热解碳界面层对碳＼碳化硅复合材料拉伸性能的影响

本文研究了用化学气相渗工艺的均热法制备炭纤维增强碳化硅（Ｃ／ＳｉＣ）复合材料，其中有部分材料在沉积碳化硅之前先沉积少量热解碳，以作为界面层。对有界面层和无界面层的材料进行了拉伸试验。用金相显微镜和扫描电镜观察了材料微观结构及继口形貌。结果表明，Ｃ／ＳｉＣ材料力学性能主要取决于纤维与基体的界面。有热解碳界面层的Ｃ／ＳｉＣ材料，在拉伸断裂时出现大范围脱粘，断口类似毛刷，材料强度大，断裂功也大，有很大的     

碳化硅纤维增强锂铝硅玻璃陶瓷界面粗糙度研究

采用复合材料界面微脱粘仪，根据纤维回推技术对ＳｉＣ纤维增强锂铝硅（ＬＡＳ）玻璃陶瓷基复合材料的纤维／基体界面粗糙度进行测试。结果表明该复合材料的界面粗糙度约８～１５ｎｍ。用ＴＥＭ，ＥＥＬＳ等手段，对界面的组成的形貌进行观察。分析和讨论了基体成分以及复合材料的热暴露对界面粗糙度的影响。发现Ｎｂ２Ｏ５在基体中的加入有助于减小界面粗糙度，而Ｂ２Ｏ３则使界面粗糙度上升。空气中热暴露使界面粗糙度急剧上升。     

化学气相渗（CVI）C／SiC复合材料性能控制

本研究用化学气相渗技术制备了四种Ｃ／ＳｉＣ复合材料：在ＣＨ３ＳｉＣｌ３＋Ｈ２（普通）＋Ａｒ（高纯）系统中制各了两种材料：材料Ａ为１Ｋ炭布层叠无热解炭界面层，材料Ｂ为１Ｋ炭布层叠有热解炭界面层；在ＣＨ３ＳｉＣｌ３＋Ｈ２（高纯）＋Ａｒ（高纯）系统中制备了另两种材料：材料Ｃ和材料Ｄ分别为１Ｋ、Ｔ３００炭布层叠有热解炭界面层．分别对其中每两种材料进行了相互比较，研究了骨架纤维、界面层及基体对整个复合材料性能的影响；通过控制上述三方面因素可以对Ｃ／ＳｉＣ复合材料的总体结构进行设计从而控制其材料最终性能。     

聚醚砜／碳纤维复合材料的断裂行为研究

本文用湿法制造无纬预浸布，用模压法成型两种不同基体村质的聚醚砜／碳纤维复合材料层压板。分别用ＥＮＦ试样和三点弯曲试样（裂纹方向和纤维方向一致）研究了ＰＥＳ／ＣＦ复合材料的Ⅱ型层间断裂行为及Ⅰ型纤维层间断裂行为，用仪器化Ｃｈａｒｐｙ冲击试验方法研究了ＰＥＳ／ＣＦ复合材料的冲击性能。断口形貌的电镜分析表明，ＰＥＳ／ＣＦ复合材料的界面粘接情况良好。     

涂层工艺对C/C复合材料结构和弯曲性能的影响

采用热处理和包埋工艺制备了Ｃ／Ｃ复合材料的ＭｏＳｉ２／ＳｉＣ抗氧化涂层,对组织结构、界面、弯曲断口进行了显微观察,分析了氧化保护涂层及其工艺对其机械性能的影响,结果表明,该工艺在Ｃ／Ｃ复合材料表面生成涂层的同时,使基材内部的界面也被硅化;并且发现,热解炭基体比炭纤维更易与Ｓｉ反应生成ＳｉＣ。Ｃ／Ｃ复合材料经涂层工艺处理后,弯曲强度降低;热处理过程中发生的材料氧化是弯曲强度下降的主要原因     

平纹编织碳纤维增韧碳化硅复合材料的力学性能及损伤演化

通过平纹编织碳纤维增韧碳化硅复合材料的拉伸、压缩和剪切的单向与循环加–卸载实验,分别研究了材料在拉伸载荷、压缩载荷和剪切载荷作用下的力学性能和损伤演化过程。结果表明:在压缩载荷作用下,材料的压缩性能下降很小,基体开裂,纤维界面脱粘和纤维束断裂为主要的失效机理;材料在拉伸和剪切载荷作用下,损伤演化过程有所区别。材料拉伸损伤演化经历损伤初始阶段、损伤加速阶段和损伤减缓阶段,为韧性断裂,损伤破坏主要表现为:基体开裂、横向纤维束开裂,界面层脱粘、层间剥离和纤维断裂;在剪切载荷作用下,经历损伤加速阶段和损伤减缓阶段,基体开裂、界面层脱粘和纤维断裂为主要的损伤机理,试样最后在最窄截面位置形成平断面。基于实验研究结果,采用回归分析方法,分别给出了材料在拉伸载荷和剪切载荷作用下损伤演化方程式。     

