机械结构相似度评价及可靠性预计研究

在用传统的相似产品法进行可靠性预计时,所选取的相似产品与评价对象之间差异较大,会造成预计结果的偏差较大。为解决这一问题,提出了一种基于"功能—运动—动作"结构化分解的可靠性预计新方法。通过明确产品的各大运动功能建立功能层,分析完成各功能的机械部件运动建立运动层,确定实现各机械部件运动的元动作运动单元建立元动作层,建立了可靠性预计的"功能—运动—元动作运动单元"层次模型。引入区间层次分析法,确定了"功能—运动—元动作运动单元"层次模型中各子代运动单元对父代运动单元的可靠性影响权重,并构建了由子代运动单元预计父代运动单元可靠性的数学模型。确定影响评价机械结构相似度的因素,构建了区间数综合评判云模型并选取与元动作运动单元相似的参考结构,以区间数综合评价云模型得出的相似度值修正参考结构的可靠性数据来预计元动作运动单元的可靠性。将元动作运动单元的可靠性预计值代入数学模型,层层预计父代运动单元的可靠性,从而得出整个产品的可靠性水平。最后以数控转台为例进行了分析,得出了可靠性预计值,并将该方法与传统方法进行了比较。结果表明,新的可靠性预计方法具有较好的可行性和较高的准确性。     

Proline-derived in situ synthesis of nitrogen-doped porous carbon nanosheets with encaged Fe2O3@Fe3C nanoparticles for lithium-ion battery anodes

The homogeneous incorporation of heteroatoms into two-dimensional C nanostructures, which leads to an increased chemical reactivity and electrical conductivity as well as enhanced synergistic catalysis as a conductive matrix to disperse and encapsulate active nanocatalysts, is highly attractive and quite challenging. In this study, by using the natural and cheap hydrotropic amino acid proline—which has remarkably high solubility in water and a desirable N content of ~12.2 wt.%—as a C precursor pyrolyzed in the presence of a cubic KCl template, we developed a facile protocol for the large-scale production of N-doped C nanosheets with a hierarchically porous structure in a homogeneous dispersion. With concomitantly encapsulated and evenly spread Fe₂O₃ nanoparticles surrounded by two protective ultrathin layers of inner Fe₃C and outer onion-like C, the resulting N-doped graphitic C nanosheet hybrids (Fe₂O₃@Fe₃C-NGCNs) exhibited a very high Li-storage capacity and excellent rate capability with a reliable and prolonged cycle life. A reversible capacity as high as 857 mAh•g^–1 at a current density of 100 mA•g^–1 was observed even after 100 cycles. The capacity retention at a current density 10 times higher—1,000 mA•g^–1—reached 680 mAh•g^–1, which is 79% of that at 100 mA•g^–1, indicating that the hybrids are promising as anodes for advanced Li-ion batteries. The results highlight the importance of the heteroatomic dopant modification of the NGCNs host with tailored electronic and crystalline structures for competitive Li-storage features.

     

发动机进气系统高通量富氧膜的研制

采用交联改性的方法对较低分子量的乙烯基硅橡胶进行了改性研究,制备了高通量的富氧膜,结合单因素实验法和Design-expert正交实验设计,考察了原料配比、交联反应时间、固化温度和固化时间等因素对富氧膜性能的影响,确定了最佳富氧性能膜的制备条件:原料配比4.3,反应时间2.15h,固化温度86.25℃,固化时间1.75h;获得了富氧浓度为28.68%,透气量为4696.33 barrer的富氧膜,该膜的富氧浓度与常规商品化膜相当,透气量为常规商品化膜的2~4倍,有应用于发动机富氧进气系统的前景。通过扫描电镜检测、机械性能检测等手段对复合膜进行了进一步表征。     

Enhanced mortar approach to characterize the effect of reclaimed asphalt pavement on virgin binder true grade

The asphalt community seeks a solvent-free method to determine the properties of RAP binder and those of its blends with virgin binders. A promising approach is to test mortars composed of fine fractions of RAP and a virgin binder, and to calculate grade change rate (GCR) to predict blended binder true grade at any binder replacement rate (BRR). However, the existing mortar approach underestimates the effect of RAP on binder grade, particularly at high temperatures. This study identified the use of a shift factor in the existing method as the source of underestimations. An alternative data analysis method was developed, which eliminates the shift factor by using the relationship between binder and mortar properties. Dynamic shear rheometer tests were conducted on a total of 12 mortar combinations, including 4 virgin binders and 3 RAP sources at a BRR of 15%, and then, RAP GCR values were determined by following both the existing and the alternative methods. Satisfactory comparisons were only observed between grades predicted with the alternative method and measured values of manual RAP binder blends: the average difference was lower than 1 °C for BRR of 15 and 30%, and < 4 °C for BRR of 100%. This not only validated the alternative method but also substantiated that RAP GCR is constant, i.e., the grade of RAP blends linearly increased with BRR. Further evaluation of the enhanced mortar approach is recommended at intermediate and low temperatures as well as with blends including recycled asphalt shingles.     

Numerical and experimental investigations of laser shock forming aluminum alloy sheet with mold

Laser shock forming (LSF) technology employs shock waves to form sheet metal into three-dimensional complex parts, and has application potential in manufacturing sheet metal parts. In this paper, the forming of 2024 aluminum alloy sheet with LSF was investigated through numerical and experimental methods. The numerical model was established with the commercial code ABAQUS/Explicit. The formed conical cup was obtained from the simulation, and validated by the experiment. With the verified numerical model, the deformation behaviors, including deformation velocity, sheet thickness variation and strain distribution, were studied. In addition, the influence of different shock wave pressures on the forming precision was also investigated. The experimental and numerical results show that the metal sheet loaded by shock wave can take the shape of the mold, and the non-uniform thickness is distributed in the formed cup. The investigations also display that there exists reverse deformation at the central region of deforming sheet owing to severe collision during LSF. In order to obtain formed part with better quality, an appropriate pressure of applied shock waves is required.