Linear stress relations for a metal matrix composite sandwich beam with any core material

In this paper, it is shown that shear stresses are developed in the interface between the facing material and the core of a sandwich beam. The sandwich beam is composed of a core of any suitable material sandwiched between an upper unreinforced metal facing and a bottom facing made from metal matrix composite (MMC) material. The shear stress is shown to be a consequence of the differences in the core and facing elastic moduli. The magnitude of the shear stress increases as the core stiffness is made to diminish. The shear stress can exceed the bond strength between facing and core, resulting in delamination. Consequently, structural materials using this type of construction and particularly flexural experiments should contain a relatively stiff core. The magnitude of the facing stresses is shown to be relatively insensitive to the assumption or neglect of these shear stresses. In the worst case considered, neglecting the interfacial shear stresses results in an overestimation of the compressive and tensile stresses by less than 5%.     

Influence of SiC reinforcement on precipitation and hardening of a metal matrix composite

The influence of fibre reinforcement (10 vol % SiC fibres) on the precipitation and hardening behaviour of a metal matrix composite was studied using microhardness tests and transmission electron microscopy observations. It was shown that the hardening kinetics is enhanced by the SiC reinforcement due to the fact that precipitation preferentially develops on dislocation lines. Moreover, the high-temperature deformation strongly increases the precipitation rate as the material is reinforced.     

A new approach to the analysis of strength of a matrix composite with a high content of hard filler

A mathematical model of the formation and failure of a hard skeleton in sintered composites with a high content of high-melting filler is presented. On the basis of an analysis of joining particles in sintering the characteristics of the structure of composites (in particular, a connectivity and contiguity of skeleton) are determined. A mathematical model of skeleton failure which is based on the theories of percolation and reliability is developed. The influence of the characteristics of the composite structure on the strength of composite is studied.     

Direct measurements of non-linear stress-strain curves and elastic properties of metal matrix composite sandwich beams with any core material

A theory for measuring non-linear stress-strain curves and elastic properties of metal matrix composite (MMC) sandwich beams subjected to pure bending loads is discussed. The beam is made from any core material sandwiched between an upper facing of unreinforced metal and a lower facing of MMC with unidirectional fibre reinforcement or vice versa. The model developed shows that the determination of the position of the neutral axis is critical to the measurements discussed in this paper. The analysis removes the restriction of the effects of the core. With the aid of this model, we show that the position of the neutral axis can be determined directly from surface strain measurements. Measurements of neutral axis position lead directly to the determination of the beam elastic properties and, thus, directly obtained from surface strain measurements. It is shown that the model predicts longitudinal stresses and strains within any layer of the beam. The analysis includes the limiting case of a very weak core material. A consequence of this model is the determination of the MMC facing fibre volume fraction. A detailed error analysis predicts that the longitudinal elastic modulus of an MMC material facing can be obtained with an uncertainty between 4 and 6% if the surface strain measurements and beam dimensions can be obtained with an uncertainty of 1%. The volume fraction can be obtained within 10% uncertainty, although better methods are available for that measurement.     

On the behaviour of a particulate metal matrix composite subjected to cyclic temperature and constant stress

The paper describes a method of characterising the behaviour of an idealised particulate metal matrix composite composed of elastic particles and an elastic–perfectly plastic matrix subjected to constant macro stress and a cyclic temperature history. The computational method, the Linear Matching Method, was originally developed for structural life assessment studies, and allows a direct evaluation of the load ranges for which differing modes of behaviour occur in the steady cyclic state; shakedown, reverse plasticity and ratchetting. A simple homogenised model is considered, consisting of spherical particles embedded in a cubic matrix array. The resulting solutions are presented as non-dimensional equations derived from numerical solutions for two composites, alumina and silicon carbide particles embedded in an aluminium matrix.     

