Search

Three quarters of the world's significant urban centers are located in coastal regions where clay minerals are prevalent. The microstructures and physico-mechanical properties of clay sediments are highly susceptible to alterations in pore water chemistry. The pore water chemistry in soil changes easily due to groundwater pollution, seawater erosion, degradation, etc. However, there are several inconsistencies in the literature on the change of physical and mechanical properties of clay soils caused by the change of pore water chemical properties, i.e., disparate experimental results were reported for the same soil property, or varying explanations were proposed for the identical experimental results. Currently, the research in this field mainly focuses on the macroscopic behavioral modifications while lacking the explanations of microscopic mechanism. Therefore, this paper presents a comprehensive review of researches conducted over the past four decades on the impact of pore water chemistry (including salt type, salinity, ion valence, pH) on soil properties such as the microstructure, settlement, Atterberg limits, shear strength, conductivity, unsaturated soil mechanics properties and thermal properties. The fundamental mechanisms underlying the varied experimental observations on clay sediments affected by salt and pH are systematically explored, and deficiencies in this field are identified. The observed dispersion in the literatures is attributed to the spatial variation and heterogeneity of soil compositions, different test methods, and insufficiency of the fundamental microscopic mechanisms of the observed soil behaviors, etc. Therefore, it is necessary to further explore the essential mechanisms of the test results in the future to establish a unified conclusion. [ABSTRACT FROM AUTHOR]

As a typical form of damage, wear greatly affects the service properties of products, and non-destructive evaluation of the degree of wear is urgently needed. In this paper, the wear degree of AISI 1045 steel was evaluated by magnetic Barkhausen noise (MBN) testing. The root mean square (RMS) and full width at half maximum (FWHM) of MBN were extracted to establish the quantitative relationships between the tribological indicators and the stress state. The results indicate that the RMS decreases linearly and the FWHM increases quadratically with increasing tribological indicators, which can distinguish among different wear stages, including abrasive, adhesive and fatigue wear. However, the RMS shows a complicated nonlinear relation with the residual stress during the wear process. In addition, the MBNenergy parameter is also calculated to reveal the features of the hysteresis loop at the wear scar. Both the coercivity Hc and the maximum magnetic permeability μmax are linearly related to the tribological indicators and quadratically related to the stress, which reflects the effect of tribo-magnetisation on the MBN signals. The variation mechanism of MBN under different wear stages is attributed to the combined effect of plastic deformation and the stress state by microstructure observations. [ABSTRACT FROM AUTHOR]

To efficiently isolate oxygen and block free radical reactions， sodium alginate (SA), sodium polyacrylate (PAAS), attapulgite (ATP), and melatonin (MLT) were selected to develop an oxygen-insulating physicochemical synergistic inhibitor. The water loss experiment, EPR experiment, and programmed temperature rise experiment were used to characterize the performance of the inhibitor. The results show that the optimal ratio of the oxygen barrier physicochemical synergistic inhibitor is 2.5 wt% SA, 1.5 wt‰ PAAS, 9 wt% ATP, 6 wt% MLT, and 3 wt% CaCl2. In the oxygen-insulating physicochemical synergistic inhibitor, the MLT can react with oxidizing radicals in the coal to slow down the process of the oxidation reaction of the coal, and the SA gel can fill the pore space to prevent oxygen adsorption on the coal surface, the inhibition rate of the inhibitor reaches 70% at 120°C. Compared with the original coal, the CO concentration of the treated coal samples is reduced by 253.9ppm compared with that of the original coal, the generation rate is reduced by 1. 13 × 10−11 mol·cm−3·s−1, and the rate of oxygen consumption is reduced by 90. 65 × 10−11 mol·cm−3·s−1 at 120°C. The above results show that the oxygen-insulating physicochemical synergistic inhibitor developed in this paper can effectively improve the fire extinguishing efficiency is environmentally friendly and pollution-free, and has good application prospects. [ABSTRACT FROM AUTHOR]

