Dimensional changes in the form of necking and bulging occur in the shape of cylindrical and hourglass commercially pure aluminum specimens subjected to axial push-pull cyclic loading. The present report deals with the effect of these changes on the resistance to deformation and fracture by fatigue. It is found that the change in shape due to instability affects the stress range response of the material during cycling. The control of shape permits a steady-state response with cycling regardless of the prior state of strain in the material. With an appropriate correction for the shape constraint effect, the steady-state stress range achieved is the same with or without shape control. Frequent removal of the surface material to control the specimen profile during cycling leads to a stabilized hysteresis loop and an indeterminate extension in the fatigue life.

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