含盐量对MBER土壤固化剂加固土性能的影响试验

为分析MBER固化剂在咸水地区、盐渍土地区应用的可能性,通过试验分析了不同NaCl溶液浓度对MBER固化土的无侧限抗压强度、应力—应变关系和弹性模量的影响规律。结果表明,当NaCl浓度低于0.5%时,无侧限抗压强度及弹性模量均随溶液浓度的增加而增加,应力—应变曲线空隙闭合阶段随溶液浓度增加呈减小趋势;NaCl浓度高于0.5%时,无侧限抗压强度及弹性模量均随溶液浓度的增加而降低,应力—应变曲线空隙闭合阶段随溶液浓度增加呈增加趋势;弹性模量与无侧限抗压强度随NaCl浓度变化的趋势基本一致,两者存在较好的线性相关性;适量浓度的NaCl溶液对固化土早期强度的提升效果显著;NaCl浓度低于1%时,可应用于固化土工程建设。研究成果可指导MBER土壤固化剂在盐渍土地区的应用。     

高温合金GH4145／SQ和R26应力腐蚀性能研究

本文叙述了慢应变速率应力腐蚀试验(SSRT),研究GH4145/SQ和R26两种合金在几种不同介质条件下应力腐蚀开裂(SSC)的过程。结果表明,两种合金在去离子水室温充氧为1kg/cm~2,温度为315℃的封闭环境中对应力腐蚀开裂不敏感;在10％NaOH水溶液,温度为315℃的封闭环境或42％MgCl_2水溶液沸腾(温度为431℃)环境中两种合金都程度不同地发生了应力腐蚀开裂的现象,但GH4145/SQ合金抗应力腐蚀开裂(SCC)的性能优于R26合金。     

42%MgCl_2沸腾溶液中Super304H应力腐蚀特性的研究

通过固溶和敏化两种状态下Super304H奥氏体不锈钢在42%MgCl_2沸腾溶液中的应力腐蚀敏感性的试验,对固溶和敏化两种状态试样的应力腐蚀敏感性进行了评价,分析了不同状态下的应力腐蚀裂纹及断口的形态以及在42%MgCl_2沸腾溶液中发生应力腐蚀的机理。得出了敏化和固溶两种状态下,Super304H奥氏体钢在42%MgCl_2应力腐蚀中发生穿晶的解理+准解理开裂,开裂机理符合滑移溶解理论。     

905mm末级叶片应力腐蚀和腐蚀疲劳研究

本文研究了引进型300MW汽轮机905mm末级叶片材料在80℃、22％氯化钠介质中的应力腐蚀开裂行为;测定了材料在空气,蒸馏水和80℃、22％氯化钠介质中不同平均应力时的条件疲劳极限。结果表明,在上述介质条件下,905mm末级叶片材料的应力腐蚀敏感性和腐蚀疲劳强度与869mm末级叶片材料相近。     

高韧性铜镍合金制备工艺优化研究

针对当前在材料应用方面对高韧性铜镍合金的需求,在以往研究的基础上,对铜镍合金中掺入铁、锰和锌等元素,并对比其与其他铜合金的性能。结果表明,在热挤压阶段,掺入部分微量元素后,在不同应变温度和应变速率下,铜镍合金的应变力随着温度和速率的增加而不断提高。当温度和速率增加到一定值后,应力开始趋于平稳。同时在热锻阶段,在不同温度和处理工艺下,随着温度的升高,其硬度在2 h时达到最大,并且时效处理温度为550℃。最后通过在耐磨性方面的对比,验证了本文制备合金的耐磨性能要高于传统的合金,验证本文制备材料的可行性。     

膨胀悬挂器管材耐电化学腐蚀性能研究

为了确定膨胀后的尾管与外部不同材质的技术套管之间是否存在电化学腐蚀,选择膨胀后的尾管J55-1、J55-2材料和外部技术套管材料N80和P110,利用线性极化法、电化学阻抗谱图法进行电化学腐蚀试验,通过测量不同金属的极化曲线和电化学阻抗谱,判定电偶腐蚀的敏感性。结果表明,不同膨胀率的J55钢材与外部的N80或P110套管配合使用时,发生电偶腐蚀的敏感性较小。在4种地层水溶液中,J55-2钢腐蚀速率高于J55-1钢,应当优先选用J55-1钢,且J55-2钢和P110钢的腐蚀速率高于J55-1钢和N80钢。4种材料在地层水溶液1中腐蚀速率最大,高浓度的碳酸氢根离子对材料在氯离子溶液中的腐蚀具有很强的促进作用。     

