强噪声载荷下2D-C/SiC复合材料平板失效机理

2D-C/SiC复合材料壁板结构是高超声速飞行器热防护系统的发展方向,高超声速飞行器面临着严酷的力、热、噪声等复杂环境对结构材料性能、结构动力学特性、自动控制等都产生了严重影响。基于自行研制的热噪声试验系统,选取C/SiC薄壁结构试验件,开展噪声为156～165 dB的噪声试验,试验后通过红外热成像检测观察整体形貌,采用SEM对裂纹的起始位置和扩展位置的断面进行分析,揭示出强噪声激励下2D-C/SiC平板的失效机理。     

热声载荷下C/SiC薄壁层合板结构动力学响应计算与寿命分析

高超音速飞行器薄壁结构在工作环境下承受着复杂的高温强噪声载荷，高温会使材料性能发生变化，导致局部区域出现热声疲劳破坏，影响结构的耐久性和完整性。针对此类问题，基于薄壁结构大挠度非线性振动理论，构建热声载荷下四边固支C/SiC薄壁层合板结构的数值仿真模型，并对其进行了动力学响应计算，研究了不同热声载荷组合下的振动响应规律，并采用线性累计损伤理论对结构进行疲劳寿命的预估和分析。结果表明，热声载荷对碳/碳化硅薄壁层合板的非线性响应影响不同，热载荷通过改变结构基频来影响结构非线性响应。四边固支C/SiC薄壁层合板在热声载荷作用下表现出非线性随机振动特性，并且呈现在平衡位置随机振动、随机跳变等多种运动状态，跳变运动给结构造成更大的的损伤更大。     

1500℃高温氧化环境下C/SiC复合材料结构的热/力联合试验

针对高超声速飞行器新型超高温结构力/热/氧化关键性能参量试验测试的迫切需求,自行设计并建立了可实现在高达1 500℃极端高温氧化环境下进行结构断裂性能测试的辐射式热/力联合试验系统,并对耐高温C/SiC复合材料结构在1 500℃等高温氧化环境下的断裂强度以及出现断裂时的时间点等关键性能参数进行了试验测试,当试验温度从1 000℃上升至1 500℃,C/SiC复合材料试验件的断裂强度下降了47.5%,断裂时间缩短50.1%。本极端高温载荷试验系统为高超声速飞行器结构热强度研究提供了重要的氧化环境下的热/力联合试验测试手段。研究结果表明:通过高温预加载可以明显提高C/SiC复合材料结构的断裂强度,增幅为38%,承载时间提高61.1%。试验结果为高超声速飞行器复合材料部件在极端热环境下的安全可靠性设计以及强度性能的改进提供了重要依据。     

含SiC阵列改性涂层的新型SiC/Cf复合材料吸波性能研究

以葡萄糖、Si粉、碳纤维为原料, 采用化学镀结合高温烧结两步法制备了具有SiC阵列改性涂层的新型SiC/C_f复合材料。采用不同手段表征SiC/C_f复合材料的相组成、微观结构和吸波特性。结果表明: 碳纤维表面包覆大量结合紧密、垂直表面向外生长的SiC阵列, 且阵列分布均匀, 高度约为1.4 μm。当SiC/C_f复合材料厚度在1~2 mm范围内时, 随厚度增加, 最小反射损耗(RL_min)由高频向低频移动; 当厚度为1.8 mm时, 在8.31 GHz下的RL_min为-40.653 dB, 有效吸收带宽为1.11 GHz(RL < -10 dB); 当厚度为1.5 mm时, 有效吸收带宽可达2.42 GHz, 且厚度为1.3~1.8 mm时, RL_min均小于-20 dB。SiC阵列改性碳纤维新型SiC/C_f复合材料有望成为一种轻质高效的电磁波吸收材料。     

SiC/SiC复合材料层板低速冲击及其剩余强度试验研究

高速飞行器中的陶瓷基复合材料结构在服役过程中不可避免地会遇到低速冲击问题,低速冲击后的损伤形式以及剩余承载能力是影响飞行器结构安全的关键问题。本研究以二维编织SiC/SiC复合材料板件为研究对象,在不同能量下开展了低速冲击试验,分析了低速冲击载荷下试验件的表面损伤状态,通过计算机断层扫描技术观察了试验件内部的损伤形貌,结合冲击过程中的冲击响应曲线以及应变历史曲线,分析了SiC/SiC复合材料低速冲击过程的损伤机理。针对含勉强目视可见损伤的试验件开展了冲击后剩余强度试验,研究了勉强目视可见损伤对SiC/SiC复合材料剩余承载性能的影响。结果表明,在低速冲击载荷的作用下,试验件的表面损伤主要包括无表面损伤、勉强目视可见损伤、半穿透损伤以及穿透损伤,试验件的内部损伤主要有锥形体裂纹、纱线断裂以及分层损伤。低速冲击损伤会严重影响SiC/SiC复合材料的剩余性能,虽然试验件损伤勉强目视可见,但其剩余压缩强度为无损件81%,剩余拉伸强度仅为无损件的68%。     

