Nanoindentation Testing – What to Do and Not to Do

Nanoindentation is a method of measurement of the mechanical properties of small volumes of materials using an instrumented indentation technique. Elastic modulus, hardness, fracture toughness, creep and dynamic properties such as storage and loss moduli can be measured. In this and subsequent articles, we will look at some of the issues facing the user of a nanoindentation instrument. Our purpose is to educate and inform the prospective user of this type of equipment as to what can be measured and what factors influence the results obtained.

Figure 1. The IBIS Nanoindentation system from Fischer-Cripps Laboratories.

Things To Do While Performing Nanoindentation Testing

Here is a list of things to do while performing a nanoindentation test:

• Wait for thermal equilibrium before starting your test rather than to try and correct for thermal drift later.
• Be aware of the thickness of your sample and select an appropriate minimum and maximum load.
• Mount your sample firmly with the minimum of adhesive and ensure a good solid contact.
• Apply corrections, they are important, don't ignore them.
• Be aware that creep in the specimen, piling-up, indentation size effects, etc may affect your results.
• Calibrate your tip regularly, especially if you are not the only user. Who knows what damage a previous user has inflicted without notifying anyone.
• Remember to calculate E for the specimen from the reduced modulus E* before quoting results for E.
• Make a brief mention of the corrections applied and the test conditions when you quote your results in the literature.

Things Not To Do While Performing Nanoindentation Testing

Here is a list of things not to do while performing a nanoindentation test:

• Blindly analyse data without examining if the fit to the unloading is reasonable.
• Try to fit an equation to your indenter area function, better to capture local variations in indenter shape than try and impose an artificial mathematical function on it.
• Accept the manufacturer's values for instrument compliance implicitly, measure it yourself on a known sample so that you can get a feeling for the compliance of your sample mounting method.
• Rush. Nanoindentation requires time and patience.

The Importance of The Indenter

One of the most important parts of any nanoindentation instrument is the indenter. If you are using an instrument with a public indenter tip, then there is no way for you to have confidence in your results unless you yourself perform an area function and compliance determination. Indenter tips, although made from diamond, they do wear and become chipped. Unless you have your own tip, it is best to check each time you come to use the instrument.

Verification, Compliance Determination and Publication of Results

When you present your results in an academic journal, the referee will most likely want to see some indication of how the instrument was verified before accepting the results. Mention of compliance determination and area function are important indicators of knowledge on behalf of the writer, so include these issues in your text.

Much more valuable information about nanoindentation can be found in Fischer-Cripps' free downloadable IBIS Handbook of Nanoindentation

This information has been sourced, reviewed and adapted from materials provided by Fischer-Cripps Laboratories.

For more information on this source, please visit Fischer-Cripps Laboratories.