缝纫层合板的本构关系研究(II)——缝纫层合板刚度分析与试验

在缝纫单层板有效弹性常数分析模型的基础上,建立了缝纫层合板的本构关系,分析了缝纫参数对缝纫层合板拉伸、弯曲、剪切和扭转刚度的影响,并对拉压刚度进行了试验研究,结果表明,分析结果与试验结果吻合得较好。     

Mechanical behavior and microstructure characterization of 3D stitched quartz fibers-reinforced silica composites

The mechanical properties of silica material in the monolithic form are ;far from acceptable levels. In this paper, 3D stitched quartz preform was used for the fiber reinforcement, and quartz fibers- reinforced silica composites were prepared by the silica sol-infiltration-sintering method. The density of the composite was up to 1.71 g/cm3 after 10 infiltration-sintering cycles. The flexural strength and the in-plane shear strength were 61.7 MPa and 20.3 MPa, respectively. The flexural stress-deflection curve exhibited mostly nonlinear behavior, which was different from that of monolithic ceramics. Because of the existence of the fiber in Z axis direction, shearing property between the different layers of 3D stitched composites were greatly enhanced. Toughness effect of the 3D stitched quartz preform was conspicuous. The as-fabricated composites showed non-catastronhic failure behavior resulting from weak fiber/matrix interface.     

Warp and weft directional tensile properties of multistitched biaxial woven E-glass/polyester composites

The objective of this research work was to understand the warp and weft directional tensile properties of the two-dimensional multistitched multilayer E-glass/polyester woven composites. The warp and weft directional specific tensile strength and modulus of unstitched structure were higher than those of multistitched structures as stitching caused minor warp and weft yarn filament breakages. Contrarily, the specific tensile strains of unstitched structure were slightly lower than those of all multistitched structures. The stitching yarn type, the number of stitching directions, and the stitching density generally influenced the warp and weft directional tensile properties of multistitched E-glass/polyester woven composites. The failure of warp and weft directional multistitched woven E-glass/polyester composite structures was matrix breakages, and partial and complete yarn breakages in their surfaces. They had a local delamination in their cross-sections and the delamination did not propagate to the large areas due to multidirectional stitching. Also, the failure was confined at a narrow area and resulted in the catastrophic fiber breakages. The warp and weft directional specific damaged areas of multistitched structures, in particular four-directional stitching, were significantly lower than those of the unstitched structures. This indicated that the multistitching made the structures better damage-tolerance materials.     

周边固支缝合复合材料层板的小波配置精细积分法

建立了缝合复合材料面内纤维弯曲几何描述模型,将拟Shannon小波配置法和缝合单层板的刚度矩阵应用到缝合层合板的Hamilton正则方程中,构造了缝合板平面方向离散、而厚度方向解析的Hamilton正则方程,然后用精细积分法求解。用拟Shannon尺度函数表示的近似解很适于求解固支边界问题。数值算例结果表明,小波配置精细积分法在缝合复合材料层板位移、应力分析方面,较低网格密度下即可获得较精确的结果。从而为缝合层合板静力学问题分析提供了一种方法。     

缝纫泡沫夹芯复合材料的刚度预测与试验验证

基于材料细观结构,建立了缝纫泡沫夹芯复合材料的刚度预测模型,并进行了刚度性能的相关试验验证。其中,对缝纫复合材料层合面板部分,考虑了缝纫角对单胞尺寸和富脂区大小的影响,以及缝纫前后层合面板厚度的变化对复合材料面板纤维体积含量的影响,采用改进的纤维弯曲模型计算了缝纫复合材料层合面板的刚度;对缝纫增强的泡沫夹芯部分,把缝线树脂柱看作是泡沫基体中的增强相,将其简化为特殊的单向增强复合材料,提出了用串并联组合模型来预测其刚度。试验测试了缝纫泡沫夹芯复合材料板试件的刚度。应用本文模型对缝纫层合面板和缝纫泡沫夹芯复合材料板的刚度进行预测,结果均与试验结果吻合较好。采用理论模型系统研究了缝纫参数和结构参数对缝纫泡沫夹芯复合材料刚度的影响。     

