前缘类复合材料制件固化变形控制的研究及应用

研究了前缘类复合材料制件的固化变形问题。通过设计并制造前缘局部特征试验件,分析了材料种类、结构形式、铺设层数、夹芯材料种类及厚度等因素对试验件固化变形量的影响;基于局部特征试验件的型面检测数据,开发一套前缘类复合材料制件固化变形规律及其补偿量预测方法显得尤为重要。在工艺设计阶段,根据该预测方法,可以获取变形规律和补偿量,建立工艺数模、补偿成型模型面,制造前缘试验件。结果表明,试验件型面能够满足设计要求,所建立的固化变形规律及其补偿量预测方法在工程上行之有效,解决了前缘类复合材料制件的固化变形问题。     

非均衡嵌入式等高复合材料加筋板制备

介绍了一种"工"字型加筋板试验件及其玻纤复合材料加载板的研制工艺过程,采用手糊玻纤复合材料垫板及泡沫塑料做挡条的模压成型工艺,研制出非均衡嵌入式等高加筋板,玻纤复合材料加载板与加筋板长桁达到等高且嵌入式无缝隙填充,消除试验夹具的误差,达到设计要求.     

纤维增强轻质热防护材料隔热性能仿真研究

对陶瓷纤维增强气凝胶复合材料试验件建立有限元传热模型,对试验件非线性高温环境系的隔热性能进行研究。将计算结果与实验数据进行了对比,验证了此数值模拟方法的有效性。本文讨论的非线性边界条件下热传导模型为轻质隔热材料的安全设计提供了参考依据。     

确定雷达罩设计许用值的方法研究

按照CCAR25.613条款"材料与结构许用值"的要求,民用飞机雷达罩需进行许用值设计。本文通过研究确定了进行雷达罩玻璃纤维复合材料设计许用值试验的试验项目、试验采用的标准、试验环境、试验件数量以及试验数据的处理方法等,并将采用ASTM标准测试得到的许用值试验数据与用GB标准得到的测试数据进行了比较。结果表明,按照ASTM标准进行玻璃纤维复合材料结构设计许用值试验得到的数据分散性小,许用值的测试数据高,避免了采用国内标准导致的性能数据低的情况。该设计许用值已成功应用于新型涡扇支线飞机雷达罩的设计和静力试验。     

复合材料蜂窝夹层结构四点弯曲性能研究

对某型号复合材料夹层结构内力情况进行分析,进行理论计算,建立力学模型;使用patrannastran大型有限元软件建立复合材料蜂窝夹层结构有限元模型,模拟试验件受力特点计算出蜂窝夹层结构失效过程,建立了合理的数学模型;采用ASTM C393试验标准对复合材料蜂窝夹层结构试验件进行试验,获得某型号复合材料蜂窝夹层结构强度,并将试验结果与计算结果进行对比分析,得出蜂窝夹层结构的受力特点及验证模型的准确性。     

复合材料单搭多钉连接钉载分配研究

为了研究多钉连接载荷分配,设计了复合材料4钉单搭连接拉伸试验件,测量了试验件拉伸过程中的应变分布,并计算出各钉的承载。结果表明,单搭接连接件由于次弯曲影响很难准确测量出载荷分布;4钉承载比例不均匀,中间两钉承载较小,外侧两钉承载较大。     

电磁窗用蜂窝夹层复合材料内部缺陷超声C扫描检测

对某型号复合材料夹层结构内力情况进行分析,进行理论计算,建立力学模型;使用patrannastran大型有限元软件建立复合材料蜂窝夹层结构有限元模型,模拟试验件受力特点计算出蜂窝夹层结构失效过程,建立了合理的数学模型;采用ASTM C393试验标准对复合材料蜂窝夹层结构试验件进行试验,获得某型号复合材料蜂窝夹层结构强度,并将试验结果与计算结果进行对比分析,得出蜂窝夹层结构的受力特点及验证模型的准确性。     

复合材料夹层结构翼形件的模态有限元分析

采用Ansys软件对复合材料夹层结构翼形件进行了有限元模态分析和研究,给出了翼形件的前5阶固有频率和振型.根据计算结果,对翼形件泡沫密度进行了调整,使得翼形件的固有频率和振动幅度有较大的下降,满足了设计要求.通过模压工艺制作了8片翼形件并进行了模态测试,结果表明,理论计算结果与试验结果具有较好的一致性.     

