Experimental investigation of engineered geopolymer composite for structural strengthening against blast loads

The recent increase in blast/bombing incidents all over the world has pushed the development of effective strengthening approaches to enhance the blast resistance of existing civil infrastructures.Engineered geopolymer composite(EGC)is a promising material featured by eco-friendly,fast-setting and strain-hardening characteristics for emergent strengthening and construction.However,the fiber optimization for preparing EGC and its protective effect on structural elements under blast scenarios are uncertain.In this study,laboratory tests were firstly conducted to evaluate the effects of fiber types on the properties of EGC in terms of workability,dry shrinkage,and mechanical properties in compression,tension and flexure.The experimental results showed that EGC containing PE fiber exhibited suitable workability,acceptable dry shrinkage and superior mechanical properties compared with other types of fibers.After that,a series of field tests were carried out to evaluate the effectiveness of EGC retrofitting layer on the enhancement of blast performance of typical elements.The tests include autoclaved aerated concrete(AAC)masonry walls subjected to vented gas explosion,reinforced AAC panels subjected to TNT explosion and plain concrete slabs subjected to contact explosion.It was found that EGC could effectively enhance the blast resistance of structural elements in different scenarios.For AAC masonry walls and panels,with the existence of EGC,the integrity of specimens could be maintained,and their deflections and damage were significantly reduced.For plain concrete slabs,the EGC overlay could reduce the diameter and depth of the crater and spallation of specimens.

Preparation, interfacial regulation and strengthening of Mg/Al bimetal fabricated by compound casting: A review

Mg/Al bimetal combines the advantages of both aluminum and magnesium and has broad application prospects in automotive, aerospace,weapons, digital products and so on. The compound casting has the characteristics of low cost, easy to achieve metallurgical combination and suitable for the preparation of complex bimetallic parts. However, bimetallic joint strength is low due to differences of physical properties between Al and Mg, oxide film on metallic surface and interfacial Al-Mg IMCs, which is closely related to the interfacial microstructure and properties. Therefore, how to control the interface of the bimetal to achieve performance enhancement is the focus and difficulty in this field. At present, there are mainly the following strengthening methods. First, the “zincate galvanizing” and “electrolytic polishing+anodic oxidation” technology were exert on the surface of Al alloy to remove and break the oxide film, which improved the wettability between Al and Mg. Second, the undesirable Al-Mg IMCs were reduce or elimination by adding the interlayers(Zn, Ni and Ni-Cu). Thirdly, the evolution process of interfacial microstructure was changed and fine strengthening phases were formed by adding Si element to Al alloy or rare earth element to Mg alloy. Fourthly, mechanical vibration and ultrasonic vibration were applied in the process of the filling and solidification to refine and homogenize the interfacial structure. Finally, some other methods, including secondary rolling, thermal modification, heat treatment and constructing exterior 3D morphology, also can be used to regulate the interfacial microstructure and compositions. The above strengthening methods can be used alone or in combination to achieve bimetallic strengthening. Finally, the future development direction of the Mg/Al bimetal is prospected, which provides some new ideas for the development and application of the Mg/Al bimetal.

On the strengthening and slip activity of Mg-3Al-1Zn alloy with pre-induced{1012¯}twins

{1012¯}twins were introduced into the magnesium(Mg)plate AZ31 via pre-rolling along its transverse direction.The plates,both with and without the pre-induced{1012¯}twins,were subjected to uniaxial tension along different directions.Using crystal plasticity modeling,we found that the strengthening effect of the pre-induced{1012¯}twins on the macroscopic flow stress primarily arised from the increased slip resistance caused by the boundaries,rather than the orientation hardening due to the twinning reorientation(although the latter did make its contribution in some specific loading directions).Besides,the pre-existing{1012¯}twins were found,by both experiments and simulation,to promote the activity of prismatic and pyramidal<c+a>in the parent matrix of the material.Further analysis showed that the enhanced non-basal slip activity is related to the{1012¯}twin boundaries’low micro Hall-Petch slope ratios of non-basal slips to basal slip.With the critical resolved shear stress(CRSS)obtained from crystal plasticity modeling and the orientation data from EBSD,a probability-based slip transfer model was proposed.The model predicts higher slip transfer probabilities and thus lower strain concentration tendencies at{1012¯}twin boundaries than that at grain boundaries,which agrees with the experimental observation that the strain localization was primarily associated with the latter.The present findings are helpful scientifically,in deepening our understanding of how the pre-induced{1012¯}twins affect the strength and slip activity of Mg alloys,and technologically,in guiding the design of the pre-strain protocol of Mg alloys.

