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51.
The high temperature phase transitions of orthorhombic La0.95MnO3 from room temperature to 1273 K were studied using high temperature XRD technique in air. Two-phase transitions were found in temperature ranges, 373–473 K and 973–1273 K, respectively. The crystal symmetry increases from orthorhombic to rhombohedral then cubic, while the second transition was not completed in the observation of the present study. The first transition could be due to the depression of Jahn–Teller distortion, while the second one could be caused by the ionic oscillation at high temperature. The lattice thermal expansion coefficients of rhombohedral La0.95MnO3 from 473 to 973 K were also calculated using lattice parameters. 相似文献
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Distortion as a result of the quenching process is predominantly due to the thermal gradient and phase transformations within
the component. Compared with traditional liquid quenching, the thermal boundary conditions during gas quenching are relatively
simple to control. By adjusting the gas-quenching furnace pressure, the flow speed, or the spray nozzle configuration, the
heat-transfer coefficients can be designed in terms of both the component geometry and the quenching time. The purpose of
this research is to apply the optimization methodology to design the gas-quenching process. The design objective is to minimize
the distortion caused by quenching. Constraints on the average surface hardness, and its distribution and residual stress
are imposed. The heat-transfer coefficients are used as design variables. DEFORM-HT is used to predict material response during
quenching. The response surface method is used to obtain the analytical models of the objective function and constraints in
terms of the design variables. Once the response surfaces of the objective and constraints are obtained, they are used to
search for the optimum heat-transfer coefficients. This process is then used instead of the finite-element analysis. A one-gear
blank case study is used to demonstrate the optimization scheme. 相似文献
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坯壳应力引起的鼓肚变形是影响铸坯质量的重要因素,为防止过大的鼓肚变形,依据湍动能理论、热流传递理论和粘弹性理论,建立了异形坯三维热-力耦合模型,开发了鼓肚分析软件,从而避免了漏钢事故的发生.该模型将温度场和应力场的计算相互耦合,交替进行.结果表明:异形坯截面最危险点位于腹板中部,其次为翼板中点,在两者相结合的圆角部,由于凝固坯壳比较薄,其应力值也比较大;当坯壳厚度小于20 mm时,两点的鼓肚变形量将分别超过其极限变形量,铸坯出结晶器时必然发生漏钢事故.该模型通过预测坯壳应力和鼓肚变形量为现场安全生产提供了理论依据. 相似文献
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T. Nguyen I. Zarudi L.C. Zhang 《International Journal of Machine Tools and Manufacture》2007,47(1):97-106
This paper studies an innovative development of a steel grinding–hardening technology using an inert cryogen—liquid nitrogen. It was found that phase transformations took place during grinding with the application of liquid nitrogen and resulted in hardened surface layer in a ground component. The layer had a fine laths martensite structure which gave rise to a remarkably high hardness. It was also shown that the treatment can produce superior surface integrity, with compressive surface residual stresses and without surface oxidation. Due to the inert nature of the liquid nitrogen, the grinding process becomes environmentally conscious. 相似文献
59.
Gang Yao William Yi Wang Chengxiong Zou Ke Ren Peixuan Li Xingyu Gao Deye Lin Jun Wang Shufeng Yang Yiguang Wang Haifeng Song Jinshan Li 《Journal of the American Ceramic Society》2022,105(6):4260-4276
High-entropy carbides (HECs) are regarded as potential candidate structural materials with attractive mechanical properties due to their ultra-high hardness. It is essential to reveal the atomic and electronic basis for strengthening mechanism in order to develop the advanced HECs. In the present work, C (M = Nb, Ti, V) are selected as case studies. The effects of transition metals (M) on the lattice parameters, bulk modulus, enthalpy of formation, electron work function (EWF), and bonding morphology/strength of HECs are comprehensively studied by first-principles calculations. It is found that the lattice parameters, equilibrium volumes, and bulk modulus of HECs are improved with the increase of M atomic volumes. The atomic-size differences among various groups of elements not only result in the lattice mismatch/distortion but also contribute to the formation of weak spots. In the view of bonding charge density, the electron redistributions caused by the coupling effect of the lattice distortion and valance electron differences can be revealed obviously, which identify the different bonding strength. Moreover, in terms of EWF, the proposed power-law-scaled hardness of HECs is validated and matches well with those reported theoretical and experimental results, providing a strategy to design advanced HECs with excellent mechanical properties. 相似文献
60.
该文利用附属柔性分离盘对圆柱涡激振动(VIV)控制问题进行了风洞试验研究。针对弹性支撑的圆柱及不同长度柔性分离盘的试验模型,在雷诺数7 500-40 000情况下,测定不同约化速度(3.5-18.7)下的振动瞬态位移。结果表明:柔性分离盘长度(L)/圆柱直径(D)比为0.6、0.8和1三种圆柱的横向无因次均方根振幅远小于单圆柱,涡激振动抑制效果很好,均在77.6%以上,其中L=0.8D的圆柱抑制效果最佳,几乎无振动;而L=1.2D和1.5D的圆柱反而出现振动增强,约4.5%和9%。对比单圆柱的共振区,附属柔性分离盘的圆柱共振区在约化速度上更靠后且范围更大。 相似文献