Stresses In Metal Matrix Composites Research Articles

An Overview of Techniques for Measuring Residual Stress in Metal Matrix Composites

Measurement of residual stress is significant to ensure safety, reliability and the life of composites, and currently has been a hot issue in scientific research. The fabrication processes such as machining, and heat treatment inherit either kind of residual stress which had either positive consequences or negative ones, for example, the fatigue limit of a component enhances by compressive stress, whereas corrosion resistance gets reduced by tensile stress. This study is aimed at a brief overview of the recent advancement in this field to help researchers in the in-depth study of measuring residual stress. It helps them in selecting the most appropriate techniques among destructive methods i.e., mainly Contour, ring core, deep hole-drilling method, and non-destructive techniques i.e., diffraction, ultrasonic method, depending on their requirements and applications. For each available technique, working methodology, physical limitations, and applications are discussed. At the end of this paper, future trends regarding an assessment of residual stress have been forecasted.

Multiscale modeling of macroscopic and microscopic residual stresses in metal matrix composites using 3D realistic digital microstructure models

This work presents a hierarchical multiscale method for predicting accurately and efficiently the macroscopic and microscopic residual stresses (RSes) in MMCs based on large-size realistic digital microstructure models. Effects of various conditions on the multiscale modeling are systematically studied. Results indicate that the hierarchical multiscale model shows both a good self-consistency and a good accuracy. Compared with the kinematic uniform boundary conditions, the static uniform boundary conditions lead to more accurate prediction of the thermal misfit RS. The size of the volume element has significant effects on the predicted values of the thermal misfit RS. The hierarchical multiscale model gains significant advantages over the hybrid-semiconcurrent one with respect to both computational efficiency and computer memory cost. The local fluctuation profiles and total variations of the total RS are dominated by those of the thermal misfit RS at the microscale and by those of the macroscopic RS at the macroscale, respectively.

Internal Stresses in Metal Matrix Composites in Relation with Matrix Phase Transformations

For metal matrix composites, internal stresses are a key factor for understanding the interactions between matrix and reinforcements and the mechanical properties of the composite. From in situ high energy X-ray diffraction on a steel matrix composite reinforced with TiC, the evolutions of the phase fractions and mean cell parameters of each phase during thermal treatment have been determined. In addition, a methodology is developed in order to get more information on the stress state evolutions in each phase during the treatment.

Analysis of transient mechanical loss due to thermal stresses in metal matrix composites

Mechanical spectroscopy has been used to study the thermal stress relaxation at the interfaces in magnesium matrix composites. The mechanical loss spectra measured as a function of temperature show an intrinsic component superimposed on transient damping. A model of thermal stress relaxation by dislocation motion controlled by a solid friction mechanism, where the transient damping depends non linearly on T ˙ / ω is developed. A systematic method is developed to identify the correct level of transient damping.

S102 Residual Stresses in Metal Matrix Composites for Heat Sink Applications During Thermal Cycling

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A Novel Method for Determining Interfacial Residual Stress in Fiberreinforced Composites

A method for measuring the residual stress at the interface in fiberreinforced composites is presented in this study. The residual strains (stresses) at the interface are released by pushing the fiber out. The released residual strains are measured using an electron moire technique, which can fabricate grids with frequencies up to 10,000 lines/mm on the composites surface so that a displacement sensitivity of 100nm can be achieved. This method can be applied to almost all fiber-reinforced composites, such as metal-matrix composites (MMCs) and fiberreinforced plastics (FRPs). It provides a new experimental technique for measuring interfacial residual stress in MMCs, and a unique method for FRPs. Measurements of the interfacial residual stresses in SiC/Ti-15-3 and boron/epoxy composites show the validity of the method.

Thermal Mismatch Dislocations in Macroscopic Graphite Particle-Reinforced Metal Matrix Composites Studied by Internal Friction

Thermal stresses in metal matrix composites (MMCs) can induce plastic deformation in the region close to the reinforcements. In this paper, commercially pure aluminium (Al)-based MMCs reinforced with 68 and 88% macroscopic graphite (Gr) particles were characterized by internal friction (IF) measurements. The macroscopic Gr particle size was of the order of a millimetre (0.8–1.2 mm). The MMC specimens were prepared by an air-pressure infiltration process. The IF, as well as the relative dynamic modulus, was measured using a multifunction internal friction apparatus at low frequencies of 0.5, 1.0, and 3.0 Hz over a temperature range of 20–400 °C with continuous heating. An IF peak is observed at about 260 °C in the IF–temperature spectrum; this phenomenon is absent in the corresponding unreinforced, commercially pure Al specimens. The position of the IF peak is essentially frequency independent and shifts towards higher temperature with increasing heating rate. The presence of dislocations in the MMCs is highlighted on the basis of transmission electron microscopy studies. In the light of IF measurements and microstructural studies, the IF peak is attributed to the generation and motion of dislocations produced by the difference in the coefficient of thermal expansion between the Al matrix and Gr reinforcement at matrix–particle interfaces. The objectives of this paper are to provide an overview of the sources of dislocation generation in the MMCs, and to provide an insight into the effects that dislocations have on the damping response of the MMCs.