TiB2／SiCw复合材料增韧机理的微观分析

在ＴｉＢ２／ＳｉＣｗ基体中加入适量的ＳｉＣｗ可以明显地提高其断裂韧 性ＫＩＣ，其它机械性能也有不同程度的改善。ＳＥＭ、ＴＥＭ微观分析表明：在具有较高ＫＩＣ值的ＴｉＢ２／ＢｉＣｗ陶瓷复合材料中，ＳｉＣｗ与ＴｉＢ２晶粒之间有较适宜的界面结合，两相之间未发现有明显的界面化学反应用，当该复合材料发生断裂时，其内部出现晶须拔出，裂纹桥连，裂纹偏转三种增韧机制。     

Al2O3／SiCw陶瓷材料晶须拔出的有限元分析

采用有限元的方法分析了Ａｌ２Ｏ３／ＳｉＣｗ陶瓷材料晶须拔出时中的应力状态及应力分布，研究了晶须拔出时材料界面的断裂模式。结果表明：当裂纹扩展到晶须时，在裂纹尖端附近晶须与基体界面处存在较大的剪应力，从而使界面首先发生剪切破坏，当晶须在裂纹面之间桥联时，由于晶须与基体界面存在较大的径向拉应力而使界面首先发生径向拉伸破坏。     

溶胶-凝胶法制备Al_2O_3f/Al_2O_3复合材料及其性能研究

本文采用化学气相渗透法(CVI)在三维氧化铝纤维预制体上沉积热解碳(PyC)界面层,通过溶胶-凝胶法制备氧化铝纤维/PyC/氧化铝基体复合材料和无界面复合材料。通过三点弯曲实验分析其力学性能,扫描电子显微镜观察其断口微观结构。结果表明,当热解碳界面层厚度分别为0.6μm和0.8μm时,复合材料所对应的弯曲强度分别为231.3 MPa和158.2 MPa,与无界面复合材料弯曲强度55.8 MPa相比,力学性能分别提高314.5%和183.5%。通过微观结构分析发现利用热解碳界面可充分发挥连续纤维拨出、界面脱粘和裂纹偏转等增韧机制,实现材料脆韧转变。     

CVI法制备三维碳纤维增韧碳化硅复合材料

利用三维编织的碳纤维预制体，采用等温ＣＶＩ的方法制备出了碳纤维增韧碳化硅复合材料。对于无碳界面层的复合材料（Ｃ／ＳｉＣ），弯曲强度和断裂韧性随密度的提高而提高，最大值分别为５２０ＭＰａ和１６．５ＭＰａ·ｍ＾１／２。密度高的复合材料呈明显的脆性断裂，而密度较低的材料在断裂过程中存在纤维束的拔出而表现出韧性断裂行为。密度较高和无碳界面的复合材料，经１５５０℃高温处理后，弯曲强度明显降低（３５０ＭＰａ）     

Modeling matrix multicracking development of fiber-reinforced ceramic-matrix composites considering fiber debonding

In this paper, the effect of fiber debonding on matrix multicracking development of different fiber-reinforced CMCs is investigated using the micromechanical approach. The Budiansky–Hutchinson–Evans shear-lag model is adopted to analyze the fiber and matrix stress distributions of the damaged composite. The fracture mechanics approach is used to determine the fiber/matrix interface debonding length. Combining the critical matrix strain energy criterion and fracture mechanics fiber/matrix interface debonding criterion, the stress-dependent matrix multicracking development is analyzed for different fiber volume fraction, fiber/matrix interface properties and matrix cracking characteristic stress. The experimental matrix multicracking development of unidirectional C/Si₃N₄, SiC/Si₃N₄, SiC/CAS, SiC/CAS-II, SiC/SiC, SiC/Borosilicate and mini-SiC/SiC composites are predicted.     

