Macro Performance Research Articles

Experimental study on ageing characteristics of electric locomotive ethylene propylene rubber cable under mechanical–thermal combined action

The train-mounted ethylene propylene rubber (EPR) cables of electric locomotive are partly restricted by the body structure and spatial layout and are in a combined environment of strong mechanical bending and thermal ageing. The degradation characteristics of the insulation layer have not yet received sufficient attention. In order to study the ageing characteristics of EPR cables of electric locomotive under the combined action of machine and thermal, this paper designs a bending–thermal combined ageing test platform for cables with a temperature of 135°C, bending diameter of 393.52 mm, 590.28 mm and unbending cables, and tests after ageing. The product has been tested by infrared spectroscopy, scanning electron microscopy, elongation at break and broadband dielectric spectroscopy. The research results show that the bending outer part of the train-mounted EPR cable is a pain point. Under the combined action of bending and thermal, whether it is microstructure or macro performance, the degradation rate and degree of the bending of outer insulation layer are greater than the value under a single thermal ageing condition. Mechanical bending has an accelerating effect on the ageing of the EPR insulation layer. The research results can provide a reference for the ageing characteristics of the train-mounted EPR cable under the bending–thermal synergy and the evaluation of operating state of the train-mounted EPR cable under bending–thermal operating conditions.

Investigation of the macro performance, mechanism, and durability of multiscale steel fiber reinforced low-carbon ecological UHPC

China proposes a carbon peak by 2030 and carbon neutrality by 2060; reducing carbon dioxide emissions and capturing and using carbon dioxide has become a research focus. As a low-carbon ecological cement, sulphoaluminate cement (SAC) has gradually replaced ordinary Portland cement and has become a research hotspot. SAC has the advantages of high early strength, low CO2 emission, fast setting, and fast hardening. It is widely used in emergency repairs, rapid repairs, and offshore engineering. This paper developed a new low-carbon ecological ultra-high-performance concrete with high strength and excellent durability, namely sulfoaluminate cement-based reactive powder concrete (SACRPC). This work researched the effect of different scale steel fiber on macro performance (including rheological property, workability, and mechanical properties), durability, and micro/ nanostructure of SACRPC. Various characterization methods showed that the addition of mSF (micro steel fiber) improved the pore structure of the SACRPC, it was increased the porosity of the matrix, and provided enough space for the growth of hydration products AFt (ettringite), AH3 (gibbsite), and C-S-H (Calcium Silicate Hydrate); thus, it accelerated the hydration process of the SACRPC. The hydration products filled the pores of the SACRPC tightly bonded the fiber and the matrix. It was revealed that the multi-level and multiscale reinforced mechanism, namely hydration products, contributed to micro/nanostructure, mSF bridged micro-cracks, and MSF (macro steel fiber) prevented macro-cracks. In the sulfate erosion experiment, SO42- ions entered the matrix and occurred a chemical reaction; AFt regenerated on the surface and inside the SACRPC with a fibrous morphology and smaller crystals. The regenerated AFt filled the pores of the SACRPC and refined the pore structure. The whole process was similar to the self-healing effect of concrete. The unhydrated cement particles reacted with water and formed new hydration products that healed the cracks.

Micro and macro experimental study of using the new cement-based self-stress grouting material to solve shrinkage problem

Self-stress grouting can effectively improve the weak reinforcement caused by shrinkage of the ordinary cement-based grouting materials (OGM). However, the research on self-stressing grouting materials is still not perfect, and the micro and macro performance discrepancies between it and OGM are rarely analyzed. Aiming to this, this paper developed a new cement-based self-stress grouting material (LS-1). By analysing the mechanical mechanism of self-stress reinforcement, it is found that self-stress reinforcement can reduce the effective shear stress of the rock fracture surface, thereby avoiding shear slip failure. Furthermore, by orthogonal testing, the optimal ratio of content of LS-1 was obtained as 10% of U-type expansive agent (UEA), 1.2% of polycarboxylic acid high-efficiency water-reducing agent (PC) and 1.2% of the early-strength concrete agent (EHD). The control experiment was conducted to investigate the performance discrepancy between the two types of grouting materials. The result showed that in terms of longitudinal restricted expansive displacement, under the same experimental conditions, the LS-1 expanded by 1.521 mm while OGM shrunk by 10.374 mm. Then, the damage model of both grouted coal specimens under the impact of acoustic emission (AE) with uniaxial load was established and analyzed. Besides, scanning electron microscope (SEM) was used to verify the effect of LS-1. It was found that for the OGM grouted coal specimen, the damage variable and degree was more extensive, and the bearing capacity is lower, indicating the expansive needle-shaped crystals that are formed after LS-1 solidification are beneficial to improve the density of the grout and avoid the shrinkage. This research will provide a reference for theoretical research and the engineering application of cement-based grouting material.

