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1.
Mechanisms of longitudinal creep deformation and damage were studied in an eight-ply unidirectional-reinforced SCS-6/Ti-6Al-4V
composite. The composite was creep tested in air under constant tensile load at temperatures from 427 °C to 650 °C and stresses
from 621 to 1380 MPa.In situ acoustic emission (AE) monitoring and post-test metallographic evaluation were used to study fiber fracture and damage during
creep. At low creep stresses, creep rates continuously decreased to near-zero values. This was attributed to a mechanism of
matrix relaxation and the time-dependent redistribution of load from the ductile matrix to the elastic fibers. At higher stresses,
progressive fiber overload occurred during creep loading. In this case, the composite exhibited a stage of decreasing creep
rate (due primarily to matrix relaxation), followed by a secondary stage of nearly constant creep rate due to fiber fracture.
The results indicate that interfacial oxidation damage and inefficient load transfer at elevated temperatures significantly
decreased the capability of broken fibers to carry load. As a result, additional time-dependent stress redistribution occurred
in the composite, which was responsible for the secondary creep stage. 相似文献
2.
Thermal cycling-induced deformation of fibrous composites with particular reference to the tungsten-copper system 总被引:1,自引:0,他引:1
Yoda S. Kurihara Nobuya Wakashima K. Umekawa S. 《Metallurgical and Materials Transactions A》1978,9(9):1229-1236
Dimensional stability of fibrous composites under conditions of elevated temperature cycling has been examined with reference
to the familiar model system, tungsten wirereinforced copper. Preferential growth of the matrix in the direction parallel
to the reinforcing fibers, the amount of which increased with the number of cycles, was observed in specimens subjected to
hundreds of repctitive thermal cycles in the temperature range between 0.35 and 0.8 of the matrix homologous temperature.
The amount of growth per unit length after a given number of cycles was found to increase with increasing the holding time
at the upper cycling temperature; it was also dependent on such composite variables as the fiber length, fiber diameter, and
fiber volume fraction. This observation strongly suggests that interface sliding plays an important role in elevated temperature
deformation of this class of material. On the basis of a model which assumes a viscous nature of the phase boundaries, the
phenomenon observed is theoretically explained in terms of interfacial sliding-induced relaxation of the internal stress built
up in the composite due to differential thermal expansion of the composite constituents.
Formerly Graduate Student. 相似文献
3.
The effect of isothermal exposure and thermal cycling on the toughness of B/Al (1100), B/Al (6061), and A12O3/A1 composites has been investigated. In B/Al (1100), isothermal exposure at 773 K for 45 × 104 s (125 hours) reduced toughness, measured by the work of fracture, from 76 kJm-2 to 10 kJm-2, and a similar reduction occurred after equivalent thermal cycling. The corresponding reduction in toughness after isothermal
exposure in B/Al (6061) was from 44.5 kJm-2 to 8 kJm-2; however, the effect of thermal cycling was less detrimental. In the FP-A12O3/A1 composite, the work of fracture was insensitive to both forms of thermal treatment. Changes in the toughness of the B/Al
composites have been correlated with and analyzed in terms of modifications to matrix, fiber, and interface properties, in
particular, matrix softening, interface reaction products, and fiber notch sensitivity.
The latter currently on
The latter currently on 相似文献
4.
《Acta Metallurgica Materialia》1994,42(12):4015-4024
The transverse properties of a SiC fiber reinforced Ti alloy matrix composite subjected to transverse mechanical and cyclic thermal loading have been investigated. Fibers and matric have a mismatch in the coefficients of thermal expansion that induces thermal stresses in addition to those caused by mechanical loading. When fluctuations occur in the operating temperature the thermal stresses change and this could cause an incremental accumulation of plastic strain or increase in creep rate. The composite under consideration has a modest mismatch and it was found that the strain accumulation is caused by creep deformation in the matrix at the high temperature portion of the thermal cycles. In the early stages of the deformation for low transverse loading the interface is in compressive contact and the creep rate is accelerated by the cyclic thermal stresses. After debonding has occurred the cyclic thermal stress component is diminished and the creep rate is given by a matrix with holes. 相似文献
5.
