PLLA纳米纤维编织缝合线的制备及生物相容性研究

以PLLA为原料,采用静电纺丝和圆盘定向收集得到具有有序排列的纳米纤维束,并将其编织成线,得到PLLA纳米纤维缝合线.对新型可吸收PLLA缝线的微观形貌、血液相容性、细胞毒性进行了性能表征,并测试了其力学性能.结果表明,纳米纤维在一定的圆盘转速下表现出较好的定向性,力学性能良好.缝线在溶血试验中溶血率＜5%,符合医用材料的溶血要求.MTT实验结果表明缝线材料无细胞毒性,且显示出较高的增殖率,说明新型可吸收PLLA纳米纤维缝线具有良好的生物相容性和安全性.     

三维五向编织复合材料纵向性能的实验研究

通过对具有不同编织结构参数的三维五向编织复合材料试件的纵向拉伸和压缩实验,分析了该类材料的纵向拉、压刚度和强度随编织工艺参数的变化规律以及材料的失效形式.三维五向编织复合材料在破坏前基本保持线弹性,纵向拉、压破坏具有脆性特征,拉伸模量和压缩模量比较接近,但拉伸强度远大于压缩强度.编织角和纤维体积含量对材料性能的影响显著,纱线粗细的影响不大.提高第五向纱线的比例,可提高材料的纵向性能.此外,研究中采用短标距薄板试件,以避免试件产生整体屈曲和端部纤维束开裂破坏.     

2.5维编织复合材料力学性能的有限元分析

在已有研究的基础上,提出了一个新的2.5维编织复合材料有限元模型,该模型较为真实地模拟了织物内纤维束的轮廓结构和走向,可用于2.5维编织复合材料力学性能的有限元数值分析.利用该模型采用有限元法对2.5维编织复合材料进行了有效弹性性能的数值预报,并合理确定了复合材料内部应力场分布;同时提出经向纤维束横截面宽厚比是影响2.5维编织复合材料有效弹性性能的主要因素,分析了其影响情况.采用VARTM工艺制备了试验件,并对其进行力学性能测试.通过实验值和理论值的对比,结果表明:有限元计算得到的结果与实验值吻合较好,从而验证了该模型的有效性.     

三维四向编织复合材料改进模型的细观分析

三维编织复合材料现有的成型方法将导致编织物单胞模型发生变化,据此提出了一种改进的具有矩形截面的单元内胞模型,假设编织纱线具有平行六边形横截面,分析了不同区域胞体内部纤维束的空间构型,建立了三维四向编织复合材料内部单胞三维实体模型。通过分析编织物内纱线间的空间接触关系,采取合理的假设,推导了编织工艺参数和模型结构参数的关系,并计算了三维四向编织复合材料的纤维体积含量,为该种材料后续力学性能分析奠定了基础。该模型适用于部分不规则成型工艺,并有可能应用于其他形式的编织工艺研究。     

凝固工艺对自生复合Cu-Cr合金电车线综合性能的影响

自生复合Cu-Cr合金是一种高强度与高导电率兼顾的新型电车线材料。本文采用定向凝固连续铸造技术成功制备了纤维增强的自生复合Cu-Cr合金电车线线坯,考察了合金成分、定向凝固连铸的工艺参数对电车线的力学性能、导电性能及综合性能M指标的影响。     

二维二轴1×1编织复合材料细观结构模型及力学性能有限元分析

考虑纤维束相互挤压及横截面形状变化, 采用纤维束截面六边形假设, 建立了二维二轴1×1编织复合材料的参数化单胞结构模型。通过引入周期性位移边界条件, 基于细观有限元方法, 对编织材料的弹性性能进行预测, 讨论了编织角及纤维体积含量对面内弹性常数的影响, 并分析了典型载荷下单胞细观应力场分布。研究表明: 单胞结构模型有效反映了纤维束的空间构型和交织特征, 实现了不同编织工艺参数下模型的快速建立; 基于单胞有限元模型的弹性性能预测结果与试验结果较为吻合; 模型给出了单胞合理的应力场分布, 为二维编织复合材料的结构优化和损伤预测奠定基础。      

