How to behave in voltage, if you have a change section?

"There is an opinion: stretched plastic rod of steel with a stress concentration in the center, let them cut. As soon as this stress reaches the yield stress when the load increases, these stresses(in concentration) cease to grow, and grow only in the parts where there is no cutout (i.e., normal cross-section)"

This is the correct view or am I misunderstood?

If it can be in practice, then here's my question:

Actually it is not clear how this voltage when it reaches the yield stress ceases to grow in place of concentration?
In the diagram, stretching the metal continues to deform without increasing load.

But if the rod is loaded by a force greater than the yield stress the place of stress concentration, then what??
according to the first statement clear to all the pressures at the concentrations cease to grow, we can say that through the plot(he is in the center, and pull the bottom) just passed efforts on the upper part of the stem (where the yield stress has not yet occurred) and, accordingly, influence, and of course the lower part is also exposed to load.

But that's impossible! I think that voltage in place of concentration with the increasing workload continue to grow and be more yield stress.
The same can be the case that in the place of stress concentrations will limit strength in the upper and lower parts have not arrived even yield?

You can certainly say that the stress concentration is not taken into account, if the size of the truncated cross-section slightly smaller than the normal cross section of the sample, but then where is the line when you can slightly much?
July 8th 19 at 11:50
1 answer
July 8th 19 at 11:52
Upon reaching the place of stress concentration of the yield strength and slight increase in load the zone of plastic deformation increases to fill the entire cross section (a so-called plastic hinge). Further, with the increase in load is part of "hardening" with the achievement in the place of stress concentration of tensile strength and further there is a gap starting from the weak points in the place of stress concentration.

in the strength of materials is the formula of the plastic resistance moment W (cm3) bending of a rod of rectangular cross section. From this we can find strength where the rod is formed in a dangerous section of plastic hinge - that is, when the entire cross section is in the zone of plastic deformation

This is one man I clearly explained)

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