Large Compression Research Articles

Research on freeze-thaw damage to RC column based on incompatibility deformation from pores

In cold environment, the durability of reinforced concrete (RC) structure mainly depends on its frost resistance. Based on the incompatibility deformation from pores, the meso-calculation model was established for concrete under freeze–thaw cycles (FTCs). Meanwhile, the meso-numerical model of RC columns with FTCs under eccentric compression was established to verify the calculation method. Moreover, the mechanical behavior of RC columns with different FTCs was discussed by the calculation method. The results show that the frost damage of concrete can be effectively reflected by the meso-calculation method, and the calculation method was verified by comparing theoretical calculation results and test results. Moreover, the non-linear characteristics of the specimen under eccentric compression can be obtained from the calculation model. And the deterioration of concrete caused by 100 FTCs has a significant effect on the ductility of specimens. With the increase of FTCs, the failure mode of specimens under large eccentric compression transforms to the failure of specimens under small eccentric compression, which is consistent with the test results. This numerical simulation method can be used to predict the mechanical behavior of RC structures after FTCs, and the theoretical calculation results have certain safety reserves for RC structures.

Physical and mechanical properties of calcareous soils: A review

Calcareous soil is widely distributed throughout tropical areas. Due to its unique sedimentary environment and soil behaviors, severe engineering problems and disasters have occurred in many regions. To understand the differences in the mechanical properties of calcareous soils in different regions, material composition, physical and mechanical properties of calcareous soils, including specific gravity and void ratio, compression properties, shear properties, and strength properties, were analyzed. The relationship between the sedimentary environment, material composition, and mechanical properties of calcareous soil was examined based upon the results. Results show that the calcareous soil in the South China Sea has a high calcium carbonate content, large particle size, high compressibility, and low bearing capacity, while sand from the Kish Island in the Persian Gulf and Agami sand from Egypt have low compressibility and high bearing capacity. In the South China Sea, Calcareous soil is more difficult to crush than those from the Hormuz Island and Bushehr Port in the Persian Gulf, Dog’s Bay in Ireland, and Quiou in France. Overall, calcareous soils from various locations exhibit significant differences in properties based upon their physical traits. It is suggested that the influence of sedimentary environment and geological conditions should be considered in engineering constructions.

Transition from engineering strain to the true strain in analytical description of metals hardening

Purpose of the work is related with the impossibility of correctly estimating the strain hardening of metals (alloys) in the area of their large total deformations due to absence of additivity in the traditionally used value of engineering strain g, its nonlinear change in the area of large values, and absence of data in the technical literature Hall-Petch coefficient Ai for logarithmic true deformations, which led to the task of correct transition from the values of the engineering strain 0 < g < 50...60 % to the value of the true logarithmic strainn 0 < e < 1...3. Methodology. The theoretical analysis of the regularities of deformation hardening of metals (alloys) from the engineering strain is carried out, the transition from engineering to logarithmic ("true") strain of metals (alloys) by analytical representation of metal hardening graphs as a function of logarithmic (true) strain. in contrast to the degree of engineering strain is presented. Originality. Analytical expressions are presented that allow the use of known theoretical data on the strain hardening of metals (alloys) at small (50...60 %) total engineering strains g during cold pressure treatment to transition to logarithmic (true) strain e with large total deformations. Practical value. The obtained mathematical expressions allow to use the accumulated in the technical literature experimental data on the hardening of metals and alloys with small engineering strains in the processes of cold processing of metals (alloys) by pressure to determine the hardening with large total logarithmic (true) strains. These data can also be used to solve metallophysical problems of metal processing by pressure associated with large total compressions.
 Keywords: cold forming of metals and alloys; hardening; degree of deformation

