超细纤维增强复合材料Ⅰ型层间断裂韧性分析

采用静电纺丝技术制备了厚度约0.1mm的超细纤维无纺布薄膜, 并入层合板中间界面, 固化成型后加工为双悬臂梁(DCB)试样。根据ASTM D5528标准测试了 Ⅰ 型层间断裂韧性。实验结果表明, 增强试样比空白试样的 Ⅰ 型临界应变能释放率(G_{Ⅰ C})提高了约35％。同时采用有限元分析方法研究了含无纺布薄膜试样和空白试样的裂纹扩展过程, 数值结果与实验结果吻合较好, 更好地解释了含无纺布薄膜层合板的层间断裂机理。      

复合材料的Ⅰ型层间断裂韧性

本文采用铰链式双悬臂梁试件对碳/双马来酰亚胺复合材料的Ⅰ型层间断裂韧性进行了研究,分析比较了层间断裂韧性G_IC的表达方法,用三次多项式和幂函数拟合实验柔度的方法得到的结果比较满意,实验结果表明纤维桥连对单向层合板的G_IC的影响是显着的,用刀片切割桥连纤维后G_IC值下降百分之二十,分散性也有显着下降。另外发现G_IC值随试件厚度增加而增大。      

复合材料的Ⅰ型层间断裂韧性

本文采用铰链式双悬臂梁试件对碳/双马来酰亚胺复合材料的Ⅰ型层间断裂韧性进行了研究,分析比较了层间断裂韧性G_IC的表达方法,用三次多项式和幂函数拟合实验柔度的方法得到的结果比较满意,实验结果表明纤维桥连对单向层合板的G_IC的影响是显着的,用刀片切割桥连纤维后G_IC值下降百分之二十,分散性也有显着下降。另外发现G_IC值随试件厚度增加而增大。     

玻璃纤维增强复合材料的I型层间断裂韧性

介绍了玻璃纤维增强复合材料Ⅰ型层间断裂韧性“Ｒｏｕｎｄ Ｒｏｂｉｎ Ｔｅｓｔ”的结果。随着偶联剂浓度的改变，Ｉ型裂纹的扩展方式从稳态向非稳态转变。这类断裂韧性强烈地依赖界面性能。     

圆弧形单向纤维增强树脂复合材料的Ⅰ型层间断裂韧性测试及分析

层合板的Ⅰ型层间断裂韧性的测量方法通常为单向纤维增强树脂复合材料的末端切口(End notched flexure,ENF)试样的双悬臂梁(Double cantilever beam,DCB)试验.为了得到带有弧度的层合复合材料结构的Ⅰ型层间断裂韧性,对圆弧形末端切口(Arc-ENF)试样进行DCB试验.基于梁的弯曲...     

玻璃纤维增强复合材料的Ⅰ型层间断裂韧性

介绍了玻璃纤维增强复合材料Ⅰ型层间断裂韧性“RoundRobinTest”的结果随着偶联剂浓度的改变，Ⅰ型裂纹的扩展方式从稳态向非稳态转变这类断裂韧性强烈地依赖界面性能关键词##4界面性能;;Ⅰ型断裂韧性;;裂纹扩展;;稳态;;非稳态     

圆弧形单向纤维增强树脂复合材料的I型层间断裂韧性测试及分析

层合板的I型层间断裂韧性的测量方法通常为单向纤维增强树脂复合材料的末端切口(End notched flexure, ENF)试样的双悬臂梁(Double cantilever beam, DCB)试验。为了得到带有弧度的层合复合材料结构的I型层间断裂韧性,对圆弧形末端切口(Arc-ENF)试样进行DCB试验。基于梁的弯曲理论和Irwin-Kies公式得到Arc-ENF试样的柔度公式与I型临界能量释放率G_IC公式,并且利用ABAQUS软件对DCB试验进行数值模拟。最终,通过对比分析理论公式计算结果、数值模拟结果和DCB试验结果来验证柔度公式和G_IC公式的合理性和有效性,对带有任意弧度的DCB试样的I型层间断裂韧性的测试与分析具有参考价值。      