Eun U. Lee 《Metallurgical and Materials Transactions A》1992,23(8):2205-2210
The stresses and strains, induced by coefficient of thermal expansion (CTE) mismatch, are analyzed for a metal matrix composite
(MMC) with a spherical reinforcement particle. The spherical reinforcement particle is found to be in a hydrostatic stress
state and remains in the elastic state. The stresses and strains are largest, and plastic deformation occurs in the matrix
adjacent to the reinforcement particle. Accordingly, the reinforcement particle/matrix interface becomes a potential crack
initiation site under thermal cycling. The critical internal pressure for plastic deformation is less than two-thirds of the
yield stress of the matrix material and decreases with increasing range of thermal cycle. 相似文献
6.
H. Li D. Z. Wang J. B. Li Z. G. Wang C. R. Chen 《Metallurgical and Materials Transactions A》1998,29(7):2001-2009
The thermal stresses (TS) in the matrix of a SiC
p
/6061Al composite during thermal cycling were measured by X-ray diffraction. Also, the TS during thermal cycling and residual
stress distribution (RSD) at room temperature in the two phases of composite were calculated by finite element modeling (FEM).
The measured and calculated results indicated that the closed stress-temperature loop was formed during thermal cycling. The
stress state in the matrix changed from tension to compression during heating and from compression to tension during cooling.
Plastic deformation took place in the matrix of the composite during thermal cycling. The general change trend of TS with
temperature during thermal cycling was in agreement between the experiment and calculation. 相似文献
7.
H. H. Grimes R. A. Lad J. E. Maisel 《Metallurgical and Materials Transactions A》1977,8(12):1999-2005
We have systematically studied the variation of ultimate tensile strength with thermal treatment of B-Al composite materials
and of boron fibers chemically removed from these composites in an attempt to determine the mechanism of the resulting strength
degradation. This knowledge will be of value in designing to extend the use-temperature of these composites. Our findings
indicate that thermally cycling B-Al represents a more severe condition than equivalent time at temperature. Degradation of
composite tensile strength from about 1.3 GN/m2 to as low as 0.34 GN/m2 was observed after 3000 cycles to 420°C for 203 μm B-1100 Al composite. In general, the 1100 Al matrix composites degraded
somewhat more than the 6061 matrix material studied. Measurement of fiber strengths confirmed a composite strength loss due
to the degradation of fiber strength. Microscopy indicated a highly flawed fiber surface. On the basis of the thermal cycling
studies in air and in the absence of air and of electron diffraction analysis of the reaction zone, a mechanism is favored
in which B reacts with Al, freshly exposed by cold working during cycling, to form AIB2. The nonuniform interface reaction
leads to a highly flawed and weakened B fiber. 相似文献
8.
《Acta Metallurgica Materialia》1993,41(6):1665-1681
The combined effects of thermal residual stresses anmd fiber spatial distribution on the deformation of a 6061 aluminum alloy containing a fixed concentration unidirectional boron fibers have been analyzed using detailed finite element models. The geometrical structure includes perfectly periodic, uniformly spaced fiber arrangements in square and hexagonal cells, as well as different cells in which either 30 or 60 fibers are randomly placed in the ductile matrix. The model involves an elastic-plastic matrix, elastic fibers, and mechanically bonded interfaces. The results indicate that both fiber packing and thermal residual stresses can have a significant effect on the stress-strain characteristics of the composite. The thermal residual stresses cause pronounced matrix yielding which also influences the apparent overall stiffness of the composite during the initial stages of subsequent far-field loading along the axial and transverse direction. Furthermore, the thermal residual stresses apparently elevate the flow stress of the composite during transverse tension. Such effects can be traced back to the level of constraint imposed on the matrix by local fiber spacing. The implications of the present results to the processing of the composites are also briefly addressed. 相似文献
9.
