Applications of indentation in polymer industry
Polymeric materials have traditionally been characterized by large scale test instruments such as tensile testing or compression. However, with the development of new polymeric materials, more local testing methods are now required. Among the most important mechanical properties belongs elastic modulus as well as creep and viscoelastic properties. Many polymers also have special surface treatments or are applied in form of surface coatings and paints. Instrumented indentation has successfully been applied for various types of measurements in all these areas. This application report presents typical applications of nanoindentation for characterization of viscoelastic, creep and temperature dependent properties of polymers.
Instrumented indentation and mainly nanoindentation has been used for characterization of polymers in several areas, mainly for determination of their viscoelastic properties. These properties can easily be studied by nanoindentation in form of either dynamic mechanical testing (Sinus mode on Anton Paar nanoindenters) or by creep measurements. The great advantages of using nanoindentation for testing of polymers are mainly:
1) Small size of the sample,
2) Characterization in small volumes,
3) Possibility to perform creep and dynamic
measurements.
Indeed, nanoindentation requires only small samples that are usually easier to obtain than large, bulk samples. Furthermore, many samples are available only in form of films or sheets and their testing by conventional test machines is complicated.
The nanoindentation is applying low loads (in the range of ~0.01 mN up to ~500 mN), which results in small indentation depths. The results (hardness, elastic modulus, viscoelastic properties, etc.) are obtained from small volumes and the measurements are thus very local. Nanoindentation can therefore be used for testing of small samples or areas such as films, coatings, surface treatments of polymers or various microstructures.
The ultra nanoindentation tester (UNHT3) and the nanoindentation tester (NHT3) can perform both Sinus mode and creep measurements or relaxation measurements, which is used for determination of viscoelastic and creep properties. In addition, both UNHT3 and NHT3 can be used for local stress-strain characterization using spherical indenters. All these methods are widely used in polymer industry for characterization of polymers.
This application report presents several applications of nanoindentation for characterization of polymers. The main part is dedicated to characterization of viscoelastic properties of polymers but the
nanoindentation stress-strain technique as well as indentation at elevated temperatures are mentioned.
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