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1.
The embedded molybdenum fibre in a copper matrix composite was elongated apparently uniformly although the interface was so weak that necking in the fibre could not be suppressed by the matrix. To explain this result, a possible mechanism was suggested where suppression of necking in the fibre is caused by strain hardening of the composite as a whole and by an increment in strain rate in the cross-section where the fibre starts necking, but the incremental deformation amount and the incremental strain rate of the cross-section are small. On the basis of this mechanism, and with the aid of Hart's criterion, a new instability approach to tensile behaviour of the composite is presented. It was found that the stability of the composite is determined mainly by the strain-hardening exponent of the composite, which is determined by the modified rule of mixtures. The present derived condition of instability of the composite is in good agreement with that proposed by Mileiko.  相似文献   

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3.
By using the single carbon-steel fibre-copper matrix composites, the important parameters controlling dislocation motions in the fibre, matrix and composite, namely flow stress, internal stress, effective stress, change in flow stress due to change in strain-rate or temperature, stress exponent of strain-rate, effective stress exponent of dislocation velocity, activation volume and activation enthalpy were measured at the stage in which the mechanical interaction between the components was negligible. It was found that all the composite parameters were determined only by the properties of the components and for each parameter, a modified rule of mixtures was derived.  相似文献   

4.
A model to predict the increase in critical flaw size or stable crack growth potential which can occur by the inclusion of ductile fibers in a brittle matrix is considered. The model is based upon the super-position of two known stress intensity solutions; one for the crack opening mode resulting from a remotely applied stress and the second, an opposing stress intensity that results from a crack closing force exerted by unbroken fibers spanning the crack surfaces. The extent of stable growth possible is computed at the ultimate stress of the brittle phase as functions of fiber strength and of volume fraction for various amounts of fiber rupture. A hot pressed beryllium matrix is used as an example. The crack surface displacement over which a given fiber is capable of deforming without rupture is found to be sensitive to the fiber-matrix interface strength. The factors leading to maximum crack surface displacement without rupture are a high strain hardening capability of the fiber and an interface designed to fail at fiber stresses between yield and ultimate strengths.  相似文献   

5.
SiC particle reinforced Al 2025 aluminum alloy composite is used for tensile tests. The ductile fracture by nucleation, growth and coalescence of micro voids, particle cracking and the interfacial debonding under the different constraint conditions, which are obtained by changing the notch radius, is analyzed. The effect of the local constraint on the respective damage phenomenon is analyzed using the axi-symmetric unit cell FE model by changing the local stress triaxiality and side constraint. The results show that the fracture process of the notched tensile bar is simulated well and the damage phenomena agree qualitatively with the experimental ones. Finally the effect of constraint on the void configuration and coalescence is investigated experimentally using three-dimensional fracture surface observations using the SEM (scanning electron microscope) and three-dimensional imaging analysis method. The constraint effect is analyzed by changing the specimen’s shape. The experimental results show that the void aspect ratio is decreased with increases of SiC particle volume fraction in aluminum alloy. The final void volume fraction at fracture also changes by the specimen shape and the material’s structure.  相似文献   

6.
Damage models for studying ductile matrix failure in composites   总被引:2,自引:0,他引:2  
The contribution aims at assessing different computational models for their capabilities in describing the initiation and growth of ductile cracks in inhomogeneous materials at the constituent level. The main emphasis is put on the ductile damage models of Gurson and Rousselier and on a ductile damage indicator triggered model. The models were implemented via user subroutines into the finite element code ABAQUS/Standard, a nonlocal approach being used to overcome their well-known mesh-dependence.  相似文献   

7.
In this work, an attempt is made to model the ductile fracture behaviour of two Cu‐strengthened high strength low alloy (HSLA) steels through the understanding of their deformation behaviour. The variations in deformation behaviour are imparted by prior deformation of steels to various predetermined strains. The variations in parameters such as yield strength and true uniform elongation with prior deformation is studied and was found to be analogous to that of initiation fracture toughness determined by independent method. A unique method is used to measure the crack tip deformation characterized by stretch zone depth that also depicted a similar trend. Fracture toughness values derived from the stretch zone depth measurements were found to vary in the same fashion as the experimental values. A semiempirical relationship for obtaining ductile fracture toughness from basic deformation parameters is derived and model is demonstrated to estimate initiation ductile fracture toughness accurately.  相似文献   

8.
Various models of creep deformation of composite materials are reviewed and their predictions compared with available experimental data. The implications of rule-of-mixtures strengthening when (a) both matrix and reinforcing phase are subject to creep deformation and (b) the reinforcement extends elastically in a creeping matrix for the establishment of steady state creep and for the representation of creep data for composites are discussed.Evidence of deviation from rule-of-mixtures behaviour is given, particularly where the dispersed phase can lead to either strengthening or weakening of the matrix. The value of analysing transient creep following stress changes to elucidate the creep mechanisms will be discussed. It will be shown that the reinforcement can influence matrix creep by (i) introducing a threshold stress and (ii) altering the deformation kinetics. In some nickel-base alloys, the latter factor can lead to significant strain softening that prevents the establishment of steady state creep.  相似文献   

9.
A method of construction of the effective strength surface of matrix composites based on the properties of their components taking into consideration the arbitrary anisotropy of the strength, elastic, and geometric parameters of these composites has been developed. The method is based on use of determinations of the first and second moments of the tensors of stresses in the components of composite materials.Translated from Problemy Prochnosti, No. 12, pp. 47–51, December, 1991.  相似文献   

