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. Extensometers with high resolution typically have limited travel and must be removed from the specimen during a test.
Non-contacting extensometers such as the Advanced Video Extensometer (AVE) or Standard Video Extensometer (SVE) have the resolution and flexibility to measure modulus and strain to failure for most plastics.