Crack Initiation in Unidirectional Brittle-Matrix Composites

This paper describes the initiation of matrix cracking for glass and glass-ceramic matrix composites reinforced with small-diameter silicon carbide and carbon fibers under uniaxial tensile loading. Acoustic emission, replication, and optical microscopy in conjunction with stress-strain curves are employed to detect the initiation of matrix cracking. The proportional limit of the stress-strain curve is found to overestimate the initiation of matrix cracking in the material systems studied. The matrix cracking iniates at axial strains from 0.07% to 0.15%. The ACK model overestimates the initiation of the matrix cracking for the material systems studied in this paper.     

Viscoelastic Effect of Heat Treatment on the Fracture Toughness of Metal-Particulate/Glass-Matrix Composites

The fracture toughness ( K _Ic) of a 90/10 glass-matrix/metal-particulate composite was measured as a function of treatment temperature and hold time. The toughness was 20% higher at a heat-treatment temperature 15°C below T _g than at the other four treatment temperatures examined. K _Ic also varied as a function of time at temperature. The volume fraction of exposed particulate phase on the fracture surface was proportional to the increase in the fracture toughness.     

Interfacial Bonding and Friction in Silicon Carbide [Filament]-Reinforced Ceramic- and Glass-Matrix Composites

Interfacial shear strength and interfacial sliding friction stress were assessed in unidirectional SiC-filament-reinforced reaction-bonded silicon nitride (RBSN) and borosilicate glass composites and 0/90 cross-ply reinforced borosilicate glass composite using a fiber pushout test technique. The interface debonding load and the maximum sliding friction load were measured for varying lengths of the embedded fibers by continuously monitoring the load during debonding and pushout of single fibers in finite-thickness specimens. The dependences of the debonding load and the maximum sliding friction load on the initial embedded lengths of the fibers were in agreement with nonlinear shear-lag models. An iterative regression procedure was used to evaluate the interfacial properties, shear debond strength (T _d ), and sliding friction stress (T _f ), from the embedded fiber length dependences of the debonding load and the maximum frictional sliding load, respectively. The shear-lag model and the analysis of sliding friction permit explicity evaluation of a coefficient of sliding friction (μ) and a residual compressive stress on the interface (σ₀). The cross-ply composite showed a significantly higher coefficient of interfacial friction as compared to the unidirectional composites.     

Strength and Toughness of Continuous-Alumina-Fiber-Reinforced Glass-Matrix Composites

Unidirectional, continuous-fiber composites were fabricated using polycrystalline alumina fibers and four different silicate glass matrices of differing thermal expansion. Fracture toughness measurements, strength measurements, and fractographic analysis of failed specimens are used to identify the failure mechanism. Results show that the elastic modulus mismatch between the matrix and the fibers shields the reinforcing fibers from matrix crack extension, thereby increasing composite toughness without fiber pullout. Fractographic analysis shows that fiber shielding leads to fiber failure ahead of matrix crack. Composite toughness increases linearly with increases in the residual compressive stress in the matrix phase. Ultimate composite strengths are dependent upon thermal-expansion-induced residual stresses and fiber strength.     

Electrophoretic Deposition Forming of Nickel-Coated-Carbon-Fiber-Reinforced Borosilicate-Glass-Matrix Composites

The present paper introduces a novel processing technique that involves in situ electrophoretic deposition (EPD), followed by pressureless sintering, to produce dense, defect-minimized, carbon-fiber-reinforced borosilicate-glass-matrix composites with a nickel interface. The process relies on the deposition of submicrometer-sized, colloidal charged particles onto unidirectionally aligned nickel-coated carbon fibers. The preparation and characterization of a kinetically stable nanosized borosilicate sol suitable for EPD are described. The most-important EPD processing parameters in the formation of dense, fully infiltrated, green-body compacts are described, and issues that concern the infiltration of very tight carbon fiber preforms are discussed and effectively solved. Using the crack-path-propagation test, the metallic nickel interface is determined to be very effective to improve the composite mechanical performance, in terms of the nonbrittle fracture behavior. Catastrophic crack growth is prevented by such mechanisms as constrained plastic deformation of the interface and fiber debonding and pullout. The proposed processing technique has great potential to fabricate defect-minimized and damage-tolerant fiber-reinforced brittle-matrix composites with a ductile interface. Overall, this new approach offers a cost-effective and short-time processing route for the fabrication of continuous-fiber-reinforced ceramic-matrix composites.     

Tensile Tests of Ceramic-Matrix Composites: Theory and Experiment

A model describing the salient features of tensile stress-strain curves of ceramic–fiber composites has been developed. The model incorporates statistics of fiber failure. Furthermore, the compliance of the testing machine is included so that the onset of instability can be predicted. An experiment conducted on a composite consisting of a glass-ceramic matrix reinforced with SiC fibers exhibits excellent agreement with the predicted behavior.     

