复合材料工字梁结构分析

由于层压板梁的各向异性,载荷下结构响应和刚度特性难以确定。为了解决有限元方法在进行复合层压板梁的结构分析时参数确定的难题,提出了一种层压板工字梁的应力分析方法,并在MATLAB上编程实现,通过与理论计算值和有限元软件ANSYS分析结果进行对比,证明该方法可行,且适合于进行参数化研究设计。     

焊接热输入对近焊缝区组织性能的影响

采用焊接热模拟技术模拟不同焊接热输入条件下,峰值温度为1 350℃时对应近焊缝区的组织和性能,并对母材进行宏观力学特性测试;对比分析不同焊接热输入条件下所得近焊缝区的组织和性能。结果表明:经过3种不同焊接热输入所得近焊缝区的组织均由板条状贝氏体和少量碳化物组成;随着焊接热输入的增加,近焊缝区组织晶粒变大,贝氏体板条束变粗变厚,析出的碳化物数量增多,并且强度降低、韧性增强,但总体上跟母材的性能基本一致;当焊接线能量为12 kJ/cm时近焊缝区达到最佳的强韧性匹配。     

Fe73.5Cu1Nb3Si13.5B9纳米晶软磁粉体的制备工艺与微波电磁性能

研究热处理工艺、材料粒度对Fe73.5Cu1Nb3Si13.5B9材料微波电磁性能的影响,对该类材料的微波电磁性能和吸波性能进行测试。结果表明:热处理工艺对材料的微波电磁性能产生较大的影响,达到晶化条件的热处理工艺有利于提高材料的电磁性能;随着材料粒度的减小,微波电磁性能提高,电磁参数之间的匹配性提高;Ⅴ级粒度材料的最低反射率达到-12 dB,低于-5 dB的频宽达12.5 GHz。     

Sharpening polycrystalline phase boundary for potassium sodium niobate ceramics with MnF2 modification

The influence of anion on structure and performance is unclear in potassium sodium niobate ((K,Na)NbO₃; KNN)-based ceramics, while cation doping has been widely researched. Here, the phase structure and electrical properties are explored in MnF₂-doped KNN ceramics. Significantly, sharp rhombohedral–orthorhombic (R–O) and orthorhombic–tetragonal (O–T) phase boundary as well as reduced diffusion degree is exhibited in the ceramics along with little changed phase transition temperatures due to the optimized F⁻ content at O site, which is different from that of cation replacement for A and B sites. Notably, the domain wall motion is facilitated due to the increased A vacancy and decreased O vacancy along with strengthened polarity, originating from the higher valence state and electronegativity of F⁻ with respect to O²⁻. And then, enhanced ferroelectricity is realized via MnF₂ modification, the piezoelectricity is elevated in turn. This work presents a new idea of anion doping for controlling structure and properties in perovskite materials.     

Evolution of microstructure and properties of Si3N4 whisker reinforced composites during densification by polymer infiltration and pyrolysis

Si₃N₄ whisker (Si₃N_4w) reinforced composites were prepared by a near-net shaping process, i.e., gel-casting of the Si₃N_4w preform followed by polymer infiltration and pyrolysis (PIP) densification using polysilazane as precursor. The densification process by PIP was described mathematically, after which several key parameters affecting densification efficiency were discussed. The small pore size (0.04 ～ 1 μm) of Si₃N_4w preform can cause filtration effect (low permeability of precursor with a molecular size bigger than pore size), which resulted in the density gradient of the composites. Porosity (P) dependence of flexural strength and elastic modulus of Si₃N_4w/Si₃N₄ followed a power law of (1 – P). With increasing density, the response of Si₃N_4w when confronting cracks transformed from whisker debonding to whisker fracture, which was supposed to be due to the increase of whisker/matrix interface strength. The Si₃N_4w/Si₃N₄ developed by us achieved a good balance between high strength and low dielectric constant, making it promising for high-temperature wave-transparent application.     

Compositional tailoring effect on crystal structure,mechanical and thermal properties of γ-AlON transparent ceramics

In view of the practical application of γ-AlON as a promising transparent structural ceramic, in-depth insight into its mechanical and thermal properties is essential. The solid-state MAS NMR technique was combined with XRD Rietveld refinement to confirm the crystal structure of Al_(8+x)/3O_4-xN_x (x = 0.299–0.575). These structural parameters were further applied to predict hardness and elastic properties based on theoretical exploration, which are in good agreement with the experimental values. A slight enhancement of mechanical properties with increasing nitrogen concentration is attributed to the stronger chemical bond in octahedra. The experimental thermal conductivity of γ-AlON transparent ceramics was improved slightly with the rise of x in the temperature range from 298 K to 1074 K. The intrinsic lattice thermal conductivity was determined by eliminating the extrinsic phonon scattering as well as the thermal radiation. The reason for the discrepancy between experimental and intrinsic thermal conductivity was revealed. The present methods provided powerful and accessible guidelines in optimizing the mechanical and thermal properties of oxynitride materials.     

Rheology of natural fibers thermoplastic compounds: Flow length and fiber distribution

The presented study investigates the flow length and the corresponding fiber content distribution in the injection‐moulded natural fiber reinforced thermoplastics and its relation to fiber type and processing parameters such as injection pressure, temperature, injection rate and mould tempering by increasing die temperature. In this research, polypropylene compounds with nominally 30 wt % hemp and sisal fibers are investigated. The influence of the injection pressure (500 and 1000 bar), melt temperature (180°C, 200°C, and 220°C), and die temperature (23°C and 80°C) on the fiber content distribution all over the sample is investigated. An increasing linear trend of fiber content along the spiral length is observed as an evidence of a fiber/polymer multiflow system. A pattern for fiber content distribution with respect to the fiber length along the injected spiral can be distinguished, where the longer fibers are usually found at the end of the injected part and the shorter fibers remain near mould entrance point. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39861.     

Crosslinking effect on polydimethylsiloxane elastic modulus measured by custom‐built compression instrument

A macroscopic compression test utilizing a simple custom‐built instrument was employed to measure polydimethylsiloxane (PDMS) elastic modulus. PDMS samples with varying crosslinking density were prepared with the elastomer base to the curing agent ratio ranging from 5 : 1 to 33 : 1. The PDMS network elastic modulus varied linearly with the amount of crosslinker, ranging from 0.57 MPa to 3.7 MPa for the samples tested. PDMS elastic modulus in MPa can be expressed as 20 MPa/PDMS base to curing agent ratio. This article describes a simple method for measuring elastic properties of soft polymeric materials. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41050.     

Physicochemical Property and Fatty Acid Profile of Cephalotaxus fortunei Nut Oils

This paper focused on the main composition of Cephalotaxus fortunei nuts, the physicochemical property of its oils, the fatty acid profiles and the content of alkaloids and tocopherol in the nuts oils. And these elements were compared among three kinds of C. fortunei nuts and their oil. The results showed the C. fortunei nuts contained about 65 % crude oil. Meanwhile, the content of crude protein, crude fiber, moisture, ash and reduced sugar were presented, respectively. The important physicochemical indicators of the crude C. fortunei nuts oils were presented, including specific gravity, refractive index, viscosity, acid value and saponification value, etc. The contents of alkaloids were 0.41 % in NUT1, 0.24 % in NUT2 and 0.31 % in NUT3. The contents of tocopherol were low. The analysis of the fatty acid composition showed that the three kinds of oils were all rich in unsaturated fatty acids, oleic acid and linoleic acid, and the main triacylglycerols were dioleoyl-monolinoleoyl (OLO) and triolein (OOO). This work might help with the exploration of the applications of C. fortunei nuts and its oil.