The poor mechanical and tribological properties limit the higher requirements of aluminum alloys in engineering and industrial applications, which leads to the rapid development of aluminum matrix composites (AMCs). Particulate reinforced AMCs have attracted extensive attention in automobile, electronics and military industries due to their low density, high strength, and excellent wear resistance. However, the interfacial reaction between reinforcements and the Al matrix tends to occur in conventional preparation processes owing to the higher reaction temperatures. The spark plasma sintering (SPS) technique is considered to be an efficient method for the fabrication of metal matrix composites, which can achieve rapid sintering, lower sintering temperatures, and higher densities than conventional fabrication processes. In addition, SPS can produce AMCs with excellent non-porous microstructure, fine grain size, and a strong bonding interface between reinforcement and Al matrix. Therefore, the interfacial reaction is effectively controlled and the structural integrity is maintained, resulting in enhanced strength and ductility. Based on the advantages of particulate reinforced AMCs and the SPS technique, the particulate reinforced AMCs fabricated by SPS have been extensively studied in recent decades, but have not been systematically evaluated. Therefore, this paper reviews the state-of-the-art particulate reinforced AMCs fabricated by SPS, focusing on the microstructure characterization, strengthening mechanisms, and mechanical and physical properties. Furthermore, the future research priorities and challenges of the high-performance particulate reinforced AMCs fabricated by SPS are also prospected. [ABSTRACT FROM AUTHOR]

In this paper, the contact heating technology was combined with the warm and hot stamping process of high-strength aluminum alloy, and the corresponding experimental device was developed. For the contact heating-warm stamping process, it's found that as the heating temperature increases, the mechanical properties of the parts first decrease and then increase, while the springback decreases. Meanwhile, for the contact heating-hot stamping process, it's found that the aluminum alloy sheets experience large plastic deformation during contact heating, resulting in the refinement of microstructure and the increase in dislocation density, and the performance of the formed parts is improved. [ABSTRACT FROM AUTHOR]

Natural pozzolan is a promising supplementary cementitious material for hydraulic concrete due to the pozzolanic effect, especially in the area where fly ash is scarce. In this paper, the physical properties of pozzolan were evaluated. The effects of pozzolan fineness and content on the microstructure, compressive strength, and early-age chemical shrinkage of pozzolan blended cement pastes were investigated. The results showed that the addition of pozzolan decreased the compressive strength of hardened cement pastes. The pozzolanic reactivity was closely related to the fineness of pozzolan, and higher pozzolan content led to lower strength. X-ray diffraction (XRD) and thermogravimetric (TG) analysis proved that Ca(OH)2 was consumed by reacting pozzolan, forming new calcium silicate hydrated (C-S-H). Besides, the addition of pozzolan caused the increase in porosity, which was reflected by the increase in macro-pores content. The chemical shrinkage of cement pastes was mainly determined by the hydration rate of cement, so the early-age chemical shrinkage was notably reduced after adding pozzolan due to its lower reactivity than cement clinker. In addition, finer pozzolan particles resulted in less macro-defects in the cement matrix, which enhanced the deformation resistance of hardened cement paste, and thus the chemical shrinkage was also decreased. [ABSTRACT FROM AUTHOR]

Asphalt mixture recycled technology (Al-Saffar et al. 2021) is an efficient method for achieving asphalt pavement sustainability. The optimum asphalt content of recycled asphalt mixture is first determined by the Marshall test in this paper. Second, Materials Studio software was used to simulate the interface effect between three different asphalts and aggregate, and the adhesion between asphalt and aggregate was characterised based on the interface energy. The mesoscopic structural characteristics of three asphalt mixtures were then analysed using digital image processing technology. Finally, through three macro experiments, the influence of old asphalt on the mechanical properties of recycled asphalt mixture was studied from a macro perspective. At the microscopic level, the results show that the presence of the old asphalt reduces the adhesion between the asphalt and the aggregate. At the mesoscopic level, the presence of old asphalt reduces the porosity of the asphalt mixture. At the macroscopic level, the addition of old asphalt improves the high temperature and water stability of recycled asphalt mixture while decreasing the low temperature crack resistance. The microscopic and mechanical properties of old asphalt on recycled asphalt mixture are explained on three levels, and new ideas for research on recycled asphalt mixtures are provided. [ABSTRACT FROM AUTHOR]

AbstractThis paper investigated the role of nano-particles in the resistance of marine concrete to chloride ion (Cl-) corrosion under the combined influence of flexural fatigue load and freeze-thaw cycles. We analyzed the nano-particles to improve the mechanism of Cl- attack resistance of the concrete. The results indicated that the combined effect of freeze-thaw cycles and flexural fatigue load promoted the migration of Cl- into the concrete. The free Cl- content in the compressive zone of concrete initially decreased and subsequently increased with the increasing stress level and combined action stage. In the tensile zone of concrete, the free Cl- content increased significantly with the stress level and combined action stage. The nano-SiO2 and nano-CaCO3 could effectively improve the Cl- attack resistance of concrete and the optimal amounts of nano-CaCO3 and nano-SiO2 were 1% and 2% (Nano-particles were substituted for equal amount of cement), respectively. According to the SEM and XRD results, nano-particles could help cement hydrate and lower the size and orientation of Ca(OH)2 in the interfacial transition zone (ITZ). Nano-SiO2 exhibited a good pozzolanic effect, while the pore structure and ITZ of concrete with nano-SiO2 was denser compared to the concrete with nano-CaCO3. [ABSTRACT FROM AUTHOR]

