泡沫铝连接件焊接工艺的应用现状与展望

泡沫铝兼具结构与功能特性,为充分发挥泡沫铝的各种性能,常将其与致密金属进行复合得到三明治结构,以提高其综合力学性能并降低成本。三明治结构的连接方法众多,而焊接手段是最可靠的连接方式。首先介绍了泡沫铝的性能特点及焊接难点,综述了其焊接方法,包括常规电弧焊、激光焊、钎焊、扩散焊、搅拌摩擦焊、等离子焊以及超声波焊,再对各工艺的局限性进行阐述,最后对泡沫铝连接件焊接工艺的发展方向进行浅析。     

微孔结构对PMI泡沫准静态压缩性能的影响

基于BBC点集建立了聚甲基丙烯酰亚胺(PMI)闭孔泡沫的Kelvin十四面体模型和Laguerre模型,并采用有限元方法研究了其在准静态载荷作用下的压缩性能。分析了孔径大小、泡孔体积离散系数对压缩弹性模量、初始峰值应力和能量吸收能力的影响。结果表明:Kelvin十四面体模型可以较好地预测PMI泡沫的压缩弹性模量和峰值应力;在相同相对密度条件下,小孔径泡沫的初始峰值应力和能量吸收能力均高于大孔径泡沫,而压缩弹性模量则低于大孔径泡沫;随着泡孔体积离散系数的增大,闭孔PMI泡沫压缩弹性模量、初始峰值应力和能量吸收能力均减小。     

泡沫钢的制备及压缩吸能特性

为制备高强轻质泡沫钢吸能材料,本文以430L不锈钢粉为原料、CaCl₂为造孔剂,采用粉末冶金烧结-溶解法制备了孔隙率为64%~80%,孔径1~4 mm的泡沫钢.利用SEM和XRD对试样进行微观组织结构分析,并对试样进行轴向准静态压缩测试,分析讨论了孔隙率和孔形对泡沫钢压缩变形行为和吸能特性的影响,以及变形过程中孔结构变形和坍塌机理.研究表明：泡沫钢孔结构呈近球形且分布均匀,孔之间通过孔壁上的微孔形成有效连通.在压缩变形过程中,变形区首先发生在孔形不规则且孔壁较薄处,后诱发周围孔变形并形成多个变形带.泡沫钢试样压缩屈服平台应力随着孔隙率的增加而减小,当孔隙率为64.81%~78.82%时,其对应的屈服平台应力为59.37~17.04 MPa.在孔隙率相同的条件下,孔形为近球形的泡沫试样,其屈服平台应力远高于孔形不规则的试样.当应变量为40%时,孔隙率为64.81%~78.82%的泡沫钢,其单位体积的能量吸收值为23.92~7.32 MJ/m³,约为泡沫铝的5~7倍.4种不同孔隙率泡沫钢样品的理想吸能效率(I)均达0.85以上,表明泡沫钢可以作为一种理想的吸能材料.     

复合泡沫填充管的高g值冲击防护特性

目的 为避免或减小高g值冲击对弹内轻质元器件的破坏,应加强对轻质元器件缓冲防护结构的研究。方法 基于新型复合泡沫和通孔泡沫铝的2种泡沫填充管,通过万能试验机和落锤冲击系统研究了2种泡沫填充管的静动态力学特性,并运用数值模拟方法研究高g值冲击下等质量的泡沫填充管与夹芯管的加速度缓冲效果和吸能机制。结果 数值模拟所得结构变形和落锤加速度与实验结果较为一致,验证了数值模拟方法的可靠性。复合泡沫平台应力具有显著的应变率效应,其填充管压溃载荷平稳且高于泡沫铝填充管,比泡沫铝填充管体现出更优异的高过载防护性能。等质量的泡沫夹芯管的抗冲击性能优于填充管,2种泡沫填充而成的夹芯管具有相似的高过载防护性能,泡沫材料压缩行为对夹芯管压溃载荷特征的影响低于填充管。结论 所得结果对轻质元器件的高g值缓冲防护有较强的指导意义。     

