冷压成型压力对HMX基PBX微结构影响的SANS研究

为了探索冷压成型压力对高聚物粘结炸药(PBX)微结构的影响,采用衬度变换中子小角散射(SANS)技术测试了不同压力成型奥克托今(HMX)基PBX的中子小角散射信号,利用Porod定理获得了样品中炸药晶体-粘结剂-孔洞三者之间界面面积随成型压力的演化。结果表明,成型压力由64 MPa增加至178 MPa时,样品密度由1.55 g·cm~(-3)增加至1.72 g·cm~(-3),HMX与粘结剂之间的界面结合率由23.7%增加至26.7%,单位质量PBX内部总界面面积Stotal减小6.1%(实验误差3%),HMX与粘结剂之间的界面面积SHB增加15.2%,HMX与孔洞之间的界面面积SHV基本不变,而粘结剂与孔洞之间的界面面积SBV则下降38.0%,表明这个过程中造型粉和粘结剂被逐渐压实;成型压力由178 MPa增加至382 MPa时,样品密度增加至1.79 g·cm-3,HMX与粘结剂之间的界面结合率增加至42.3%,Stotal减小11.2%,SHB增加49.0%,SHV减少25.8%,SBV下降45.5%,说明这个过程中除了造型粉和粘结剂被压实外,还有大量的粘结剂流动至HMX晶体表面。此外,成型压力由64 MPa增加至382 MPa时,SHV与SHB之和(即单位质量PBX样品内HMX炸药晶体总的界面面积)基本保持不变,说明该冷压过程并未导致HMX晶体大量穿晶破碎,这与光学显微观察结果一致。     

Fabrication and characterization of a new-style structure capillary channel in reaction bonded silicon carbide composites

A new-style structure capillary channel was fabricated by using boron carbide powder mixtures with an appropriate multimodal particle size distribution to promote the liquid silicon infiltration in reaction bonded silicon carbide composites. Two types of core–rim structure were observed and the secondary SiC produced in the siliconisation reaction existed in two forms: nucleating on the original SiC and occupying the original positions of the residual silicon. The size of the secondary SiC in the latter form was in a range of tens to hundreds nanometers. These nano-sized SiC grains and the additive of fine boron carbide particles refined the crystalline structure and broke up the residual silicon phase into small pieces. Using this method, the microstructure was refined and the mechanical properties improved significantly. The lowest residual silicon volume fraction was 4.0% and the flexural strength and fracture toughness reached peak values of 526 ± 21 MPa and 6.2 ± 0.4MPa m^1/2, respectively.     

GFRP端部约束对粘接修理效果的影响

以环氧树脂E44为基体,玻璃纤维为增强材料形成复合材料补片修复损伤铝合金,以端部未加约束试样为对照组,通过拉伸试验,研究了在补片端部加入约束后,补片长度和补片层数变化对修理效果的影响。研究结果表明,补片长度相同时,端部采用压条约束的修复效果明显高于端部无压条约束的修理试样,补片端部添加压条约束后,补片长度变化对修理效果的影响规律没有改变,抗拉强度随补片长度增大而增加,当补片长度达到一定值后基本不再提高,但是初始值有明显提高。此外,补片采用压条和缠绕的端部约束后,即在FRP-铝合金界面引入压应力,可改善FRP-铝合金之间的界面性能,有效缓解补片端部的应力集中。特别是当补片层数较多时,端部约束可有效改善由于补片层数增加引起的变形协调难的问题,而且缠绕约束方式的修复效果优于压条修复。     

高聚物粘结炸药与金属的接触腐蚀研究

利用ＸＰＳ和激光共聚焦扫描显微镜等表面分析技术研究了高聚物粘结炸药（ＴＡＴＢ或ＨＭＸ为基）与不锈钢（１Ｃｒ１８Ｎｉ９Ｔｉ）、铝（ＬＹ－１２）接触后,混合炸药成分、相对湿度以及温度对金属的腐蚀,对其腐蚀产物进行了定性及定量检测。结果表明：湿度对金属腐蚀最大,混合炸药成分对金属也有腐蚀,炸药中所含无机氯离子对金属腐蚀有促进作用。     

Influence of the interface ply orientation on the fatigue behaviour of bonded joints in composite materials

The paper deals with the study of the fatigue behaviour of bonded joints in composite materials. The influence of the orientation of the composite layer at the adhesive–adherend interface is investigated on single lap joints prepared by carbon fabric/epoxy laminates bonded together with a two-part epoxy adhesive. Different laminate lay-ups ([45/0₂]_s and [45₂/0]_s), overlap lengths (20 and 40 mm) and corner geometry of bonded area (square edge and fillet, respectively) were investigated under tension–tension fatigue. Particular attention was devoted to the analysis of the fatigue damage evolution to identify initiation and subsequent growth of cracks. A previous model developed by the authors, for the prediction of the fatigue life of bonded joints as the sum of an initiation and propagation phase, was successfully applied to summarise the new data.     