Rate of Strength Decrease of Fiber-Reinforced Ceramic-Matrix Composites during Fatigue

An experimental investigation was performed to study the rate at which strength-controlling fatigue damage evolves in a ceramic-matrix composite. Tensile specimens of a unidirectional SiC-fiber-reinforced calcium aluminosilicate matrix composite were cycled to failure or to a preselected number of cycles under similar loading histories. The residual strength of the precycled specimens was found to be similar to that of virgin specimens. Microstructural investigations showed that the fracture surfaces of the specimens cycled to failure had a central region where fiber pullout was negligible. It is proposed that frictional heating (due to interfacial sliding) is the cause of fatigue failure. High interfacial temperatures are assumed to cause the formation of a strong interface bond, leading to internal embrittlement.     

单向玻纤增强BMI复合材料的酸雨和温热老化行为

针对潮湿和酸雨多发地域的航空器用复合材料老化问题,模拟酸雨和温热(普通热水)环境,研究了单向玻璃纤维增强双马来酰亚胺树脂(BM I)复合材料(UGFRBC)吸水行为,通过红外光谱仪、力学测试装置、热力学分析装置分别表征了老化前后复合材料基体的结构、弯曲性能、层间剪切性能、动态粘弹性和玻璃化转变温度,分析了酸雨与温热环境下吸湿率对复合材料力学性能影响,建立了一种预测该复合材料酸雨和温热老化力学性能的经验公式。     

玻纤对湿热环境下的环氧复合材料拉伸性能的影响

为了研究湿热环境下玻璃纤维对环氧复合材料拉伸性能的影响,建立试验模型,以不同浸润剂配方生产的相同单丝直径及TEX值的玻璃纤维进行浸胶制样,样条在95℃下1%浓度的NaCl溶液中浸泡24 h、72 h后,样条拉伸强度变化,从而得出玻璃纤维对在湿热环境下环氧复合材料拉伸性能的影响,即选用合适的偶联剂生产的玻璃纤维,对复合材料湿态拉伸强度有明显的提升。     

Tensile and Impact Properties of Hollow Glass Bead‐Filled PVC Composites

The tensile and notched Izod impact properties of poly(vinyl chloride) (PVC) composites filled with hollow glass beads (HGB) were measured at room temperature by means of an Instron materials testing machine to investigate the effects of the filler content and size on these mechanical properties. The results showed that the tensile yield strength (σ_yc) decreased gently with increasing HGB volume fraction (ϕ _f), while the tensile break strength (σ_bc) of the composites was somewhat greater than that of the unfilled PVC within ϕ _f = 0–20%. In addition, the dependence of σ_bc on ϕ _f was not obvious. The effect of HGB size on both σ_yc and σ_bc was insignificant. When ϕ _f < 5%, the notched impact strength (σ_IC) of the composites decreased quickly with increasing ϕ _f, and then it decreased slightly with the increase of ϕ _f. Similarly, the influence of the filler size on the impact properties was insignificant. Furthermore, the σ_yc of the samples was estimated using a tensile equation proposed in a previous paper. A good agreement was shown between the calculations and the measured data.     

The Mechanical Properties and Chemical Resistance of Short Glass-Fiber-Reinforced Epoxy Composites

ABSTRACT

Epoxy–short glass fiber composites were prepared by directly blending two-pack system of Araldite (CY-230) and hardner (HY-951) with short glass fibers. The short glass fiber content was varied from 2% to 10% by weight of the total matrix. These composites were then characterized for morphology using scanning electron microscopy, mechanical properties, that is, tensile and flexural properties and resistance toward various chemicals. The epoxy-glass fiber composites showed improved tensile and flexural properties but increased dispersion among the properties with increasing fiber content. Several reasons to explain these effects in terms of reinforcing mechanisms were discussed. These composites were stable in most chemicals but were completely destroyed in concentrated sulfuric acid, nitric acid, and pyridine.     

Tensile Strength and Ultimate Elongation of Rubber-Fibrous Compositions

Abstract

Data are presented which show that the mechanism of fracture in rubber-fiber composites is governed by the adhesion of the matrix material to the fiber as well as the strength of the matrix. Degree of orientation of the fiber is also important.     

PP／无机粒子复合材料拉伸强度的预测模型及影响因素分析

综述了预测PP／无机粒子复合材料拉伸强度的数学模型,并从材料结构方面分析了影响拉伸强度的因素。最后指出,实现影响因素的定量表征和多因素分析是今后的重要研究方向。     

Ultrahigh Flowability and Excellent Mechanical Performance of Glass Fiber/PA6 Composites Prepared by Hyperbranched Polymers

Lightweighting of automotives is crucial for the decrease of fuel and energy consumption, as well as CO₂ emission and environmental pollution. Polymer composites, especially the high strength glass fiber/polyamide (GF/PA) composites, have great potential in lightweight; however, they have not been universally accepted due to their insufficient performance. Here, a stearate-ended hyperbranched polyester (HBP-12-n) is designed and high-performance GF/PA6 composites with high GF content are prepared. The flowability of the composites can be further increased by combining carboxyl-ended hyperbranched polymer (HyPer C181) with HBP-12-n. Compared with unmodified GF/PA6 composites, the melt flow index (MFI) can be increased remarkably to 587% by adding a 0.7 wt% mixture of HBP-12-75 and HyPer C181, and the strength and toughness remain competitive. The simultaneous improvement in MFI and impact strength of GF/PA6 composites is the first discovery of this kind, and a synergistic mechanism of amphiphilic bridging-deformation slipping-interfacial strengthening of hyperbranched polymers is proposed to account for this phenomenon. This work provides a simple strategy to fabricate GF/PA6 composites with the extensive application for automotive parts and has great prospects in making automotives lightweight and reduction of CO₂ emissions.     