蜂窝夹层复合材料成型用压力垫的研制

讨论了丙烯酸酯橡胶匀压垫的性能、成型工艺及蜂窝夹层结构／层压件复合材料在热压罐成型过程中的应用。试验证明：应用该材料制造的产品符合设计要求。     

复合材料部件设计制造一体化研究

20世纪80年代后期以来,随着CAD/CAM技术、计算机信息技术、网络技术的蓬勃发展,以美国为首的西方发达国家开始研究并首先应用了一项新技术即复合材料设计制造一体化技术。设计制造一体化技术可以提高产品的研制生产效率,保障产品质量,降低产品成本。选取某复合材料部件数字化设计制造的关键环节提出研究内容,应用复合材料制造和分析软件FiberSIM对演示验证件进行数字化制造,克服相关技术难点,打通了复合材料由设计到制造的生产流程。最终通过演示验证件的数字化设计流程分析复合材料数字化制造与传统的复合材料生产过程的差异,客观评价两种制造方案的优缺点。     

A modified specimen holder for cone calorimeter testing of composite materials to reduce influence from specimen edges

ISO 5660-1 specifies the cone calorimeter method for characterizing the ignition and surface burning behavior of materials. The specimen is irradiated through a square opening in the frame of the specimen holder. The frame is intended to protect the edges of the specimen from irradiation but covers the edges with only a few mm. In tests with products such as composite laminates and sandwich wall panels, the production of pyrolysis gases from the edges and, in many cases, burning have been observed. Early contribution from the edges in the test is not representative for surface burning. A modified specimen holder was developed with a larger specimen size to allow better protection of the edges. The opening for exposure to irradiance of the retainer frame is circular and of the same area as that of the original frame. The distance between the exposed surface and the specimen edges is larger in order to prevent early exposure of edges. Tests using the standard specimen holder resulted in pyrolysis and burning from edges that took place outside of the specimen holder. Comparative tests using the modified specimen holder showed that it prevented the exposure and pyrolysis from edges for an extended time. However, the influence on ignition time and peak heat release due to the increased size of the modified specimen holder has not been characterized fully, and test results should not be used for direct comparison with those of the standard holder.     

Variability in porous ceramic fracture: Influence of apparent density and critical pores

Gypsum specimen failure under four-point bending is investigated both experimentally and numerically. The analysis accounts for the variation in specimen thickness (in a large range from 10 to 90 mm), in pore volume fraction (related to a variation in elastic and fracture properties) and for the presence of macropores that are likely to trigger failure. Examination of specimen fracture surfaces reveals several isolated macropores near the specimen face loaded under tension. The critical pore size does not depend on the specimen volume. The pore criticity does not only depends on its size but also on its location with respect to the specimen face sollicitated under tension. Both pore volume fraction variations between samples and the presence of critical pores induce failure stress scattering for a given specimen width, which is well reproduced numerically using the coupled criterion.     

微孔镁尖晶石碳耐火材料的抗渣性能研究

以方镁石-尖晶石微孔陶瓷、电熔镁砂为骨料,以电熔镁砂细粉、鳞片石墨、金属铝粉为基质材料,以酚醛树脂为结合剂制备了含微孔陶瓷骨料的镁尖晶石碳试样.采用感应炉浸渍法对试样进行了抗渣试验,并对渣蚀后的试样进行了SEM和EDAX分析.结果发现:熔渣和熔钢冲刷是损毁的主要原因,熔损并不显著.显微结构分析表明,在侵蚀层和原质层之间可以发现MgO致密层的形成,MgO致密层的形成可抑制渣对试样进一步的侵蚀和渗透.渣对MSO颗粒的侵蚀主要是FeO和MnO等在方镁石中的固溶,导致MgO颗粒出现结构剥落;方镁石-尖晶石微孔陶瓷骨料的蚀损主要是尖晶石被渣中的CaO和SiO2所侵蚀,而渣对微孔骨料渗透并不严重.     

A methodology for detecting interfacial debonding in clay/epoxy nanocomposites

A novel methodology is presented for detecting the onset of debonding in clay-based nanocomposites. The procedure is based on constant illumination of the test specimen as it is subjected to tensile deformation by sequential strain-steps. After each strain-step, an image of the specimen is taken along its gauge length using a digital camera and the image is stored in a computer for later analysis using image analysis software. Test results from a nanocomposite containing a weak interface between the clay and the matrix indicate that interface debonding begins to occur above 1% strain, as evidenced by a reduction in the transmitted light through the specimen with increasing strain. Based on related research, the darkening of the specimen was interpreted as clay/matrix debonding. In contrast to the approximately 11% failure strain of the base epoxy resin, the nanocomposite specimen with the weak interface failed at 3.6% strain.     