Specification Requirement for Thermal Stability of Sintered NdFeB Materials for Electrical Machines

Based on IEC standards and Chinese national standards of sintered NdFeB materials, in the paper the hightemperature, room-temperature properties and thermal stability of about one hundred samples of NdFeB materials for electrical machines were measured and analyzed.These materials are produced by ten representative manufactories in China.Combined with the analysis results, the paper points out that the magnetic properties of sintered NdFeB materials for electrical machines should meet not only the specific values in standards, such as Br, (BH)max ,HcJ ,but also the requirement of temperature coefficients a (Br) , a (HcJ).     

Predicted Anisotropic Thermal Conductivity for Crystalline 1,3,5‐Triamino‐2,4,6‐trinitobenzene (TATB): Temperature and Pressure Dependence and Sensitivity to Intramolecular Force Field Terms

The anisotropic thermal conductivity of the layered molecular crystal 1,3,5‐triamino‐2,4,6‐trinitrobenzene (TATB), an insensitive secondary high explosive, is determined using classical molecular dynamics on the P=0.0 GPa isobar for temperatures 200 K≤T≤700 K and on the T=300 K isotherm for pressures 0.0 GPa≤P≤2.5 GPa. Sensitivity of the predicted (300 K, 0.0 GPa) conductivity to intramolecular terms in the force field is investigated. Two conduction directions are considered, one nominally within and the other exactly perpendicular to the stacked planar single‐molecule‐thick layers comprising the TATB crystal. The thermal conductivity λ(T,P) along both directions is found to decrease approximately as λ∝1/T with increasing temperature and increase approximately linearly λ ∝ T with increasing pressure. The temperature dependence is found to be highly anisotropic with nearly twice as large a reduction in absolute conductivity within the molecular layers (Δλ=−0.67 W m⁻¹ K⁻¹) compared to between them (Δλ=−0.35 W m⁻¹ K⁻¹). Anisotropy in the conductivity is predicted to decrease with increasing temperature; the P=0.0 GPa conductivity is 68 % greater within the layers than between them at 200 K, but only 49 % greater at 700 K. The pressure dependence is also anisotropic, with a 51 % and 76 % increase in conductivity within and between the layers, respectively. Predicted values for the conductivity are found to differ by less than 12 % for several instructive modifications to the intramolecular force field. Completely eliminating high‐frequency N H bond vibrations using the SHAKE algorithm leads to an isotropic reduction in the conductivity that scales as the corresponding reduction in the classical heat capacity, indicating that optical phonons are likely significant contributors to the total conductivity. Replacing harmonic bond potential energy functions with anharmonic Morse functions results in an isotropic ≈6 % reduction that is likely due to stronger phonon‐phonon coupling and corresponding reduction in the phonon mean free path.     

Cylindrical grinding of bearing steel with electrolytic in-process dressing

Cylindrical surfaces are increasingly utilized in various areas, and related high-efficiency and high-quality fabricating technologies are of great importance and significant benefit to modern industry. To provide fundamental knowledge for the bearing industry, studies have been conducted on the use of cast-iron-bonded cubic boron nitride (cBN) superabrasive wheels, based on electrolytic in-process dressing (ELID) technique for realizing high-efficiency grinding of steel cylindrical workpieces. Therefore, in this investigation, experiments were carried out on an ordinary cylindrical grinder with a hydrodynamic spindle, and straight type grinding wheels of different grit sizes were used. The effects of grit sizes on surface roughness as well as waviness, roundness, and surface stress were evaluated in both the traverse and plunge grinding modes. Comparison of ELID grinding with other processes was also carried out. Mirror surface grinding of different materials was achieved with the #4000 CIB-cBN wheel. ELID grinding was confirmed to induce compressive stress and to be more cost effective for small batch production of larger components when it works in the traverse mode.     

山东沭河特大桥T梁制作技术

通过科学合理的施工现场平面布置,攻破了大跨度预应力预制T梁施工技术难关,确保了桥梁按期架设贯通。