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The paper analyzes new publications on the brittle fracture mechanics of prestressed materials. It is found out that new scientific results published in the International Journal of Solids and Structures in 2002 are a particular case of the results obtained at the Institute of Mechanics 20 years ago [ABSTRACT FROM AUTHOR]

Material parameter identification using constitutive models of elasticity, viscoelasticity, rateindependent plasticity and viscoplasticity has a long history with regard to homogeneous and inhomogeneous deformations. For example, uniaxial tensile tests, pure shear tests, torsion experiments of thin-walled tubes or biaxial tensile tests are used to obtain the material parameters by solving the inverse problem. Frequently, the parameters are determined by numerical optimization tools. In this paper, we investigate some very basic single- and two-layered examples regarding identifiability, because these tests are the basis for more complex geometrical and physical nonlinear problems. These simple examples are the uniaxial tensile/compression case, biaxial tensile tests of a cruciform specimen, torsion of a thin-walled tube, a thick-walled tube under internal pressure and the indentation test. For the thick-walled tube under internal and external pressure with an axial pre-strain with several layers, an analytical solution is provided directly suitable for programming. The aim is to get an understanding whether some problems lead to non-identifiable parameters. [ABSTRACT FROM AUTHOR]

Various formulations of the problem of stability of uniaxial tension of a band under superplastic strains are analyzed. A more general formulation (as compared to those available ) is proposed; criteria of stability are obtained. Various methods of describing the behavior of materials in the superplasticity regime are considered. [ABSTRACT FROM AUTHOR]

Abstract  This paper presents an infrared image processing procedure that was developed to study calorific effects accompanying material fatigue. This method enables us to separately estimate patterns of thermoelastic and dissipative sources. Heat sources were estimated on the basis of partial derivative operators present in a local form of the heat equation by using a set of approximation functions that locally fits the temperature field and takes the spectral properties of the sought sources into account. Numerical examples were used to check the validity of the method and to highlight its capabilities along with its limits. The paper concludes with examples of thermal image processing extracted from fatigue tests performed on a dual-phase steel. The coupling sources were compared to the theoretical predictions induced by a basic thermoelastic model, while the heterogeneous character of the fatigue development was highlighted in terms of dissipation sources. [ABSTRACT FROM AUTHOR]

We study thermally induced vibrations of laminated plates with attached or embedded piezoelectric layers. A model governing the bending motion under changing thermal environments is developed. The modeling is based on the kinematic assumption of Kirchhoff; consistently, the thickness distribution of the electric potential is considered being of second order. The electric potential distribution is found as a function of mechanical strain and temperature distribution; mechanical strain accounting for the direct piezoelectric effect and temperature entering via the pyroelectric effect. The plate theory incorporates the direct piezoelectric effect by means of effective plate stiffness and the pyroelectric effect by means of effective thermal loading. The theory is capable to model piezoelectric layers with the electrodes left open by using nonlocal constitutive relations. Moreover, nonlocal terms enter the effective thermal loading. These nonlocal relations introduce a new aspect into thin plate theory. [ABSTRACT FROM AUTHOR]

This paper concerns the flow of an incompressible, viscous fluid past a porous spherical particle enclosing a solid core, using particle-in-cell method. The Brinkman's equation in the porous region and the Stokes equation for clear fluid are used. At the fluid-porous interface, the stress jump boundary condition for the tangential stresses along with continuity of normal stress and velocity components are employed. No-slip and impenetrability boundary conditions on the solid spherical core have been used. The hydrodynamic drag force experienced by a porous spherical particle enclosing a solid core and permeability of membrane built up by solid particles with a porous shell are evaluated. It is found that the hydrodynamic drag force and dimensionless hydrodynamic permeability depends not only on the porous shell thickness, particle volume fraction γ and viscosities of porous and fluid medium, but also on the stress jump coefficient. Four known boundary conditions on the hypothetical surface are considered and compared: Happel's, Kuwabara's, Kvashnin's and Cunningham's (Mehta-Morse's condition). Some previous results for the hydrodynamic drag force and dimensionless hydrodynamic permeability have been verified. [ABSTRACT FROM AUTHOR]

