3. Preventing plastic instability damage

3.1 Definition

Beyond the threshold of excessive deformation, two antagonistic effects appear as the applied load increases:

• strain-hardening of the material results in an increase in the stress to be applied to the material to continue its deformation (this effect was neglected in the assessment of limit loading), until the tensile strength (noted R _m ) of the material is reached;

• modification of the shape tends firstly to improve resistance (the cylinder tends to take on the shape of a sphere, for example) and secondly, through the combined effect of increasing the diameter and reducing the resistant cross-section, tends on the contrary to weaken it....