缝线区域及界面特性对缝纫复合材料单向板力学性能的影响研究

通过试验和显微观察研究了缝纫复合材料单向层压板缝线及其周围区域的结构和损伤的形貌，以及缝纫对复合材料单向板的宏观力学性能的影响。建立了缝线与基体界面强弱对复合材料单向板的强度和刚度影响的两种有限元分析模型，并与试验结果进行了比较分析。结果表明，缝线与基体的结合处的界面特性对复合材料单向板的强度和刚度都有影响，对拉伸强度的影响尤为显著；另外，缝线区域形成的富树脂区的存在也是影响复合材料强度刚度的重要因素。     

缝合复合材料层合板的层间细观应力分析

介绍了缝合复合材料代表体单元（RVE）的三维细观有限元分析模型,模型考虑了缝线的实际形状以及缝合对层合板面内纤维的影响。在分析中引入了保证胞单元边界面的应力和位移周期性连续的边界条件。着重分析了三种平均应力状态下不同角度铺层间层间应力的分布情况。研究结果表明：缝合复合材料单胞内部层间应力分布也是不均匀的;促使材料发生分层破坏的主要层间应力和外载荷有关。     

缝合参数对缝合泡沫夹芯结构复合材料VARTM工艺树脂充模的影响

对不同缝合参数的缝合泡沫夹芯结构复合材料真空辅助树脂传递模塑成型(VARTM)工艺进行数值模拟,研究了针距、行距、缝针直径、芯板厚度及纤维面板厚度等缝合参数对缝合泡沫夹芯结构复合材料VARTM工艺树脂流动充填的影响。结果表明,改变缝合行距对树脂的流动充填速度影响不大,缝合行距越大,树脂在下层纤维面板流动的同步性越差,制品出现空隙及干斑的可能性越大;缝合针距越小,树脂完成充填的时间越长;分别增加缝针直径和泡沫芯板的厚度,树脂完成充填时间呈线性增长,缝针直径越大,下层纤维面板树脂浸润效果越好;纤维面板厚度增加,树脂完成充填的时间变长,且相对于其他缝合参数,纤维面板厚度对树脂流动充填时间影响最大;缝合针距、泡沫芯板的厚度及纤维面板的厚度都不影响树脂在下层纤维面板的浸润效果。     

缝合泡沫夹层复合材料低速冲击数值模拟及实验

在ABAQUS分析平台中建立了缝合泡沫夹层复合材料在低速冲击下的动力学有限元模型,采用杆单元模拟缝线树脂柱的作用,基于Hashin破坏准则模拟层板面内损伤,通过各向同性硬化本构模型利用等效塑性变形模拟泡沫夹芯损伤演化。针对相同铺层的缝合和未缝合泡沫夹层结构,模拟了相同冲击能量下的低速冲击响应过程及面板、泡沫的损伤情况,数值结果与实验结果吻合较好,证明了该方法的有效性和准确性。研究结果表明,在低速冲击下,泡沫夹层结构引入缝线后虽然降低了泡沫缓冲吸能的作用,使得面板表面受到较大的冲击破坏,但增强了整体刚度,增大了面板抵抗弯曲变形的能力,减小了内部面板的损伤,使其在改善复合材料面板易分层缺陷的同时还依然拥有优良的面内性能。     

T型壁板RFI缝合复合材料的屈曲性能

在实验研究BS3-94-10型环氧树脂膜流变学性能、叠层预制件厚度方向压实性能、RFI缝合随炉试件层间剪切和弯曲性能的基础上,优化设计了树脂膜融渗及缝合工艺参数,并制备了高性能T型壁板RFI复合材料制件。缝合前后T型壁板屈曲性能测试结果表明,缝合可显著提高T型壁板的屈曲性能。