Composite materials with complex internal microstructures, such as the flax nonwoven bio-composite studied in this work, require advanced numerical models in order to predict their mechanical performance. Otherwise, the micro-structural interactions that take place between their components makes very difficult to obtain their mechanical properties and failure mechanisms. This paper presents a novel methodology that couples two homogenization formulations: a phenomenological one, the serial-parallel mixing theory; and a numerical multiscale procedure. The resulting methodology has a minimal computational cost, while it is capable to account for the different interactions that take place among the composite constituents. With the proposed approach, it is possible to characterize the mechanical response of nonwoven composites and to predict their structural failure. The methodology developed is applied to a flax nonwoven bio-composite manufactured and tested by the German Aerospace Center (DLR). The good results obtained from the simulation, when compared with the experimental values, allow considering the proposed procedure an excellent approach for the analysis of large structures made with complex microstructures, such as nonwoven biocomposites. [ABSTRACT FROM AUTHOR]

The mechanical property of the thin-ply composite are improved, which has more uniform microstructure and fewer manufacturing defects compared with the standard ply composite. Based on the micromechanics theory, an RVE analysis method is proposed considering the interlaminar resin region in this paper. The influence of the interlaminar resin region on the RVE model of thin-ply composites is studied. The initiation and propagation of cracks are discussed in the thin-ply laminate under transverse tensile, and the in-situ transverse strength of 90° ply is predicted with different thicknesses. The results show that considering the interlaminar resin region has a great influence on the in-situ strength prediction results. Reducing the ply thickness can change the fracture mechanism and improve the transverse in-situ strength of the material. [ABSTRACT FROM AUTHOR]

A study of the mechanical properties of Ti64 alloy through Small Punch Test is presented in this paper. The method and the validity of the correlation coefficients developed for nuclear steels are first verified on wrought alloy and then applied to additive manufactured material. The yield strength values obtained agree with the literature and domains of negative strain rate sensitivity could be highlighted for the microstructure resulting from additive manufacturing. The creep tests carried out showed good agreement between the present results and those reported in the literature on usual creep representations. This allows to validate the models used and to extend the small punch methods to the case of titanium alloys. The results are used for comparing the mechanical behaviour of additive manufactured Ti64 alloy to that of wrought alloys. [ABSTRACT FROM AUTHOR]

The paper deals with results of long-term stress rupture tests on "cross-weld" specimens made of Super 304 H – P92 heterogeneous welds. Stress rupture tests were carried out at temperatures of 625°C and 650°C up to 20,000 hours to rupture. Creep rupture strength and WSF values of Super 304 H – P92 welds for 10,000 hours at both 625°C and 650°C were calculated. The preferential location of failure was the intercritical part of the heat affected zone in P92 steel. Hardness of both base materials did not show significant changes during creep exposure at both 625°C and 650°C. However, gradual hardening of the weld metal occurred. Metallographic studies were performed in individual parts of heterogeneous welds. A special attention was paid to precipitation reactions in both base materials and heat affected zones. A residual content of vanadium in Super 304 H steel affected precipitation processes. Vanadium partly substituted niobium in the modified Z-phase ((V,Nb)CrN). [ABSTRACT FROM AUTHOR]

For heat resistant alloys, long-term structural stability at high temperatures is a critical issue for alloy design and applications. In this paper, the long-term creep behaviours and structural stabilities of six heat resistant high Ni alloys and austenitic stainless steels have been studied. The longest creep rupture life is up to 359 283 hours. High Ni and Cr alloys show a good combination of high creep and oxidation resistances. Precipitation of nano MX particles with a very low growth rate improves long-term creep resistance at high temperatures. Long-term stable multiple nanoprecipitates of MX, Cu-rich, Laves and M23C6 phases can greatly contribute to the creep strength. Low Ni austenitic stainless steels show comparatively low oxidation and creep resistances. It was first found that at 800°C, Cr2N could form in the low Ni steel with a long-term crept by the absorption of nitrogen from the air into the matrix. [ABSTRACT FROM AUTHOR]