Multi-scale Modeling and Finite Element Analyses of Thermal Conductivity of 3D C/SiC Composites Fabricating by Flexible-Oriented Woven Process

Thermal conductivity is one of the most significant criterion of three-dimensional carbon fiber-reinforced SiC matrix composites(3D C/SiC).Represent volume element(RVE)models of microscale,void/matrix and mesoscale proposed in this work are used to simulate the thermal conductivity behaviors of the 3D C/SiC composites.An entirely new process is introduced to weave the preform with three-dimensional orthogonal architecture.The 3D steady-state analysis step is created for assessing the thermal conductivity behaviors of the composites by applying periodic temperature boundary conditions.Three RVE models of cuboid,hexagonal and fiber random distribution are respectively developed to comparatively study the influence of fiber package pattern on the thermal conductivities at the microscale.Besides,the effect of void morphology on the thermal conductivity of the matrix is analyzed by the void/matrix models.The prediction results at the mesoscale correspond closely to the experimental values.The effect of the porosities and fiber volume fractions on the thermal conductivities is also taken into consideration.The multi-scale models mentioned in this paper can be used to predict the thermal conductivity behaviors of other composites with complex structures.

Tensile Properties of 3-Dimension-4-directional Braided C_f/Si C Composite based on Double-scale Model

The longitude tensile properties of 3-Dimension-4-directional（3D-4d） braided C/Si C composites（CMCs） were investigated with the help of a double scale model. This model involves micro-scale and unit-cell scale. In micro-scale, the tensile properties of fiber tows which involves matrix cracking, interfacial debonding, and fiber failure are studied. The unit-cell scale model can reflect the braided structure and simulate the tensile properties of 3D-4d CMCs by introducing the tensile properties of fiber tows into it. Quasi-static tensile tests of 3D-4d braided CMCs were performed on a PWS-100 test system. The predicted tensile stressstrain curve by the double scale model is in good agreement with that of the experimental results.

3D Evaluation Method of Cutting Surface Topography of Carbon / Phenolic (C/Ph) Composite

3D evaluation method of cutting surface topography for C/Ph composites was established.The cutting surface was measured by Talyscan 150,using 3D non-contact measurement.Through the results of 2D and 3D roughness evaluating for C/Ph composite and Duralumin,the 2D evaluation method of the cutting surface topography of C/Ph composite loses a lot of information,the characteristics of the surface topography of C/Ph composite can be comprehensively and authentically evaluated only by 3D evaluation method.Furthermore,3D amplitude and spatial parameters were adopted to evaluate the surface.The results show that： the topography of the C/Ph composite is anisotropic,there are more valleys in the machined surface of C/Ph than that of duralumin,and there are not obvious feeding textures for C/Ph,which indicates the machining mechanism is different from the metal.In conclusion,the topography of the C/Ph composite cutting surface is anisotropic;the cutting surface of C/Ph composite needs 3D evaluation method.

Analytical Model of Elastic Modulus and Coefficient of Thermal Expansion for 2.5D C/SiC Composite

To make better use of 2.5D C/SiC composites in industry, it is necessary to understand the mechanical properties. A finite element model＇of 2.5D composites is established, by considering the fiber undulation and the porosity in 2.5D C/SiC composites. The fiber direction of warp is defined by cosine function to simulate the undulation of warp, and based on uniform strain assumption, analytical model of the elastic modulus and coefficient of thermal expansion （CTE） for 2.5D C/SiC composites were established by using dual- scale model. The result is found to correlate reasonably well with the predicted results and experimental results. The parametric study also demonstrates the effects of the fiber volume fraction, distance of warp yarn, and porosity in micro-scale on the mechanical properties and the coefficients of thermal expansion.

Elastic Modulus Prediction of Three-dimension-4 Directional Braided C_f/SiC Composite Based on Double-scale Model

Double-scale model for three-dimension-4 directional（3D-4d） braided C/SiC composites has been proposed to investigate its elastic properties. The double-scale model involves micro-scale that takes fiber/ matrix/porosity in fibers tows into consideration with unit cell which considers the 3D-4d braiding structure. Micro-optical photographs of composites have been taken to study the braided structure. Then a parameterized finite element model that reflects the structure of 3D-4d braided composites is proposed. Double-scale elastic modulus prediction model is developed to predict the elastic properties of 3D-4d braided C/SiC composites. Stiffness and eompliance-averaging method and energy method are adopted to predict the elastic properties of composites. Static-tension experiments have been conducted to investigate the elastic modulus of 3D-4d braided C/SiC composites. Finally, the effect of micro-porosity in fibers tows on the elastic modulus of 3D-4d braided C/SiC composites has been studied. According to the conclusion of this thesis, elastic modulus predicted by energy method and stiffness-averaging method both find good agreement with the experimental values, when taking the micro-porosity in fibers tows into consideration. Differences between the theoretical and experimental values become smaller.

