8. Meaning and composition of constraints

8.1 Comparison between constraints of different origins

The effect of one stress is not equal to that of another of the same value. For example, the stress of a diaphragm in the thickness of a pipe, under the effect of pressure, which does not relax with plastic deformation or creep, is clearly more dangerous than that due to thermal expansion. The latter can exceed the elastic limit, cause plastic deformation and relax without any practical consequences for the pipe. In general, stresses evenly distributed throughout the thickness of the pipe are more dangerous than bending stresses, which can cause damage through cyclic stress repetition, i.e. through fatigue alone.

This state of affairs has been known to specialists for a long time, but in the absence of clear...