《Acta Metallurgica Materialia》1991,39(10):2275-2284
The role of fiber debonding and sliding on the toughness of intermetallic composites reinforced with ductile fibers is examined. The toughness is shown to be a function of the matrix/fiber interface properties, residual stresses and the volume fraction, size and flow behavior of the fibers. Mechanical testing and in situ microstructural observations were carried out on a Ti-25at.%Ta-50at.%Al intermetallic matrix reinforced with W-3Re fibers. The fibers were coated with a thin oxide layer in order to induce debonding and prevent interdiffusion between the fiber and the matrix. The ductility, high strength and debond characteristics of coated tungsten-rhenium fibers promote a large increase in toughness. However, the mismatch in thermal expansion coefficients is the source of large residual tensile stresses in the matrix that induces spontaneous matrix cracking. Matrix cracking and composite toughness are examined as a function of the interfacial properties, residual stresses and properties of the fiber. 相似文献
10.
K. S. Chan 《Metallurgical and Materials Transactions A》1993,24(7):1531-1542
Pertinent failure processes in unidirectional fiber metal-matrix composites (MMCs) have been identified and analyzed. The
critical conditions for interface delamination in several composites are compared with the theoretical delamination diagram
proposed by He and Hutchinson, in which interface delamination and fiber fracture are delineated on the basis of their relative
tough-ness values. It is shown that the delamination diagram does not provide information about the extent of interface cracking
or the onset of fiber bridging. An alternative failure diagram that depicts composite fracture processes, such as matrix yielding
followed by fiber fracture, inter-face cracking, and fiber bridging, is proposed. Development of the composite failure diagramvia micromechanical modeling of individual mechanisms is presented together with experimental results from the literature. Good
correlation between theory and experiment suggests that the composite failure diagram might be used for tailoring composite
properties through control of the dominant fracture mechanism. 相似文献
11.
P. K. Liaw E. S. Diaz K. T. Chiang D. H. Loh 《Metallurgical and Materials Transactions A》1995,26(12):3225-3247
Flexural fatigue behavior was investigated on titanium (Ti-15V-3Cr) metal matrix composites reinforced with cross-ply, continuous
silicon carbide (SiC) fibers. The titanium composites had an eightply (0, 90, +45, -45 deg) symmetric layup. Fatigue life
was found to be sensitive to fiber layup sequence. Increasing the test temperature from 24 °C to 427 °C decreased fatigue
life. Interface debonding and matrix and fiber fracture were characteristic of tensile behavior regardless of test temperature.
In the tensile fracture process, interface debonding between SiC and the graphite coating and between the graphite coating
and the carbon core could occur. A greater amount of coating degradation at 427 °C than at 24 °C reduced the Ti/SiC interface
bonding integrity, which resulted in lower tensile properties at 427 °C. During tensile testing, a crack could initiate from
the debonded Ti/SiC interface and extend to the debonded interface of the neighboring fiber. The crack tended to propagate
through the matrix and the interface. Dimpled fracture was the prime mode of matrix fracture. During fatigue testing, four
stages of flexural deflection behavior were observed. The deflection at stage I increased slightly with fatigue cycling, while
that at stage II increased significantly with cycling. Interestingly, the deflection at stage III increased negligibly with
fatigue cycling. Stage IV was associated with final failure, and the deflection increased abruptly. Interface debonding, matrix
cracking, and fiber bridging were identified as the prime modes of fatigue mechanisms. To a lesser extent, fiber fracture
was observed during fatigue. However, fiber fracture was believed to occur near the final stage of fatigue failure. In fatigued
specimens, facet-type fracture appearance was characteristic of matrix fracture morphology. Theoretical modeling of the fatigue
behavior of Ti/SCS-6 composites is presented in Part II of this series of articles.
