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1.
The transverse tensile properties of boron fiber reinforced aluminum have been determined as a function of fabrication parameters,
matrix alloy and fiber types, fiber content, specimen geometry, and thermal environment. Matrix alloys investigated include
2024, 6061, 5052, 5056, 2219, 1100, and Al-7 pct Si. The fibers investigated include 4.0 mil boron, 4.2 mil BORSIC, R.F. boron,
5.6 mil boron, 5.7 mil BORSIC, and 4.0 mil silicon carbide. It was shown that the composite transverse tensile performance
is a function of all of these variables and that transverse strengths of up to 45,000 psi can be achieved by the choice of
the proper combination of matrix, fiber type and fabrication procedures. 相似文献
2.
Reji John M. Khobaib Paul R. Smith 《Metallurgical and Materials Transactions A》1996,27(10):3074-3080
Titanium matrix composites (TMCs) incorporating unidirectional fiber reinforcement are considered as enabling materials technology
for advanced engines which require high specific strength and elevated temperature capability. The resistance of unidirectional
TMCs to deformation under longitudinally applied sustained loading at elevated temperatures has been well documented. Many
investigators have shown that the primary weakness of the unidirectional TMC is its susceptibility to failure under very low
transverse loads, especially under sustained loading. Hence, a reliable model is required to predict the creep-rupture life
of TMCs subjected to different transverse stress levels over a wide range of temperatures. In this article, we propose a model
to predict the creep-rupture life of unidirectional TMC subjected to transverse loading based on the creep-rupture life of
unidirectional TMC subjected to transverse loading based on the creep-rupture behavior of the corresponding fiberless matrix.
The model assumes that during transverse loading, the effective load-carrying matrix ligament along a row of fibers controls
the creep-rupture strength and the fibers do not contribute to the creep resistance of the composite. The proposed model was
verified using data obtained from different TMC fabricated using three matrix compositions, which exhibited distinctly different
types of creep behavior. The results show that the creep-rupture life of the transverse TMC decreases linearly with increasing
ratio of the fiber diameter to the ply thickness. The creeprupture life is also predicted to be independent of fiber spacing
along the length of the specimen. 相似文献
3.
《Acta Metallurgica》1987,35(11):2607-2619
A stress intensity approach is used to analyze tensile failure of brittle matrix composites that contain unidirectionally aligned fibers held in place by friction. In general, failure may initiate either by growth of a crack in the matrix, or by fracture of fibers that bridge the matrix crack. Subsequently, these failure processes may continue either unstably or stably with increasing applied stress. Solutions to the fracture mechanics analysis are obtained numerically in normalized form, with one microstructural variable, the normalized fiber strength. The analysis defines transitions between failure mechanisms and provides strength/crack-size relations for each mechanism. Explicit relations are derived for the matrix cracking stress (noncatastrophic failure mode), the condition for transition to a catastrophic failure mode, and the fracture toughness in a region of catastrophic failure, in terms of microstructural properties of the composite. 相似文献
4.
5.
原位自生钛基复合材料以其高比强度和高比模量引起了人们的广泛关注,尤其是如何提高其高温性能成为近年来钛基复合材料研究的热点.该文详细综述了原位自生钛基复合材料的各种制备方法、增强体与钛基体的选择、各种增强体的反应体系以及原位自生钛基复合材料的组织结构与力学性能,指出了原位自生钛基复合材料今后的发展方向. 相似文献
6.
原位合成钛基复合材料的最新进展 总被引:2,自引:0,他引:2
原位合成钛基复合材料以其高比强、高比模量引起了人们的广泛关注,尤其是如何提高其高温性能成为近年来钛基复合材料研究的热点.本文综合评述了原位合成钛基复合材料的最新进展,包括各种制备方法、增强体与钛基体的选择、各种增强体的反应体系以及原位合成钛基复合材料显微组织与力学性能,指出了原位合成钛基复合材料今后的发展方向. 相似文献
7.