Cyclic Nanoindentation for Local High Cycle Fatigue Investigations: A Methodological Approach Accounting for Thermal Drift

Cyclic nanoindentation allows characterizing the influence of single phases and their interactions on fatigue mechanisms. Herein, a method for high cycle fatigue testing by nanoindentation is presented. By combining high- and low-frequency indentation modes, high cycle numbers are achieved while obtaining sufficient data points to reconstruct force–displacement hysteresis loops. A challenge is the stochastic course of thermal drift which is addressed by measuring drift rate in regular low-force holding segments. Drift rates are used to correct the displacement values, yielding reproducible cyclic deformation data as it is shown for two very different materials, a ductile metal and a brittle ceramic.     

Thermodynamic studies on the complete phase diagram of aqueous two phase system containing polyethylene glycol dimethyl ether 2000 and di-potassium hydrogen phosphate at different temperatures

The liquid-liquid equilibrium of polyethylene glycol dimethyl ether 2000 (PEGDME₂₀₀₀)+K₂HPO₄+H₂O system has been determined experimentally at T=(298.15,303.15,308.15 and 318.15) K. The liquid-solid and complete phase diagram of this system was also obtained at T=(298.15 and 308.15) K. A nonlinear temperature dependent equation was successfully used for the correlation of the experimental binodal data. Furthermore, a temperature dependent Setschenow-type equation was successfully used for the correlation of the tie-lines of the studied system. Moreover, the effect of temperature on the binodal curves and the tie-lines for the investigated aqueous two-phase system have been studied. Also, the free energies of cloud points for this system and some previously studied systems containing PEGDME₂₀₀₀ were calculated from which it was concluded that the increase of the entropy is the driving force for formation of aqueous two-phase systems. Additionally, the calculated free energies for phase separation of the studied systems were used to investigate the salting-out ability of the salts having different anions. Furthermore, the complete phase diagram of the investigated system was compared with the corresponding phase diagrams of previously studied systems, in which the PEGDME₂₀₀₀ has been used, in order to obtain some information regarding the phase behavior of these PEGDME₂₀₀₀+salt+water systems.     

改良BBS法评价聚氨酯发泡催化剂

改良BBs法用光电法测发泡高度-时间曲线,用机械手完成投掷钢球动作,过程用微机控制。本文对此法测得的三乙胺、四甲基乙二胺、二甲基乙醇胺、双(二甲基氨基乙基)醚、三乙烯二胺等催化剂在聚氨酯软质泡沫塑料形成过程中的胶化-发泡曲线进行了讨论,并评价了它们的催化特性。改良BBs法与手工BBs法相比,具有检测精度高,样本采集点多的优点。     

气泡混合轻质土置换高速公路路堤工后沉降研究

以申嘉湖杭高速公路（练杭段）堆载预压处理段路基沉降速率较大断面采用气泡混合轻质土置换高速公路路堤为例,采用土体弹塑性本构模型及Sjerrum等时e—lgp曲线理论,对置换后地基土体的应力路径变化进行理论分析,地基土处于超固结状态;通过现场实测沉降资料,置换前处理段沉降观测点月沉降量在14mm～18mm,置换后沉降观测点月沉降量在2nm～4mm,沉降速率收敛较快,处理后效果明显,能够有效减少工后沉降。结果表明,采用气泡混合轻质土置换高速公路路堤不仅施工方便,质量容易控制,而且处理效果显著,是一种有效的减少软土地基工后沉降的控制方法。     

冲击速度对开孔泡沫金属冲击动力学性能影响

利用有限元软件ANSYS中的LS-DYNA模块,建立起了泡沫金属胞元方孔模型,采用能更好反应实际情况的幂函数塑性模型,研究了冲击速度对泡沫金属冲击动力学性能的影响,对泡沫金属在冲击载荷作用下的应力传递和分布以及变形过程进行了数值模拟,分析了冲击速度对泡沫金属应力传递和分布以及变形的影响。研究表明,随着初始撞击速度的提高,泡沫铝屈服强度有所提高,应力传递速度和接触端面处的泡孔变形速度加快。