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Tensile strength increasing as material is removed? 1
- Thread starter chadmc
- Start date
bobjustbob
Materials
I think we need more information to determine what is going on. What material are you testing. What sizes of test bars are you testing and what were your results?
Bob
Bob
EdStainless
Materials
There are lots of reasons why this happens.
Tell us your material, any heat treatment, original size, final sizes, and actual property changes, and them maybe we can help you.
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P.E. Metallurgy
Tell us your material, any heat treatment, original size, final sizes, and actual property changes, and them maybe we can help you.
= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy
- Thread starter
- #4
Hi Bob,
the material is 1/2" 360 brass H02. the original diameter is raw bar stock, UTS= 68 ksi. I cut down the material on a lathe to 3/8" and it increased to 71 ksi, then for 1/4" it went to 73 ksi. These are average values over several tests of the same heat lot. I've also noticed this pattern for shear tests. the products the company i work for makes are very dependent on the ultimate strengths of materials as they are designed to fail at specific loads.
-Chad
the material is 1/2" 360 brass H02. the original diameter is raw bar stock, UTS= 68 ksi. I cut down the material on a lathe to 3/8" and it increased to 71 ksi, then for 1/4" it went to 73 ksi. These are average values over several tests of the same heat lot. I've also noticed this pattern for shear tests. the products the company i work for makes are very dependent on the ultimate strengths of materials as they are designed to fail at specific loads.
-Chad
- Thread starter
- #5
Aren't you possibly changing the material properties during machining, as compared to the as-fabricated billets?
TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! faq731-376 forum1529 Entire Forum list
TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! faq731-376 forum1529 Entire Forum list
- Thread starter
- #7
IRstuff,
I don't think so, the material is easily machinable and is cool to the touch right off the machine;I'm using coolant. One of the few things i can find on the internet is "size factor". But there isn't enough information to help me understand.
I don't think so, the material is easily machinable and is cool to the touch right off the machine;I'm using coolant. One of the few things i can find on the internet is "size factor". But there isn't enough information to help me understand.
SWComposites
Aerospace
Perhaps the grain structure is not uniform thru the bar stock thickness.
SWComposites
Aerospace
And what exactly is the test specimen geometry? Is there a grip stress concentration that is changing?
If you are designing essentially a fuse (fail at specific load) are you testing every lot of material?
If you are designing essentially a fuse (fail at specific load) are you testing every lot of material?
- Thread starter
- #12
It’s not diameter measurement error. Even if my micrometer was off by 5 thousandths it wouldnt account for the difference. My gut feeling is that there are several things going on, dislocations and impurities increase with diameter and that mechanical properties aren’t uniform in the radial direction do to mill processes. We test each 12 foot bar on the ends and middle. I’ve been trying to find some theory on shear strengths but not much is published other stress=F/a. so I’m searching for an answer through tensile strengths. In reality I’ve found it’s much more complicated lol
Guest
Segregation carried over from the original ingot could be a factor.
A difference of 3% UTS might not be far outside the scatter range for tensile testing.
Take a full cross section of the original material and do a hardness survey to determine the pattern.
"Everyone is entitled to their own opinions, but they are not entitled to their own facts."
A difference of 3% UTS might not be far outside the scatter range for tensile testing.
Take a full cross section of the original material and do a hardness survey to determine the pattern.
"Everyone is entitled to their own opinions, but they are not entitled to their own facts."
-
1
- #14
EdStainless
Materials
The grain structure varies with location. If you took a piece and split lenghtwise and then made two mid-radius bars from it they would match each other. Different grain size and different thermo-mechanical history at different radius.
You don't say it but you are also seeing shifts in yield and elong correct?
You are making shear pins?
You must qualify each lot and adjust the root diameter of your notch for them.
There is no master calibration unless you use material that has been very specially processed (and therefor too expensive).
= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy
You don't say it but you are also seeing shifts in yield and elong correct?
You are making shear pins?
You must qualify each lot and adjust the root diameter of your notch for them.
There is no master calibration unless you use material that has been very specially processed (and therefor too expensive).
= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy
Hi Chadmc,
As you are measuring the ultimate tensile stress which depends on area and thus the diameter, so I think, if you are testing then cutting the same sample to test again probability is that it is due to strain Hardening, but also what I also think is, that the load sustaining capacity of the material does not change as the material does not change as all the samples are separate,then due to the reduction in the area, the stress is increasing.
To the point that it is not increasing proportionately, I really don't have a good point although I think it is due to the removal of material.
This is just my opinion to the problem, Kindly enlighten me if I have gone wrong anywhere as I am still learning.
As you are measuring the ultimate tensile stress which depends on area and thus the diameter, so I think, if you are testing then cutting the same sample to test again probability is that it is due to strain Hardening, but also what I also think is, that the load sustaining capacity of the material does not change as the material does not change as all the samples are separate,then due to the reduction in the area, the stress is increasing.
To the point that it is not increasing proportionately, I really don't have a good point although I think it is due to the removal of material.
This is just my opinion to the problem, Kindly enlighten me if I have gone wrong anywhere as I am still learning.
mfgenggear
Aerospace
on product I have worked with shear necks, are designed to fail at this area, the shear neck diameter is based on the hardness values,
higher on the Rockwell scale (tensile) the diameter is machined smaller to have the specific tensile shear.
is material is lower on the Rockwell scale, the diameter is larger to allow for tensile shear.
according data this material is cold worked H02 (1/2 hard ) clearly the tensile property changes thru the center and the outside.
just compensate for it, but it appears there is an issue with the tensile testing ( is tensile tester calibrated?)
higher on the Rockwell scale (tensile) the diameter is machined smaller to have the specific tensile shear.
is material is lower on the Rockwell scale, the diameter is larger to allow for tensile shear.
according data this material is cold worked H02 (1/2 hard ) clearly the tensile property changes thru the center and the outside.
just compensate for it, but it appears there is an issue with the tensile testing ( is tensile tester calibrated?)
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