热处理工艺对喷射沉积7090/SiC_p复合材料断裂韧性的影响

通过实验对不同热处理制度时挤压态7090/SiCp复合材料的断裂韧性以及微观组织进行了研究。挤压态7090/SiCp复合材料经固溶和时效的热处理后,断裂韧性均有不同程度的提高。随着时效处理的进行,挤压态7090/SiCp复合材料的断裂韧性先升高后降低再升高,而470℃/1h+490℃/1h双级固溶+120℃/28h峰时效状态的复合材料强度最高,但KIC值较小。研究了7090/SiCp复合材料的断裂模式,结果可以看出复合材料的断裂是以穿晶断裂为主兼有沿晶断裂的混合型断裂。     

Improvement of Mode I Interlaminar Fracture Toughness of Stitched Glass/Epoxy Composites

This study examines the improvement of Interlaminar Fracture Toughness (IFT) of multilayered 3D glass/epoxy textile composites when through thickness reinforcement is introduced. Three stitching techniques have been examined: Modified Lockstitch (ISO-301), Single-yarn Orthogonal-stitch (ISO-205) and Double-yarn Orthogonal-stitch (ISO-205). It was found that the use of class ISO-205 manual-type stitched reinforcement significantly enhanced the Mode I-IFT, G_IC measured using a Double Cantilever Beam technique. Furthermore, in every case, the use of class ISO-205 stitching and high stitch densities offer a significant improvement of 74.5 % on Mode I-IFT against interlaminar delamination.     

The Transfer of Matrix Toughness to Composite Mode I Interlaminar Fracture Toughness in Glass-Fibre/vinyl Ester Composites

The transfer of matrix toughness to composite mode I interlaminar fracture toughness (G _Ic ) has been investigated in unidirectional glass-fibre reinforced composites with brittle and rubber-toughened vinyl ester matrices. Single-edge-notch bend (SENB) and double cantilever beam (DCB) specimens were used for matrix and composite G _Ic characteristion, respectively. The initial crack opening displacement rate was used as the parameter for comparison of G _Ic results. Matrix G _Ic was completely transferred to composite G _Ic for crack initiation (G _Ic-init) in the brittle-matrix composites, but in the toughened composites transfer was only partial due to the presence of fibres. The conclusion is that the maximum contribution to energy absorption by the matrix is more accurately reflected by G _Ic-init, and should be used for further assessment of the enhancing effect of fibre bridging during steady-state crack propagation, instead of matrix G _Ic . A plot of composite G _Ic for steady-state crack propagation, G _Ic-prop versus G _Ic-init indicates that the enhancing effect of fibre bridging is greater in the toughened composites. This enhancement is related to a larger deformation zone size in the toughened matrices.     

Interlaminar Fracture Toughness of CF/PEI and GF/PEI Composites at Elevated Temperatures

An experimental study has been conducted to assess temperature effects on mode-I and mode-II interlaminar fracture toughness of carbon fibre/polyetherimide (CF/PEI) and glass fibre/polyetherimide (GF/PEI) thermoplastic composites. Mode-I double cantilever beam (DCB) and mode-II end notched flexure (ENF) tests were carried out in a temperature range from 25 to 130°C. For both composite systems, the initiation toughness, G _IC,ini and G _IIC,ini, of mode-I and mode-II interlaminar fracture decreased with an increase in temperature, while the propagation toughness, G _IC,prop and G _IIC,prop, displayed a reverse trend. Three main mechanisms were identified to contribute to the interlaminar fracture toughness, namely matrix deformation, fibre/matrix interfacial failure and fibre bridging during the delamination process. At delamination initiation, the weakened fibre/matrix interface at elevated temperatures plays an overriding role with the delamination growth initiating at the fibre/matrix interface, rather than from a blunt crack tip introduced by the insert film, leading to low values of G _IC,ini and G _IIC,ini. On the other hand, during delamination propagation, enhanced matrix deformation at elevated temperatures and fibre bridging promoted by weakened fibre/matrix interface result in greater G _IC,prop values. Meanwhile enhanced matrix toughness and ductility at elevated temperatures also increase the stability of mode-II crack growth.     

Study of Debond Fracture Toughness of Sandwich Composites with Metal Foam Core

Two types of experiments were designed and performed to evaluate the adhesive bond in metal foam composite sandwich structures.The tensile bond strength of face/core was determined through the flatwise tensile test (FWT).The test results show that the interfacial peel strength is lower than the interlaminar peel strength in FWT test.The mode I interfacial fracture toughness(GIC)of sandwich structures containing a pre-crack on the upper face/core interface is determined by modified cracked sandwich beam(MCSB...     