Enhancement of Heat Ageing Properties of Epoxidised Natural Rubber Blend

In recent years, automotive hose and belt specifications have changed, requiring longer product life in terms of swelling, wear and heat ageing. Diene-based rubbers, such as natural rubber (NR) and styrene-butadiene rubber (SBR), have been widely used in diverse industries. However, some apparent defects such as limited ageing resistance and large compression set, have been demonstrated in some rubbers cured by sulfur or peroxides. In the making of general and industrial rubber goods, short production and sufficient scorch time is crucial especially by using an injection moulding. In this work, blend of Epoxidised Natural Rubber (ENR 25) and Butadiene was developed with two types of curing systems namely Conventional and Efficient Vulcanisation system. The aim of the study is to produce a satisfactory heat resistance rubber compounds and adequate process safety for rubber manufacturing. Results showed that curing system applied significantly affected thermal stability property of the compounds. Modulus and hardness of the blends appeared to decrease progressively with ageing. However, greater thermal stability especially ageing at 100°C for 200h was observed with compound containing efficient curing system compared to conventional curing system which corresponded to the cross link density attributed by the torque value and dynamic mechanical analysis. The results on stiffness however was effected by the curing system applied. The influence of cure temperature on the chemical crosslink density on both cure systems are being investigated. The network results will be correlated with the technical properties.

Investigating Effect of Strain and Geometric Defects on Single Polarization Vortex in PbTiO3 Nanowires

The single polarization vortex structure in nanowire can be used to store binary data in Non-Volatile Ferroelectric Random Access Memories (NVFRAM or FRAM). However, at the nanoscale, mechanical strains or geometry defects (cracks) can affect the polarization vortex and they are one of the reasons to reduce the service life as well as the reliability of the device. In this study, the atomic simulation method using the interactive potential function based on the core-shell model is selected to investigate the effects of strain, cracks and domain wall deviations (DW) on the single polarization vortex in PbTiO3 (PTO) nanowires. The results obtained showed that the polarization vortex can appear or disappear depending on the position and size of the crack. Deviations in the DW position make the polarization vortex change the size and shape. Besides, the magnitude of the vortex investigated increases under tension strain and decreases under compression strain. Especially, in large compression strain (10%), the vortex can be disappeared.

Capillary-Induced Wrinkle-to-Fold Transitions Under Biaxial Compression.

Wrinkles in bilayer systems comprising a thin stiff film attached to a soft substrate can globally transition into folds under sufficiently large compression. This phenomenon has been extensively studied primarily using uniaxially compressed systems. However, inducing the wrinkle-to-fold transition at designated locations on a wrinkled surface under small biaxial compression remains a challenge. In this study, we describe a method for causing randomly oriented wrinkles to locally evolve into folds using water droplets. When a droplet comes into contact with the random wrinkles that have spontaneously formed upon film deposition owing to residual biaxial compressive strains, radially extended folds instantaneously emerge at the droplet boundary. Upon water evaporation, the wrinkles beneath the droplet also undergo a transition, leaving a fold network. By contrast, the surface regions distant from where the droplet was placed retain the wrinkle morphology. The folded areas can be controlled by adjusting the volume and number of droplets. These transitions are enabled by the capillary forces of water that help to increase the local compressive strains. This capillary-induced wrinkle-to-fold transition provides a simple mechanism to develop folds in selected locations on wrinkled surfaces of film-substrate systems subject to small biaxial compression, which is unachievable with conventional approaches.

The Effect of Compressibility and Outer Boundaries on Incipient Viscous Fingering

