Behavior and Flexural Prediction of Special Cementitious Bonding Material for Fiber Reinforced Strengthening Systems

Strengthening of RC structures with externally bonded FRP （fiber reinforced polymers） has become an important challenge in civil engineering. Epoxy is the main bonding agent used so far, but in the case of a fire, it is subjected to complete loss of his bonding capabilities. Mineral based composites strengthening systems consist of FRPs and a cementitious bonding agent which form a repair or strengthening system that is more compatible with the concrete substrata, and roved its efficiency. The current research introduces the use of a special cementitious material ＂Grancrete＂ as a bonding agent. Test results of 32 T-section RC beams strengthened with various FRG （fiber reinforced Grancrete） strengthening systems are presented. The results demonstrated that most of the specimens were likely to fail by debonding of the FRP from the concrete either at the ends or at intermediate flexural cracks. This paper presents an in-depth study aimed at the development of a better understanding of debonding failures in RC beams strengthened with externally bonded FRP systems. Different analytical models, published in the literature for plate end debonding, are reviewed and compared to test results. The results also demonstrated that when using U-wraps, the specimens were likely to fail by FRP sheet rupture.

Strengthening mechanism of T8-aged Al-Cu-Li alloy with increased pre-deformation

The microstructure evolution and mechanical properties of a T8-aged Al-Cu-Li alloy with increased pre-deformation(0-15%) were investigated,revealing the microstructure-strength relationship and the intrinsic strengthening mechanism.The results show that increasing the pre-deformation levels remarkably improves the strength of the alloy but deteriorates its ductility.Dislocations introduced by pre-deformation effectively suppress the formation of Guinier-Preston(GP) zones and provide more nucleation sites for T1 precipitates.This leads to more intensive and finer T1 precipitates in the samples with higher pre-deformation levels.Simultaneously,the enhanced precipitation of T1 precipitates and inhibited formation of GP zones cause the decreases in number and sizes of θ′ precipitates.The quantitative descriptions of the strength contributions from different strengthening mechanisms reveal that strengthening contributions from T1 and θ′ precipitates decrease with increasing pre-deformation.The reduced diameters of T1 precipitates are primarily responsible for their weakened strengthening effects.Therefore,the improved strength of the T8-aged Al-Cu-Li alloy is mainly attributed to the stronger strain hardening from the increased pre-deformation levels.

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.

Enhanced mechanical properties of molybdenum alloy originating from composite strengthening of Re and CeO_(2)

To enhance the mechanical properties of molybdenum alloys at both room and high temperatures,Mo-14Re-1CeO_(2)alloy was synthesized using the powder metallurgy method,and the corresponding microstructure and mechanical properties were characterized.The results indicate that the ultimate tensile strength of Mo-14Re-1CeO_(2)reaches 657 MPa,with a total elongation of 35.2%,significantly higher than those of pure molybdenum(453 MPa,and 7.01%).Furthermore,the compression strength of Mo-14Re-1CeO_(2)at high temperature(1200℃)achieves 355 MPa,which is still larger than that of pure molybdenum(221 MPa).It is revealed that there is a coherent interface between CeO_(2)and the Mo-14Re matrix with CeO_(2)particles uniformly distributed in both intergranular and intragranular regions.The improvements in mechanical properties are primarily attributed to the formation of Mo-Re solid solution,grain refinement,and dispersion strengthening effect of CeO_(2).

3d-visualization of magnesium strengthening mechanisms for a description of experimentally obtained data of alloying effect in Mg-Ga system

Based on laws of theory of materials strengthening were discribed the experimentally obtained alloying effect in Mg-Ga system and shown using program for 3d atomic structures.As known from our experiments a homogeneous"wavy"microstructure of the diffusion zone forms as result of mass-transfer of molten gallium into the volume of magnesium alloys.SEM chemical composition shows Mg 65%wt.and Ga 35%wt.and X-ray spectra diffraction data-Mg5Ga2 intermetallic phase formation.Such intermetallic diffusion zone provides the significant strengthening effect of microstructure which was determined experimentally by the indentation method.The 3-d visualization shows the reaction and changing of an original crystal structure of magnesium atomic lattice upon diffusion doping with foreign atoms of gallium and then is shown the coalescence of Mg5Ga2 intermetallic crystal with crystals surfaces of Mg-matrix.So,investigated Mg-alloy strengthening at alloying with Ga explained by two main factors.At first is the formation of intermetallic phases with the ordering and consolidation of the crystal structure of the matrix by the ligature atoms,which is the key factor of the strengthening mechanism fixed experimentally.Second,when hexagonal and orthorhombic atomic structures growth according to their spatial type,a significant disorientation of structural fragments occurs,an increase in the density of the amorphous transition layer,a twinning of the structure in the interphase boundaries,which leads to the formation of intrinsic mutual deformation and a high level of internal stresses.

