钢结构模拟在管道应力分析中的应用

管道应力分析与计算是管道设计的基础之一,它研究管道在各种荷载作用下产生的力、力矩和应力,进行管道安全性评价,使设计的管道尽可能经济合理.文章介绍了钢结构模拟在管道应力分析中的应用,并以海上平台火炬放空系统管道为例,应用CAESAR Ⅱ软件比较了单纯管道模型与管道-钢结构复合模型计算结果的差异,为管道应力分析提供有价值的参考.     

基于机器视觉的发光体断面温度辐射测量方法

研究了弥散介质下高温发光体断面温度的辐射测量方法,在线监控高炉回旋区煤粉燃烧工况,对单波长和双波长辐射图像灰度和温度模型进行了理论和实验研究.提出的摄像机快门控制模型解决了面阵电子耦合器件在高温测试中信号输出过饱和导致的"图像发白"现象,提高了辐射测温动态范围.通过不同波长、不同快门时间和光圈条件下辐射测温实验,得出了不同测量条件的比色测温曲线和比色测温误差,实现了高炉风口燃烧带喷射火焰实时温度测量和回旋区工况监控.     

超低温加、卸载下水泥砂浆变形特性试验研究

为了提高我国LNG储罐的自主设计能力,模拟现实工程环境结合自行设计的超低温试验装置对水泥砂浆分别在0℃,-40℃,-80℃,-120℃,-160℃,-165℃下进行了7级单轴加载和再卸载以及卸载和再加载应变测试,对水泥砂浆变形特性进行了试验研究.试验表明:采用分级加、卸载强化了水泥砂浆变形的线性特性,可以减少变形参数的计算误差.在同一目标温度下,各级加载曲线和卸载曲线近乎平行,可用各级载荷下变形模量均值表征水泥砂浆的变形特性.在所有目标温度下加载曲线计算的变形模量和泊松比大于再卸载曲线计算的变形模量和泊松比,卸载曲线计算的变形模量和泊松比小于或等于再加载曲线计算的变形模量和泊松比.水泥砂浆变形模量随着温度的降低逐渐增大,在-165℃增幅可达59％.不过水泥砂浆泊松比随温度变化较小,在数值建模分析时可设为定值.根据以上分析,提出水泥砂浆在超低温下简单应力状态加、卸载本构关系,并对各个目标温度下塑性滞回能进行计算,发现塑性滞回能随着温度的降低先增大后减小,拟合出温度作为变量的塑性滞回能公式.本研究为LNG储罐设计提供了试验支撑,为超低温下数值建模提供了变形参数.     

火炮同步点火管的燃烧实验和数值模拟

为增加火炮点火的同步性,对一种爆轰波传火的火炮同步点火管进行了燃烧实验,测量了点火管不同位置的压力-时间曲线.在考虑火药燃烧过程中同步点火特征、气体湍流和新增燃气质量流流入的基础上,建立了点火管内的燃烧计算模型,用CFD软件对点火管的燃烧过程进行了三维数值模拟计算,并将计算得到的压力-时间曲线与实验曲线进行对比分析.结果表明,点火管具有很高的点火同步性,模拟计算的压力-时间曲线与实验结果基本吻合.     

氧化锆陶瓷超塑性变形行为及机理

研究了不同晶粒尺寸的3Y-TZP在高温下的变形行为,探究了压头速度和变形温度对材料超塑性变形的影响。结果表明,3Y-TZP陶瓷的超塑性变形抗力随变形温度的提高和压头速度的降低而降低。变形后晶粒尺寸增大,但仍保持等轴晶。在1250℃采用应力突变法对不同晶粒尺寸的材料进行压缩试验,实验结果与经典的蠕变方程相吻合。在一定的晶粒尺寸范围内,3Y-TZP陶瓷的应力指数随着晶粒尺寸的增大而减小。在温度1250℃时,3Y-TZP的主要变形机制为伴随扩散的晶界滑动。     

