Characterisation of Early Age Deformations in Cement Paste: Case of Chemical and Autogenous Shrinkage

Concrete is commonly seen as a durable and long-lasting construction material. However, the long-term performance of a concrete structure can be greatly compromised by early-age cracking. This work is an experimental contribution to study early age deformations of cement paste. Its aim is, firstly, to develop an experimental dispositive for assessing chemical and autogenous shrinkage, and secondly, to measure these volumetric deformations in cement paste. The setup was done following the gravimetric method of measurement, which exploits the Archimedes’ principle. It is made up of an electronic balance, a data accusation unit, a temperature control unit and a buoyancy bath. Investigations were done on Portland cement (CPA-CEM II) at the following W/C ratios: 0.25, 0.3, 0.35, 0.4 and 0.5. It was noticed that the water-cement ratio does not influence the magnitude of the chemical shrinkage in a significant manner but had a kinetic effect;a lower W/C induces a faster rate of chemical shrinkage. Autogenous shrinkage was discovered to be highly inversely proportional to the W/C and was also noticed to be in a function of chemical shrinkage within the first 2 to 4 hours when the paste was still liquid.

Effect of bio-tissue deformation behavior due to intratumoral injection on magnetic hyperthermia

Thermal damage of malignant tissue is generally determined not only by the characteristics of bio-tissues and nanoparticles but also the nanofluid concentration distributions due to different injection methods during magnetic hyperthermia.The latter has more advantages in improving the therapeutic effect with respect to the former since it is a determining factor for the uniformity of nanofluid concentration distribution inside the tumor region.This study investigates the effect of bio-tissue deformation due to intratumoral injection on the thermal damage behavior and treatment temperature distribution during magnetic hyperthermia,in which both the bio-tissue deformation due to nanofluid injection and the mass diffusion after injection behavior are taken into consideration.The nanofluid flow behavior is illustrated by two different theoretical models in this study,which are Navier–Stokes equation inside syringe needle and modified Darcy’s law inside bio-tissue.The diffusion behavior after nanofluid injection is expressed by a modified convection–diffusion equation.A proposed three-dimensional liver model based on the angiographic data is set to be the research object in this study,in which all bio-tissues are assumed to be deformable porous media.Simulation results demonstrate that the injection point for syringe needle can generally achieve the maximum value in the tissue pressure,deformation degree,and interstitial flow velocity during the injection process,all of which then drop sharply with the distance away from the injection center.In addition to the bio-tissue deformation due to injection behavior,the treatment temperature is also highly relevant to determine both the diffusion duration and blood perfusion rate due to the thermal damage during the therapy.

Hot deformation behavior of Super304H austenitic heat resistant steel

The hot compression tests of Super304H austenitic heat resistant steel were carried out at 800-1200℃and 0.005-5 s^-1 using a Gleeble 3500 thermal-mechanical simulator,and its deformation behavior was analyzed.The results show that the flow stress of Super304H steel decreases with the decrease of strain rate and the increase of deformation temperature; the hot deformation activation energy of the steel is 485 kJ/mol.The hot deformation equation and the relationship between the peak stress and the deformation temperature and strain rate is obtained.The softening caused by deformation heating cannot be neglected when both the deformation temperature and strain rate are higher.

Numerical analysis of joint temperature evolution during friction stir welding based on plastic deformation heat

3D numerical model for friction stir welding （FSW） was developed by using ABAQUS software considering the plastic deformation heat. Effects of the rotation and welding speeds on the temperature field of FSW 2024-73 aluminum alloy were systematicaUy investigated. The temperature measurement was performed to validate the reliability of the model. The simulation results are in good agreement with the experiments. Results show that changing the rotation speed has no influence on the time for reaching the peak temperature at certain point in the workpiece at a constant welding speed. While increasing the welding speed has significant effect on the time for reaching the peak temperature but the value of peak temperature changes little.

Influence of Bed Temperature on Heat Shrinkage Shape Error in FDM Additive Manufacturing of the ABS-Engineering Plastic

In case of manufacturing hexahedral ABS (Acrylonitrile Butadiene Styrene) plastic components using a FDM (Fused Deposition Modeling)-based 3D printer, undesirable shape errors occur in the product due to heat shrinkage. This paper experimentally ob-served the influence of the bed temperature change on the deformed shape errors of a hexahedral specimen of 100 × 50 × 50 mm3 produced by using a 3D printer. During printing work, the head nozzle temperature was kept at 240?C and the head speed was set at 50 mm/s. The chamber was enclosed with a PC-plate. 3D printing was conducted at four different bed temperatures;50?C, 70?C, 90?C, and 110?C. After the produced specimens naturally cooled down to room temperature, their deformed shape errors were measured. As a result, the higher the bed temperature, the lower the deformed shape errors of the specimens were. However, if the bed temperature had exceeded 120?C, laminating adhesion became poor. That seems to occur because of the material phase change and can make 3D printing work very hard as a consequence. Results of this study can be helpful to set optimum bed temperature condition in FDM additive manufacturing.

