A new non destructive method to measure residual stresses

A nondestructive technique for measuring residual stresses has been developed on the basis of a Hertzian analysis of the elastic contact of a sphere, cylindrical die or long ellipsoidal die with a semiinfinite body bounded by a plane. The residual stress measurement technique is related to a method for assessing the yield limit at any point of a structure. In a contact test with a spherical die, the onset of nonlinearity in the relationship between the induced stress tensor and the applied load indicates the appearance of plasticity within the specimen. A contact test involving an ellipsoidal die and assessments of plasticity based on acoustic emissions is also reported.