碳纳米管加入方式对碳纤维/环氧树脂复合材料层间性能的影响

针对碳纤维/环氧树脂预浸料,对比了直接在树脂中加入碳纳米管(CNTs)后制备预浸料以及将CNTs喷涂在预浸料表面2种CNTs加入方式对CNTs-碳纤维/环氧树脂复合材料层合板I型与II型层间断裂韧性及层间剪切强度的影响。通过对树脂黏度、固化反应以及玻璃化转变温度的考察,分析了CNTs含量对树脂性能的影响,考察了添加方法对CNTs长度与形态的影响。分析了2种CNTs加入方式对CNTs-碳纤维/环氧树脂层合板断裂韧性及层间剪切强度的改善效果与作用规律。结果表明:CNTs的加入使树脂的黏度提高,固化反应程度下降;2种分散方法对CNTs的长度与形态无明显影响;直接在树脂中加入CNTs对CNTs-碳纤维/环氧树脂复合材料I型与II型层间断裂韧性的提高效果低于在碳纤维/环氧树脂预浸料表面喷涂CNTs的方式,后者的CNTs利用率较高;由于CNTs团聚及对树脂固化反应的影响,CNTs含量过高会使得其对CNTs-碳纤维/环氧树脂层合板的增韧效果下降。     

Bisphenol A based polyester binder as an effective interlaminar toughener

Bisphenol A based thermoplastic polyesters are commonly used in the industry as binders, or tackifiers, to produce cost-saving preforms in Liquid Composite Moulding processes such as Vacuum Assisted Resin Transfer Moulding (VARTM). However, it is often reported that the presence of these polyesters has a detrimental effect on the mechanical properties of the resulting composite laminates. In contrast, this study shows that interlaminar toughness can be increased without negatively affecting other properties by coating the reinforcing plies with a bisphenol A based thermoplastic polyester if some precautions are taken in mind.The polyester was added to an epoxy resin in order to study its effect on the thermophysical properties and fracture toughness of the bulk epoxy. The polyester molecules acted as a plasticizer for the epoxy resin when the polyester was added in low amounts. This increased the bulk fracture toughness of the epoxy resin by 30%. Polyester modified glass/epoxy laminates were produced and tested for Mode I interlaminar fracture toughness and flexural properties. The increased toughness of the epoxy matrix led to a 60% increased Mode I interlaminar fracture toughness of the laminates, without negatively affecting flexural stiffness and strength of the laminates.     

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,但其面内拉伸性能、面内压缩性能和疲劳性能稍有下降。文中从Z-pin增强复合材料的性能特点出发,针对其层间韧性、抗冲击性、面内力学性能和疲劳性能进行了综述。指出Z-pin在Ⅰ型断裂模式、Ⅱ型断裂模式和混合断裂模式下的增韧机制;总结了Z-pin在提高复合材料低能量冲击后剩余压缩性能方面的作用;介绍了Z-pin增强复合材料在平面拉伸和压缩载荷下的破坏模式,从纤维损伤角度归纳了其面内拉伸及压缩性能下降的原因;总结了Z-pin增强复合材料在循环压缩载荷下的破坏模式。最后从材料体系和工艺优化两方面出发,为降低纤维损伤提供了建议。对Z-pin增强技术的进一步应用进行了展望。     

Interlaminar fracture of commingled-fabric-based GF/PET composites

A 45:55 weight% mixture of commingled glass/polyethylene terephthalate (PET) fabric was selected to study the relationships between material microstructure, Mode I and Mode II interlaminar fracture toughnesses and failure mechanisms. Composite laminates subjected to different cooling histories were manufactured within a steel mould using a laboratory heat press. Mode I and Mode II interlaminar fracture tests were performed using double cantilever beam and end-notched flexure specimens. PET matrix morphology appeared to be sensitive to the thermal histories, although this occurred on a subspherulitic scale (in contrast to observations made with polypropylene-based composites). The spherulitic textures were generally very fine and no evidence of interspherulitic fracture paths could be identified. When the composites were subjected to low cooling rates or an isothermal crystallization process, many small matrix cracks developed between fibres within the reinforcing bundles. The lower the cooling rate, the higher the density of matrix cracks per unit volume of material. The interlaminar fracture toughness in the laminates with slow cooling rates was much lower than in the case where a quasi-quenched condition was applied.     

