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

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.

Multi-Aperture Optical System of Photon Counting in the Image for Aberration-Free Space Debris Observations through a Turbulent Atmosphere (Part I)

The paper solves the problem of space debris monitoring to ensure the safety of space exploration. Space debris fragments are small-sized control objects with angular sizes up to 0.002 arcsecond. Therefore, optoelectronic systems of high resolution and permeability allowing one to measure the coordinates and recognize these weak control objects with a given accuracy and probability having integral brightness up to +18 stellar magnitude are necessary for the location (search, detection, measurement, and identification) of space debris fragments. To solve the optical location problems of space debris the Part I of the article proposes the concept of building a ground-based optoelectronic control system. The system consists of three consecutive and interrelated information channels: an image formation channel based on the matrix of individual telescopes and aperture synthesis technology; image detection channel based on scanning raster detectors and photon counting technology in the image; and image processing channel based on digital correlation compensation technology of atmospheric distortions. Advantages of a matrix of separate telescopes, photodetection and correlation processing are noted in the article. The proposed concept is protected by a patent of the Russian Federation, which is discussed in detail in Part II.

Digital correlation method for power measurement

The method of frequency transformations measurement for digital power of electrical signals meters is offered. The method is based on instantaneous power correlation processing. Such approach allows increasing noise immunity of the proposed method, and, as a consequence, its accuracy. Proposed mathematical theory to estimate the variance measurement error of the power of electrical signals. Proposals have been made to reduce the error in measuring the power of electrical signals. The analysis of the interference immunity of the correlation method for measuring power can be extended to the condition under which the interference spectra in voltage and current signals are different.

SARAS CD/EoR Radiometer: Design and Performance of the Digital Correlation Spectrometer

In the currently accepted model for cosmic baryon evolution, Cosmic Dawn (CD) and the Epoch of Reionization (EoR) are significant times when first light from the first luminous objects emerged, transformed and subsequently ionized the primordial gas. The 21[Formula: see text]cm (1420[Formula: see text]MHz) hyperfine transition of neutral hydrogen, redshifted from these cosmic times to a frequency range of 40[Formula: see text]MHz to 200[Formula: see text]MHz, has been recognized as an important probe of the physics of CD/EoR. The global 21[Formula: see text]cm signal is predicted to be a spectral distortion of a few 10’s to a few 100’s of mK, which is expected to be present in the cosmic radio background as a trace additive component. Shaped Antenna measurement of the background RAdio Spectrum (SARAS) is a spectral radiometer purpose designed to detect the weak 21[Formula: see text]cm signal from CD/EoR. An important subsystem of the radiometer, the digital correlation spectrometer, is developed around a high-speed digital signal processing platform called pSPEC. pSPEC is built around two quad 10-bit analog-to-digital converters (EV10AQ190) and a Virtex 6 (XC6VLX240T) field programmable gate array, with provision for multiple Gigabit Ethernet and 4.5[Formula: see text]Gbps fiber-optic interfaces. Here, we describe the system design of the digital spectrometer, the pSPEC board, and the adaptation of pSPEC to implement a high spectral resolution (61[Formula: see text]kHz), high dynamic range ([Formula: see text]:1) correlation spectrometer covering the entire CD/EoR band. As the SARAS radiometer is required to be deployed in remote locations where terrestrial radio frequency interference (RFI) is a minimum, the spectrometer is designed to be compact, portable and operating off internal batteries. The paper includes an evaluation of the spectrometer’s susceptibility to RFI and capability to detect signals from CD/EoR.

The Buckling and Post-Buckling of Steel C-Columns in Elevated Temperature

This work deals with the investigation of a steel thin-walled C-column subjected to compression due to temperature increase. These experimental studies of the compressed columns in post-buckling state were conducted to determine their load-carrying capacity. To ensure appropriate supports and keeping of columns, plates with grooves were constructed. The tests of the columns’ compression for different preloads were carried out. By comparing the experiment results, numerical calculations based on the finite element method (FEM) and the semi-analytical method (SAM) of solution were performed. The computations were executed with the use of full material characteristics with consideration of large strains and deflections. Furthermore, while observing the deformation of columns, a non-contact Digital Correlation ARAMIS® system was employed whose calculated results of deformations are very close to the results of the numerical method. The paper revealed that maximum recorded loads under temperature rise are comparable regardless of a value of initial load. A good correlation in results between used methods was achieved. The main goal of the present work was to assess of behavior of thin-walled compressed steel columns in a temperature-controlled environment till their full damage.

Blister propagation in sandwich panels

This paper deals with the problem of face/core interfacial disbonds in sandwich panels that are pressurised, i.e. the disbond has an initial fluid pressure that causes the disbond to deform. The problem is often referred to as a blister. The panel with a blister is then subjected to an in-plane compressive load. Four different panels are analysed and tested, having different size disbonds and different initial internal pressure. The cases are analysed using a finite element approach where the blister is modelled using fluid elements enabling the pressure inside the blister to vary as the in-plane load is applied. The analysis uses non-linear kinematics, and in each load step, the energy release rate is calculated along the disbond crack front. This model is used for failure load predictions. The four cases are then tested experimentally by filling a pre-manufactured disbond cavity with a prescribed volume of air. This air volume is then entrapped, and the panel is subjected to an in-plane compressive load. The load and blister pressures are measured throughout the test and compared with the finite element analysis. Surface strains and blister deformations are also measured using digital correlation measurements. The predicted failure loads compare well with the experimental results, and so does the blister pressures, the latter at least qualitatively.