Property Modeling across Transition Temperatures in PMC's: Part II. Stress Rupture in End-Loaded Bending

The quasi-static properties (strength and stiffness) of polymer matrix composites (PMC's) exhibit significant temperature dependence in tension. Part I of the present paper introduced a new model enabling the computations of the strength and stiffness of PMC's in tension as an explicit function of temperature. In the second part, this model was used to model the behavior of unidirectional PMC's (AS4/PPS) in end-loaded bending. A new set of stress-rupture experiments was performed on the amorphous composite in bending in order to complete the data available in the literature (based on semi-crystalline composite). A model enabling the computation of the rupture life of the bent specimen as a function of temperature and applied load was established. The theoretical simulations were successfully compared to a set of 7 independent end-loaded bending experiments. This paper demonstrates the validity and the ease of integrating the polymer stiffness-temperature model in mechanics of composite materials, and completes the theoretical and experimental basis for the modeling of the end-loaded behavior of PMC's.     

Property Modeling across Transition Temperatures in PMC's: Part III. Bending Fatigue

Parts I [1] and II [2] of the present paper introduced systematic models for the computation of thermal effects on strength and stiffness of unidirectional polymer matrix composites (PMC's) as well as the life prediction of these materials in end-loaded bending at elevated temperatures. The last step of this study was the possibility of introducing such models in durability codes such as MRLife [3]. A recent method was developed for the experimental characterization of end-loaded bending fatigue behavior of composites at elevated temperatures. The literature dealing with the durability of composite materials in bending focuses mainly on 3 and 4 point bending [4–6]. A limited set of data as well as the basis for theoretical modeling for fatigue end-loaded bending is available in the literature [7]. However, the life prediction scheme required elevated temperature experiments. New experiments in fatigue bending were performed in order to complete the available data. Microscopic observations revealed new information for the understanding of the damage process of unidirectional AS4/PPS composites in end-loaded fatigue bending. Finally, the models developed in Parts I and II were integrated into the MRLife integral enabling the life prediction of unidirectional PMC's under combined mechanical and thermal loads from room temperature experimental data.     

Property Modeling across Transition Temperatures in PMC's: Part I. Tensile Properties

Numerous studies report the effects of temperature on the stiffness and strength of polymer matrix composites (PMC's). Due to the complexity of the relaxation phenomenon in the matrix, these studies are mainly qualitative. In the present paper models were developed that can explicitly relate the mechanical response of the composite to temperature. These models are related to the microstructure of the constituents, and therefore can be applied to any polymer matrix composite. The possibility of using these models was illustrated by the study of the mechanical behavior of carbon fiber AS4/polyphenylene sulfide (PPS) at elevated temperatures. Part I of this paper relates to the modeling of the temperature-dependent composite tensile properties (stiffness and strength). Parts II and III focus on the life prediction of AS4/PPS undergoing static and fatigue end-loaded bending at elevated temperatures.     

基于碳纤维表面修饰制备碳纤维织物增强聚苯硫醚(CFF/PPS)热塑性复合材料

碳纤维织物增强聚苯硫醚(CFF/PPS)复合材料是重要的热塑性航空复合材料,其难点为提高碳纤维(CF)与基体的浸润性及界面强度。探讨了CF表面修饰对CFF/PPS界面结合强度的影响,对比了热处理去浆及三种表面修饰剂对碳纤维单丝及CFF/PPS复合材料的改性效果。采用X射线光电子能谱分析(XPS)、扫描电子显微镜(SEM)、单丝强度测试、复合材料静力学测试和动态力学分析等手段对CF表面修饰效果进行评价,建立了基于CF表面修饰制备高性能CFF/PPS热塑性航空复合材料的方法。制备的复合材料层间剪切强度达91.4MPa,弯曲强度953.7MPa,拉伸强度797.4MPa,模量68.4GPa,冲击强度58.3kJ/m2,用SEM观察到CF表面包覆大量PPS树脂。     

Delamination Effect on Bending Behaviour in Carbon–Epoxy Composites

Abstract: This paper presents the results of experimental and numerical studies on the bending behaviour of carbon fibre‐reinforced epoxy composite containing delamination located at different positions along the laminate thickness. Experimental tests were conducted in three‐point bending using specimens with and without delamination to evaluate their bending behaviour. Numerical simulations were also performed in order to evaluate the maximum load as a function of the defect position and its size. The numerical model includes two‐dimensional solid elements of the ABAQUS software and a cohesive mixed mode damage model to simulate delamination propagation. The numerical and experimental results concerning the maximum load were found to be concordant. It was concluded that delaminations affect the bending behaviour of laminates mainly due to alterations in shear stress profiles.     

