端面处理对钻芯法检测混凝土强度的影响

基于12组混凝土芯样的试验数据,对不同端面处理后的抗压强度计算方法进行了研究,重点分析了直径和强度等级的影响。结果表明,高径比为1:1的混凝土芯样经端面磨平处理后的试验数据与同条件养护标准立方体试块抗压强度最接近。试验数据为DG/TJ 08-2020—2007标准提供了理论依据。最后,在试验的基础上,提出了混凝土芯样抗压强度换算公式及端面处理系数的建议。     

高温后陶瓷纤维增强地聚物混凝土性能与声学损伤的关系

以矿渣和粉煤灰为原料,制备了陶瓷纤维增强地质聚合物混凝土(CFRGC)。通过抗压强度试验、超声波测试和裂缝宽度检测,引入小波变换理论,研究了不同温度、不同纤维掺量下CFRGC强度、波速、频谱特征的变化规律以及温度裂缝的开展演化情况。结果表明,高温后CFRGC内部结构受损,导致抗压强度降低,纵波波速和声阻抗减小,温度裂缝宽度增大;声波测试信号经小波分解后在各频段内的功率谱密度分布及能量随损伤的增大有较为明显的变化,某一频段内的信号能量对损伤比波速更敏感;纤维体积掺量为0.3%时,陶瓷纤维对地质聚合物混凝土的高温性能具有良好的改善效果。     

用纵波波速推算混凝土抗压强度的对比试验及其分析

基于波在无限体和一维杆中的传播理论,通过对标准立方体试块的超声、抗压强度试验和温柔凝土梁的超声、纵波波速试验进行对比,统计分析混凝土抗压强度、超声声速和纵波波速三者间的关系,进而将由纵波波速推算混凝土抗压强度用于工程实践。     

高温作用下沥青混凝土路用性能分析

针对高温环境下沥青混凝土的软化问题,以阿尔及利亚MN4道路升级改造项目为工程背景,研究了不同赋存温度环境、不同煤矸石掺量下沥青混凝土的路用性能.结果表明:随着沥青混凝土赋存温度的升高,单轴抗压强度逐渐降低,塑性变形逐渐增大,车辙深度逐渐加深,动稳定度逐渐减小;随着煤矸石掺量的增大,沥青混凝土的单轴抗压强度逐渐减小,塑性...     

保温时间对Ti2AlNb基合金高温拉伸强度的影响

高温拉伸试验标准仅规定保温时间下限,对保温时间上限没有提及.以Ti2AlNb基合金650℃高温拉伸试验为例,证明保温时间对拉伸强度结果有影响,提出对于这种高温拉伸试验过程出现保温时间效应的特殊材料,标准应明确规定各应变速率下的保温时间范围,保证不同检验部门试验结果的一致性和可对比性.     

高温下混凝土动态力学特性试验

基于自行研制的适用于100 mm分离式霍普金森压杆(split Hopkinson pressure bar,SHPB)装置的高温试验设备,采用相应高温试验技术在100 mm SHPB装置上对混凝土分别在常温、200、400、600、800和1000℃下的动态力学特性进行了试验研究。结果表明:高温下混凝土的动态应力应变曲线体现出温度效应和应变率效应,随温度和应变率增大,曲线逐渐表现出塑性特性;高温下混凝土的动态抗压强度随温度升高或平均应变率增长先提高后降低;高温下混凝土的动态峰值应变随温度升高或平均应变率增大而不断提高,动态峰值应变与平均应变率之间存在近似线性增长关系;高温下的动态峰值应变大于常温下,相对增幅随温度升高或应变率增大而不断提高。     

用回弹法测试自密实堆石混凝土强度

自密实堆石混凝土由于块石粒径较大，而无法预留试块来测定其抗压强度。回弹法作为测试混凝土抗压强度的无损检验方法，既方便又可靠。用回弹法对两个自密实堆石混凝土试件进行了抗压强度测试，试验结果表明，①自密实混凝土在1．5m范围内的堆石体中流动可形成匀质性较好的自密实堆石混凝土体。②用回弹法检测自密实堆石混凝土的抗压强度，其结果准确性高、安全可靠。③自密实堆石混凝土28d（天）的抗压强度可用预留自密实混凝土立方体试块的方法来控制。     

高温均匀化处理对1.3C-5Cr-0.7Mo-0.6V钢中碳化物形貌及力学性能的影响

为改善1.3C-5Cr-0.7Mo-0.6V钢中一次碳化物形貌,在1170 ℃下对其进行了不同时间的高温均匀化处理并水淬至室温,之后对其进行退火-淬火-回火处理。采用扫描电镜(SEM)、透射电镜(TEM)、X射线衍射仪(XRD)及压缩试验等方法对不同时间高温均匀化处理后样品的形貌、物相及力学性能进行分析。结果表明,高温均匀化处理可以有效改善一次碳化物的尺寸及形貌,由网状变为均匀分布的小球状。试验钢在高温均匀化处理3 h时取得了抗压强度4703 MPa、工程应变37.3%的压缩力学性能;较未均匀化处理的钢而言,其压缩强度和压缩应变分别提升 14.5%和30.8%。     

