直流接触器断电不释放问题分析与研究

针对某型直流幅压接触器断电不释放问题,主要从接触器在长时间通电后,铁心剩磁因积累效应而增大产生的剩磁力,以及上下铁心吸合时极面上的防锈油漆在高温下出现较大黏结力两个方面进行了分析与研究。详细叙述了剩磁力和油漆黏结力对接触器的影响,通过计算和试验验证,明确了油漆黏结力高温下较大导致某型直流接触器断电不释放,并提出了相应的改进措施。     

改进的复合材料斜接结构胶层应力半解析法

引入微分概念和复合材料铺层刚度分配原则,形成一种改进的求解复合材料斜面对接结构胶层应力的半解析方法 MAM(Modified semi-Analytical Method)。首先,针对铺层角度及铺层数不一致的情况,采用有限元法(FEM)平面应变模型对MAM进行验证;然后,分别用平均剪应力法、FEM及MAM预测了复合材料斜接结构的承载能力并与试验值进行对比;最后,利用MAM分析工程应用问题,考虑了被粘结体刚度不匹配及胶层厚度的变化。研究结果表明:MAM适于设计复合材料斜接结构;采用MAM能得到胶层应力的尖峰值,且应力分布与FEM计算一致。     

Microfluidic Spinning of Cell‐Responsive Grooved Microfibers

Engineering living tissues that simulate their natural counterparts is a dynamic area of research. Among the various models of biological tissues being developed, fiber‐shaped cellular architectures, which can be used as artificial blood vessels or muscle fibers, have drawn particular attention. However, the fabrication of continuous microfiber substrates for culturing cells is still limited to a restricted number of polymers (e.g., alginate) having easy processability but poor cell–material interaction properties. Moreover, the typical smooth surface of a synthetic fiber does not replicate the micro‐ and nanofeatures observed in vivo, which guide and regulate cell behavior. In this study, a method to fabricate photocrosslinkable cell‐responsive methacrylamide‐modified gelatin (GelMA) fibers with exquisite microstructured surfaces by using a microfluidic device is developed. These hydrogel fibers with microgrooved surfaces efficiently promote cell encapsulation and adhesion. GelMA fibers significantly promote the viability of cells encapsulated in/or grown on the fibers compared with similar grooved alginate fibers used as controls. Importantly, the grooves engraved on the GelMA fibers induce cell alignment. Furthermore, the GelMA fibers exhibit excellent processability and could be wound into various shapes. These microstructured GelMA fibers have great potential as templates for the creation of fiber‐shaped tissues or tissue microstructures.     

Effect of the Ni/Pd/Au-Cu pre-plated finish lead frame surface structure treated by various surface roughening methods on packaging properties

Two roughening methods involving micro-etching and mixed mode etching of pre-plated finish (PPF) surfaces were used to examine the nickel-coated layer thickness effect on the surface morphology. The PPF lead frames treated by micro-etching (ME) surface roughness drastically decreased with increased nickel-coated layer thickness, while the PPF lead frames treated by mix mode roughening (MMR) maintained comparatively good surface roughness even with thick nickel-coated layers. The shear strength of the PPF of a lead frame treated by ME and MMR reached up to five times that of the untreated PPF based on a moisture sensitivity level button shear test. The failure mechanism of the PPF lead frame treated by ME was the formation of cracks through the interface between the lead frame and the epoxy molding compound, which led to the breakage. An experimental basis is provided for the application of PPF lead frames, as well as a theoretical foundation for increasing the adhesion strength of rough surfaces. Therefore, this study is of great theoretical and practical significance.     

