A theory for physically nonlinear elastic fiber-reinforced composites

A three-dimensional constitutive relationship for the fiber-reinforced composite with a nonlinearly elastic matrix material is derived. The composite is modeled by a medium consisting of thin nonlinear matrix layers alternating with effective linearly elastic fibrous layers. Shear wave propagations are investigated. The formation of shock wave, its stability and growth behaviors are discussed.     

Deformation behavior of aluminum alloy matrix composites reinforced with few-layer graphene

Microstructure and mechanical properties of aluminum alloy 2024 (Al2024)/few-layer graphene (FLG) composites produced by ball milling and hot rolling have been investigated. The presence of dispersed FLGs with high specific surface area significantly increases the strength of the composites. The composite containing 0.7 vol.% FLGs exhibits tensile strength of 700 MPa, two times higher than that of monolithic Al2024, and around 4% elongation to failure. During plastic deformation, restricted dislocation activities and the accumulated dislocation at between FLGs may contribute to strengthening of Al2024/FLG composites.     

Deformation parameters in single steel wire-copper matrix composites

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.     

Stability of plates from a granular composite with physically nonlinear inclusions and a damageable matrix

We present formulation and solution of the problem on the bifurcational stability of rectangular plates from granular composites with a damageable matrix and physically nonlinear inclusions. Translated from Problemy Prochnosti, No. 2, pp. 91–101, March–April, 2009.     

Deformation behaviour of elastomeric matrix composites under static loading conditions

Damage mechanisms of elastomeric matrix composites (EMCs), propose a complex interplay between material properties and service conditions. The occurrence of defects such as the cavitations in EMCs specimens in using conditions is an important problem. This situation requires the well understanding of the damage mechanisms of EMCs used in automotive and aeronautical fields.Elastomeric matrix composites subjected to static and fluctuating loads basically fail due to the initiation and growth of defects (cracks, cavities, etc.). In fact, high hydrostatic pressures influence mechanical behaviours of EMCs. This paper reviews the damage mechanism of EMCs under static loading. In order to evaluate mechanical properties and fracture behaviour of EMCs, in situ observations were made by using X-rays computed tomography (CT). Two types of specimens are investigated in this work; Natural rubber, NR vulcanised and reinforced by carbon black, and synthetic rubber (styrene-butadiene-rubber), SBR. A detailed study was carried out by scanning electron microscopy (SEM) for a better understanding the damage mechanisms and confirming the CT results.     

钨丝/铜合金复合材料高速撞击后的变形分析

为研究钨丝增强铜合金复合材料弹体撞击混凝土靶后的弹体变形,采用渗流铸造的方法将铜合金与钨丝相复合制备出钨丝增强铜合金复合材料,并用二级轻气炮来完成高速撞击试验,试验速度为2 km/s.撞击后对复合材料弹体宏观形貌进行了观察,发现弹体内部钨丝的排布发生了变化,呈现双曲线排布条纹.用数学和力学的方法对撞击后钨丝的排布方式变化进行了分析,发现钨丝排布的变化是由于钨丝束发生绕中心轴的扭转造成的,说明棒状弹体高速撞击混凝土靶时发生了扭转.     

Deformation and fracture properties of damage tolerant in-situ titanium matrix composites

This paper discusses the tensile response and fracture toughness of in-situ titanium alloy metal matrices discontinuously-reinforced with whiskers of titanium boride which were success-fully produced by ingot metallurgy techniques. Additions of elemental boron resulted in a near uniform dispersion of the rod-like titanium boride (TiB) reinforcements in the alloy matrix. Such composites have engendered considerable scientific and technological interest due to their attractive combinations of improved mechanical properties and low manufacturing cost. The improved elastic moduli of the composites are explained using shear lag and rule-of-mixtures theories. The increased strengths of the in-situ composites are rationalized by considering the combined effects of deformation restrains imposed by the stiff whiskers and strengthening contributions arising from the substructure that evolves from the presence of additional dislocations.     