SummaryThe knowledge of the effects of instability and heterogeneity on displacements, primarily enhanced oil recovery, and carbon dioxide storage are well known, although they remain difficult to predict. The usual recourse to modeling these effects is through numerical simulation. Simulation remains the gold standard for prediction; however, its results lack generality, being case-specific. There are also several analytic models for displacements that are usually more informative than simulation results. However, these methods apply to steady-state, incompressible flow.Carbon dioxide injection for storage uses compressible fluids and, in the absence of producers, will not approach steady-state flow (Wu et al. 2017). Consequently, it is unlikely that storage will be in reservoirs of open boundaries (steady-state flow). Flow of compressible fluid necessitates the use of closed or partially sealed boundaries, a factor that is consistent with compressible flow.This work deals with the conditions that cause the onset of incipient viscous fingering or Saffman-Taylor (ST) instability. The actual growth and propagation of fingers, a subject of much recent literature, is not discussed here. The original ST formalism of M > 1 for gravity-free flow is highly restrictive: it is for linear flow of nonmixing incompressible fluids in steady-state flow. In this work, we relax the incompressible flow restriction and thereby broaden the ST criterion to media that have sealing and/or partially sealing outer boundaries. We use the nonlinear partial differential equation for linear flow and developed analytic solutions for a tracer flow analog and also for a two-fluid compressible flow. The analysis is restricted to stabilized flow and to constant compressibility fluids, but we are not restricted to small compressibility fluids.There is no transition (mixing) zone between displacing and displaced fluids; the displacement is piston-like. The absence of a transition zone means that the results apply to both miscible and immiscible displacements, absent dispersion, or local capillary pressure. The assumption of a sharp interface is to focus on the combined effect of mobility ratio and compressibility. We use the product of the fluid compressibility and pressure drop (cfΔP) to differentiate the compressibility groups (Dake 1978; Dranchuk and Quon 1967), where ΔP is defined as the pressure drop within the specific fluid region.The results will be based on proposed analytical solutions compared to numerical simulation. The proposed formulation is less restrictive than the original ST formalism of M > 1 and allows evaluation of viscous fingering initiation or ST stability criterion in the presence of different boundary conditions (open vs. closed boundaries) with compressible fluids under the stated assumptions, which is the scope of this work.The key contribution here is the effect of external boundaries, which consequently makes necessary the use of compressible fluids. Absent compressibility, the necessary condition for the growth of a viscous finger is simply the mobility ratio, M > 1. It is the objective of this work to study how the ST criterion is affected by the presence of sealing and partially sealing outer boundaries with the consequent inclusion of compressible flows as in carbon dioxide storage and enhanced oil recovery by gas injection.The results show that adding compressibility always makes displacements more unstable for stabilized background flow, even for a favorable mobility ratio (M < 1) at extremely large compressibility (e.g., cf > 5×10−3 1/psi). For a sealed external boundary (no production or leakage), displacements will become more stable as a front approaches an external boundary for all mobility ratios (M) investigated.

Dispersion relations for waves in visco-gravitating anisotropic magnetoplasmas

The effect of Braginskii's full viscosity tensor on an infinite non-conducting, gravitating anisotropic plasma in which the medium is trapped in a strong magnetic field is discussed in the context of Braginskii's magnetohydrodynamic model with Chew–Goldberger–Low double adiabatic approximation and finite Larmor radius (FLR) correction. Through linearization of the perturbed equations, the general dispersion relation is derived for the separate compression, shear, and drift viscosity components as well as the FLR corrections. We investigate the stability for parallel and transverse perturbations with respect to the direction of the magnetic field, and both gravitational and fire-hose instabilities are found. The role of each viscous term is to suppress instability, but each component works in different ways. The FLR acts in a way that is very similar to the drift viscosity. The instability threshold is found to be independent of viscosity for compression and shear viscosity, but both the drift viscosity and FLR corrections can change the critical wavenumber for the instability. The compression viscosity is most effective at reducing the growth rate of the gravitational instability, whereas the shear viscosity works to suppress the fire-hose instability. The result of the present study may be useful for the study of large scale compression, shear, and drift plasma flow in and around clusters of galaxies and galactic disks and for the solar and stellar wind.

Современные подходы к лечению механической желтухи на фоне злокачественного поражения панкреатобилиарной зоны

