RTM专用双马来酰亚胺树脂体系化学流变特性

进行了RTM 工艺专用双马来酰亚胺(BMI) 树脂体系的化学流变特性及工艺过程研究。采用DSC 热分析技术和粘度测量手段, 研究了该树脂体系固化特性以及固化过程中粘度与温度的关系, 根据对等温粘度曲线的分析, 建立了双阿累尼乌斯粘度模型和工程粘度模型。对比所建立的两种粘度模型, 结果显示两种模型都可以适用于RTM 工艺注射阶段, 工程模型在粘度转折点附近的预测精度要优于双阿累尼乌斯粘度方程。同时建立了恒温温度-凝胶时间之间的数学关系。验证了所建立的工程模型在工程中的实用性, 并指出了工程粘度模型的使用范围在固化体系交联结构形成之前, 所建立的工程粘度模型能够有效地预测体系RTM 工艺的粘度变化和工艺过程, 为复合材料成型工艺模拟分析以及工艺参数的准确制定奠定了基础。      

双马来酰亚胺(BMI)-玻璃布复合材料成型工艺及性能研究

研究了作为改性ＢＭＩ一种的ＨＦ－９４０９树脂体系与玻璃布复合材料的成型固化工艺。在此工艺条件下,分别用ＡＢＳ树脂和氯磺化聚乙烯（ＣＭＳ）橡胶对ＨＦ－９４０９树脂体系进行改性。实验结果表明,加入１０％（质量比）ＡＢＳ树脂后,ＨＦ－９４０９树脂体系与玻璃布复合材料的拉伸强度和冲击强度分别提高了２２．３７％和１５．４６％,加入３０％（质量比）ＣＭＳ橡胶后复合材料的韧性提高了８．５１％,并从理论上分析了产生这种实验结果的原因。     

热塑性树脂增韧双马来酰亚胺树脂的研究

本文讨论了用热塑性(TP)树脂聚砜(PSF)和聚醚砜(PES)增韧双马来酰亚胺(BMI)树脂的研究.实验表明,增韧后的树脂在150℃的粘度小于0.5(Pa·S),其复合材料的成形压力为0.3～0.7(MPa),固化温度为180℃,上述特性满足热压罐成形的工艺要求.树脂的预浸料具有较好的粘性和铺叠性,贮存期一个月以上(室温).树脂保持了较好的耐热性能,可在177℃长期使用.其复合材料的冲击强度明显提高,经聚砜增韧后提高了90%.PSF的增韧效果比PES明显.研究表明,只有当TP树脂含量不低于15%时,方可获得较明显的增韧效果.TP树脂是以球形颗粒分散于BMI基体中,这些颗粒起到了抑止微裂纹扩展的作用.      

A morphological investigation of thermosets toughened with novel thermoplastics. I. Bismaleimide modified with hyperbranched polyester

The morphology of a bismaleimide (BMI) toughened with a thermoplastic hyperbranched aliphatic polyester (HBP) was studied by scanning electron microscopy (SEM). The effect of thermoplastic architecture, molecular weight, and end group on the size and arrangement of the dispersed phase was investigated and compared with the thermoset fracture toughness. SEM micrographs showed that higher molecular weight HBP formed roughly spherical dispersed domains of up to ∼ 60 μm, which contained BMI inclusions. Lower molecular weight HBP formed spherical dispersed thermoplastic domains, with diameters up to ∼ 10 μm with no BMI inclusions. A low molecular weight linear polyester with a repeat unit structure, which was similar to that of the HBP, was prepared and used as a control. Within error, BMI toughened with the linear control yielded the same fracture toughness as the best values obtained with HBP‐modified BMI, but the morphology differed. The linear polyester phase separated into particles with a larger average diameter and also possessed some phase‐inverted regions. End group effects were studied by modifying the hydroxy‐terminated HBP to unreactive nitrophenyl, phenyl, and acetyl end groups. The nitrophenyl‐terminated HBP did not phase separate from the thermoset, whereas the nonpolar phenyl‐ and acetyl‐terminated HBP phase separated to form small (≤1 μm and ∼ 2 μm, respectively) spherical domains. Some comparisons were made to other results with HBP thermoplastics in BMI and epoxy thermosets. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1065–1076, 1999     

二元胺改性双马来酰亚胺树脂的固化工艺

借助红外光谱、DSC分析了二元胺改性双马来酰亚胺树脂的结构特征及固化反应机理,其固化过程分2个阶段:链式聚合阶段和固化交联阶段。通过凝胶特性、DSC、弯曲强度的综合分析以及实践经验,确定了改性双马来酰亚胺树脂合理的固化工艺:阶梯升温20℃/0.5 h,保温程序:120℃×1 h,180℃×2 h,220℃×2h,235℃×2 h,再自然降温。     

Linear Diophantine equation (LDE) decoder: A training-free decoding algorithm for multifrequency SSVEP with reduced computation cost

Multifrequency steady-state visual evoked potentials (SSVEPs) have been developed to extend the capability of SSVEP-based brain-machine interfaces (BMIs) to complex applications that have large numbers of targets. Even though various multifrequency stimulation methods have been introduced, the decoding algorithms for multifrequency SSVEP are still in early development. The recently developed multifrequency canonical correlation analysis (MFCCA) was shown to be a feasible training-free option to use in decoding multifrequency SSVEPs. However, the time complexity of MFCCA is shown to be $O(n^3)$, which will lead to long computation time as $n$ grows, where $n$ represents the input size in decoding. In this paper, a novel decoding algorithm is proposed with the aim to reduce the time complexity. This algorithm is based on linear Diophantine equation solvers and has a reduced computation cost $O(nlogn)$ while remaining training-free. Our simulation results demonstrated that linear Diophantine equation (LDE) decoder run time is only one fifth of MFCCA run time under respective optimal settings on 5-s single-channel data. This reduced computation cost makes it easier to implement multifrequency SSVEP in real-time systems. The effectiveness of this new decoding algorithm is validated with nine healthy participants when using dry electrode scalp electroencephalography (EEG).     

居住环境绿化水平对居民体质指数(BMI)和自评健康的影响研究——以上海为例

城市建成环境对居民的健康影响一直是国内外学者关注的热点问题,但既有文献显示学界对绿地对居民健康效应(如肥胖等)并未达成共识,原因之一在于不同学科对于绿化的测量方法和研究精度不同,结论不统一.基于世界卫生组织全球老龄化与成人健康调查数据,选择高密度地区上海作为研究案例,包括23个社区数据5000多个样本.基于卫星遥感技术...