scholarly journals Testing of Auxetic Materials Using Hopkinson Bar and Digital Image Correlation

2018 ◽  
Vol 183 ◽  
pp. 02045 ◽  
Author(s):  
Tomáš Fíla ◽  
Petr Zlámal ◽  
Jan Falta ◽  
Tomáš Doktor ◽  
Petr Koudelka ◽  
...  
Keyword(s):  
Digital Image Correlation ◽  
Digital Image ◽  
Poisson’S Ratio ◽  
High Speed ◽  
Split Hopkinson Pressure Bar ◽  
Lattice Structure ◽  
Frame Rate ◽  
Image Correlation ◽  
Poisson's Ratio ◽  
Strain Gauges

In this paper, a split Hopkinson pressure bar (SHPB) was used for impact loading of an auxetic lattice (structure with negative Poisson’s ratio) at a given strain-rate. High strength aluminum and polymethyl methacrylate bars instrumented with foil strain-gauges were used for compression of an additively manufactured missing-rib auxetic lattice. All experiments were observed using a high-speed camera with frame-rate set to approx. 135.000 fps. High-speed images were synchronized with the strain-gauge records. Dynamic equilibrium in the specimen was analyzed and optimized pulse-shaping was introduced in the selected experiments. Longitudinal and lateral in-plane displacements and strains were evaluated using digital image correlation (DIC) technique. DIC results were compared with results obtained from strain-gauges and were found to be in good agreement. Using DIC, it was possible to analyze in-plane strain distribution in the specimens and to evaluate strain dependent Poisson’s ratio of the auxetic structure.

scholarly journals TESTING OF HYBRID NICKEL-POLYURETHANE FOAMS AT HIGH STRAIN-RATES USING HOPKINSON BAR AND DIGITAL IMAGE CORRELATION

2018 ◽  
Vol 18 ◽  
pp. 72 ◽  
Author(s):  
Marcel Adorna ◽  
Petr Zlámal ◽  
Tomáš Fíla ◽  
Jan Falta ◽  
Markus Felten ◽  
...  
Keyword(s):  
Digital Image Correlation ◽  
Digital Image ◽  
High Speed ◽  
Split Hopkinson Pressure Bar ◽  
Dynamic Equilibrium ◽  
Polyurethane Foams ◽  
Frame Rate ◽  
Image Correlation ◽  
Correlation Technique ◽  
High Speed Camera

In this paper Split Hopkinson pressure bar (SHPB) was used for dynamic testing of nickel coated polyurethane hybrid foams. The foams were manufactured by electrodeposition of a nickel coating on the standard open-cell polyurethane foam. High strength aluminium alloy bars instrumented with foil strain-gauges were used for dynamic loading of the specimens. Experiments were observed using a high-speed camera with frame-rate set to approx. 100-150 kfps. Precise synchronisation of the high-speed camera and the strain-gauge record was achieved using a through-beam photoelectric sensor. Dynamic equilibrium in the specimen was achieved in all measurements. Digital image correlation technique (DIC) was used to evaluate in-plane displacements and deformations of the samples. Specimens of two different dimensions were tested to investigate the collapse of the foam structure under high-speed loading at the specific strain-rate and strain.

scholarly journals DETERMINATION OF THE POISSON’S RATIO IN CONCRETE BY USING DITIGITAL IMAGE CORRELATION

2021 ◽  
pp. 26-32
Author(s):  
Yaroslav Blikharskyy
Keyword(s):  
Digital Image Correlation ◽  
Digital Image ◽  
Poisson’S Ratio ◽  
Concrete Strength ◽  
Correlation Method ◽  
Image Correlation ◽  
Poisson's Ratio ◽  
Digital Correlation ◽  
Transverse Stresses

The article presents the results of the experimental investigation of concrete prismsand determination of the Poisson's ratio using the method of digital image correlation (DIC). Toachieve the goals and objectives of the research, a concrete prism measuring 100x100x400 mm ofclass C50 / 60 was formed. The surface of the prism was cleaned and levelled to a smooth surfacewith a mechanical device and grinding stone. The surface of the prism is then cleaned with a solventto remove dust residues. After that, speckles were applied to determine the strain using the DICmethod. For determine the strain, by using digital image correlation, were used Two FlirGrasshopper 3 cameras with a Computar F25 / 2.8 lens and a Sigma 70-200 mm f2.8 APO EX DGHSM Macro II lens. Stains for image correlation were recorded at a speed of 250 ms. 2 LED lampswere used for lighting. Since the press is not able to record the load in time, to record the load useda camera at a speed of 50 frames/sec. The load was applied evenly at the same rate to the physicaldestruction of the test samples. As a result, the images were processed using VIC-2D software toobtain vertical and transverse strains. The advantage of the image correlation method is the abilityto obtain deformations and, accordingly, the stress of the full surface of the sample. Thus, if weanalyse the horizontal (transverse) stresses for a prism with a concrete strength of C50 / 60, it ispossible to see the appearance of internal cracks in the sample before it occurs outside, at a timewhen cracks cannot be visually fixed. As a result of work the technique of testing of concrete sampleswith use of digital correlation of the image is developed and presented. The Poisson's ratio from thebeginning of loading to the destruction of the sample was determined experimentally by the developedmethod.

