Theoretical and experimental study of the thermal strength of anticorrosive lined steel pipes

Bimetallic lined steel pipe （LSP） is a new anti-corrosion technology. It is widely used to transport oil, gas, water and corrosive liquid chemicals. At present, the hydroforming pressure for LSP has been investigated theoretically and experimentally by most researchers. However, there are a few reports on the thermal strength of bimetallic LSP. Actually, the bimetallic LSP will be subjected to remarkable thermal load in the process of three layer polyethylene （3PE） external coating. Reverse yielding failure may occur on the inner pipe of the bimetallic LSP when it suffers from remarkable thermal load and residual contact pressure simultaneously. The aim of this paper is to study the thermal load and strength of the bimetallic LSP. A mechanical model, which can estimate the thermal strength of the bimetallic LSP, was established based on the elastic theory and the manufacture of the bimetallic LSP. Based on the model, the correlation between the thermal strength of the bimetallic LSP and residual contact pressure and wall thickness of the inner pipe was obtained. Reverse yielding experiments were performed on the LSP （NT80SS-316L） under different thermal loads. Experiment results are consistent with calculated results from the theoretical model. The experimental and simulation results may provide powerful guidance for the bimetallic LSP production and use.

Curing mechanism of furan resin modified with different agents and their thermal strength

The curing mechanism of furfuryl alcohol and urea-formaldehyde furan resins was investigated using infrared spectroscopy(IR) technique.The curing productions of urea-formaldehyde furan resins modified with different agents(i.e.sorbitol,polyester polyol,phenol and acetone) and the productions of incomplete curing were characterized by differential thermal analysis(DTA) and thermal gravity analysis(TG).The results indicate that except for polyester polyol,the other modifiers have little effect on the thermal strength of urea-formaldehyde furan resin.Furthermore,the thermal strength can be improved at a temperature of higher than 550℃.

Triaxial compression strength for artificial frozen clay with thermal gradient

A series of triaxial compression tests for frozen clay were performed by K0DCGF (freezing with non-uniform temperature under loading after K0 consolidation) method and GFC (freezing with non-uniform temperature without experiencing K0 consolidation) method at various confining pressures and thermal gradients. The experimental results indicate that the triaxial compression strength for frozen clay in K0DCGF test increases with the increase of confining pressure, but it decreases as the confining pressure increases further in GFC test. In other words, the compression strength for frozen clay with identical confining pressure decreases with the increase in thermal gradient both in K0DCGF test and GFC test. The strength of frozen clay in K0DCGF test is dependent of pore ice strength, soil particle strength and interaction between soil skeleton and pore ice. The decrease of water content and distance between soil particles leads to the decrease of pore size and the increase of contact area between particles in K0DCGF test, which further results in a higher compression strength than that in GFC test. The compression strength for frozen clay with thermal gradient can be descried by strength for frozen clay with a uniform temperature identical to the temperature at the height of specimen where the maximum tensile stress appears.

Strength and thermal behavior of low weight foam geopolymer using circulating fluidized bed combustion fly ash

A comparative study of the influence of elevated temperature on foam geopolymer using circulating fluidized bed combustion fly ash(CFA) was reported. Foam geopoymers were prepared with different amounts of foam agent and different Si O2/Al2O3 molar ratios of 3.1, 3.4, and 3.8. The mechanical, thermo-physical properties and microstructure of the foam geopolymers before and after exposure to elevated temperature of 800, 1000, and 1200 °C were investigated. The specimen with Si O2/Al2O3 molar ratio of 3.8 exhibits the highest compressive strength, better microstructure and dimension stability before and after firing. Carnegeite, nepheline, and zeolite crystalline phases appearing after exposure may contribute to the good post-exposure strength. Low weight foam geopolymer using CFA can increase strength and maintain higher stability as high as 1000 °C.

Enhanced Thermal Conductivity and Bending Strength of Graphite Flakes/aluminum Composites Via Graphite Surface Modification

The effect of graphite surface modification on the thermal conductivity(TC) and bending strength of graphite flakes/Al composites(Gf/Al) prepared by gas pressure infiltration were investigated. Al3 Ni and Al4C3 phase may form at the interface in Ni-coated Gf/Al and uncoated Gf/Al composites, respectively, while the Al-Cu compound cannot be observed in Cu-coated Gf/Al composites. The Cu and Ni coatings enhance TC and the bending strength of the composites in the meantime. TC of Cu-coated Gf/Al composites reach 515 Wm^-1·K^-1 with 75 vol% Gf, which are higher than that of Ni-coated Gf/Al. Meanwhile, due to Al3 Ni at the interface, the bending strength of Ni-coated Gf/Al composites are far more than those of the uncoated and Cu-coated Gf/Al with the same content of Gf. The results indicate that metal-coated Gf can effectively improve the interfacial bonding between Gf and Al.