热变形温度对82B盘条变形抗力的影响

通过在Gleeble-1500热/力模拟实验机上的热压缩实验,研究了不同热变形条件下SWRH82B盘条的变形抗力. 由所得数据,确定钢样的应力-应变曲线,分析了变形温度对变形抗力的影响,结果表明,在选定变形程度范围0.3~0.8内,变形温度从860℃升至1110℃过程中,不同变形程度的变形抗力明显减小;当变形速率分别为0.1, 1, 10, 40 s-1时,变形抗力随变形温度的增大而减小;当变形温度为860, 910, 960, 1010, 1060, 1110℃时,变形抗力减小趋势随变形速率增大而趋于平缓;建立了82B盘条变形抗力与变形温度关系模型为：s=162.6283exp(-2.28815T+8.04316),拟合精度达99%以上.     

蜂窝陶瓷蓄热体的热应力研究

建立蜂窝陶瓷的正六边形单通道数学模型,利用CFX流体计算软件,对蜂窝陶瓷在蓄热和放热时的温度分布规律进行了研究,并将数值计算结果与实验结果进行了对比分析,来验证仿真计算结果的可信性。计算分析了不同入口速度以及相同入口条件下不同时刻蜂窝陶瓷的热应力分布情况,结果表明,蓄热体的入口速度越大,应力越大;相同入口条件下,拉应力在蓄热体两端较大,中间较小。     

随机孔模型应用于煤焦燃烧的动力学研究

采用热重法研究煤焦在变温和等温条件下的燃烧过程,分析升温速率和温度对煤焦燃烧行为的影响,用随机孔模型(RPM)研究煤焦的燃烧失重过程,得到了煤焦燃烧变温和等温动力学方程. 实验结果表明,变温实验中,随着升温速率的增加,煤焦燃烧的失重曲线向高温方向移动,最大燃烧速率增加,升温速率由5℃/min增加到20℃/min时,最大燃烧速率由3.2%/min增加到11.3%/min;等温实验中,随着燃烧温度的提高,煤焦最大燃烧速率增加,燃烧温度由510℃增加到630℃时,最大燃烧速率由2.1%/min增加到8.3%/min,煤焦燃烧性能得到改善. 动力学计算结果表明,RPM能较好描述煤焦变温和等温燃烧过程中煤焦转化率与温度和时间的关系,煤焦变温和等温燃烧的表观活化能分别为84.27和64.16 kJ/mol.     

耐火材料高温弯曲应力-应变关系测试方法及影响因素

介绍了耐火材料弯曲应力-应变测试仪的基本构成以及对试验炉、加荷装置、变形量测量装置和计算机控制系统等各构件的要求;重点介绍了使用该仪器研究耐火材料应力-应变关系的方法以及影响测试结果的相关的因素。该方法可以用来研究耐火材料在高温下承受弯曲应力时的变形问题,确定耐火材料在各温度下的应力-应变关系,测试和判断耐火材料的弹性、塑性和粘滞流动的温度范围,并根据应力-应变关系计算耐火材料在不同温度下的弹性模量。     

温度与占压综合作用下埋地含缺陷聚乙烯管道数值分析

为分析温度与占压载荷综合作用下埋地含缺陷聚乙烯管道应力水平,运用ABAQUS有限元分析软件建立管土作用模型,通过热力分析实现温度与占压综合作用,分析温度载荷、占压载荷对在役管道的影响规律,并探讨埋深、占压位置、土体弹性模量、管土摩擦因数对最大应力的影响。分析表明,在规程要求的工作压力下,不能忽略温度荷载对埋地含缺陷聚乙烯管道受力的影响;温度和占压载荷综合影响下在役管道最大应力最终位于内壁3点钟方向,与完好管道的最终位置规律一致,缺陷位于截面3点钟方向管道最易失效;管道埋深和土体弹性模量的影响明显大于管土摩擦因数和占压位置偏移距离。     

Investigation of the stress and strain state of clay pipes under fire condition

The focus of this paper is given to investigating the testing and evaluation method of stress and deformation behaviour of clay pipe elements like chimneys under cyclic high temperature. The experimental study on the temperature–time curves and on the radial deformation–temperature curves of a series of fire-resistant clay pipes was carried out. The tensile strength and the compressive strength, the elastic modulus before and after fire, the stress and deformation properties and the cracking behaviour of the clay pipes under fire conditions have been analyzed. The theoretical analysis corresponds well with the experimental results and tends to prove that the elastic deformation can be the most significant component in fixed-end clay pipes. This study is useful for evaluation of the stress–strain properties of ceramic pipes and provides a beneficial test method for the pipe member in small-scale or in full-scale tests under fire temperatures.     

