改性羰基铁粉/ 硅橡胶材料的制备及其力学性能

以微米级改性羰基铁粉为填充剂,甲基乙烯基硅橡胶为基体,制备了高温硫化的羰基铁粉/硅橡胶复合材料.研究了偶联剂种类、用量及羰基铁粉填充量对复合材料力学性能的影响,利用扫描电镜对硫化胶断面的微观结构进行了观察.结果表明,采用硅烷偶联剂KH570、KH151改性羰基铁粉都能提高复合材料的拉伸强度,其中KH151的改性效果要优于KH570;KH151的最佳用量为羰基铁粉质量的1%;在一定范围内随着改性羰基铁粉体积分数的增加,复合材料的拉伸强度增大.羰基铁粉体积分数超过60%后,混炼困难.     

Multi-objective optimization of different dome reinforcement methods for composite cases

A multi-objective optimization method was proposed for different dome reinforcement methods of a filament-wound solid rocket motor composite case based on a Radial Basis Function (RBF) model. Progressive damage of the composite case was considered in a simulation based on Hashin failure criteria, and simulation results were validated by hydraulic burst tests to precisely predict the failure mode, failure position, and burst pressure. An RBF surrogate model was established and evaluated by Relative Average Absolute Error (RAAE), Relative Maximum Absolute Error (RMAE), Root Mean Squared Error (RMSE), and R² methods to improve the optimization efficient of dome reinforcement. In addition, the Non-dominated Sorting Genetic Algorithm (NSGA-II) was employed to establish multi-objective optimization models of variable-angle and variable-polar-radius dome reinforcements to investigate the coupling effect of the reinforcement angle, reinforcement layers, and reinforcement range on the case performance. Optimal reinforcement parameters were obtained and used to establish a progressive damage model of the composite case with dome reinforcement. In accordance with progressive damage analysis, the burst pressure and performance factor were obtained. Results illustrated that variable-angle dome reinforcement was the optimal reinforcement method compared with variable-polar-radius dome reinforcement as it could not only ensure the reinforcement angle’s continuous changing but also decrease the mass of composite materials. Compared with the unreinforced case, the reinforced case exhibited an increase in the burst pressure and performance factor of 36.1% and 23.5%, respectively.     

电弧增材制造7075铝合金的微观组织与力学性能

7xxx系铝合金电弧增材制造过程中因组织不均匀与元素偏析导致成形试样性能较低,针对这一问题,对电弧增材制造7075铝合金薄壁件进行固溶+人工时效热处理(T6态),对比研究了热处理前后微观组织与力学性能的变化。结果表明,7075铝合金沉积态试样中晶粒被网状共晶组织包围,Zn、Mg和Cu元素在晶界富集,产生元素偏析。经过T6态热处理后,大部分共晶组织溶解,元素分布的不均匀性得到明显改善。与沉积态试样相比,热处理后试样的抗拉强度与断后伸长率增加,抗拉强度从(279.4±5.3)MPa提高至(493.9±10.2)MPa,断后伸长率从3.78%±0.35%增加到9.66%±1.70%。T6态试样的拉伸断口表面密布着韧窝,断裂方式为韧性断裂。     

铝锂合金加筋壁板剪切屈曲性能

为研究剪切载荷下2A97铝锂合金加筋壁板的屈曲与后屈曲行为,设计了加筋壁板和夹具,完成了壁板的剪切试验;得到了加筋壁板的失稳载荷、破坏载荷以及破坏模式;采用受剪板屈曲与张力场理论计算了加筋壁板的剪切屈曲失稳载荷;建立有限元数值计算模型对加筋壁板屈曲行为进行计算分析,并将数值结果与试验结果对比。结果表明：加筋壁板的屈曲模式为筋条间蒙皮的局部屈曲;加筋壁板的破坏模式为沿加载对角线方向蒙皮的凸起,破坏原因为蒙皮的塑性变形、撕裂以及筋条的扭转变形;利用张力场理论可以得到较准确的屈曲失稳载荷,与试验误差为6.56%;数值模拟得到的屈曲与破坏模式与试验吻合,失稳载荷和极限载荷与试验结果误差分别为1.22%和11.52%。     

Microstructure and mechanical properties of hybrid fabricated 1Cr12Ni2WMoVNb steel by laser melting deposition

 Laser melting deposition was carried out to deposit a 1Cr12Ni2WMoVNb steel bar on a wrought bar of same material. Room-temperature tensile properties of the hybrid fabricated 1Cr12Ni2WMoVNb steel sample were evaluated, and microstructure, fracture surface morphology, and hardness profile were analyzed by an optical microscope (OM), a scanning electron microscope (SEM), and a hardness tester. Results show that the hybrid fabricated 1Cr12Ni2WMoVNb steel sample consists of laser deposited zone, wrought substrate zone, and heat affected zone (HAZ) of the wrought substrate. The laser deposited zone has coarse columnar prior austenite grains and fine well-aligned dendritic structure, while the HAZ of the wrought substrate has equiaxed prior austenite grains which are notably finer than those in the wrought substrate zone. Besides, austenitic transformation mechanism of the HAZ of the wrought substrate is different from that of the laser deposited zone during the reheating period of the laser deposition, which determines the different prior austenite grain morphologies of the two zones. Microhardness values of both the laser deposited zone and the HAZ of the wrought substrate are higher than that of the wrought substrate zone. Tensile properties of the hybrid fabricated 1Cr12Ni2WMoVNb steel sample are comparable to those of the wrought bar, and fracture occurs in the wrought substrate zone during the tensile test.     

Nb-Si 基超高温合金的研究进展

Nb-Si基超高温合金由于熔点高、密度低和优良的高温强度等特点受到广泛关注,极具作为下一代高推重比航空发动机和超然冲压发动机的热端部件用材料的潜力.本文主要介绍了国内外在合金化、粉末冶金、定向凝固和热处理工艺对Nb-Si基合金组织和性能影响等方面的研究现状,并展望了其发展趋势.     

Electron Beam-Physical Vapor Deposited TiAl-based Laminated Composite Sheet with Nb Layer Toughening

The TiAl-based laminated composite sheet of 150mm×100 mm×0.2mm, with 24 TiAl layers and 23 Nb layers laid alternately one on another, was successfully fabricated using the electron beam-physical vapor deposition (EB-PVD) method. The microstructure and properties of the sheet were investigated on an atomic force microscope (AFM), a scanning electron microscope (SEM) and a tensile testing machine. The results indicate that the evenly distributed Nb layers are well joined with the TiAl layers, and the interfaces between layers are transparent, and every interlayer spacing is of about 8 μm. The fractures appear to be a mixture of intergranular fractures and somewhat ductile quasi-cleavage ones. Despite its slight influence on ultimate tensile strength, the inserts of Nb layers efficiently in-crease the room temperature ductility of TiAl-based alloys due to the crack deflection effect.     

矩阵初等变换的一些性质及应用

矩阵的初等变换是线性代数中应用十分广泛的重要工具。文章证明了矩阵初等变换的两个性质 ,以此为基础 ,归纳说明了矩阵的初等变换在线性代数课程中的应用 ,并给出了一些实例。     

应用TESTWORK3.02软件测试不锈钢带的力学性能

介绍了用ＴＥＳＴＷＯＲＫ３．０２测试软件对不锈钢带力学性能的测试过程。从而获得了不锈钢带的弹性模量、抗拉强度、非比例伸长应力、断后伸长率等指标。