Fuzzy neural network analysis on gray cast iron with high tensile strength and thermal conductivity

To develop a high performance gray cast iron with high tensile strength and thermal conductivity, multivariable analysis of microstructural effects on properties of gray cast iron was performed. The concerned parameters consisted of graphite content, maximum graphite length, primary dendrite percentage and microhardness of the matrix. Under the superposed influence of various parameters, the relationships between thermal conductivity and structural characteristics become irregular, as well as the effects of graphite length on the strength. An adaptive neuro-fuzzy inference system was built to link the parameters and properties. A sensitivity test was then performed to rank the relative impact of parameters. It was found that the dominant parameter for tensile strength is graphite content, while the most relative parameter for thermal conductivity is maximum graphite length. The most effective method to simultaneously improve the tensile and thermal conductivity of gray cast iron is to reduce the carbon equivalent and increase the length of graphite flakes.

Effect of pre-oxidation on strength and thermal shock behavior of ZrB_2-SiC-graphite ceramic composites

A novelty technique,namely,pre-oxidation,has been proposed to improve the strength and thermal shock behavior of ZrB2-SiC-graphite ceramic composites,which is a promising candidate for ultra-high temperature ceramics (UHTCs) in aerospace engineering. The composite is pre-oxidized at temperatures of 900 ℃ and 1100 ℃ for 1 h and 3 h in air. A theoretical model considering surface heat transfer has been given and analyzed. A water-quenching technique is adopted at different temperatures from 300 ℃ to 600 ℃ in order to investigate the thermal shock behavior of pre-oxidized composites. The critical thermal shock temperature improves more than 40% after pre-oxidizing at 1100 ℃ for 3 h. However,the composites strength is not improved as a result of the insensitivity to surface defects.

Deformation behavior and strength evolution of MIM compacts during thermal debinding

Effects of the debinding atmosphere,powder characteristic,solid loading and heating rate on the compact deformation were investigated.The compact strength after thermal debinding was measured by bending mode.The experimental results indicate that the vacuum atmosphere is beneficial to improving the deformation resistance compared with nitrogen atmosphere.Small particle size,irregular particle shape and high solid loading are suitable for decreasing the deformation defects.Besides,too fast heating rate may induce deformation defects.It is also indicated that effect of the factors for the deformation defects is different in different debinding stages.The strength evolution of the compacts during thermal debinding was also discussed.

EFFECT OF INTERFACIAL THERMAL MISMATCH ON INTERFACIAL STRENGTH OF COMPOSITES

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Crack patterns corresponding to the residual strength plateau of ceramics subjected to thermal shock

The formation strength plateau of ceramics is addressed. A set of of 99A1203 are conducted, mechanism of the residual subjected to thermal shock thermal shock experiments where the thin specimens of 1 mm× 10 mm×50 mm exhibit parallel through edge cracks, and thus permit quantitative measurements of the crack patterns. The cracks evolve with the severity of ther- mal shock. It is found that there is a correlation between the length and density of the thermal shock cracks. The increase of crack length weakens the residual strength, whereas the increase of crack density improves it. In a considerably wide temperature range, the two contrary effects just counteract each other; consequently a plateau appears in the variation curve of the residual strength. A comparison between the numerical and experimental results of the residual strength is made, and they are found in good agreement. This work is helpful to a deep understanding of the thermal shock failure of ceramics.

Thermal Activation Analyses of Dynamic FractureToughness of High Strength Low Alloy Steels

A formula is derived for determining the influence of temperature and loading rate on dynamic fracture toughness of a high strength low alloy steel (HQ785C) from thermal activation analysis of the experimental results of three-point bend specimens as well as introducing an Arrhenius formula. It is shown that the results obtained by the given formula are in good agreement with the experimental ones in the thermal activation region. The present method is also valuable to describe the relationship between dynamic fracture toughness and temperature and loading rate of other high strength low alloy steels.

