主余震序列作用下钢筋混凝土框架结构损伤分析

一次强震过后通常伴有多次余震发生。由于主震和其后续余震之间的间隔时间较短,使得主震损伤结构未能得到及时修复而进一步遭受余震作用,产生“二次损伤”。为此,以一栋5层按我国相关设计规范设计的钢筋混凝土框架结构为研究对象,对主余震序列对结构造成累积损伤及余震对结构造成的增量损伤进行了研究。选取75条真实主震及其余震记录构成序列型地震动输入。同时,采用真实主余震序列中的主震记录,分别采用重复法和随机法两种人工余震构造方法,构造两组人工主余震序列作为地震输入。采用改进的Park-Ang损伤指数作为结构损伤指标,对结构在主震及其在真实和人工主余震序列作用的损伤进行计算,并对余震产生的结构增量损伤进行评估。进一步以峰值加速度、谱加速度、Arias强度作为主震和余震强度参数,研究了余震与主震强度比与余震增量损伤之间的相互关系。分析结果表明：基于随机法的人工主余震序列会对结构造成最显著的增量损伤;采用余震和主震强度比可以较好地预测余震增量损伤的显著性。     

Coupled effects of saline solutions and temperature on the swelling deformation property of GMZ bentonite-sand mixtures

Based on the results of one-dimensional free swelling tests, the coupled effects of NaCl-Na₂SO₄ solutions and temperature on the swelling deformation property of compacted GMZ bentonite-sand mixtures were analyzed. The concentrations of the NaCl-Na₂SO₄ solutions were 0, 0.008, 0.04, 0.08 and 0.16 mol/L, the temperatures were 20 °C, 40 °C, 60 °C, 80 °C and 90 °C and the sand contents were 0, 30 and 50%. X-ray diffraction (XRD) and mercury intrusion porosimetry (MIP) tests were also performed to find the influences of the temperature, solution concentration and sand content on the mineral composition and microstructure. The results showed that the maximum swelling strain of the specimens increased with an elevated temperature, while it decreased with increases in the solution concentration and sand content. The swelling process was accelerated by the rising temperature. The XRD tests indicated that the combined effect of a high temperature and a high solution concentration may have caused more Na⁺ from the saline solutions to enter the interlayer, partly displacing the divalent cations. The MIP tests demonstrated that adding sand to the bentonite could reduce the amount of inter-granular pores and increase the intra-aggregate pores. These findings are advantageous to the transfer of heat and pour fluid in the specimens; and thus, the swelling deformation capacity of the bentonite-sand mixtures was higher than that of pure bentonite under the same conditions.     

三肢剪力墙在水平荷载作用下内力位移解析解法

随着高层结构应用日益广泛,多肢剪力墙及其组合结构成为高层结构中不可或缺的一部分,但是在土木类规范、教材中对于多肢剪力墙内力求解的核心部分：对连梁约束弯矩构成的微分方程组采取叠加分配的计算方法有失偏颇。文章对连梁约束弯矩求解过程中产生的2个二阶微分方程组采取转化为4个一阶微分方程组,进而求微分方程组系数矩阵的基解矩阵的办法,从而给出多肢剪力墙中三肢剪力墙在3种水平荷载作用下内力、位移的解析计算公式。比较两种方法的内力计算结果与Midas计算模型内力的差距,发现运用传统方法连梁的内力结果较计算模型和文中计算小10%左右。该方法避免对连梁刚度以及连梁相对位置和墙肢整体性等一系列参数的讨论,避开分配系数这个概念,改进传统解析方法,为剪力墙与框架组合结构内力、位移解析表达式的推导夯实基础。     

乳化沥青对水化硅酸钙孔结构及微观形貌的影响

针对未掺乳化沥青的纯水化硅酸钙和用Na_2SiO_3·9H_2O,Ca(NO_3)_2·4H_2O,NaOH,去离子水及阴离子乳化沥青合成的水化硅酸钙,采用氮吸附-脱附试验、X射线衍射(XRD)和扫描电镜(SEM)等测试方法对比研究了乳化沥青对水化硅酸钙孔结构及微观形貌的影响,并运用FHH模型分析了其表面分形特征.结果表明:纯水化硅酸钙和掺杂乳化沥青的水化硅酸钙比表面积相差较小,且微孔分布几乎一致,说明掺杂乳化沥青后插层作用和"开孔"效应并未发生;乳化沥青可促进水化硅酸钙形成孔径较大的中孔,减少孔径较小的中孔,而对大孔及微孔的孔结构几乎没有影响;纯水化硅酸钙和掺杂乳化沥青的水化硅酸钙表面分形特征存在差异;沥青表面乳化剂中的—COOM基团与Ca键合可使水化硅酸钙胶束包裹在乳化沥青颗粒表面.     