William J. Baxter 《Metallurgical and Materials Transactions A》1992,23(11):3045-3053
There is intensive interest in metal matrix composites (MMCs) for automotive components, and the first production applications
in Japan use discontinuous fibers as the reinforcements. These fibers are randomly oriented, resulting in an MMC with isotropic
properties. However, there are conflicting reports on the tensile strengths attainable. In some cases, the strength increases
with increasing volume fraction(V
f) of fibers, while in other cases, there is little or no benefit. A simple method is proposed to calculate the strength of
this type of MMC. It is shown that the fibers oriented perpendicular to the stress direction play a key role, and the strength
depends upon the strength of the interfacial bond. Upper and lower limits of the composite strength are calculated. If the
bond strength is larger than the matrix strength, the composite strength has a maximum value which increases withV
f. If the bond strength is weaker than the matrix, the composite strength has a minimum value which is either weakly dependent
or even independent ofV
f. These calculations are in good agreement with examples taken from the literature of aluminum composites reinforced with
either A12O3, graphite, or SiC. The strength of the matrix alloy is shown to be a very important parameter: weak alloys are easily strengthened,
while in certain cases, strong alloys may be weakened. 相似文献
8.
9.
U. Ramamurty 《Metallurgical and Materials Transactions A》1999,30(8):2237-2248
Many applications of the Ti alloy matrix composites (TMCs) reinforced with SiC fibers are expected to use the selective reinforcement
concept in order to optimize the processing and increase the cost-effectiveness. In this work, unnotched fatigue behavior
of a Ti-6Al-4V matrix selectively reinforced with SCS-6 SiC fibers has been examined. Experiments have been conducted on two
different model panels. Results show that the fatigue life of the selectively reinforced composites is far inferior to that
of the all-TMC panel. The fatigue life decreases with the decreasing effective fiber volume fraction. Suppression of multiple
matrix cracking in the selectively reinforced panels was identified as the reason for their lack of fatigue resistance. Fatigue
endurance limit as a function of the clad thickness was calculated using the modified Smith-Watson-Topper (SWT) parameter
and the effective fiber volume fraction approach. The regime over which multiple matrix cracking occurs is identified using
the bridging fiber fracture criterion. A fatigue failure map for the selectively reinforced TMCs is constructed on the basis
of the observed damage mechanisms. Possible applications of such maps are discussed. 相似文献
10.
Titanium matrix composites (TMC) and their behavior under mechanical fatigue loads was the subject of this research. The primary
objective was to explain fatigue damage modes in center-notched TMC specimens. Two modes of damage have been observed in continuously
reinforced, zero-degree unidirectional, SCS-6/Ti-15V-3Cr-3Al-3Sn (SCS-6/Ti-15-3) laminates. The fatigue specimens were destructively
analyzed using optical microscopy to determine where cracks originated and how they grew throughout the specimen. A micromechanical
model was developed to explain the fatigue crack patterns observed in the interface region surrounding the fibers of the woven
and acrylic-binder TMC material systems. A two-dimensional (2-D) model of a longitudinal lamina with a center hole was used
to obtain a set of displacement boundary conditions for an element near the notch, yet within the net section where the spiral
crack patterns were observed. These boundary conditions were then used on a three-dimensional (3-D) unit cell model of the
fiber, matrix, and interface.
This article is based on a presentation made in the symposium “Fatigue and Creep of Composite Materials” presented at the
TMS Fall Meeting in Indianapolis, Indiana, September 14–18, 1997, under the auspices of the TMS/ASM Composite Materials Committee. 相似文献
11.
竹纤维表面碱处理对纤维增强树脂基摩擦材料摩擦学性能的影响 总被引:3,自引:0,他引:3
通过对竹纤维采用不同工艺的碱处理后,采用热压法制备改性竹纤维增强树脂基复合材料,并对竹纤维表面结构、复合材料的摩擦学性能以及磨损表面形貌进行研究。结果表明:对竹纤维进行碱处理,可有效提高纤维增强树脂基摩擦材料制动时的摩擦因数及摩擦因数稳定性。当NaOH溶液的质量浓度为200 g/L、处理时间为48 h时,该复合材料具有较好的摩擦磨损性能,平均摩擦因数由未处理时的0.21提高到0.26,总体积磨损率由2.57×10-7cm3/(N·m)降低至1.18×10-7 cm3/(N·m),摩擦因数偏差保持在0.08的较低水平。竹纤维经碱处理后木质素中的不同基本结构单元均发生不同程度的分解,表面变得粗糙,纤维束分裂成更小的纤维,纤维取向更接近轴向,提高了竹纤维与树脂基体界面粘结能力;同时经碱处理后的竹纤维可保持对基体和填料的强支撑作用,在高温下复合材料不易出现热衰退现象,摩擦学性能得到改善。 相似文献
12.
