颗粒增强复合材料中的界面层

本文对氧化铝(Al₂O₃)、氟化钙(CaF₂)和玻璃微珠颗粒填充环氧基(E51环氧—胺固化体系)复合材料的密度和动态力学性能进行了研究。结果发现由于颗粒填料表面和环氧基体的相互作用,从填料表面开始形成了一层致密的聚合物界面层。它的性质与本体树脂有明显的差别。把填充复合材料看成由填料、界面层和树脂本体组成的三元体系,从“临界填料含量”概念出发,求得了界面层的密度,界面层的厚度和界面层的体积分数。     

界面层对复合材料强度的影响

本文对氧化铝(Al₂O₃),氟化钙(CaF₂)和玻璃微珠颗粒填充环氧基(双酚A类E-51-胺固化体系)复合材料的断裂和抗拉强度进行了研究,并考察了复合材科抗拉强度与填料体积分数的关系。复合材料中,从填料固体表面开始形成了有一定厚度的密界面层。界面层的强度性质对复合材料的强度有重要作用。得到了三种复合材料界面层的抗拉强度。并提出了颗粒填充复合材料抗拉强度的计算公式:σ_o=〔σ_mS_m+σ₁S₁a₁〕η计算结果和实验数据有较好的一致性。     

CF/PEEK复合材料界面层结构与性能关系研究

本文根据聚醚醚酮(PEEK)在碳纤维表面形式的横晶层的结构特征分析,建立了CF/FEEK复合材料界面层微观力学性能的理论方程,计算了界面层的杨氏模量.通过超声浸渍法测量复合材料的力学性能验证了计算结果,证明所进行的分析合理.计算结果表明,PEEK界面横晶层在垂直于纤维方向的杨氏模量E_r随PEEK结晶度的增大,或随横晶中PEEK晶片长度的增大而增大,并随晶片厚度的增大而减小.该界面层的上述模量值始终高于界面层附近球晶的模量值E_s,两者之间的比值E_T/E_s;依赖于横晶及球晶中的晶片长度b、厚度c和宽度a.由于界面层的模量高于非界面层的模量,当复合材料中纤维表面形成横晶时,复合材料将有较高的刚性.     

微米和纳米SiO2改性聚四氟乙烯的摩擦磨损性能

使用超细及纳米SiO₂颗粒填充改性聚四氟乙烯塑料。测量其摩擦系数、磨损系数、结晶度,得到了填加量与复合材料摩擦系数、磨损系数和结晶度的关系曲线,并使用扫描电镜(SEM)对其表面形貌进行了分析。结果表明,无论微米或纳米SiO₂、表面处理后的纳米SiO₂,均使PTFE的摩擦系数有所提高,而耐磨损性能也有大幅度的提高。填充量小于6%时,填加未经偶联剂处理的纳米SiO₂的SiO₂/PTFE复合材料的磨损率降低98.5%;填充量大于6%以后,磨损率趋于稳定;填充量为6%时,摩擦系数仅从未加填料时的0.1提高为0.12。而偶联剂表面处理的纳米SiO₂复合材料的摩擦系数提高幅度最小。     

片状Al2O3对Al2O3/FEP复合材料热导率的影响

通过混炼工艺制备了片状Al₂O₃填充聚全氟乙丙烯(FEP)复合材料，以颗粒状Al₂O₃为对比样品，研究了片状Al₂O₃形状和尺寸对 FEP基复合材料热导率的影响，利用SEM观察了FEP基复合材料的微观形貌。结果表明：在低填充量下，Al₂O₃颗粒在FEP基体中呈“海岛”状分布，没有形成连续的导热网链，但其热导率明显提高；复合材料拉伸强度与断裂伸长率随Al₂O₃含量的增加而减小；低填充量时复合材料热导率的提高主要来自Al₂O₃的微细片状结构，这种微细片状结构一方面提高了有效导热路径，另一方面增加了颗粒与基体之间接触面积，因此有利于热导率的提高。     

纤维增强复合材料横向弹性常数

本文提出了一个计算单向纤维增强复合材料横向弹性模量和泊松系数的边界元计算模型.泊松系数ν₁₂、ν₃₂、ν₁₃和ν₂₃的计算结果与实验结果吻合得很好.碳纤维增强复合材料横向模量E₂和E₃的计算值也和实验结果完全吻合,而玻璃纤维/环氧横向模量E₂、E₃的计算值却比实测值偏小约10%～25%.予计这是由于本文计算模型未考虑界面层的性能,它对材料的宏观性能产生了较明显的影响.     

