共查询到19条相似文献,搜索用时 171 毫秒
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《硅酸盐学报》2016,(2)
为了评价内养护与膨胀剂复合作用对混凝土综合抗裂性能的改善效果,采用温度–应力试验法研究了在实际温度历程下受强约束状态时,掺高分子吸水树脂(SAP)和膨胀剂(UEA)的混凝土的温度–应力发展,并研究了SAP和UEA复掺对混凝土工作性、力学性能和长期变形性能的影响。结果表明:SAP和UEA复掺,增大了混凝土升温阶段的压应力,降低了降温阶段拉应力发展速率和混凝土的开裂温度,开裂温降提高了10℃以上,延长了混凝土的开裂时间。SAP和UEA复掺对混凝土工作性影响不明显,略微降低了混凝土的抗压强度。变形性能试验表明:SAP和UEA复掺使混凝土的极限拉伸值提高了10%~30%,混凝土的干燥收缩降低了10%~20%;14 d水养护混凝土限制膨胀率在0.05%左右,转为恒温恒湿的空气中养护时,42 d膨胀率在0.04%左右。因此,内养护与膨胀剂复合作用显著改善了混凝土的综合抗裂性能。 相似文献
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针对钢化真空玻璃球形支撑物对玻璃压痕的应力场分布问题,采用接触力学,对Hertzian压痕方程进行了修正,推导了三维应力场方程,同时,对完全发展的锥形裂纹的应力强度因子进行了数值求解。结果表明,在球体与玻璃接触区域内,所有的主应力都是压应力,主应力σ1导致了裂纹的萌生,而主应力σ2形成了环形裂纹。与玻璃表面正交的最小主应力从接触边缘向外偏离,形成的近似平行的曲线即为锥形裂纹的形状,而最大拉应力总是垂直于这些曲线。因此,在最大主拉应力的作用下,球体加载后裂纹遵循最小主应力的轨迹。裂纹尖端的应力强度因子决定了断裂韧性,随着裂纹的扩展,应力强度因子减小,在离表面一定距离后,应力强度因子达到临界值,裂纹停止。不同压痕载荷下的归一化应力强度因子是一组具有相似形状的曲线。 相似文献
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大体积混凝土是指最小断面尺寸1m以上的混凝土结构.由于其断面尺寸较大,在混凝土硬化期间,水泥水化热产生的温度变化和混凝土收缩,以及外部条件的共同作用,而产生的温度应力和收缩应力,会导致混凝土内部产生有害裂纹.在大体积混凝土施工时,按施工规范的要求,为了有效地控制裂纹的出现和发展,必须从混凝土的水化温升、延缓降温速率、减少混凝土收缩、提高混凝土极限拉伸强度、改善约束条件和设计构造等方面全面考虑,采取措施,控制有害裂纹的产生. 相似文献
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哈氏合金C276管道焊接残余应力与变形的有限元分析 总被引:1,自引:0,他引:1
针对哈氏合金C276焊接特点,运用有限元分析软件ABAQUS,对哈氏合金C276管道多道焊残余应力进行了有限元模拟。利用单元生死技术,模拟焊缝金属的形成;利用FORTRAN语言编写子程序DFLUX,实现了移动的高斯分布热源;考虑对流、传导、辐射以及高温下的材料性能,获得了残余应力和变形的分布规律。计算结果表明,在焊缝及热影响区,轴向拉应力对内壁裂纹的产生有主要的影响,环向拉应力对外壁裂纹的产生有主要的影响。线能量对温度和变形的影响较大,而对残余应力影响不大。 相似文献
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建立了风栅中玻璃的冷却模型,数值模拟玻璃冷却的温度和应力变化规律,反演了不同季节风温时的合理匹配风压。结果表明,在玻璃淬冷过程,约3 s时玻璃表面拉应力达到最大,若该应力大于玻璃此时的抗拉强度,玻璃将破裂。此后玻璃从外到内降温速率逐渐减小,在约15~17 s时玻璃表层受内部影响减弱,表面应力趋于稳定。与钢化玻璃表面应力测试结果相比,数值模拟结果略小,但相对误差不超过5%。随冷却风温降低,玻璃钢化所需的风压逐渐减小。在玻璃钢化程度接近的情况下,风压随风温降低近似线性减小,钢化风压调节量与环境温度变化量的相关系数为0.103 kPa/K。 相似文献
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《Ceramics International》2023,49(7):10287-10297
In this paper, the interfacial stress state is used to analyze the interfacial crack initiation mechanism of the thermal barrier coatings (TBCs) during isothermal oxidation. The influence of thermal growth stress, initial residual stress, and creep behavior on the stress distribution is considered to have an accurate simulation result. A parameter that integrates the effects of interfacial normal and tangential stress is modified for evaluating interfacial crack initiation. It is found that, in the cooling stage, the interfacial cracks sprout at the top coat (TC)/thermally grown oxide (TGO) interface valley region and the TGO/bond coat (BC) interface peak region, which agrees with the experimental results. Furthermore, the influence of interfacial roughness on crack initiation is investigated. The result shows that different interfacial roughness affects the sprouting region of interfacial cracks and cracks within the TC layer. 相似文献
