Development and Qualification of an Algorithm for the Determination of the Initial Linear Portion of a Force Versus Displacement Record

What is it about?

Force and displacement are recorded in many technical tests such as tensile, fracture toughness and instrumented hardness tests. The force versus displacement record contains an initial linear elastic portion which needs to identified in order to determine characteristic values of force and/or plastic displacement. In the past, force versus displacement was recorded using an autographic plot (e.g. x-y plotter). The determination of the initial linear portion was done with a ruler and a pen. This of course required experience and good engineering judgement. Nowadays most of the data is recorded using data acquisition systems and the data can be analyzed in an automatic or semi-automatic way. Current international standards, however, do not give any guidance on how to determine the linear portion of the curve and commercial software contains proprietary algorithm. The development of an automated software for the analysis of tensile tests at SCK-CEN, showed that the correct determination of the initial linear portion is the most critical part. In this paper, the algorithm used to determine the initial portion is described and validated. This paper can also be used as a support for international standard development.

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