Aim. To study the role of tumors of the pancreatobiliary zone in the development of obstructive jaundice. To evaluate the effectiveness of endoscopic methods of diagnosis and treatment of this pathology. Materials and methods. The study is based on the results of the activities of JSC “MSU Neftyanik” in Tyumen for 2011-2020. During this period, 1284 patients with obstructive jaundice were admitted for emergency indications. Of this number, 181 patients had signs of cancerous lesions of the organs of the pancreatobiliary zone. The results obtained were used to evaluate effective endoscopic methods of diagnosis and treatment of patients in this group. Results. Malignant lesion of the pancreatobiliary zone is 14.3% of all cases of emergency treatment of patients with obstructive jaundice. The main cause is cancer of the pancreas, cancer of the bile ducts, as well as cancer of the large duodenal papilla and compression of the bile ducts “from the outside”. Performing emergency duodenoscopy on the first day after admission of patients made it possible to accurately verify the cancerous nature of the disease in the vast majority of patients. The most effective method for the relief of biliary hypertension syndrome in this group is bile duct stenting. Despite the varied nature of the cancer lesion, effective stenting was achieved in 71.3% of patients. If it is technically impossible to carry out stenting, minimally invasive puncture catheterization of the intrahepatic bile ducts is performed. Conclusion. Currently, cancer of the pancreatobiliary zone was established in every 5-7 patients with obstructive jaundice. Emergency duodenoscopy and ERCH is an effective diagnostic method that allows you to verify the “cancerous” nature of jaundice with a probability close to 100%. The most effective method of bile duct decompression in this group of patients is endoscopic transpapillary stenting.

Influence of buried depth on seismic capacity of underground subway stations through performance-based evaluation

Buried depth is an important physical factor that affects the seismic performance of underground structures yet remains scarcely considered in existing seismic design. This paper aims to determine the influence of buried depth variation on the seismic capacity of underground subway stations in the framework of performance-based seismic design with particular focus on the influence on the inter-storey drift ratio limit. A brief introduction is presented to determine the performance level of subway station structures based on the pushover method. The influence of buried depth on the seismic performance index (inter-storey drift ratio) of subway station structures is investigated, as well as its influence on the shear distribution and failure mode of the key structural component, that is the middle column. It is found that the inter-storey drift ratio limit generally decreases with increasing buried depth and the station ductility worsens. The failure mode of the middle column changes from large eccentric compression to small eccentric compression with increasing buried depth owing to increased axial compression. The results are applied to estimate an optimum buried depth that improves the overall safety of subway station structures.

Off/on switchable smart electromagnetic interference shielding aerogel

Summary Smart electromagnetic interference (EMI) shielding materials with tunable EM wave response characteristics are attractive for future EM devices. Here, we report an off/on switchable EMI shielding material that can be tuned from EM wave transmission to shielding and vice versa by mechanical compression and decompression. This smart material is prepared by filling conductive carbon nanoparticles into wood-derived lamellar carbon aerogel, showing reversible compressibility and strain-sensitive conductivity. The original aerogel has good impedance matching and low dielectric loss, allowing the EM wave to pass through. Mechanical compression enables the carbon nanoparticles to establish highly conductive pathways in the aerogel, which significantly increases the conductivity of aerogel and thus activates its EMI shielding performance. This function switch is reversible by repeatedly compressing and decompressing the aerogel. The availability of such a never-before-realized off/on switchable EMI shielding material provides an opportunity for the development of advanced smart EM devices.

Edge-aware coding tree unit hierarchical partitioning for quality scalable compression of depth maps

The scalable extension of the high efficiency video coding standard (SHVC) combines the large compression efficiency and high visual quality of HEVC, with the possibility of encoding different versions of the same video in a single bitstream. However, this comes at the cost of high computational complexity. In this context, many research works aim to reduce this complexity for texture images. We aim at achieving the same objective, but for depth maps whose characteristics make them different from conventional texture images. Depth maps are indeed characterized by areas of smoothly varying grey levels separated by sharp discontinuities at object boundaries. Preserving these discontinuities is crucial to enable high quality of synthesized views at the receiver side. In this paper, we propose a fast depth maps encoding scheme for quality scalable HEVC while exploiting depth maps characteristics, SHVC Coding Unit (CU) depth information and the correlation between the Base Layer (BL) and the Enhancement Layers (ELs) of SHVC. If a CU corresponds to a depth smooth region, we maintain the same best coding depth of its co-located in the BL. If a CU is a sharp region, the best coding depth is computed in the same way as in the original SHVC. Experiments are conducted and satisfying results are obtained as the proposed method improves the SHVC coding speed without a significant impact on the synthesized views Rate-Distortion tradeoff

Mechanical characterisation and modelling of a thermoreversible superamolecular polyurethane over a wide range of rates

