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。     

分层界面角度对CFRP层板Ⅱ型分层的影响

Ⅱ型层间断裂韧度是复合材料结构损伤容限设计的关键力学参数。针对5种具有不同预置分层界面的国产T300复合材料端部缺口弯曲(ENF)实验件,开展Ⅱ型分层测试,获得预嵌薄膜末端开裂的Ⅱ型层间断裂韧度 G Ⅱc,NPC 和预开裂裂纹处扩展的Ⅱ型层间断裂韧度 G Ⅱc,PC 。结果表明:5种分层界面下 G Ⅱc,NPC 均比 G Ⅱc,PC 高,并且对于 G Ⅱc,NPC 值,0°/0°分层界面的最高,0°/90°分层界面的最低;而对于 G Ⅱc,PC 值,0°/45°分层界面的最高,0°/90°分层界面的最低。同时,采用虚拟裂纹闭合技术(VCCT)模拟不同分层界面处的Ⅱ型分层扩展,获得了分层扩展过程中分层前缘应变能释放率分布,结合实验结果分析了分层界面角度对Ⅱ型断裂韧度测量值的影响。     

低温环境下测试复合材料Ⅰ型层间断裂韧性的简易方法

目前ASTM复合材料Ⅰ型层间断裂韧性测试标准需不断观测裂纹扩展长度。然而在低温环境下,裂纹扩展长度不易测量且过程繁琐。为克服这一缺陷,本文采用双柔度法测试复合材料低温环境下Ⅰ型层间断裂韧性,该方法的步骤与ASTM标准基本相同,但不需观测裂纹扩展长度便能获得低温下Ⅰ型层间断裂韧性。为了验证该方法的可靠性和精度,采用5件碳纤维增强环氧树脂基复合材料双悬臂梁（DCB）试样在-10℃环境下进行Ⅰ型层间裂纹扩展实验,应用ASTM标准所推荐的三种方法及本文的双柔度法进行数据处理获得复合材料Ⅰ型层间断裂韧性。结果表明:ASTM标准的三种方法与双柔度法得到的Ⅰ型层间断裂韧性结果一致,相对差别小于5%,而本文的双柔度法不需测量裂纹扩展长度,因此更简单,为测试低温环境下Ⅰ型层间断裂韧性提供了一种准确、简单的新方法。      

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.     

PBO纤维增强环氧树脂复合材料层间Ⅰ型断裂韧性的DIC技术测量

Ⅰ型双悬臂梁(DCB)试验通常用于单向复合材料的层间抗拉性能研究,目标是测量Ⅰ型层间断裂韧性,其可作为复合材料分层扩展及失效机制研究的重要输入参数。在DCB试验中必须经常暂停试验以实现多次测量裂纹长度,这不仅会对裂纹传播产生潜在影响,造成测量误差且多次反复试验的时效性较差。数字图像相关(DIC)测试技术应用于裂纹扩展长度测量具有实时跟踪、精确定位的优点,可有效提高Ⅰ型断裂韧性试验的测量效率,但应用于非连续变形行为仍存在局限性,且易受到图像噪声的干扰,产生测量误差。本文发展了一种基于DIC测试技术的实时获取裂纹长度的检测方法,通过图像匹配算法获取试件的非连续变形位移场,并提出一种根据全局横向位移离散程度的辨别方法,实现了裂纹尖端的实时捕捉。再通过DCB试验,与传统测量方式对比,裂纹长度的测量误差平均不超过2.76%,验证了该方法的准确性和高效性,同时也克服了聚对苯撑苯并双噁唑(PBO)/环氧树脂复合材料侧表面毛糙、散斑质量较差及纤维桥接对测量结果的干扰,最终获取了有效的Ⅰ型层间断裂韧性初始值及稳态扩展值。     

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     

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(GIC)的基础上, 分析和阐明了缝合工艺参数(缝合密度)与GIC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.     

