I do not mean only conventional hardness but also other properties, including time-dependent that might be calculated or derived from data obtained from macroindentation test on viscoelastic material.
Hi Alexandra Aulova,
I think macro-indentation is mainly for hardness measurement and not for other material property. if you want other properties you can go for some other characterization such as tensile strength measurement. Or else you can prefer nano-indentation to get mechanical properties such as hardness , young's modulus, stiffness of your material if your sample is in the form of thin film.
the main reasons are as follows
1) the berkovich indenter is used in nanoindenter which produces plasticity at very low loads so that you can get precise load-displacemet curve. all the mechanical properties can be derived easily from this load-displacemet curve.
2) You can minimize the substrate effect if you use low indentation load. this is possible in nanoindenter.
With a nano-indenter, hardness, Young's modulus, strength, and creep in viscoelastic samples can be measured.
Thank you for the answers!
I am talking about macroindentation test. I understand that with increase of the range of applied forces and displacements the resolution and accuracy drops immediately.
However, I am interested in mechanical and time-dependent properties that can be obtained from macroindentation test.
Some more information would be helpful. What sort of material are you trying to test?
Is your indenter instrumented, so that depth and force may be measured during the test? Traditional Vickers machines (etc!) are not, but many companies are now producing instrumented macroindenters. With an instrumented indenter, it is possible to measure Young's modulus, creep, viscoelastic effects, etc.
Do you have access to an AFM? By using an AFM to get a really accurate measurement of the indent size and shape, it is possible to extract a lot of information about plastic anisotropy, etc. Of course, measuring the indent size and shape after the test may not work for viscoelastic (or viscoplastic?) materials.
I would caution against trying to extract any meaningful fracture toughness data from indentation tests. Plenty of people use this sort of technique, but there's enough evidence that it just isn't reliable; better tests are available.
Dear Alexandra Aulova,
This paper may help you
"Instrumented Macroindentation Techniques for Polymers and Composites – Mechanical Properties, Fracture Toughness and Time-Dependent Behaviour
as a Function of the Temperature"
Macromol. Symp. 2012, 315, 125–131
(or)
https://www.researchgate.net/publication/230691543
Article Instrumented Macroindentation Techniques for Polymers and Co...
As indentation is a self similar process, if you stay far from any tip roundness effect, size effect or for high loads far from massive damage (cracking) and substrate effect you should be able to get the same properties as the ones obtained with micro or ano indentation which are hardness, reduced modulus and not the Young's modulus one (unless you make a strong hypothesis on the Poisson's ratio), storage and loss moduli for dynamic measurments. I strongly agree with P Howie, that hardness testing is not a suitable technique for measuring a fracture toughness value. Regarding time dependent properties viscosity may also be measured by instrumented indentation.
As I said in my earlier answer, I would caution against trying to use any kind of indentation process to study fracture. The stress state under an indenter tip is much more complex than we would like for a fracture toughness test, and consequently fracture toughness results from indentation are both highly scattered and in poor agreement with results from macroscopic tests.
If anyone is interested in measuring the fracture toughness of hard films and coatings, there are a number of better options. I worked with Shiyu Liu and others here at the University of Cambridge to develop a test based on our micropillar compression work which gives excellent agreement with macroscopic values - see one of the papers I have uploaded here. Some of the recent work elsewhere on bulge testing of thin films is also very interesting.
Due to self similarity, if you use a conical indenter (or Vickers or Berckovichor cube corner) an indentation curve gives the same informations whatever the load is. The advantage of macro indentation is that at this scale you can find spherical indenters (cannot be found at the nano scale). an indentation curve obtained with spherical indenter can give you more informations about the material properties that the one obtained with conical indenter. You can find a lot of work in the literature on methods to determine the hardneing law of a material (plastic properties) and you can find some on time dependent behavior.
Regards
Yes, with viscoelastic analysis, the time dependent properties can be extracted from the loading curve, inside the linear deformation region.
Please check the attached paper, hope it could help.
Best
Meiyu
Article Viscoelastic Modeling of Nanoindentation Experiments: A Mult...
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