单层和三层结构的PVDF基复合材料介电与储能特性

通过水热合成法制备CaCu₃Ti₄O₁₂球型颗粒填料,以PVDF为基底,采用溶液逐层涂覆法制备单层和三层结构的PVDF基复合材料。利用X-射线衍射仪和扫描电镜表征材料的微观组织结构,LRC测试仪和铁电综合测试工作站测试其电学性能,研究低填充浓度和多层结构对PVDF基复合材料微观结构、介电特性、极化强度、耐电压特性和储能特性的影响规律。结果表明,CaCu₃Ti₄O₁₂填料的尺寸约为200 nm,增加其填充浓度,可以提高单层PVDF/CaCu₃Ti₄O₁₂复合材料的介电特性与极化强度；在3.0vol.%填充量下,复合材料达到最大的介电常数13.2、介电损耗0.074和电位移极化强度4.04 μC/cm²；而在0.5vol.%的超低填充量下,复合材料达到最大的释放能量密度3.51 J/cm³。三层结构的PVDF基复合材料体系中,在上下层复合材料的高介电极化特性与中间层材料的击穿阻挡特性的协同作用下,获得了综合储能特性优化的PVDF基复合材料,使其在300 kV/mm的低电场强度下,达到最高的释放能量密度4.36 J/cm³。     

不同纳米材料与石墨混合填充PTFE复合材料摩擦磨损性能

利用MM-200型磨损试验机考察了载荷对纳米SiO₂、TiO₂、Al₂O₃与石墨混合填充PTFE复合材料摩擦磨损性能的影响,采用扫描电子显微镜观察分析磨损表面形貌及磨损机理。结果表明,纳米材料及其与石墨混合都可以不同程度地提高PTFE的耐磨性,而它们对PTFE耐磨性的提高程度各不相同,其中以纳米SiO₂-石墨填充PTFE复合材料的磨损质量损失最小,纳米Al₂O₃-石墨填充PTFE复合材料的磨损质量损失较大;填充PTFE复合材料同钢对磨时的摩擦系数表现出不同的性能,纳米SiO₂-石墨填充PTFE的摩擦系数与纯PTFE相差不大。     

SiC颗粒增强铝合金基梯度复合材料弯曲力学性能及其评价

采用三点弯曲法,对SiC颗粒增强铝合金基梯度复合材料的弯曲力学性能进行了研究,提出了梯度复合材料抗弯强度比R₁和R₂两个新的力学性能评价指标。结果表明:金属基梯度复合材料(MMGC)的弯曲力学性能与其基本组分力学性能的关系不符合ROM法则,材料的抗弯强度和最大挠度强烈地受到SiC颗粒梯度分布方式与弯曲方向的影响;当基体处于受拉侧,高SiC含量组分处于受压侧时,MMGC能充分发挥其性能优势;MMGC在受梯度应力作用下的力学性能优势和其方向性特征受到材料状态、材料宏观不均匀性和微观连续性等因素的影响;MMGC的抗弯强度比R₁反映了这类材料的性能优势,而抗弯强度比R₂则反映了材料的方向性能特征。     

