This part of ISO 527 specifies the test conditions for determining the tensile properties of moulding and extrusion plastics. These properties include ultimate strength, strain at failure, and modulus. The mechanical properties of plastics can change dramatically when certain additives are incorporated into the formulation. Some of these properties include strength, ductility, and toughness. For the measurement of modulus of elasticity, the speed of testing should be taken from the standard.
The following groups of materials are suitable for use with this method:
- Rigid and semi-rigid thermoplastics moulding, extrusion and cast materials in their unfilled form. This includes these materials reinforced with short fibers, small rods, plates, or granules, but excludes textile fibers.
- Rigid and semi-rigid thermosetting molding and cast materials. This includes these materials reinforced with filler and reinforced compounds, but excludes textile fibers.
- Thermoplastic liquid crystal polymers.
All specimens should be made to the sizes specified in the standard and be free from visible surface flaws, including molding flash, shorts, or surface scratches.
As is the case with other materials, an extensometer is required to accurately measure strain. A plastic stress curve versus strain curve most often contains a linear elastic region, as well as a non-linear plastic region. Very little strain occurs within the linear region, and because modulus is measured within this region, extensometers with a high resolution are necessary. Both the 2630-series extensometers and the MFX have the resolution necessary to measure modulus. The 2012 revision of ISO 572-2 allows for use of a 75 mm gauge length, which is available in our 2630-series extensometers (2630-123).
A suitable system for testing these types of samples would be to use an Instron 3300 or 5900 electromechanical testing machine with mechanical wedge grips. The choice of jaw faces may vary depending on sample type, but typically serrated faces are used. In addition to mechanical wedge grips, we also recommend pneumatic side-acting grips for testing plastics.