The Effect of the TIG Method-based Melting of Welds on the Properties and the Structure of Welded Joints Made of Austenitic Steel

The article discusses the effect of TIG method-based melting on the properties and the structure of welded joints made of austenitic steel AISI 304. The tests involved the making of 2 mm thick joints followed by their subsequent melting performed in two different ways, i.e. with maintaining interpass temperature and immediately after welding. The study also included the performance of mechanical tests, macro and microscopic metallographic tests as well as hardness measurements and corrosion resistance tests. Results obtained in the tests justified the conclusion that the melting process and its conditions significantly affect the properties and the structure of welded joints.

Study on aging index of mechanical and electrical properties of high temperature vulcanized silicone rubber

Composite insulators are affected by various factors in operation. With the increase of operation time, the shed of silicone rubber composite insulators will become hard and brittle. In this paper, it is found that the hardness of long-term silicone rubber shed meets the standard requirements. The tear strength, tensile strength, elongation at break, resistance to electric tracking and corrosion loss decrease significantly after 5-10 years of operation. The decline of silicone content on the micro surface and the escape of inorganic fillers are the reasons for the deterioration of macro performance. Finally, the evaluation system for aging performance of insulators is preliminarily established, according to the aging degree of insulator, operation and maintenance suggestions are proposed.

Property enhancement in relaxor-PbTiO3 single crystals by alternating current poling: Evaluation of intrinsic and extrinsic contributions

Piezoelectric activity has always been the most concerned performance for PbTiO3-based relaxor ferroelectrics. Recently, the alternating current poling (ACP) method has been developed as a simple and economical technique to optimize piezoelectric performance. However, the mechanism of the ACP method is still debatable. In this work, we carried out the ACP on the 0.27Pb(In1/2Nb1/2)O3-0.46Pb(Mg1/3Nb2/3)O3-0.27PbTiO3 single crystal, a noticeable piezoelectric improvement of 20% has been achieved in comparison with the direct current poled sample, meanwhile, the dielectric loss is reduced by 26%. We found that the ACP sample demonstrates a uniform domain pattern with a large domain size dominated by 109° domain walls, in contrary to the complicated domain structures which contain both 109° and 71° domains in the DCP sample. With this uniform and simple domain structure, the crystal lattice is weakly constrained and very susceptive to external stimulation, resulting in enhanced piezoelectric response in ACP poled sample. Meanwhile, dielectric loss is reduced for the low domain wall density. The current work gives a comprehensive description of the ACP poled samples, including the microscopic domain structure, the quantitative estimation of contributions arise from lattice deformation and domain wall motions, and reveals the interactions between domain structure and the macro performance, which provide important guidelines for the design of high-performance ferroelectrics utilizing domain tailoring techniques.

Effects of Fiber Diameter on Crack Resistance of Asphalt Mixtures Reinforced by Basalt Fibers Based on Digital Image Correlation Technology.

