碳纤维增强复合材料层压板的热膨胀系数测量及理论计算方法

随着复合材料在飞机结构中的应用增加,复合材料与金属混杂结构中复合材料与金属材料的热膨胀系数不匹配带来的热应力问题越来越不容忽视。为了分析结构中的热应力,材料的热膨胀系数必不可少,而复合材料热膨胀系数的各向异性、铺层依赖性以及纤维方向的低热膨胀率给其热膨胀系数的测量及层压板的热膨胀系数计算带来不便。依据ASTM E831标准和ASTM E289标准,分别采用热机械分析和剪切散斑干涉两种方法,测量了不同铺层T800级碳纤维增强复合材料层压板的热膨胀系数。研究了各种铺层层压板的热膨胀系数规律,给出了复合材料层压板面内热膨胀系数的理论计算公式。此研究结果有利于飞机结构设计阶段有限元分析中复合材料层压板热膨胀系数的快速计算。     

TG—CVIC／C复合材料裂纹缺陷成因分析

针对热梯度化学气相渗透工艺制备的C/C复合材料样件中出现的裂纹缺陷,采用偏光显微镜及扫描电子显微镜对有裂纹的C/C复合材料样件的微观结构进行了观察.分析了C/C复合材料样件中裂纹的形成原因.结果表明:较大的温差导致的热应力及强界面结合是造成C/C复合材料出现裂纹的主要原因.     

混杂纤维复合材料热性能特异性研究

本文对碳纤维、玻璃纤维混杂纤维复合材料进行了热膨胀系数计算，计算结果表明，环向碳纤维的加入可以使碳纤维增强复合材料的纵向热膨胀系数趋于正值，而同等厚度环向玻璃纤维的加入却使碳纤维增强复合材料的纵向热膨胀系数更趋于负值，从而增加了复合材料零膨胀设计范围。     

某型机外翼典型盒段样件复材加筋壁板制造技术研究

本文对某型机外翼典型盒段样件复合材料翼盒上壁板的结构形式、成型工艺、装配应用情况进行了介绍,重点对样件翼盒上壁板的成型工艺进行了研究,通过盒段样件复合材料上壁板的研制,初步掌握了大尺寸加筋壁板类零件的制造工艺;分析了产生缺陷的原因,优化工艺方案,最终制造出合格产品并交付装配车间。     

混杂纤维复合材料热性能异性研究

本文对碳纤维，玻璃纤维混杂纤维复合材料进行了热膨胀系数计算，计算结果表明，环向碳纤维的加入可使碳纤维增强复合材料的纵向热膨胀系数趋于正值，而同等厚度环向玻璃纤维的加入却使碳纤维增强复合材料的纵向热膨胀系数更趋于负值，从而增加了复合材料零膨胀设计范围。     

零膨胀单向混杂纤维复合材料的研究

本文推导了单向混杂复合材料热膨胀系数的理论估算公式,并进行了实验验证.研究了单向混杂复合材料热膨胀系数随混杂比、混杂界面数及铺层顺序等参数变化的规律.另外,也对部分零膨胀单向混杂复合材料的铺层结构进行了预测.研究结果对复合材料在航空航天上的应用有重要的意义.     

钙长石／玻璃复合材料的制备和性能研究

采用电子陶瓷工艺制备了一系列钙长石／玻璃复合材料,并对复合材料进行X射线分析、扫描电镜观察和性能测试。结果表明：复合材料的介电常数、热膨胀系数随钙长石含量的增加而增加,而介电损耗和抗折强度随钙长石含量的增加而减小。钙长石含量大于50wt％的复合材料中α-石英和方石英的析出增加了材料的热膨胀系数,但对材料的介电性能影响不大。所制备的复合材料具有低的介电常数（5．4～6．1）、低的介电损耗（0．11％～0．41％）、低的热膨胀系数（4．3×10^-6～6．1×10^-6／℃）和低的烧结温度（≤900℃）,有望用于电子封装领域。     

复合材料汽车制动缸的成型工艺和模具设计

在对国内EX1015型制动缸进行分析研究的基础上,进行了复合材料汽车制动缸的材料设计、成型工艺研究和模具设计,完成了复合材料制动缸样件的制造。为建立复合材料汽车制动缸工业化生产提供理论和试验基础,为汽车行业零部件复合材料化提供有实用价值的参考。     

复合材料近零膨胀研究

本文研究了铺层对复合材料热膨胀性能的影响。针对3种优化典型铺层,通过理论计算、有限元分析及试验检测对比,得出复合材料的热膨胀系数及模量与复合材料铺层关系的综合设计方法。希望对复合材料的铺层设计指导。     

