I want to know is the reduced modulus can give an indication of materials failure after performing mechanical tests like compression or tension?
I would say yes, If you compare two hardness tests that were conducted on two separate (annealed) samples of a similar metallic alloy, in which one of the sample was tested after a compression or tension test.and the other sample was tested as it is. The value of both hardness tests should be different because of the the strain hardening of the cold worked(mechanically tested) sample.
You have to be more clear in your question are talking about metals or polymers? Are you considering loading in elastic or plastic regime?
As Khaled said if you perform compression or tension test in plastic regime on a metallic sample, its hardness will change in comparison to the pristine condition. There is no reason for change in elastic modulus.
See the attached publication.
Article Correlation Between Dislocation Density and Nanomechanical R...
Yes, Indeed, there will be a dislocation density difference between the two samples, as the implication of Afrooz, see the above answer.
Dear Prof. Khaled and Afrooz
Thank you for your valuable answers.
I'm considering metals, and I need to confirm my result after compression. I m accomplishing plastic regime loading; one of the samples failed and the other not, so I used nanoindentation to confirm the results and as you answered the reduced modulus affected clearly by the failure.
Is this type of test reliable as an indication for failure of the sample?
Hi Fadhil
Using “failure” term do you mean fracture of sample or just after crossing the yield point or UTS point?
Dr. Barnoush mentioned that there is no reason for change in elastic modulus. This is true until yield point (or even Elastic limit). After crossing this point (in plastic regime) sometime elastic module tends to decrease even hardness may increase due to strain hardening. So change of both values may be useful for conclusion.
From the physical point of view the elastic properties are only depending on the interatomic potentials. Therefore, even during the plastic deformation we don't expect any changes to happen to the elastic properties. However depending on the measurement method, due to the interaction of stress field of the microstructural features and defects, we my measure changes in the elastic properties.
Nanoindentation method is not a very precise technique for measurement of elastic properties. It's very sensitive to surface properties and a precise definition of the tip geometry (area function). On top of that the indentation depth is calculated based on assumption which are not always valid specially when there is pile up or sink in around the indent.
Hi Hayk
I meant fracture of the sample. Yes, I agree with you, it should give certain indication about failure at least from elastic modulus.
Dear Afrooz
But if the material is damaged, don't you think the elastic modulus will be affected at least due to porosity and high interstitial spaces. I think from the physical point of view there will be some effect on grain boundaries that may lead to weaken the connection between them.
Yes,
Any mechanical tests cause the residual stresses in the material. This residual stresses should be sufficient enough to get the different properties from that normal sample during indentation. Since in nanoindentation getting consistent results is very difficult, it is preferable to do experiments in below conditions.
i) sample should have an ultra smooth surface (below 2nm).
ii) at lower loads with atomic force microscopy.
- Badges
- Science topic
- Similar topics
- Chemistry
- Nanotechnology
- Nano