Tension test methods

Tension test methods (in-plane) Measurement of the tensile properties are covered in two parts (i.e. Parts 4 and 5) of the general standard EN ISO 527 covering tensile testing of all plastics. The other parts are: Part 1 - General Principles, Part 2 - Plastics and moulding materials, including short fibre reinforced materials and Part 3 - Films.

Several of the conditions used in Part 4 and 5 were set by Part 1 on General Principles, which was published previously. Part 4 was based on the ISO 3268 and EN 61, with input from other methods (e.g. ISO 527-1, ASTM D3039, JIS 7073 and CRAG 300). ISO 527 - 4 was prepared to harmonise with the new Part 5 and replaced both the ISO and EN source documents. It covers all non-unidirectional materials, such as mat, fabrics, multidirectional and random.

Part 5 required more detailed work as it was not drawn directly from any individual previous standard although input was obtained from ISO 3268/EN61/EN (Aerospace) 2561 and 2597). Obtaining agreement between ISO, CEN General series, EN Aerospace - carbon fibre only, ASTM and JIS on specimen sizes for unidirectionally reinforced materials was a notable first step towards harmonisation of the test methods, particularly as the 0.5 inch wide ASTM specimen had been in extensive use for many years and contributed to many databases.

Following agreement on the specimen sizes, which is the same in all standards series except the EN Aerospace for glass-fibre systems, several other aspects of the test method were decided during the drafting of the new standard. For example, a glass-fibre fabric/epoxy, aligned at ±45° to the specimen axis, was chosen as the preferred tabbing material, but alternatives were allowed providing it was shown that the strength was at least equal to that obtained with the preferred tab material and that there was no increase in scatter. A tab angle of 90° was adopted as in EN 2561 and CRAG (3rd edition), with additional support from Japanese round-robin (RR) results.

The modulus is calculated in Parts 4 and 5 as the chord value between 0.05% and 0.25% strain to agree with Part 1 of ISO 527. In the ASTM standard a similar strain range is used but between 0.1% and 0.3% strain. This difference applies to all plastics test methods and the effect of this difference is being studied by ASTM D20 Plastics Committee. Uniquely, the EN Aerospace standards as well as being fibre specific, measures modulus between two load levels, "peak load divided by 2" and "peak load divided by 10".