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Stress Rupture

straingauge (Aerospace)

(OP)

25 Jun 02 10:48

If I have 2 different cross sectional test pieces one square and one round, am I able to use the same parameters on both test pieces for destructive testing using area only, or do I have to take into acount the second moment of area? If so can somebody guide me as to the formulae, the test piece parameters for the round cross section are: stress=22000kpa, elongation 10% and reduction in area 5%

TVP (Materials) · Answer 1 · 2002-06-25 12:29:45

Is this an axial test? If so, then you only need the cross-sectional area. If it is to be performed in bending or torsion, then the second moment is necessary. The second moment for a solid of circular cross-section is

I = (pi/64) * diameter^4 or 0.049 * diameter^4

for a square cross-section it is

I = x^4 / 12 where x is the length of one of the sides

straingauge (Aerospace) · Answer 2 · 2002-06-26 03:44:47

Thankyou for your prompt answer. The test to be performed is a tensile stress rupture pull, does this make any difference.

TVP (Materials) · Answer 3 · 2002-06-26 08:15:52

Are you familiar with ASTM E 139, Standard Test Methods for Conducting Creep, Creep-Rupture, and Stress-Rupture Tests of Metallic Materials? If not I would highly recommend that you obtain a copy (www.astm.org). Section 7.5 specifically mentions that rectangular sections can be used. As I mentioned before, in an axial test, you only need to know the cross-sectional area in order to obtain the proper stress.

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