Compressive strength gives a good indication of the short term loading capabilities of different plastic materials. It is measured by applying an increasing force on cylindrical or cubical specimens held between two plates, while measuring both pressure and elongation.
With thermoplastics, the property of compressive strength at break is not always the relevant measurement, because for many ductile materials the specimen deforms without clear breakage. Excessive deformation under load would thus not be a good indication for success in any real industrial application. For these reasons, the compressive load is not normally given at break, but is instead given at a defined deformation point (commonly 1%, 2% or 10%). It is very important to check the test conditions before comparing compressive values from different sources!
It should also be noted that the addition of carbon fibre or glass fibre reinforcement generally improves the compressive strength of the polymer, but the macroscopic effect is more visible in the long term rather than in short term load performance, due to the improvement of creep properties.
Composite fibre-reinforced products: