Tensile Creep Behavior and Thermal Stability of Orthogonal Three-Dimensional Woven TyrannoTM ZMI Fiber/Silicon-Titanium-Carbon-Oxygen Matrix Composites

This article presents experimental results for tensile creep behavior of orthogonal three-dimensional woven Tyranno™ ZMI fiber/Si-Ti-C-O ceramic matrix composites at 1300°–1450°C in air. The composite contained Tyranno ZMI (56% silicon, 1% zirconium, 34% carbon, and 9% oxygen) fibers with a BN coating layer to improve interface properties, and it exhibited excellent tensile properties at elevated temperature in air. For creep stresses between 60 and 140 MPa, the creep rate decreased continuously with time, with no apparent steady-state regime observed at 1300°–1450°C. Under the test conditions, the microstructure of the Tyranno ZMI fiber and Si-Ti-C-O matrix was unstable, resulting in weight loss and SiC grain growth. As a result, the viscosity of the fiber and matrix increased, because increased viscosity caused a creep rate that continuously decreased, which made steady-state creep impossible under these conditions.     

In-Plane Cracking Behavior and Ultimate Strength for 2D Woven and Braided Melt-Infiltrated SiC/SiC Composites Tensile Loaded in Off-Axis Fiber Directions

The tensile mechanical properties of ceramic matrix composites (CMC) in directions off the primary axes of the reinforcing fibers are important for the architectural design of CMC components that are subjected to multiaxial stress states. In this study, two-dimensional (2D)-woven melt-infiltrated (MI) SiC/SiC composite panels with balanced fiber content in the 0° and 90° directions were tensile loaded in-plane in the 0° direction and at 45° to this direction. In addition, a 2D triaxially braided MI SiC/SiC composite panel with a higher fiber content in the ±67° bias directions compared with the axial direction was tensile loaded perpendicular to the axial direction tows (i.e., 23° from the bias fibers). Stress–strain behavior, acoustic emission, and optical microscopy were used to quantify stress-dependent matrix cracking and ultimate strength in the panels. It was observed that both off-axis-loaded panels displayed higher composite onset stresses for through-thickness matrix cracking than the 2D-woven 0/90 panels loaded in the primary 0° direction. These improvements for off-axis cracking strength can in part be attributed to higher effective fiber fractions in the loading direction, which in turn reduces internal stresses on weak regions in the architecture, e.g., minicomposite tows oriented normal to the loading direction and/or critical flaws in the matrix for a given composite stress. Both off-axis-oriented panels also showed relatively good ultimate tensile strength when compared with other off-axis-oriented composites in the literature, both on an absolute strength basis as well as when normalized by the average fiber strength within the composites. Initial implications are discussed for constituent and architecture design to improve the directional cracking of SiC/SiC CMC components with MI matrices.     

三维正交机织物的冲击拉伸响应

本文利用MTS810．23材料测试系统和自行设计的分离式Hopkinson拉杆装置对三维正交机织物（3DOr-thogonalWovenFabric,3DOWF）进行测试,得到不同应变率（1×10-5s-1～2308s-1）下该织物的冲击拉伸响应。结果发现：3DOWF是应变率敏感材料,随着应变率提高,拉伸强度和失效应变均明显提高,且高应变率下应力一应变曲线具有双阶段韧性现象。研究表明：织物特殊结构效应引起应力波反射与透射差异,从而导致3DOWF双阶段韧性现象。     

三维正交机织复合材料的力学性能

测试了5种不同规格型号的三维正交机织复合材料以及同种型号增强体与两种不同树脂基体得到的复合材料的抗拉伸、抗弯曲力学性能,并分析了其破坏模式。结果表明:三维机织复合材料能有效阻止分层破坏,且纬向的力学性能明显好于径向,其力学性能也会随树脂基体力学性能的提高而有所提高,模量的变化尤其明显。     

三维正交机织铜丝／玻璃纤维层间混杂复合材料的拉伸和弯曲性能研究

本文设计和制作了两种层间混杂结构的三维正交机织铜丝／玻璃纤维复合材料,分别为铜丝单面混杂和双面混杂复合材料。两种复合材料的拉伸性能和弯曲性能测试结果表明,单面铜丝／玻璃纤维混杂复合材料的归一化拉伸强度和模量分别为1214MPa和83GPa;高于双面铜丝／玻纤混杂复合材料44％和51％。单面铜丝／玻璃纤维混杂复合材料的归一化弯曲强度为964NPa,高于双面铜丝／玻纤复合材料27％。两者的弯曲模量比较接近,均为60GPa左右。由于铜丝的混杂效应,三维正交机织铜丝／玻璃纤维层间混杂复合材料的拉伸和弯曲性能与相同结构的玻璃纤维复合材料相比有一定的下降。     