Tensile Properties of Arenga pinnata Fiber-Reinforced Epoxy Composites

The aim of this study is to determine the tensile properties of Arenga pinnata fiber as a natural fiber and epoxy resin as a matrix. The Arenga pinnata fibers were mixed with epoxy resin at the various fiber weight percentages of 10%, 15%, and 20% Arenga pinnata fiber and with different fiber orientations such as long random, chopped random, and woven roving. Hand lay-up processes in this experiments were to produce specimen test with the curing time for the composite plates is in the room temperature (25–30°C). Results from the tensile tests of Arenga pinnata fiber reinforced epoxy composite are that the 10 wt.% woven roving Arenga pinnata fiber showed the highest value for maximum tensile properties. The tensile strength and Young's modulus values for 10 wt.% of woven roving Arenga pinnata fiber composite are 51.725 MPa and 1255.825 MPa, respectively. The results above indicate that the woven roving Arenga pinnata fiber has a better bonding between its fiber and matrix compared to long random Arenga pinnata fiber and chopped random Arenga pinnata fiber. Scanning electron microscopy (SEM) tests were carried out after tensile tests to observe the interface of fiber and matrix adhesion.     

Limitation of Griffith Flaws in Glass-Matrix Composites

The effect of the limitation of Griffith flaws, introduced in an abraded surface of glass, on the strength of glass-tungsten composites was investigated for small sizes of Griffith flaws. Hasselman and Fulrath's proposed fracture theory for this type of system extended to small flaw sizes. The use of tungsten spheres with two particle sizes or a wide distribution about one average size as the dispersed phase in a glass matrix decreased the average mean free path in the matrix more than could be achieved with a single particle size dispersion. Average mean free paths determined experimentally by statistical techniques were in good agreement with those calculated by Fullman's equation. This technique was successfully used when the dispersed phase had two particle sizes or a wide particle size distribution. The strong effect of internal stresses caused by a mismatch of thermal expansion of the phases in reducing the strength of a composite was demonstrated.     

Cracking and Damage in a Notched Unidirectional Fiber-Reinforced Brittle Matrix Composite

Results of four-point bend tests on notched beams of a laminated unidirectional fiber-reinforced glass matrix composite are presented. The failure sequence has been established through in situ examination. The dominant damage mode is a mixed-mode, split crack that runs parallel to the predominant fiber directions. The crack interacts with and crosses over imperfectly aligned fibers. The resulting bridging tractions are sufficient to cause the critical strain energy release rate to increase substantially as the crack extends. Several other damage modes are also observed. These include mode I (tensile) matrix cracks bridged by fibers, mode II (shear) cracks, and compressive damage at the loading points.     

碳纤维复合材料在民品中的应用

详细介绍了碳纤维复合材料的基本特性，应用在民用产品中的工艺过程，以及需解决的一些问题。     

聚丙烯/纳米CaCO3复合材料的拉伸性能

采用2种填料粒子表面处理方法[（表面活化（SI）和钛酸酯偶联剂处理（SII）]分别制备了纳米级CaCO3填充聚丙烯复合材料。应用万能材料试验机在室温下考察TCaCO3粒子表面处理和CaCO3含量对复合材料拉伸力学性能的影响。结果表明，随着纳米粒子CaCO3体积分数（φ）的增加，2种试样的弹性模量和拉伸强度有轻微的变化，而粒子表面处理的影响不太明显。当φ为0．5％时，SI的拉伸断裂强度达至最大，然后随着φ的增加呈非线性函数形式下降；除个别测量点外，SII的拉伸断裂强度基本上随着φ的增加呈非线性函数形式下降。在相同的条件下，SI的拉伸断裂强度高于SII，而断裂伸长率则相反。     

Surface Modification of Carbon Fibers by Free Radical Graft‐Polymerization of 2‐Hydroxyethyl Methacrylate for High Mechanical Strength Fiber–Matrix Composites

Free radical polymerization of vinylic monomers in the presence of carbon fibers results in the grafting of polymers onto the carbon fiber surface. Graft polymers cannot be removed by intense washing with good polymer solvents. The density and size of these structures are successfully controlled by reaction conditions. Grafting of the carbon fiber surface with hydroxyethyl methacrylate allows for introducing functional groups suitable for the reaction with an epoxy‐based resin. The resulting fiber‐reinforced composites show enhanced mechanical properties compared to samples prepared from carbon fibers equipped with a standard sizing for epoxy resins. Thus, tensile strength increases by 10%, while interlaminar shear strength improves by 20%.