赢创硬质泡沫应用于中国商用客机

赢创公司推出的ROHACELLPMI（聚甲基丙烯酰亚胺）硬质泡沫最近成功用于制造中国第一架大型商用客机C919的后压力框部段样件。在商用飞机中使用复合材料作为主承力结构,在国内尚属首次。后压力框部段样件是C919在研制过程中完成的第一个大型复合材料部段样件,     

铝合金RTM模具制备设计研究

复合材料成型工艺中树脂传递模塑(RTM)成型已在航空航天、汽车等制造领域得到广泛应用。但由于传统钢制模具质量太大,限制了大型复合材料制件采用RTM成型工艺的发展。设计研究了采用铝合金制备RTM成型模具的减轻质量效果,分析了克服铝合金材质热膨胀系数对模具形变影响的解决方案。结果表明,铝合金模具减轻质量效果尤为明显,相较钢模减轻50%;通过减小模具型腔尺寸,提高注胶和脱模温度、设置必要的保护装置等方法,可克服铝合金热膨胀系数大、硬度低等缺陷;并且其成型出的制品表面光洁,内部无分层和脱胶现象,尺寸精度达到设计要求。     

自硬化磷酸钙骨水泥的微结构分析

应用SEM研究了磷酸四钙(TTCP)和无水磷酸氢钙(DCPA)组成的磷酸钙骨水泥(CPC)体系水化过程中浆体的微结构.结果表明:完全硬化的CPC由纳米级针状羟基磷灰石微晶组成,微晶与人体骨有类似的低结晶度和结构特性.CPC产物结晶形态与Ca与P摩尔比有关,Ca与P摩尔比减小,CPC水化产物的轴比增大而形态较细长.     

交联剂含量对交联聚乙烯滚塑制品冲击性能与结构的影响

制备了不同交联剂含量的交联聚乙烯(XLPE)材料及滚塑制品,比较了交联母料不同稀释比例下所得材料的流变特性、交联行为,研究了交联剂含量对样品力学性能(弯曲强度、缺口冲击强度)、不同温度时的落锤冲击强度以及厚度梯度方向的晶体尺寸、结晶度以及交联度等微观结构的影响。结果显示:随交联母料稀释比增大,交联反应略有延迟、交联反应程度降低,制品结晶度增加、缺口冲击强度降低、弯曲模量升高;交联母料稀释比在1:6~1:12时,测试温度25℃时样品落锤冲击强度均为25 J/mm以上,测试温度由25℃逐步下降至-40℃时,交联剂含量高的滚塑样品(M1-6)的落锤冲击强度可保持25 J/mm以上,稀释比例较大的滚塑样品出现韧性-脆性转变(-40℃落锤冲击为1 J/mm)。     

Solution‐processable colorless polyimides with ultralow coefficients of thermal expansion for optoelectronic applications

This work reports colorless polyimides (PIs) that are applicable as plastic substrates in image display devices, which produce an ultralow coefficient of thermal expansion (CTE) by solution casting without thermal imidization and mechanical stretching. An effective monomer molecular design is proposed for this purpose. Chemical imidization (CI) process compatibility is the key factor in attaining the target properties. We focused on a PI system derived from 1,2,3,4‐cyclobutanetetracarboxylic dianhydride (CBDA) and a novel para‐amide‐linked diamine (AB‐TFMB) with CF₃ groups as it has great potential as an ultralow CTE material, although it offers no CI process compatibility because of its poor solubility. The CBDA/AB‐TFMB system was modified by copolymerizing with 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride. This approach drastically improved CI process compatibility. The CTE of the PI films linearly decreased with increasing CBDA content. At a CBDA content of 70 mol%, the PI achieved an ultralow CTE of 7.3 ppm K^?1, non‐coloration/non‐turbidity, a very high glass transition temperature of 329 °C and sufficient ductility. The ultralow CTE results from the highly oriented main chains along the X–Y direction during the casting process as supported by the very high birefringence exceeding 0.1. Thus, our materials almost achieved the target properties required for novel coating‐type high‐temperature plastic substrate materials. © 2016 Society of Chemical Industry     

The fracture properties of metal-ceramic composites manufactured via stereolithography

In this work, metal-ceramic composite parts based on aluminum and alumina were manufactured in a two-stage process. First, silica was printed using a vat photopolymerization technique, followed by a curing and sintering stage, which resulted in ceramic precursors. Subsequently, these samples were subjected to a metal infiltration process to form interpenetrating metal-ceramic composites (IPCs). These composites have attracted considerable attention in the aerospace and defense sector due to the ductility associated to the metal phase and the strength offered by the ceramics. A novel application with utility includes composite tooling which requires a low coefficient of thermal expansion (CTE) for high temperatures. The investigated specimens were tested for surface quality and shrinkage, followed by a mechanical characterization. It was recorded that the samples presented a 12%–18% of shrinkage after the sintering process. The mechanical testing showed that the hardness, compression, and flexural strength of the composites were superior to the printed and sintered ceramics. A thermal analysis on the composite showed that its CTE is more than two times lower than the common composite tooling materials. It is expected that the present work can provide the foundations for further studies on these systems in the refractory, automotive, and armor-based fields.     