微纳米SiO2/PP复合材料增强增韧的实验研究

为了研究无机刚性颗粒对通用塑料聚丙烯 (PP) 的力学性能的影响, 采用熔融共混方法制备了经硅烷偶联剂A-151处理的SiO₂/PP 复合材料, 并通过其缺口冲击、 拉伸、 弯曲试验和冲击断面的形貌观察, 分析研究了微纳米SiO₂颗粒大小、 填充量、 表面改性以及不同颗粒大小SiO₂混合物对PP复合材料增韧、 增强效果的影响。实验结果表明: 纳米SiO₂的加入可以同时改善其韧性、 刚性和强度; 填充量相同, 颗粒越细, SiO₂/PP复合材料的力学性能越好。SiO₂经改性后填充到PP基体中, 明显改善了颗粒在基体中的分散性及基体与颗粒之间界面结合性能, 使复合材料的综合力学性能得到提高。不同颗粒大小的SiO₂混合后填充到PP基体中, 混合SiO₂的协同效应使复合材料拉伸、 弯曲性能进一步提高, 对PP基体具有更好的增强效果, 但其冲击性能下降。     

玻璃微珠改性聚丙烯的熔融、结晶与形态

采用玻璃微珠改性聚丙烯并对复合材料的熔融、结晶行为与形态结构进行了研究.结果表明,玻璃微珠一定程度上起到了异相成核作用,有利于PP的结晶,提高了结晶速率.与单螺杆挤出复合材料相比,双螺杆挤出复合材料的塑化效果较好,玻璃微珠与基体的粘接情况也较好.冲击断面呈现典型的脆性断裂特征,玻璃微珠大量蓄积在冲击断面.而拉伸破坏断面表现出显著的塑性变形,形成大量带状或纤维状形变区域,材料最终的拉伸性能则取决于玻璃微珠与基体粘接和脱粘的综合效果.     

Tensile behaviour and fracture toughness of EPDM filled with untreated and silane-treated glass beads

The Essential Work of Fracture (EWF) theory has been applied to study the fracture behaviour of untreated and silane-treated glass bead-filled EPDM composites. The experimental values of both Young's modulus and tensile strength have been compared with those predicted by the main theoretical and semiempirical models, and the influence of the composite processing temperature on the tensile properties has been studied, noticing a marked drop of stiffness and strength from a processing temperature of 200 °C. A good adhesion between EPDM matrix and glass beads was achieved with the silane Z-6032, resulting in higher tensile strength, and it has been observed that glass bead presence induces plasticity in the EPDM matrix. No differences of the specific essential work of fracture were found in the three filled samples, although results show that the higher adhesion degree between matrix and particles, the higher value of the specific plastic work of fracture, and also the higher final instability in crack propagation.     

PP/PET原位成纤复合材料的增强效应

用挤出-拉伸-注塑法制得了PP/PET原位成纤增强复合材料,以不拉伸的普通共混材料作对照,研究了PET质量含量(C_m)对PET成纤性和材料拉伸强度(σ_t)及模量(E)的影响及其作用机制。结果表明,C_m由0增至20%时,PET纤维数量增多,纤维直径及其分散性以C_m=15%为界先减少后增大;材料的σ_t、E在C_m=15%时有最大值,分别比纯PP提高约20%和70%。熔体拉伸时分散相液滴的聚结-形变成纤对PET相形态随C_m的变化起关键作用,分散相对基体增强效应与两相界面缺陷效应的相互竞争,纤维对基体增刚作用受纤维数量和细度的双重控制,分别是决定材料σ_t~C_m、E~C_m关系的支配因素。     

The fracture of particulate-filled epoxide resins

The double torsion test technique was used to investigate the fracture properties of two commercial epoxide resins filled with glass beads. The influence of varying the volume fraction of glass, the mean particle size and the pre-treatment of the glass surface on the stress intensity factor have been determined. A correlation has been found between the compressive yield strength and the stability of fracture in these composites, similar to that found for unfilled epoxide resins.     

