The plastic zone and residual stress near a notch and a fatigue crack in HSLA steel

The plastic zone and residual stress around a notch under load and with the load removed, and around a fatigue crack (at the same stress intensity factor as for the notch) have been examined, with automated X-ray techniques and a microbeam. There is good agreement between the measured plastic zone size and Hutchinson's theory for a work hardening material. Residual stresses exist well behind the tip, and vary with depth, so that measurements of crack closure on a surface may not be directly related to closure stress (which samples the bulk). Instabilities in the dislocation arrangement can be detected by comparing X-ray line broadening of bulk specimens under load, and with the load removed. formerly Research Assistant, Department of Materials Science and Engineering, The Technological Institute, Northwestern University, Evanston, IL