3D C/SiC-TaC复合材料烧蚀性能及机理

采用浆料浸渗结合化学气相浸渗SiC工艺制备出高体积分数TaC的3D C/SiC-TaC复合材料。采用氧-乙炔烧蚀试验研究其烧蚀性能,利用SEM和XRD对烧蚀后材料的微观结构和相组成进行表征,并分析复合材料的抗烧蚀机理。结果表明:TaC在高温高速氧-乙炔焰作用下,形成玻璃态的黏滞Ta2O5相,对C/SiC基体起到封填表面开气孔的作用,阻碍氧化性气氛进入试样内部,从而达到抗高温氧化,提高复合材料的抗烧蚀能力的目的;在超高温阶段,TaC和Ta2O5共同起到抗烧蚀作用。

3D-C/SiC复合材料在室温和1300℃的拉-拉疲劳行为

采用应力比为 0 .1,频率为 6 0 Hz的正弦波在室温和 130 0℃ ,10 - 4Pa真空中对 3D- C/Si C复合材料进行了拉 -拉疲劳试验。同时用 SEM分析了疲劳断口特征。结果表明 :若取循环基数为 10 6 ,130 0℃疲劳极限为 2 85 MPa,约为抗拉强度的 94 % ;室温疲劳极限为 2 35 MPa,约为抗拉强度的 85 %。 130 0℃疲劳断口的纤维拔出长度比室温短。疲劳损伤主要起源于纤维束编织交叉部位 ,随着疲劳循环次数的增加 。

3D C/SiC复合材料的热辐射性能

利用稳态量热计法和傅里叶红外光谱仪分别测定了3D C/SiC复合材料在90℃时的半球向总发射率和室温法向光谱反射率,研究了表面形貌、涂层厚度及高温氧化对3D C/SiC热辐射性能的影响。结果表明:3DC/SiC具有优异的热辐射性能,其总发射率可达0.83;随着SiC涂层厚度的增加,3D C/SiC总发射率先降低后上升;高温氧化后,3D C/SiC的热辐射性能有所提高。

料浆浸渗法结合CVI制备3D C/SiC-TaC复合材料及其烧蚀性能研究

采用含1μmTaC微粉4%(体积分数)的料浆向10mm厚的3D碳纤维预制体中引入TaC,得到微粉含量高、中、低的三种预制体,CVI沉积SiC致密化后制得3DC/SiC-TaC多元基复合材料。氧-乙炔烧蚀试验后采用XRD和SEM对烧蚀产物和显微结构进行分析。结果表明:料浆法结合CVI可制备出C/SiC-TaC复合材料,高含量的TaC微粉烧蚀后形成的TaC和Ta2O5的固液混合物,能对烧蚀面进行有效包覆,有助于提高烧蚀性能。

3D-C／SiC复合材料的高温疲劳性能

采用应力比为0.1和0.5,频率为60和20Hz的正弦波从室温至1500℃,在10-4Pa真空中对3D-C/SiC复合材料进行拉—拉疲劳实验;获得其在应力比0.1频率60Hz条件下室温、1100、1300和1500℃的疲劳曲线,以及应力比0.1频率20Hz和应力比0.5频率20Hz条件下1500℃的疲劳曲线。结果表明,若取循环基数为106周,应力比0.1频率60Hz条件下,3D-C/SiC复合材料在室温、1100、1300和1500℃的疲劳极限分别为235、350、285和240MPa,约为其拉伸强度的87%、97%、94%和90%;疲劳极限与比例极限和拉伸强度随温度有相似的变化规律,即随温度升高而增加,在1100℃达到最大值,尔后随温度增加而下降;但是S—Nf曲线的斜率的变化规律恰好与此相反。应力比的增加和频率的降低,均使复合材料1500℃的疲劳极限有所减小。

双组元液体动力环境下3D C/SiC复合材料喷管烧蚀性能

为明确C/SiC陶瓷基复合材料喷管在液体火箭发动机工作环境的烧蚀特性,采用先驱体浸渍-裂解(PIP)工艺制备得到3D C/SiC复合材料喷管,并对喷管进行多种工况环境下的地面热试车烧蚀考核。结果表明:制备得到的3D C/SiC复合材料喷管能够满足液体火箭发动机多种工况环境下抗烧蚀性能要求,喷管喉部线烧蚀率约为3.92×10^(-4) mm/s;热试车烧蚀实验后喷管入口圆柱段、收敛段、喉部及扩张段外型面均残留有大量白色物质SiO_(2),喉部局部出现烧蚀坑洞现象;C/SiC复合材料液体火箭发动机工作环境下的烧蚀机理为机械冲刷烧蚀和氧化烧蚀。

