C/SiC拉伸强度与声发射演化的关联性EI北大核心CSCD

对平纹编织C/SiC复合材料样品拉伸破坏过程的声发射进行监测,采用基于改进遗传算法的无监督聚类方法对声发射信号进行模式识别,统计分析各类声发射模式的特征及其演化过程,结合断口分析,研究了C/SiC复合材料的拉伸强度、损伤机制与声发射信号演化之间的关系.结果表明:维断裂的声发射能量能够反映纤维/基体界面结合强度;低强度C/SiC材料中存在引起应力集中的基体富集区,在加载初期基体开裂事件占比超过50%;中强度C/SiC材料由于较强的界面,纤维损伤以单丝或部分纤维断裂事件为主;高强度C/SiC材料界面结合强度适中,纤维簇断裂是主要的失效模式.     

C/SiC拉伸强度与声发射演化的关联性

对平纹编织C/SiC复合材料样品拉伸破坏过程的声发射进行监测,采用基于改进遗传算法的无监督聚类方法对声发射信号进行模式识别,统计分析各类声发射模式的特征及其演化过程,结合断口分析,研究了C/SiC复合材料的拉伸强度、损伤机制与声发射信号演化之间的关系。结果表明:维断裂的声发射能量能够反映纤维/基体界面结合强度;低强度C/SiC材料中存在引起应力集中的基体富集区,在加载初期基体开裂事件占比超过50%;中强度C/SiC材料由于较强的界面,纤维损伤以单丝或部分纤维断裂事件为主;高强度C/SiC材料界面结合强度适中,纤维簇断裂是主要的失效模式。     

2维C/SiC复合材料的拉伸损伤演变过程和微观结构特征

通过单向拉伸和分段式加载-卸载实验,研究了二维编织C/SiC复合材料的宏观力学特性和损伤的变化过程.用扫描电镜对样品进行微观结构分析,并监测了载荷作用下复合材料的声发射行为.结果表明:在拉伸应力低于50MPa时,复合材料的应力-应变为线弹性;随着应力的增加,材料模量减小,非弹性应变变大,复合材料的应力-应变行为表现为非线性直至断裂.复合材料的平均断裂强度和断裂应变分别为23426MPa和0.6%.拉伸破坏损伤表现为:基体开裂,横向纤维束开裂,界面层脱粘,纤维断裂,层间剥离和纤维束断裂.损伤累积后最终导致复合材料交叉编织节点处纤维束逐层断裂和拔出,形成斜口断裂和平口断裂.     

三维编织Cf/SiC复合材料的拉伸破坏行为

通过三维编织碳纤维(carbon fiber，Cf)／SiC复合材料样品单向拉伸以及单向拉伸加卸载实验．结合样品断口观察．从宏观上分析了三维编织Cf／SiC复合材料单向拉伸时的力学响应，为进一步描述三维编织Cf／SiC复合材料力学行为奠定了实验基础。实验结果表明：三维编织Cf／SiC复合材料单向拉伸时，卸载模量衰减与应力呈线性关系，残余应变的增加与应力呈二次函数关系。微裂纹主要在编织节点处萌生，沿纤维束界面扩展，最终在编织节点处汇合，导致样品发生破坏。     

基于深度学习的平纹Cf/SiC复合材料原位拉伸损伤演化与断裂分析

为揭示平纹C_f/SiC复合材料的拉伸损伤演化及失效机理,开展了X射线CT原位拉伸试验,获得材料的三维重构图像,利用深度学习的图像分割方法,准确识别出拉伸裂纹并实现其三维可视化。分析了平纹C_f/SiC复合材料损伤演化与失效机理,基于裂纹的三维可视化结果对材料损伤进行了定量表征。结果表明:平纹C_f/SiC复合材料的拉伸力学行为呈现非线性,拉伸过程中主要出现基体开裂、界面脱黏、纤维断裂及纤维拔出等损伤;初始缺陷易引起材料损伤,孔隙多的部位裂纹数量也多;纤维束外基体裂纹可扩展至纤维束内部,并发生裂纹偏转。基于深度学习的智能图像分割方法为定量评估陶瓷基复合材料损伤演化与失效机理提供了有效分析手段。     

