DS CWA 15261-3:2005

Pasiguritë e matjeve në provat mekanike të materialeve metalik - Pjesa 3: Vlerësimi i pasigurisë në provën e rrjedhjes

Measurement uncertainties in mechanical tests on metallic materials - Part 3: The evaluation of uncertainties in creep testing

Scope

This procedure covers the evaluation of uncertainties in the determination of the results of constant load creep tests carried out according to the following testing standard [4]:

European Standard EN 10291-2000: Metallic Materials - Uniaxial Creep Testing In Tension - Method of Test.

European Creep Collaborative Committee Recommendations (Vol.3 part 1) [6] have also been incorporated.

This Agreement Practice is aimed at determination of uncertainties in the results of a single creep test.

Test repetition under nominally the same conditions, or at a series of stresses or temperatures, can reduce the uncertainty, but too many repetitions may be outside the budget and the time scale: it should be found the right equilibrium between uncertainty reduction and other necessities ([1], Section 4).

Uncertainty contributions caused by systematic errors due to incorrect testing procedure, systematic or correctable errors (i.e. implicit nonconformity to EN 10291) are not regarded in this Agreement Practice. It is assumed that these kinds of errors can be avoided by carefully applying the Standard EN10291: measuring equipment has to be appropriately calibrated, a written test procedure which minimises typical measurement errors has to be outlined, and the test has to be conducted by a trained operator.
In any case it has to be highlighted that uncertainty determination according to this document does not include any implicit acceptance limitation for creep test results: the fulfillment of EN 10291 requirements is generally regarded being fully sufficient for acceptance of creep test quality.
The problem of tests repeatability is not widely treated in this Standard Practice, because, due to economical reasons, the creep tests are not usually repeated. Nevertheless, the use of consistency checks, like alignment of experimental points on forecast straight lines, is regarded as potentially applicable, but needs further investigations.