Effect of structural changes of silica filler on the coefficient of thermal expansion (CTE) of underfill encapsulant

This study investigates the effect of degree of crystallinity (DC) of silica on the CTE value of epoxy filled silica composite. Various DC of silica was produced through high intensity grinding process in a jet mill by varying the grinding pressure. The ground silica with the DC ranging from 76% to 100% was filled at 45% volume and the CTE values were measured. The obtained results showed that CTE of composite was reduced as the filler's degree of crystallinity decreased.     

Evaluation of the high temperature performance of HfB2 UHTC particulate filled Cf/C composites

Room and high temperature flexural strength and coefficient of thermal expansion (CTE) of HfB₂ ultra‐high temperature ceramic (UHTC) particulate filled C_f/C composites are determined along with UHT oxidation behavior. Both room and high temperature strength of the composites were found to be broadly comparable to those of other thermal protection system materials currently being investigated. The CTE of the composites was measured both along and perpendicular to the fiber direction up to 1700°C and the values were found to depend on fiber orientation by approximately a factor of 3. Arc‐jet testing of the UHTC composites highlighted the excellent ultra‐high temperature oxidation performance of these materials.     

Epoxy nanocomposites with reduced coefficient of thermal expansion

Control of the coefficient of thermal expansion (CTE) of polymeric materials is critical in many applications, particularly the electronics industry where CTE mismatches have caused failures. In theory, adding exfoliated nanoplatelets with high aspect ratios would offer an effective solution for reducing CTE, but reported results have not been compelling due to poor dispersion. In this study, α-zirconium phosphate (ZrP) nanoplatelets, along with organic surfactants, were added to epoxy thermosets. The CTE reduction and glass-transition temperature (T_g) were measured while the molecular weight of the surfactant was varied. High-molecular-weight surfactants are effective for ZrP exfoliation and dispersion, but they can also lead to a reduction in T_g and hinder the drop in CTE. A combination of two low-molecular-weight tetrabutylammonium hydroxide and 2-methoxyethylamine surfactants for exfoliation of ZrP were found to give a CTE reduction of 40% with just 3.5 vol % of ZrP added. This CTE reduction correlates well with theory. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47703.     

玻璃组成对Li2O-Al2O3-SiO2系统微晶玻璃膨胀系数的影响

以Li2O-Al2O3-SiO2系统微晶玻璃的标准样的组成为基础配方,改变玻璃组成中各种氧化物的含量,采用传统的熔融法制备了Li2O-Al2O3-SiO2系统微晶玻璃,利用SEM、XRD、DTA及热膨胀系数测定等分析手段,重点研究了玻璃组成中Li2O、Al2O3、SiO2的含量对微晶玻璃热膨胀系数的影响.研究结果表明:在标准试样的基础上,改变Li2O的含量,对热膨胀系数影响很大;热膨胀系数随Al2O3含量增大而增大,而SiO2含量的变化,对热膨胀系数影响不大.     

Effect of geometric parameter on thermal stress generation in fabrication process of double-ceramic-layers thermal barrier coating system

In this work, quenching stress generated during the deposition process and the Coefficient of Thermal Expansion (CTE) thermal mismatch stress produced during the cooling down process of Double-Ceramic-Layers Thermal Barrier Coating System (DCL-TBCs) have been intensively examined. The thickness ratio of Lanthanum Zirconate (LZ, La₂Zr₂O₇) coating to stabilized Zirconia (YSZ, ZrO₂-8%Y₂O₃) coating, have been theoretically analyzed. In addition, DCL-TBCs specimens with different thickness ratio of LZ to YSZ coatings were fabricated, to study the effect of this thickness ratio by specimen curvature and crack density analysis. Meanwhile, Finite Element Method (FEM) has been carried out to validate results obtained theoretically. The results reveal that by comparison to CTE thermal mismatch stress, quenching stress has remarkable effect on total thermal stress. By increasing thickness ratio of YSZ to LZ coatings, average thermal stress and crack densities in YSZ and LZ coatings increased. Nevertheless, the curvature ratio of DCL-TBCs specimen decreases.