent with FEM results. Residual stress profile in aged Cu-Ni-Si alloy bar with different working ratio could be well explained by microstructure observations. The time costing in strip residual stress detecting by rotate structure could be reduced to half compared with slitting method that could meet the commands of residual stress quick detecting in metallic plate under large ratio of width to thickness. Buckling model was simulated according to residual stress distribution and buckling altitude calculated was well fit with measured results.