C/SiC_w复合体的制备及其吸波性能研究

以酚醛树脂为碳源,正硅酸乙酯为硅源,采用凝胶-碳热还原法制备C/SiC w复合体,考察了催化剂、碳热还原温度等工艺条件对C/SiC w复合体的结构和性能的影响。结果表明,碳硅比为3∶1的前驱体,在FeCl3催化作用下,1 500℃制备的C/SiC w-50复合体具有良好的吸波性能,1∶2的石蜡介质测试样在2~18 GHz频率范围内,3 mm厚度的最大反射损耗为-27.2 dB,反射损耗低于-5 dB的频率范围为6.3~10.8 GHz,频宽达4.5 GHz。     

C/SiC复合材料应力氧化失效机理

研究了干氧和湿氧两种气氛、疲劳和蠕变两种应力下C/SiC复合材料在1300℃的应力氧化行为. 试验结果和断口形貌SEM分析表明: C/SiC复合材料在疲劳应力下比在蠕变应力下具有更强的抗氧化能力和更长的持续时间; 干氧环境中的蠕变试样以C纤维氧化失效为主; 水蒸气的存在加剧了SiC基体的氧化, 并且使受蠕变应力的C/SiC复合材料以SiC基体氧化失效为主.     

热声载荷下C/SiC层合薄板动态响应分析及寿命预测

鉴于处在热声载荷下的薄壁结构工作条件恶劣,极易发生屈曲和声疲劳从而影响构件的稳定性和使用寿命。以四边固支C/Si C复合材料层合板结构为研究对象,运用有限元方法计算结构在不同温度和声压级组合下的振动响应,分析屈曲前后响应特性并总结了典型的非线性振动响应特性;基于复合材料层合板高比强和特殊的结构疲劳损伤机理特点,运用改进的雨流法统计了层合板在超高温度强噪声工况下的应力响应,结合材料对称循环疲劳性能试验所得数据拟合地考虑平均应力影响的等效寿命公式和Palmgren-Miner线性累积损伤准则估算层合板的疲劳寿命。     

C/SiC箱型结构的热模态试验研究

飞行器速度随着科学技术的发展不断提高,导致飞行器面临着极其严酷的高温环境,因此在地面上的热模态试验具有重要意义。作为具有应用前景的一种结构,箱型结构具有重要的研究价值;以箱型结构的C/SiC典型构型件为研究对象,对其在高温环境中的振动特性进行了研究。结合现有的试验技术,该研究提供了一套热模态试验的方案,给出了C/SiC典型构型件在高温环境中的模态频率和模态振型;其优点在于能够最大程度的保证试验件的独立完整性,不会在激励和测量的过程中产生附加刚度、附加质量等影响。研究成果为箱型结构在高温环境中的模态研究提供参考。     

2D-C/SiC复合材料低温动态Z向压缩性能

采用Hopkinson压杆试验装置,对2D-C/SiC复合材料进行了低温条件下的Z向动态压缩性能试验研究,低温条件通过控制酒精和液氮的配比系数得到,通过改变波形整形器几何尺寸的方法来实现恒应变率加载,以得到准确、可信的试验结果。试验结果表明: 由于复合材料内部含有大量初始微缺陷,2D-C/SiC复合材料在低温动态加载条件下呈现伪塑性行为,其破坏时并未表现出典型的脆性破坏,而是在应力达到压缩强度时出现了显著的应变软化现象,在经历了较大的变形后才最终破坏。随着温度的降低,复合材料的动态Z向压缩强度增加,但失效应变减小。2D-C/SiC复合材料在低温环境下,其内部纤维和基体之间界面结合力增强,同时强的界面结合力可以导致高的压缩强度。     