铸造水玻璃废砂在混凝土中的应用

对铸造废砂取代天然细集料制成水泥混凝土的性能进行了初步探讨，对处理后和未经过处理的铸造废砂对混凝土性能（抗压强度和抗折强度）的影响进行了对比。试验结果表明，铸造废砂经过处理后对混凝土的抗压和抗折强度的提高，具有明显的效果。并对其作用机理也进行了初步的探讨。     

回火时间对高压锅炉管组织性能的影响

对15CrMo,12Cr1MoV和12Cr2MoWVTiB钢进行了不同回火时间处理后的各项常温和高温性能试验，结果表明，缩短该类钢高压锅炉管现行标准的回火时间对其金相组织，室温性能及高温持久强度影响不大。     

Effects of Post-weld Heat Treatment on Microstructure,Mechanical Properties and the Role of Weld Reinforcement in 2219 Aluminum Alloy TIG-Welded Joints

In as-welded state, each region of 2219 aluminum alloy TIG-welded joint shows diff erent microstructure and microhardness due to the diff erent welding heat cycles and the resulting evolution of second phases. After the post-weld heat treatment, both the amount and the size of the eutectic structure or θ phases decreased. Correspondingly, both the Cu content in α-Al matrix and the microhardness increased to a similar level in each region of the joint, and the tensile strength of the entire joint was greatly improved. Post-weld heat treatment played the role of solid solution strengthening and aging strengthening. After the post-weld heat treatment, the weld performance became similar to other regions, but weld reinforcements lost their reinforcing eff ect on the weld and their existence was more of an adverse eff ect. The joint without weld reinforcements after the post-weld heat treatment had the optimal tensile properties, and the specimens randomly crack in the weld zone.     

The First Phase of the SRIF Industrialized Base in ＂West Area＂ Has Been Put into Operation

After nearly two years＇ tense construction, the first phase of industrialized base of Shenyang Research Institute of Foundry （SRIF）, located at the Tiexi Casting and Forging Industrial Park in the west of Tiexi District, has now been completed and formally put into operation.     

Thermodynamics Study on the Decomposition of Chromite with KOH

Institute of Process Engineering, Chinese Academy of Sciences, China, has proposed a method for oxidative leaching of chromite with potassium hydroxide. Understanding the mechanism of chromite decomposition, especially in the potassium hydroxide fusion, is important for the optimization of the operating parameters of the oxidative leaching process. A traditional thermodynamic method is proposed and the thermal decomposition and the reaction decomposition during the oxidative leaching of chromite with KOH and oxygen is discussed, which suggests that chromite is mainly destroyed by reactions with KOH and oxygen. Meanwhile, equilibrium of the main reactions of the above process was calculated at different temperatures and oxygen partial pressures. The stable zones of productions, namely, K2CrO4 and Fe2O3, increase with the decrease of temperature, which indicates that higher temperature is not beneficial to thermodynamic reactions. In addition, a comparison of the general alkali methods is carried out, and it is concluded that the KOH leaching process is thermodynamically superior to the conventional chromate production process.     

Influence of Heat Treatment on Damping Behaviour of the Magnesium Wrought Alloy AZ61

The effect of isochronal heat treatments for 1h on variation of damping, hardness and microstructural change of the magnesium wrought alloy AZ61 was investigated. Damping and hardness behaviour could be attributed to the evolution of precipitation process. The influence of precipitation on damping behaviour was explained in the framework of the dislocation string model of Granato and Lücke.     

Effect of Rare Earth Doping on Impedance,Modulus and Conductivity Properties of Multiferroic Composites:0.5(BiLa_xFe_(1-x)O_3)–0.5(PbTiO_3)

The Lanthanum-doped bismuth ferrite–lead titanate compositions of 0.5(Bi LaxFe1-xO3)–0.5(Pb Ti O3)(x = 0.05,0.10,0.15,0.20)(BLxF1-x-PT) were prepared by mixed oxide method.Structural characterization was performed by X-ray diffraction and shows a tetragonal structure at room temperature.The lattice parameter c/a ratio decreases with increasing of La(x = 0.05–0.20) concentration of the composites.The effect of charge carrier/ion hopping mechanism,conductivity,relaxation process and impedance parameters was studied using an impedance analyzer in a wide frequency range(102–106Hz) at different temperatures.The nature of Nyquist plot confirms the presence of bulk effects only,and non-Debye type of relaxation processes occurs in the composites.The electrical modulus exhibits an important role of the hopping mechanism in the electrical transport process of the materials.The ac conductivity and dc conductivity of the materials were studied,and the activation energy found to be 0.81,0.77,0.76 and 0.74 e V for all compositions of x = 0.05–0.20 at different temperatures(200–300 °C).     