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.

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.

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.

Strengthening Weak Healthcare Systems for Maternal and Neonatal Care in Low and Middle Income Countries: The Missing Link

Introduction: Preventable maternal and newborn mortalities still occur in local communities in Kenya since access to maternal and newborn healthcare services remains a big challenge. Barriers to access in resource-constrained settings have not been examined adequately in literature. The World Health Organization (WHO) has 6 building blocks for strengthening healthcare systems that informed this study. This paper examines how user-side and institutional factors influence access and use of Maternal and Newborn Healthcare (MNH) Services in Matayos sub-County-Busia County. Methods: A mixed method approach, with an ethnographic inquiry and a descriptive cross-sectional design, was adopted to assess access to MNH services in Matayos-Busia County, Western Kenya. Postpartum women who had delivered within the previous 12 months and health care providers in the study area were recruited as respondents. A total of 348 postpartum women were selected through stratified systematic random sampling for the survey. Purposive sampling was used to select postpartum women, conventional and traditional health care providers for 16 in-depth interviews and 7 focus group discussions. Data were analyzed using descriptive and inferential statistics. Qualitative data analysis was done thematically. Results: Institutional delivery was low at 68% and family planning at 75% although demand for services was high at 99%. User-side barriers to access included shared beliefs and practices in the community;high direct transport costs from home;and high costs for missing drugs and other supplies in hospitals. Middle (5th-7th) order deliveries occurred at home with traditional birth attendants. The choice of place of delivery in households was influenced by spouses to respondents and communities of residence where respondents lived or were married. All 6 WHO health system building blocks were weak in Matayos sub-County and needed system-wide strengthening involving all pillars. The user-community voice alone was insufficient and the 7th pillar for user-community engagement was absent. The underlying factors were weak governance and underfunding for healthcare. Conclusion: The six WHO building blocks were inadequate due to weak governance and inadequate funding. User-community engagement, the 7th Pillar, was absent in these resource-limited settings. We recommend user-community empowerment, engagement and participation, adoption of a system thinking approach and adequate funding.

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.

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.

Strengthening effects of BFRP on reinforced concrete beams

Reinforced concrete （RC） beams externally bonded with basalt fiber reinforced polymer （BFRP） are experimentally investigated by using different numbers of bonding plies, transverse anchorages as well as the initial conditions of strengthened beams. The performances of the BFRP strengthening are compared with those of the carbon fiber reinforced polymer （CFRP） and the glass fiber reinforced polymer （GFRP） under the same experimental condition. Experimental results indicate that the strength and ductility of the strengthened beam with two plies of the BFRP are improved remarkably than those with one ply. The strengthening effects of the BFRP lie between those of the CFRP and the GFRP. The BFRP strengthening is little influenced by pre-cracks of concrete. Most failures are caused by interfaciai debonding induced by flexural cracks in the experiment. Clamping of Uwraps along the whole beam is less efficient than endpoint anchorage for increasing the ultimate load of the strengthened beam. Finally, the models suggested by the five guidelines for predicting the debonding strain of the CFRP are extended to the BFRP and the conservative estimates of the debonding strain of the BFRP are given as well.

