断后伸长率A测量结果的不确定度评定

文章按照GB/T 228-2002《金属材料室温拉伸试验方法》标准的要求,对冷轧奥氏体不锈钢板的断后伸长率进行了测试,并对检测结果的不确定度进行了评定。当k=2时,置信概率p=95%,断后伸长率不确定度评定结果为A=62.5%±2.0%。     

碳短纤维-ZrB2陶瓷基复合材料的制备与性能研究

对ZrB2-Sic（ZS）材料和碳短纤维，ZrB2-SiC（ZSC）材料的断裂韧性、室温至900℃弯曲强度进行了测试和研究。结果表明：短纤维的加入可以显著提高材料的断裂韧性、从4．25MPa．m^1/2提高到6．56MPa．m^1/2，纤维拔出和脱粘以及裂纹的桥接和偏转是材料断裂韧性提高的原因；ZS和ZSC材料弯曲强度从室温到900℃经历了不同的过程，但都是两种因素共同作用的结果，即温度升高，晶界软化所带来的对裂纹的愈合作用与温度升高所带来的界面结合强度下降的作用。     

Fracture dynamics of sprayed and laser-glazed titania by an inverse processing of elastic waves

A new elastic wave (EW) or acoustic emission (AE) monitoring and signal processing system has been developed and used to elucidate the fracture behavior of sprayed and laser-glazed ceramic coatings. The system measures the minute surface displacements excited by the propagation of elastic waves. It enables elucidation of the fracture dynamics (fracture mode and kinetics) of stressed coatings. The surface displacement at the sensor position was computed by the convolution integral of an assumed source wave with the dynamic Green’s function until signals resembled the measured wave. This new signal processing method was used to determine the fracture strength and dynamics of microcracks in sprayed and laser-glazed titania subjected to four-point bending. It was found that mode II shear cracking along the interface between the coating and substrate occurred prior to mode I cleavage cracking. The fracture strength of laser-glazed titania was higher than that of as-sprayed titania in most cases; however, this depended on the coating structure. This article introduces the principle of source inversion processing of elastic waves, the monitoring system, laser glazing of sprayed titania, and experimental work on the fracture behavior of titania coatings.     

基于结构静动态设计方法的数控机床滑座结构改进

对单自由度系统，其静刚度与固有频率的平方有正比关系。复杂机械结构的静、动刚度与结构的布局有关，但对其某一低阶固有频率和该方向的静刚度，适用上述结论。故通过提高结构的固有频率，可同时改善结构静、动刚度。有限元分析（FEA）方法应用于结构的静、动态设计中，可大大提高结构设计效率。以一数控机床滑座结构为实例，基于结构静、动刚度的关系和FEA方法，对结构进行了改进，使滑座重量减少一半的同时，提高了其结构的静、动态特性。     

变焦-临界穿透束流极值法测量电子束流动态焦点——一种焦点测量方法介绍

通过试验研究发现了电子束焊接过程中工件传导电流的传导比均值与输入束流的函数规律，函数的极大值是电子束焊接动态过程工件被穿透的临界状态转变点。利用电子束焊接过程的临界穿透束流特性，讨论了电子束受金属蒸气影响后的焦点状态与漂移空间传输的电子束焦点状态存在不同特性，提出了一种测量电子束焊接过程动态焦点的方法，变焦-临界穿透束流极值焦点测量法。     

铁路车辆铆钉拉伸断口不平整原因分析

采用光学显微镜、扫描电镜对失效铁路车辆铆钉的微观组织与断口进行分析.结果表明,铆钉拉伸断口上产生凸台阶的主要原因是在槽口边缘形成的裂纹扩展到心部之前,又在中心形成新的裂纹,且在这些中心裂纹处发生塑性变形.通过调整热处理工艺与控制材料中夹杂物级别可以解决断口不平问题.     

