Z-pin增强复合材料层合板断裂韧性试验研究

针对Z-pin增强复合材料层合板, 开展了断裂韧性的试验研究。研究选取了3种Z-pin直径(0.28、 0.52、 0.80mm)且每种直径下分别以3种分布形式(5×5、 8×8、 10×10)排布Z---pin的增强方式, 为了确定比较基准, 试验中同时测试了不含Z-pin的复合材料层合板试样。通过Z-pin拔出试验测试了3种直径Z-pin从基体拔出过程中的载荷位移关系。利用双悬臂梁试验和端部开口弯曲试验分别测试了不含Z-pin和含Z-pin试样的Ⅰ型断裂应变能释放率G_ⅠC、 Ⅱ型断裂应变能释放率G_ⅡC。试验结果表明:? 与不含Z-pin的结构相比, Z-pin增强试样的Ⅰ型断裂应变能释放率G_ⅠC增大了83%~1110%, Ⅱ型断裂应变能释放率G_ⅡC增大了23%~438%; 在相同Z-pin体积含量下, 与增大Z-pin直径相比, 增大Z-pin分布密度能更有效地提高复合材料层合板的断裂韧性。      

Z-pin增强CMC层间Ⅰ+Ⅱ混合型断裂韧性

提出手工预缝纫方法将3K丝束的T300碳纤维引入预成型体,采用CVI工艺在预成型体和缝线处同时渗透SiC基体,制备了Z-pin增强平纹编织C/SiC陶瓷基复合材料。通过三点弯曲试验测定了Ⅰ+Ⅱ混合型应变能释放率,分析了材料的裂纹扩展行为和Z-pin增强机理。结果表明:随着裂纹扩展长度的增大,Ⅰ+Ⅱ型裂纹扩展阻力不断增大,相同裂纹扩展长度,增加Z-pin植入密度可以提高粘结强度,增大止裂作用。Z-pin增强平纹编织C/SiC陶瓷基复合材料裂纹扩展的耗能途径主要是层间界面剥离、Z-pin弹性剪切和拉伸变形。     

含孔复合材料层合板孔边的应力集中

针对含孔有限宽复合材料层合板的应力集中问题,提出一种计算孔边应力分布及应力集中因子的方法：先利用经典层板理论,将复合材料层合板化归为各向异性板;再将各向异性板等效转换为一偏轴拉伸的单向纤维层板;最后利用含孔偏轴单向板的孔边应力计算公式来分析一般铺层层合板孔边应力集中情况。根据所推导的计算公式,分析讨论了板宽/孔径比、铺层比例、铺层方式、材料性能参数等因素对孔边应力集中的影响。     

带中心孔的钛合金扩散连接层合板裂纹扩展特性

为了研究含孔TC4钛合金扩散连接层合板的裂纹扩展行为,进行了含ϕ6中心孔的8mm厚单层板材、三层(3+2+3)扩散连接层合板和三层(3+2+3)含ϕ12止焊区扩散连接层合板的疲劳对比试验,试验中施加标识载荷,通过断口判读裂纹形态和尺寸,得到裂纹扩展(a,N)数据,建立了裂纹扩展da/dN-a曲线,对单层板、层合板和止焊层合板的裂纹扩展行为和规律进行了对比。结果表明:单层板出现规则的半椭圆形孔壁裂纹;层合板由于存在层合界面的影响,出现不规则的半椭圆孔壁裂纹;而止焊层合板以角裂纹为主,裂纹扩展过程分为三阶段;三类试件的da/dN-a曲线可用双对数线性关系描述;三层板的裂纹扩展特性不弱于单层板;止焊层合板的裂纹扩展性能有明显改善,提高了含孔层板的损伤容限特性。     

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。      

Z-pin增强酚醛复合材料层合板的层间拉伸性能

本文探索研究了Z-pin的植入对酚醛复合材料层合板层间拉伸性能的影响。通过向酚醛复合材料层合板中植入体积分数为0.78%(植入间距5mm×5mm)的石英/酚醛Z-pin,对其进行层间拉伸性能测试,结果表明,随着Z-pin的植入,层合板的层间拉伸性能显著提高,并伴随破坏模式的变化、材料韧性的增加。最后,根据复合材料力学,建立Z-pin增强层合板的简单力学模型,通过桥率试验与层间拉伸试验,对其进行验证和修正,得出Z-pin植入对层合板的层间性能的影响规律。     

Z-pin增强复合材料Ⅰ型断裂韧性数值分析

采用细观力学方法以及虚拟裂纹闭合法(VCCT)对含有Z-pin增强复合材料双悬臂梁(DCB)结构Ⅰ型断裂韧性进行了研究。利用有限元法建立了结构模型,采用实体单元模拟复合材料层压板结构和非线性弹簧元模拟Z-pin。通过计算应变能释放率对含有不同体积分数Z-pin的复合材料层压板Ⅰ型断裂韧性与不含Z-pin的复合材料层压板Ⅰ型断裂韧性进行了对比分析。研究表明,含有Z-pin增强复合材料双悬臂梁(DCB)结构Ⅰ型断裂韧性在裂纹扩展过程中受到Z-pin桥联作用的影响而显著增强,且其增强效果与Z-pin的体积分数、处在桥联区的Z-pin数目均相关,这表明Z-pin增强方法能够有效提高复合材料层压板的分层扩展阻力。     