An Application of the Modified Shear Lag Model to Study the Influence of Thermal Residual Stresses on the Stiffness and Yield Strength of Short Fiber Reinforced Metal Matrix Composites

The modified shear lag model proposed recently was applied to calculate thermal residual stresses and subsequent stress distributions under tensile and compressive loadings. The expressions for the elastic moduli and the yield strengths under tensile and compressive loadings were derived which take account of thermal residual stresses. The asymmetries in the elastic modulus and the yield strength were interpreted using the derived expressions and the obtained results of the stress calculations. The model predictions have exhibited good agreements with the experimental results and also with the other theoretical predictions

Design of a test structure based on chevron-shaped thermal actuator for in-situ measurement of the fracture strength of MEMS thin films

A novel test structure to characterize the fracture strength of MEMS(Micro-electro-Mechanical Systems)thin films is presented.The test structure is comprised of a micro fabricated chevron-shaped thermal actuator and test specimen.The test structure is capable of producing large displacement and stresswhile keeping a relatively low temperature gradient across the test specimen.A voltage is applied across the beams of the chevron-shaped actuator,producing thermal expansion force to fracture the test specimen.Actuator deflection is computed based on elastic analysis of structures.To verify the test structure,simulations have been implemented using COMSOL Multiphysics.A 620μmlong,410μm wide,10μm thick test structure produced stress of 7.1 GPawhile the applied voltage is 5 V.The results indicate that the test structure is suitable for in-situ measurement of the fracture strength of MEMS thin films.

复合型水性丙烯酸树脂乳液的制备和性能

采用低玻璃化转变温度、高分子量的丙烯酸树脂乳液与高玻璃化转变温度、低分子量的丙烯酸树脂分散体混合的方式,制备了无交联剂水性丙烯酸树脂复合乳液,用于彩印包装纸与塑料薄膜的热复合。以丙烯酸、丙烯酸丁酯、苯乙烯、丙烯酸羟乙酯等为原料,采用种子乳液聚合法制备了相对分子质量(1.48~1.84)×10^(5)、玻璃化转变温度(T_(g))﹣20~﹣40℃的丙烯酸酯乳液。以丙烯酸、丙烯酸丁酯、苯乙烯、α-甲基苯乙烯、马来酸单酯等为原料,采用本体聚合法制备了相对分子质量(1.34~1.65)×10^(4)、T_(g) 20~45℃、软化点80~105℃的固体树脂,进一步采用自乳化方法将固体树脂制备成树脂水分散体。考察了不同Tg的丙烯酸酯乳液与水分散体以不同比例混配后的乳液混合体的性能。研究结果表明,T_(g)为﹣27.6℃的丙烯酸酯乳液与Tg为28.2℃固体树脂的分散体以质量比8:2混合后,用于PET膜-黑色印刷纸的热复合,剥离强度达到5.6 N/25 mm,持粘性达270 h,可以充分满足覆膜材料的附着力和耐压纹等性能要求。

稠油热采井射孔孔眼应力分析及影响因素

针对稠油热采井生产过程中,射孔井段套管频繁出现损伤断裂的问题,基于弹塑性和热力学理论,采用有限元方法建立注汽—焖井—生产过程射孔套管有限元热力学耦合模型,对各阶段射孔套管应力分布特征进行研究,并开展不同射孔参数下射孔套管强度影响规律分析。研究表明:生产过程中射孔孔眼位置出现明显应力集中现象,在温差及内外压差等共同作用下,注采前期套管应力最大可达498.16 MPa,并逐渐产生塑性失效现象,当注采作业完成时,套管塑性失效现象最严重;随着射孔相位角增大,射孔密度对Mises应力值的影响逐渐减小,而套管孔眼最大应力与射孔相位角成反比关系。该研究对延长稠油热采井射孔套管使用年限和保障正常生产作业具有十分重要的意义。

装饰用UV延迟固化环保型胶粘剂制备及性能分析

针对传统热固化技术中效率低、材料强度低等问题,制备一种UV延迟固化胶粘剂,并对其工艺进行优化,研究其强度、热稳定性、耐化学性等。试验结果表明,选择25%EP3作为活性稀释剂,1%TR-PAG-20101作为阳离子光引发剂,光固化时间为10 s;试验制备的25%EP3UV延迟固化胶粘剂的粘接强度为(3.52±0.16)MPa,拉伸剪切强度为3.6 MPa,固化反应时间在5 min之内,热分解温度在300℃以上;材料在沸水和酸性溶液(pH=2)环境下,强度依然较好,其中,酸性溶液浸泡后强度为(3.36±0.40)MPa。因此,试验制备的UV延迟固化胶粘剂具备良好的力学性能。