碳纤维三维编织复合材料横向变形损伤声发射监测

利用声发射(Acoustic Emission,简称"AE")技术和数字图像相关(Digital Image Correlation,简称"DIC")方法,结合破坏断口形貌,研究三维五向编织复合材料横向拉伸状态下的变形与损伤规律,分析横向拉伸力学响应、表层变形场及声发射信号特征。结果表明:三维五向编织复合材料的横向拉伸极限载荷较小,力学曲线分线性和非线性两个阶段,破坏曲线为非线性,与横向拉伸破坏机理有关。撞击累计数的递增趋势能较好地反映材料的损伤演化过程。三维编织复合材料横向拉伸破坏断口沿纤维编织方向呈非平齐状,失效模式主要为基体开裂和纤维脱粘以及少量的纤维断裂。表面全场信息很好地反映了材料横向拉伸损伤演化特征,为三维编织复合材料结构健康监测提供了依据。     

2D-SiC/SiC陶瓷基复合材料的拉伸本构模型研究

通过单向拉伸试验,研究了2D-SiC/SiC复合材料的应力-应变行为.结果表明,材料单向拉伸应力-应变曲线表现出明显的双线性特征,且线弹性段较长.通过试件断口照片,分析了2D-SiC/SiC复合材料单向拉伸破坏机理和损伤模式.基于对损伤过程的假设,建立了二维连续纤维增强陶瓷基复合材料的双线性本构模型,并将其应用于2D-SiC/SiC复合材料的应力-应变曲线模拟,模拟结果与试验值吻合很好.同时,分析计算表明,2D-SiC/SiC复合材料的单轴拉伸行为主要由纵向纤维柬决定,横向纤维对材料的整体模量和强度贡献很小.     

碳纤维编织复合材料拉伸变形测量及声发射监测

采用声发射和数字图像相关互补技术,结合破坏断口微结构特征,研究碳纤维编织复合材料的损伤变形与失效机理。在复合材料试件拉伸加载的同时,实时获取变形特征和损伤声发射信号,分析复合材料力学响应与位移场、声发射特征的关系。结果表明,复合材料试件实时拉伸位移场、损伤破坏过程的声发射相对能量、撞击累积数及幅度等特征参数反映了复合材料表面变形与内部损伤演化过程。复合材料试件断裂时出现较多高持续时间、高幅度、高相对能量的声发射信号,宏观断口平齐,表现为脆性断裂。     

碳纤维复合材料层合板面内压缩损伤及声发射特征分析

针对碳纤维复合材料层合板面内压缩损伤问题,基于声发射技术分析不同损伤阶段的声发射信号特征。根据加载过程中时间–载荷曲线以及试样破坏断面微观形貌,将损伤过程分为三个阶段:初始损伤阶段主要产生少量基体开裂与纤维–基体界面脱粘,裂纹迅速扩展阶段开始产生纤维剪断以及失稳变形,平稳损伤阶段主要产生失稳变形以及分层裂纹扩展。结合声发射信号的振幅、振铃计数研究损伤过程,并基于小波变换进行损伤信号的时频分析,发现不同损伤类型可通过声发射振幅及频率特征有效识别。     

三维针刺C/SiC复合材料的结构特征和力学性能

采用化学气相渗透法制备了在厚度方向上具有纤维增强的三维针刺碳纤维增强碳化硅(C/SiC)陶瓷基复合材料,复合材料的密度和气孔率分别为2.15 h/cm3和16%.三维针刺C/SiC复合材料中的针刺纤维将各层紧密结合在一起,其层间抗剪切强度显著提高,为95MPa,比二维碳布叠层C/SiC复合材料的剪切强度(35MPa)高171.4%.三维针刺C/SiC复合材料的拉伸强度和弯曲强度分别为159MPa和350MPa,断裂模式为非脆性断裂,包括:裂纹扩展、偏转,碳纤维的拉伸断裂和逐步拔出.     