Stressed state of a matrix and an inclusion made from a twisted composite superconductor in cladding when a circular current interacts with a magnetic field

This paper discusses the stressed state of the matrix and a long wire made from a twisted multicore composite superconductor and encased in cladding when the circular component of the transport current interacts with a magnetic field. Pis’ma Zh. Tekh. Fiz. 24, 1–6 (January 26, 1998)     

Analytical study of photodegradation of inclusion complexes of nimodipine with alpha-, gamma-cyclodextrin, methyl-beta-cyclodextrin, and hydroxypropyl-beta-Cyclodextrin

The inclusion behavior of alpha-cyclodextrin (alpha-CD), gamma-cyclodextrin (gamma-CD), hydroxypropyl-beta-cyclodextrin (HP-betaCD), and methyl-beta-cyclodextrin (M-betaCD) with nimodipine (NM) in solution and in the solid state was investigated. Inclusion complexes of nimodipine with cyclodextrins (at a molar ratio of 1:1) in the solid state were obtained by the kneading method. Photochemical stability of NM in the solid inclusion complexes was assessed by IR spectrometry. The modified derivatives of beta-CD and alpha-CD were found to slow the photodegradation rate, whereas in the presence of gamma-CD the photodegradation of NM was a bit faster than in the corresponding physical mixture. Photochemical degradation of NM in liquid inclusion complexes was monitored by UV spectroscopy. According to the slowing effect on photodegradation of NM in the inclusion complexes, the studied cyclodextrins can be ordered as gamma-CD < alpha-CD < HP-betaCD < M-betaCD.     

Transverse properties of a Ti-6-4 matrix/SiC fibre-reinforced composite under monotonic and cyclic loading

The transverse response of a Ti-6-4/SM1140+ fibre-reinforced composite to both monotonic and cyclic loading has been investigated. Five distinct regions were found in the monotonic stress versus strain curve: (I) elastic deformation of the composite, (II) failure of the fibre/matrix interfaces, (III) elastic deformation of the remaining matrix ligaments, (IV) yielding of the matrix ligaments, and (V) gross plastic deformation, which ultimately leads to specimen failure. The stresses at which interface debonding, matrix yield and final failure occurred rose with increased displacement rate. Stressing to levels above the interface failure stress caused significant damage and limited (0.025%) plastic deformation. A non-linear stress-strain response was observed on unloading/reloading, because the presence within the specimen of constrained holes (containing debonded fibres) resulted in non-homogeneous elastic straining of the matrix. The transverse low-cycle fatigue lives of Ti-6-4/SM1140+composite specimens were strongly dependent on maximum stress for values up to the interfacial failure stress, but less so for maximum stresses greater than 260–265 MPa, where full fibre/matrix debonding had occurred. Fatigue life was also dependent on the uniformity of fibre spacings within the composite.     

Analytical beam theory for the in-plane deformation of a composite strip with in-plane curvature

The variational-asymptotic-method (VAM) provides a mathematically rigorous way to reduce a three-dimensional elasticity formulation to a one-dimensional beam theory without ad hoc assumptions. In this work, the VAM is employed to develop a beam theory to analyze the in-plane deformation of a laminated strip-beam with initial in-plane curvature. The cross-sectional stiffness constants and recovery relations for stress and strain are presented as analytical expressions. For the case of zero initial curvature, consistency of the expressions with those of plate theory is demonstrated. For strip-beams with initial curvature in the in-plane direction, results obtained show explicit dependence on the curvature. Results are verified by comparison with those obtained from VABS, the accuracy and consistency of which with three-dimensional finite elements has been reported in several published works. In addition to the internal consistency check this work provides and its utility in helping to validate VABS (which is based on the principles of VAM), it is hoped that the results obtained herein, since they are all analytical expressions, will help researchers and engineers validate the effect of initial curvature in their beam theories, whether existing or new.     

Mechanical behavior of a cellular composite under quasi-static, static, and cyclic compression loading

The quasi-static, static, and cyclic compressive behavior of a novel epoxy matrix cellular composite reinforced with glass foam granules is investigated. Three different grain-size fractions of the granules are used: 0.5–1, 1–2, and 2–4 mm. The density of the cellular composite varies between 0.65 and 0.82 g/cm3. The material exhibits high specific compressive strength and stiffness within the class of cellular materials; these properties can be varied using appropriate size of granules. The glass foam granules increase the stiffness of the cellular composite compared to neat epoxy foam with the same weight. The measured elastic properties are in good agreement with results obtained from analytical and numerical homogenization methods. The fatigue behavior is determined in static tests and in cyclic tests at 1 and 20 Hz on one type of cellular composite. The fatigue process for cyclic loading is a result of an interaction between static and cyclic damage. The sensitivity to static damage is found to be higher than to cyclic damage. The damage behavior is investigated by evaluation specimen’s stiffness and using scanning electron microscopy.     