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超/超超临界锅炉垂直水冷壁中间集箱附近的水冷壁异形鳍片区域向火侧易出现横向裂纹,可能导致水冷壁泄漏或爆管。以某660 MW超超临界锅炉为对象,介绍了水冷壁异形鳍片区域温度和热应力的数值计算模型。针对横向裂纹问题,基于计算数据分析了该区域的温度和热应力分布特征,以及锅炉负荷变化和水冷壁尺寸的影响。结果表明,异形鳍片旁的管壁向火侧顶点的轴向拉应力和等效应力大,锅炉变负荷运行易产生交变热应力,导致横向裂纹;异形鳍片中心为整个模型温度最高处,轴向应力和等效应力值也较大,需要重点关注;异形鳍片与管壁交接处等效应力大,材料失效时容易产生裂纹,可能向旁边的异形鳍片区域管壁向火侧延伸。 相似文献
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固态渣层能够保护气流床气化炉的水冷壁,防止其受到高温合成气直接辐射以及液态熔渣的侵蚀。本文提出一种数值模拟渣层热应力的改进方法,并应用该改进方法对降温阶段渣层热应力的变化进行模拟研究。在渣层热应力的数值模拟研究中,经常假定水冷壁渣层的热应力变化基于一个固定的参考温度(比如环境温度25℃)。然而对于降温阶段的水冷壁气流床气化炉,一个固定的参考温度值并不能表征渣层"无应力"的初始状态,在此基础上计算将会得到一个不合理的渣层应力分布结果。针对该问题,提出了一种改进方法:将水冷壁渣层分割为多个子计算域,每个子计算域内单独设置参考温度,以此实现在整个水冷壁渣层上施加一个近似为降温初始时刻的参考温度分布,从而使渣层在降温初始时刻处于"无应力"状态。同时,对前人文献中的三维水冷壁渣层结构在降温过程中的热应力变化情况进行计算,以此测试改进方法的准确性,改进方法得到的模拟结果与其他参考文献得到的渣层热应力变化趋势一致。 相似文献
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Acoustic Emission from a Porcelain Body during Cooling 总被引:1,自引:0,他引:1
Yutaka Ohya Yasutaka Takahashi Minori Murata Zenbe-e Nakagawa Kenya Hamano 《Journal of the American Ceramic Society》1999,82(2):445-448
Quartz grains in porcelain bodies cause cracking. Under the present conditions, acoustic emission (AE) has shown that the cracking occurred in a temperature range of 900°–800°C during cooling from firing at a temperature of 1200°C. This cracking can be explained by a large thermal expansion mismatch that was due to the negative thermal expansion of quartz at temperatures >1000°C and no stress relaxation of the glass phase. At a temperature of 573°C, which is the transition temperature of quartz, AE was not detected by the measuring system that was used, although there were many peripheral cracks around the large quartz grains. The energy release rate of the peripheral cracks at a temperature of 573°C was too low to be detected by the equipment that was used. 相似文献
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Numerical modeling for non-steady thermal stress analysis of slag layer in a membrane wall entrained-flow gasifier 总被引:1,自引:0,他引:1
Membrane wall entrained-flow gasifier (MWEFG) generally has a long service life for the protection of the solid slag layer adhered to the metal wall during operation. However, cracking will generate in the slag layer when the temperature changes greatly in the gasifier, which results from the thermal stress exceeding the strength of slag deposit. In this study, the gasification experiment was performed in a bench-scale MWEFG and a three-dimensional model was developed for non-steady thermal stress analysis of slag layer. Based on experimental data, the thermal stresses of cooling process were numerically simulated using transient thermal