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Influence of different random pattern creation forms on the results of experimental modal analysis performed by high-speed digital image correlation

100%

Hagra M. , Schrötter M. , Lengvarsky P.

tom Vol. 8, no. 1

22--26

In this contribution an influence of random contrast patterns creation on the quality of the obtained results of experimental modal analysis performed by high-speed digital image correlation is described. Three common forms of random pattern creation were investigat-ed. While the first form was presented by the black speckles printed on white matt vinyl foil and bonded on the sample surface, in the sec-ond and the third case, respectively, the black speckles were sprayed on white sprayed sample surface or on paint white one. For the pur-poses of modal parameters estimation in the form of natural frequencies, mode shapes and damping ratios the program called Modan3D, developed in the authors department, was used. The results obtained by Modan3D were compared with the results achieved by system Pulse specialized for vibration analysis.

Digital image correlation (DIC) on fresh cement mortar to quantify settlement and shrinkage

84%

Dzaye E. D. , Tsangouri E. , Spiessens K. , de Schutter G. , Aggelis D. G.

2019

tom Vol. 19, no. 1

205--214

The displacement of fresh cementitious media initiated by water evaporation and cement hydration is very complex. In the plastic state, the cement particles deform in the plane and move at different rates leading to the development of plastic shrinkage cracks. In parallel, the material settles as bleed water is released. Tracking the particles three-dimensional heterogeneous displacement requires a highly-sensitive monitoring technique. Digital image correlation (DIC) has been selected to quantify settlement and shrinkage strain evolution. DIC excels compared to classical LVDT point-transducers since it is non-contact and the analysis is full field providing a three-dimensional (3D) view of deformations and strains. 3D visualization maps of early-age deformation contribute to the interpretation of early age mobility. DIC enables the measurement of non-uniform surface displacement due to material heterogeneity and geometry that affects the shrinkage distribution which cannot be detected by traditional LVDTs. The procedure through which the DIC speckle pattern is applied on a wet rough surface is critically discussed.

Comparison between direct and indirect measurement methods for bulge tests

84%

Marinho E. , Silva-Jr A. , Batalha G.

Archives of Materials Science and Engineering

2013

tom Vol. 61, nr 2

77--86

Purpose: To reinforce the standardization of the bulge test measuring procedures by comparison of two different bulge forming measurement methods. Design/methodology/approach: Two different bulge forming measurement methods are used simultaneously in order to reinforce the standardization of the bulge test measuring procedures. An indirect method, Digital Image Correlation (DIC), is compared with a direct one, ultrasound pulse-echo method. Findings: The main conclusion is that the DIC system is a valid indirect measurement method to study bi-axial sheet metal forming. Research limitations/implications: The constant pressure bulge test method was used and it yielded positive results for comparing the direct and indirect method (considering thickness measurement of the bulge dome), as an important research implication is that the touch less measurement method could be applied to other sheet metal forming processes. Practical implications: Tension tests are used as a standard accepted procedure to determine material parameter values for characterizing the forming sheet behaviour. However, by using a tension test, only a limited strain range can be considered for determining the true stress – true strain curve. Based on this limitation, the bulge test is used to achieve a much larger strain range under bi-axial loading conditions. Originality/value: An indirect method, Digital Image Correlation (DIC), is compared with a direct one, ultrasound pulse-echo method, in situ, real time and on the same specimen.