缝合层合板的Ⅰ型层间断裂韧性研究

通过缝合的方法改善织物增强复合材料层合板的层间断裂韧性.采用双悬臂梁(DCB)试验测试和研究了缝合层合板的层间断裂韧性与断裂行为.为了评价缝合工艺参数(缝合密度)对层间断裂韧性的影响,用改进的插入型夹具在实测不同缝合工艺层合板的Ⅰ型层间断裂韧性值(G_IC)的基础上,分析和阐明了缝合工艺参数(缝合密度)与G_IC间的关系;以提高层合板的平均层间断裂韧性值为目标,以拉伸和弯曲强度为约束条件优化了缝合工艺;采用摄影显微镜对分层断裂面进行了观察,分析和考察了缝合对其它性能的影响.结果表明:改进的插入型夹具可方便地完成缝合层合板的Ⅰ型层间断裂韧性测试;缝合后裂纹不连续扩展,缝合密度对裂纹扩展行为有较大影响;随着缝合密度的增大,层间断裂韧性值增大,但拉伸和弯曲强度降低,缝合密度存在最佳值.     

织物增强复合材料层合板Ⅰ型层间断裂特性

采用双悬臂梁(DCB)试验测试和研究了织物增强复合材料层合板的层间断裂韧性与断裂行为。为了评价测试温度和试样几何尺寸的变化对层间断裂韧性的影响，分别在室温(RT)和液氮温度(77K)条件下对不同尺寸的试样进行了双悬臂梁试验。采用扫描电镜对分层断裂面进行了观察，分析和验证了层间断裂特性。     

Prediction of Mode I interlaminar fracture toughness of stitched flax fiber composites

This paper aims to propose a simulation procedure to predict the interlaminar fracture toughness of stitched flax fiber composites through a virtual double cantilever beam test. The proposed procedure is constituted of two steps. First, the interlaminar failure of unstitched flax fiber laminate, as the parent laminate, is modeled using cohesive elements with a nonlinear softening law in order to model the large-scale fiber bridging occurred during delamination. The experimental results are used to calibrate the parameters of the cohesive law. Second, two-node beam elements are superposed onto the cohesive interface of the parent laminate at a prescribed stitch density and distribution to model the bridging stitches present in the validation samples. The stitch material behavior and properties are obtained from the tensile test of impregnated stitch fibers. The out-of-plane flax yarn stitching was found to generate a twofold increase in the delamination resistance of the composite laminate at a medium stitch density. The FE analysis results agreed well with the experimental results, where a good fit between the predicted and experimental R-curves was achieved.     

Mode I interlaminar fracture toughness properties of advanced textile fibreglass composites

The Mode I interlaminar fracture toughness properties of vinyl ester-based composites reinforced with fibreglass manufactured by the advanced textile technologies of braiding, knitting, stitching and through-the-thickness weaving are assessed in comparison to a variety of traditional composites made from fibreglass such as unidirectional or woven rovings. The interlaminar fracture toughness (G_Ic) of braided and knitted composites are higher than traditional composites by factors of more than two and four, respectively. Toughening in these textile composites was caused by extensive crack branching as the interlaminar crack was forced to follow a tortuous path through the complex fibre architectures. The G_Ic values of the composites reinforced in the through-thickness direction by weaving or stitching were higher than traditional composites by factors of nearly two and three, respectively, with the main toughening mechanism being crack bridging by the through-thickness binder yarns/stitches. A review of Mode I interlaminar fracture data collected from papers shows that advanced textile techniques are capable of manufacturing composites with substantially improved delamination resistance.     

Mode I interlaminar fracture toughness of commingled carbon fibre/PEEK composites

Carbon fibre/poly (ether-ether-ketone) (PEEK) composites were fabricated from plain weave cloth using the commingled yarn of carbon fibres with PEEK filaments. The undirectional specimen was made from the warp of commingled yarn and the weft of PEEK yarn, while the two-dimensional specimen was made from commingled yarns both of the warp and the weft. During the hot-pressing process, PEEK filaments melt to form the matrix of the composite. The interlaminar fracture toughness of the commingled composite was measured and compared with that of the prepreg composite. The critical strain energy release rates,/'G _Ics, obtained for the commingled composites were higher than the prepreg composite. In particular, the two-dimensional composite exhibited higherG _Ic than the unidirectional commingled composite. Factors increasing the fracture toughness of commingled composites have also been investigated by SEM observation of the fractured surface.     