Understanding the mechanical response of thermo-recoverable elastomers to applied deformation at different strain rates and temperatures is crucial for more effective exploitation of these reusable materials in industrial applications. The research presented in this paper aims to understand the thermal and mechanical responses of a healable, elastomeric supramolecular polyurethane, examining morphology, rheology and mechanical responses from low to high strain rates. In particular, measurement of the high strain rate response of low modulus, or low strength, materials is challenging, and the current paper addresses this by incorporating a modelling framework based on low-rate characterization. To support this research, significant characterization experiments have been performed, which also show, for the first time, the excellent reusability of the polymer. The structure of specimens with different thermal histories was characterized using nuclear magnetic resonance spectroscopy, gel permeation chromatography and small angle X-ray scattering. Differential scanning calorimetry and Rheometry were used to investigate thermomechanical performance during heating and cooling cycles, whilst large strain compression characterization was performed on a commercial screw-driven test frame, a hydraulic loading system and a split-Hopkinson pressure bar. To describe the mechanical response of the polymer, a viscoelastic softening model was developed and characterized. The model incorporates data from rheometry and dynamic mechanical analysis using the principle of time-temperature superposition in a Prony series, combined with a non-linear large strain response, and recovery. The model was able to describe low strain rate behaviour under monotonic and cyclic loading, as well as predicting the response to monotonic loading at medium-to-high strain rates from 40 to 1220 s−1. The paper therefore demonstrates the effectiveness of using the viscoelastic theory and its analytical model to calibrate and further predict the mechanical behaviour of polymers at different strain rates: this is particularly useful for low modulus materials for which high strain rate characterization is challenging.

Zero Energy Consumption Motor Cooling Device Based on Vortex Tube Effect

In the daily operation of the industry, due to the long-term operation of machinery, the motor load is too large, resulting in motor overheating. In this paper, a kind of large-scale machine tool is designed, which uses the energy wasted in the non-working state of the large-scale machine tool to convert kinetic energy into air energy to produce compressed air with larger compressibility. Then, the compressed gas is sent to the special vortex tube. By using the structural characteristics of the vortex tube device, the cooling gas with lower temperature can be generated, which can rapidly cool the motor and improve the motor operation. The efficiency and the service life of the motor reduce the probability of motor failure in the actual production process.

Improved mechanical properties and strengthening mechanism with the altered precipitate orientation in magnesium alloys

Aging prior to twinning deformation was proposed to alter the precipitate orientation of the plate-shaped β-Mg17Al12 from (0002)α basal planes (named basal plates) to {101¯0}α prismatic planes (named prismatic plates) in AZ31 Mg alloy. The experimental results showed that the compressive yield strength (CYS) of the sample containing prismatic plates increased 40 MPa and the compression ratio raised by 22% compared to that containing basal plates. The underlying strengthening mechanism was analyzed via a yield strengthen (YS) model with a function of grain size, precipitate characters (size, oritention, fraction) and Schmid factor (SF). It revealed that the improvement of CYS was mainly attributed to the altered precipitate orientation and refined grain size produced by twinning deformation. Particularly, the prismatic plates always have a stronger hardening effect on basal slip than basal plates under the same varites of precipitate diameter and SF. Besides, the decreased CRSS ratio of prismatic slip to basal slip revealed that the activity of non-basal slip in Mg alloy might be enhanced. More activated slip systems provided more mobile dislocations, contributing to the large compression ratio of the Mg rolled sheet with prismatic plates.

Limitations of plastic bending resistance for composite beams deviated from strain-limitation

Due to the demand for sustainable constructions, composite structures have become more important and lead to slim and economic solutions with a low structural self-weight. EN 1994-1-1 distinguishes between four different cross-section classes for the determination of moment resistance. For the plastic moment resistance, it is assumed, that each cross-sectional fibre can plastify without any limit on the strain. For standard composite beams with sagging moments and a high plastic neutral axis, plastic resistance and strain-limited resistance give similar results. For sections with a large compression zone height xpl and limited rotation capacity, concrete failure in the compression zone can occur before the plastic moment resistance Mpl,Rd, is reached. The strain limit design becomes critical. This paper points out the impact of the concrete part on the design of composite beams. A parametric study comparing plastic and strain limited moment resistance of a considerable variety of cross-sections has been carried out to develop the beam design methods considering compression zone height for the next generation of Eurocodes.