10.
Abstract

Three-dimensional finite element analyses were carried out to study the deformation behaviour in ductile matrix-hard particle composite systems. Models with transversely aligned and staggered particle distributions were used. The deformation constraints in the models were investigated and the development of triaxial stress states in the models was studied. It was determined that the strengthening behaviour arises as a result of geometrical hardening in the early stage of composite deformation. Special deformation stages in the overall stress-strain behaviour of the composite microstructures such as initiation of microyielding, expansion of the plastically deformed region, and spread of plastic flow were determined by following the development of plasticity.  相似文献   

11.
Three distinct stages of kink band formation and propagation exist in ductile matrix composites subjected to compressive loading. These stages are called incipient kinking, transient kinking and kink band broadening. Each stage involves a different deformation mode. The mechanics governing each stage are discussed. Incipient kinking, where the peak load is attained, and kink band broadening, where the load attains a steady-state, are important in structural design. Two design philosophies are presented. References to pertinent literature are made throughout.  相似文献   

12.
An experimental study was carried out to find material parameters for making fiber reinforced cementitious composites (FRCC) more ductile. One of the dominant factors to control the ductility might be hidden in fracture property of matrix as well as the interface property between fiber and matrix. Therefore this study varied air content and water-binder ratio as the parameters to change the fracture property of matrix and experimentally examined their influence on the ductility of FRCC by three-point bend test with notched beams. As a result, it is concluded that fracture toughness of the matrix could be one of key parameters to control the ductility of FRCC. In case of a polyethylene fiber used in this study, the optimum value of the fracture toughness (critical strain energy release rate): GIC of the matrix was obtained to be 7.5-8.0 N/m.  相似文献   

13.
Finite element calculations are performed on models of particulate metal-matrix composites to study the applicability of a quadratic yield function and an associated flow rule. The matrix, here taken to be Al, is described by a J2 flow rule for an isotropic material and the reinforcing particles, either SiC or TiC, are taken to be elastic. Two different types of three-dimensional models of the composite are considered: (1) a simple cubic lattice of spherical particles and (2) random digital models that are approximately isotropic. Only in the second type of model can the existence of a flow rule be established. The validity of a flow rule in random models is associated with the absence of shear planes that extend throughout the solid without intercepting any particles. Such planes can be drawn in the simple cubic lattice for some shear deformations and particle volume fractions. Localized shear bands occurring on these planes results in a shear response essentially identical to that of the unreinforced matrix material, which precludes the determination of the shear response from the uniaxial deformation of the composite.  相似文献   

14.
为了探究石墨烯增强铝基复合材料的制备工艺及其热变形行为,本文采用湿混球磨结合真空热压烧结法制备了0.5wt.%石墨烯增强铝基复合材料,并利用场发射扫描电子显微镜、能谱仪和X射线衍射仪对其进行微观组织观察、成分和物相分析,用Gleeble 3800热模拟机对复合材料进行等温压缩试验,建立了材料的本构方程并分析其热变形机理...  相似文献   

15.
Two types of fracture toughness specimens, double cantilever beam and single-edge notch, were constructed from nickel wires in an epoxy resin matrix. The critical stress intensity factor to cause propagation of an unbridged matrix crack arrested at a wire was found to be greater than that for plain resin. Subsequent crack propagation could be described by taking account of the stress intensity factor due to known forces in the crack-bridging wires which subtracted from that due to the applied forces. The debonding and pull-out behaviour observed previously in single-wire specimens was confirmed in the multi-wire fracture toughness specimens.  相似文献   

16.
Institute of Strength Problems, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Problemy Prochnosti, No. 12, pp. 18–25, December, 1988.  相似文献   

17.
A computationally efficient multiscale–multiphysics model aimed at predicting mechanical response of thermoplastic composites subjected to different levels of moisture was developed. The mathematical model of the coupled moisture‐diffusion–mechanical‐deformation phenomenon was stated at the microscale, based on the observed experimental data, and then upscaled using a mathematical homogenization approach. A two‐way coupling between moisture diffusion and mechanical deformation was introduced by which diffusivity was enhanced by hydrostatic strain, whereas strength and stiffness were assumed to degrade because of moisture ingression, which also gives rise to swelling. The computational complexity of analyzing the two coupled physical processes at multiple scales was reduced via a model reduction scheme for multiple physical processes. The model was validated for 30% by weight filled glass fiber and carbon fiber reinforced thermoplastic composites. The moisture conditioning and uniaxial tension experiments were utilized to identify diffusion and mechanical properties at a fine scale. The identified properties were then used to validate the formulation in the three‐point bending test. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

18.
Synchrotron radiation diffraction during in situ tensile tests has been used to evaluate the internal elastic strains within the grains of magnesium alloy, AZ31, unreinforced and reinforced with 5 and 10% volume of SiC particles. Composites present initial thermal residual stresses, which are positive (tensile) in the matrix and negative (compressive) in the reinforcing particles. Internal elastic strains evolve in a similar behaviour in the unreinforced AZ31 and in both composites. However, the accumulated elastic strains are reduced in the case of the composite because a part of the applied load is borne by the ceramic particles.  相似文献   

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20.
The article reviews the possibilities, technical peculiarities, and advantages of the new experimental method of determining quantitatively the level of damage to ductile structural materials at the onset of macrofailure. The method is based on the analysis of the change of elastic properties of the ductile material in the zone of macrofailure at supercritical stages of loading (corresponding to the descending branch of the stress-strain diagram). On the example of the aluminum alloy AMtsS and steels St. 3, 08Kh18N10T the article analyzes the kinetics of damage cumulation at the stages of deformation preceding the onset of macrofailure, and the effect of stress raisers on the limit damage to the material at the instant of the onset of macrofailure. The article presents experimental data indicating that the limit damage of the tested materials is constant in the process of the self-similar growth (without change of micromechanisms) of the ductile macrocrack.Institute of the Strength of Materials, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Problemy Prochnosti, No. 9, pp. 14–18, September, 1989.  相似文献   

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