Comparison of Interlaminar Fracture Toughness in Unidirectional and Woven Roving Marine Composites

This paper investigates the effect of fibre lay-up and matrix toughness on mode I and mode II interlaminar fracture toughness (G_Ic and G_IIc) of marine composites. Unidirectional and woven roving fibres were used as reinforcements. Two vinyl ester resins with different toughness were used as matrices. Results from both modes showed toughness variation that is consistent with matrix toughness. Values of G_Ic were not significantly influenced by fibre lay-up except at peak load points in the woven roving/brittle-matrix composite. Each peak load point, caused by interlocked bridging fibres, signified the onset of unstable crack growth. For unidirectional specimens, crack growth was stable and G_Ic statistically more reliable than woven roving specimens, which gave fewer G_Ic values due to frequent unstable crack growth. Mode II tests revealed that, except for crack initiation, G_IIc was higher in woven roving composites. This was due to fibre bridging, perpendicular to the crack growth direction, which encouraged stable crack growth and increased energy absorption. Mode II R-curves were obtained for the woven roving specimens. These R-curves provide additional information useful for characterising delamination resistance. The paper concludes that composites with woven roving fibres show similar mode I delamination characteristics to the unidirectional composites; but their mode II delamination characteristics, after crack initiation, are quite different.     

C/C复合材料室温及高温断裂韧性的测试及表征

评述了Ｃ／Ｃ复合到温及高温断裂韧性测试的各种影响因素,以及当前Ｃ／Ｃ复合材料断裂韧性的表征方法,表明了Ｃ／Ｃ复合材料室温及高温断裂韧性测试和评价规范化的迫切性。     

Test Conditions Effect on the Fracture Toughness of Hollow Glass Micro-sphere Filled Composites

Abstract:  Low-density sheet-moulding compounds based on hollow glass micro-spheres are usually classified as syntactic foams if the filler content is relatively high. Syntactic foams are potentially suitable materials for applications where impact loads occur as they are able to reduce impact force. The addition of hollow micro-spheres tends to increase the specific values in terms of impact force and, marginally, in flexural modulus for high-volume fractions of micro-spheres. In this study, the effects of load rate and of immersion of the specimens in water up to 67 days were studied on the flexural mechanical properties and particularly on the fracture toughness, K _IC. Hollow micro-spheres (Verre ScotchitTM-K20) with epoxy and polyester polymer binder were used. Fracture toughness, K _IC, flexural stiffness modulus and ultimate strength were obtained as functions of load rate and immersion time. The increase of load rate tends to increase stiffness modulus, but effects on K _IC were found to be only marginal. Ultimate strength increases significantly with the increase of load rate for epoxy-based composites, but for the case of the polyester-based foams, only a negligible effect was observed. The increase of the immersion time in water tends to reduce stiffness modulus. K _IC decreases slightly after 15 days for the polyester-based composites and after 67 days for epoxy-based foams, and only negligible effects on ultimate strength were observed.     

坯体结构对炭/炭复合材料增密速率的影响

通过改变无纬布炭纤维类型、单元厚度，制备了不同的坯体，进行CVD增密，以研究坯体结构对增密速度的影响。结果表明：无纬布纤维为进口炭纤维B，C的针刺毡坯体CVD增密速率较快，产品最终密度较高；减小单元厚度(即增加每厘米所铺无纬布和网胎的数量)。相当于增加整个坯体的针刺密度，有利于提高CVD增密速度；压差式CVD增密的产品存在径向密度梯度。有必要进一步改进坯体结构，以弥补增密工艺的不足。     

Mo对于Nb/Nb5Si3原位复合材料室温韧性的影响

利用真空电弧熔炼制备了Nb/Nb5Si3复合材料,在1200℃×100h热处理后,利用单边切口悬臂梁法(SENB)测定了Nb-Si合金的室温断裂韧性.研究了合金化元素Mo对Nb/Nb5Si3复合材料微观结构和室温韧性的影响.结果发现适量Mo的加入明显地改善了Nb-18Si的室温韧性.     

无压熔渗制备TiC/Ni_3Al复合材料的微观组织与断裂韧性研究(英文)

