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Abstract - Tensile stress measurement is a standard technique for evaluation of material properties of the sample under test. This method is standardized for small specimen up to 1x0.25x0.005 mm size. Even smaller specimen can be measured, but the overall dimensions of the complete testing device are much larger. Such dimensions pose limiting factor for performing tensile stress measurement using techniques like high energy X-ray diffraction measurement. Our goal was to design an experimental mini-tensile stress load cell with small enough outer dimensions and mechanical actuation. This paper presents few different designs of such mechanical load cells and evaluates its benefits and limitations.
Keywords: Tensile stress, measurement, mini sample, deformation, load cell
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1. Introduction
Material tensile testing is generally performed using procedures in accordance with standardized tensile-test methods, such as ISO 6892-1, ASTM E8/E8M-11, ISO 527-1-5, ISO 18872, ASTM D882 [1- 5] for metals and plastic materials respectively. These methods are valid for different specimen dimensions down to 1x0.25x0.005 mm in size. Unfortunately dimensions of gripping devices as well as the testing machines are much greater.
Thus minimal dimensions of the test system are typically hundreds of millimeters [6]. Such dimensions pose problems when the sample deformation has to be studied by additional techniques using microscopes, spectrometers, diffractometers, and others.
Facing this dimensional problem, new systems for tensile measurement of very small samples was developed with reduced dimensions of grips [7] and the whole testing device [8, 9]. Unfortunately the overall dimensions of such a test cell still keep dimensions about 20 mm.
Such dimensions are sufficiently small for the majority of microscopes, but are still way too big for interaction chambers of high-brilliance X-ray radiation (synchrotron) facilities.
The tensile measurements by X-ray and electron diffraction and spectroscopy techniques are used especially for even smaller specimens of dimensions at micro and nano scales, for example graphene and other single layer nanomaterials.
Graphene is a two-dimensional carbon material condensed in a honeycomb lattice of carbon atoms. It was established as the strongest known material by deformation testing using AFM nanoindentation technique [10]. Another measurement technique uses the sensitivity of phonons in graphene to measure the tension deformation by Raman spectroscopy [11, 12].
The diffractometry technique evaluating the lattice deformation...