Published paper
Maurice Whelan Institute for Health and Consumer Protection, European Commission DG-JRC, Italy
ABSTRACTThe design and testing of a reference material for the calibration of optical systems for strain measurement is described, together with the design and testing of a standardized test material that allows the evaluation and assessment of fitness for purpose of the most sophisticated optical system for strain measurement. A classification system for the steps in the measurement process is also proposed and allows the development of a unified approach to diagnostic testing of components or sub-systems in an optical system for strain measurement based on any optical technique. The results described arise from a European study known as SPOTS whose objectives were to begin to fill the gap caused by a lack of standards.
International audienceThis paper presents the use of a sensitivity study to find the best combinations of free length and fibre angle in an unnotched Iosipescu test processed with the virtual fields method. The sensitivity to noise coefficients arising from the special virtual fields procedure are used to build up a cost function. This function is aimed at balancing out the coefficients of the different orthotropic stiffnesses so that the same confidence level can be reached on all these parameters. Then, experimental validation was performed using a speckled interferometry (ESPI) system. Full-field strains were measured and stiffnesses identified and compared between the usual 0°, 30 mm configuration and an improved 25°, 40 mm configuration. The outcome of the optimisation was confirmed by testing the same specimen several times and comparing scatter between the two configurations. This is a first promising result on the way to the design of a new test for orthotropic stiffness identification on a single specimen from full-field measurements
Purpose -The purpose of this paper is to rigorously determine the tensile properties of a selective laser sintering (SLS) material. Emphasis was placed on the anisotropy and inhomogeneity of the material, the repeatability of the SLS process, and the effect of age (actually moisture absorption) on the material properties. Design/methodology/approach -Two builds of 144 dogbone tensile specimens each were tested, with 18 specimens stored for 43 days in a non-desiccated environment before testing. Specimens were distributed throughout the build volume and aligned with the apparatus' principal axes. Tensile properties were treated statistically, using the t-test to determine the differences between various samples. Findings -The material was transversely isotropic in Young's modulus and strain to failure, and generally orthotropic in ultimate tensile strength. The material was inhomogeneous throughout the build volume and affected by age, with a 57 per cent reduction in University of Technology after 43 days (the changes in properties were suggested to be due to moisture absorption). Properties varied by up to 25 per cent from build-to-build with no change in nominal process parameters. Research limitations/implications -It was not possible to confirm the "ageing" effect was caused by moisture absorption, and further work is suggested in this area. The causes of inhomogeneity and the effect of re-coater action should also be studied further. Originality/value -This is the most complete study of an SLS material's mechanical properties to date. The statistical analyses used further allow increased confidence in the conclusions drawn. This is also the only study to use cross-fill scanning to produce specimens, and, therefore, isolate the effect of the re-coater action.
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