3D针刺C/SiC断裂韧性缺口敏感性及破坏研究

碳化硅陶瓷基复合材料是高超声速飞行器及高推重比发动机等发展所需的关键材料之一,对冲击断裂韧性、缺陷及裂纹的敏感性有较高要求。采用夏比冲击试验测定3D针刺C/SiC复合材料的断裂韧性,研究其处于U型、V型缺口分别在与针刺平行、垂直的不同分布方向时对冲击断裂韧性的影响,并通过扫描式电子显微镜及光学显微镜等手段详细分析断口形貌。结果表明:U型试样的断裂韧性较V型试样对缺口线与针刺相对位置更为敏感,且缺口线与针刺纤维束平行时断裂韧性最差;针刺纤维束与0°和90°无纬布铺层交叉部位相对薄弱,原材料抗剪能力削弱。

预疲劳对3D-C/SiC复合材料拉伸性能的影响

采用应力比为0.1,频率为20Hz的正弦波于1300℃条件下对3D-C/SiC复合材料进行200MPa和80MPa的疲劳实验,在循环106次后在室温对其进行拉伸实验,并通过SEM观察其断口形貌,用光学显微镜观察基体裂纹密度。结果表明,经过200MPa疲劳处理的3D-C/SiC试样的比例极限、抗拉强度和断裂应变值与预疲劳前原始试样相比,分别提高110%,17%和29%,弹性模量比原始试样下降49%,基体裂纹密度和纤维的拔出长度等均明显增加;当最大疲劳应力低于基体开裂应力时,预疲劳处理对3D-C/SiC的拉伸性能几乎没有影响。

Bolt Design of Ceramic Matrix Composite and Superalloy Bolted Joint Based on Damage Failure Load

Ceramic matrix composite(CMC)and superalloy bolted joints are commonly used high temperature connection structures in aerospace and aeronautical fields.In this paper,a finite element model coupled with progressive damage analysis of 2D C/SiC composites and superalloy bolted joint was implemented to simulate the uniaxial tensile loading process by using the ABAQUS finite element software.The parametric effects of raised head bolt on stress distribution,tensile performance,and damage process were studied for the CMC⁃superalloy bolted joint structures.The results showed that the final failure load increased first to the maximum value,and then decreased with the rise of bolt diameter,bolt head diameter,and bolt head thickness,respectively.When the three parameters were 5.0 mm,9.5 mm,and 2.8 mm for the current studied bolt configuration,the joint structure gave the maximum load bearing capacity for the considered parameter ranges.It was also found that around 42%potential improvement in load bearing capacity could be achieved by very small adjustments in bolt parameters of the joints.

SiC晶须和Ti(C,N)颗粒协同增韧Al_2O_3陶瓷刀具的研究

采用热压工艺烧结制备了SiCW Ti(C ,N) Al2 O3(Y2 O3)陶瓷刀具复合材料。研究了不同烧结温度(16 0 0～ 175 0℃ )下 ,材料的致密度和力学性能 (断裂韧性KIC ,维氏硬度HV和抗弯强度σf)随晶须含量 (10 %～4 0 % )的变化关系 ;探讨了SiC晶须和Ti(C ,N)颗粒对Al2 O3基体的协同增韧机理。同时与SiCW Al2 O3陶瓷及Ti(C ,N) Al2 O3陶瓷作对比研究。结果表明 :SiCW Ti(C ,N) Al2 O3(Y2 O3)陶瓷材料在 175 0℃ ,晶须含量为 2 0 %时获得最佳的综合力学性能 :KIC =7 11MPa m1 2 ,HV =2 1 16GPa ,σf=82 0MPa ;明显高于SiCW 含量为 2 0 %的SiCW Al2 O3陶瓷和不加晶须的Ti(C ,N) Al2 O3陶瓷。第三相Ti(C ,N)颗粒的加入与晶须一起产生明显的迭加增韧效果 ,而且对SiCW 的各种增韧机制起到了促进作用。