三维编织复合材料面内刚度和强度性能研究

以修正的经典层合板理论为基础, 分析三维编织复合材料的力学性能。在单胞的长度方向积分和平均, 预测编织结构复合材料的有效弹性模量; 采用蔡-胡多项式失效准则, 得到三维编织复合材料的强度性能。另外, 进行编织结构复合材料的力学性能实验, 探讨纺织工艺参数, 如纤维编织角、横向编织角、轴向纱数与编织纱数之比、纤维体积含量等对力学性能的影响, 理论预报和试验结果进行对比, 发现该力学模型能较好地预报三维编织复合材料的刚度和强度性能。      

三维编织复合材料的力学性能研究现状

对近年来关于三维编织复合材料力学性能的研究方法和内容进行了综述.归纳出三类主要研究方法:实验研究、细观结构力学模型研究、数值仿真研究.实验研究集中于测试各种编织参数和载荷对其力学性能指标的影响.细观结构力学模型研究主要是通过三维编织体的拓扑结构建立力学分析模型,主要是"米"字枝状模型、纤维倾斜模型和3细胞模型.数值仿真研究是基于材料的线弹性力学,利用有限元分析法对其力学性能进行数值仿真.本工作对当前研究的关键问题进行了分析,就今后的研究工作发表了一些看法.     

三维编织锥体织物的减纱技术

研究了由大端直径开始编织三维锥体织物的减纱技术，包括列向、环向减锭减纱、减细纤维束减纱等多种减纱技术及其组合；分析比较了各种减纱技术对织物结构完整性、操作简便性、机械化编织等方面的影响。减细纤维束减纱技术是特殊的环向减锭技术，具有保持织物结构整体完整、工艺操作简便、纱锭运动可实现机械化等优点，但不同纱束直径纤维编织使织物单元结构构造变得复杂多变。     

纤维束排布细度对编织C/C复合材料致密化过程及性能的影响

纤维束排布细度是径棒法编织预制体结构重要参数之一,选用3种纤维排布细度参数制备完成径棒法编织预制体,以化学气相沉积(CVI)和液相浸渍碳化混合工艺致密,研究了纤维束排布细度对材料致密化过程及性能的影响。结果表明,在CVI致密过程中,纤维束排布细度最小的试样A在相同的致密化周期内的密度增长幅度略低,液相碳化阶段试样间致密速率相当。纤维束排布细度最低的试样A抗弯强度较C型材料提高了85%,且线膨胀系数最低。     

Spectral background and transmission characteristics of fiber optic imaging bundles

The emission and transmission properties of three commercially produced coherent fiber optic imaging bundles were evaluated. Full fluorescence excitation versus emission data were collected from 250 to 650 nm excitation for high-resolution Sumitomo, Fujikura, and Schott fiber bundles. The results generated show regions of autofluorescence and inelastic Raman scattering in the imaging bundles that represent a wavelength-dependent background signal when these fibers are used for imaging applications. The high-resolution fiber bundles also exhibit significant variation in transmission with the angle of illumination, which affects the overall coupling and transmission efficiency. Knowledge of these properties allows users of high-resolution imaging bundles to optimally design systems that utilize such bundles.     

Use of image correlation system to study the bond behavior of FRCM-concrete joints

This paper presents a non-contact measurement approach, based on digital photogrammetry, applied to the experimental study of the bond behavior of fiber reinforced cementitious matrix composite to concrete joints tested in single-lap direct shear tests. The use of digital photogrammetry techniques and traditional contact measurement approaches for determining displacement and strain are investigated and compared. The results show that measurements of strain in the fiber bundles determined using the image correlation system (ICS) correlate well with those obtained from electrical strain gauges. However, differences of 38–52% were observed between the maximum strain measured with either ICS or electrical strain gages attached to the fiber bundles and the maximum strain in the fiber bundles computed from the maximum applied load. ICS is also used to measure slip and strain of bare fiber bundles, and results show that the load distribution among fiber bundles is non-uniform. The proposed measurement approach shows higher spatial measurement resolution and increased accuracy compared to traditional contact approaches by enabling measurements in each fiber bundle and overcoming the need to attach additional elements to the tested specimen.     