Shaking table test and investigation of rocking effect in a high-rise isolated structure

Laminated rubber bearings have a large compression stiffness and small tension stiffness and isolation layers show rocking deformation under bending moments. The application of isolation technology is limited in high-rise structures due to the unequal compression and tension stiffnesses. The rocking effect of a high-rise isolated structure was investigated in this work. To do this, a dynamic model of a high-rise isolated structure considering non-linear tension behaviour of the isolator and the stiffness centre offset was established. The limit criterion of the rocking angle and the corresponding input peak ground acceleration of the tension limit, damage limit and collapse limit were determined. A shaking table test of the isolated model was conducted and the aspect ratio was found to have a great influence on the structural rocking response. The response of the large aspect ratio (LAR) model was larger than that of a model with a small aspect ratio. The bearings in the LAR model were more likely to be tensioned. The test results and numerical simulations were close, confirming the accuracy of the proposed dynamic model and the limit criteria. Subsequently, dynamic analysis of frame–shear wall structures was conducted and the influence of aspect ratio and earthquake level was investigated. The proposed theories can be applied for direct predictions of rocking response and the performance state of isolators.

Creep of CFRP confined reinforced concrete members under large eccentric compression

Based on the multiaxial stress statetheory of concrete under and B3 model for calculating concrete creep, combined with the mechanical characteristics of reinforced concrete members under large eccentric compression, considering the influence of member deflection, reinforcement configuration and hoop force, the creep model of CFRP confined reinforced concrete members under long-term load is established. Compared with the experimental results, the theoretical calculation results are in good agreement with the experimental values. It has a certain guiding significance to the actual engineering structure.

Assessment of Physical and Mechanical Properties of Polyurethane as Ground Improvement Material for Peat

Peat is considered problematic soil due to its large void ratio, high compressibility and low shear strength. Various ground improvement methods have been developed in recent years to improve peat’s strength properties. Polyurethane grouting is one of the ground improvement methods that is gaining recognition as effective and fast way to stabilize soil. Polyurethane is a lightweight material produced by mixing polyol and isocyanate chemicals. Upon mixing, a polyurethane foam is created which expands up to a few times of its original volume. In this study, the strength characteristics of polyurethane with different mix ratios of polyol to isocyanate were evaluated to determine the optimum ratio suitable to be used to stabilize peat. Polyol to isocyanate ratio of 1:1, 1:1.5, 1:1.2, 1:2.5 and 1:3 were tested in this this research. The propagation, microstructure and density of polyurethane were investigated. Compressive strength of polyurethane determined using Unconfined Compression Strength test. Polyurethane created with higher ratio of isocyanate bears higher density and compressive strength compared to the polyurethane with lesser quantity of isocyanate. The cell structure of the polyurethane also is smaller with thicker cell walls. However, the curing time consumed by the polyurethane with high ratio of isocyanate is 8 times greater than the normal polyurethane. Thus, polyurethane ratio with fast curing time and high compressive strength was chosen as the optimum mix ratio to be used to stabilize peat.

A Sheet Beam Electron Gun With High Compression Ratio and Long Transmission Distance Performance for W-Band TWT Applications

A sheet beam electron gun with high compression ratio and long transmission distance performance for $W$ -band traveling-wave tube (TWT) is presented. A beam focusing electrode (BFE) with two pairs of unequal length outstretched structures is designed to provide equal positions of beam waist in both horizontal and vertical planes, which is beneficial to obtain large compression ratio and keep the beam cross section shape over a long distance. The operational voltage is set as 30 kV. The beam current is 0.505 A, and the corresponding cathode current density is about 5.59 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The simulation results show that the electron gun can provide a stable sheet beam under a 0.85-T magnet field. The compression ratio of the obtained sheet beam can be over 35, and the sheet beam can be transported through a 126-mm beam tunnel without interception with a 0.6 fill factor. The parameter sensitivities of the gun are analyzed and discussed as well.