S. Nourbakhsh W. H. Rhee O. Sahin H. Margolin 《Metallurgical and Materials Transactions A》1994,25(6):1259-1265
A series of single-crystal A12O3 fiber (Saphikon), reinforced Ni3Al-based composites were fabricated by a liquid metal infiltration technique, pressure casting. Tensile testing and indentation
techniques have been employed to measure fiber strength and fiber/matrix interfacial debond shear stress. The Weibull mean
strength of the fiber has been observed to decrease drastically upon handling, exposure to high temperature, and casting.
Alloying of Ni3Al with Ti has resulted in a further decrease in fiber strength. Thermal expansion mismatch between the fiber and matrix led
to the formation of compressive twins in the fiber. These twins, forming on
planes, produced cracks at their intersections, which were parallel to the fiber axis,c-axis. Twin-induced fiber cracking was observed in all cases, but most predominantly when Cr was present. While addition of
Cr at the 1 at. pct level had no appreciable effect on the interfacial debond shear stress, addition of 0.5 at. pct Cr resulted
in an approximately threefold increase in debond stress, from 19 MPa to about 54.5 MPa. Alloying of Ni3Al with Cr has also resulted in partial dissolution of the A12O3 fiber. Addition of Ti had a moderate effect on increasing the fiber/matrix bond strength. 相似文献
13.
The transverse stress-strain behavior of several titanium metal-matrix composites (TiMMCs) has been studied in-situ. Debonding of 1140+/Ti-6-4 composites occurs over a range of stresses. The sharpness of the first “knee” is affected by the
fiber volume fraction and by the relative moduli of the matrix regions and the reinforced composite. It has been observed
that debonding occurs mainly at the interface between two sublayers of carbon/carbon coatings in 1140+/Ti-6-4 composites and
mainly at the interface between the carbon/reaction zone in the as-processed and peak-aged 35 pct SCS-6/Tiβ21s composites. At surface positions, this process starts at very low stresses (≥50 MPa) from the positions with sharp changes
of curvatures (or undulations), voids, or debris at the periphery of the interface. Cracking of the outermost carbon sublayer
and of the reaction zone in the 1140+/Ti-6-4 composites and the reaction zone in the SCS-6/Tiβ21s composites occurs during elastic deformation of the matrix. This has been directly observed in a field-emission gun (FEG)-scanning
electron microscope (SEM) under incremental loading. Although these cracks are arrested and blunted by the matrix material,
they cause local stresses and, thus, stimulate local plastic deformation of the matrix and subsequent development of a second
knee on the stress-strain curve. The in-situ observations are discussed in terms of the effects of fiber volume fraction and fiber type on the loci and dynamic processes
of interfacial debonding, cracking of carbon coatings and reaction zones, and plastic deformation of the matrix. 相似文献
14.
Titanium matrix composites (TMCs) reinforced with Sigma 1140+ SiC fiber have been manufactured by a combination of low pressure plasma spraying (LPPS spray/wind) and simultaneous fiber winding, followed by vacuum hot pressing (VHP). Fiber damage during TMC manufacture has been evaluated by measuring fiber tensile strength after fiber extraction from the TMCs at various processing stages, followed by fitting of these data to a Weibull distribution function. The LPPS spray/wind processing caused a decrease in mean fiber strength and Weibull modulus in comparison with as-received fibers. A number of fiber surface flaws, primarily in the outer C layer of the fiber, formed as a result of mechanical impact of poorly melted particles from the plasma spray. Coarse feedstock powders promoted an increase in the population of fiber surface flaws, leading to significant reduction in fiber strength. The VHP consolidation promoted further development of fiber surface flaws by fiber bending and stress localization because of nonuniform matrix shrinkage, resulting in further degradation in fiber strength. In the extreme case of fibers touching, the stress concentration on the fibers was sufficient to cause fiber cracking. Fractographic studies revealed that low strength fibers failed by surface flaw induced failure and contained a large fracture mirror zone. Compared with the more widely investigated foil-fiber-foil route to manufacture TMCs, LPPS/VHP resulted in less degradation in fiber strength for Sigma 1140+ fiber. Preliminary results for Textron SCS-6 fiber indicated a much greater tolerance to LPPS/VHP damage. 相似文献
15.