三维正交机织物组织结构的几何表征和数学表征

切取三维正交机织物沿经向和纬向的连续横截面,在三维视频显微镜下拍摄和分析织物横截面中经纱、纬纱和Z纱的横截面形态、纱线空间构型,用参数方程表征理想状态下织物中经纱、纬纱和Z纱截面尺寸及屈曲形态。基于三维绘图软件Pro/E,重构三维正交机织物单胞模型及大尺寸织物模型,使其能更准确、更真实地反映三维正交机织物真实细观结构。     

平纹机织玄武岩纤维/环氧树脂复合材料冲击拉伸行为

以常规机织工艺生产织物增强体,以真空辅助树脂转移模塑法(VARTM)制备成型复合材料,研究单层平纹玄武岩长丝增强环氧树脂复合材料在准静态和高应变率加载下的拉伸性能。准静态和高应变率拉伸试验分别在MTS-810.23试验仪和分离式霍普金森拉杆(SHTB)测试系统上完成。试验结果表明该材料的力学性能具有应变率依赖性:随着应变速率的增加,拉伸模量和拉伸强度单调增加,失效应变单调减小,弹性能先增加后减小。材料的失效破坏特征也呈现明显的应变率效应:准静态拉伸时,材料断口整齐,树脂的破碎少,几乎没有纤维的抽拔和经纬向纤维束间的滑移;高应变率拉伸时,材料断口参差错乱,树脂完全破碎,纤维束抽拔严重、相互崩裂和滑移,织物增强体结构的整体性破坏严重。     

三维正交机织玄武岩/芳纶混编复合材料的拉伸和剪切性能研究

本文设计和制作了两种混杂模式的三维正交机织玄武岩/芳纶混编复合材料,分别是层间混杂和层内混杂模式。对其拉伸性能和剪切性能进行了测试和分析,结果表明,层内混杂复合材料的拉伸性能和剪切性能比层间混杂复合材料的好,层内混杂复合材料的归一化强度和归一化模量分别比层间混杂复合材料的高22.12%和16.9%,层内混杂复合材料的剪切强度和剪切模量分别比层间混杂复合材料的高19.61%和26.03%;对于层间混杂复合材料,纬向的归一化强度比经向的高4.06%,但厚度方向上纱线的存在和织造工艺中经纱预加张力的影响,使纬向的归一化模量比经向的降低11.44%。     

Tensile Creep and Creep-Strain Recovery Behavior of Silicon Carbide Fiber/Calcium Aluminosilicate Matrix Ceramic Composites

The tensile creep and creep strain recovery behavior of 0° and 0°/90° Nicalon-fiber/calcium aluminosilicate matrix composites was investigated at 1200°C in high-purity argon. For the 0° composite, the 100-h creep rate ranged from approximately 4.6 × 10⁻⁹ s⁻¹ at 60 MPa to 2.2 × 10⁻⁸ s⁻¹ at 200 MPa. At 60 MPa, the creep rate of the 0°/90° composite was approximately the same as that found for the 0° composite, even though the 0°/90° composite had only one-half the number of fibers in the loading direction. Upon unloading, the composites exhibited viscous strain recovery. For a loading history involving 100 h of creep at 60 MPa, followed by 100 h of recovery at 2 MPa, approximately 27% of the prior creep strain was recovered for the 0° composite and 49% for the 0°/90° composite. At low stresses (60 and 120 MPa), cavities formed in the matrix, but there was no significant fiber or matrix damage. For moderate stresses (200 MPa), periodic fiber rupture occurred. At high stresses (250 MPa), matrix fracture and rupture of the highly stressed bridging fibers limited the creep life to under 70 min.     

三维正交机织复合材料弹道冲击实验及破坏模式

本文用钢芯弹对三维机织复合材料作弹道冲击测试。得到了弹体的入射速度和剩余速度,比较了常见几种材料的弹道性能评价参数的差异,并考察侵彻破坏模式和靶体最后的损伤破坏形态。在300-800m/s冲击速度范围下观测了材料的冲击破坏形态,发现机织复合材料受弹面和子弹出射面破坏形态不一样,受弹面主要是以纤维的压缩、剪切破坏以及基体开裂为主,出射面以纤维的拉伸、厚度方向的纱线断裂为主要破坏模式。通过对破坏模式和形态的分析,可以帮助建立更加准确的破坏准则,从而在设计抗弹材料时起到一定的作用。     

