沥青混凝土铺筑中的压茬接缝施工

提出了机械铺筑沥青混凝土中的接缝问题,论述了压茬接缝法施工工艺.     

Microwave joining of two long hollow tubes: an asymptotic theory and numerical simulations

A nonlinear heat equation which models the microwave assisted joining of two large SiC tubes is analyzed. By exploiting the small fineness ratio of the structure and disparate time scales an asymptotic theory for this problem is systematically deduced. Specifically, a one-dimensional nonlinear heat equation is described which governs the temperature in the outer region. This is a numerically well posed problem and it is efficiently solved using standard methods. This solution is not valid in the inner region which includes the microwave source. An inner asymptotic approximation is derived to describe the temperature in this region. This approximation yields two unknown functions which are determined from matching to the outer solution. The results of the asymptotic theory are compared to calculations done on the full problem. Since the full problem is numerically ill conditioned, the asymptotic theory yields enormous savings in computational time and effort.     

Laser-supported joining of SiC-fiber/SiCN ceramic matrix composites fabricated by precursor infiltration

SiC-fiber/SiCN ceramic matrix composites were manufactured by means of polymer infiltration and pyrolysis. The fiber preform was made by slurry infiltration and winding using a computer-controlled winding module. Multiple infiltration steps using a Si–C–N precursor were included to increase the density. The influence of the sintering conditions on the microstructure of the CMC was demonstrated.Pipe sections made of the CMC materials were joined using a laser-supported heating technology with an Y–Al–Si–O glass–ceramic filler. The thermal response of the CMC components was controlled by the anisotropic thermal conductivity. Fast heating by laser beam was achieved for elements rotating in the direction of the fiber winding. SEM micrographs of the joints showed the good wettability of the CMC by the glass–ceramic filler. Nearly defect-free joints were obtained using a nitrogen process atmosphere. The laser-supported technology was shown to be promising for the joining of CMC components.     

Interface structure and mechanical property of the brazed joint of graphite and copper

A kind of self-made AgCuTiSn braze alloy powder was used to join graphite and copper. The whole brazing process was performed under vacuum circumstances at different temperatures (1033-1193 K) for several holding time (300-1800 s). According to scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and electron probe X-ray microanalysis (EPMA) results, the reaction products of the interface are TiC, Ti3Sn, Cu(s. s), Ag(s. s) and Cu-Sn compound. As the brazing parameters increase, the quantity of Ag(s. s) in the braze alloy and C fibers on graphite/AgCuTiSn interface reduce, while that of Cu (s. s) in the braze alloy improves. When the brazing temperature is 1093 K and holding time is 900 s, the joint can obtain the maximum room temperature shear strength 24 MPa.     

Interfacial Bonding Strength Between Brazing Alloys and CVD Diamond

Three groups of brazing alloys were compared in brazing chemical-vapor-deposited (CVD) diamond, including two nickel-based alloys (Ni-3Fe-7Cr-3B-0.5Si-0.02C and Ni-14Cr-10P-0.02C), one copper-based alloy (Cu-10Sn-15Ti), and two silver-based alloys (Ag-5Cu-1Al-1.25Ti and Ag-34.25Cu-1In-1.75Ti). The nickel-based alloys catalytically transformed the sp³-bonded diamond into sp²-bonded carbon during high-temperature brazing operation though with the existence of Cr as the active metal. The bonding strength was very low and the fracture primarily propagated through the sp²-bonded carbon. For Cu-10Sn-15Ti brazing alloy, the transformation of the sp³-bonded diamond into sp²-bonded carbon during high-temperature brazing operation was marginal. The bond strength was adequate and fracture took place primarily through the brazing alloy bulk, due to the high concentrations of Sn and Ti that caused the precipitation of abundant intermetallic compounds in the brazing alloy bulk. For Ag-based alloys having very low concentrations of Ti, no visible degradation of diamond was observed and the bonding strength was very high. Crack primarily propagated through the brazed interface or even the CVD diamond bulk.     

微波助燃Ni-Al高温自蔓延连接CVD SiC

采用高放热反应且摩尔比为1∶1的镍-铝二元系作为焊料,利用微波引燃的方法使体系以内部加热的方式迅速升温到燃烧温度并发生自蔓延高温合成反应,最终实现化学气相沉积碳化硅陶瓷(CVD SiC)的连接,研究不同反应产物对连接强度的影响规律.研究表明:反应层平均厚度约300 μm,反应产物与碳化硅基体之间的界面结合良好,但接头内存在着大量气孔,致密度较低.母材与中间层产物的热错配应力问题使接头界面处存在大量微裂纹.由于自蔓延连接的复杂性与高度不平衡性使反应产物较难控制,接头断面的XRD结果表明不同接头中生成了不同相的镍-铝系金属间化合物以及氧化物,但均未检测到残余单质Ni或Al.氧化物的出现会极大影响接头的剪切强度,导致试样接头强度的数值偏差较大.     

MoSi2/不锈钢的梯度连接及其接头组织

采用放电等离子烧结技术和有限元分析设计的MoSi2/316L梯度材料作为过渡层连接MoSi2与316L不锈钢,研究了各层及界面组织.结果表明:MoSi2与梯度过渡层材料间热膨胀系数的有效匹配,可防止低韧性MoSi2由连接温度(1 200 ℃)冷却时产生的残余应力而引起的开裂;使用9层MoSi2/316L梯度材料过渡层体系可获得一种组织致密且均匀的接头;MoSi2/316L不锈钢梯度过渡层在宏观上呈现明显的梯度,微观上则表现出成分连续变化,且各层成分分布均匀.     

圆筒法兰连接结构下圆筒的模态试验研究

本文采用单输入多输出（SIMO）的模态试验方法对圆筒法兰连接结构的下圆筒进行了自由状态下的模态试验，用频率多参考（Polyffequence）的模态拟合方法分析试验数据，获得了结构的模态参数，对其动态特性有了初步了解，试验结果可为圆筒法兰连接结构动力学建模提供模型修正数据。     

Drilling of graphite/bismaleimide composite material

Drilling study of graphite/bismaleimide composite material was conducted by using different cutter materials (high-speed steel, carbide, and polycrystalline diamond) and drill geometries. It was found that polycrystalline diamond tools outperformed all other tools in terms of minimal surface damage, delamination, and fiber pullout. The drilling forces exerted in machining graphite/bismaleimide were recorded by using a dynamometer, and the morphology of drilled surfaces was evaluated with surface profilometry and optical and scanning electron microscopy. The drilling characteristics were evaluated in terms of cutting forces, tool wear, and surface morphology.     

NiTi合金智能传力垫的研究及应用

为了解决关键结构螺栓组的载荷不均和超载断裂问题, 利用ＮｉＴｉ 合金的压缩拟弹性功能,设计了一种智能传力垫, 分析了其调节载荷的功能特性, 并在内燃机车上进行了实际应用与测试。结果表明： ＮｉＴｉ 合金智能传力垫可以使螺栓组各螺栓间的受力不均匀度得到调整, 动载荷降低。因而,具有良好的自动均载限载防断功能, 可以大幅度提高螺栓连接的安全性和可靠性。