Analytical study of heat and mass transfer in hardening concrete during heat treatment in a chamber with heat-emitting surfaces

The results of an experimental and analytical study of the heat treatment of concrete objects in chambers with heat-emitting surfaces are presented.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 28, No. 1, pp. 57–62, January, 1975.     

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.     

The shock response,simulation and microstructural determination of a model composite material

The capability to assess microstructural details in a polymer matrix composite is important in addressing composite design for engineering applications. The generation of three-dimensional microstructure using a non-invasive high-resolution experimental diagnostics method will advance our knowledge within this field. An inert composite has been studied, and both X-ray microtomography (XRT) for microstructural investigation in 3D and a parallel series of shock experiments (with associated modelling) have been conducted. The experimental aims of this study lay in several areas: firstly, to adequately define the bulk morphology; secondly, to determine the geometry of defects within the material; and finally, to demonstrate a direct linkage with the mechanical response determined by finite element analysis. This work is the first step in finding a way to non-invasively link 3D microstructural invesigation and numerical simulation to predict the shock performance of a composite material.     

Mechanical properties of a zircon matrix composite reinforced with silicon carbide whiskers and filaments

The influence of a silicon carbide whisker reinforcement on room temperature mechanical properties of a monolithic zircon ceramic and zircon composites uniaxially reinforced with silicon carbide monofilaments was studied in a flexure mode. The strength of a monolithic zircon was increased by the addition of whisker reinforcement, but the composite failure was still brittle in nature. In contrast, zircon composites reinforced with SiC whiskers and filaments showed toughened composite-like behaviour and produced higher first matrix cracking strength and toughness than the composites reinforced with only SiC filaments. In addition, the whisker reinforcement had insignificant influence on the ultimate strength of filament-reinforced composites. These results were related to changes in measured fibre-matrix interfacial properties, which indicated that composites with high first matrix cracking strength and toughness can be designed and fabricated via independently tailoring the matrix and the fibre-matrix interfacial properties.     

A viscous pressure bulge test for the determination of a plastic hardening curve and equibiaxial material data

The importance of an accurate material modeling for the accuracy and reliability of sheet forming simulations has become increasingly evident during the last years. More advanced material models have, however, to be supported by novel methods for material characterization. The recent eight parameter yield functions Yld2000-2d and BBC2003 demand, besides data from the ordinary uniaxial tensile tests, also equibiaxial data. In the present paper a Viscous Pressure Bulge (VPB) test is described. The test yields the equibiaxial stress point and r-value, as well as a plastic hardening curve for large values of plastic strain. The test setup is based on an ARGUSS? optical measuring system, and provides the desired result data in a very smooth and easy way. In order to verify the results from the current test, comparisons have been made with compression tests performed at Corus RD&T and hydraulic bulging tests performed at RWTH in Aachen. A discussion on how to determine the equibiaxial yield stress and how to transform the biaxial stress-strain curve to an effective stress-strain curve is included in the paper.     

The orientation of the Hertzian cone crack in soda-lime glass formed by oblique dynamic and quasi-static loading with a hard sphere

High speed photographic studies, made at a framing speed of 10⁶ frames per second, of the oblique impact of 2 mm diameter tungsten carbide spheres on blocks of soda-lime glass are described. The oblique impact causes sliding, which has a very marked influence on the orientation of the Hertzian cone crack with respect to the surface normal. An explanation of this effect is also provided. Similar observations are made from oblique quasi-static loading experiments.     

Prediction of the yield strength and shrinkage of a diamond-containing composite with a porous matrix under pressure

A theoretical model for the assessment of the yield strength of a granular composite material with a porous matrix has been developed. Parametric analysis of the model has been made; the effect of the loading type, porosity of the matrix material, and volume content of rigid inclusions on the macroscopic yield strength of the composite has been studied. An expression of the plasticity potential for a porous matrix composite, which provides a satisfactory agreement with the results of a numerical analysis of the model over the whole range of structural parameters variations, has been derived. The applicability of the developed approach to the investigation of making blanks of products from composite materials has been shown.