It is now more popular to use basalt fibers in the engineering programs to reinforce the crack resistance of asphalt mixtures. However, research concerning the impact of the basalt fiber diameter on the macro performance of AC-13 mixtures is very limited. Therefore, in this paper, basalt fibers with three diameters, including 7, 13 and 25 μm, were selected to research the influences of fiber diameter on the crack resistance of asphalt mixtures. Different types of crack tests, such as the low temperature trabecular bending test (LTTB), the indirect tensile asphalt cracking test (IDEAL-CT), and the semi-circular bend test (SCB), were conducted to reveal the crack resistance of AC-13 mixtures. The entire cracking process was recorded through the digital image correlation (DIC) technique, and the displacement cloud pictures, strain, average crack propagation rate (V) and fracture toughness (FT) indicators were used to evaluate the crack inhibition action of the fiber diameter on the mixture. The results showed that the incorporation of basalt fiber substantially improved the crack resistance, slowed down the increase of the displacement, and delayed the fracture time. Basalt fiber with a diameter of 7 μm presented the best enhancement capability on the crack resistance of the AC-13 mixture. The flexibility index (FI) of the SCB test showed a good correlation with V and FT values of DIC test results, respectively. These findings provide theoretical advice for the popularization and engineering application of basalt fibers in asphalt pavement.

Microstructure and improved plasticity of (FeCoNi1.5CrCu)p/Al composites subject to adjusted deep cryogenic treatment (DCT)

This study aimed to reveal the effects of Deep Cryogenic Treatment (DCT) on the microstructure and mechanical properties of (FeCoNi1.5CrCu)p/Al composites. Precisely, the microwave sintering-prepared samples were soaked in liquid nitrogen to optimize the DCT parameter. The results demonstrated that the (111) and (200) crystal face indexes were induced by released internal stress during DCT to turn to (220). The preferential orientation plays a vital role in plasticity improvement. The compression experiments show that the plasticity of DCT 36 is greatly improved, reaching 142%, compared to the untreated sample. The macro performance shows that the cracks change from one-way to two-way propagation, and the fracture toughness of DCT 36 increased by 155.6% compared to untreated due to multi-system slip.

Dynamic forecasting performance and liquidity evaluation of financial market by Econophysics and Bayesian methods

In a complex financial system, what is the forecasting performance of macro and micro evolution models of Econophysics on asset prices? For this problem, from the perspective of machine learning, we study the dynamic forecasting and liquidity assessment of financial markets, based on econophysics and Bayesian methods. We establish eight dynamic prediction methods, based on our proposed likelihood estimation and Bayesian estimation methods of macro and micro evolution models of econophysics. Combined machine learning thinking and real data, we empirically study and simulate the out-of-sample dynamic forecasting analysis of eight proposed methods and compare with the benchmark GARCH model. A variety of loss functions, superior predictive ability test (SPA), Akaike and Bayesian information criterion (AIC and BIC) methods are introduced to further evaluate the forecasting performance of our proposed methods. The research of out of sample prediction shows that (1) the method of the simplified stochastic model with Bayesian method for only sample return has the best forecasting performance; (2) the method of the stochastic model with Bayesian method for only return samples has the worst forecasting performance. For the liquidity assessment problem, there is a strong correlation between the trading probability evaluated by the proposed eight methods and the real turnover rate, and an increase of liquidity is correspond to the increase of asset risk. In other words, it suggests that all proposed methods can well evaluate market liquidity.

Assessing the Commodity Market Price and Terms of Trade Exposures of Macroeconomy in Emerging and Developing Countries

ABSTRACT This paper provides novel evidence on commodity market exposure, i.e., the impacts of commodity price and terms of trade fluctuations on macro performance amongst 46 emerging and developing countries (EMDCs) in Africa, Asia and the Latin American and Caribbean (LAC) region. We estimate the exposure of six macroeconomic variables to the commodity prices and terms of trade. Our results indicate that in overall terms, there is a strong and statistically significant long-run relationship between the vector of analyzed world trade prices and macro variables in all EMDCs. However, based on the short-term reactions, only about 10% of the macroeconomic variation amongst the EMDCs is due to commodity market-related exposures. Our results also indicate that the commodity market exposure is not unanimous across countries, amongst regions, or especially between measures of exposure.

The Return of Global Macro - why investors should be wary of irrational expectations

With the collapse of LTCM in 1998, global macro investing / trading suffered a severe blow in terms of acceptance in the markets. Because of many highly leveraged hedge funds, investors and counterparts lost serious money, markets were at the brink of destabilisation and the regulators had to come to help. Hedge funds which use so-called global macro strategies were suddenly out of fashion. In 2000, Soros and Robertson left the global macro business and restructured their activities. It seemed that global macro would disappear as a major strategy, traded only by a small number of fund managers, and other strategies such as long / short equity would dominate alternative investment strategies. However, in 2002 many investors noticed th epositive performance of gloabl macro (+14% in the CSFB Tremont Subindex) and felt that they should consider investments into it. Hence many firms will launch new fund sto satisfy this new demand. However, some established funds have recently returned capital to their investors due to the lack of opportunities or the smaller return potential. In this paper we analyse global macro investing and discuss th epotential rewards and risks for investors.