Significant strengthening of copper-based composites using boron nitride nanotubes

Nanotubes, such as boron nitride nanotubes (BNNTs) and carbon nanotubes (CNTs), exhibit excellent mechanical properties. In this work, high-quality BNNTs were synthesized by ball milling and annealing. Subsequently, well-dispersed 3vol%BNNTs/Cu and 3vol%CNTs/Cu composites were successfully prepared using ball milling, spark plasma sintering, and followed by hot-rolling. Moreover, the mechanical properties and strengthening mechanisms of BNNTs/Cu and CNTs/Cu composites were compared and discussed in details. At 293 K,both BNNTs/Cu and CNTs/Cu composites exhibited similar ultimate tensile strength (UTS) of~404 MPa, which is approximately 170%higher than pure Cu. However, at 873 K, the UTS and yield strength of BNNTs/Cu are 27%and 29%higher than those of CNTs/Cu, respectively.This difference can be attributed to the stronger inter-walls shear resistance, higher thermomechanical stability of BNNTs, and stronger bonding at the BNNTs/Cu interface as compared to the CNTs/Cu interface. These findings provide valuable insights into the potential of BNNTs as an excellent reinforcement for metal matrix composites, particularly at high temperature.

Assessing the predictive capabilities of precipitation strengthening models for deformation twinning in Mg alloys using phase-field simulations

Precipitation strengthening is a key strategy for improving the overall mechanical properties of Mg alloys. In Mg-Al alloys, basal precipitates are known to strengthen against twinning, resulting in an increase in the critical resolved shear stress(CRSS) necessary for continued deformation. Although several models have been proposed to quantify the influence of precipitate shape, size, and distribution on the CRSS, the accuracy, scope, and applicability of these models has not been fully assessed. Accordingly, the objectives of this study are:(i)to analyze the accuracy of analytical models proposed in the literature for precipitation strengthening against twin thickening and propagation(in Mg-Al alloys) using phase-field(PF) simulations,(ii) to propose modifications to these model forms to better capture the observed trends in the PF data, and(iii) to subsequently test the predictiveness of the extended models in extrapolating to experimental strengthening data.First, using an atomistically-informed phase-field method, the interactions between migrating twin boundaries(during the propagation and thickening stages) and basal plates are simulated for different precipitate sizes and arrangements. In general, comparison of the increase in CRSS determined from the PF simulations and the predictions from four precipitation strengthening models reveals that modifications are necessary to the model forms to extend their applicability to precipitation strengthening against both twin thickening and propagation. A subsequent comparison between predictions from the extended models and experimental strengthening data for peak age-hardened samples reveals that the(extended) single dislocation and dislocation wall models provide reasonably accurate values of the increase in CRSS.Ultimately, the results presented here help elucidate the fidelity and applicability of the various hardening models in predicting precipitation strenghtening effects in technologically important alloys.

Quantifying Solid Solution Strengthening in Nickel-Based Superalloys via High-Throughput Experiment and Machine Learning

Solid solution strengthening(SSS)is one of the main contributions to the desired tensile properties of nickel-based superalloys for turbine blades and disks.The value of SSS can be calculated by using Fleischer’s and Labusch’s theories,while the model parameters are incorporated without fitting to experimental data of complex alloys.In thiswork,four diffusionmultiples consisting of multicomponent alloys and pure Niare prepared and characterized.The composition and microhardness of singleγphase regions in samples are used to quantify the SSS.Then,Fleischer’s and Labusch’s theories are examined based on high-throughput experiments,respectively.The fitted solid solution coefficients are obtained based on Labusch’s theory and experimental data,indicating higher accuracy.Furthermore,six machine learning algorithms are established,providing a more accurate prediction compared with traditional physical models and fitted physical models.The results show that the coupling of highthroughput experiments and machine learning has great potential in the field of performance prediction and alloy design.