Synthesis of phenyl silicone resin with epoxy and acrylate group and its adhesion enhancement for addition-cure silicone encapsulant with high refractive index

A novel phenyl silicone resin with epoxy and acrylate group (PSREA) was successfully synthesized via the non-hydrolytic sol-gel condensation reaction of 3-glycidoxypropyltrimethoxysilane, 3-methacryloyloxypropylmethyldimethoxysilane, and diphenylsilanediol, and was employed as the adhesion promoter for addition-cure silicone encapsulant (ASE) with high refractive index. The structure of PSREA was confirmed by Fourier transform infrared spectroscopy, ¹H nuclear magnetic resonance spectroscopy, and ²⁹Si nuclear magnetic resonance spectroscopy. The influence of PSREA on the properties of ASE was studied. It was found that PSREA could markedly enhance the adhesion strength of ASE to aluminum (Al) and poly(p-phenylene terephthamide) (PPA) substrate. When the content of PSREA was 1.5 phr, the shear strength of ASE was 4.43 and 2.27 MPa for Al and PPA substrate, which was about 71 and 266% higher than that of ASE without the adhesion promoter, respectively. In addition, PSREA had little effect on the mechanical properties, refractive index, and viscosity of ASE.     

Synthesis and Characterization of Linear and Tri-Block PLLA–PEG–PLLA Blends

This study was conducted to synthesize poly(L-lactide)–poly(ethylene glycol)–poly(L-lactide) triblock copolymer (PEGLA) with different poly(L-lactide) block length, and explore its applicability in a blend with linear poly(L-lactide) (3051D NatureWorks) with the intention of improving heat seal and adhesion properties at extrusion coating on paperboard. Poly(L-lactide)–poly(ethylene glycol)–poly(L-lactide) was obtained by ring opening polymerization of L-lactide using poly(ethylene glycol) (molecular weight 6000 g mol^?1) as an initiator and stannous octoate as catalyst. The structures of the PEGLAs were characterized by proton nuclear magnetic resonance spectroscopy. The melt flow and thermal properties of all PEGLAs and their blends were evaluated using dynamic rheology and differential scanning calorimeter. All blends containing 10 wt% of PEGLAs displayed similar zero shear viscosities to neat poly(L-lactide), while blends containing 30 wt% of PEGLAs showed slightly higher zero shear viscosity. However, all blends displayed higher shear thinning and increased melt elasticity (based on tan δ). No major changes in thermal properties were distinguished from differential scanning calorimetric studies. High molecular weight PEGLAs could be used in extrusion coating with 3051D without problems.     

湿法超声机械镀锌-铝层耐蚀性的研究

采用湿法超声机械镀设备制备了Zn-5%Al复合镀层。用多功能扫描电子显微镜及其配备的能谱分析仪观察并分析了复合镀层的形貌及成分,用划格法测试了复合镀层与基体间的结合强度,并用中性盐雾腐蚀试验法测试了复合镀层的耐蚀性。结果表明:湿法超声机械镀Zn-5%Al复合镀层表面平整、结合强度高、耐蚀性好,是一种综合性能优良的防护镀层。     

用于难加工材料高效切削异面涂层刀具的研制

针对切削难加工材料时刀具前后刀面磨损机理不同、刀具寿命较短的问题,提出了在刀具前后刀面分别制备不同性能涂层的新方法,并对制备的异面涂层刀具进行了切削性能试验。首先对切削难加工材料时刀具磨损机理进行了研究,结果表明,刀具前刀面易于发生粘结磨损,后刀面易于发生磨粒磨损;然后,通过多弧离子镀方法,在前刀面制备了抗粘结能力强的Al Cr N多元涂层,在后刀面上制备了抗磨粒磨损能力强的Ti CN涂层。最后,对制备好的刀具进行了切削性能测试,结果表明,异面涂层能显著提高刀具的综合力学性能。     

半轴套管冲孔连皮缺陷问题研究及工艺优化

半轴套管是汽车桥壳的重要零件,针对北京机电研究所开发的半轴套管热挤压成形技术在进行工艺调试过程中,穿孔及正挤压工序中管端易出现冲孔连皮粘连缺陷的问题进行了分析,探讨了造成连皮粘连的原因,确定连皮过厚和冲头偏心是造成这一缺陷的主要因素。采用Deform-3D有限元软件分别对连皮过厚和冲头偏心的冲孔情况进行模拟,模拟结果较好地反映了实际情况。运用BP神经网络结合遗传算法,对冲孔工序的工艺数据进行优化,确定了合适的连皮厚度。最后,采用优化后的连皮厚度,并对各工序凸模和凹模进行对正检查,生产出合格的半轴套管产品。