不同化学改性方法提高玉米芯骨料混凝土的性能

玉米芯具有较低的导热系数,可以作为天然的保温材料,用于混凝土砌块中。然而,由于玉米芯的多孔结构,导致玉米芯骨料混凝土的抗压强度偏低,亟需进行改性。为了推广玉米芯的规模化利用,该研究以玉米芯为原料改善混凝土砌块的性能,通过红外光谱、拉曼光谱和扫描电镜等测试手段,探讨了3种不同改性技术对玉米芯骨料混凝土水化产物化学键、分子结构、界面过渡区微观结构、抗压强度和导热系数的影响。结果表明:与环氧树脂改性相比,陶粒法改性和裹浆法改性不仅增加了玉米芯骨料混凝土界面过渡区的水化硅酸钙凝胶含量,同时也降低了界面过渡区的厚度,优化了混凝土砌块的微观结构、提高了混凝土砌块的抗压强度、降低了混凝土砌块的导热系数。其中,陶粒法改性技术的效果尤为明显。界面过渡区厚度水化硅酸钙特征峰由大到小顺序分别为陶粒法改性、裹浆法改性、环氧树脂改性。经过陶粒法改性、裹浆法改性和环氧树脂改性后,玉米芯骨料混凝土的界面过渡区分别为无明显界面过渡区、55~66 μm和93~101 μm之间。和未改性玉米芯骨料混凝土相比,掺30%陶粒法改性玉米芯骨料混凝土的抗压强度的导热系数分别降低了51.5%和32.2%。当掺入不超过15%的改性玉米芯骨料时,混凝土砌块满足国家标准GB/T8239-2014中对抗压强度的要求。为了改善玉米芯骨料混凝土砌块的综合性能,建议掺入不超过15%的陶粒法改性玉米芯骨料。研究结果为玉米芯在混凝土砌块中的大规模利用提供了依据,同时也为进一步改善混凝土砌块的相关性能提供了参考。

粉煤灰-矿渣基泡沫地聚合物微观孔隙结构与宏观性能

以粉煤灰和矿渣为主要原材料,H_(2)O_(2)为发泡剂,通过碱激发方法制备粉煤灰-矿渣基泡沫地聚合物.研究碱激发剂模数和粉煤灰掺量对泡沫地聚合物微观孔隙结构、抗压强度及导热系数的影响.基于X射线衍射仪(XRD)、光学显微镜和CT扫描分析了反应产物和孔隙结构参数对泡沫地聚合物性能影响的内在机理.同时,基于灰色关联分析得到泡沫地聚合物的孔隙结构参数与其导热系数和强度的相关关系.结果表明:泡沫地聚合物的导热系数主要由孔隙率决定,两者呈指数负相关;泡沫地聚合物的抗压强度与孔隙连通度、孔隙率、平均孔径及分级孔隙占比有关,其中孔隙连通度和孔隙率影响最显著.

钛酸铝-堇青石复相陶瓷的制备和性能研究

本研究以MgO为稳定剂,以堇青石为增强剂,通过固相反应法成功制备了钛酸铝-堇青石复相陶瓷,并系统研究了MgO和堇青石以及烧结温度对复相陶瓷物相组成、显微结构、烧结性能和热力学性能的影响。结果表明,MgO的引入促进了钛酸铝晶粒的合成和长大,降低了烧结温度,并通过形成Mg_(x)Al_(2(1-x))Ti_((1+x))O_(5)固溶体提高了钛酸铝陶瓷的热稳定性。堇青石在烧结致密化和力学性能方面起着重要作用。在1325℃烧结条件下,MgO含量为8.00%、堇青石含量为15.00%的样品表现出良好的性能,体积密度为3.49 g/cm^(3),气孔率仅为2.2%,抗弯强度达到66.8 MPa,热膨胀系数为2.6×10^(-6)K^(-1)(室温至1000℃)。研究结果为设计和制备具备优异综合性能的高温结构陶瓷提供了新的思路。

水灰比对泡沫混凝土性能的影响研究

泡沫混凝土作为一种多孔材料被广泛应用于建筑中,其性能直接受内部气孔结构的影响,而水泥浆的性质是影响泡沫稳定存在的重要因素。为探究水灰比对泡沫混凝土性能的影响,该文配制了三种不同水灰比的水泥浆制备泡沫混凝土,并测量其干密度、抗压强度、导热率和吸水率,探究其性能与水灰比的关系。结果表明,随着水灰比减小,水泥含量增加,水泥粘度增加,泡沫混凝土密度逐渐增加,强度逐渐增加,导热率逐渐增大,吸水率逐渐减小。在合适的水灰比下,泡沫混凝土相比纯水泥浆密度降幅最大,达到41.76%;强度降幅最小,抗压强度达到9.8 MPa;导热率降幅达到最大,为0.212 W/m·K;吸水率达到21.5%。