Adhesion of PBO fiber in epoxy composites

A composite of poly p-phenylene-2,6-benzobisoxazole (PBO) fiber and epoxy resin has excellent electrical insulation properties. However, it is a challenging issue to improve its mechanical properties because of poor adhesion between PBO fiber and matrix. The relatively smooth and chemically inactive surface of PBO fiber prevent efficient chemical bonding in the composite interface. Here, we report the surface modification of PBO fibers by UV irradiation, O₂ and NH₃ plasma, as well as acidic treatments. We found that the surface free energy and roughness are increased for both sized and extracted fibers after plasma treatments together with maleic anhydride grafting. The sized fiber shows marginal improvement in adhesion strength and no change in fiber tensile strength because of the barrier effect of the finish. For the extracted fiber, however, the tensile strength of the fiber is sensitive to surface treatment conditions and considerable strength reduction occurred, particularly for cases of acidic treatments and UV irradiation. This is because that the treatments increase the surface roughness and introduce more surface flaws. The extracted fiber surface has no adequate wetting and functional groups, which in turn results in coarse interface structures and causes reduction or no apparent variation of the adhesion strength. The fracture surfaces after single fiber pull-out tests exhibit adhesive interfacial failure along the fiber surface, which is further confirmed by similar adhesion strength and interlaminar shear strength values when the fiber was embedded in various epoxy resins with different temperature behavior.     

有机黏土对碳纤维/聚醚砜-环氧复合材料层间断裂韧性的影响

采用溶剂法和热熔法制备了不同有机黏土质量分数的有机黏土/聚醚砜（PES）-环氧复合材料,通过对其微观形态和力学性能的研究,揭示了复合材料的增韧机制。在有机黏土/PES-环氧复合材料中添加T800H（12K）碳纤维,制备了T800H-有机黏土/PES-环氧复合材料预浸料单向带,采用热压罐工艺制备了复合材料单向板,对其I型、II型层间断裂韧性进行了研究。结果表明:T800H-有机黏土/PES-环氧复合材料的层间断裂韧性随有机黏土质量分数变化趋势与有机黏土/PES-环氧复合材料的断裂韧性趋势一致,证明了增韧机制的正确性。      

Oxygen plasma processing and improved interfacial adhesion in PBO fiber reinforced epoxy composites

The effects of oxygen plasma processing on the improved interfacial adhesion properties of poly(1,4-phenylene-cis-benzobisoxazole) (PBO) fiber reinforced epoxy composites have been investigated in this paper. Both As-spun (AS) and high-modulus (HM) PBO fiber systems were studied. The characterization techniques included microscopy, surface analysis, and composite interfacial adhesion tests. The results showed that the high-modulus fiber surface free energy could be increased significantly by 42.2% from 46.2 to 65.7 mJ/m², while the tensile strength was only slightly decreased by 3.4% from 5.87 to 5.67 GPa. In addition, the interfacial adhesion strength of PBO fiber reinforced epoxy composite was improved by 37.5% from 32.5 to 44.7 MPa for the HM fiber system. The improvement has been attributed to the enhanced cohesive failure that dissipated more fracture energy.     

Controlling fracture toughness of matrix for ductile fiber reinforced cementitious composites

An experimental study was carried out to find material parameters for making fiber reinforced cementitious composites (FRCC) more ductile. One of the dominant factors to control the ductility might be hidden in fracture property of matrix as well as the interface property between fiber and matrix. Therefore this study varied air content and water-binder ratio as the parameters to change the fracture property of matrix and experimentally examined their influence on the ductility of FRCC by three-point bend test with notched beams. As a result, it is concluded that fracture toughness of the matrix could be one of key parameters to control the ductility of FRCC. In case of a polyethylene fiber used in this study, the optimum value of the fracture toughness (critical strain energy release rate): G_IC of the matrix was obtained to be 7.5-8.0 N/m.     

单向连续碳纤维-玻璃纤维层间混杂增强环氧树脂基复合材料的力学性能

为了研究连续单向纤维的层间混杂方式对复合材料力学性能及破坏方式的影响,采用碳纤维-玻璃纤维体积比为1∶1,以拉-挤成型法制备了具有不同层间混杂结构的连续单向纤维增强环氧树脂基复合材料,并研究了不同层间混杂结构的连续单向碳纤维-玻璃纤维增强环氧树脂基复合材料的力学性能及破坏形式。结果表明：具有层间混杂结构的复合材料抗拉强度处于纯碳纤维/环氧树脂复合材料和纯玻璃纤维/环氧树脂复合材料之间,复合材料的拉伸断裂方式为劈裂;具有层间混杂结构的复合材料的层间剪切强度均优于纯碳纤维/环氧树脂复合材料和纯玻璃纤维/环氧树脂复合材料,复合材料的剪切断裂方式为层间断裂。