蜘蛛丝/聚-L-乳酸静电纺纤维束的形貌和力学性能

以1%(质量分数,下同)蜘蛛丝和9%聚-L-乳酸(PLLA)的混合液为纺丝溶液,采用静电纺丝方法制备了蜘蛛丝/PLLA复合纤维构成的连续纱线。探讨了纺丝温度、卷绕速度、后拉伸倍数等对纤维和纱线的形态结构及力学性能的影响。研究发现,加入蜘蛛丝蛋白后,PLLA复合纱线的强度提高了13%,纤维直径从1.1μm减小到了550nm;加热区温度为150℃时纱线强度最大;卷绕速度为(105±5)r/min时可以实现稳定纺丝;拉伸1.5倍时,纱线断裂强度和初始模量分别提高了66%和92%,断裂伸长率下降。     

Inelastic behavior and fracture of high modulus polymeric fiber bundles at high strain-rates

The tensile behavior and fracture mechanisms of poly(phenylene terephthalamide) (PPTA) and high modulus polyethylene (HMPE) fiber bundles were studied at high strain-rates using a tension Kolsky bar. For all fiber bundles investigated, a significant amount of strain energy was found to be dissipated by inelastic processes in addition to that due to fracture. The differences in microstructure and properties between the fibers were shown to have a noticeable influence on the inelasticity and fracture behavior in PPTA fiber bundles. No significant strain-rate effect on inelastic behavior and maximum strength was found in HMPE fiber bundles. Scanning electron micrographs of the fracture surfaces of PPTA fiber showed that the failure occurs mainly by fibrillation resulting in pointed breaks, and showed no fundamental difference in fracture mechanism at quasi-static and high strain-rates. However, the fracture mechanism in the HMPE fiber was different at quasi-static and high strain-rates, crazing was dominant at high strain-rates and plate formation under quasi-static conditions. This difference was more substantial in HMPE fibers with lower degree of crystalline order, which suggested that the inelastic behavior is governed by a precise mechanism of load transfer between the crystalline and amorphous phases present in HMPE fibers as a function of loading rate. At high strain-rates, HMPE fibers appear to be able to dissipate more strain energy than PPTA fibers due to this intrinsic change of deformation mechanism. Our results also support the idea that the mechanical behavior of a PPTA fiber bundle is inherently statistical including variations in strength distribution and alignment of the individual filaments.     

Plasma surface treatment and modification of glass fibers

New helical coupling plasma system for continuous surface treatment and modification (surface processing) of fiber bundles has been developed and tested for glass fibers. The system enables surface processing of single filaments and flat substrates as well. Surface processed glass fibers and their bundles were examined as reinforcements for glass fiber/polyester composite systems. Processing of fibers comprised a surface treatment using argon gas and a surface modification using hexamethyldisiloxane and vinyltriethoxysilane monomers. Interfacial and interlaminar shear strengths of plasma processed glass fiber/polyester systems were compared with those of untreated and commercially sized fibers.     

Fracture behavior and toughening mechanism in Zanchor reinforced composites under mode II loading

The mode II interlaminar fracture behavior and the toughening mechanism of Zanchor reinforced composite laminates were investigated by using the End Notched Flexure (ENF) and Interlaminar Shear (ILS) specimens. The ENF test results demonstrated that the Zanchor process was highly effective to improve the mode II fracture toughness of composite laminates, where the fracture toughness increased almost linearly with the Zanchor density. The R-curves of Zanchor composites were roughly divided into the transition and stable regions, where the width of the transition region became larger as the Zanchor density increased. The macroscopic fracture behavior of the Zanchor composites was still brittle under mode II loading like that of the base composite, where the crack tip process zone was estimated to be rather small regardless of the Zanchor density. The ILS test results demonstrated that the square of the normalized shear strength increased linearly with the Zanchor density and agreed quantitatively with the normalized fracture toughness. The wedge effect was supposed to be the dominant toughening mechanism against the mode II fracture, where the entangled fiber bundles partly sustained the shear stress in the vicinity of the crack tip. The entangled fiber bundles played an important role to form the mode II fracture surface, where the microscopic fracture pattern of the entangled fiber bundles was mainly the breakage of the fiber bundles rather than the pull-out or debonding of the fiber bundles.     