The Effectiveness Perceptual Skills Rebuilding Program on Improving Motor Problem in Student With Developmental Coordination Disorder

Background and Aims: Developmental coordination disorder is one of the most obvious deficiencies in the development of motor skills in primary school children. The aim of this study was to investigate the effect of perceptual skills program on improving motor problems in children with developmental coordination disorders in elementary students. Methods: The research was quasi-experimental with a pretest-posttest design. The statistical population includes all students (age range 7-9 years) in the city of Mashhad who had referred to rehabilitation centers in this city in 1396 and their number was 40 people. After identifying students with developmental coordination disorder, 20 of them were randomly selected to receive training and trained for 16 sessions of 30 minutes. The instruments used in the study were Developmental Coordination Disorder Questionnaire Version 7 for Parents (DCDQ-7), Wechsler Intelligence Test for Children (short form) and Broninex-Ozertsky Motor Skills Test. Results: Analysis of statistical results showed that reconstruction of perceptual skills had a significant effect on the growth of perceptual-motor macro performance (P<0.001, F= 51.25 ) perceptual-motor equilibrium performance (P<0.001, F= 25.11). And fine motor perceptual function( P<0.001, F= 42.32) in children with developmental coordination disorder, and the results of the study indicate a significant effect of perceptual exercises on motor skills of subjects in the experimental group compared to the group. It was control. Conclusion: The present study showed that perceptual skills training can have useful and significant applications for improving motor problems in children with developmental coordination disorders and can provide various and valuable services for assessment, educational methods and treatment of these children.

Laboratory experiments of various bio-asphalt on rheological and microscopic properties

Bio-oil is widely used to prepare bio-asphalt, which has attracted more and more attention. However, bio-asphalt performance is different for bio-oil is various, so it is challenging to have a unified standard evaluation. In order to investigate the characteristics of various kinds of bio-asphalt, this paper used five bio-oils (vegetable oil, soybean oil, castor oil, straw oil, waste oil) to modify the neat asphalt. Meanwhile, the rock asphalt was selected to modify the bio-asphalt, and its content is 5% by weight of the neat asphalt. By testing the rheological performance of rock asphalt modified bio-asphalt, the modification effects of different bio-oils were compared, and the advantages and disadvantages of different bio-oils were analyzed and compared. Finally, through Fourier transform infrared spectroscopy (FTIR) test and scanning electron microscope (SEM), the mechanism of bio-oil and rock asphalt composite modified neat asphalt was studied. The test results show that the rheological properties of different rock asphalt modified bio-asphalt are intensely different. Also, the infrared spectra of bio-oils from different sources are extremely different. There is no obvious correspondence between the infrared spectra of bio-oils and the macro performance of bio-asphalts. Besides, neat asphalt, bio-oil, and rock asphalt have favorable mixing compatibility. This paper determines the applied situations of various bio-oil and evaluates the modification effect of different types of bio-oil on neat asphalt. At the same time, this work reveals the modification mechanism of rock asphalt modified bio-asphalt, which provides a basis for future bio-asphalt application.

Study on the microscopic damage of porous asphalt mixture under the combined action of hydrodynamic pressure and ice crystal frost heave