复合材料C/C-SiC及Ti植骨界面Caspase-3、Bcl-2、Bax表达比较研究

目的观察C/C-SiC复合材料对周围骨组织细胞凋亡情况的影响。方法选用8只日本大耳白兔,雄性,随机分为2组(每组4只)。将实验材料(C/C-SiC复合材料)和对照材料(Ti)各8枚植入兔子股骨内。3个月后,将带有实验材料和对照材料股骨标本脱钙、进行免疫组化(Caspase-3、Bax、Bcl-2)染色。观察植入材料周围骨组织细胞生长和凋亡的表达情况,并利用Imagepro Plus 6.0图像分析软件分析棕染细胞的灰度值。然后利用SPSS 17.0统计软件进行独立样本t检验分析结果。结果实验动物麻醉及手术效果较理想。植入材料与骨结合紧密、无松动,大部分植入材料表面有新生骨组织。光镜下观察,Caspase-3、Bcl-2、Bax免疫组化呈阳性反应骨细胞胞质及部分细胞膜棕褐色染色。C/C-SiC实验组棕褐色染色平均灰度值与纯钛对照组棕褐色染色平均灰度值相比无显著差别。结论 C/C-SiC复合材料植入兔股骨内术后3个月,材料周围骨细胞凋亡程度与纯钛材料无显著差别。

C/C-SiC-ZrC-Al_(2)O_(3)复合材料的制备及抗烧蚀性能研究

以葡萄糖为碳源,硅溶胶为硅源,氧氯化锆为锆源,硫酸铝为铝源,采用水热共沉积-碳热还原法制备了C/C-SiC-ZrC-Al_(2)O_(3)复合材料,并采用压汞仪测得了孔径分布,采用三点弯曲法计算出了抗弯强度。C/C-SiC-ZrC-Al_(2)O_(3)复合材料陶瓷基体相晶粒细小,分布均匀,其抗弯强度为169.1 MPa,比C/C-SiC-ZrC复合材料提高了21.9%,Al_(2)O_(3)有助于提高复合材料的力学性能。在等离子体火焰下烧蚀120 s后,质量烧蚀率和线烧蚀率分别为6.5×10^(-5)g/(cm^(-2)·s)和2.9×10^(-4) mm/s,分别比C/C-SiC-ZrC复合材料降低了69.3%和37.0%。Al_(2)O_(3)的加入有助于形成莫来石晶须,莫来石晶须作为增强相提高了熔融玻璃层的粘度,提高了熔融玻璃层抵抗冲刷的能力,熔融层的平整性得到了提升。粘度的提高也抑制了气相CO、SiO扩散时形成气泡的能力,熔融层的完整性得到了提高,进而抑制了氧化性气氛的向内扩散,提高了复合材料的抗烧蚀性能。

声发射技术在三维编织C/SiC复合材料拉伸损伤分析中的应用

通过声发射技术(Acoustic Emission简称AE)对三维编织C/SiC复合材料试件单向拉伸实验过程进行全程动态监测,利用声发射特征参数的综合分析法揭示了三维编织C/SiC复合材料单向拉伸时损伤演化过程和规律。实验结果表明三维编织C/SiC复合材料单向拉伸时损伤发展的四个阶段及声发射特性并利用声发射相对能量定义了材料临界损伤强度。

三维针刺C/SiC复合材料无纬布纤维方向对材料力学性能的影响

通过化学气相渗透法结合反应熔体浸渗法制备了三维针刺C/SiC复合材料,采用扫描电子显微镜观察材料的显微结构,并研究了无纬布纤维方向对材料力学性能的影响。结果表明,三维针刺C/SiC复合材料由0°无纬布层、短纤维胎网层、90°无纬布层以及针刺纤维束组成,无纬布层纤维方向对材料性能有显著影响。试样的拉伸强度和弯曲强度随着无纬布纤维方向与试样长度方向的夹角θ(0～45°)值的增大而减小,面内剪切强度和冲击韧性随θ角的增大而增大。

二维编织C/SiC复合材料的热膨胀系数预测

根据二维编织C/SiC复合材料的细观结构及其制备工艺特点,提出了一种预测该材料面内热膨胀系数的单胞模型。模型充分考虑了编织结构复合材料中的纤维束弯曲和CVI工艺制备陶瓷基复合材料产生的孔洞对热膨胀系数的影响。利用单胞模型预测了二维编织C/SiC的结构参数、纤维体积含量、孔洞含量对复合材料热膨胀系数的影响规律,结果表明:随着纤维束扭结处产生间隙与纱线宽度比值的增大,热膨胀系数增大;当其它参数不变时,随着纤维体积含量的增大,热膨胀系数反而下降;随着孔洞含量的增加,热膨胀系数也出现了下降的趋势。利用DIL402C热膨胀仪测试了二维编织C/SiC复合材料纵向热膨胀系数,试验结果与模型预测结果吻合较好。