The recent development of neutronic techniques for determination of residual stresses

Neutron diffraction is a well-established non-destructive method for the measurement of residual stress deep inside materials. This paper gives a short overview of the use of neutrons for materials research and measurement techniques. Neutron diffraction has been applied in determining residual stresses in metal matrix composites. Measurement and prediction of residual stress for plastic deformation are presented. More recently, the neutron diffraction technique has also been applied for the determination of plastic strain which results from microstructural defects and leads to peak broadening. Influence of the shot penning treatment on austenitic steel is presented.

Numerical aspects of finite element simulations of residual stresses in metal matrix composites

Numerical aspects of finite element simulations of residual stresses in metal matrix composites

Phase-stress partition and residual stress in metal matrix composites

Finite element (FE) modeling based on axisymmetrical cells was performed for relating the phase-stress partition and residual phase stress in metal matrix composites (MMCs) to the reinforcement volume fraction and shape, matrix hardening behavior and applied strain levels. The phase stress is defined as mean effective stresses in the constituent phases. The elastic, plastic phase-stress partition behavior during loading, and the resultant residual stress in matrix followed unloading are delineated. A set of formulas is given for predicting the value of the phase stress in each phase, and residual stress in matrix from the inclusion volume fraction and aspect ratio, as well as matrix hardening exponent and applied strain level.

Application of Moire Interferometry to the Analysis of Residual Stresses in Metal-Matrix Composites

Moire interferometry has been used to observe the in-situ displacement fields in B/Al CFMMC specimen heated to different temperature levels. It is shown that the method has potential application in measuring the in-situ residual strains developed during processing of metal-matrix composites. Being a whole field method, it is illustrated to be capable of identifying the regions of high strain gradients which may be present due to inherent manufacturing defects or may develop during testing.

Application of Moire Interferometry to the Analysis of Residual Stresses in Metal-Matrix Composites

Moire interferometry has been used to observe the in-situ displacement fields in B/Al CFMMC specimen heated to different temperature levels. It is shown that the method has potential application in measuring the in-situ residual strains developed during processing of metal-matrix composites. Being a whole field method, it is illustrated to be capable of identifying the regions of high strain gradients which may be present due to inherent manufacturing defects or may develop during testing.

Effect of Time-Dependent Matrix Behavior on the Evolution of Processing-Induced Residual Stresses in Metal Matrix Composites

The usefulness of load-relaxation experiments in investigating the need for rate-dependent matrix material models for predicting the processing-induced residual stresses in metal matrix composites (MMCs) is examined in this study. The experimental data is used in the selection of the appropriate constitutive equations for modeling the cooling process after composite consolidation. Boron/Al-2024 MMC is chosen as the model material system. Bodner-Partom unified model and a classical creep-plasticity model based on the relaxation experiments are used to represent the rate-dependent behavior of Al-2024. The results show that conventional B-P model based on purely monotonic strain-rate tests is not able to capture the inelastic strain variations under practical cooling conditions. The classical creep-plasticity model has been shown to be an effective alternative for this purpose as it considers load-relaxation data while deriving the material constants for the constitutive equations.

Thermal stresses in metal matrix composites studied by internal friction

Thermal stresses in metal matrix composites (MMC) can induce plastic deformation and damage accumulation in the region close to the reinforcements. In this connection, Al-4% Cu-based MMC reinforced with 10, 20 and 30% Al 2O 3 short fibres were characterized by internal friction (IF) measurements. As a function of the temperature, a maximum of damping has been observed in the composites at ca 150 K during cooling. This maximum is absent in the corresponding unreinforced AlCu alloy. The maximum is attributed to the generation and motion of dislocations produced by high thermal stresses at metal-fibre interfaces. The height of the maximum is found to be an index of the extent of relaxation of thermal stresses by the plastic deformation of the metal matrix. IF measurements have allowed us to identify whether plastic flow in the matrix or damage accumulation at matrix-fibre interfaces take place for different composites.