Enhancement of mechanical performance of epoxy/carbon fiber laminate composites using single-walled carbon nanotubes

Carbon nanotubes (CNT) in their various forms have great potential for use in the development of multifunctional multiscale laminated composites due to their unique geometry and properties. Recent advancements in the development of CNT hierarchical composites have mostly focused on multi-walled carbon nanotubes (MWCNT). In this work, single-walled carbon nanotubes (SWCNT) were used to develop nano-modified carbon fiber/epoxy laminates. A functionalization technique based on reduced SWCNT was employed to improve dispersion and epoxy resin-nanotube interaction. A commercial prepregging unit was then used to impregnate unidirectional carbon fiber tape with a modified epoxy system containing 0.1 wt% functionalized SWCNT. Impact and compression-after-impact (CAI) tests, Mode I interlaminar fracture toughness and Mode II interlaminar fracture toughness tests were performed on laminates with and without SWCNT. It was found that incorporation of 0.1 wt% of SWCNT resulted in a 5% reduction of the area of impact damage, a 3.5% increase in CAI strength, a 13% increase in Mode I fracture toughness, and 28% increase in Mode II interlaminar fracture toughness. A comparison between the results of this work and literature results on MWCNT-modified laminated composites suggests that SWCNT, at similar loadings, are more effective in enhancing the mechanical performance of traditional laminated composites.     

Modelling off-axis ply matrix cracking in continuous fibre-reinforced polymer matrix composite laminates

The fracture process of composite laminates subjected to static or fatigue tensile loading involves sequential accumulation of intra- and interlaminar damage, in the form of transverse cracking, splitting and delamination, prior to catastrophic failure. Matrix cracking parallel to the fibres in the off-axis plies is the first damage mode observed. Since a damaged lamina within the laminate retains certain amount of its load-carrying capacity, it is important to predict accurately the stiffness properties of the laminate as a function of damage as well as progression of damage with the strain state. In this paper, theoretical modelling of matrix cracking in the off-axis plies of unbalanced symmetric composite laminates subjected to in-plane tensile loading is presented and discussed. A 2-D shear-lag analysis is used to determine ply stresses in a representative segment and the equivalent laminate concept is applied to derive expressions for Mode I, Mode II and the total strain energy release rate associated with off-axis ply cracking. Dependence of the degraded stiffness properties and strain energy release rates on the crack density and ply orientation angle is examined for glass/epoxy laminates. Suitability of a mixed mode fracture criterion to predict the cracking onset strain is also discussed.     

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.     

湿热环境对碳纤维增强树脂基复合材料力学性能的影响及其损伤机理

采用加速吸湿法研究经3种湿热环境(湿度为85%RH,温度分别为25,70,85℃)处理后CFRP层合板的吸湿特性,对吸湿前后的碳纤维增强树脂基复合材料(CFRP)层合板分别进行拉伸、压缩、剪切实验,研究其力学性能变化规律,利用扫描电镜和红外光谱分析湿热环境中CFRP层板的损伤机理,最后采用最小二乘法拟合提出湿热环境下CFRP层合板力学性能的预测公式。结果表明:CFRP层合板的吸湿初期特性符合Fick定律;相同湿度下环境温度越高,CFRP的吸湿速率和平衡吸湿率越大,达到吸湿平衡所需时的间越长;3种湿热环境处理后的CFRP层板的90°拉伸和剪切力学性能下降最明显;经湿热环境处理后水分子通过氢键与环氧树脂发生缔合,但CFRP层合板中的各组分未发生化学结构变化;拟合建立的不同湿热条件下力学性能衰退公式与实验结果基本一致。     

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.     

不同湿热条件下碳纤维/环氧复合材料湿热性能实验研究

对比研究了环氧5228A树脂及碳纤维/环氧5228A树脂复合材料层合板在3种湿热环境(水煮、70℃水浸,70℃85%相对湿度)下的湿热性能,考察了湿热条件对复合材料层间剪切性能的影响规律,并从吸湿特性、物理化学特性、树脂力学性能、湿应力等方面分析了不同湿热环境下复合材料性能衰减的机制。研究表明,碳纤维/高温固化环氧树脂复合材料层间剪切性能主要是由吸湿率决定,相同吸湿率不同湿热条件下性能的下降幅度基本相同;3种湿热条件下该树脂及其复合材料未发生化学反应、微裂纹等不可逆变化,复合材料层合板湿热老化机制主要是吸入水分后基体增塑和树脂、纤维湿应变不一致导致的湿应力对复合材料性能的负面作用。     

阳极氧化工艺对纤维-铝合金层板力学性能的影响

通过改变铝合金表面阳极氧化工艺参数, 研究了阳极氧化电压和时间对玻璃纤维-铝合金(GLARE)层板抗拉强度和层间剪切强度的影响。通过SEM观察了铝合金表面Al₂O₃多孔膜和层板断面形貌, 分析了铝合金/树脂胶接界面对层板力学性能的影响。结果表明, 阳极氧化电压为20 V时, GLARE层板抗拉强度和层间剪切强度随着阳极氧化时间延长而增大, 在20 min时出现最大值, 继续延长阳极氧化时间, 层板强度随之下降; 阳极氧化时间为20 min时, GLARE层板抗拉强度和层间剪切强度随着阳极氧化电压增大而增大, 在20 V时出现最大值, 继续增大电压, 强度随之下降。     