On conversion of plastic work to heat during plastic deformation of tin-lead alloy and mild steel

The temperature rise caused by plastic deformation during the quick upsetting of tin-lead alloy and mild steel was investigated via experiments and numerical simulations aiming at a better understanding of the heat generation mechanism in friction welding. The results show that the compression amount and deformation temperature influence significantly the temperature rise during the upsetting of tin-lead alloy. The temperature rise increases with increasing the compression but decreases with increasing the deformation temperature. The simulation results are in good agreement with the experimental inspection for Sn63A alloy. The simulation results of mild steel present a similar tendency with tin-lead alloy. Moreover, the temperature rise of mild steel at elevated temperatures is comparable to that of tin-lead alloy at low temperatures.

Simulation on the deformation controlling of T-joint LBW with auxiliary heat source for high strength aluminum alloy

To avoid the angular deformation of aluminum alloy T-joint weldments, a new method named welding with auxiliary heat source is proposed. The welding simulation is performed with the commercial finite element software Abaqus and FORTRAN programme encoding a special conical heat source with Gaussian volumetric distribution of flux. The influence of the local model on the temperature, residual stress, and welding deformation distributions is investigated. The findings show that angular deformation achieved through numerical computation completely consists with the experimental result which has proved the effectiveness of the finite element methods developed. Various measurements performed on small-scale welded test specimens provide a data base of experimental results that serves as a bench mark for qualification of the simulation result. Finally, the residual stress and strain states in a T-joint are predicted.

Influence of deformation and heat treatment on electrical conductivity of CuMoCr alloy

The solution heat treatment,cold deformation and subsequent aging were performed on CuMoCr alloy.And the influence of deformation and aging treatment on the electrical conductivity of CuMoCr alloy was studied through metallograph,transmission electron microscopy(TEM) and electrical conductivity measurement.Results show that deformation without subsequent aging can reduce the electrical conductivity of CuMoCr alloy,but deformation followed by the optimum aging treatment can effectively improve the electrical conductivity of CuMoCr alloy.Aging at 500 ℃ for 4 h after 80% deformation,the much better electrical conductivity of CuMoCr alloy can be obtained.Reduction of Cr content in the Cu matrix could be the reason for the enhancement of electrical conductivity.

NEW METHOD OF REDUCING HEAT DEFORMATION OF SLIDEWAY GRINDERS

A new concept used for designing large-scale and high-precision NC slideway grinders which are called self-collimation slideway grinders is introduced to eliminate thermal deformation of them. Its principle is to make use of gravitational deformation of machine beds and their foundations automatically to compensate for thermal deformation caused by environmental temperature fluctuation and friction heat between machine tables and machine beds by decreasing longitudinal section stiffness of machine beds and foundations. By FEM analysis and application of more than 10 years, it shows that they have advantages of high precision and low cost, moreover, no constant temperature rooms are required. The linearity error of parts machined with them is less than 0.003 mm/m, and machining precision can almost keep constant for a long time.

Study on seepage and deformation characteristics of coal microstructure by 3D reconstruction of CT images at high temperatures

To study the seepage and deformation characteristics of coal at high temperatures,coal samples from six different regions were selected and subjected to computed tomography(CT)scanning studies.In conjunction with ANSYS software,3 D reconstruction of CT images was used for the establishment of fluidsolid conjugate heat transfer model and coal thermal deformation model based on the microstructures of coal.In addition,the structure of coal was studied in 2 D and 3 D perspectives,followed by the analysis of seepage and deformation characteristics of coal at high temperatures.The results of this study indicated that porosity positively correlated with the fractal dimension,and the connectivity and seepage performances were roughly identical from 2 D and 3 D perspectives.As the porosity increased,the fractal dimension of coal samples became larger and the pore-fracture structures became more complex.As a result,the permeability of coal samples decreased.In the meantime,fluid was fully heated,generating high-temperature water at outlet.However,when the porosity was low,the outlet temperature was very high.The average deformation of coal skeleton with different pore-fracture structures at high temperatures showed a trend of initial increase and subsequent decrease with the increase of porosity and fractal dimension.The maximum deformation of coal skeleton positively correlated with connectivity but negatively correlated with the fractal dimension.