平纹织物结构对织物增强复合材料层间断裂韧性影响的研究

本文采用粘贴片式双悬臂梁(DCB)试件和端部切口弯曲(ENF)试件研究了平纹织物的经纬纱密度对玻璃平纹织物/环氧树脂复合材料的Ⅰ型和Ⅱ型层间断裂韧性的影响。实验结果表明织物的密度对层间断裂韧性有显著的影响。提出了在织物增强复合材料层合板中,基体在织物孔洞中形成层间铆接,并且就其与层间G_IC和G_IC的关系进行了研究。      

复合材料层板开孔拉伸损伤分析

针对纤维增强复合材料层板开孔拉伸, 将复合材料层板的失效分为层内失效和层间失效, 建立了复合材料层板开孔拉伸损伤分析模型。该模型基于逐渐损伤分析, 对不同复合材料开孔层板进行了失效预测, 并与文献试验结果进行了对比, 破坏强度和失效模式均与文献试验结果非常吻合。结果表明本文中所建立的层板开孔拉伸损伤分析模型能够模拟含孔层合板拉伸过程中的损伤起始、 损伤扩展和最终破坏模式, 并最终预测含孔层合板拉伸失效模式和破坏强度。      

一种改进的基于两单胞模型的三维角联锁机织复合材料弹性性能数值预测方法及实验验证

为准确预测三维角联锁机织复合材料的宏观弹性性能,对基于CT图像几何参数实测数据建立的内单胞和面单胞细观实体模型进行数值分析,其中面单胞模型采用组合面单胞形式,并开展了三维角联锁机织超高分子量聚乙烯(UHMWPE)纤维/聚氨酯复合材料的经向拉伸实验。结果表明:基于两单胞模型预测该复合材料的宏观弹性模量与实验结果吻合较好,组合面单胞的经向拉伸模量小于内单胞;经向拉伸时复合材料在经纱间接触面处、纬纱沿宽度方向的端部和经纱与基体的交界面处易出现应力集中现象;当纬纱层数小于30层时,应该考虑表面区域对复合材料整体力学性能的影响。      

Investigation into Z-Pin Reinforced Composite Skin/Stiffener Debond under Monotonic and Cyclic Bending

Skin/stiffener debonding has been a longstanding concern for the users of stiffened composite panels in long-term service. Z-pinning technology is an emerging solution to reinforce the composite assembly joints. This work experimentally characterizes the progressive debonding of Z-pinned skin/stiffener interface with the skin under static bend loading. The three-stage failure process is identified as: flange edge debonding, pin/laminate debonding, and ultimate structural failure. Three different distribution patterns were compared in terms of the static debonding properties revealed the affirmative fact that locating pins in high normal stress regions, that is close to the flange edges in skin/stiffener structures, is more beneficial to utilize the full potential of Z-pinning reinforcement. The unit strip FE model was developed and demonstrated effective to analysis the effect of Z-pin distribution on the ultimate debond load. On the other hand, the evolution of fatigue cracks at Z-pinned skin/flange interface was investigated with a series of displacement-controlled fatigue bending tests and microscopic observations. Results show that Z-pinning postpones crack initiations at low displacement levels, and the remarkable crack-arresting function of pins enables the structure a prolonged fatigue life. However, pins become less effective when the maximum displacement exceeds the crack initiation level due to gradually pullout of pins.     

复合材料微细杆增强复合材料研究进展

纤维增强树脂基复合材料具有轻质高强的特点,但复合材料层合板层间韧性和抗冲击性能差,复合材料微细杆(Z-pin)增强技术极大地改善了这一不足,被广泛应用于各工业制造领域.近年来,Z-pin增强复合材料的制备工艺不断发展,目前主要有热压罐法和超声植入法(UAZ).Z-pin增强复合材料的层间增韧和抗冲击性能提高效果显著,但...     