The role of poly(ethylene terephthalate-co-isophthalate) as interfacial agent in polypropylene–matrix composites

The effect of modifying the particle/matrix interfacial region on the morphology and tensile behaviour of glass bead-filled polypropylene (PP) composites was studied. The interface modification was promoted by blending PP with a small concentration (5% by weight) of poly(ethylene terephthalate-co-isophthalate) (co-PET). Ten different PP/co-PET/glass beads ternary composites were prepared, characterized and compared with the homologous PP/glass beads binary ones. Maleic anhydride-grafted PP was added as a compatibilizing agent for PP and co-PET in some of the studied formulations, and its effect studied. Furthermore, four different silane-treated glass beads were used to prepare the composites (50 wt.%). Results showed that three different interfaces, corresponding to three different levels (low, middle and high) of particle/matrix adhesion, could be obtained in these composites by varying the matrix composition and the silane coupling agent on the glass bead surface, which resulted in a wide range of tensile properties, from ductile composites with low tensile strength and high elongation to brittle ones with high tensile strength. It was found that co-PET embeds glass bead surface independently of the silane coupling agent employed. Finally, the adhesion degree differences between the different composite phases seemed to be the main cause to explain the differences found in the sensitivity of the composite tensile characteristics to the strain rate.     

Fracture toughness of glass microsphere-filled polypropylene and polypropylene/poly (ethylene terephthalate-co-isophthalate) blend-matrix composites

The fracture behaviour of glass microsphere-filled polypropylene/poly(ethylene terephthalate-co-isophthalate) blend-matrix composites was investigated in comparison with that of the glass microsphere-filled PP composites. Depending on the deformability displayed by the composite, it was carried out through the linear-elastic fracture mechanics or by applying the J-integral concept. The matrix ductility was regulated in the composite through the glass bead surface treatment applied with different silane-coupling agents, as well as with the addition of maleated PP as polymer compatibilizer. Whereas all the composites failed in a brittle manner at moderate impact speed, quasi-brittle fracture behaviour was only observed at low strain rate in composites having high and medium interfacial adhesion level. Results showed that composites containing both aminosilane-treated glass microspheres and maleated PP showed the highest values of fracture toughness. In composites with low adhesion level between matrix and glass beads, the critical J-integral value diminished due to the presence of PET.     

The effect of low energy impact on the tensile strength of coated and uncoated glass particulate composites

The residual tensile strength of glass filled particulate composites has been determined after low energy impact for various energy values. The material systems constructed for the needs of this research consisted of epoxy resin filled with glass beads. The glass beads were either uncoated or alternatively coated with a reactive silane based bonding agent. Specimens with various filler volume fractions were available. The effect of silane coating as well as the filler volume fraction was analytically discussed. Finally, a model developed in previous work for continuous fibre reinforced composite laminates was adopted to describe the residual tensile strength after impact. In most of the cases the predicted curves fit the experimental results very well.     

Coated glass beads epoxy composites: influence of the interlayer thickness on pre-yielding and fracture properties

An elastomeric adduct based on a liquid rubber, an epoxy prepolymer and a liquid diamine has been prepared and deposited around glass beads reinforcing an epoxy matrix. The pre-yielding and fracture properties of such composites are studied and compared with those of untreated glass beads based composites. A linear dependence ofK _lc (critical stress intensity factor) versus volume fraction is obtained for untreated glass beads composites, whereas a maximum is reached at 20% volume fraction of filler for those with coated glass beads. Introduction of an elastomeric layer improves fracture toughness and the influence of interlayer thickness is studied. A maximum forK _lc is found for (e/r)=3% in connection with a strong decrease ofK/M ratio (work-hardening rate compression modulus) determined in the pre-yielding stage. The toughening mechanism is discussed primarily in terms of crack pinning and plastic deformation.     

Investigation of debonding processes in particle-filled polymer materials by acoustic emission: Part I Acoustic emission and debonding stress

Debonding processes in model composites under tensile deformation were investigated by acoustic emission analysis. The composites were prepared from epoxy and polyethylene matrix filled with glass beads of various sizes and with different coatings. The detected acoustic emission signals were identified as debonding processes at the filler–matrix interphase, and are discussed as a rupture process on the basis of the Weibull probability distribution function. For the model composites, the effect of the filler size is discussed using a theory based on Griffith’s criterion of rupture. This revised version was published online in November 2006 with corrections to the Cover Date.