Retardation of Fatigue Crack Growth in Ceramics by Glassy Ligaments: A Rationalization

In high-temperature fatigue crack growth (FCG) experiments on ceramic materials containing amorphous grain boundary phases, the crack growth rates under cyclic loads were observed to be lower than those predicted solely on the basis of crack growth velocities measured under static loads. In this paper, a rationalization was offered for such a behavior by means of a phenomenological glass-bridging model which takes the relaxation behavior of glass into account. In ceramics which exhibit subcritical crack growth through cavitation ahead of the crack tip, the maximum stress intensity factor of the fatigue cycle required to initiate FCG was observed to be always greater than or equal to the threshold stress intensity factor for crack growth under sustained far-field loads. This trend was also explained with the aid of the glass-bridging model and invoking the equivalence between bridging and damage zones. The elevated temperature FCG behavior of nitride-based ceramics which exhibit grain bridging in the wake during crack propagation was discussed and contrasted with oxide-based ceramics which show glass bridging.     

Fabrication and high-temperature properties of Y-TZP ceramic helical springs by a gel-casting process

A rectangular cross-section ceramic helical spring of yttria-stabilized tetragonal zirconia polycrystals (Y-TZP) was prepared by the gel-casting process. Both the compressive curves and comprehension rebound curves were tested at room temperature and high temperature. The results showed that springs obeyed Hooke׳s Law at room temperature, as the compression resilience ratio of the samples was nearly 100% under the condition of spring׳s security and no damping loss occurred during the process. Besides, mechanical failures of springs occurred under loads around 128 N with the deformation of 10%. With increasing test temperature the maximum load-carrying capacity of the spring decreased, while the maximum deformation increased. Besides, the load–compression curve showed a yield step when the test temperature was above 800 °C. At elastic stage of spring under high temperature, the compression resilience ratio was also nearly 100%; however, the anelastic effect took place and energy loss increased with the increase in test temperature.     

Deformation of nonfired refractories based on phosphate binders. 5. Creep specifics in cement mixtures

The results of experimental studies of aluminosilicate cement are described identifying two temperature intervals of deformation, which differ in their creep regularities. The first range is typical of composites with an unstable low-temperature structure (heat treatment up to 800°C), and the second interval is typical of relatively stable high-temperature structures (> 1000°C). Two ranges of deformation are identified based on stress. In the first range the deformation process is determined by sintering shrinkage under a load which is lower than the surface tension; the second deformation range is typical of loads exceeding the surface tension. __________ Translated from Novye Ogneupory, No. 5, pp. 47–51, May, 2007. Continuation. See beginning in Vol. 48, Nos. 1–2, 2007.     

Approximate Theory of Thermal Stress Resistance of Brittle Ceramics Involving Creep

The effect of stress relaxation by creep on the thermal stress fracture of brittle ceramics at high temperature under conditions of quasi-static heat flow is discussed. It is shown that, to a good approximation, thermal stress relaxation rates can be calculated on the basis of creep rates which correspond to the minimum temperature of the ceramic workpiece. For materials exhibiting linear stress-creep rate dependence, expressions for the relaxation time and maximum temperature difference or heat flux to which ceramic bodies can be subjected are derived in terms of the material variables affecting thermal stress fracture and stress relaxation by creep. A numerical example shows that high-temperature creep can materially affect the thermal stress behavior of brittle ceramics. Appropriate thermal stress parameters are proposed to form the basis of proper material selection for high-temperature environments involving thermal stress and stress relaxation by creep. Conditions for which thermal stress calculations should be based on an elastic or viscoelastic analysis are outlined.     