Quantitative Analysis of the Crystallographic Orientation Relationship Between the Martensite and Austenite in Quenching–Partitioning–Tempering Steels

The orientation relationships(ORs)between the martensite and the retained austenite in low-and medium-carbon steels after quenching–partitioning–tempering process were studied in this work.The ORs in the studied steels are identified by selected-area electron diffraction(SAED)as either K–S or N–W ORs.Meanwhile,the ORs were also studied based on numerical fitting of electron backscatter diffraction data method suggested by Miyamoto.The simulated K–S and N–W ORs in the low-index directions generally do not well coincide with the experimental pole figure,which may be attributed to both the orientation spread from the ideal variant orientations and high symmetry of the low-index directions.However,the simulated results coincide well with experimental pole figures in the high-index directions{123}_(bcc).A modified method with simplicity based on Miyamoto’s work was proposed.The results indicate that the ORs determined by modified method are similar to those determined by Miyamoto’method,that is,the OR is near K–S OR for the low-carbon Q–P–T steel,and with the increase of carbon content,the OR is closer to N–W OR in medium-carbon Q–P–T steel.     

Using Finite Element and Contour Method to Evaluate Residual Stress in Thick Ti-6Al-4V Alloy Welded by Electron Beam Welding

This work was to reveal the residual stress profile in electron beam welded Ti-6Al-4V alloy plates(50 mm thick) by using finite element and contour measurement methods.A three-dimensional finite element model of 50-mmthick titanium component was proposed,in which a column–cone combined heat source model was used to simulate the temperature field and a thermo-elastic–plastic model to analyze residual stress in a weld joint based on ABAQUS software.Considering the uncertainty of welding simulation,the computation was calibrated by experimental data of contour measurement method.Both test and simulated results show that residual stresses on the surface and inside the weld zone are significantly different and present a narrow and large gradient feature in the weld joint.The peak tensile stress exceeds the yield strength of base materials inside weld,which are distinctly different from residual stress of the thin Ti-6Al-4V alloy plates presented in references before.     

Microstructures and Tensile Properties of Ultrafine-Grained Ni–(1–3.5) wt% SiC_(NP) Composites Prepared by a Powder Metallurgy Route

Silicon carbide nanoparticle-reinforced nickel-based composites(Ni–Si CNP),with a Si CNPcontent ranged from1 to 3.5 wt%,were prepared using mechanical alloying and spark plasma sintering.In addition,unreinforced pure nickel samples were also prepared for comparative purposes.To characterize the microstructural properties of both the unreinforced pure nickel and the Ni–Si CNPcomposites transmission electron microscopy(TEM) was used,while their mechanical behavior was investigated using the Vickers pyramid method for hardness measurements and a universal tensile testing machine for tensile tests.TEM results showed an array of dislocation lines decorated in the sintered pure nickel sample,whereas,for the Ni–Si CNPcomposites,the presence of nano-dispersed Si CNPand twinning crystals was observed.These homogeneously distributed Si CNPwere found located either within the matrix,between twins or on grain boundaries.For the Ni–Si CNPcomposites,coerced coarsening of the Si CNPassembly occurred with increasing Si CNPcontent.Furthermore,the grain sizes of the Ni–Si CNPcomposites were much finer than that of the unreinforced pure nickel,which was considered to be due to the composite ball milling process.In all cases,the Ni–Si CNPcomposites showed higher strengths and hardness values than the unreinforced pure nickel,likely due to a combination of dispersion strengthening(Orowan effects) and particle strengthening(Hall–Petch effects).For the Ni–Si CNPcomposites,the strength increased initially and then decreased as a function of Si CNPcontent,whereas their elongation percentages decreased linearly.Compared to all materials tested,the Ni–Si CNPcomposite containing 1.5% Si C was found more superior considering both their strength and plastic properties.     

Directional Growth of Tin Crystals Controlled by Combined Solute Concentration Gradient Field and Static Magnetic Field

A new method was introduced to achieve directional growth of Sn crystals. Microstructures in liquid(Pb)/liquid(Sn) diffusion couples were investigated under various static magnetic fields. Results show that the β-Sn crystals mainly reveal an irregular dendritic morphology without or with a relatively low static magnetic field(B0.3 T). When the magnetic field is increased to 0.5 T, the β-Sn dendrites close to the final stage of growth begin to show some directional character. With a further increase in the magnetic field to a higher level(0.8–5 T), the β-Sn dendrites have an enhanced directional growth character, but the dendrites show a certain deflection. As the magnetic field is increased to 12 T, the directional growth of the β-Sn dendrites in the center of the couple is severely destroyed. The mechanism of the directional growth of the β-Sn crystals and the deflection of the β-Sn crystals with the application of static magnetic field was tentatively discussed.     

电化学噪声数据处理方法概述

综述了常见的电化学噪声数据处理方法,介绍了直流趋势剔除、统计分析、快速傅立叶变换(FFT)法计算功率谱密度(PSD)以及小波变换处理电化学噪声信号的基本过程,并阐释了各种数学处理及所得参数的物理意义。