三维五向及全五向编织复合材料的三单胞结构模型

针对三维五向及全五向编织复合材料,基于四步法编织工艺携纱器的运动规律,研究了各单胞区域纱线的运动轨迹和空间走向,给出了材料内胞、面胞和角胞的纱线拓扑结构。通过给定一系列的位置节点和节点间线性插值函数的方法来描述纱线空间轨迹。考虑纱线间的相互挤压状况,在假设编织纱和轴纱横截面形状分别为扁平椭圆形和正方形的基础上,系统建立了三维五向及全五向编织复合材料的三单胞参数化结构模型。给出了两种编织材料的纤维体积含量计算公式并进行了对比分析,明确了三维全五向编织复合材料的轴向性能优势。分析了三维五向编织材料的表面多胞结构及三维全五向编织材料的内胞截面图,并与实际试件结构进行对比,结果表明本文所建模型合理准确。

三维五向编织复合材料的一种改进细观三单胞建模

基于三维五向编织复合材料的编织工艺,分析纤维束的运动轨迹及空间拓扑关系,建立了一种改进的细观三单胞(三单胞指内胞、面胞、角胞)模型。该模型假设纤维束的横截面形状在编织过程中发生渐进变化,考虑了纤维束间的相互挤压变形及扭转弯曲特征,并确定了材料整体尺寸与各编织工艺参数间的关系,实现了三单胞模型的参数化建立。将模型理论预测值与实测值进行比较验证,结果表明,模型预测值与试样实测值比较吻合,且在织物排列结构的行数m和列数n相等时(编织角22.3°、26.5°时),两者吻合度最高,可见本模型适用性好,且对行列相等的织物排列结构尤为适用。

基于改进三胞模型考虑孔隙缺陷的三维四向编织复合材料多尺度力学性能分析

编织复合材料在制造过程中不可避免地会出现孔洞缺陷,这些缺陷直接影响编织复合材料的力学性能。基于开源软件TexGen[1]实现编织复合材料内胞、面胞和角胞的参数化建模,在面胞和角胞模型中均考虑了纱线轨迹在空间中的偏移和受到打紧工序时纱线之间的相互挤压。利用random函数在微观尺度微观模型的基体中引入孔隙单元来模拟纤维束内干斑,在细观尺度上的三单胞模型基体中引入孔隙单元来模拟纤维束间孔隙,在宏观尺度上建立含内胞、面胞、角胞细观单元宏观均质模型对宏观弹性常数进行预测。结果表明:(1)孔隙率对细观尺度三类单胞模型的弹性常数影响程度不同;(2)纤维束内干斑孔隙对宏观弹性性能的影响要大于纤维束间孔隙,随着干斑孔隙率Pm增加,纵向泊松比减小,而随着纤维束间孔隙率Pn增加,纵向泊松比呈现出递增的趋势。

基于细观结构的径向轴纱三维五向圆形编织复合材料的刚度预测

在细观尺度下,根据1种径向轴纱的三维五向圆形编织纱线的空间结构,考虑纱线相互挤压后的截面形状,通过引入圆形单胞的周期性边界条件,建立了包含上、下表面子单胞以及内部单胞的三维五向圆形编织复合材料单胞模型。基于该单胞模型,采用刚度体积平均法,建立了三维五向圆形编织复合材料的刚度预测模型,对花节长度分别为0.6、0.7、0.8 mm的三维五向圆形编织复合材料进行刚度预测,并与复合材料力学刚度理论计算方法所得结果进行了对比。结果表明:3种花节的纤维体积分数分别为24.94%、23.33%、22.04%,纤维体积分数、编织角与花节长度呈负相关;单胞模型的弹性模量预测结果分别为16.42、15.63、14.83 GPa,理论计算结果分别为16.96、16.25、15.34 GPa,纵向刚度与花节长度负相关;单胞几何模型考虑了复合材料成型后纱线的相互挤压,使得单胞模型中的纤维体积含量略小于理论计算方法,造成理论计算结果略大于单胞预测结果。研究结果能够有效提高三维五向圆形编织复合材料刚度预测精度,扩展了细观单胞法的应用领域,为今后三维五向圆形编织复合材料的应用提供必要的理论依据。

三维编织复合材料细观结构建模关键问题研究

基于细观力学的数值分析方法是研究三维编织复合材料力学性能的有效方法,其中细观模型的建立是力学分析的基础。纤维束的空间走向和细观结构几何参数表征是细观结构建模中的两个关键问题。围绕这两个关键问题,针对三维四向编织复合材料的三单胞模型开展研究,全面分析了单胞45°划分方式和水平划分方式中纤维束的各种空间走向,获得了详细的三单胞的纤维束方向余弦;针对三种形状的纤维束横截面,分析推导了编织工艺参数与单胞几何参数的复杂关系,利用编织工艺参数作为初始参数对单胞结构进行定量化表征,并获得了纤维束体积分数和纱线填充系数的计算方法。研究工作为三维多向编织复合材料的细观结构建模提供理论参考,具有一定的工程实用价值。

