Contrôle de qualité : essais de traction en série sur une machine conventionnelle

Quality control : automatic tensile testing on a conventional machine

Laboratoire de connaissance des Matériaux, Ecole d’ingénieurs de Genève, Suisse.

Abstract

We have tried to use a conventional traction machine which has been interfaced with a computer for acquisition-control purpose in order to mak large scale testings. We had to computerise most of the operations, from the loading of the test-bar to the statistical treatment of the results while satisfying the standards for tension testing. Our goal was to obtain very fast and accurate test results by non-specialized operators. Two major problems had to be solved.

Firstly a low cost and reliable extensometer had to be developped. It was dimensioned so that it could be used to determine the yield strength of metal alloys with the precision requested by the Standards and at the same time measure up to a 100 % strain in order to follow the test until fracture. In addition, various accessories were developped to enable measurings of different gage length and test-bar dimensions while maintaining short set-up time. Finally, the extensometer had to support without dommage the choc generated by the fracture.

Secondly a computer program in Basic was developped to ensure maximum automation and optional processings including data storage and treatment. It enables untrained operators to follow well detailled explanations on the program and its settings but avoids repeating the messages when the operator acquires experiance.

The configuration of this traction machine allows very interesting testing rates and a good performance considering the low investments required. One of the most interesting advantages of the Basic program is that it is easilly transformable enabling customised testings. The results are interesting not only for industrial quality control but also for researchand développement labs and practical training in Technical Institutes.