Interlaminar shear behaviors of 2D needled C/SiC composites under compressive and tensile loading

The interlaminar shear strength of 2D needled C/SiC composites was measured using the double-notch shear test method. Interlaminar shear tests were performed under compressive and tensile loading. Shear stress–strain response and shear strain field evolution were studied using the digital image correlation (DIC) technique. The results show that the interlaminar shear strength of the specimen using the compressive loading method is 15% higher than that of the tensile loading method. Severe shear strain concentration was observed near the upper notch of the tensile loading specimen. Acoustic emission (AE) was utilized to monitor the damage during the tests. Typical damage mechanisms were categorized according to AE signal characteristics. The statistical results show that more matrix cracks were produced in the tensile loading specimen and no separate fiber/matrix debonding signal was detected in both specimens.     

Mechanical Properties of Two Plain-Woven Chemical Vapor Infiltrated Silicon Carbide-Matrix Composites

The elastic and inelastic properties of a chemical vapor infiltrated (CVI) SiC matrix reinforced with either plain-woven carbon fibers (C/SiC) or SiC fibers (SiC/SiC) have been investigated. It has been investigated whether the mechanics of a plain weave can be described using the theory of a cross-ply laminate, because it enables a simple mechanics approach to the nonlinear mechanical behavior. The influences of interphase, fiber anisotropy, and porosity are included. The approach results in a reduction of the composite system to a fiber/matrix system with an interface. The tensile behavior is described by five damage stages. C/SiC can be modeled using one damage stage and a constant damage parameter. The tensile behavior of SiC/SiC undergoes four damage stages. Stiffness reduction due to transverse cracks in the transverse bundles is very different from cross-ply behavior. Compressive failure is initiated by interlaminar cracks between the fiber bundles. The crack path is dictated by the bundle waviness. For SiC/SiC, the compressive behavior is mostly linear to failure. C/SiC exhibits initial nonlinear behavior because of residual crack openings. Above the point where the cracks close, the compressive behavior is linear. Global compressive failure is characterized by a major crack oriented at a certain angle to the axial loading. In shear, the matrix cracks orientate in the principal tensile stress direction (i.e., 45° to the fiber direction) with very high crack densities before failure, but only SiC/SiC shows significant degradation in shear modulus. Hysteresis is observed during unloading/reloading sequences and increasing permanent strain.     

Damage monitoring of carbon fiber reinforced silicon carbide composites under random vibration environment by acoustic emission technology

Carbon fiber-reinforced silicon carbide (C/SiC) composites are widely used in high-temperature thermo-structural applications. They are subjected to extreme loading conditions, such as random vibrations, which are likely to damage the structure. Structural micro-damage identification during vibration is very difficult, owing to the randomness of the environmental vibration and the complicated response it causes in structures. This study aims to determine a method for monitoring the damage properties of a C/SiC structure under a random vibration environment using acoustic emission (AE) technology. First, a pencil break experiment is conducted to verify the feasibility of the AE technology. Then, an AE monitoring experiment of the structural damage in a vibration environment is systematically conducted. Two types of experiments are designed for simulating the damage formation process inside the structure. In addition, the parameter characteristics of typical AE signals in the random vibration test are analyzed, and the relationships between the AE signal parameters and vibration loading are obtained. Lastly, the different stages of material damage development and damage types in each stage are provided to reveal the damage evolution processes of C/SiC composites. The results indicate that AE technology can be effectively applied to investigate the damage behaviors of C/SiC composites in random vibration environments.     

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.     

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.     

