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sayeeprasadr (Materials) (OP)
22 Feb 03 23:32
For a recently tested batch of E71T1(welded as per ASME Section II C requirements), the all weld tensile showed a YS and UTS of 83400psi with 24% elongation. The  yield strength was measured by checking the gage length continuously and by the dial on the load readings itself. The material did show necking but after the yield strength was reached there was no increase in the load readings. Can the yield strength and UTS for this material be the same? What could be the possible reasons for such an occurence, I know that the yield load reading might be wrong, but any better ways of arriving at the yield strength? This testing was done on the older type machines where there is no automatic plotting of the stress-strain curve.

Thanks and regards
Sayee Prasad R
Ph: 0097143968906
Mob: 00971507682668
End of all knowledge is the attainment of immortality!

Metalguy (Materials)
23 Feb 03 2:42
You'd have to measure that gage length VERY accurately to measure the YS.  The stretch is almost all elastic (+0.2% of the GL), so you're dealing in thousanths of an inch.

In all probability you missed the YS as it "went by". <g>
sayeeprasadr (Materials) (OP)
23 Feb 03 3:14
Thks metalguy, but the thing is that the load readings where you have the minor fluctuations on actually reaching the load @ yield point also was similar. I mean the load continuously increased and showed fluctuations at a particular load, where the gage length measurement indicated yield point as well and then without any increase in load, the specimen started necking and then fractured. I am rusty in my metallurgy, but does this seem all right? One more question for what type of materials can we expect YS~UTS? In the sense that material shows elastic behaviour and then necks without much elastic-plastic behaviour? Also why do some codes put a restriction on the ratio of yield strength to UTS(or the other way round) for some materials? An earlier post http://www.eng-tips.com/gviewthread.cfm/lev2/15/lev3/57/pid/330/qid/40730 has mention of the ares under the curves being defined as Toughness and resilience? What is the interpretation of such results where the YS~UTS and what is the significance of the areas under the curves for such materials( If at all possible)

Thanks and regards
Sayee Prasad R
Ph: 0097143968906
Mob: 00971507682668
End of all knowledge is the attainment of immortality!

Metalguy (Materials)
23 Feb 03 8:18
The reason why codes do not allow the YS to be close to the UTS is because they want tough materials, which means it absorbs a lot of energy in the plastic-yielding region.  Since the YS is very close to the start of plastic yielding, the energy has to be absorbed BETWEEN the YS and the UTS.

I may be reading your message wrong, but not all metals have an actual "drop-of-beam" at the YP-where the load actually drops off a little before it increases to the UTS-in fact, many/most steels do not have it.

The area under the curve in the elastic region (before the YP) is very small compared with the area of the plastic region in a tough steel.
Helpful Member!  nousakmj (Materials)
24 Feb 03 10:47
The yield and tensile strength for an E71T-1 weld deposit are not the same, but also not very far apart.  The minimum specified yield is 58 ksi, the minimum specified tensile is 70 ksi and the minimum elongation is 22%.  Yield usually runs somewhere around 65 to 70 ksi and tensile in the as-welded condition is typically 80 to 85 ksi.  The 0.2% offset method is to be used, not the yield point.  For that you'll have to attach an extensometer to the gage length and get a load curve.  You are simply not going to get a decent value by visual observations.

Matt Nousak, P.E.
Senior Staff Engineer
Middough Associates Inc.
nousakmj@middough.com
HardMetal (Materials)
25 Feb 03 14:45
sayeeprasadr,
I'm not sure how you expect to measure yield strength by that method, but that is not the correct method.  How would you know when you've reached 0.2% permananent deformation?  It's not possible to do that visually.  How do you know when the curve started to deviate from linearity without a plot of the load vs. elongation?  If you're saying that the yield strength is at or just before necking begins, you've measured it well passed the point where it should be.  

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