Acoustic emission study of the plastic deformation of quenched and partitioned 35CrMnSiA steel

Acoustic emission （AE） monitored tensile tests were performed on 35CrMnSiA steel subjected to different heat treatments. The results showed that quenching and partitioning （Q-P） heat treatments enhanced the combined mechanical properties of high strength and high ductility for commercial 35CrMnSiA steel, as compared with traditional heat treatments such as quenching and tempering （Q-T） and austempering （AT）. AE signals with high amplitude and high energy were produced during the tensile deformation of 35CrMnSiA steel with retained austenite （RA） in the microstructure （obtained via Q-P and AT heat treatments） due to an austenite-to-martensite phase transformation. Moreover, additional AE signals would not appear again and the mechanical properties would degenerate to a lower level once RA degenerated by tempering for the Q-P treated steel.

FINITE ELEMENT ANALYSIS OF THERMOELASTIC BEHAVIOR OF PIEZOELECTRIC STRUCTURES UNDER FINITE DEFORMATION

It is noted that the behavior of most piezoelectric materials is temperaturedependent and such piezo-thermo-elastic coupling phenomenon has become even more pronounced in thecase of finite deformation. On the other hand, for the purpose of precise shape and vibrationcontrol of piezoelectric smart structures, their deformation under external excitation must beideally modeled. This demands a thorough study of the coupled piezo-thermo-elastic response underfinite deformation. In this study, the governing equations of piezoelectric structures areformulated through the theory of virtual displacement principle and a finite element method isdeveloped. It should be emphasized that in the finite element method the fully coupledpiezo-thermo-elastic behavior and the geometric non-linearity are considered. The method developedis then applied to simulate the dynamic and steady response of a clamped plate to heat flux actingon one side of the plate to mimic the behavior of a battery plate of satellite irradiated under thesun. The results obtained are compared against classical solutions, whereby the thermal conductivityis assumed to be independent of deformation. It is found that the full-coupled theory predicts lesstransient response of the temperature compared to the classic analysis. In the steady state limit,the predicted temperature distribution within the plate for small heat flux is almost the same forboth analyses. However, it is noted that increasing the heat flux will increase the deviationbetween the predictions of the temperature distribution by the full coupled theory and by theclassic analysis. It is concluded from the present study that, in order to precisely predict thedeformation of smart structures, the piezo-thermo-elastic coupling, geometric non-linearity and thedeformation dependent thermal conductivity should be taken into account.

Physical Model of Drying Shrinkage of Recycled Aggregate Concrete

We prepared concretes（RC0, RC30, and RC100） with three different mixes. The poresize distribution parameters of RAC were examined by high-precision mercury intrusion method（MIM） and nuclear magnetic resonance（NMR） imaging. A capillary-bundle physical model with random-distribution pores（improved model, IM） was established according to the parameters, and dry-shrinkage strain values were calculated and verified. Results show that in all pore types, capillary pores, and gel pores have the greatest impacts on concrete shrinkage, especially for pores 2.5-50 and 50-100 nm in size. The median radii are 34.2, 31, and 34 nm for RC0, RC30, and RC100, respectively. Moreover, the internal micropore size distribution of RC0 differs from that of RC30 and RC100, and the pore descriptions of MIM and NMR are consistent both in theory and in practice. Compared with the traditional capillary-bundle model, the calculated results of IM have higher accuracy as demonstrated by experimental verifi cation.

Experimental and numerical study on the shrinkage-deformation of carrot slices during hot air drying

In order to further understand the mechanism of material volume change in the drying process,numerical simulations(considering or neglecting shrinkage)of heat and mass transfer during convective drying of carrot slices under constant and controlled temperature and relative humidity were carried out.Simulated results were validated with experimental data.The results of the simulation show that the Quadratic model fitted well to the moisture ratio and the material temperature data trend with average relative errors of 5.9%and 8.1%,respectively.Additionally,the results of the simulation considering shrinkage show that the moisture and temperature distributions during drying are closer to the experimental data than the results of the simulation disregarding shrinkage.The material moisture content was significantly related to the shrinkage of dried tissue.Temperature and relative humidity significantly affected the volume shrinkage of carrot slices.The volume shrinkage increased with the rising of the constant temperature and the decline of relative humidity.This model can be used to provide more information on the dynamics of heat and mass transfer during drying and can also be adapted to other products and dryers devices.

