金属垫片密封表面形貌的分形表征

引言 金属垫片密封结构常见于石油、化工、核能等装置中,广泛应用于高温、高压及强腐蚀介质等操作条件恶劣、密封要求高、一般的垫片无法满足要求的场合.     

A study of the effect of filler metal thickness on tensile strength for a stainless steel plate-fin structure by experiment and finite element method

This paper presents a study of the effect of filler metal thickness on tensile strength for a stainless steel plate-fin structure by finite element method and experiment. The results show that the filler metal thickness has a great effect on tensile strength. The tensile strength is increased with the filler metal thickness increase, then it keeps stable when the filler metal thickness is 105–140 μm. But it decreases rapidly when the filler metal thickness is larger than 140 μm. The fracture location is shown at the end of vertical fin when the filler metal thickness is 105–140 μm. Specimens with filler metal thickness smaller or larger than 105–140 μm rupture in the brazed filler metal. The optimal filler metal thickness is 105 μm, using which can get higher strength for 304 stainless steel plate-fin structures.     

Methanation of carbon dioxide and fluidization quality in a fluid bed reactor—the influence of a decrease in gas volume

A large decrease of fluidization quality was observed when methanation of carbon dioxide was carried out in a fluid-bed reactor even if the catalyst particles had the optimal properties for good fluidization. The cause of this phenomenon was explored by measuring pressure fluctuations, bubble frequency and extent of CO₂ conversions. The results indicated that the decrease of the fluidity was caused by a reduction in volume of reactant gases due to the reaction. The voidage in the emulsion phase is considered to be an important factor affecting the fluidity. The fluidization quality and contacting efficiency could be improved by such devices as baffle internals or two-stage spargers.     

小冲孔试样弹塑性蠕变损伤的有限元分析

综合考虑了小冲孔试样实验过程中的弹性、塑性及蠕变等因素,采用了Mises型流动法则和改进的K-R蠕变损伤本构方程,建立了ABAQUS有限元模型,模拟计算了550℃三种载荷条件下,Cr5Mo试样的弹塑性蠕变过程,分析试样的中心蠕变挠度、蠕变应变随时间的变化规律,当量应力的分布情况,以及试样的蠕变损伤与位置的关系,同时分析了挠度与应力对网格的敏感性。结果表明:模拟结果与实验结果很接近,且与单轴实验的应变曲线十分相似;整个试样在中心损伤比较严重,呈现明显局部化特征;讨论了试样网格的敏感性,试样半径方向0mm~1mm之内应力变化幅度比较大(除约束点),并且应力的最大值也出现在这个区域,在这个区域进行网格细化提高计算的精确性,而其他区域采用粗网格减少计算成本,达到精确性和经济性的平衡。径向上网格大小对挠度影响比较大,应力对网格大小不敏感。     

SPV50Q高强钢焊接接头在湿H2S环境下的开裂敏感性研究

具有较高强度和良好韧性的SPV50Q钢常用于制造液化石油气(liquefied petroleum gas,LPG)球罐,球罐通过焊接制造后一般不经过焊后热处理,因此在焊接接头处将有焊接残余应力存在.服役经历和现场检测表明,较高H2S浓度和焊接残余应力将会导致材料产生环境失效如氢鼓泡(hydrogen blistering,HB)或氢致开裂(hydrogen-induced cracking,HIC)、硫化物应力腐蚀开裂(sulfide stress corrosion cracking,SSCC)以及应力诱导氢致开裂(stress-oriented hydrogen induced cracking,SOHIC).文中通过1×10-6s-1的慢应变速率拉伸试验,对手工电弧焊焊接的SPV50Q焊接接头在不同浓度H2S水溶液中的开裂敏感性以及开裂特征进行研究.试验结果表明,SSCC和HIC发生在靠近焊接接头热影响区的母材上,不同温度下的焊后热处理将降低材料的应力腐蚀开裂敏感性,实施正确焊后热处理可提高SPV50Q焊接接头抵抗SSCC或HIC能力,而不降低钢的力学性能尤其是韧性.     

基于粗糙集和贝叶斯的薄膜蒸发器参数评估

为了分析薄膜蒸发器过程参数对生产结果的影响,合理优化操作参数,结合粗糙集理论与概率论中的贝叶斯公式预测主要影响属性,提取评判规则。利用可辨识矩阵处理数据来过滤冗余属性,求得约简与核,再计算以综合决策、产量及蒸发强度作为结果属性的重要性,并引入贝叶斯公式计算其规则下的条件概率。计算结果表明,进料流量、进料温度、导热油温度和系统真空度对生产结果的影响最大,从而为工程应用编制软件提供参考。     

Comparison of computational approaches for predicting the effects of missense mutations on p53 function

We applied our recently developed kinetic computational mutagenesis (KCM) approach [L.T. Chong, W.C. Swope, J.W. Pitera, V.S. Pande, Kinetic computational alanine scanning: application to p53 oligomerization, J. Mol. Biol. 357 (3) (2006) 1039–1049] along with the MM-GBSA approach [J. Srinivasan, T.E. Cheatham 3rd, P. Cieplak, P.A. Kollman, D.A. Case, Continuum solvent studies of the stability of DNA, RNA, and phosphoramidate-DNA helices, J. Am. Chem. Soc. 120 (37) (1998) 9401–9409; P.A. Kollman, I. Massova, C.M. Reyes, B. Kuhn, S. Huo, L.T. Chong, M. Lee, T. Lee, Y. Duan, W. Wang, O. Donini, P. Cieplak, J. Srinivasan, D.A. Case, T.E. Cheatham 3rd., Calculating structures and free energies of complex molecules: combining molecular mechanics and continuum models, Acc. Chem. Res. 33 (12) (2000) 889–897] to evaluate the effects of all possible missense mutations on dimerization of the oligomerization domain (residues 326–355) of tumor suppressor p53. The true positive and true negative rates for KCM are comparable (within 5%) to those of MM-GBSA, although MM-GBSA is much less computationally intensive when it is applied to a single energy-minimized configuration per mutant dimer. The potential advantage of KCM is that it can be used to directly examine the kinetic effects of mutations.     

The effect of carbon nanotube orientation and content on the mechanical properties of polypropylene based composites

Finite element method (FEM) is used to predict the tensile and compressive stress–strain curves of single wall carbon nanotube (SWCNT) reinforced polypropylene (PP) composites. The numerical simulations, using shell and tetrahedron elements, are first carried out to investigate the effect of SWCNT orientation on the mechanical properties of the nano-composites. Second, the Grunfest–Young constitutive equation is selected to determine the effect of strain rate and solve the finite element program to analyze the mechanical behavior of the nano-composites. Third, the effect of SWCNT volume fraction is studied. In all cases, the shear and normal stresses distribution along the nanotube axis are investigated and compared with the macroscopic tensile or compressive stresses on the composites. At the same time, the stresses of the interface between SWCNT and the matrix along the loading direction are analyzed. Finally, the effects of SWCNT orientation, content and strain rate on the strength of the nano-composites are studied. From the results obtained, it was shown that strain rate can substantially affect the tensile and shear stresses of the composites, but do not significantly influence the initial tensile or compressive elastic moduli. This is especially the case for SWCNT orientation angles less than 30° and volume fractions higher than 0.74%.