复合材料输电线杆应力－应变关系研究

采用自制的复合材料动态变温拉伸实验装置,研究了玻璃布-环氧层板（GFRP）在0℃、-30℃低温环境下的冲击拉伸力学性能,获得了在0℃、-30℃时GFRP材料的动、静态拉伸力学性能参数。结果表明：在10％到1/s应变率范围和低温条件下GFRP材料具有明显的应变率效应和温度效应。在低温环境下,当应变速率提高时,拉伸强度明显增大;和室温情形相比,在低温环境下,GFRP材料的拉伸强度有所提高。实验还发现,在低温环境下GFRP材料具有动态韧性。     

加载速率对3OCr1Mo1V汽轮机转子钢低周疲劳特性的影响

以30Cr1MolV汽轮机转子钢为研究材料,选取0.1%/s、0.3%/s和0.5%/s的加载速率,采用控制总应变的方法,在RDL 05电子蠕变疲劳试验机上研究了加载速率对材料低周疲劳特性的影响.同时,还提出在538℃下加载速率对30Cr1Mo1V汽轮机转子钢应力和低周疲劳寿命影响的关系式以及低周疲劳寿命与总应变幅值的关系式.结果表明:在538℃时,随着加载速率的提高,转子钢循环应力增大,低周疲劳寿命延长;在同一应变下,加载速率越大,所对应的应力幅值越大;随着应变幅值的增大,应力增大,低周疲劳寿命缩短.     

汽轮机转子钢应力腐蚀试验研究

通过对不同强度等级的汽轮机转子钢进行应力腐蚀试验,研究发现,转子钢在一般水介质中应力腐蚀敏感性很小,但在230℃附近应力腐蚀敏感性突然增加,这可能是发生了蓝脆,增加了应力腐蚀。     

微型燃气轮机原表面回热器应力有限元分析

本文通过建立微型燃气轮机CW(Cross Wavy)原表面回热器热-结构耦合有限元分析模型,对其在设计工况下运行后的应力进行了有限元分析,验证了回热器所选材料的可靠性,并分析了压比和燃气入口温度对回热器的应力影响。分析结果表明:不考虑热应力,只计及压力时,回热器燃气出口侧最大应力和应变高于燃气进口侧最大应力和应变;与之相反,计及热应力时,在压力和温度耦合作用下,回热器燃气进口侧最大应力和应变高于燃气出口侧最大应力和应变;无论是计及热应力还是不考虑热应力,空气通道的波谷处应力最大,并且应力沿波谷处左右对称分布,计及热应力后,其最大应力增长较大,对应各处增幅最高达到34.1%;回热器空气通道向燃气通道侧变形,空气通道变大,燃气通道减小;随着空气侧和燃气侧压比的增加,回热器通道的最大应力也随之增加,当压比增加到8.4时,已达到换热片材料的强度极限;当燃气与空气出口温度不变、回热度减小时,随着燃气入口温度增加,最大应力随之增加,燃气入口温度每增加50 K,回热器最大应力增加约2.3 MPa。研究结果为回热器的设计提供了一定的参考依据。     

On the role of hydrogen in the stress corrosion cracking behavior of Q345R steel in HF vapor environment

The stress corrosion cracking (SCC) behavior of Q345R steel in hydrofluoric acid (HF) vapor environment was investigated. It is shown that Q345R has a high susceptibility to SCC in HF vapor environment, which is negatively correlated with the strain rate. Several different crack morphologies and cracking factors are verified: flat cracks in ferrite are associated with anodic dissolution triggered by micro-galvanic corrosion, and porous cracks at the pearlite and pearlite-ferrite interfaces are mainly influenced by hydrogen. The results of hydrogen charging tests show that pre-charging has little effect on the hydrogen embrittlement of Q345R steel, while in-situ charging leads to severe brittle fracture of the material, because hydrogen interacts with large number of moving dislocations generated by in-situ stretching process and penetrates more readily into the material. The synergistic relationship between hydrogen and dislocation motion is found to be the main mechanism for the transition from ductile to brittle fracture.     