无弯曲纤维织物面内渗透率的结构相关性

建立无弯曲纤维织物(Non-crimped fabrics, NCF)的几何结构单胞, 应用树脂在纤维束内与束间耦合流动的模型, 数值模拟树脂的细观流动行为, 结合Darcy定律, 计算单胞的面内等效渗透率, 并对计算方案进行验证。在此基础上, 探讨织物的纤维束间距离、纤维束高度以及束内渗透率等细观结构参数与单胞面内等效渗透率之间的关系。结果表明: 单胞面内等效渗透率随纤维束间距离的增大而增大, 其倒数的对数之间呈正的线性关系; 纤维束高度对单胞面内等效渗透率的影响类似于纤维束间距离对其的影响; 单胞面内等效渗透率随纤维束内渗透率的增加而线性增加。      

基于改进遗传算法的C/SiC拉伸损伤声发射模式识别

采用层次聚类及基于改进遗传算法的无监督模式识别方法,对2D-C/SiC复合材料常温拉伸试验过程的声发射数据进行分析,结合试样断口的扫描电镜(SEM)照片,得到拉伸过程中5类损伤模式及其典型声发射特征参数。通过对各类损伤的能量分布、累计事件数和累计能量的分析,研究C/SiC复合材料的损伤演化过程,发现其过程可分为基体微裂纹和界面失效为主的初始损伤阶段、基体微裂纹停滞导致层间剥离及纤维失效占主导地位的裂纹饱和阶段、基体长裂纹和界面失效为主的损伤积累发展阶段和纤维束大量失效的宏观断裂阶段。     

Surface chemistry of electrospun cellulose nitrate nanofiber membranes

Electrospinning is a rapidly developing technology that provides a unique way to produce novel polymer nanofibers with controllable diameters. Cellulose nitrate non-woven mats of submicron-sized fibers with diameters of 100-1200 nm were prepared. The effects of processing equipment collector design void gap, and steel drum coated with polyvinylidene dichloride (PVDC) were investigated. The PVDC layer applied to the rotating drum aided in fiber harvesting. Electron microscopy (FESEM and ESEM) studies of as-spun fibers revealed that the morphology of cellulose nitrate fibers depended on the collector type and solution viscosity. When a rotating steel drum was employed a random morphology was observed, while the void gap collector produced aligned fiber mats. Increases in viscosity lead to larger diameter fibers. The fibers collected were free from all residual solvents and could undergo oxygen plasma treatment to increase the hydropholicity.     

How to improve mechanical properties of polylactic acid with bamboo fibers

Bamboo fibers (BF) were mixed in polylactic acid (PLA) to improve its mechanical properties: impact strength and heat resistance. Three different types of BF were extracted from raw bamboo by either sodium hydroxide (NaOH) treatment or steam explosion in conjunction with mechanical processing. They were designated as “short fiber bundle,” “alkali-treated filament” and “steam-exploded filament,” respectively. Composite samples were fabricated by injection molding using PLA/BF pellets prepared by a twin-screw extruding machine. Among them, the highest bending strength was obtained when steam-exploded filaments were put into PLA matrix. Impact strength of PLA was not greatly improved by addition of short fiber bundles as well as both filaments. In order to improve the impact strength of PLA/BF composites, PLA composite samples were alternatively fabricated by hot pressing using medium length bamboo fiber bundles (MFB) to avoid the decrease in fiber length at fabrication. Impact strength of PLA/MFB composite significantly increased, in which long fiber bundles were pulled out from the matrix. The addition of BF improves thermal properties and heat resistance of PLA/BF composites due to the constraint of deformation of PLA in conjunction with crystallinity promoted by anneal (at 110 °C for 5 h).