Nonuniform residual-stress measurement by hole-drilling method

Considering the general stress field as the summation of two terms of a power series, a method for the measurement of nonuniform stress fields in thin plates by the hole-drilling method has been devised. The relieved-strain equations for the uniform and linear terms of the assumed power series have been calculated and the related constants of these equations for a range of hole diameter have been plotted.From the relieved-strain equations, it is shown that for a linear approximation of a field, a rosette gage with at least five grid elements is needed. A special rosette is proposed for the linear approximation of the residual-stress fields. In addition the equations used to determine the uniform parts, the direction, and the slopes are given. An example of the linear approximation is presented. It is shown that for some residual-stress fields, the conventional equations based on a uniform stress field produce erroneous results. The improved equations, however, provide the correct solution.