National Physical Laboratory

Mapping the Mechanical Properties of Polymers


Figure 1: NanoTest instrumented indentation platform (Micro Materials)
Figure 1: NanoTest instrumented
indentation platform (Micro Materials)

The mechanical properties of polymers are conventionally obtained from tensile tests specimens that are specifically produced for the purpose. However, the microstructure and properties of these specimens are often very different to those found in actual components, due to the different processing conditions used in their manufacture. This is particularly a problem in mouldings with intricate designs, micromouldings and coatings in which the material properties can vary significant through the component. Nanoindentation test procedures have therefore been developed to obtain mechanical properties (hardness, modulus and creep) directly from manufactured components.


The nanoindentation technique (Figure 1) involves indenting a specimen with a well-characterised diamond tipped indenter. By monitoring the force applied to the indenter and the depth it penetrates into the specimen it is possible to determine the mechanical properties of the material. Variations in the properties can then be mapped across a specimen by conducting an array of separate indentation experiments across the surface of a specimen.

Case study

Figure 2: Young's modulus of injection-moulded POM clip obtained from nanoindentation
Figure 2: Young's modulus of injection-moulded
POM clip obtained from nanoindentation

Modulus values obtained by mapping a 1 mm2 cross-section of an injection-moulded clip are shown in Figure 2. Significant variations can be seen from 3.2 GPa at the core of the moulding to 2.6 GPa at the surface. These large variations in modulus are due to variations in crystallinity. At the core of the moulding the cooling rate is slow allowing a large proportion of the material to crystallise (41%) producing higher modulus values. Conversely, close to the surface the cooling rate is faster which leads to lower levels of crystallinity (28%) and lower modulus values.

Current developments

We are currently extending our research in nanoindentation in two European Metrology Research Projects (EMRP). In the first MeProVisc we are developing procedures to obtain the visco-elastic creep properties of polymers using nanoindentation and in the second T3D we are developing techniques to conduct testing at elevated temperatures.



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Last Updated: 28 Feb 2013
Created: 25 Feb 2013


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