ISO 7743:2008 specifies methods for the determination of the compression stress-strain properties of vulcanized or thermoplastic rubber using a standard test piece, a product or a part of a product.
Three methods are given:
- using a standard test piece with the metal plates lubricated;
- using a standard test piece with the metal plates bonded to the test piece;
- using a product or a part of a product with the metal plates lubricated.
The three methods do not give the same results. With lubricated test pieces, the results are dependent only on the modulus of the rubber and are independent of the test piece shape, provided that complete slip conditions are achieved. Effective lubrication is sometimes difficult to achieve, however, and it is prudent to inspect the variance in the test results from replicate test pieces for indications of erratic slip conditions. With bonded test pieces, the results are dependent on both the modulus of the rubber and the test piece shape. The dependence on test piece shape is strong and consequently the results will be markedly different from those obtained with lubricated test pieces. For products, the result is dependent on the shape, but as tests on products are mainly comparative this is acceptable.
NOTE For well-specified product shapes, such as O‑rings, the result may be correlated to the hardness value.
The methods are not suitable for materials that exhibit high set.