悬浮法制备PPS／CF复合材料

采用ＰＳＳ粉粒，二苯醚，酮制成一家配比的乳浮液，与连续碳纤维浸渍，以点加热方式去除溶剂，熔融ＰＰＳ粉粒，获得ＰＰＳ／ＣＦ预浸带，并压制成单向复合材料。通过电镜、短梁剪试验和断裂韧性测试，对预浸料和复合材料进行了质量评定。     

基于均匀化理论的三维编织复合材料弯曲细观应力数值模拟

从基于小参数渐近展开的多尺度均匀化理论出发,对三维编织复合材料的弯曲细观应力进行数值模拟。首先给出了等效弹性模量和细观应力的均匀化列式及有限元求解方程,然后讨论了三维编织复合材料细观单胞周期性边界条件的施加方法,最后对三点弯曲作用下三种单胞内应力分布进行了数值模拟。通过模拟比较了不同类型单胞及不同编织角材料弯曲应力的差异,总结出一些有益的结论,这些结论与实验结论都比较吻合。     

Tensile Stress Rupture Behavior of a Woven Ceramic Matrix Composite in Humid Environments at Intermediate Temperature — Part I

The stress rupture strength of the SYL-iBN/BN/SiC composite was evaluated at 550 and 750 °C with moisture content levels of 0.0, 0.2, and 0.6 atm partial pressure of water vapor, pH₂O. The stress rupture strengths decreased with respect to time with the rate of decrease related to the temperature and the amount of moisture content. In all cases the degradation was more severe initially and then approached a run-out threshold level. The thresholds were reached at approximately 100+, 60, 80 h for the 550 °C with 0.0, 0.2, and 0.6 pH₂O, respectively. The thresholds were reached at approximately 40, 20, and 10 h for the 750 °C cases. The interpolated stress rupture strengths at 100 h for 0.0, 0.2, and 0.6 pH₂O at 550 °C were 82%, 68%, and 51% of the room temperature monotonic tensile strength. At 750 °C these strengths were 67%, 51%, and 50%. Analysis of Field Emission Scanning Electron Microscopy images showed evidence of embrittlement of the fiber/matrix interphase. Little to no embrittlement was observed at both temperatures with 0.0 pH₂O. At both 550 and 750 °C with 0.2 and 0.6 pH₂O, evidence of embrittlement increased with temperature and test duration with the most extensive embrittlement observed at 750 °C with 0.6 pH₂O.     

聚苯硫醚纯化研究

在高温下,用N-甲基吡咯烷酮(NMP)与聚乙二醇(PEG)组成的混合试剂对商品PPS树脂进行纯化处理。纯化产品测试表明,这种方法能有效地去除树脂中存在的无机离子杂质和有机低聚物。进一步的研究表明,与未纯化树脂比较,纯化后树脂的加工性能以及热性能都得到明显的改善,可用于纺丝、薄膜和电子封装材料等用途。     

轴肩圆角拉弯时应力集中系数的最新研究结果

过去出版物中弹性应力集中系数在受弯状态低估了21％，受拉状态低估了40％．对轴肩圆角应力集中系数所列的图表是根据对其它类似几何形状的分析结果提供的近似值。经过对含各种尺寸的轴肩圆角模型进行拉弯状态下详细的有限元分析，在三方面得出有用结论：直修正弹性应力集中系数；2修正冯·密歇斯等效应力集中系数；3圆角处最大应力位置。最新结果以人们熟悉的图形形式表示．而由曲线回归出的经验公式适用于设计中的数字计算。     

基于图像处理的纤维分布与取向分布对水泥基材料弯曲性能的影响

聚乙烯醇(PVA)纤维增强水泥基材料的弯曲性能与纤维在水泥基体内的分布和取向分布相关。采用抛光断面后涂荧光粉的显微成像法,基于图像处理程序对PVA纤维在水泥基材料中的分布和取向分布进行量化测定,对不同基体结构特征影响纤维分布的机理进行了讨论。结合弯曲试验结果,研究了纤维分布和取向分布对材料弯曲性能的影响。纤维分布测定结果表明,均匀的基体结构特征利于纤维的分布,同时对于材料组分和加工制作过程完全相同的试件,纤维分布系数越大,试件的弯曲强度与韧性越大;纤维取向分布测定结果表明,乱向分布的纤维当其长度方向与抛光断面方向的角度接近90°分布概率越大,试件的弯曲韧性也越大。     

