2" Diameter Hole Stress Raiser Question

[maxwolf]

I'm trying to determine how much yielding around a 2" diameter hole in the side of a 7" diameter pipe column is acceptable. The column is subject to bending and axial load.

We've modeled the hole with FEM solid modeling and pretty well defined the areas of yielding - a shallow zone around the side walls of the hole. But does any know of any literature or code that gives any guidlines on the maximum dimensions and degree of overstress?


Thanks,

mw

 

[ishvaaag]

I suggest a trick, repeat the analysis with your circular section hole substituted by an elliptical one that removes the plastified zone. It the situation is just about the same, i.e., the plastified zone doesn't become much bigger, it means entirely disregarding the plastified zone works (in fact in the first model material providing equilibrium), you are likely in a safe situation. This can be, as follows, an unnecessary effort.

Let's think a moment about plastification, just to Fy. In strong axis bending of over compact shapes, the stress is allowed to go entirely to Fy, relative to the elastic condition in each half of the shape; this is the Galileo's beam, that accurately predicted before such limit strength over the later (historically) developed elastic behaviour of the beam. So it seems that progression of plastification can go and will proceed not only in minute magnitude, but clearly, circumnstances permitting, in magnitudes of the same order of the section of the member.

What that means is that, according to the minimum energy of deformation principle, the structure will be taking more and more deformation to meet the external work as long as it can. So, if your small ring of plastified zone is critical or not depends much on the cause of the plastification. If it was coming from a bolt wanting to pull out of an area entirely plastified, it would be critical, since you would be forcing such material to enter in the strain hardening region to meet the loads at unwanted deformations; but, if, as it is your case, it comes from beamcolumn action, and your shape is quite compact, you are more in the Galileo's beam case, and the plastification will have ample capacity to "redistribute" loads, or, if you want, will have enough confinement ring action from the elastic material surrounding it as to prevent progress of the plastification and the state of equilibrium be correctly defined by some area at Fy and the rest at under Fy and meeting equilibrium. For relatively thick parts, a simple average on some zone may work to ascertain if you have capacity there. For bending action and thick parts, under the plastic capacity (as mandated reduced), you have.

Not to forget that the thickness can be small, there can be fatigue and as you indicate a stress concentration factor may have been or not taken unto account. For all these other cases better to look for a start Galambos' book, Pilkey's for a stress concentration factor etc or AISC's details or other for fatigue ans see in what extent can influence your problem.