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Aspetti economici nelle valutazioni delle incertezze nei risultati delle diverse prove meccaniche sui materiali

pubblicazioni - Articolo

Aspetti economici nelle valutazioni delle incertezze nei risultati delle diverse prove meccaniche sui materiali

The different characteristics of duration, cost, instruments variety and complexity of the different types of mechanical tests are discussed, with reference to the different views of the mechanical test labs, being independent small organisations offering test services to the market of the industry needs, R&D labs hosted in university departments, testing teams of independent contract research organisations, or internal labs of product qualification belonging to large production industries.

Based on the consideration of these boundary conditions of the clients of uncertainty procedures, as well as in compliance to the general recommendations contained in uncertainty measurements standards, the uncertainty Codes of Practice (CoP) developed by the UNCERT project were adopting two routes: use of statistical treatment of periodical test results on Certified Reference Materials, and the so called “uncertainties budget” analysis (i.e. the explicit identification of uncertainty sources and effects). The basic features of both methods are reviewed. While both routes are in principle always possible, however practical (cost) reasons are making the choice almost obliged, namely recommending the former approach for impact and hardness tests, and the latter for all other test types, e.g. fatigue crack growth, low cycle fatigue, creep, linear elastic fracture toughness, J-integral tests, high cycle fatigue, fatigue thresholds, ect. Finally problems still remaining are discussed, as well as the practicality (often highly desirable by many test labs) of defining a constant uncertainty value for the measurements carried out according to a particular test standard method, i.e. not requiring new estimation efforts each time a new test is done according to the same test method.

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