The solution space of many systems of ordinary differential (OD) or partial differential (PD) equations in engineering or mathematical physics 'can/cannot' be parameterized by a certain number of arbitrary functions behaving like potentials. Among the well-known OD examples, we recall that a classical control system is parametrizable if and only if it is controllable. One interesting PD case is concerned with continuum mechanics where the first-order stress equations admit a rather simple second-order parametrization by means of the single Airy function in dimension 2. The purpose of this paper is to apply the new techniques of 'Algebraic Analysis', a mixture of differential geometry and homological algebra, in order to give a positive and explicit answer concerning the possibility to obtain a first-order parametrization of the stress/couple-stress equations met in the study of Cosserat media. At the same time, as a corollary of the homological test involved, we shall give for the first time the reason for which the compatibility conditions (CC) for the deformation tensor in classical elasticity theory are 'second order' while the corresponding CC for the Cosserat fields are only 'first order' and explain why this order is equal to the order of the corresponding parametrization. Finally, a close link existing between Cosserat elasticity and Weyl electromagnetism is also provided within a conformal framework. [ABSTRACT FROM AUTHOR]

This paper presents the results of new microtensile tests conducted to investigate the mechanical properties of submicron-thick freestanding copper films. The method, used in this study, allows the observation of materials response under uniaxial tensile loads with measurements of stress at strain rates up to 5.5 × 10−4/s. It also facilitates tension–tension fatigue experiments under a variety of mean stress conditions at cyclic loading frequencies to 20 Hz. The sample processes involve fabrication of a supporting frame with springs and alignment beams all made of electroplated nickel. Electroplating took place on top of a previously deposited sample rather than creating a structure by subtractive fabrication. Tensile sample loading is applied using a piezoelectric actuator. Load was measured using a capacitance gap sensor with a novel mechanical coupling to the sample. Tension–tension fatigue experiments were carried out with feedback to give load control. Fatigue tests were conducted on sputter-deposited 500 and 900 nm copper films with grain sizes ∼50 nm. Fatigue life reached 105 cycles at low mean load, which decreased with an increase in the mean load. The results indicate decreasing plasticity with increasing mean load. [ABSTRACT FROM AUTHOR]

This paper presents a critical review of literature on fracture analysis of concrete structural components. Review includes various fracture models, tension softening models, methodologies for crack growth analysis and remaining life prediction. The widely used fracture models which are based on fictitious crack approach and effective elastic crack approach have been explained. Various tension softening models such as linear, bi-linear, tri-linear, etc. have been presented with appropriate expressions. From the critical review of models, it has been observed that some of the models have complex expressions involving many parameters. There is a need to develop some more generalised models. Studies have been conducted on crack growth analysis and remaining life prediction using linear elastic fracture mechanics (LEFM) principles. From the studies, it has been observed that there is significant difference between predicted and experimental observations. The difference in the values is attributed to not considering the tension softening effect in the analysis. [ABSTRACT FROM AUTHOR]

The castings produced by the evaporative pattern casting (EPC) process have blow holes. The blow holes in EPC castings are because of the non-escape of the gas produced as a result of burning of polystyrene pattern in the sand mold. To overcome the problem of blow holes, the EPC process is combined with the vacuum (V)- process. The vacuum applied to EPC mold draws the decomposed gases and improves the casting quality produced by the EPC process. The developed hybrid process has been termed as the vacuum assisted evaporative pattern casting (VAEPC) process. The objective of this paper to investigates the effect of process parameters, i.e, degree of vacuum, pouring temperature, grainfineness number, amplitude of vibration and time of vibration on the impact strength of Al-7% Si alloy castings in VAEPC process. In order to evaluate the effect of selected process parameters, the response surface methodology (RSM) is used to formulate a mathematical model which correlates the independent process parameters with the desired impact strength. The central composite rotatable design has been used to conduct the experiments. The results indicate that the impact strength decreases with increases in the grainfineness number and pouring temperature. Whereas, it has an inverse relationship with amplitude of vibration, time of vibration and degree of vacuum. The best value of impact strength (2.34 N/mm2) has been obtained at 400 mm Hg degree of vacuum imposed, 650°C as pouring temperature, 60 as sand grainfineness number, 460 μm as amplitude of vibration, and 70 s as time of vibration. [ABSTRACT FROM AUTHOR]