热处理对玻璃纤维布/聚苯硫醚非织造布复合板材力学性能的影响

以玻璃纤维布和聚苯硫醚（PPS）非织造布分别作为增强体和树脂基体原料,采用热压成型法制备出玻璃纤维布/PPS非织造布复合板材,然后在烘箱中进行热处理。利用万能试验机（Instron）、XRD、偏光显微镜（PLM）和SEM等手段对玻璃纤维布/PPS非织造布复合板材的力学性能、结晶度、晶粒类型和尺寸及微观形貌等进行了测试和表征。结果表明：随着热处理温度和时间的提高,玻璃纤维布/PPS非织造布复合板材的弯曲强度、弯曲模量和缺口冲击强度得到明显提高。当热处理温度为220℃、热处理时间为2 h时,其力学性能最佳,其弯曲强度、弯曲模量和缺口冲击强度分别达到285.7 MPa、7.8 GPa和85.0 MPa。和未进行热处理的玻璃纤维布/PPS非织造布复合板材相比,分别提高了63.2%、469.0%和37.8%。微观形貌结果表明,玻璃纤维布/PPS非织造布复合板材界面粘结得到了明显改善。     

高温持久试验的若干影响因素

结合多年的实践经验,概括介绍了高温持久试验过程中对试验结果有影响的各种故障因素,出现故障时的原因分析,并提出了切实可行的预防措施,以确保试验结果的准确性和可靠性。     

高导热C/C复合材料的研究进展

综述了高导热C/C复合材料的研究现状及进展.从C/C复合材料的导热机理出发,分析了C/C复合材料的热物理性能以及影响其导热性能的因素.介绍了不同类型碳纤维、基体炭的导热性能,以及高导热C/C复合材料的制备及改性.     

In situ observation of kink-band formation in a unidirectional carbon fiber reinforced plastic by X-ray computed tomography imaging

A compression test of a unidirectional carbon fiber reinforced plastic (CFRP) rectangular coupon was performed in an X-ray computed tomography (CT) system. Internal compressive failure of the CFRP was observed under loading. Two-dimensional fiber microbuckling developed non-uniformly in the specimen, and enlarged locally at one side. Fiber failure then initiated at the side edge and propagated through the whole cross section. A two-dimensional kink-band developed as a result of two-dimensional fiber microbuckling. The out-of-plane and in-plane band widths and band angles were almost the same. The coupon specimen twisted slightly owing to the two-dimensional kink-band, which resulted, macroscopically, in a transverse and through-thickness shear failure mode. The scenario of kink-band failure in a unidirectional CFRP coupon was revealed by X-ray CT imaging.     

FE Stress Analysis of Thick Composite Laminates with a Hole in Bending

In this work, the stress analysis of isotropic and ortotropic laminae both with a hole and without a hole and laminated both with a hole and without a hole composite plates have been examined using the finite element method. In order to solve the problem, a computer program has been written by using characteristics of eight-node isoparametric plane element. The calculations have been tested on various composite and steel materials by this program. The results have been shown in diagrams and tables and compared with literature. It was observed that the stress distributions in the plate with a hole was totally different from the plate without a hole. The analyses have showed that, the elastic stresses have been gradually reduced as moving from the first layer to the second.     

晶粒细化剂对K403合金返回料微观组织及持久性能的影响

目的 探索不同浇注温度下晶粒细化剂添加的有无对K403合金返回料微观组织及持久性能的影响,并建立合金的浇注工艺与微观组织和持久性能的关系.方法 通过调整浇注温度及晶粒细化剂的有无制备了8组合金,并进行了微观组织表征与高温持久性能测试.结果 晶粒细化剂的加入对K403合金的晶粒组织有细化作用,在较高浇注温度下的细化作用更...     

铜合金自来水表外壳破裂失效分析

采用宏观检验、断口分析、能谱分析、金相检验以及化学成分分析等方法,对某铜合金自来水表外壳在使用中发生破断开裂、造成泄露的原因进行了分析。结果表明:该铜合金自来水表外壳在使用过程中发生破裂属于应力腐蚀破裂,致使其发生应力腐蚀的原因主要与使用环境中含有硫化物有关。     

碳纤维复合材料旋转超声钻孔装置研究

探索碳纤维复合材料旋转超声钻孔设备及工艺，换能器采用压电陶瓷材料，进给由步进电机驱动，从而使结构大为简化。单片机作为中心控制，实验预定轴向力进给加工，而且超声波发生器具有频率自动跟踪的能力。试验表明，此项研究可望作为一种有效的新工艺方法。     

单晶高温合金的高温蠕变断裂

研究了ＮＡＳＡＩＲ１００单晶在铸态以及热处理的的组织及高温持久寿命。发现γ／γ＇共晶、富Ｗ相、显微疏松以及γ－γ＇等相界面处是形成蠕变空穴的场所。单晶合金的高温持久断裂过程是：蠕变空穴在温度和应力的联合作用下长大为韧窝，并通过撕裂棱连接起来。