Using a pulsed electric current to reduce the susceptibility of high-strength steel to the stress corrosion cracking caused by hydrogen

Under the tensile loading, the damage of metals in the corrosive medium is the most destructive and harmful. In this study, the stress corrosion cracking behavior of H-charged high-strength steel in 3.5 wt% NaCl solution after electropulsing treatment was investigated. The experimental results from elongation, yield strength, fracture morphology, and polarization curves all demonstrate the positive effect of the pulsed processing, as it reduced the susceptibility of steel to stress corrosion cracking by removing hydrogen by electropulsing. The reduction in hydrogen content of the pulsed high–strength steels was attributed to electromigration and increased system free energy, which drove the hydrogen atoms in the steel to de–trap and reduced the susceptibility to stress corrosion cracking.     

Finite element modeling of hydrogen atom diffusion and distribution at corrosion defect on aged pipelines transporting hydrogen

Repurposing existing natural gas pipelines for hydrogen transport has attracted wide interests. However, the corrosion defect present on these aged pipelines can affect hydrogen (H) atom accumulation, potentially causing hydrogen embrittlement. In this work, a finite element-based model was developed by coupling solid mechanics and H atom diffusion to investigate the distribution of H atoms at a corrosion defect on a steel pipe segment under applied longitudinal tensile strains. The applied strain causes local stress (both Mises stress and hydrostatic stress) and strain concentrations at the corrosion defect, affecting the H atom diffusion and distribution. In the absence of the tensile strain, the H atoms, once entering the interior of pipe, diffuse uniformly into the pipe body along the radial direction driven by a concentration gradient. When a strain is applied on the pipe, the H atom diffusion is driven by hydrostatic stress. The maximum H atom concentration exceeds the initial concentration of H atoms entering the steel pipe, indicating the H atom accumulation at the corrosion defect. The applied tensile strain also affects the location where the H atoms accumulate. For both internal and external corrosion defects, more H atoms will be concentrated at the defect center when the defect length reduces and the depth increases.     

Stress corrosion cracking behavior of ZK60 magnesium alloy under different conditions

The stress corrosion cracking (SCC) behavior of ZK60 magnesium alloy was investigated under different conditions, i.e. thin electrolyte layer (TEL) and solution, by slow strain rate tensile tests, electrochemical techniques, Auger electron spectroscopy, scanning electron microscopy coupled with electron backscattered diffraction, and time of flight secondary ion mass spectrometry. Results indicated that the ZK60 magnesium alloy in solution exhibits a higher SCC susceptibility with a combined SCC mechanism of weaker anodic dissolution (AD) and stronger hydrogen embrittlement (HE) compared to under TEL. Moreover, the HE mechanism under various conditions was discussed.     

Effects of Nb on stress corrosion cracking of high-strength low-alloy steel in simulated seawater

In this study, simulated heat-affected zone (HAZ) of Nb-free and Nb-bearing steel were obtained, and SEM, TEM, and slow strain rate tensile (SSRT) tests were performed to investigate the effect of Nb on the stress corrosion cracking (SCC) behavior of high-strength low-alloy (HLSA) steel in simulated seawater with or without hydrogen charging. The addition of Nb significantly refined the grains and uniformed the microstructure of HLSA. Nb hardly affected the SCC susceptibility of BM and HAZ without hydrogen-charging. However, after charging with 10 mA cm⁻², the SCC resistance of Nb-bearing steel, especially the coarse grain HAZ (CGHAZ) improved drastically, and the process of crack initiation and propagation was inhibited owing to the hydrogen trap function of NbC precipitates.     

Analysis of electrochemical hydrogen permeation through X-65 pipeline steel and its implications on pipeline stress corrosion cracking

Electrochemical hydrogen permeation tests were performed to measure the hydrogen permeation current through the X-65 pipeline steel in the electrolytes simulating the soil conditions to initiate near-neutral pH stress corrosion cracking (SCC) in pipelines. The hydrogen permeation current was analyzed following the constant concentration model. It is shown that, AQDS, simulating the organic compound in the soil, inhibits hydrogen permeation by decreasing the sub-surface hydrogen concentration, while sulfide promotes hydrogen permeation by inhibiting the hydrogen recombination and thus increasing the sub-surface hydrogen concentration. The steel specimen is more susceptible to stress corrosion cracking in the soil solution with a higher sub-surface hydrogen concentration, indicating that hydrogen is involved in near-neutral pH SCC in pipelines. It is suggested that hydrogen promotes the cracking of the steel, accompanying with the anodic dissolution on the crack sides and at the crack tip.     