Experiments and modeling of double-peak precipitation hardening and strengthening mechanisms in Al-Zn-Mg alloy

The aim of the present work is to develop a model for simulating double-peak precipitation hardening kinetics in Al-Zn-Mg alloy with the simultaneous formation of different types of precipitates at elevated temperatures based on the modified Langer-Schwartz approach. The double aging peaks are present in the long time age-hardening curves of Al-Zn-Mg alloys. The physically-based model, while taking explicitly into account nucleation, growth, coarsening of the new phase precipitations and two strengthening mechanisms associated with particle-dislocation interaction （shearing and bypassing）, was used for the analysis of precipitates evolution and precipitation hardening during aging of Al-Zn-Mg alloy. Model predictions were compared with the measurements of Al-Zn-Mg alloy. The systematic and quantitative results show that the predicted hardness profiles of double peaks via adding a shape dependent parameter in the growth equation for growth and coarsening generally agree well with the measured ones. Two strengthening mechanisms associated with particle-dislocation interaction （shearing and bypassing） were considered operating simultaneously in view of the particle size-distribution. The transition from shearing to bypassing strengthening mechanism was found to occur at rather early stage of the particle growth. The bypassing was found to be the prevailing strengthening mechanism in the investigated alloys.

Investigation on sintering and deformation strengthening of Mo-Cu alloy

Mo-Swt%Cu nanocomposite powders were fabricated by mechanical alloying, and full density alloy was obtained via liquid-phase sintering and post-treatment process. The microstructure of Mo-8wt%Cu alloy was investigated by scanning elec-tron microscope （SEM） , and the effects of process parameters on relative density, tensile strength and elongation were stud-ied. The results indicate that the relative density of Mo-Cu alloy is 98. 6% after sintering at 1 250℃ for 30 min, and its micro-structure is composite network The full density of Mo-Cu alloy can be obtained when specimens are treated through deforma-tion strengthening process of rotating forging and hydrostatic extrusion The tensile strength and elongation rate are 576 MPa and 5. 8% ,respectively, when hydrostatic extrusion deformation degree is 40%.

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.

Effect of thermo-mechanical treatment on microstructure and mechanical properties of wire-arc additively manufactured Al-Cu alloy

Wire-arc additive manufacture(WAAM)has great potential for manufacturing of Al-Cu components.However,inferior mechanical properties of WAAM deposited material restrict its industrial application.Inter-layer cold rolling and thermo-mechanical heat treatment(T8)with pre-stretching deformation between solution and aging treatment were adopted in this study.Their effects on hardness,mechanical properties and microstructure were analyzed and compared to the conventional heat treatment(T6).The results show that cold rolling increases the hardness and strengths,which further increase with T8 treatment.The ultimate tensile strength(UTS)of 513 MPa and yield stress(YS)of 413 MPa can be obtained in the inter-layer cold-rolled sample with T8 treatment,which is much higher than that in the as-deposited samples.The cold-rolled samples show higher elongation than that of as-deposited ones due to significant elimination of porosity in cold rolling;while both the T6 and T8 treatments decrease the elongation.The cold rolling and pre-stretching deformation both contribute to the formation of dense and dispersive precipitatedθ′phases,which inhibits the dislocation movement and enhances the strengths;as a result,T8 treatment shows better strengthening effect than the T6 treatment.The strengthening mechanism was analyzed and it was mainly related to work hardening and precipitation strengthening.

MgO-attached graphene nanosheet(MgO@GNS)reinforced magnesium matrix nanocomposite with superior mechanical,corrosion and biological performance

Magnesium(Mg)alloys are gaining great consideration as body implant materials due to their high biodegradability and biocompatibility.However,they suffer from low corrosion resistance and antibacterial activity.In this research,semi-powder metallurgy followed by hot extrusion was utilized to produce the magnesium oxide@graphene nanosheets/magnesium(MgO@GNS/Mg)composite to improve mechanical,corrosion and cytocompatibility characteristics.Investigations have revealed that the incorporation of MgO@GNS nanohybrids into Mg-based composite enhanced microhardness and compressive strength.In vitro,osteoblast cell culture tests show that using MgO@GNS nanohybrid fillers enhances osteoblast adhesion and apatite mineralization.The presence of MgO@GNS nanoparticles in the composites decreased the opening defects,micro-cracks and micro-pores of the composites thus preventing the penetration of the corrosive solution into the matrix.Studies demonstrated that the MgO@GNS/Mg composite possesses excellent antibacterial properties because of the combination of the release of MgO and physical damage to bacterium membranes caused by the sharp edges of graphene nanosheets that can effectively damage the cell wall thereby facilitating penetration into the bacterial lipid bilayer.Therefore,the MgO@GNS/Mg composite with high mechanical strength,antibacterial activity and corrosion resistance is considered to be a promising material for load-bearing implant applications.

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.