Characterization of mechanical stresses in metal matrix composites by internal friction

In MMC the matrix is exposed to plastic deformation and damage accumulation in the region close to the reinforcements, following mechanical or thermal stress. In this connection, Al—4% Cu based MMC reinforced with 10, 20 and 30% Al 2O 3 fibers were studied by internal friction ( IF) measurements. When mechanical stresses are relaxed by damage accumulation at interfaces, the IF measurements as a function of the vibration amplitude exhibit a peak P which has been connected with solid friction at metal—fiber interfaces and interface loosening. When, on the other hand, mechanical stresses at interfaces are relaxed by plastic deformation of the metal matrix, a saturation is observed in the vibration amplitude reached after three vibration cycles. On this basis, the IF measurements allowed us to characterize the relaxation of mechanical stresses at matrix—fiber interfaces in different composites.

Detection of Internal Stresses in Metal Matrix Composites by Stress Relaxation Measurements

Detection of Internal Stresses in Metal Matrix Composites by Stress Relaxation Measurements

Thermal residual stresses in metal matrix composites: A review

Recently, metal matrix composites (MMCs) have generated a considerable interest in the materials field because of their attractive physical and mechanical properties. However, during the fabrication of MMCs, thermal residual stresses are reportedly developed in the matrix as a result of the mismatch of the thermal expansion coefficients between the reinforcement and the matrix. It is well established that these residual stresses have a significant effect on the composite properties. For example, due to the presence of thermal residual stresses, it is almost never possible to achieve the maximum elastic response of the composites. In addition, yield stress and fracture toughness of the composites are significantly affected by thermal residual stresses. In this paper, a critical review of the published literature on thermal residual stresses in MMCs and their effect on composite properties are presented. Also, experimental and numerical techniques that are currently available to measure and estimate thermal residual stresses are reviewed and discussed.

Measurement of Residual Stresses in Metal Matrix Composites

Metal matrix composites (MMC) are expected to develop internal residual stresses on cooling from fabrication due to the large thermal expansion mismatch between reinforcing fibers and the matrix. This work was undertaken to measure experimentally these residual stresses and compare them with analytical calculations in order to establish clearly their levels and dependence on material parameters. Two techniques for residual stress measurement were investigated: (1) X-ray diffraction (sin2-psi method) and (2) neutron diffraction. Both techniques gave results in good agreement with analytical predictions for several systems (SCS-6/Ti-24Al-11Nb, W/NiAl, and Al2O3NiAl). The results obtained showed a dependence of residual stresses on thermal expansion coefficients, elastic moduli, volume fraction fibers, and matrix yield strengths. The fibers showed compressive stress states, and the matrix, tension. Average stresses were higher in the fiber direction than transverse to fibers.

Residual stress optimization in metal-matrix composites using discretely graded interfaces

Thermally induced residual stresses in metal-matrix composites can be large enought to yield, and in some cases fail, the matrix material immediately surrounding the fiber. The focus of this research is to evaluate the effect of interfacial layers between the fiber and matrix on these residual stresses and, more specifically, to determine the optimum design of such discrete interfacial layers in order to reduce the damaging levels of residual stress. One outgrowth of this investigation is the development of a software package that can determine the optimum design of a fiber/interfacial layer/matrix model for a variety of user-specified conditions (parameters). The optimization algorithm adopted in this procedure utilizes the method of feasible directions and accepts any combination of design variables, constraints and objective functions. The analysis model consists of a generalized plane-strain concentric cylinder assemblage that can handle both elastic and elasto-plastic analysis. An arbitrary number of cylinders can be included in the model, each with independent material properties. The inelastic analysis is performed using the method of successive elastic solutions. As an example, the circumferential stress distribution corresponding to a −1425°F drop in temperature for a SiC Ti-24A1-11Nb system is evaluated. Through optimization, it is possible to identify the coefficient of thermal expansion (CTE) of the interfacial layer which will minimize the matrix circumferential stress, while keeping the circumferential stress in the interfacial layer less than, say, 650.0 ksi. Utilizing this optimization algorithm, an interfacial layer having a CTE of 2.8 times that of the matrix is found to reduce the critical matrix stress from 46.7 to 23.2 ksi, while satisfying the prescribed interfacial layer stress constraint.

Stress dependence of the raman frequencies for carbon fibers and residual stresses in metal matrix composites

A technique is described for determining residual stresses in metal matrix composites using Raman spectroscopy. It is based on the measurement of Raman frequency shifts for both carbon fibers under applied uniaxial stress and fibers in the metal matrix composites. The deformation of fibers was achieved using a tensile rig to obtain the calibration curve. A selective area electropolishing method was utilized to locally expose the constrained fibers in the metal matrix composites so that Raman measurement can be performed. It has been demonstrated that Raman microprobe can be used to determine the residual stresses in the Raman-active fiber reinforced MMC's. The ability of this new residual stress measurement method to measure the localized stress in an individual fiber offers us a useful tool to explore the fiber/matrix interface and to understand the behavior of these important material. Extensive experimental measurements are still required to define the sensitivity and applicability of this approach.