From the decomposition theorem of elastic beams, two classes of exact stress states are investigated for the equations of three dimensional elasticity governing elastic beams in bending deformations with free faces. One of these is the analogue of the Levy solution for elastic plates and is designated as the interior state. The other complementary class corresponds to a decaying state and is designated as the Papkovich-Fadle state. The appropriate boundary conditions have been established recently for the prescribed data at the end edge of beams to induce only an exponentially decaying elastostatic state. The present paper describes how these conditions may be used to determine the boundary conditions of these two states. The decomposition theorem of beams effectively allows us to split the prescribed edge-data correctly into two parts, one for the interior solution components and the other for the decaying solution components. An analytical solution of the decaying state is formulated to verify the validity of our boundary conditions. The results in turn show that the necessary conditions for the Papkovich-Fadle state are also sufficient conditions. The boundary conditions obtained for the interior state show that the interior solution determined by these conditions is the correct solution in the beam interior up to exponentially small terms. Moreover, with the separate consideration of the interior and decaying solution components, a relatively simple analytical solution is often practical and desirable, and the numerical computation process is essentially simplified. As an illustrative example, the present results are applied to the end-loaded cantilever beam. [ABSTRACT FROM AUTHOR]

This paper studies the stress and displacement distributions of continuously varying thickness beams with one end clamped and the other end simply supported under static loads. By introducing the unit pulse functions and Dirac functions, the clamped edge can be made equivalent to the simply supported one by adding the unknown horizontal reactions. According to the governing equations of the plane stress problem, the general expressions of displacements, which satisfy the governing differential equations and the boundary conditions at two ends of the beam, can be deduced. The unknown coefficients in the general expressions are then determined by using Fourier sinusoidal series expansion along the upper and lower boundaries of the beams and using the condition of zero displacements at the clamped edge. The solution obtained has excellent convergence properties. Comparing the numerical results to those obtained from the commercial software ANSYS, excellent accuracy of the present method is demonstrated. [ABSTRACT FROM AUTHOR]

In this paper we present a mixed stabilized finite element formulation that does not lock and also does not exhibit unphysical oscillations near the incompressible limit. The new mixed formulation is based on a multiscale variational principle and is presented in two different forms. In the first form the displacement field is decomposed into two scales, coarse-scale and fine-scale, and the fine-scale variables are eliminated at the element level by the static condensation technique. The second form is obtained by simplifying the first form, and eliminating the fine-scale variables analytically yet retaining their effect that results with additional (stabilization) terms. We also derive, in a consistent manner, an expression for the stabilization parameter. This derivation also proves the equivalence between the classical mixed formulation with bubbles and the Galerkin least-squares type formulations for the equations of linear elasticity. We also compare the performance of this new mixed stabilized formulation with other popular finite element formulations by performing numerical simulations on three well known test problems. [ABSTRACT FROM AUTHOR]

This paper compares the efficiency of multibody system (MBS) dynamic simulation codes that rely on different implementations of linear algebra operations. The dynamics of an N-loop four-bar mechanism has been solved with an index-3 augmented Lagrangian formulation combined with the trapezoidal rule as numerical integrator. Different implementations for this method, both dense and sparse, have been developed, using a number of linear algebra software libraries (including sparse linear equation solvers) and optimized sparse matrix computation strategies. Numerical experiments have been performed in order to measure their performance, as a function of problem size and matrix filling. Results show that optimal implementations can increase the simulation efficiency in a factor of 2–3, compared with our starting classical implementations, and in some topics they disagree with widespread beliefs in MBS dynamics. Finally, advices are provided to select the implementation which delivers the best performance for a certain MBS dynamic simulation. [ABSTRACT FROM AUTHOR]

The Performance Efficiency of a Material (MPE) in a given engineering component is taken as the sum total of the performance indices of the material for various required properties and mandates of design. The performance index for a property is defined as the product of the weight (W) of the property among all the requirements (weight being distributed out of 100 total points among all of the required properties and factors) and satisfaction index (SI), a parameter ≤1.0 that defines how efficiently the property of the material satisfies the requirement imposed by design. New methods are given in this paper for estimating the weights and SIs of the various required properties and evaluating the MPE for a chosen material in an engineering application. The method is illustrated considering the steel in use in a low-pressure steam turbine rotor and its possible replacement with a lighter-titanium alloy. [ABSTRACT FROM AUTHOR]

Abstract  Dynamic failure events such as armor penetration and explosive fragmentation are too complex to be treated by classical single-crack continuum fracture mechanics. In such cases deformation and fracture result from multiple cracks, voids, and shear bands acting simultaneously and influencing one another’s evolution. An alternative “meso” fracture mechanics is needed that treats microfailure activity while permitting fast and inexpensive predictive computations. This paper discusses the approach and experiments that elucidate and quantify failure physics on the micron level. “Rosetta Stone” experiments that isolate a damage mode, produce statistical distributions of damage features, and “freeze in” damage at various stages of development are described and illustrated. The observations and data lead to equations describing nucleation and growth of cracks, voids, and shear bands. The resulting mesomechanical material failure models link the microworld with the macroworld and can be used in continuum hydrocodes for fast, efficient simulations of dynamic fracture scenarios. [ABSTRACT FROM AUTHOR]