Shear Strengthening of Reinforced Concrete (RC) with FRP Sheets Using Different Guidelines

The aim of this study is to investigate the influence of fiber reinforcement polymer (FRP) on shear behavior of reinforcement concrete (RC) beams with various guidelines. The FRP thickness, beam depth and concrete strength at ultimate load are considered as main strength parameters. A finite element (FE) by using ANSYS computer program was used to analyze the reinforced concrete beams. The numerical models were used to investigate the effect of beam depth, concrete strength, CFRP sheet configuration, and CFRP sheet thickness on the behavior of reinforced concrete beams strengthened with CFRP sheets compared with different guidelines. The results from ACI guideline show little difference compared with FE, which make it suitable for RC beams strengthened with FRP sheets.

Research on Practical Pathways of Strengthening Labor Education for College and University Students in the New Era

Labor education is an essential component of college and university education that can help students to develop a strong work ethic,acquire practical skills,and better understand the value of work.Strengthening labor education for college and university students is an urgent need of the high-quality development of the society and the internal requirement of promoting the all-round development of individuals.This study analyzes the importance of strengthening labor education for college and university students in the new era and proposes four practical pathways which draw on labor courses and campus activities,social practices,scientific research projects,and internships.After implementing these pathways,a survey of 967 students showed that students’understanding and awareness of labor was deepened,their hands-on skills and interests in science and labor practices were improved,and they became more cordially respectful to the working class.Taken together,the exploration and practice of these pathways helps college and university students to recognize their abilities,strengths,and interests,and guides them to form good labor habits that permeate all aspects of their studies and lives.

Current progress of research on heat -resistant Mg alloys: A review

With the increasing attention received by lightweight metals,numerous essential fields have increased requirements for mag-nesium(Mg)alloys with good room-temperature and high-temperature mechanical properties.However,the high-temperature mechanic-al properties of commonly used commercial Mg alloys,such as AZ91D,deteriorate considerably with increasing temperatures.Over the past several decades,extensive efforts have been devoted to developing heat-resistant Mg alloys.These approaches either inhibit the gen-eration of thermally unstable phases or promote the formation of thermally stable precipitates/phases in matrices through solid solution or precipitation strengthening.In this review,numerous studies are systematically introduced and discussed.Different alloy systems,includ-ing those based on Mg–Al,Mg–Zn,and Mg–rare earth,are carefully classified and compared to reveal their mechanical properties and strengthening mechanisms.The emphasis,limitations,and future prospects of these heat-resistant Mg alloys are also pointed out and dis-cussed to develop heat-resistant Mg alloys and broaden their potential application areas in the future.

A novel immiscible high entropy alloy strengthened via L1_(2)-nanoprecipitate

The low-cost Fe-Cu,Fe-Ni,and Cu-based high-entropy alloys exhibit a widespread utilization prospect.However,these potential applications have been limited by their low strength.In this study,a novel Fe_(31)Cu_(31)Ni_(28)Al_(4)Ti_(3)Co_(3) immiscible high-entropy alloy(HEA)was developed.After vacuum arc melting and copper mold suction casting,this HEA exhibits a unique phase separation microstructure,which consists of striped Cu-rich regions and Fe-rich region.Further magnification of the striped Cu-rich region reveals that it is composed of a Cu-rich dot-like phase and a Fe-rich region.The aging alloy is further strengthened by a L1_(2)-Ni_(3)(AlTi)nanoprecipitates,achieving excellent yield strength(1185 MPa)and uniform ductility(~8.8%).The differential distribution of the L1_(2) nanoprecipitate in the striped Cu-rich region and the external Fe-rich region increased the strength difference between these two regions,which increased the strain gradient and thus improved hetero-deformation induced(HDI)hardening.This work provides a new route to improve the HDI hardening of Fe-Cu alloys.

High-efficiency Carbonation Modification Methods of Recycled Coarse Aggregates

To solve the problem of only surface carbonation and realize high-efficiency carbonation of recycled coarse aggregate,the method of carbonated recycled coarse aggregate with nano materials pre-soaking was first put forward.The carbonation effect of modified recycled coarse aggregate with three different carbonation methods was evaluated,and water absorption,apparent density and crush index of modified recycled coarse aggregate were measured.Combined with XRD,SEM,and MIP microscopic analysis,the high-efficiency carbonation strengthening mechanism of modified recycled coarse aggregate was revealed.The experimental results show that,compared with the non-carbonated recycled coarse aggregate,the physical and microscopic properties of carbonated recycled coarse aggregate are improved.The method of carbonation with nano-SiO_(2) pre-soaking can realize the high-efficiency carbonation of recycled coarse aggregate,for modified recycled coarse aggregate with the method,water absorption is reduced by 23.03%,porosity is reduced by 44.06%,and the average pore diameter is 21.82 nm.The high-efficiency carbonation strengthening mechanism show that the pre-socked nano-SiO_(2) is bound to the hydration product Ca(OH)_(2) of the old mortar with nano-scale C-S-H,which can improve the CO_(2) absorption rate,accelerate the carbonation reaction,generate more stable CaCO_(3) and nano-scale silica gel,and bond to the dense three-dimensional network structure to realize the bidirectional enhancement of nano-materials and pressurized carbonation.It is concluded that the method of carbonation with nano-SiO_(2) pre-soaking is a novel high-efficiency carbonation modification of recycled coarse aggregate.