Study on interfacial debonding stress and damage mechanisms of C/SiC composites using acoustic emission

Among ceramic matrix composites (CMCs), carbon fiber-reinforced silicon carbide matrix (C/SiC) composites are widely used in numerous high-temperature structural applications because of their superior properties. The fiber–matrix (FM) interface is a decisive constituent to ensure material integrity and efficient crack deflection. Therefore, there is a critical need to study the mechanical properties of the FM interface in applications of C/SiC composites. In this study, tensile tests were conducted to evaluate the interfacial debonding stress on unidirectional C/SiC composites with fibers oriented perpendicularly to the loading direction in order to perfectly open the interfaces. The characteristics of the material damage behaviors in the tensile tests were successfully detected and distinguished using the acoustic emission (AE) technique. The relationships between the damage behaviors and features of AE signals were investigated. The results showed that there were obviously three damage stages, including the initiation and growth of cracks, FM interfacial debonding, and large-scale development and bridging of cracks, which finally resulted in material failure in the transverse tensile tests of unidirectional C/SiC composites. The frequency components distributed around 92.5 kHz were dominated by matrix damage and failure, and the high-frequency components distributed around 175.5 kHz were dominated by FM interfacial debonding. Based on the stress and strain versus time curves, the average interfacial debonding stress of the unidirectional C/SiC composites was approximately 1.91 MPa. Furthermore, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDXS) were used to observe the morphologies and analyze the chemical compositions of the fractured surfaces. The results confirmed that the fiber was completely debonded from a matrix on the fractured surface. The damage behaviors of the C/SiC composites were mainly the syntheses of matrix cracking, fiber breakage, and FM interfacial debonding.     

Effect of multiple loading sequence on time-dependent stress rupture of fiber-reinforced ceramic-matrix composites

In this paper, the effect of multiple loading sequence on time-dependent stress rupture of fiber-reinforced ceramic-matrix composites (CMCs) at intermediate temperatures in oxidative environment is investigated. Considering multiple damage mechanisms, a micromechanical constitutive model for time-dependent stress rupture is developed to determine damage evolution of matrix crack spacing, interface debonding and oxidation length, and fiber failure probability under single and multiple loading sequences. The relationships between multiple loading sequence, composite strain evolution, time, matrix cracking, interface debonding and oxidation, and fiber fracture are established. The effects of fiber volume, matrix crack spacing, interface shear stress in the slip and oxidation region, and environment temperature on the stress/time-dependent strain, interface debonding and oxidation fraction, and fiber broken fraction of SiC/SiC composite are analyzed. The experimental stress rupture of SiC/SiC composite under single and multiple loading sequences at 950°C in air atmosphere is predicted. Compared with single loading stress, multiple loading sequence affects the interface debonding and oxidation fraction in the debonding region, leading to the higher fiber broken fraction and shorter stress-rupture lifetime.     

Effect of a Boron Nitride Interphase That Debonds between the Interphase and the Matrix in SiC/SiC Composites

Typically, the debonding and sliding interface enabling fiber pullout for SiC-fiber-reinforced SiC-matrix composites with BN-based interphases occurs between the fiber and the interphase. Recently, composites have been fabricated where interface debonding and sliding occur between the BN interphase and the matrix. This results in two major improvements in mechanical properties. First, significantly higher failure strains were attained due to the lower interfacial shear strength with no loss in ultimate strength properties of the composites. Second, significantly longer stress-rupture times at higher stresses were observed in air at 815°3C. In addition, no loss in mechanical properties was observed for composites that did not possess a thin carbon layer between the fiber and the interphase when subjected to burner-rig exposure. Two primary factors were hypothesized for the occurrence of debonding and sliding between the BN interphase and the SiC matrix: a weaker interface at the BN/matrix interface than the fiber/BN interface and a residual tensile/shear stress-state at the BN/matrix interface of melt-infiltrated composites. Also, the occurrence of outside debonding was believed to occur during composite fabrication, i.e., on cooldown after molten silicon infiltration.     

Effect of the fabrication process on the microstructural evolution of carbon fibers and flexural property on C/SiC composites by the NITE method

Nano-infiltration and transient eutectic phase (NITE) SiC matrix composites are designed for application in aerospace propulsion systems, particularly in fasteners and thrusters. A variety of carbon fibers with different properties have been selected as reinforcements for SiC matrix composites. Carbon fibers are known to be stable at high temperatures; however, the effects of high applied pressure at high temperatures on the fiber microstructure evolution and mechanical properties are not well-known. As a scoping study for fabricating NITE C/SiC composites, the behaviors of various carbon fibers in SiC composites. Pitch-based fibers, namely, GRANOX XN-05 and YS-90A, and a polyacrylonitrile-based fiber, namely, TORAYCA T-300B, were selected for matrix reinforcement. The 3-point bending test results indicated pseudo-ductile behaviors in the cases of YS-90A and T-300B fiber reinforcements. Fracture resistance evaluation based on the single-notch bending test indicated that the YS-90A fiber reinforced composite afforded the highest fracture resistance among the three C/SiC composites. The microstructure evolution on YS-90A and T-300B fibers was limited to near the fiber surface. Therefore, YS-90A and T-300B carbon fibers are potential candidates for reinforcement in NITE C/SiC composites.     