This article is based on a presentation made in the symposium entitled “Creep and Fatigue in Metal Matrix Composites” at the
1994 TMS/ASM Spring meeting, held February 28–March 3, 1994, in San Francisco, California, under the auspices of the Joint
TMS-SMD/ASM-MSD Composite Materials Committee. 相似文献
12.
《Acta Metallurgica Materialia》1990,38(12):2411-2424
This paper presents a simple shear lag model of interfacial sliding at a free surface in a layered or continuous fiber composite. The interface is characterized by a critical interfacial shear stress, τ0, which might represent the critical stress for frictional sliding at a weakly bonded interface, or the shear flow stress of a thin, ductile interface layer at a well bonded interface. We calculate the history during heating and cooling of the relative normal displacement of the reinforcing inclusions and the matrix on a free surface cut normal to the inclusions. The calculated history is shown to depend on both the absolute value and the temperature dependence of τ0, as well as on the magnitudes of the bulk residual stresses. Analytical results are obtained for the first few heating and cooling cycles and the equilibrium hysteresis loop under thermal cycling of uniform amplitude. The variety of possible displacement histories suggests that they are a rich source of information about τ0 and the residual stresses. A discussion of feasible experiments and some results for continuous fiber titanium and titanium aluminide composites are presented in a companion paper. 相似文献
13.
A micromodeling analysis of unidirectionally reinforced Ti-6-4/SM1140+ composites subjected to transverse tensile loading
has been performed using the finite-element method (FEM). The composite is assumed to the infinite and regular, with either
hexagonal or rectangular arrays of fibers in an elastic-plastic matrix. Unit cells of these arrays are applied in this modeling
analysis. Factors affecting transverse properties of the composites, such as thermal residual stresses caused by cooling from
the composite processing temperature, fiber-matrix interface conditions, fiber volume fraction, fiber spacing, fiber packing,
and test temperature are discussed. Predictions of stress-strain curves are compared with experimental results. A hexagonal
fiber-packing model with a weak fiber-matrix interfacial strength predicts the transverse tensile behavior of the composite
Ti-6-4/SM1140+ most accurately. 相似文献
14.
W. C. Revelos J. W. Jones E. J. Dolley 《Metallurgical and Materials Transactions A》1995,26(5):1167-1181
The influence of thermal cycling and isothermal exposures in air on the residual ambient temperature strength of SCS-6/Ti-15Mo-2.7Nb-3Al-0.2Si
(weight percent) metal-matrix composites comprised of [0]4 and [0/90]s laminates has been determined. A maximum temperature of 815 °C was used in thermal cycling and isothermal exposure. Temperature
range, cycle count, maximum/minimum temperature, environment, and hold time at temperature were systematically varied. Postexposure
ambient-temperature tension testing, scanning electron and optical microscopy, and fractography were performed on selected
specimens to determine the degree of damage. A reduced residual strength was noted in thermal fatigue with increasing cycle
count, maximum temperature, and hold time for all specimens tested in air. Isothermal exposures at 815 °C also substantially
reduced residual ambient-temperature strength. Considerably less reduction in strength occurred in inert environment than
in air. Damage processes included matrix cracking, fiber/matrix interface damage, matrix embrittlement by interstitials, and
oxide scale formation at specimen surfaces and, in some cases, at matrix/fiber interfaces. Fiber orientations which allowed
rapid ingress of oxygen lead to greater matrix embrittlement and resulted in more pronounced reductions in strength.
Formerly with the Materials Directorate, Wright Laboratory, Wright Patterson AFB, Dayton, OH 45433 相似文献
15.