Intelligent Design of High Strength and High Conductivity Copper Alloys Using Machine Learning Assisted by Genetic Algor

Metallic alloys for a given application are usually designed to achieve the desired properties by devising experimentsbased on experience, thermodynamic and kinetic principles, and various modeling and simulation exercises.However, the influence of process parameters and material properties is often non-linear and non-colligative. Inrecent years, machine learning (ML) has emerged as a promising tool to dealwith the complex interrelation betweencomposition, properties, and process parameters to facilitate accelerated discovery and development of new alloysand functionalities. In this study, we adopt an ML-based approach, coupled with genetic algorithm (GA) principles,to design novel copper alloys for achieving seemingly contradictory targets of high strength and high electricalconductivity. Initially, we establish a correlation between the alloy composition (binary to multi-component) andthe target properties, namely, electrical conductivity and mechanical strength. Catboost, an ML model coupledwith GA, was used for this task. The accuracy of the model was above 93.5%. Next, for obtaining the optimizedcompositions the outputs fromthe initial model were refined by combining the concepts of data augmentation andPareto front. Finally, the ultimate objective of predicting the target composition that would deliver the desired rangeof properties was achieved by developing an advancedMLmodel through data segregation and data augmentation.To examine the reliability of this model, results were rigorously compared and verified using several independentdata reported in the literature. This comparison substantiates that the results predicted by our model regarding thevariation of conductivity and evolution ofmicrostructure and mechanical properties with composition are in goodagreement with the reports published in the literature.

Effect of Mn content on microstructure and properties of AlCrCuFeMnx high-entropy alloy

AlCrCuFeMnx(x=0,0.5,1,1.5,and 2)high-entropy alloys were prepared using the vacuum arc melting technology.The microstructure and mechanical properties of AlCrCuFeMnxwere analyzed and tested by XRD,SEM,TEM,nanoindentation,and electronic universal testing.The results indicate that the AlCrCuFeMnxhigh-entropy alloy exhibits a dendritic structure,consisting of dendrites with a BCC structure,interdendrite regions with an FCC structure,and precipitates with an ordered BCC structure that form within the dendrite.Manganese(Mn)has a strong affinity for dendritic,interdendritic,and precipitate structures,allowing it to easily enter these areas.With an increase in Mn content,the size of the precipitated nanoparticles in the dendritic region initially increases and then decreases.Similarly,the area fraction initially decreases and then increases.Additionally,the alloy’s strength and wear resistance decrease,while its plasticity increases.The Al Cr Cu Fe Mn1.5alloy boasts excellent mechanical properties,including a hardness of 360 HV and a wear rate of 2.4×10^(-5)mm^(3)·N^(-1)·mm^(-1).It also exhibits impressive yield strength,compressive strength,and deformation rates of 960 MPa,1,700 MPa,and 27.5%,respectively.

Effect of Plastic Deformation on Microstructure and Properties of Cu-(1 wt%-6 wt%) Ag Alloy

In the present study,the Cu-(1 wt%-6 wt%)Ag alloys were prepared by melting,forging and wire drawing.The effects of plastic deformation on microstructure evolution and properties of the alloys were investigated.The results show that non-equilibrium eutectic colonies exist in the Cu-(3 wt%-6 wt%)Ag alloy and no eutectic colonies in the 1 wt%-2 wt%Ag containing alloys.These eutectic colonies are aligned along the drawing direction and refined with the increase of draw ratio.Attributed to the refinement of eutectic colonies,the Cu-Ag alloy exhibits higher strength with the increase of draw ratio.The Cu-6Ag alloy exhibits excellent comprehensive properties with a strength of 930 MPa and a conductivity of 82%IACS when the draw ratio reaches 5.7.