Experimental study on high temperature performances of silica-based ceramic core for single crystal turbine blades

Silica-based ceramic cores are widely utilized for shaping the internal cooling canals of single crystal superalloy turbine blades. The thermal expansion behavior, creep resistance, and high temperature flexural strength are critical for the quality of turbine blades. In this study, the influence of zircon, particle size distribution, and sintering temperature on the high-temperature performance of silica-based ceramic cores were investigated. The results show that zircon is beneficial for narrowing the contraction temperature range and reducing the shrinkage, improving the creep resistance and high-temperature flexural strength significantly. Mixing coarse, medium and fine fused silica powders in a ratio of 5:3:2, not only reduced high temperature contraction, but effectively improved the creep resistance. Properly increasing the sintering temperature can slightly reduce the thermal deformation and improve the high-temperature flexural strength of the silica-based core, but excessively high sintering temperature negatively impacts the creep resistance and high-temperature flexural strength.     

Ceramic Composite Pipes Produced by a Centrifugal-Exothermic Process

Ceramic composite pipes were produced by a centrifugal-exothermic process in a short time without the use of a high-temperature furnace. The process is characterized by an exothermic reaction following a thermite reaction. The reactions occur under the influence of centrifugal force. Two-layer ceramic pipes composed of molybdenum carbide or boride combined with aluminum oxide were produced using mixtures of MoO₃, Al, and C or B powders.     

蜂窝陶瓷蓄热体的抗热震性研究进展

本文针对高风温燃烧技术和煤矿乏风瓦斯氧化技术的蜂窝陶瓷蓄热体,系统地综述了影响蓄热体抗热震性的因素,数值模拟分析了蓄热体在热冲击下的温度场和热应力场的分布特点,总结了蜂窝陶瓷蓄热体热震损伤机理等的研究进展情况,并提出今后的研究及发展方向。     

Discharge characteristics of pre-polarized doped lead zirconate titanate under impact at room and high temperature

Piezoelectric materials have more and more applications in modern smart fuzes due to their multiple uses such as energy storage and sensing. The electrical output characteristics of piezoelectric ceramics under high temperature and high overload environments are critical to the reliability of the device. In this paper, the mechanical and electrical response of pre-polarized doped lead zirconate titanate (PZT-5H) under impact at room temperature to 250°C, that is, above the Curie temperature, was investigated through a split-Hopkinson pressure bar experiment with an additional electrical output measurement system. The depolarization effect caused by temperature and the mechanical load was analyzed. A thermoviscoelastic constitutive model considering temperature and the strain rate was built based on the experimental data. The model can successfully predict the mechanical and electrical response of PZT-5H under impact at different temperatures. The discharge characteristics of PZT-5H under impact in the cooling stage after high-temperature depolarization were also investigated, and the apparent flexoelectric coefficient of the PZT after complete depolarization was calculated. The research results show that the dynamic piezoelectric coefficient of PZT-5H has a nonlinear relationship with temperature. During the high-temperature cooling process, PZT has a shock-induced polarization under the impact, and the output voltage is less than the polarized piezoelectric ceramic but higher than the flexural polarization at the same temperature. After complete depolarization, the apparent flexoelectric coefficient of PZT-5H is 127 μC/m.     

液化天然气储罐顶部进液管的有限元分析

低温管道系统结构复杂,在工作时承受内压、温差及重力载荷,且承载时系统内各部件又相互影响和制约,采用传统材料力学或结构力学很难分析该系统内各部件应力情况。应用ANSYS软件对某液化天然气储罐的顶部进液管进行了结构强度分析,分析得到了顶部进液管在承受内压、自身重力以及温差应力作用下的变形和应力分布情况,基于此对进液管的布置进行结构调整。研究结果表明:优化设计后进液管道最大主应力小于原设计进液管最大主应力的1/6,极大地保证了储罐在使用过程中的安全性。