A series of high-temperature fatigue crack growth experiments was conducted on a continuous-fiberreinforced SM1240/TIMETAL-21S
composite using three different temperatures, room temperature (24 °C), 500 °C, and 650 °C, and three loading frequencies,
10, 0.1, and 0.02 Hz. In all the tests, the cracking process concentrated along a single mode I crack for which the principal
damage mechanism was crack bridging and fiber/matrix debonding. The matrix transgranular fracture mode was not significantly
influenced by temperature or loading frequency. The fiber debonding length in the crack bridging region was estimated based
on the knowledge of the fiber pullout lengths measured along the fracture surfaces of the test specimens. The average pullout
length was correlated with both temperature and loading frequency. Furthermore, the increase in the temperature was found
to lead to a decrease in the crack growth rate. The mechanism responsible for this behavior is discussed in relation to the
interaction of a number of temperature-dependent factors acting along the bridged fiber/matrix debonded zone. These factors
include the frictional stress, the radial stress, and the debonding length of the fiber/matrix interface. In addition, the
crack growth speed was found to depend proportionally on the loading frequency. This relationship, particularly at low frequencies,
is interpreted in terms of the development of a crack tip closure induced by the relaxation of the compressive residual stresses
developed in the matrix phase in regions ahead of the crack tip during the time-dependent loading process. 相似文献
16.
W. O. Soboyejo Y. Li S. I. Rokhlin B. M. Rabeeh Y. C. Chu A. Lavrentenyev 《Metallurgical and Materials Transactions A》1997,28(8):1667-1687
The results of a systematic study of the effects of microstructure on the strength and fatigue behavior of a symmetric [0/90]2s Ti-15Al-3Cr-3Al-3Sn/SiC (SCS-6) composite are presented along with relevant information on failnure mechanisms in the composite
constituents, i.e., the interface, fiber, and matrix materials. Damage micromechanisms are elucidated via optical microscopy, scanning electron microscopy (SEM), and nondestructive acoustic emission (AE) and ultrasonic techniques.
Composite damage is shown to initiate early under cyclic loading conditions and is dominated by longitudinal and transverse
interfacial cracking. Subsequent fatigue damage occurs by matrix slip band formation, matrix and fiber cracking, and crack
coalescence, prior to the onset of catastrophic failure. However, the sequence of the damage is different in material annealed
above or below the β solvus of the Ti-15-3 matrix material. Mechanistically based micromechanics models are applied to the
prediction of the changes in modulus induced by fatigue damage. Idealized fracture mechanics models are also employed in the
prediction of the fatigue lives of smooth specimens deformed to failure at room temperature. The article highlights the potential
to develop mechanistically based predictive models based on simplified mechanics idealizations of experimental observations. 相似文献
17.
《Acta Metallurgica Materialia》1993,41(11):3147-3156
The anisotropic mechanical behavior of a continuous fiber reinforced Ti alloy matrix composite which possesses a weak fiber matrix interface is modeled numerically. Effects of interface properties and residual stresses incurred during the fabrication are addressed in detail. The computational modeling is guided by comparison with experimental data. The study provides an understanding which will be used to model the multiaxial behavior of weakly bonded composites and to provide a tool for predicting the failure of composite structures. 相似文献
18.
P. K. Brindley S. L. Draper J. I. Eldridge M. V. Nathal S. M. Arnold 《Metallurgical and Materials Transactions A》1992,23(9):2527-2540
The tensile stress-strain behavior and failure mechanisms of Ti-24Al-11Nb and a SiC/ Ti-24Al-11Nb composite with continuous
SCS-6 fibers oriented parallel to the loading direction have been examined over a range of temperatures from 23 °C to 815°C in air. Failure in Ti- 24Al-11Nb occurred at strains of approximately 4 pct soon after crack initiation at low tem- peratures.
Ductility increased with temperature up to a maximum of 20 pct elongation at 600 °C, as surface-initiated cracks did not propagate
readily at intermediate temperatures. At higher temperatures, the onset of grain boundary and interfacial void nucleation
limited ductility. Com- posite failure appeared to be controlled by fiber fracture at all temperatures; for practical en-
gineering purposes, composite failure occurred at 0.8 pct strain at all temperatures. At temperatures of 425 °C and less,
fiber fractures occurred at intervals along the lengths of the fibers and appeared to be cumulative, while at temperatures
of 650 °C and greater, fiber fractures were only observed locally to the fracture surfaces. The decreased radial residual
stresses, interfacial strengths, and matrix properties at 650 °C and 815 °C allowed the composite to unload at 0.8 pct strain,
due to fiber fractures, followed by a reloading in which fibers pulled out and the matrix failed, resulting in composite failure.