碳—铝复合材料的破坏过程

通过测定拉伸强度,结会拉伸过程监测到的声发射信息及断口形貌的分析,研究了C/Al复合材料的破坏过程。研究结果表明C/Al复合材料的破坏过程是极其复杂的,它的拉伸强度,断口形貌,声发射特征三者之间有密切的关系。      

三维编织C/SiC复合材料的拉压实验研究

针对三维编织C/SiC复合材料进行了拉伸试验和压缩试验,得到了材料拉伸、压缩的主要力学性能参数、损伤发展情况及破坏规律。从宏观角度比较了在两种载荷下材料弹性性能及强度的区别,得到了一些试验研究结论。结果表明:三维编织C/SiC在拉伸和压缩载荷下的应力-应变曲线有明显的非线性特性;拉伸模量低于压缩模量;拉伸强度高于压缩强度;声发射数据可以用来检测材料内部损伤的发展。      

Si/C/N纳米粉体的吸波特性研究

采用ＸＲＤ研究了氮原子百分含量为１１．６１%的Ｓｉ/Ｃ/Ｎ纳米粉体的相组成,并测定了粉体介电常数根据介电常数,分别优化设计了单层和双层的吸波徐层,设计的吸波涂层对８~１８ＧＨｚ范围的电磁波有较好的吸收作用．设计厚度为２．７ｍｍ的单层吸波涂层,在８~１５ＧＨｚ范围内反射率＜－５ｄＢ设计厚度为２．８ｍｍ的双层吸波涂层,在８~１８ＧＨｚ频率范围内电磁波的反射率均＜－５ｄＢ,反射率＜－８ｄＢ的频带为６ＧＨｚ．针对纳米粉体的吸波特性,提出了Ｓｉ/Ｃ/Ｎ纳米粉体的吸波机理．     

Reliability analysis of nonlinear laminated composite plate structures

A procedure for the reliability analysis of laminated composite plate structures subjected to large deflections under random static loads is presented. The nonlinear analysis of laminated composite plate structures is achieved via a corotational total Lagrangian finite element formulation which is based on the von Karman assumption and first order shear deformation theory. This formulation is applicable for the nonlinear analysis of plate structures with large rotations but moderate deformation and thus accurate enough to predict the behavior of the structures at the point of failure. The reliability assessment of laminated composite plate structures with random strength subjected to random loads is approached by the determination of limit state surfaces in load space. The limit space surfaces are obtained by performing a series of first ply failure analyses following different load paths in load space using the proposed nonlinear structural analysis technique and an appropriate failure criterion. A numerical technique is then proposed to evaluate the reliability of the plate structures. Examples of the reliability analyses of laminated plates with different layer orientations subject to random loads are given for illustration.     

Free Vibration Analysis of Folded Plate Structures by the FSDT Mesh-free Method

Based on the first-order shear deformation theory, a mesh-free Galerkin method for free vibration analysis of stiffened and un-stiffened folded plates and plate structures is presented in this paper. The folded plate or plate structure is modelled as a composite structure that consists of flat plates. The stiffness and mass matrices of the flat plates are derived based on the mesh-free formulation. To avoid the failure of direct superposition, a treatment is introduced to modify the stiffness and mass matrices. The global stiffness and mass matrices of the entire folded plate or plate structure are then obtained by superposing the modified stiffness and mass matrices of the flat plates. The analysis of the stiffened folded plates or plate structures proceeds in a similar fashion, as they are regarded as composite structures of stiffened and un-stiffened flat plates. The stiffness and mass matrices of the stiffened flat plates are also given by the mesh-free method. As no meshes are used in deriving the stiffness and mass matrices, the proposed method is more flexible in studying problems for which remeshing is inevitable with the finite element methods. Several numerical examples are computed with the proposed method to demonstrate its accuracy and convergence. The results show good agreement with the solutions that have been given by other researchers and ANSYS.     