各向异性复合材料开孔板拉伸强度预测及模型验证

基于有限断裂力学方法建立了一种预测多向复合材料开孔板拉伸强度的通用和半经验模型。该模型同时采用基于应力形式的失效准则和基于能量形式的失效准则预测失效。模型仅需铺层弹性常数、无缺口层合板的强度以及0°铺层的断裂韧性等参数。基于线弹性断裂力学建立了多向复合材料层合板的断裂韧性与0°铺层断裂韧性之间的关系, 进而预测了任意铺层复合材料开孔板发生纤维主导拉伸失效时的强度。将模型预测结果与开孔板拉伸强度的试验数据进行了对比验证, 预测误差最大为9.7%, 与点应力和平均应力等方法的对比表明, 该模型的预测精度高于传统的特征长度方法。      

纤维桥联效应下复合材料层合板的屈曲及分层扩展模拟

纤维增强复合材料层合板由于层间力学性能弱,容易出现分层损伤。分层的扩展往往伴随着纤维桥联效应,纤维桥联能显著增大层合板尤其是多向层合板分层扩展的阻力。考虑纤维桥联效应的三线性内聚力模型能表征分层扩展实验中断裂韧性的“R曲线”特征,比传统的双线性模型能更为准确地描述复合材料的分层扩展行为。本论文基于三线性内聚力模型,对含圆形分层复合材料层合板的轴向压缩进行数值模拟,探讨纤维桥联效应对分层扩展及后屈曲行为的影响规律。研究结果发现,纤维桥联对层合板的屈曲载荷影响较小;混合屈曲模式下,三线性模型预测的上下子板相对法向位移明显低于双线性模型;相同分层深度下,三线性模型预测的层合板后屈曲更早转变为整体屈曲模式。随着分层深度的增加,层合板的屈曲模式由局部屈曲逐步过渡为混合屈曲和整体屈曲;当分层深度较浅时,Ⅰ型分层扩展占主导;随着分层深度的增加,Ⅰ型分层逐渐减弱,而Ⅱ型和Ⅲ型分层扩展则显著增强;当分层接近板中面时,Ⅰ型分层停止扩展,以Ⅱ型及Ⅲ型分层为主。     

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。     

Analysis of mixed-mode interlaminar fracture and damage behavior of GFRP woven laminates at cryogenic temperatures

The objective of this work is to investigate the interlaminar fracture and damage behavior of glass fiber reinforced polymer (GFRP) woven laminates loaded in a mixed-mode bending (MMB) apparatus at cryogenic temperatures. The finite element analysis (FEA) is used to determine the mixed-mode interlaminar fracture toughness of MMB specimen at room temperature (RT), liquid nitrogen temperature (77 K) and liquid helium temperature (4 K). A FEA coupled with damage is also employed to study the damage distributions within the MMB specimen and to examine the effect of damage on the mixed-mode energy release rate. The technique presented can be efficiently used for characterization of mixed-mode interlaminar fracture and damage behavior of woven laminate specimens at cryogenic temperatures.     

A modification of the mixed-mode bending test apparatus

In this article, the mixed-mode bending test appartaus was modified in order to reduce the influence of the weight of the lever on the mixed-mode fracture toughness during the measurement. A unidirectional glass fibre reinforced polyamide 12 composite laminate was measured at G_I/G_II ratios of 3/1 and 1/1, by using the original and the modified MMB apparatus respectively, and the results of the mixed-mode interlaminar fracture toughness data were compared. It has been found that the modified MMB apparatus can be used to avoid the preloading on the specimens caused by the weight of the lever, and the fracture toughness can directly be calculated by applying the beam theory or the modified beam theory equations without the lever-weight correction.     

湿热环境下复合材料的混合型层间断裂特性研究

采用混合型挠曲(MMF)试件,研究了材料吸湿和环境温度对T300/5405复合材料混合型层间断裂韧性的影响。给出了在不同温度下,不同吸湿含量试件分层临界扩展时的Ⅰ型分量和Ⅱ型能量释放率分量散点图。结果表明:在吸湿和温度的综合作用下,分层尖端存在塑性变形;常温下,吸湿对材料的层间断裂韧性影响不明显,在高温环境中,随吸湿量增加,层间断裂韧性显著增加;温度对干态材料的断裂韧性影响较小,试件吸湿后,随温度升高,韧性增强。      

Influence of adsorption behaviour of a silane coupling agent on interlaminar fracture in glass fibre fabric-reinforced unsaturated polyester laminates

The relationship between the interphase consisting of physisorbed and chemisorbed silane on glass fibres and the resultant composite Mode I delamination fracture toughness in glass fibre fabric laminate, was studied. The Mode I interlaminar fracture toughness of the laminate specimen was obtained by using a double cantilever beam (DCB) specimen. The delamination resistance of the laminate specimen finished with two silane concentrations and washed in methanol solvent, is discussed on the basis of the interlaminar fracture toughness. In order to determine the amount of physisorbed and chemisorbed silane on the glass fibre, the amount of total carbon was determined using an analysis instrument. The physisorbed silane migrated into the resin matrix and influenced the mechanical properties and interlaminar fracture of the laminate specimen. The amount of unsaturated polyester resin blended with a silane coupling agent was measured using dynamic mechanical spectroscopy, and a DCB specimen for mechanical properties and fracture toughness.     