The decreasing residual stresses with increasing temper- ature determined from an elastic-plastic concentric cylinder model
were shown to affect the stress-strain response of the composite and were consistent with the measured decreasing inter- facial
shear stresses, the increased fiber pullout with temperature, and the circumferential de- bonding observed around the fibers
at higher temperatures. 相似文献
19.
J. H. Chen Y. Chen M. Q. Jiang X. W. Chen H. M. Fu H. F. Zhang L. H. Dai 《Metallurgical and Materials Transactions A》2014,45(12):5397-5408
The evolution of micro-damage and deformation of each phase in the composite plays a pivotal role in the clarification of deformation mechanism of composite. However, limited model and mechanical experiments were conducted to reveal the evolution of the deformation of the two phases in the tungsten fiber reinforced Zr-based bulk metallic glass composite. In this study, quasi-static compressive tests were performed on this composite. For the first time, the evolution of micro-damage and deformation of the two phases in this composite, i.e., shear banding of the metallic glass matrix and buckling deformation of the tungsten fiber, were investigated systematically by controlling the loading process at different degrees of deformation. It is found that under uniaxial compression, buckling of the tungsten fiber occurs first, while the metallic glass matrix deforms homogeneously. Upon further loading, shear bands initiate from the fiber/matrix interface and propagate in the metallic glass matrix. Finally, the composite fractures in a mixed mode, with splitting in the tungsten fiber, along with shear fracture in the metallic glass matrix. Through the analysis on the stress state in the composite and resistance to shear banding of the two phases during compressive deformation, the possible deformation mechanism of the composite is unveiled. The deformation map of the composite, which covers from elastic deformation to final fracture, is obtained as well. 相似文献
20.
A. B. Pandey B. S. Majumdar D. B. Miracle 《Metallurgical and Materials Transactions A》2000,31(13):921-936
Mechanical tests were performed on a powder-metallurgically processed 7093/SiC/15p discontinuously reinforced aluminum (DRA)
composite in different heat-treatment conditions, to determine the influence of matrix characteristics on the composite response.
The work-hardening exponent and the strain to failure varied inversely to the strength, similar to monolithic Al alloys, and
this dependence was independent of the dominant damage mode. The damage consisted of SiC particle cracks, interface and near-interface
debonds, and matrix rupture inside intense slip bands. Fracture surfaces revealed particle fracture-dominated damage for most
of the heat-treatment conditions, including an overaged (OA) condition that exhibited a combination of precipitates at the
interface and a precipitate-free zone (PFZ) in the immediate vicinity. In the highly OA conditions and in a 450°C as-rolled
condition, when the composite strength became less than 400 MPa, near-interface matrix rupture became dominant. A combination
of a relatively weak matrix and a weak zone around the particle likely contributed to this damage mode over that of particle
fracture. Fracture-toughness tests show that it is important to maintain a proper geometry and testing procedure to obtain
valid fracture-toughness data. Overaged microstructures did reveal a recovery of fracture toughness as compared to the peak-aged
(PA) condition, unlike the lack of toughness recovery reported earlier for a similar 7XXX (Al-Zn-Cu-Mg)—based DRA. The PA material exhibited extensive localization of damage and plasticity. The low toughness of
the DRA in this PA condition is explored in detail, using fractography and metallography. The damage and fracture micromechanisms
formed the basis for modeling the strength, elongation, toughness, and damage, which are described in Part II of this work.
This article is based on a presentation made in the Symposium “Mechanisms and Mechanics of Composites Fracture” held October
11–15, 1998, at the TMS Fall Meeting in Rosemont, Illinois, under the auspices of the TMS-SMD/ASM-MSCTS Composite Materials
Committee. 相似文献