Hydrodynamic pressure and frost heaving damage of ice crystals are the main reasons for the damage of porous asphalt mixture pavement in winter. Therefore, the author takes the open graded friction course (OGFC) asphalt mixture as an example, uses ANSYS finite element software to conduct multi-field coupling analysis of fluid and temperature for OGFC-13 asphalt mixtures with different porosities, pore structures, and different temperatures. Results show that the phenomena of “washing” and “pumping” of dynamic water exist in the connected pores at the same time. Under low-temperature conditions, low speed and heavy load are the most disadvantageous to the pores of the pavement surface. The maximum positive and negative pressures were 1.162 and −0.616 MPa, respectively. The wall shear stress distributed at the entrance and exit of the pores also reached peaks of 33.40, 25.77, and 20.07 kPa at the load duration T/2. In the early stage of ice crystal development, the temperature was lower, the temperature difference was greater, and the freezing rate was faster. In the later stage, the temperature difference decreased, the freezing rate decreased, and the same temperature value as the asphalt mixture matrix was finally reached. In addition, under the combined influence of temperature and air voids contents, the maximum stress value in the bonding surface near the connected pores was 2.89 MPa, which was 1.5 times the maximum stress value in the asphalt mortar. Under the interaction of hydrodynamic pressure and frost heave force, the upper layer of porous asphalt concrete pavement in contact with the wheels is destroyed earlier than the internal structure of the pavement. This article provides a quantitative expression for the hydrodynamic pressure and frost heave damage of porous asphalt pavement. Also, it reveals the influence of ice and snow melt on the macro performance of asphalt pavement from a meso-level perspective.

Multitechnique investigation of concrete with coal gangue

Although the research of coal gangue as construction aggregate has been conducted for many years, the fundamental knowledge about the links between the microscopic properties of coal gangue and the macroscopic properties of concrete has not been discovered yet. In this paper, gravel was entirely replaced by coal gangue to improve the utilization rate. The compressive strength, fluidity, and compactness of concrete were studied to explore the macro performance of coal gangue concrete (CGC). Meanwhile, mercury intrusion porosimeter (MIP), scanning electron microscope (SEM), and nanoindentation were used to comprehensively analyze the pore structure, morphology, and micromechanical properties of coal gangue as aggregate. The experimental results showed that coal gangue has a hierarchical structure, wide pore distribution, and poor mechanical properties in microcosmic. Compared with ordinary concrete (OC), both the fluidity and compressive strength of CGC were lower. However, due to the large porosity and water absorption of coal gangue, the bonding surface between coal gangue and cement was denser, which makes the overall compactness of CGC better than OC. The width of the interface transition zone (ITZ) of CGC did not change significantly with the water-cement ratio (w/c), while that of OC did. When w/c was greater than 0.4, the compressive strength of CGC was only about 10% lower than that of OC. The pore structure and micromechanical properties of coal gangue determined the compactness and strength of CGC.

The influence of fly ash content on ITZ microstructure of coal gangue concrete

Coal gangue is the main solid waste produced in coal mining, and the resource utilization of coal gangue has become a popular topic in the industry. It is gradually applied that coal gangue concrete (CGC) prepared by replacing crushed stone with coal gangue in a certain proportion. Further, adding fly ash (FA) to CGC improves not only the performance of CGC, but also the resource utilization rate of coal-based solid waste, and this helps meet low carbon and environmental protection requirements. The effect of FA on the macro performance of CGCs has been investigated extensively; however, only few studies have examined microinterface structure changes, interface transition zone (ITZ) characteristics, and mortar microcharacteristics, which are closely related to the macro performance of concrete. Therefore, exploring the effect of FA on the microstructure performance of CGC has great scientific value and engineering significance. In this study, concrete with a 40% replacement rate of coal gangue, which is widely used in engineering practice, is considered the research object. The effect of 0%, 10%, 20%, 30%, and 40% FA on ITZ thickness, mortar pore structure, and micromorphology of CGC aggregates and the relationship between the microstructure parameters and mechanical properties of concrete are analyzed using microhardness tests, mercury intrusion porosimetry, and scanning electron microscopy. The research results indicate that, (1) with an increase in FA content, the decreasing range of the ITZ thickness of gangue concrete first increases and then decreases, and the total porosity of the mortar area increases, but the proportion of serious damage pores decreases; (2) the thickness of the coal gangue ITZ is smaller than that of crushed stone ITZ, which is attributed to the refinement of FA and the filling of ITZ pores; and (3) FA has a dual improvement effect on the ITZ performance of the gangue concrete and the pore structure of the mortar area. These research results provide a reference for further research on the influence of mineral admixtures on concrete ITZ and theoretical guidance for the modification methods of CGC.