Micromechanical analysis of nonlinear thermal deformation of filamentary metal matrix composites

A micromechanical model was developed to predict the thermomechanical deformation of unidirectional filamentary metal matrix composites. The composite is represented by two concentric cylinders, the inner one simulating the fiber and the outer one the matrix. Both elastic and elastic-plastic analyses were performed. In the model the fiber was assumed to be linear-elastic and the matrix a work-hardening elastoplastic material. The elastoplastic analysis was based on the deformation theory of plasticity in conjunction with the von Mises yield criterion. The matrix cylinder in the model was divided into a number (N) of concentric layers with each layer having different values of tangent modulus and Poisson's ratio depending on the amount of plastic deformation. An elastic analysis of a composite cylinder with (N+1) layers was then performed and served as a subroutine for a computer program.The computer program was applied to the study of thermal deformation in the longitudinal and transverse directions of a filamentary silicon carbide/aluminum composite subjected to thermal cycling up to 177°C (350°F). Longitudinal and transverse thermal strains were measured using strain gages. The critical temperature at which the strain-temperature curves become nonlinear was experimentally determined and predicted by the model. Above this critical temperature the longitudinal thermal expansion coefficient decreases while the transverse one increases. The complete three-dimensional state of stress in the fiber and the matrix was computed. It was determined that in addition to the longitudinal stresses high transverse stresses were also developed in the matrix. The experimental thermal strain curves verified the theoretical predictions.     

Deformation and fracture behaviour of flax fibre reinforced thermosetting polymer matrix composites

The mechanical properties of unidirectional flax fibre reinforced unsaturated polyester resin composites were studied with particular emphasis on their tensile deformation behaviour. These materials displayed characteristic non-linear behaviour when loaded parallel to the axis of the fibre, with a distinct knee preceding a drop in stiffness. Further deformation resulted in strain hardening behaviour. Load cycling and acoustic emissions analysis were used to investigate the nature of the knee and it was found that this corresponded with yielding behaviour in the composite. A well-defined yield point could be identified, which in composites of around 60% fibre volume fraction, occurred at a strain of some 0.12% and a tensile stress of 32 MPa. Varying the interfacial properties, through chemical modification of the fibre prior to lamination, was found to have a marked effect upon the onset of yielding and the yield point itself, as well as the deformation and fracture behaviour of the laminate. It is considered that this behaviour is intimately linked to the straining behaviour of the fibre as well as the fibre–matrix interaction and hypotheses to explain the observed behaviour are presented.     

Nonaxisymmetric deformation of physically nonlinear composite shells with phase interaction

The article suggests an algorithm for calculating the state of stress and strain of shells of revolution made of composite materials and subjected to a nonaxisymmetric load. The algorithm is based on the nonlinear correlation between stresses and strains. In the calculation of the physicomechanical characteristics of the composite the interaction between phases on the interface of the components is taken into account. On the example of the calculation of a conical shell the suggested approach is demonstrated.Translated from Problemy Prochnosti, No. 4, pp. 55–57, April, 1991.     

Design with metal matrix composites

Abstract

Applications for metal matrix composites (MMCs) have not emerged at the rate needed to justify the development costs. A reason for this may be that material developments have not been adequately linked to identified commercial needs. It is certainly true that some of the expectations raised about the potential offered by MMCs have been misguided. As the MMC business contracts, there is an ever greater need for a systematic method of linking material properties to the needs of engineering designers. This paper presents a methodology for evaluating materials in design, with the aim of linking MMCs to applications. The methodology has two main components: first, the use of performance indices and materials selection charts for specific design goals, to compare existing MMCs with competing materials; and secondly, the conceptual design of new MMC systems guided by those design goals. A selection of case studies illustrates that in mechanical applications the gains in using MMCs are frequently marginal, whereas in design for thermal management and vibration control, the materials can show very substantial improvements in performance. The methodology is general, and could be applied to other material systems.

MST/3094     

Deformation behavior of interpenetrating-phase composites

A simple, unit-cell model has been proposed to predict the deformation behavior of composites having two interpenetrating phases, continuous in three dimensions. By dividing the unit cell into several elements and using the isostress and isostrain bimaterial loading configurations, the composite deformation behavior has been constructed in terms of the behavior of its components. The formulation allows calculation of the deformation behavior of an interpenetrating-phase composite by a simplified numerical iteration. The estimates from this simplified model have been compared with experimental data on the stress/strain behavior of equi-volume Cd---Zn and Cu---Ag alloys and infiltrated Fe---Ag composites. A limited assessment of the present approach, in the light of the other methods of calculation such as finite-element and self-consistent methods, has been made.     

Design of ribbed shells subject to physically nonlinear deformation

The method of successive loadings is used together with special discontinuous functions to study the stress-strain state of ribbed shells subject to physically nonlinear deformation. In the solution of differential equations with variable and singular coefficients, the surface of the shell is divided into elements and the variable coefficients are averaged within each element. The solutions of the equations are constructed in the form of a combination of functions of regular and special discontinuous functions, which makes it possible to convey the irregular nature of the stress state and account for the physical nonlinearity of the material.Translated from Problemy Prochnosti, No. 4, pp. 91–98, April, 1996.     