Direct measurement and master curve construction of viscoelastic Poisson's ratio with digital image correlation

Strain ◽  
2018 ◽  
Vol 54 (6) ◽  
pp. e12294 ◽  
Author(s):  
Yusuke Hoshino ◽  
Kazuki Tamai ◽  
Yuelin Zhang ◽  
Satoru Yoneyama
Keyword(s):  
Digital Image Correlation ◽  
Direct Measurement ◽  
Digital Image ◽  
Poisson’S Ratio ◽  
Master Curve ◽  
Image Correlation ◽  
Poisson's Ratio

scholarly journals The use of charge-coupled device cameras for characterizing the mean deflected shape of an aerospace panel during broadband excitation

2018 ◽  
Vol 54 (1) ◽  
pp. 13-23 ◽  
Author(s):  
Elias Lopez-Alba ◽  
Christopher M Sebastian ◽  
William JR Christian ◽  
Eann A Patterson
Keyword(s):  
Digital Image Correlation ◽  
Digital Image ◽  
High Speed ◽  
High Volume ◽  
Random Excitation ◽  
Frame Rate ◽  
Image Correlation ◽  
Charge Coupled Device ◽  
The Mean ◽  
Standard Frame

In vibration experiments demanding long-duration measurements, traditional point-wise techniques are often employed, despite the availability of high-speed digital image correlation. This is due to the high volume of images generated by the latter technique, which limit acquisition times and lengthen post-processing times. In this experimental investigation, it is demonstrated that standard frame rate charge-coupled device cameras yield results for the mean deflected shape of a reinforced aerospace panel subject to a random broadband excitation between 0 and 800 Hz that are not statistically different to those from high-speed cameras. The images from both types of camera were processed using digital image correlation to generate out-of-plane displacement maps, which were then decomposed using Chebyshev descriptors for ease of comparison and to determine the mean deflected shape. The results indicate that, with appropriate sampling rates and durations, standard frame rate charge-coupled device cameras can be used to study broadband random excitation behavior of structures when mean behavior needs to be characterized over long time scales compared to the excitation wavelengths. This is contrary to accepted procedures, but offers comparable accuracy with substantially reduced computational resources compared to using high-speed cameras, as well as effectively unlimited data acquisition periods, which is useful in condition monitoring, for example.

Determination of creep compliance, recovery and Poisson's ratio of elastomers by means of digital image correlation (DIC)

2017 ◽  
Vol 59 ◽  
pp. 245-252 ◽  
Author(s):  
Leonardo Israel Farfán-Cabrera ◽  
Juan Benito Pascual-Francisco ◽  
Omar Barragán-Pérez ◽  
Ezequiel Alberto Gallardo-Hernández ◽  
Orlando Susarrey-Huerta
Keyword(s):  
Digital Image Correlation ◽  
Digital Image ◽  
Poisson’S Ratio ◽  
Creep Compliance ◽  
Image Correlation ◽  
Poisson's Ratio

scholarly journals Measurement of Nonlinear Poisson’s Ratio of Thermoplastic Polyurethanes under Cyclic Softening Using 2D Digital Image Correlation

Polymers ◽  
2021 ◽  
Vol 13 (9) ◽  
pp. 1498
Author(s):  
Yi-Xian Xu ◽  
Jia-Yang Juang
Keyword(s):  
Digital Image Correlation ◽  
Digital Image ◽  
Poisson’S Ratio ◽  
Measurement Errors ◽  
Large Strain ◽  
Reference Sample ◽  
Cyclic Softening ◽  
Image Correlation ◽  
Poisson's Ratio ◽  
Thermoplastic Polyurethanes

Thermoplastic polyurethanes (TPUs) and other elastomers are widely used in many applications for the advantages they provide in terms of high elasticity, lightness, resistance to breakage, and impact resistance. These materials exhibit strong hysteresis in the large strain stress-strain behavior, known as cyclic softening or the Mullins effect. Despite the extensive studies on this phenomenon and the importance of Poisson’s ratio, how the Poisson’s ratio of these materials changes during cyclic uniaxial tests is still unclear. Here, we measure the nonlinear Poisson’s ratio of TPU and investigate its correlation with cyclic softening using two-dimensional digital image correlation (2D-DIC) combined with the reference sample compensation (RSC) method. This accuracy-enhanced method can effectively eliminate the measurement errors induced by the unavoidable out-of-plane displacements and lens distortion. We find that the Poisson’s ratio of TPUs also exhibits large hysteresis in the first cycle and then approaches a steady state in subsequent cycles. Specifically, it starts from a relatively low value of 0.45 ± 0.005 in the first loading, then increases to 0.48 ± 0.005 in the first unloading, and remains largely constant afterward. Such a change in the Poisson’s ratio results in a slight volume increase (≈1%) at a maximum strain of 17.5%. Our findings are useful for those who use finite element method to analyze the mechanical behavior of TPU, and shed new light on understanding the physical origin of cyclic softening.

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