Residual Stress Estimates from a Ring Sample 2

[SMF1964]

I have a sample from a alloy steel pipe, 5" diameter, 3/16" wall thickness and 3" long. While cutting a longitudinal slice from the ring sample, it sprang open 3/4" (scaring the [expletive-deleted] out of my metals tech. I know there is a way to calculate the residual hoop stresses in this pipe section from the data provided, but I cannot find it in what few references I have on this subject. Any thoughts?

SMF, out

 

[JStephen]

Sounds like a residual bending stress, actually. Residual hoop stress would make the whole thing open up before you sawed it.

 

[strokersix]

You should be able to calculate this using curved beam formulas such as those found in Roark's Formulas for Stress and Strain. Marks' Handbook has it too.

 

[McLeod]

The reference you need is ASTM E1928-98, Standard practice for estimating the approximate residual circumferential stress in straight thin-walled tubing.

Max. residual circ. stress:

s = ± E*t/(1-u^2) * (Df-Di)/(Df*Di)

where

E = modulus of elasticity
u = Poisson's ratio
t = average wall thickness
Di = average initial (pre-split) diameter
Df = average final (post-split) diameter

The standard describes the process for taking measurements at various points to determine the average values.