Design of low-alloying and high-performance solid solution-strengthened copper alloys with element substitution for sustainable development

Solid solution-strengthened copper alloys have the advantages of a simple composition and manufacturing process,high mechanical and electrical comprehensive performances,and low cost;thus,they are widely used in high-speed rail contact wires,electronic component connectors,and other devices.Overcoming the contradiction between low alloying and high performance is an important challenge in the development of solid solution-strengthened copper alloys.Taking the typical solid solution-strengthened alloy Cu-4Zn-1Sn as the research object,we proposed using the element In to replace Zn and Sn to achieve low alloying in this work.Two new alloys,Cu-1.5Zn-1Sn-0.4In and Cu-1.5Zn-0.9Sn-0.6In,were designed and prepared.The total weight percentage content of alloying elements decreased by 43%and 41%,respectively,while the product of ultimate tensile strength(UTS)and electrical conductivity(EC)of the annealed state increased by 14%and 15%.After cold rolling with a 90%reduction,the UTS of the two new alloys reached 576 and 627MPa,respectively,the EC was 44.9%IACS and 42.0%IACS,and the product of UTS and EC(UTS×EC)was 97%and 99%higher than that of the annealed state alloy.The dislocations proliferated greatly in cold-rolled alloys,and the strengthening effects of dislocations reached 332 and 356 MPa,respectively,which is the main reason for the considerable improvement in mechanical properties.

Strength and ductility optimization of HPDC AlSi8MgCuZn2 alloys by modifying pre-aging treatment

Considering the components produced by high pressure die casting(HPDC)process usually with ultra-large sizes and complex morphologies,high temperature solid solution treatment is not a suitable method to further improve their mechanical properties.In this study,two-stage aging treatment with different pre-aging times was designed and employed to further improve the mechanical properties of HPDC Al8SiMgCuZn alloy.The characteristics of precipitates were evaluated by a transmission electron microscope(TEM),and the precipitation strengthening mechanism was discussed.The results reveal that the strengthening is mainly contributed by the precipitation ofβ″phase after two-stage aging,and the number density and size of the precipitates are significantly depended on the pre-aging time.The number density of precipitates is increased with the pre-aging time prolonged from 0 h to 4 h,and then decreases with the further increase of pre-aging time from 4 h to 6 h.The precipitates with the highest density and smallest size are observed after pre-aging for 4 h.After pre-aged at 100℃for 4 h and then artificial aged at 200℃for 30 min,the yield strength of 207 MPa,ultimate tensile strength of 325 MPa and elongation of 7.6%are achieved.

岸田文雄力推“新时代现实主义外交”

Japanese Prime Minister Fumio Kishida has officially designated 2023 as the year of realist diplomacy in a new era. In actual terms, the main focuses of Kishida's diplomacy in the current year are strengthening the US–Japan alliance with the outcome of the revision of the security strategy.

以高水平科技创新赋能标准化工作高质量发展

The Ministry of Science and Technology(MOST)has carried out a series of work in the areas such as strengthening the building of technological supporting system for technical standards,deploying the development of standards on new technologies and products,and pushing forward the internationalization of standards,so as to actively drive the integrative development of standardization and technological innovation,and promote the high-quality standardization development with technological innovation.

The Resilience and Flexibility of Asia-Pacific Regional Economic Cooperation in the Period of Worldwide Turbulent Changes

The world today is undergoing a new period of turbulent changes,with the post-war trade and economic system dominated by neo-liberalism facing complex challenges.The political and economic landscape of the Asia-Pacific region also fluctuates from time to time due to various factors.Meanwhile,the willingness of Asia-Pacific countries to promote regional economic cooperation remains strong,as the experience and lessons of"prosperity for all,loss for all"learned over the past few decades of development have convinced countries that continued strengthening of regional cooperation is the only right choice to ensure sustainable economic growth for their own countries.

Connecting the World for a Shared Future

The first China International Supply Chain Expo provided a perfect platform for strengthening the safety and stability of global industrial and supply chains.THE first China International Supply Chain Expo(CISCE)themed“connecting the world for a shared future”kicked off in Beijing on November 28,2023.The world’s first national-level exhibition with supply chains as its theme,the expo was divided into five areas representing five major supply chains and related services-smart vehicles,green agriculture,clean energy,digital technology,and healthy life.It also had a supply chain service exhibition area.