Thermal shock response behaviour of carbon fibre reinforced silicon carbide matrix composites prepared by chemical vapour infiltration at different heating rates

The present work investigated the effects of thermal cycles in air on the tensile properties of a two-dimensional carbon fibre reinforced silicon carbide composite (2D C/SiC) prepared by chemical vapour infiltration at different heating rates. The composite was exposed to different cycles of thermal shock between 20 °C and 1300 °C in air. The damage mechanisms were investigated by AE online monitoring and fractured morphology offline analysis. The tensile strength of 2D-C/SiC decreases with increasing thermal cycles. However, the modulus only decrease within 40 cycles. Due to oxidation, with the decrease in heating rate, the residual properties of the material decrease more obviously. Meanwhile, the results of AE online monitoring and fracture analysis show that the matrix damage is more serious at higher heating rate and that more delamination occours in tensile fractures. The above results indicate that for the thermal shock of 2D C/SiC composites in air, oxidative damage plays a key role in the residual properties.     

Ring compression properties of SiCf/SiC composites prepared by chemical vapor infiltration

SiC fiber reinforced SiC matrix (SiC_f/SiC) composites prepared by chemical vapor infiltration are one of promising materials for nuclear fuel cladding tube due to pronounced low radioactivity and excellent corrosion resistance. As a structure component, mechanical properties of the composites tubes are extremely important. In this study, three kinds of SiC_f preform with 2D fiber wound structure, 2D plain weave structure and 2.5D shallow bend-joint structure were deposited with PyC interlayer of about 150–200?nm, and then densified with SiC matrix by chemical vapor infiltration at 1050?°C or 1100?°C. The influence of preform structure and deposition temperature of SiC matrix on microstructure and ring compression properties of SiC_f/SiC composites tubes were evaluated, and the results showed that these factors have a significant influence on ring compression strength. The compressive strength of SiC_f/SiC composites with 2D plain weave structure and 2.5D shallow bend-joint structure are 377.75?MPa and 482.96?MPa respectively, which are significantly higher than that of the composites with 2D fiber wound structure (92.84?MPa). SiC_f/SiC composites deposited at 1100?°C looks like a more porous structure with SiC whiskers appeared when compared with the composites deposited at 1050?°C. Correspondingly, the ring compression strength of the composites deposited at 1100?°C (566.44?MPa) is higher than that of the composites deposited at 1050?°C (482.96?MPa), with a better fracture behavior. Finally, the fracture mechanism of SiC_f/SiC composites with O-ring shape was discussed in detail.     

Fatigue damage identification of SiC coated needled C/SiC composite by acoustic emission

The fatigue damage process of SiC coated needled C/SiC composite specimen was monitored by acoustic emission (AE) under tension-tension cyclic loading. By analyzing the collected AE parameters of the composite, it is found that Kaiser effect enhances with the increase of stable cycles in the fatigue process. Moreover, multivariate K-means cluster analysis of AE parameters was carried out after the standardization of energy, amplitude, peak frequency and duration of AE signal. By comparing the objective function values of different number of clusters, and referring to the intra group variance and the variance between groups, the damage modes of the needled C/SiC composite are finally divided into four clusters, and the characteristics of AE parameters with different damage modes can be obtained. Furthermore, by referring to the microstructure characteristics of needled C/SiC composite, various damage modes at different fatigue stages were analyzed. In addition, the fracture morphology of the specimen was also observed by scanning electron microscope after fatigue fracture.     

Wet oxidation behavior of SiC/(SiC- SiBCN)x composites prepared by CVI combined with PIOP process

Self-healing capability in wet oxygen atmospheres is the key issue for long term service of SiC/SiC composites in aero-engines. Polymer derived SiBCN ceramic (PDC SiBCN) was introduced into SiC fiber reinforced SiC as a self-healing component to obtain SiC/(SiC-SiBCN)x composites by a newly developed method, namely chemical vapor infiltration combined with polymer infiltration online pyrolysis (CVI + PIOP) process. The weight loss behavior and three-point bending performance of the samples under different temperatures (1200, 1300 and 1400°C) and different wet oxygen partial pressures were tested up to 100 hours to demonstrate the oxidation behavior of the samples in wet oxygen environments. According to these tests, the antioxidant capacities of samples prepared from different preforms were compared. It has been found that the 2D plain weave samples with higher density have the best resistance to wet oxygen corrosion while the 2D plain weave samples have the worst resistance to wet oxidation and the antioxidant capacities of 2D satin weave samples is between them.