以化学纯镍粉、钛粉、铝粉、石墨粉为原料,采用燃烧合成方法制备了TiC/Ni3Al含孔预制件,用无压熔渗法制备了TiC/Ni3Al复合材料。对TiC/Ni3Al复合材料的微观组织、硬度和断裂韧性进行了研究并采用XRD和SEM分析了复合材料的相组成、微观结构、断口形貌。采用压痕法计算了TiC/Ni3Al复合材料的断裂韧性。试验结果表明:无压熔渗法是制备致密的TiC/Ni3Al复合材料的有效方法。在完成渗透获得致密组织的前提下,渗透温度和渗透时间对TiC/Ni3Al复合材料的硬度及断裂韧性无显著影响。渗透后复合材料的组成相主要为Ni3Al和TiC两相,Ni3Al相和TiC颗粒结合良好。本文制备的Ni3Al/TiC复合材料的维氏硬度随TiC体积分数的增加而增加,TiC含量分别为70%和80%时,复合材料的维氏硬度平均值分别为569.6(Hv)和610.8(Hv)。复合材料的断裂韧性最高达到了10.5MPa.m1/2,TiC颗粒和Ni3Al界面的分离是复合材料断裂过程中存在的主要失效形式。断裂过程中Ni3Al可以有效地吸收裂纹扩展能量,阻止了裂纹的直线扩展,使裂纹扩展方向发生偏转,大大增加了材料的断裂韧性。     

高密度预制体制备炭/炭复合材料致密化研究

采用高密度3D炭纤维预制体, 以丙烯作为碳源, 氮气作为载气, 利用自制的快速CVI炉制备了板形C/C复合材料. 详细分析了压差等工艺参数在CVI制备C/C复合材料过程中对“封孔”现象的影响, 采用扫描电镜(SEM)和正交偏光显微镜(PLM)对各阶段C/C材料的微观形貌特征作了详细研究, 分析了预制体在増密过程中密度的变化, 初步探讨了“封孔”形成的机理. 实验证明: 采用多阶段CVI工艺可明显改善板形C/C材料封孔现象, 初始密度为0.94g/cm³的高密度预制体经过250h的增密, C/C复合材料密度达到了1.82g/cm³.     

颗粒增强铝基复合材料断裂韧性与拉伸延性的解析模型

基于Eshelby等效夹杂理论及Weibull统计分布,发展了SiCp/Al金属基复合材料断裂韧性与拉伸延性的力学模型.模型的计算表明:当复合材料受外力时,SiC颗粒所受的力与外加应力呈线性关系.随着外加应力的增加,SiC颗粒所受的力也线性增加.同时,外力作用下SiC颗粒的断裂分数服从Weibull统计分布,即SiC颗粒的总体含量越高,其断裂分数就越高.模型关于约化拉伸延性和断裂韧性的计算与实验结果较为吻合.模型的解析和实验结果都表明:拉伸延性与断裂韧性随SiC颗粒体积分数的增加而减小.在相同体积分数的情况下,拉伸延性与断裂韧性随SiC颗粒尺寸的增加而减小.     

喷管炭-炭材料出口锥预制体技术

介绍了喷管炭/炭材料出口锥(CCEC)预制体结构的设计原则、3种预制体成型技术,并简要讨论了预制体结构对炭/炭出口锥材料性能的影响.预制体结构设计须依据喷管工作条件,满足性能稳定、结构稳定、工艺易实现性原则;三维结构和非织造结构比二维结构预制体纤维含量高、性能更优,适合喷管出口锥的预制成型;预制体的结构均匀性、纤维含量是影响CCEC烧蚀性能的关键参数;可通过建立CCCs宏观力学性能与预制体细观结构参数之间的模型预测其结构性能.     

纳米Pd-Ga/PMMA复合体系界面的有序结构

在不使用引发剂和还原剂条件下,用超声辐射工艺双原位合成了纳米钯镓/聚甲基丙烯酸甲酯(PMMA)复合物.XRD和UV-Vis显示,超声还原生成的单质钯和超声粉碎的单质镓在PMMA基体中不是简单的物理分散,而是在生成钯镓合金Ga5Pd/PMMA复合物的同时既有纳米钯又有纳米镓与PMMA形成复合物;XPS表明,镓失去了部分外...     

苎麻/酚醛树脂复合材料的阻燃改性

采用聚磷酸铵(APP)阻燃处理酚醛树脂,并与阻燃处理过的苎麻织物复合制备酚醛树脂层压板.结果发现APP处理后的层压板的极限氧指数得到极大的提高,加入1wt％的APP即可使极限氧指数由39.1提高到52.5.锥形量热实验发现这种层压板的残炭量增加,点燃时间延长,峰值热释放速率下降.但是APP的加入使层压板的力学性能有一定程度的下降.     

NdFeB/酚醛树脂原位复合材料研究

采用原位聚合法制备了NdFeB/酚醛树脂(PF)母料,并进一步制备了粘结磁体.采用红外分析了NdFeB/PF母料的结构,并用多种方法对粘结磁体的磁性能和力学性能进行了研究.研究表明:在原位制备过程中,PF的聚合倾向于在NdFeB的表面进行,形成PF包覆的NdFeB,NdFeB磁粉进入了PF的生成体系,形成了海岛结构.比较三种工艺制备的磁体综合性能可知,采用NdFeB/PF母料粉料作粘结剂制备的磁体的综合性能最好.