Influence of paste coating thickness on the compressive strength, permeability, and mesostructure of permeable concrete

The macro performance and mesostructure of permeable concrete are largely determined by the paste coating thickness (PCT) on aggregates within the fresh mixture. Accordingly, in the present study, the strength and permeability of permeable concrete with different paste coating thicknesses were measured. The mesostructure characteristics of cement paste and pore were subsequently quantified by X-ray CT images and image processing techniques. As a result, the influence of PCT on the compressive strength and permeability, the characteristics of cement paste and pore was determined. The distribution of cement paste thickness and total pore size were used as functions of paste coating thickness, which coud be used to predict these mesostructure characteristics at the design stage of permeable concrete. The significance of this paper includes providing a deeper understanding of the relationship between macro performance and mesostructure from the perspective of paste coating thickness within mixtures.

Combination usage of nano-SiO2-coated steel fiber and silica fume and its improvement effect on SFRCC

To further improve the fiber-matrix interfacial properties and enhance the macro-mechanical performances of steel fiber reinforced cement-based composite (SFRCC), two effective modification methods, nano-SiO2-coated steel fiber (NSF) targeted at the fiber-matrix interface and silica fume targeted at cement matrix, were tried to use together. The modification effects of NSF, silica fume and their combination usage were characterized and analyzed at multi-levels. Backscattered electron image analysis (BSE-IA) was used for micro microstructure characterization and the micro-hardness test was employed to evaluate the micro-mechanical property. A fiber pull-out test was drawn up and the interfacial bond properties, including the pull-out load-displacement curve, average bond strength and pull-out energy, were obtained. Flexural and compressive tests were conducted and the bending performance, flexural and compressive strength were focused on. The results show that the modification mechanisms of NSF and silica fume on SFRCC are quite different in that the one-way modification of NSF is from interface to bulk paste whereas that of silica fume is from bulk paste to interface. Both two methods improve the microstructure and performance of SFRCC effectively. Combination usage takes full advantage of the two modification methods, matches the improvement of different micro zones by two-way modifications, improves the interfacial bond properties and thereby achieves the further enhancement effect on macro performance.

A Method for Internal Curing Water Calculation of Concrete with Super Absorbent Polymer

The internal curing method is effective in reducing the self-desiccation of concrete, and the amount of internal curing water (IC water) is greatly important to the shrinkage and strength of concrete. A method for calculating IC water of concrete with and without mineral admixture has been developed. The method is derived from Powers’ model for the phase distribution of a hydrating cement paste. To verify the method, a series of autogenous shrinkage and compressive strength of concrete with and without super absorbent polymer (SAP) were evaluated compared with the method proposed previously. To explain the macro performance of hardened concrete, the nonevaporable water content and calcium hydroxide content measurement were utilized to evaluate the degree of hydration of cement pastes. And, mercury intrusion method and image analysis method were used to explore the pore structure in hardened cement pastes and air void characteristics in hardened concrete, respectively. Furthermore, the evolution process was also studied for the relative humidity inside the concrete.

A detailed study of the substitution mechanism for improved zinc-borate: High-performance and its crystal structure variation

The substitution properties of Mn2+ to Zn2+ for Zn3B2O6 ceramic was probed at the atomic scale using the first principle calculation, involving the bond properties, electron density, and formation energy. All samples were synthesized through the solid–state reaction method, and the variation of macro performance, like sintering and dielectric properties, was discussed in detail. The sintering property was characterized by the differential-thermal & thermo-mechanical analyzer and scanning electron microscopy, the dielectric property was characterized by the Network Analyzer, and the phase formation was verified by the X-ray dispersive spectroscopy. Three sites in the Zn3B2O6 crystal are available for Mn2+ to be occupied, and the substitution process for the Zn3 site has the lowest formation energy. The ion-substitution in ZnO4 tetrahedron results in the change of the electron distribution and bond property. The dielectric performance of Zn3B2O6 ceramic has been improved, and the microstructure has been densified at 900 °C, yielding values of εr = 6.58, Q×f = 88,100 GHz (15 GHz), relative density = 96.7%, and τf = −56.5 ppm/°C as x = 0.04. Additionally, the activation energy has been decreased and the densification window shifts forward slightly.