Effect of Carbon and Silicon Carbide/Carbon Interlayers on the Mechanical Behavior of Tyranno-SA-Fiber-Reinforced Silicon Carbide-Matrix Composites

Several CVI-SiC/SiC composites were fabricated and the mechanical properties were investigated using unloading–reloading tensile tests. The composites were reinforced with a new Tyranno-SA fiber (2-D, plain-woven). Various carbon and SiC/C layers were deposited as fiber/matrix interlayers by the isothermal CVI process. The Tyranno-SA/SiC composites exhibited high proportional limit stress (∼120 MPa) and relatively small strain-to-failure. The tensile stress/strain curves exhibited features corresponding to strong interfacial shear and sliding resistance, and indicated failures of all the composites before matrix-cracking saturation was achieved. Fiber/matrix debonding and relatively short fiber pullouts were observed on the fracture surfaces. The ultimate tensile strength displayed an increasing trend with increasing carbon layer thickness up to 100 nm. Further improvement of the mechanical properties of Tyranno-SA/SiC composites is expected with more suitable interlayer structures.     

Experimental study on the mechanical behavior and failure mechanism of 3d MWK carbon/epoxy composites under quasi‐static loading

Quasi‐static tensile, out‐of compression, in‐plane compression, three‐point‐bending and shear tests were conducted to reveal the mechanical behavior and failure mechanisms of three‐dimensional (3D) multiaxial warp‐knitted (MWK) carbon/epoxy composites. The characterization of the failure process and deformation analysis is supported by high‐speed camera system and Digital Image Correlation. The results show that tensile, bending, out‐of‐plane compression, in‐plane compression stress–strain response exhibit obvious linear elastic feature and brittle fracture characteristics, whereas the shear response exhibits a distinct nonlinear behavior and gradual damage process. Meanwhile, 3D MWK carbon/epoxy composites have good mechanical properties, which can be widely used in the fields of engineering. In addition, the failure for tension behaves as interlayer delaminating, 90/+45/−45° interface debonding and tensile breakage of 0° fibers; the damage for out‐of‐plane compression is mainly interlaminar shear dislocation together with local buckling and shear fracture of fibers; the failure pattern for in‐plane compression is 90° fiber separating along fiber/matrix interface as well as 0/+45/−45° fiber shear fracture in the shear plane. The main failure for bending is fiber/matrix interface debonding and fibers tearing on the compression surface, 0° fibers breakage on the tension surface as well as fiber layers delaminating. Although the shear behavior is characterized by a gradually growing shear matrix damage, 90/+45/−45° interface debonding, +45/−45° fibers shear fracture, and final 0° fiber compression failure. POLYM. COMPOS., 37:3486–3498, 2016. © 2015 Society of Plastics Engineers     

Interfacial Microstructure and Chemistry of SiC/BN Dual-Coated Nicalon-Fiber-Reinforced Glass-Ceramic Matrix Composites

Glass-ceramic composites with improved high-temperature mechanical properties have been produced by incorporating continuous SiC fibers into a barium magnesium aluminosilicate matrix. Control of the fiber/matrix interface was achieved by a dual-layer coating of SiC/BN(C) applied to the fibers by CVD. The weakly bonded interface resulted in composites with high fracture toughness and strength up to 1100°C, and the composite system was oxidatively stable during long-term exposure to air at high temperatures. Composites with different thermal and mechanical histories were studied, and interfaces were characterized using transmission electron microscopy (TEM), Auger electron spectroscopy, and fiber pushout tests. Observations of interfacial microstructure were correlated with the mechanical properties of the composite and with interface properties determined from fiber push-out tests.     

Mechanical and thermal shock properties of Cf/SiBCN composite: Effect of sintering densification and fiber coating

In this work, resin-derived carbon coating was prepared on carbon fibers by polymer impregnation pyrolysis method, then silicoboron carbonitride powder was prepared by mechanical alloying, and finally carbon fiber-reinforced silicoboron carbonitride composites were prepared by hot-pressing process. The effects of sintering densification and fiber coating on microstructure, mechanical properties, thermal shock resistance, and failure mechanisms of the composites were studied. Fiber bridging hinders the sintering densification, causing more defects in fiber-dense area and lower strength. However, higher sintering temperature (1800–2000°C) can improve mechanical properties significantly, including bending strength, vickers hardness, and elastic module, because further sintering densification enhances matrix strength and fiber/matrix bonding strength, while the change of fracture toughness is not obvious (2.24–2.38 MPa·m^1/2) due to counteraction of higher debonding resistance and less pull-out length. However, fiber coating improves fracture toughness greatly via protecting carbon fibers from chemical corrosion and damage of thermal stress and external stress. Due to lower coefficient of thermal expansion, lower fiber loading ratio, less stress concentration at the fiber/matrix interface, and better defect healing effect, lower sintering temperature favors thermal shock resistance of composites, and thermal shock recession mechanisms are the damage of interface.