High temperature deformation behavior and mechanism of spray deposited Al-Fe-V-Si alloy

Al-8.5Fe-1.3V-1.7Si alloy was prepared by spray deposition and hot extrusion. The high temperature plastic deformation behavior of the spray deposited Al-8.5Fe-1.3V-1.7Si alloy was investigated in the strain rate range of 2.77×10-4-2.77×10-2 s-1 and temperature range of 350-550 ℃ by Gleebe-1500 thermomechanical simulator. The mechanism of the high temperature plastic deformation of the alloys was studied by TEM associated with the analysis of Rosler-Artz physical constitutive relationship based on the model of dislocation detaching from dispersion particles. The results show that Al-Fe-V-Si alloy has low strain hardening coefficient, and even exhibits work softening. Stress exponent n and activation energy Q were calculated based on Zener-Hollomon relation and Rosler-Artz physical model respectively. The Rosler-Artz physical model can give a good prediction for the abnormal behavior of high temperature deformation of spray deposited Al-Fe-V-Si alloy, that is, n larger than 8 and Q higher than 142 kJ/mol. However, because of the highly refined microstructure, the high temperature deformation behavior of spray deposited Al-Fe-V-Si alloy deviates more or less from the law predicted by using Rosler-Artz physical model.

寒区某超长隔震结构建造全过程温缩变形分析

针对严寒地区某超长隔震结构建造周期长、平面形状复杂、结构跨度大、季节温差显著及分阶段施工的特点,建立了超长隔震结构建造全过程隔震层温缩变形的计算方法,结合现场的施工进度、方案和步序,采用有限元软件对建造全过程进行了详细的模拟,分析了结构建造全过程隔震层的温缩变形大小及演化规律,并与现场实测结果进行对比验证,最后探讨了结构分阶段施工、施工路径及后浇带设置方式对隔震层温缩变形的影响规律.结果表明:建造全过程温缩变形的模拟结果与实测结果吻合较好,隔震层的温缩变形随着施工进度推移大体呈周期性变化,且与环境温度变化有很大的相关性;超长隔震结构分阶段施工时,各阶段结构之间存在相互约束作用,结构最终的温缩变形是各阶段结构协调变形的结果;合理的施工路径和结构单元划分,能有效减小隔震层的温缩变形;相较于不设置后浇带的情形,当结构后浇带处附加钢筋连通时,隔震层最大温缩变形仅降低了6.3%,而当后浇带处钢筋全部搭接时,隔震层最大温缩变形降低36.3%.

基于综合性能试验的混凝土早期开裂行为研究

为提高混凝土的早期抗裂性能,突破单因素改善其早期稳定性,进行了多因素补偿混凝土各性能缺陷方面的研究.基于调控混凝土配合比开展了胶凝材料水化热、混凝土早期收缩试验和大板加速开裂试验.通过相关收缩机理分析了不同混凝土拌和物的开裂行为;运用双参数Weibull分布分析试验结果,得出了混凝土大板裂缝经时开裂规律.试验结果表明:采用高效稳定型聚羧酸减水剂可以增加浆体的和易性,结合66.7%矿物掺合料(粉煤灰和矿渣粉与水泥质量比)、较好级配碎石和0.29的水胶比有利于延长混凝土的初裂时间和控制裂缝宽度,即提高混凝土的早期抗裂性能.同时,该调控手段也可以降低浆体的水化热,提高混凝土的抗压强度.此外,混凝土裂缝宽度的经时变化规律很好地服从双参数Weibull分布.

三维变形管MVR蒸发器用于纤维素生产末端废水零排放项目

蒸发器的换热性能对机械蒸汽再压缩(MVR)系统投资及运行均有着重要影响。MVR蒸发器的管内传热与压降性能在基于三维变形管和直圆管的情况下存在明显差异。建立了考虑盐水浓度修正的三维变形管MVR蒸发器性能准则关联式,设计一套用于纤维素生产末端废水零排放项目的新型蒸发器。应用实践表明,相对于传统直圆管的MVR蒸发器,基于三维变形管的新型MVR蒸发器节材节能效果显著,其在节省29%换热面积的情形下仍能完全满足工程实际需要。在现场调研期间MVR系统处理每吨废水的压缩机耗电量在18.81~23.78 kW∙h之间,体现出新型蒸发器高能效的技术特性,极具应用推广价值。

黄土地基中能量桩群桩承载变形性状模型试验

基于室内缩尺试验研究了含能量桩群桩在4次冷热循环过程中的桩身热力学特性及桩基承载变形特性变化规律,分析冷热循环对桩土温度、承台沉降、桩顶荷载及桩身摩阻力的影响。试验结果表明:冷热循环过程中能量桩较浅位置处桩身及桩侧土温度始终高于较深处,热循环过程中能量桩的传热效率高于冷循环过程。冷热循环会使承台顶面的工作荷载及群桩中各基桩的桩顶荷载发生往复变化,相应地引起承台发生往复倾斜,热循环引起的承台倾斜稍大于冷循环。热循环引起的能量桩桩身上部摩阻力为负,下部为正,冷循环时则相反。