Analysis of mode II interlaminar fracture and damage behavior in end notched flexure testing of GFRP woven laminates at cryogenic temperatures

Summary Interlaminar fracture and damage behavior of glass fiber reinforced polymer (GFRP) woven laminates at cryogenic temperatures is investigated for end notched flexure (ENF) pure Mode II configuration. The corrected beam theory (CBT) and finite element analysis (FEA) are used to calculate the Mode II interlaminar fracture toughness of ENF 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 specimen and to examine the effect of damage on the Mode II energy release rate. The numerical results show that damage occurs at the matrix and causes a decrease in the energy release rate. The technique presented can be efficiently used for the characterization of cryogenic Mode II interlaminar fracture and damage behavior of woven laminate ENF specimens.     

模压工艺对玻璃纤维增强聚丙烯复合材料层合板力学性能的影响

利用热模压工艺制备玻璃纤维增强聚丙烯（GF/PP）复合材料层合板,通过差示扫描量热（DSC）法试验分析,确定相变参数,运用ANSYS有限元分析,将复合材料热力学参数与温度的非线性关系定义到材料特性中,研究模压成型过程中温度场变化情况,为模压成型工艺制度的确立提供理论指导和依据。以压缩强度、层间剪切强度和冲击韧性作为力学性能评价指标,采用响应曲面法探讨和分析制备工艺对GF/PP复合材料层合板力学性能的影响,得到最优模压工艺制备参数,获得最高复合材料层合板力学性能,为GF/PP复合材料自动铺放奠定铺放工艺基础。试验结果表明:模压加热工艺参数对复合材料层合板力学性能的影响度（从大到小）依次为:热压温度、热压时间、热压压力。较优的模压加热工艺参数为:热压温度228℃、热压时间6 min、热压压力1.1 MPa,在此工艺条件下制备的GF/PP复合材料层合板,层间剪切强度为31.12 MPa,压缩强度为100.96 MPa,冲击韧性为2.27 kJ/cm2。      

DCB test simulation of stitched CFRP laminates using interlaminar tension test results

A simulation model for the delamination extension of stitched CFRP laminates and 3-D orthogonal interlocked fabric composites (3-D OIFC) has been developed using a 2-D finite element method incorporating interlaminar tension test results to simulate the experimental results of their DCB tests. The mechanical properties of through-the-thickness fiber were determined from the results of interlaminar tension tests in which the specimen included only one through-the-thickness yarn. The fracture phenomena around the through-the-thickness thread, such as debonding from the in-plane layer, slack absorption, fiber bridging, and the pull-out of broken threads from the in-plane layers, are also introduced into the FEM model. The present FEM simulation results were compared to DCB test results for certain stitched laminates and a 3-D OIFC, and the simulation results showed good agreement with the experimental results of DCB tests, including the load–displacement curve and Mode I strain energy release rate (GI). While it was difficult to estimate GI accurately when the DCB test specimen included different types of z-fiber fracture modes, the present model of FEM analysis can simulate the experimental results of DCB tests of stitched laminates and 3-D OIFC. It is suggested that the GI of CFRP with arbitrary z-fiber densities can be predicted by using this FEM analysis model together with interlaminar tension test results.     

CF/EP composite laminates with carbon black and copper chloride for improved electrical conductivity and interlaminar fracture toughness

An experimental study was conducted to improve the electrical conductivity of continuous carbon fibre/epoxy (CF/EP) composite laminate, with simultaneous improvement in mechanical performance, by incorporating nano-scale carbon black (CB) particles and copper chloride (CC) electrolyte into the epoxy matrix. CF/EP laminates of 65 vol.% of carbon fibres were manufactured using a vacuum-assisted resin infusion (VARI) technique. The effects of CB and the synergy of CB/CC on electrical resistivity, tensile strength and elastic modulus and fracture toughness (K_IC) of the epoxy matrix were experimentally characterised, as well as the transverse tensile modulus and strength, Mode I and Mode II interlaminar fracture toughness of the CF/EP laminates. The results showed that the addition of up to 3.0 wt.% CB in the epoxy matrix, with the assistance of CC, noticeably improved the electrical conductivity of the epoxy and the CF/EP laminates, with mechanical performance also enhanced to a certain extent.     