Hybrid S2/Carbon Epoxy Composite Armours Under Blast Loads

Civil and military structures, such as helicopters, aircrafts, naval ships, tanks or buildings are susceptible to blast loads as terroristic attacks increases, therefore there is the need to design blast resistant structures. During an explosion the peak pressure produced by shock wave is much greater than the static collapse pressure. Metallic structures usually undergo large plastic deformations absorbing blast energy before reaching equilibrium. Due to their high specific properties, fibre-reinforced polymers are being considered for energy absorption applications in blast resistant armours. A deep insight into the relationship between explosion loads, composite architecture and deformation/fracture behaviour will offer the possibility to design structures with significantly enhanced energy absorption and blast resistance performance. This study presents the results of a numerical investigation aimed at understanding the performance of a hybrid composite (glass/carbon fibre) plate subjected to blast loads using commercial LS-DYNA software. In particular, the paper deals with numerical 3D simulations of damages caused by air blast waves generated by C4 charges on two fully clamped rectangular plates made of steel and hybrid (S2/Carbon) composite, respectively. A Multi Materials Arbitrary Lagrangian Eulerian (MMALE) formulation was used to simulate the shock phenomenon. For the steel plates, the Johnson-Cook material model was employed. For the composite plates both in-plane and out-of-plane failure criteria were employed. In particular, a contact tiebreak formulation with a mixed mode failure criteria was employed to simulate delamination failure. As for the steel plates the results showed that excellent correlation with the experimental data for the two blast load conditions in terms of dynamic and residual deflection for two different C4 charges. For the composite plates the numerical results showed that, as expected, a wider delamination damage was observed for the higher blast loads case. Widespread tensile matrix damage was experienced for both blast load cases, while only for 875?g blast load fiber failure damage was observed. This agrees well with the experimental data showing that the composite panel was not able to resist to the 875?g blast load.     

BN/SiC复合涂层改性炭纤维的吸波性能研究

以尿素、硼酸为原料, 采用浸涂工艺先在炭纤维表面制备BN涂层, 再以三氯甲基硅烷为前驱体, 采用化学气相沉积工艺在纤维表面沉积SiC涂层, 制得了BN/SiC复合涂层改性炭纤维。对BN/SiC复合涂层改性炭纤维的微观结构、抗氧化性能、介电性能及吸波性能进行了研究。结果表明: 炭纤维表面BN涂层的厚度约为0.1 μm, SiC涂层的厚度约为0.7 μm。炭纤维经表面BN/SiC复合涂层改性后, 抗氧化性能明显提高, 开始明显氧化失重温度从560℃提高到790℃, 最终氧化温度从780℃提高到1200℃以上; 且介电性能得到有效改善, 吸波性能显著提高。相比于未改性炭纤维, 厚度为2 mm的BN/SiC复合涂层改性炭纤维的最小反射率减小到-13.3 dB, 小于-10 dB的带宽增加至2.5 GHz。     

面向一体化热防护的陶瓷基复合材料轻量化结构研究进展与挑战EI北大核心CSCD

高超声速飞行器技术是航空航天领域发展的重要方向,对国防安全起着重要作用。高超声速飞行器能在极端环境中安全服役的关键在于飞行器的热防护材料与结构。一方面,热防护材料与结构必须能够经受恶劣的气动热环境;另一方面,热防护材料与结构还要在承载的同时尽可能降低质量以提高飞行器有效载荷。因此,需要研发兼具耐高温、轻量化、承载特性的热防护结构。本文首先综述了C/SiC陶瓷基复合材料轻量化点阵结构及其制造方法,对其在室温、高温环境下的力学行为与传热行为的研究现状进行了总结,并具体讨论了基于C/SiC陶瓷基复合材料轻量化点阵结构的耐高温、轻量化、承载、一体化热防护结构研究进展情况。最后,在新设计理论与方法、新制造技术、服役特性、多功能一体化设计与实现四个方面对面向一体化热防护的陶瓷基复合材料轻量化结构的研究挑战进行了展望。本文为高超声速飞行器新型热防护结构的发展提供一定借鉴与思考。     

高轴压比、低剪跨比双钢板-混凝土组合剪力墙拟静力试验研究

双钢板-混凝土组合剪力墙可减小墙体厚度、提高承载力和延性,为研究双钢板-混凝土组合剪力墙高轴压比下的抗震性能,完成了5个剪跨比为1.0的双钢板-混凝土组合剪力墙试件的拟静力试验,研究了剪力墙在低周往复荷载作用下的受力性能和破坏模式等,分析了轴压比、距厚比等因素对抗震性能的影响。试验结果表明:低剪跨比试件发生弯剪破坏;墙体钢板在平均位移角1/83时发生局部屈曲,初始屈曲形态受距厚比影响显著;试件峰值荷载、位移延性系数、刚度等受轴压比、距厚比的影响较小;试件平均极限位移角达1/72、平均有效破坏位移角达1/52,具有良好的变形能力;距厚比增大,试件滞回性能稳定性降低;试件耗能随变形增大而迅速增长,抗震性能良好。建议低剪跨比双钢板-混凝土组合剪力墙轴压比限值取0.7。