analysis. The results indicate that the thermal stresses of the slag layer are tensile during the cooling and the Von Mises stresses (SEQVs) increase with the reduction of temperature. Comparing the results of the selected nodes, it is found that the SEQV always increases from the slag surface to the slag-SiC interface. The contributions of slag porosity and thickness were also investigated. We draw a conclusion that the maximum SEQV decreases with the increasing porosity, while it increases with the increasing slag thickness. 相似文献
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利用ABAQUS软件模拟出了焦炭塔工作周期内的温度变化、应力变化。采用顺序耦合的方法分析焦炭塔所受的热应力。分析从新塔准备直至老塔处理,其中共包括5个工作阶段。结果显示,几个阶段的温度场分布对应力结果有显著影响。试压、油气预热、生焦的初始阶段比较类似,都处于温度上升阶段,最大应力出现在裙座部位,分别为183.6、242.7、250.4 MPa,且焊缝处应力大于筒体。吹汽阶段塔体温度下降,焊缝处应力小于筒体应力。水冷阶段的应力分布类似于温度分布,存在一个随冷焦水不断移动的高应力截面,其中最大应力可达400.4 MPa,已超过了材料的屈服极限,导致筒体出现了局部塑性变形。经反复循环,会引发"热应力棘轮"现象,由于塑性变形的不断积累,故造成焦炭塔的鼓胀现象。 相似文献
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采用有限元法数值模拟了3234/T300B热固性树脂基复合材料修补片的热补仪加热固化过程,分析了工程应用范围内不同升温速率下的复合材料修补片固化历程中的温度、热应力分布和变化特征,并研究了升温速率对补片在不同时间点的残余热应力值的影响规律。研究结果表明:升温阶段热应力主要集中在补片表面中心区域及其与母板接触的区域,降温阶段复合材料修补片内部热应力高于表面热应力;升温速率越快,固化越迅速,在升温阶段修补片内部热应力及峰值热应力越大;在保温和降温阶段,修补片内热应力分布和大小不受升温速率的影响;对于较低升温速率,热应力最大值出现在升温结束时刻;对于较高的升温速率,热应力最大值出现在接近升温末期的时刻。研究结果为合理选择升温速率从而减小升温阶段的内部热应力并控制补片分层等缺陷提供了参数依据。 相似文献
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A hyperelastic–viscoplastic constitutive model for amorphous polymers was used in finite element simulations of micro‐hot embossing across the glass transition. The model was selected for its ability to capture finite strain temperature and rate dependence over a wide range of temperatures, including across the glass transition. The simulations focused on the glass transition temperature regime, and particularly probed the effects of time and temperature during cooling and mold release. The results show that strong temperature sensitivity of the material across the glass transition leads to a wide range of required embossing force and springback. The interplay between changes in material properties upon cooling and stress relaxation can lead to significant increases in embossing force during the cooling stage, especially when high cooling rates are employed. The effects of thermal expansion also complicate the problem during rapid cooling. Nonlinear material behavior is shown to affect results in parametric hot embossing studies. Careful tailoring of embossing temperature, cooling rate, and demolding temperature is critical in acceptable feature replication. The best results are found for moderate cooling rates, which allow adequate time for stress relaxation in the material prior to mold release. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers 相似文献