Z-pin增强陶瓷基复合材料I型应变能释放率

碳纤维平纹编织物和碳纤维Z-pin制备的预成型体,通过化学气相渗透(CVI)工艺制成Z-pin增强平纹编织陶瓷基复合材料层压板。通过双悬臂梁试验研究Z-pin增强平纹编织陶瓷基复合材料层压板的层间I型应变能释放率和增强机理。研究Z-pin面积密度对层间I型应变能释放率的影响。结果表明:Z-pin增强平纹编织陶瓷基复合材料层压板主要增强机理表现为层间裂纹扩展受阻,Z-pin与层压板界面解离,Z-pin桥联裂纹和Z-pin拔出;增大Z-pin面积密度,层间I型应变能释放率增大。     

The effect of thermal mismatch on Z-pinned laminated composite structures

Z-pinning is a method of improving the through-thickness properties of composite laminates by inserting a solid pin through the laminate prior to curing. The thermal expansion mismatch between the Z-pin and base laminate produces large residual stresses during the cure cycle. Finite element modelling has shown that these stresses are greater than the failure stress of standard resin systems indicating the resin around the Z-pin should fail. This was confirmed through microscopy, which showed cracking around the perimeter of the Z-pin. Changing the material properties and dimension of the model to represent different Z-pinning situations could not significantly reduce the residual stresses, indicating cracking should occur in all Z-pinned laminates. These results show that probably all published Z-pinning properties have been obtained from laminates that would have exhibited cracking, indicating that the improved through-thickness properties are due more to mechanical interlocking than bonding. Questions are raised about the suitability of using Z-pinned laminates in specific applications, and the effects of increased moisture ingress and long term durability.     

Micro-mechanical finite element analysis of Z-pins under mixed-mode loading

This paper presents a three-dimensional micro-mechanical finite element (FE) modelling strategy for predicting the mixed-mode response of single Z-pins inserted in a composite laminate. The modelling approach is based upon a versatile ply-level mesh, which takes into account the significant micro-mechanical features of Z-pinned laminates. The effect of post-cure cool down is also considered in the approach. The Z-pin/laminate interface is modelled by cohesive elements and frictional contact. The progressive failure of the Z-pin is simulated considering shear-driven internal splitting, accounted for using cohesive elements, and tensile fibre failure, modelled using the Weibull’s criterion. The simulation strategy is calibrated and validated via experimental tests performed on single carbon/BMI Z-pins inserted in quasi-isotropic laminate. The effects of the bonding and friction at the Z-pin/laminate interface and the internal Z-pin splitting are discussed. The primary aim is to develop a robust numerical tool and guidelines for designing Z-pins with optimal bridging behaviour.     

Z-pins对层合复合材料非对称分层增韧作用参数分析——Ⅰ型层间韧性

假设纤维Z-pins的桥联力与嵌入厚度成正比,建立适于非对称分层(分层位于层合板厚度方向上的任意位置)的Z-pin细观力学模型并构造相应的Z-pin单元,结合考虑一阶剪切变形的梁单元,建立了用于分析含浅部分层采用Z-pins增韧的双悬臂梁(Double cantilever beam,DCB)有限元模型,并在分层裂纹面上引入接触单元以防止分析过程中2个分层子梁在分层前缘处的相互嵌入。通过数值算例分析了Z-pins对含非对称分层的DCB试件Ⅰ型层间韧性的增强作用。参数分析表明,当分层位置靠近层合板的表面时,Z-pins的增韧作用明显下降,其较薄分层子层的厚度是决定Z-pins对Ⅰ型层间韧性增强效果的关键参数。     

Z-pins对层合复合材料非对称分层增韧作用参数分析——Ⅱ型层间韧性

利用纤维Z-pins的细观力学模型构造了相应的Z-pin单元,结合考虑一阶剪切变形的梁单元,建立了用于分析含非对称分层采用Z-pins增韧的端部开口弯曲试件(End notched flexure,ENF)的有限元模型,并在分层裂纹面上引入接触单元以防止分析过程中2个分层子梁在端部开口处的相互嵌入。通过数值算例分析了Z-pins对含非对称分层的ENF试件Ⅱ型层间韧性的增强作用。参数分析表明,当分层位置靠近层合板的表面时,Z-pins的增韧作用明显下降,Z-pins对Ⅱ型层间韧性的增强作用主要由2个分层子层中较薄子层决定,但另一分层的厚度也对Ⅱ型层间韧性有一定的影响。     

Bridging micromechanisms of Z-pin in mixed mode delamination

A numerical model for analyzing the bridging mechanisms of Z-pining in composite laminates is presented. Main failure modes of the Z-pin are: debonding between the Z-pin and matrix, split and rupture of the Z-pin material; these have been taken into account here. The cohesive zone model was utilized to simulate splitting and rupturing within the Z-pin. The interfacial contact between the Z-pin and matrix was assumed to be initially bonded, followed by debonding and frictional sliding. The present model is validated by mode I experiments; the mode II simulation is verified by similar Z-pin shear tests. It is observed that the shear bridging force component increases with the mode II ratio, while the mode I bridging response decreases slightly with the mode II ratio. An enhanced frictional zone is located near the delamination surface. The mode II bridging force in cross-ply laminates is higher than that in UD laminates, while the Z-pin is more likely to rupture in cross-ply laminates when the mode II ratio is relatively high. The presented model can be used to evaluate the Z-pin bridging response. The calculated bridging force is suitable for analyzing the mechanical performance of Z-pinned structures.