PP/甘蔗皮纤维复合材料的拉伸性能

采用热压工艺制造聚丙烯(PP)/甘蔗皮纤维复合材料,并研究其拉伸性能。研究热压温度为175℃、压力为2 MPa、时间15 min工艺条件下纤维粒径大小和质量分数对复合材料拉伸强度和拉伸弹性模量的影响。结果表明:在甘蔗皮纤维质量分数为40%条件下,复合材料拉伸性能随着粒径减小呈现先增加后减少的趋势,当纤维粒径为40~60目(0.45~0.3 mm)时材料拉伸强度最大,为8.58 MPa,此时弹性模量为2.44 GPa;在相同纤维粒径40~60目条件下,纤维质量分数为40%时PP复合材料拉伸强度最大,纤维质量分数为50%时PP复合材料拉伸弹性模量最大,达到2.65 GPa。根据实验结果,甘蔗皮纤维增强PP复合材料在纤维粒径为40~60目、质量分数在40%时综合拉伸性能最佳。     

Infiltration and Pyrolysis of Polytitanocarbosilane in an Si-Ti-C-O Fabric/Mullite Porous Composite

Incorporating Si-Ti-C-O fabric into a mullite matrix is expected to increase the fracture energy of mullite ceramics. The present paper describes the processing of an Si-Ti-C-O fabric/mullite/polytitanocarbosilane composite. A polytitanocarbosilane (a precursor of Si-Ti-C-O fiber)/xylene solution was infiltrated into a laminated porous mullite composite with 35–37 vol% fabric and thermally decomposed to an amorphous solid at 1000°C, in an argon atmosphere, to decrease the porosity and residual stress induced by the difference in thermal and mechanical properties between the Si-Ti-C-O fabric and the mullite. The decrease in porosity of the composite with pyrolysis of the precursor polymer was analyzed theoretically, and those results were used to control the effective experimental parameters. The infiltration/pyrolysis process was repeated eight times to produce a composite of 90.4% theoretical density. The composite exhibited significant pseudoductility, with a fracture energy of 11.4 kJ/m² and a flexural strength of 290 MPa.     

Effects of Preform Shear on Tensile Properties of a Woven C/SiC Composite

This article addresses effects of weave defects in an angle‐interlock C‐fiber preform on the tensile properties of the resulting fully processed C‐fiber/SiC‐matrix composite. For this purpose, a preform was intentionally sheared in a controlled manner after weaving. The resulting distortions were quantified by analyzing high‐resolution images of the preform surface after the first step of matrix processing, while the tows were still clearly visible. Comparisons are made of tensile test results on specimens cut from this composite panel and from a pristine panel in select loading orientations. Strain maps obtained by digital image correlation are used to identify local strain variations that are attributable to weave defects. The results are discussed in terms of: (i) the shear‐normal coupling that arises in loading orientations of present interest, and (ii) the geometric effects of tow misalignment on tow continuity along the specimen gauge length. The composite is found to perform in a robust manner, in the sense that the tensile properties are not sensitive to the presence of the defects.     

Effects of Fiber Architecture on Matrix Cracking for Melt-Infiltrated SiC/SiC Composites

The matrix cracking behavior of slurry cast melt-infiltrated SiC matrix composites consisting of Sylramic-iBN fibers with a wide variety of fiber architectures were compared. The fiber architectures included 2D woven, braided, 3D orthogonal, and angle interlock architectures. Acoustic emission was used to monitor in-plane matrix cracking during unload–reload tensile tests. Two key parameters were found to control matrix-cracking behavior: the fiber volume fraction in the loading direction and the area of the weakest portion of the structure, that is, the largest tow in the architecture perpendicular to the loading direction. Empirical models that support these results are presented and discussed.     

Multiple Cracking of Unidirectional and Cross-PlyCeramic Matrix Composites

This paper examines the multiple cracking behavior of unidirectional and cross-ply ceramic matrix composites. For unidirectional composites, a model of concentric cylinders with finite crack spacing and debonding length is introduced. Stresses in the fiber and matrix are found and then applied to predict the composite moduli. Using an energy balance method, critical stresses for matrix cracking initiation are predicted. Effects of interfacial shear stress, debonding length and bonding energy on the critical stress are studied. All the three composite systems examined show that the critical stress for the completely debonded case is lower than that for the perfectly bonded case. For cross-ply composites, an extensive study has been made for the transverse cracking in 90° plies and the matrix cracking in 0° plies. One transverse cracking and four matrix cracking modes are studied, and closed-form solutions of the critical stresses are obtained. The results indicate that the case of combined matrix and transverse crackings with associated fiber/matrix interfacial sliding in the 0° plies gives the lowest critical stress for matrix cracking. The theoretical predictions are compared with experimental data of SiC/CAS cross-ply composites; both results demonstrated that an increase in the transverse ply thickness reduces the critical stress for matrix cracking in the longitudinal plies. The effects of fiber volume fraction and fiber modulus on the critical stress have been quantified. Thermal residual stresses are included in the analysis.     