基于图像处理的碳纤维增强树脂基复合材料固化压力-缺陷-力学性能建模与评估

利用热压罐成型工艺制备了不同固化压力条件下的碳纤维增强树脂基复合材料层合板,分析了超声相控阵C扫描图像与微观缺陷的对应关系,研究了固化压力、孔隙缺陷及力学性能之间的关联规律。结果表明：利用超声C扫描图像差异能够表征孔隙等缺陷含量,在本实验条件下,固化压力由0 MPa提高到0.6 MPa,复合材料孔隙率降低96.7%,拉伸强度（TS）和层间剪切强度（ILSS）分别提高56.1%和68.8%。在此基础上,对不同固化压力条件下制备的复合材料层合板的超声相控阵C扫描图像进行图像处理并定义成型质量指数,实现了基于C扫描图像对孔隙缺陷的定量表征。最后,通过对孔隙缺陷检测、力学性能测试及图像定量化评价结果进行数学拟合,建立了基于图像处理的固化压力-缺陷-力学性能之间的数学关联模型（CPDMP模型）,并给出了成型质量指数阈值为81%,及可接受的孔隙率应不高于1.1%,相应的固化压力应不低于0.35 MPa。     

湿热环境下复合材料层板拉-压性能

通过对碳纤维环氧复合材料试样进行不同湿热环境下的拉伸和压缩实验,分析其吸湿特性、拉压力学性能、破坏后断口形貌以及动态力学性能,探讨湿热对该复合材料的拉伸和压缩性能的影响。结果表明:碳纤维环氧复合材料的吸湿过程满足Fick定律,饱和吸湿率约为0.86%。吸湿后材料表面变得光滑,有少量纤维拔出和树脂破坏发生,但吸湿后没有发生化学反应和新物质生成。吸湿后在130℃下,复合材料的拉伸性能保持率为96%,而压缩性能保持率仅为69%。吸湿后玻璃化转变温度比干态时下降了33℃。     

Effects of hydrothermal aging on glass–fiber/polyetherimide (PEI) composites

The moisture absorption behavior and the influence of moisture on thermal and mechanical properties of glass–fiber/polyetherimide (PEI) laminates have been investigated. The laminates were exposed to hydrothermal aging at two different temperatures and high moisture rates. The properties of as-received and hydrothermally aged samples were compared. The hydrothermally aged laminates contained a large amount of moisture which caused decrease in the glass transition temperature and deterioration in mechanical properties (interlaminar shear strength, flexural modulus, bearing strength, etc.). Fractographic analysis revealed interfacial debonding as the dominant failure mechanism, indicating a strong influence of water degradation on fracture toughness results. Alterations in visco-elastic properties of glass/PEI composite which was exposed to hydrothermal aging were analyzed with the dynamic mechanical thermal analysis (DMTA) method. DMTA tests give evidence of plasticization of the PEI matrix.     

Fracture and fatigue performance of textile commingled yarn composites

The response to mechanical loads of unidirectional commingled warp knitted and woven glass fibre reinforced polyethylene terephthalate laminates has been characterized. The mechanical properties of the two materials were determined under tension, in-plane shear and flexure. The flexural fatigue properties were determined for the woven laminates by means of three-point bending tests with a loading ratio of R=0.1 at stress levels of 50–90% of the ultimate static strength. The Mode I, Mode II and mixed mode (Mode I : II ratios 4 : 1, 1 : 1 and 1 : 4) interlaminar fracture toughnesses of the laminates were determined by means of the double cantilever beam and mixed mode bending tests, respectively. The main fractographic features, as determined by a scanning electron microscopy examination, of the Mode I dominated failures were a brittle matrix failure and larger amounts of fibre pull-out. As the Mode II loading component increased, the amount of fibre pull-out was reduced and the features of the matrix appeared to be more sheared. Cusps were found on the fracture surfaces of specimens tested in pure Mode II and mixed mode I : II=1 : 4. Cusps are normally not found in thermoplastic matrix composites. © 1998 Kluwer Academic Publishers     

Monitoring of delamination onset and growth during Mode I and Mode II interlaminar fracture tests using guided waves

A delamination monitoring method was proposed to characterize Mode I and Mode II delamination onset in carbon fiber/epoxy (CF/EP) composite laminates through interrogation of guided waves activated and captured using piezoelectric actuators and sensors in a pitch–catch configuration. Mode I and Mode II interlaminar fracture tests were conducted using double cantilever beam (DCB) and end notch flexure (ENF) specimens to evaluate the proposed method. The changes in wave propagation velocity and wave magnitude (or attenuation), and the degree of waveform similarity between excitation and response signals, were calculated as delamination-sensitive wave parameters and plotted versus displacement recorded using a materials testing system. The kink points determined from wave parameter–displacement curves agreed well with the deviation from linearity (NL), visual observation (VIS) and maximum load (Max) points, which are often used in conventional methods for determining interlaminar fracture toughness. The propagation characteristics of the A₀ wave mode in a low frequency range were demonstrated to have high sensitivity to Mode I and in particular Mode II delamination onset in CF/EP composite laminates. It was concluded that the guided waves propagating in the DCB and ENF specimens were capable of determining Mode I and Mode II interlaminar fracture toughness, complementing current practices based on visual inspection or trivial interrogation using load–displacement curve alone.