INCLINED LAMINAL COMBINATION MODEL OF 3D BRAIDED COMPOSITES

As an advanced composite material, the 3D braided composite has received more and more attention in foreign countries. However, it has received less attention in China. The geometric unit cell which can describe the basic structure and the relationship between the braiding angle and geometric parameters of the fabric and fiber volume ratio are given in this paper based on two 3D braiding processes, namely, the four-step and the twostep ones. Several existing mechanical models to predict groperties of the 3D braided comPOsites are discussed and their shortcomings are pointed out herein. Then a new model called the inclined laminal combination model is proposed, which is based on the classical laminated plate theory and can predict the basic mechanical behavior of the two 3D braided composites with four-step or two-step braid. In the model, each yarn in the unit cell is regarded as an inclined laminate and then a 3D analysis is performed. It is found that the predicted mechanical properties of the 3D braided composites by the proposed model are compared well with the experimental data.

Characterization of tricalcium phosphate solubilization by Stenotrophomonas maltophilia YC isolated from phosphate mines

The phosphate solubilizing characteristics of a strain YC, which was isolated from phosphate mines (Hubei, China), were studied in National Botanical Research Institute’s phosphate (NBRIP) growth medium containing tricalcium phosphate (TCP) as sole phosphorus (P) source. The strain YC is identified as Stenotrophomonas maltophilia (S. maltophilia) based upon the results of morphologic, physiological and biochemical characteristics and 16S rRNA sequences analysis. The results show that the strain S. maltophilia YC can solubilize TCP and release soluble P in NBRIP growth medium. A positive correlation between concentration of soluble P and population of the isolate and a negative correlation between concentration of soluble P and pH in the culture medium are observed from statistical analysis results. Moreover, gluconic acid is detected in the culture medium by HPLC analysis. It indicates that the isolate can release gluconic acid during the solubilizing experiment, which causes acidification of the culture medium and then TCP solubilization. S. maltophilia YC has a maximal TCP solubilizing capability when using maltose as carbon source and ammonium nitrate as nitrogen source, respectively, in NBRIP growth medium.

Polysaccharide, Adenosine and Crude Triterpenoid Contents of Pleurotus Eryngfi and Its Immunostimulant Capacity in vitro

Purpose of the study was to demonstrate the ability of Pleurotus eryngii （PE） extracts to stimulate the production of nitric oxide （NO） and TNF-α as well as to evaluate the cell viability by the use of chicken peripheral blood mononuclear cells （PBMCs） and RAW 264.7 macrophages in vitro. The PE contained 341.0 ± 14.5 mg/g DW, 78,2 ± 4.1 Bg/g DW and 38.4 ＋ 3.3 mg/g DW of crude polysaccharide, adenosine and crude triterpenoid contents, respectively. The results of cell viability assay showed that 95,0% of chicken PBMCs and RAW 264.7 macrophages were survived under the treatment of 9.6 mg/mL of PE extracts by microculture tetrazolium assays （MTAs）. Moreover, the cell inhibitory activity did not show the 50% cyto-toxicity effect （ICs0）. In addition, no production by stimulated chicken PBMCs and RAW 264.7 macrophages exhibited individually the linear relations with the concentration of PE extracts, and they were approximately 65 μM and 45 p.M in 1600 μg/mL, respectively. The tendency with the release of TNF-α by RAW 264.7 maerophages also corresponded with concentration of PE extracts. It is concluded, PE extracts act as an immunostimulant for both tested cells but have no serious effect on inhibiting chicken PBMCs viability, and therefore it may be suggested as immune supplements for broilers.

The blood-brain barrier permeability of 20(S) and 20(R)-protopanaxatriol epimers and dammar-20(22)E,24-diene-3β,6α,12β-triol in MDCK-pHa MDR cell monolayer model

The blood-brain barrier permeability of 20（S） and 20（R）-protopanaxatriol epimers and dammar-20（22）E,24-diene- 313,6α,12β-triol were investigated using the MDCK-pHaMDR cell monolayer model. The bidirectional permeability tests were carried out, and the apparent permeability coefficients （Papp） were calculated. The two protopanaxatriol epimers showed good permeability with Papp values of-10^-5 cm/s, whereas dammar-20（22）E,24-diene-3β,6α, 12β-triol showed poor permeability with Papp of 〈1 × 10^-7 cm/s. The three compounds showed differences in intracellular accumulations due to their different structures. Inhibition of P-gp with verapamil showed that the transport mechanisms in MDCK-pHaMDR cell monolayer for compounds 1 and 2 epimers were not only simple passive diffusion but also involving an effiux way mediated by P-gp. These findings provided new basis for the further study of compounds 1 and 2 acting on the brain.