玻纤编织布复合材料VARI工艺中树脂流动行为研究

采用可视化实验方法研究了玻纤编织布铺层真空辅助成型工艺中树脂的流动行为。结果表明,导流介质可提高树脂流动速率、缩短充模时间;边缘点浇注、树脂沿导流介质径向流动时流动前锋为抛物线且易产生白斑,树脂沿导流介质纬向浇注时流动前锋呈直线且不易产生白斑;中心点浇注只能缩短树脂沿导流介质径向流动的充模时间,整体充模时间并未得到改善;玻纤编织布为2层、4层、6层、8层时树脂流动速率相差无几。     

多向GF/CF混杂复合材料拉压力学性能研究

采用工程上常用的铺层角度,设计7组不同的铺层方式,通过拉伸与压缩实验研究了多向玻璃纤维(GF)/碳纤维(CF)混杂复合材料的拉伸和压缩性能,得到了拉伸与压缩过程中力–位移曲线图及相应的破坏形貌。提出了铺层角度混杂比(CF相对体积分数)的概念,研究了不同铺层角度的混杂比对复合材料拉伸和压缩性能的影响。结果表明,多向纤维混杂复合材料的拉伸与压缩性能与总混杂比无明显关系,而与不同铺层角度各自的混杂比有关。其中,0°铺层混杂比对其影响最大,90°铺层混杂比影响最小,±45°铺层混杂比的影响介于两者之间。当0°铺层混杂比为100%时,复合材料的拉伸与压缩性能最高,拉伸破坏表现为一次破坏,破坏时层间分离的程度最低;当0°铺层混杂比低于100%时,复合材料的拉伸破坏表现为二次破坏。复合材料的压缩破坏大多表现为一次破坏,且在破坏时GF的破坏大多表现为"屈曲失稳"的形式,从而减缓了CF的脆性断裂程度。     

Elastic Response and Effect of Transverse Cracking in Woven Fabric Brittle Matrix Composites

This paper examines the linear elastic tensile and fracture behavior of biaxial plain weave SiC/SiC ceramic woven fabric composites. Iso-phase mode and random-phase mode have been adopted to simulate multilayer stacking and to predict the initial linear elastic constants. It has been found that both modes predict very close results. Porosities in the composite affect the stiffness significantly, while fiber undulation shows only minimal effect. The nonlinear stress-strain relation of the composite is due to transverse cracks, which initiate mainly from interyarn pores. In the second part of this paper, two methods, classical fracture mechanics and energy balance approach, have been used to examine the crack initiation and growth. A finite element method and a modified shear-lag method have been developed to evaluate the stress distribution in the yarn with transverse cracks. The composite stiffness reduction due to transverse cracking has been obtained by both the finite element and shear-lag methods. Strain energy release rates of the growth of transverse cracks have been studied by the crack-closure procedure, using finite element methods. Effects of the yarn size and crack position on the strain energy release rate have been quantified. It is concluded that thinner yarns lead to higher critical strains for transverse cracking.     

Interface Debonding and Fiber Cracking in Brittle Matrix Composites

Analyses of debonding along interfaces and of the kinking of interface cracks into a fiber have been used to define the role of debonding in fiber-reinforced, brittle matrix composites. The results reveal that, for fibers aligned with the tensile stress axis, debonding requires an interface fracture energy, Γ_i, less than about one-fourth that for the fiber, Γ_f. Further-more, once this condition is satisfied, it is shown that fiber failure does not normally occur by deflection of the debond through the fiber. Instead, fiber failure is governed by weakest-link statistics. The debonding of fibers inclined to the stress axis occurs more readily, such that debonds at acutely inclined fibers can deflect into the fiber, whereupon the failure of fibers is dominated by their toughness.     

Mechanical Behavior and High-Temperature Performance of a Woven Nicalon™/Si-N-C Ceramic-Matrix Composite

A modern ceramic-matrix composite (CMC) has been extensively characterized for a high-temperature aerospace turbine-engine application. The CMC system has a silicon-nitrogen-carbon (Si-N-C) matrix reinforced with Nicalon fibers woven in a balanced eight-harness satin weave fabric. Tensile tests have demonstrated that this CMC exhibits excellent strength retention up to 1100°C. The room-temperature fatigue limit was 160 MPa, ∼80% of the room-temperature tensile strength. The composite reached run-out conditions under cyclic (10⁵ cycles at 1 Hz) and sustained tension (100 h) conditions at a stress of 110 MPa, which was ∼35 MPa above the proportional limits at temperatures up to 1100°C in air. At stress levels >110 MPa, cyclic loading at 1000°C caused a more severe reduction in life, based on time, compared with sustained tension. Further life degradation was observed in the 1000°C fatigue specimens that were exposed to a salt-fog environment. This degradation decreased the fatigue life ∼85% at the stress levels that were tested.