Hydrogen induced blister cracking and mechanical failure in X65 pipeline steels

The present work aims to investigate the role of hydrogen induced blisters cracking on degradation of tensile and fatigue properties of X65 pipeline steel. Both tensile and fatigue specimens were electrochemically charged with hydrogen at 20 mA/cm² for a period of 4 h. Hydrogen charging resulted in hydrogen induced cracking (HIC) and blister formation throughout the specimen surface. Nearly all the blisters formed during hydrogen charging showed blister wall cracking (BWC). Inclusions mixed in Al-Si-O were found to be the potential sites for HIC and BWC. Slow strain rate tensile (SSRT) test followed by fractographic analysis confirmed significant hydrogen embrittlement (HE) susceptibility of X65 steel. Short fatigue crack growth framework, on the other hand, specifically highlighted the role of BWC on accelerated crack growth in the investigated material. Coalescence of propagating short fatigue crack with BWC resulted in rapid increase in the crack length and reduced the number of cycles for crack propagation to the equivalent crack length.     

Experimental study and numerical simulation on the SSCC in FV520B stainless steel exposed to H2S+Cl− Environment

Constant displacement loading tests using wedge opening loading specimens were carried out in aqueous hydrogen sulfide solution containing sodium chloride to investigate the susceptibility of stress corrosion cracking (SCC) of FV520B precipitation hardening martensitic stainless steel. Results of the SCC tests indicated that the stress corrosion critical stress intensity factor (K_ISCC) dramatically decreased in the corrosion medium investigated and decreased with the increasing of H₂S concentration. Microstructures of fracture surfaces were analyzed using a scanning electron microscope (SEM) with an energy dispersive X-ray spectroscopy (EDS). The fracture surface was typical of sulfide stress corrosion fracture. In addition, large amount of intermittent arc-crack on the side surfaces around the tip of main crack formed even no main crack propagated.A sequentially coupling finite element analysis (FEA) program was utilized to simulate the stress field and calculate the diffused hydrogen concentration distribution of specimen exposed to the corrosion medium investigated. The FEA results indicated that corrosion pit affected the stress and diffusion hydrogen distribution around the corrosion pit where large stress gradients formed. Side surface cracks initiated from those corrosion pits and propagated under the synergy of stress and hydrogen. The effect of the corrosion pit on hydrostatic stress distribution was limited in superficial zone near the side surface, thus side surface cracks propagated along the hoop direction rather than along the direction of specimen thickness. Based on the morphology observation and FEA results, it can be concluded that the SCC mechanism of FV520B steel was hydrogen embrittlement mainly and combination of anodic dissolution. Simultaneously, corrosion pitting was the precondition of side surface crack formation while the stress induced hydrogen diffusion was the dominant factor.     

纳米级掺合料粗合成纤维湿喷混凝土施工及抗裂性能分析

为考察纳米级掺合料粗合成纤维湿喷混凝土的施工及抗裂性能,开展了凝结时间、回弹率、抗压强度、干缩、平板开裂和温度应力试验,并将其与同配制强度的硅粉钢纤维湿喷混凝土进行比较。结果表明,与硅粉钢纤维湿喷混凝土相比,纳米级掺合料粗合成纤维湿喷混凝土的凝结时间变化不大;回弹率下降了27%;1 d抗压强度提高了45%;干缩测值接近,平板总开裂面积降低,温度应力开裂时间延长,开裂敏感性降低。     

纳米级掺合料粗合成纤维湿喷混凝土施工及抗裂性能分析

为考察纳米级掺合料粗合成纤维湿喷混凝土的施工及抗裂性能,开展了凝结时间、回弹率、抗压强度、干缩、平板开裂和温度应力试验,并将其与同配制强度的硅粉钢纤维湿喷混凝土进行比较。结果表明,与硅粉钢纤维湿喷混凝土相比,纳米级掺合料粗合成纤维湿喷混凝土的凝结时间变化不大;回弹率下降了27%;1d抗压强度提高了45%;干缩测值接近,平板总开裂面积降低,温度应力开裂时间延长,开裂敏感性降低。