对原位生成TiC颗粒增强钛基复合材料进行锻造,通过金相显微镜(OPM)、扫描电镜(SEM)和能谱分析(EDS)等手段,研究锻造后材料的显微组织及拉伸断口形貌,利用CETR UMT-3多功能微摩擦磨损测试仪测定材料的摩擦磨损行为。结果表明:锻造后钛基复合材料的组织缺陷得到消除,晶粒明显细化,抗拉强度由1 126 MPa提高到1 309 MPa;材料拉伸断口为TiC解理断裂与基体局部延性断裂相结合的混合型断口。随载荷不断增加,TiC粒子首先断裂,裂纹在基体中迅速扩展,导致复合材料失效。在摩擦实验初期,材料的摩擦因数较小且较稳定,而后期摩擦因数变化幅度较大;随时间延长,磨损面上的TiC颗粒发生破碎,失去承载作用,导致磨损量变大;摩擦磨损过程中材料表面Ti发生氧化,形成氧化磨损;锻造后材料的磨损量及摩擦因数都减小。 相似文献
16.
The role of elastic shielding in reducing the local stress intensity factor (SIF) range during fatigue crack growth (FCG)
has been investigated using several single-ply composites with significantly different interfacial characteristics. The specimen
geometry necessitated the fatigue crack to initially grow through a monolithic matrix region before impinging on a set of
longitudinally oriented fibers. This facilitated the assessment of the crack shielding phenomenon from two regions: the region
where the crack interacted with the first fiber, and at high stress levels when nonbridging conditions prevailed in the fibrous
region. The extent of shielding was nearly identical in the two measurements for a given composite system. However, the shielding
contribution was found to depend on the interface bond strength; the interface with the highest bond strength provided the
largest degree of crack retardation in both cases. A preliminary assessment of this dependency has been provided. The implications
of using the correct shielding factor on both fiber strength and life prediction are also discussed.
This article is based on a presentation made in the symposium “Fatigue and Creep of Composite Materials” presented at the
TMS Fall Meeting in Indianapolis, Indiana, September 14–18, 1997, under the auspices of the TMS/ASM Composite Materials Committee. 相似文献
17.
S. L. Draper P. K. Brindley M. V. Nathal 《Metallurgical and Materials Transactions A》1992,23(9):2541-2548
To increase understanding of what controls SCS-6 SiC/Ti-24Al-11Nb (at. pct) composite strength, fibers of known strength were
incorporated into composites and the effect of fiber strength variability on room temperature composite strength was investigated.
Fiber was also etched out of a composite fabricated by the powder cloth technique, and the effect of the fabrication process
on fiber strength was assessed. The strength of the composite was directly correlated with the strength of the as-received
fiber. Fabrication by the powder cloth technique resulted in only a slight degradation of fiber strength. Examination of failed
tensile specimens revealed periodic fiber cracks, and the failure mode was concluded to be cumulative. 相似文献
18.
A theoretical model of the creep behavior of metal matrix composites having strong fiber-matrix interfaces is described in
terms of creep parameters of the matrix and fibers. The available experimental data, obtained from the unidirectionally solidified
aluminum-nickel eutectic containing 10 vol pct Al3Ni fibers, are in good agreement with the theoretical model. The creep activation energy of the composite is described in
terms of the creep activation energy of fibers and the matrix. The experimentally de-termined data of (Co, Cr)-(Co, Cr)7C3 and Al-Al3Ni eutectics are in agreement with those values as predicted.
Formerly a Visiting Scholar, Materials Department, University of California, Los Angeles. 相似文献
19.
高温钛合金和颗粒增强钛基复合材料的研究和发展 总被引:1,自引:0,他引:1
简要回顾了高温钛合金的研究和发展历程,指出现代高温钛合金进一步发展需要解决的主要难题.综述了颗粒增强钛基复合材料的研究现状,从基体的选择、增强相的选择和制备工艺等3个方面,较详细地阐述了颗粒增强钛基复合材料设计中的基本任务.最后对今后的发展趋势进行了展望. 相似文献