Steady-state longitudinal vibrations of sectional,physically nonlinear plates

The artile deals with steady-state longitudinal vibrations of plates consisting of curvilinear rings placed one inside the other without interference, under the effect of a harmonic distorting load acting along the outer periphery. The rings are made from different isotropic materials that are physically nonlinear. The problem is solved by the method of successive approximations. In each approximation the sought functions are represented in the form of expansions with respect to a small parameter. Numerical investigations were carried out for plates consiting of two concentrically arranged circular rings.Translated from Problemy Prochnosti, No. 3, pp. 24–27, March, 1991.     

Deformation of laminated epoxy composites reinforced with high-strength fibers

We study the elastic deformation behavior of laminated epoxy composites reinforced with unidirectional carbon fibers and satin-woven glass fabric. The efficiency of various experimental procedures of determination of averaged elastic characteristics of laminates is analyzed. The effect of decreasing the test temperature to 77 K on the mechanical behavior of the above-mentioned materials is studied. The possibility of predicting stiffness and compliance parameters of unidirectional or satin-woven fabric composites is discussed. __________ Translated from Problemy Prochnosti, No. 1, pp. 41–57, January–February, 2006.     

Fracture criterion of composites with a ceramic matrix

Asymptotic averaging and certain hypotheses are used to determine the structure of the stress-intensity factors and propose a mechanical fracture criterion for microscopically uniform, isotropic, linearly elastic composites with a periodic macrostructure and residual stresses. Use of the criterion makes it possible to optimize the composition of the composite. A comparison of theoretical and experimental data shows that they agree well.Translated from Problemy Prochnosti, No. 10, pp. 30–40, October, 1993.     

On the problem of fracture mechanics of physically nonlinear materials

For the construction of fracture mechanics of physically nonlinear materials, we join two different approaches. One of the approaches is the method of successive approximations in a small parameter characterizing a negligible deviation from the Hooke law. A solution of the proper problem of the linear theory of elasticity is considered as the zero approximation. By using the second method, the singularity of stresses in the vicinity of a cracklike defect is established in the process of solution of the elastic problem. According to the second method, the material is regarded as incompressible, deviations from a linear rheological law are considerable, and the material in the vicinity of a defect and in the whole plate obeys various power dependences of small elastic strains on the corresponding stresses. The interrelations between stress intensity factors are introduced for the first time, which are also valid for their critical values. By specific examples, we demonstrate the effects of the parameters of physical nonlinearity of materials, value of the applied load, and type of strain. In conclusion, we give a short survey of the scientific literature on the solution of problems concerning elastoplastic hardening of cracked bodies in the case of antiplane strain and their use for rupture cracks. Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 35, No. 3, pp. 28–38, May–June, 1999.     

Cast metal matrix composites

Abstract

Metal matrix composites have been available in certain forms for at least two decades, e.g. boron fibre reinforced aluminium and various dispersed phase alloys and cermets. Recently, a range of alumina and silicon carbide fibres, whiskers, and particles with diameters <20 μm have become available. The possibilities of incorporating these materials into metals to improve stiffness, wear resistance, and elevated temperature strength without incurring weight penalties have attracted the attention of design engineers in the aerospace and automobile industries. The aim of the present paper is to outline the manufacturing processes for such composites, in particular those based upon liquid metal technology, e.g. squeeze casting and spray forming. Some of the mechanical and physical properties which have been determined for these materials are described. An analysis of how matrix alloy selection may influence tensile and fracture behaviour of short fibre and particle reinforced composites is attempted.

MST/770     

Glass-ceramic matrix composites with high oxidation embrittlement resistance

A new concept is introduced to minimize the oxidation embrittlement problem exhibited by Nicalon fibre-reinforced glass-ceramic matrix composites. A small amount of glass is added to the matrix and deforms at temperatures of interest to prevent microcrack formation. The graphitic interphase is thus shielded from an oxidative environment. The composites fabricated with the glass-doped matrices show excellent room- and elevated-temperature strengths and withstand high stresses at elevated temperatures in air for greater than 100 h without any deterioration in properties. The modulus of the glass-ceramic phase, the stiffness percentage of dopant glass and the process temperature were found to affect composite properties significantly.