Measurement of residual stress by load and depth sensing indentation with spherical indenters

A new experimental technique is presented for making measurements of biaxia l residual stress using load and depth sensing indentation (nanoindentation ), The technique is based on spherical indentation, which, in certain defor mation regimes, can be much more sensitive to residual stress than indentat ion with sharp pyramidal indenters like the Berkovich, Two different method s of analysis were developed: one requiring an independent measure of the m aterial's yield strength and the other a reference specimen in the unstress ed state or other known reference condition, Experiments conducted on alumi num alloys to which controlled biaxial bending stresses were applied showed that the methods are capable of measuring the residual stress to within 10 -20% of the specimen yield stress, Because the methods do not require imagi ng of the hardness impressions, they are potentially useful for making loca lized measurements of residual stress, as in thin films or small volumes, o r for characterization of point-to-point spatial variations of the surface stress.