卷取机助卷辊液压踏步压力控制系统动态特性分析

在对卷取机助卷辊液压踏步位置控制系统动态特性分析的基础上[1],建立了用于液压踏步压力控制系统动态特性分析的数学模型,并利用m atlab/simu link得到了压力控制系统的动态结构框图,实现了动态仿真。     

Nb-Ti连铸坯热芯大压下轧制动态再结晶行为研究

采用热模拟单道次压缩实验，研究了Nb-Ti连铸坯热芯大压下轧制中动态再结晶行为及奥氏体晶粒转变规律。结果表明，变形温度越高，应变速率越低，发生动态再结晶的临界应变值越小，动态再结晶越充分。在变形温度1 350 ℃，继续增加应变至0.8和增加应变速率至10 s^-1，奥氏体晶粒尺寸并未得到进一步细化，反而较应变0.5和应变速率5 s^-1下的奥氏体晶粒更加粗大。这是因为高温粘塑性区的金属晶间粘性流动增加，位错增殖速度增大，在动态再结晶过程中会重新形成新的无畸变再结晶晶粒，这些新的无畸变晶粒的亚动态再结晶动力学极快，在较大驱动力下使奥氏体晶界快速迁移，从而使奥氏体发生一定程度的粗化。     

Machining characteristics and fracture morphologies in a copper-beryllium (Cu-2Be) alloy

The technology of materials removal is improved greatly by the introduction of advanced cutting tools like cubic boron nitride, ceramics, polycrystalline diamond and the more recent whisker-reinforced materials. In this paper, the influence of cutting temperature on machinability, mechanical properties, microstructure, and fracture morphology of Cu-2Be alloy using a polycrystalline diamond cutter is investigated. The information on machining, microstructure, and fracture morphology of Cu-2Be alloy are very useful to understand their fabrication characteristics and the basic mechanisms of its deformation and fracture. The machinability (in terms of surface finish) of Cu-2Be alloy is evaluated as a function of cutting temperature, resulting from wet and dry cutting. Machining is carried out on a Hardinge Cobra 42 CNC machine (Hardinge Inc., Elmira, NY), and the machining parameters used—cutting speed, depth of cut, and feed rate—are kept constant during both wet and dry cutting. The machined surface finish on Cu-2Be alloy is measured using a surface finish analyzer (Surftest 401, series 178) technique. The machined specimens are examined for their strength and hardness properties using a standard Universal Testing Machine and Rockwell hardness tester, respectively. Wet cutting (using coolants) produced a smooth surface finish when compared with dry cutting of the Cu-2Be alloy. The machined specimens are examined for their microstructural features using a Nikon optical microscope. The specimens are etched using a suitable etchant solution for revealing such microstructure constituents as grain size, phase proportions, and the possible overheated areas (especially in dry cutting). The fractured surfaces from the tensile and impact toughness tests are investigated for their fracture morphologies (dry and wet cutting) using a microprocessor-controlled scanning electron microscope (Jeol Model JSM 5910 LV). A detailed analysis is also made to understand and interpret the basic fracture mechanisms responsible for crack initiation and crack propagation. The Cu-2Be alloy showed relatively higher mechanical properties in wet cutting in comparison to dry cutting operations. Fracture studies demonstrated intergranular and ductile fractures as dominant modes of fracture mechanisms in Cu-2Be alloy.     

Resistance welding of carbon fibre reinforced polyetheretherketone composites using metal mesh and PEI film

Weldability of polyetheretherketone( PEEK) with polyetherimide( PEI) is tested. And carbon fiber reinforced PEEK laminates are resistance welded using stainless steel mesh heating element. The effects of the welding time and welding pressure on the lap shear strength of joints are investigated. Results show that PEEK can heal with PEI well in welding condition and the lap shear strength of PEEK/CF(carbon fibre) joint increases linearly with welding time, but reaches a maximum value when welding pressure ranging from 0.3 MPa to 0.5 MPa with constant welding time. The fracture characteristics of surface are analyzed by SEM techniques, and four types of fracture modes of lap shear joints are suggested.