-180℃深冷处理对7A99铝合金峰值时效强韧性能与析出行为的影响

对7A99超高强铝合金反向挤压板材采用T6峰值时效处理与-180℃冷热循环时效热处理(简称T6-DCT),通过XRD、TEM、HRTEM与3DAP研究-180℃深冷处理对7A99铝合金反向挤压板材强韧性能以及析出行为的影响。结果表明,-180℃冷热循环时效处理使得铝基体的晶格常数由由0.40551 nm 增至0.40626 nm,起到了一定的固溶强化作用;-180℃冷热循环时效处理后晶粒内部生成大量与基体非共格的η相,晶界处η相呈现断续分布并形成晶界无析出带,降低材料的拉伸强度;-180℃冷热循环时效处理促进基体中Zn和Mg元素原子的微观偏聚,导致了Zn和Mg元素的非均匀析出;-180℃深冷处理可以减小时效终态析出相的平均等效半径与析出密度,将等效半径由1.2 nm减小至1.14 nm,将析出密度由4.53×10₂₄/m₃降低至3.87×10₂₄ /m₃,削弱析出强化效果; -180℃冷热循环时效处理后合金的强韧匹配性能得到显著改善,强度略有降低,韧性显著提高。     

席夫碱与硝酸铈复配物对1060纯铝的缓蚀作用

采用极化曲线、电化学阻抗谱、扫描电镜和能谱分析,研究合成的3-吡啶-4-氨基-1,2,4-三唑-5-硫酮席夫碱及其复配物硝酸铈在质量分数为3.5%NaCl溶液中对1060纯铝的缓蚀作用。结果表明：在293 K时席夫碱可有效抑制纯铝在3.5%NaCl溶液中的腐蚀,当席夫碱浓度为0.4 g.L_-1时缓蚀率最高,可达76.0%。席夫碱为混合型缓蚀剂,其在1060纯铝表面的吸附符合Langmuir吸附模型,且同时存在物理吸附和化学吸附。0.2 g.L_-1席夫碱与0.03 g.L_-1硝酸铈复配缓蚀率可达88.2%,二者具有协同缓蚀作用。     

Zn基钎料钎焊烧结NdFeB与DP1180钢接头微观组织及性能

采用Zn-5Sn-2Cu-1.5Bi(ZSCB)钎料实现了烧结NdFeB永磁材料(NdFeB)与DP1180钢的钎焊连接。在惰性气氛控制的高频感应炉中进行钎焊,采用OM、SEM、EDS、微区XRD和NIM-2000H磁性测试仪等手段分析了接头界面的微观组织结构、NdFeB的磁性能和接头剪切强度。结果表明,NdFeB与ZSCB钎料形成Nd-Fe-Zn和Fe-Zn冶金结合,FeZn13和Fe3Zn10相在DP1180钢侧的界面处形成。焊接温度对NdFeB的磁性能影响较小。与传统方法的粘接相比,接头的剪切强度从32.50MPa提高到44.00MPa,提高了35.38%。由于NdFeB和ZSCB钎料之间的热膨胀系数差异很大,在接近NdFeB的反应层处产生较高的残余应力,导致接头从NdFeB界面处断裂。     

A brief review of brazing diamond in cutting tools

Diamond has high hardness and good wear resistance. It is widely used in cutting tools and workpieces. Brazing is an effective method to realize high quality cemented carbide joints in various materials connection technologies. This paper analyzes the research status of diamond brazing in detail. The materials used as brazing filler in diamond brazing are reviewed. Copper base filler and nickel base filler are the most commonly used brazing filler in diamond brazing. The advantages and disadvantages of diamond grinding tools under different production methods are analyzed. In addition, a series of new brazing alloys such as amorphous Ni based brazing filler metals are analyzed. Finally, the development trend of diamond brazing is pointed out.     

Effects of Dissimilar Alumina Particulates on Microstructure and Properties of Cold-Sprayed Alumina/A380 Composite Coatings

In this study,alumina/A380 composite coatings were fabricated by cold spray.The influence of alumina particulates' morphology(spherical and irregular) and content on the deposition behavior of the coatings(including surface roughness,surface residual stress,cross-sectional microstructure and microhardness) was investigated.Results revealed that the spherical alumina mainly shows micro-tamping effect during deposition,which result in remarkable low surface roughness and porosity of the coatings.In addition,very low deposition efficiency and good interfacial bonding between the coating and the substrate were achieved.For irregular alumina particles,the embedding of ceramic particulates in the coating was dominant during deposition process,resulting in high retention in the final deposit.However,it showed limited influence on porosity,surface roughness and interfacial bonding of the deposit.The coatings containing irregular alumina particulates exhibited much higher microhardness than those containing spherical alumina due to the higher load-bearing capacity of deposited alumina.     

Soldering of Zr-based bulk metallic glass and copper by Au-12Ge eutectic alloy

Zr-based bulk metallic glass and copper with different surface roughness were soldered using low temperature eutectic Au-12 Ge(wt%) solder on a thermomechanical simulator. The cross-sectional microstructures of the brazed joints were analyzed by scanning electron microscopy(SEM) and transmission electron microscope(TEM) in detail, and the compositional distribution along the interface was analyzed by energy-dispersive spectrometer(EDS). Results show that the surface roughness of base metals plays an important role in the quality of the brazed joint because the surface roughness can enlarge the effective contact area, which can improve the brazing surface quality between two materials. A moderate roughness of treated Zr-based metallic glass of 18 μm is shown to be the best for the soldering, while the surface roughness has a weak effect on the soldering behavior of Au-12 Ge solder on copper. After soldering, long-range diffusion of atoms occurs between the base metal and solder, and five distinct regions are formed at the joint region.