Hi all,
I was doing tensile testing on some tiny dog-bone-like tensile testing specimens from an Additively Manufactured Aluminium Alloy 2319 panel.
I got this very weird graph that I do not really understand how can I obtain the ductility, ultimate strength ..etc from.
It shows the Force in (N) VS the machine displacement. (No strain gauges were used).
Can anyone please explain what was going on and how to interpret this graph to extract useful data from?
Many thanks!
Mohammed
Dear Mohammad,
Usually using the machine displacement as a measure of strain is not a good idea to obtain a street strain curve. You should be aware that slippage in the grip and deformation in the shoulder section of the dogbone specimen will affect the force displacement curve. If you are only interested in the ultimate tensile strength or the strain at failure, you can obtain the engineering values from the current experiment. But if you want the stress strain curve, you need to use an extensometer or strain gauges.
Regards,
Ali
Dear Mohammad,
Usually using the machine displacement as a measure of strain is not a good idea to obtain a street strain curve. You should be aware that slippage in the grip and deformation in the shoulder section of the dogbone specimen will affect the force displacement curve. If you are only interested in the ultimate tensile strength or the strain at failure, you can obtain the engineering values from the current experiment. But if you want the stress strain curve, you need to use an extensometer or strain gauges.
Regards,
Ali
Dear Prof,
As Prof. Ali said, use of extensometer or strain gauges are appreciable. Conduct the experiment for 3 times and make a readings for every 0.1 mm displacement. The average of response will give us some useful interpretation. If no reasonable things found, then prepare the samples for micro-structure.
Dear Mohammed
The curve looks weird, I suggest that repeat the curve three time with three different types of alloys (use any Mg, AA and your alloy i.e. 3X3) then check the forces at which this phenomena appears.
Most of instruments have different ranges of forces that makes a soft (not visible) steps like the one you have.
Dear Ali,
I believe that because of possibility of slippage, the strain at failure can not be obtained from the graph.
Hello Mohammed Al Muqbel ,
The resulting indicator curve is interactive.
To give the right impression I would like to receive some more information.
1. Model of the test machine.
2. Breast catcher type, range of gripping jaws.
3. Load speed.
4. The test bodies by which standard are manufactured and what are the basic basic dimensions.
5. Has a chemical analysis of the material been carried out and a microstructural analysis of the material has been carried out.
6. the composition of the material (after casting, thermal treatment, after plastic processing, etc.)
Thanks in advance
Dear Mohammed,
In order to complete the relevant analyses here above :
For the measurement of deformations you can get a more complete picture of the behaviour with optical measurement methods as an alternative or complementary measurement method. Also the failure pattern can be registered/monitored, that you can use to interpret your loading curve.
I also believe there probably is a problem of slippage of the test specimen in the jaws; you easily can get an 'error' of 0.5 mm compared to the deformation along the standardized gauge length of the dog-bone specimen (depends on the type of jaws and how you mount the test specimen into the machine, and can vary with loading rate ...).
May I ask which test standard are you using as a reference for your test design ? Anyway, pay attention that many test standards are rather designed for Factory Production Control tests than for characterization tests (initial type tests / ITT) ; other purposes other means ...
Good luck further !
Dear Mohammad,
If I am understand your problem correctly, you can calculate the ultimate strength Fmax = 1380 N. You can measure the ductility value on the tested sample.
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