How should the yield strength of steel plates with varying thicknesses be considered?
Thread Content
I’d like to discuss this with everyone. For example, a 40mm thick Q345R steel plate is now being rolled into a cylinder; the part that connects to the straight edges of the end caps needs to be thinned, and after thinning it becomes 22mm thick. When performing calculations, I use a yield strength of 315MPa for the 40mm thickness portion. Should I use 325MPa or 315MPa for the thinned section in my calculations? My understanding is that the steel plate, whether it has been hot-rolled or normalized, is already processed before being coiled; this means that its yield strength is fixed. Residual stresses will certainly arise during coiling and thinning, or the yield strength may change during the thinning process. However, if the calculation is done directly at 325 MPa, I don’t think that’s conservative. If the equipment undergoes heat treatment, then it’s fine; but if no heat treatment is carried out, I believe it’s more conservative to use 315 MPa for the calculation.
In your case, when 40mm thick Q345R steel plates are thinned to 22mm and yield strength needs to be considered, the most conservative approach is indeed to continue using the original value of 315 MPa for the calculations. Since the thinning process may introduce additional stresses or microstructural changes, but there is no specific data indicating a significant increase in yield strength, it is a safer choice to use the original value of 315 MPa. If no additional heat treatment is carried out to relieve the residual stresses resulting from thinning, a conservative estimate should be adopted. In short, in the absence of concrete data supporting an increase in yield strength, it is more appropriate to maintain the original yield strength value. .
I think it should be calculated at 315 MPa
This post was last edited by AtlantisH on 2024-11-15 08:20. Reducing the diameter of the 40mm cylinder to 22mm and then connecting it to the straight edge of the end cap – is the strength sufficient? In general, this situation involves a connection with a spherical cap (less than half a sphere), and the thinned part corresponds to a portion of the spherical shell. Your consideration is reasonable; when the allowable stress varies due to different plate thicknesses, it is indeed necessary to check the strength of the thinned areas using the shell theory formula.
Good question. I think that in order to avoid calculations, it’s possible to reduce the thickness to unequal levels; reducing it to 150, which is within the allowable upper limit for not needing thickness reduction, means that even with a slightly greater thickness, there’s no need to consider the allowable stress
I think it is conservative to use the same yield strength for a certain range of thicknesses according to the standards; in reality, there should be differences. However, the standards classify them into one category. The approach you mentioned is simpler, after all, within the same range…
We take this calculation into account when performing edge trimming
After all, this lacks theoretical support; therefore, for designers, it’s not like finite element analysis – it’s better to be more conservative when following established rules.
I think it should be calculated based on the yield strength of thicker materials, as the classification of yield strength takes into account the decrease in density of the internal structure that occurs as thickness increases; you can’t simply say that reducing the thickness will change the internal structure of the steel. Moreover, you’re removing the better parts on both sides, leaving only the portion with a poorer internal structure in the middle.
The allowable stress should not be determined based on the thickness after thinning; even though it has been thinned, the properties of the material do not change.