Toughness properties of a three-dimensional carbon-epoxy composite

The three-dimensional (3D) orthogonal interlocked fabric contains through-the-thickness rein-forcement in order to enhance the interlaminar fracture toughness of the composite. The interlaminar fracture toughness of a carbon-epoxy orthogonal interlocked fabric composite was experimentally determined by use of the recently developed tabbed double cantilever beam specimen. The data reduction methods applicable to these tests and materials and the interpretation of the results were discussed. The results of critical strain energy release rate,G _Ic, were compared to those of a two-dimensional (2D) laminate having the same in-plane structure. The energy-dissipating crack propagation processes were described. The in-plane fracture toughness of the 3D fabric was experimentally measured and compared to that of the 2D laminate. The through-the-thickness fibres were found to create a ten-fold increase in interlaminar toughness, and a 25% improvement in the in-plane fracture toughness.     

Experimental investigation of mixed-mode fracture behaviour of woven laminated composite

In this paper, the mixed-mode interlaminar fracture behaviour of woven carbon-epoxy composite was investigated based on experimental and numerical analyses. A modified version of Arcan specimen was employed to conduct a mixed mode fracture test using a special loading device. A full range of mixed-mode loading conditions including pure mode-I and pure mode-II loading were created and tested. This test method has a simple procedure, clamping/unclamping the specimens are easy to achieve and only one type of specimen is required to generate all loading conditions. Also, finite element analysis was carried out for different loading conditions in order to determine correction factors needed for fracture toughness calculations. Interlaminar fracture toughness was determined experimentally with the modified version of the Arcan specimen under different mixed-mode loading conditions. Results indicated that the interlaminar cracked specimen is tougher in shear loading condition and weaker in tensile loading condition. Response of woven carbon-epoxy composite was also investigated through several criteria and the best criterion was selected. The interlaminar fracture surfaces of the carbon-epoxy composite under different mixed-mode loading conditions are examined by scanning electron microscopy (SEM).     

Experimental and Numerical Investigation of Mixed-Mode Interlaminar Fracture of Carbon-Polyester Laminated Woven Composite by Using Arcan Set-up

Composite materials are widely used in marine, aerospace and automobile industries. These materials are often subjected to defects and damages from both in-service and manufacturing process. Delamination is the most important of these defects. This paper reports investigation of mixed-mode fracture toughness in carbon–polyester composite by using numerical and experimental methods. All tests were performed by Arcan set-up. By changing the loading angle, α, from 0° to 90° at 15° intervals, mode-I, mixed-mode and mode-II fracture data were obtained. Correction factors for various conditions were obtained by using ABAQUS software. Effects of the crack length and the loading angle on fracture were also studied. The interaction j-integral method was used to separate the mixed–mode stress intensity factors at the crack tip under different loading conditions. As the result, it can be seen that the shearing mode interlaminar fracture toughness is larger than the opening mode interlaminar fracture toughness. This means that interlaminar cracked specimen is tougher in shear loading condition and weaker in tensile loading condition.     

Toughening and self-healing of epoxy matrix laminates using mendable polymer stitching

This paper presents an experimental study into a new type of stitched fibre–polymer laminate that combines high interlaminar toughness with self-healing repair of delamination damage. Poly(ethylene-co-methacrylic acid) (EMAA) filaments were stitched into carbon fibre/epoxy laminate to create a three-dimensional self-healing fibre system that also provides high fracture toughness. Double cantilever beam testing revealed that the stitched EMAA fibres increased the mode I interlaminar fracture toughness (by ∼120%) of the laminate, and this reduced the amount of delamination damage that must subsequently be repaired by the self-healing stitches. The 3D stitched network was effective in delivering self-healing EMAA material extracted from the stitches into the damaged region, and this resulted in high recovery in the delamination fracture toughness (∼150% compared to the original material). The new self-healing stitching method provides high toughness which resists delamination growth while also having the functionality to repeatedly repair multiple layers of damage in epoxy matrix laminates.