Understanding the impact of gamma irradiation on electrical and mechanical properties of epoxy nanocomposites

In this work, the influences of gamma irradiation on the electrical and mechanical properties of the epoxy nanocomposites were studied. The exfoliation characteristics of epoxy nanocomposite material analyzed through TEM studies. It is shown that the impact and flexural strength of the material is high with epoxy nanocomposites and gets reduced with the gamma-irradiated specimen. The AC breakdown strength of the epoxy nanocomposites is high compared with the base epoxy resin. It is also observed that a reduction in permittivity and tan(δ) of epoxy resin added with 1 wt % of nanoclay. Increase in percentage of clay shows increase in permittivity and tan(δ). Gamma irradiation of epoxy nanocomposite material shows increase in permittivity. The volume resistivity of the material is high with epoxy nanocomposite and is less with gamma-irradiated specimen compared with virgin specimen. The impact strength and flexural strength indicates correlation with breakdown strength of the material. It is observed that the increase in applied voltage shows an increase in magnitude of the charge density in the insulation structure. With the gamma-irradiated specimen, the charge density (for the applied electric field) is less compared with the virgin specimen. Electric field analysis indicates that the electric field is uniform in the bulk volume of the epoxy nanocomposite material. The rate of charge decay is high with gamma-irradiated specimen compared with virgin specimen. It is realized that material with lower resistivity has faster decay of stored charge. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Specimen temperature as a constant marginal condition and as a variable test parameter during accelerated weathering

The influence of the specimen temperature on many ageing processes is well known. Two aspects is dealt with:

• Measurements of the specimen temperature on several positions of a specimen in commercial weathering devices at different exposure conditions. Technical measures to achieve to uniform ageing at all positions of a planar and homogeneous specimen. Examples from practical use.
• Changing specimen temperatures (+60°C to ?20°C) during the course of accelerated weathering, i.e. a combination of conventional accelerated weathering with a temperature cycle test.

     

An End-Loaded Shear Joint (ELSJ) Specimen to Measure the Critical Energy Release Rate in Mode II of Tough,Structural Adhesive Joints

This paper introduces a newly developed specimen type, which is used to measure the critical energy release rate of tough, structural adhesives loaded in shear. This End-Loaded Shear Joint (ELSJ) specimen is loaded until a shear crack propagates through the adhesive layer. When the crack propagation is stopped, by unloading the specimen, the critical energy release rate in mode II, G _IIc, can be obtained by correlating the energy dissipated during the test and the measured crack area on the fracture surface of the specimen. The paper presents the dimensions of the ELSJ specimen, the corresponding test setup and the evaluation method used to obtain G _IIc. An overview of the advantages and the limitations of the new specimen type shows the need for its development and improvement when compared to some state of the art experiments. The first results of ELSJ tests are shown and discussed, using the crash-optimized structural adhesive — Henkel Terokal 5077. The experimental results presented, focus on thin adhesive layers and quasi-static test velocities.     

Mechanical response and damage mechanism of C/SiC composites impacted by high-velocity water jet

Rain erosion is a potential hazard for supersonic vehicles, with severe damage to materials that may be impacted by raindrops. In this paper, a series of impact tests of 413–572 m/s are carried out on a 3 mm-thick 2D C/SiC composite specimen using a single impact waterjet apparatus. The typical morphology of C/SiC specimen is obtained by single jet impact test. Under the multi-drop impact, the stress wave interaction is enhanced, and the internal damage of the specimen is severe, showing a funnel-shaped damage. Moreover, the C/SiC specimen is penetrated after 5 drops of impact. Quasi-static tensile tests were employed to quantify the post-impact strength of the specimen, during which the digital image correlation (DIC) method was used to obtain the strain value, at the same time acoustic emission (AE) signal was detected and processed by the K-Means to reveal the damage evolution.     

焊接残余应力的测试方法

通常采用实验的方法,包括机械方法和物理方法,测定构件中的焊接残余应力。对于前者,应区分构件是完全破坏还是部分不破坏;后者包含构件表面开小孔或环形槽的测量方法,并允许零件在测量后继续使用。     

Evaluation of mode II fatigue disbonding using Central Cut Plies specimen and distributed strain sensing technology

The lack of a widely-accepted test standard for characterizing the mode II fatigue disbond growth behavior of adhesively bonded interfaces is a challenge to the research community in terms of producing consistent and repeatable results. Typically, researchers apply the End Notch Flexure specimen, which is already used for static delamination studies. However, the needs for static and fatigue disbond growth characterization are not the same, resulting in some undesirable effects in such specimen. This study looks at a particular mode II test configuration known as the Central Cut Plies (CCP) specimen. A critical evaluation of the suitability of this specimen, including the influence of geometry, disbond measurement approaches and the stability of the disbond growth is carried out through a combination of numerical and experimental investigations. A distributed strain sensing system based on Rayleigh Backscattering provided a surface strain profile from which disbond growth rate data was obtained. A finite element model was used to verify the experimental results and determine the disbond length from the strain profiles. Results of this evaluation have shown that the CCP specimen is a promising specimen configuration for characterizing fatigue disbond growth; however, it also presents several challenges that require consideration in its application.