This paper introduces a novel method for the quality evaluation of resistance spot welds. The evaluation is based on computer vision methods, which allow non-destructive on-line real-time processing. The input of the system is the image of a weld imprint on a metal band which covers the electrodes against wear and soiling. The shape and size of the structures within the imprint correlate with the nugget area and, therefore, allow an accurate estimation of the quality of the spot weld. The system segments the electrode imprint and computes the nugget area from the minimum and maximum axis of a fitted ellipse. This method does not need training samples to perform reliable quality estimation. Additionally, the used algorithms are easy to implement and efficient, which guarantees real-time ability. Since there is only a single low-cost camera needed, the hardware can be placed directly on the gun arm, which makes a fast evaluation possible. [ABSTRACT FROM AUTHOR]

It is of great interest for economical and security reasons to understand the compressive properties of underground cemented paste backfill. In this paper, the stress–strain behaviours of cemented paste backfill (CPB) subjected to uniaxial compression and conventional triaxial tests are presented and discussed. The effect of CPB basic components, strength, ageing and confining pressure on the deformation behaviour of CPB are evaluated and discussed. The results show that the stress–strain behaviour of CPB is strongly influenced by the confinement, the age and strength of CPB, and its components. The increase in confining pressure leads to a change in the mode of failure, in the stiffness, and an increase in the strength. [ABSTRACT FROM AUTHOR]

The paper presents experimental results on the deformation, local buckling, and fracture of D16AT plates with two parallel edge cracks under tension. The distribution of strains and deflections over typical cross-sections and buckling modes are determined. The influence of the crack length and the distance between the cracks on the local buckling stresses and breaking stresses is studied. The effect of local buckling on the strength of the plate is evaluated [ABSTRACT FROM AUTHOR]

The paper is concerned with the determination of edge effect zone in a laminated composite with laminas subject to longitudinal compression. The dependence of the maximum decay length on the ratio between the period of external loading and the structure parameter is studied. The load period depends on the number of unloaded laminas. The decay of the edge effect is analyzed by numerically solving a boundary-value problem of elasticity for piecewise-homogeneous materials and using a quantitative decay criterion for the near-edge normal stresses [ABSTRACT FROM AUTHOR]

Polymer nanocomposites are particle-filled polymers in which at least one dimension of the dispersed particles is in the nanometer range. Dispersing nanosize particles in a polymer matrix induces superior mechanical properties compared to traditional macro fillers. Nanolevel reinforcement also affects the tribological properties and needs to be clearly understood before using in practical applications. Friction and wear characteristics of Nylon 6 nanocomposites under dry sliding conditions are reported in this paper. Nylon 6 with 5% organoclay was prepared by melt intercalation technique. The tensile behaviour is evaluated according to ASTM standards. A pin-on-disc type tribometer is used for evaluating the friction and wear behaviour. It is found that the Nylon 6 nanocomposites have superior tribological properties than unfilled polymer. Formation of uniform tenacious transfer layer by Nylon 6 nanocomposite on the counterface contributes to the reduction in coefficient of friction and specific wear rate. Nylon Nancomposites exhibited high wear resistance compared with the neat Nylon. [ABSTRACT FROM AUTHOR]

The paper reports on the results from analysis of some nonclassical fracture problems that allow for stresses along cracks. The results have been obtained by the author and his collaborators at the Institute of Mechanics (Kiev) since 1980 [ABSTRACT FROM AUTHOR]

The propagation behavior of Love waves in a piezoelectric layered structure with inhomogeneous initial stress is studied. Solutions of the mechanical displacement and electrical potential function are obtained for the isotropic elastic layer and transversely isotropic piezoelectric substrate, respectively, by solving the coupled electromechanical field equations. Firstly, effects of the inhomogeneous initial stress on the dispersion relations and phase velocity of Love wave propagation are discussed. Then the influence of the initial stress gradient coefficient on the stress, mechanical displacement and electrical potential distribution in the layer and the substrate is investigated in detail. The results reported in this paper are not only meaningful for the design of surface acoustic wave (SAW) devices with high performance, but also effective for evaluating the residual stress distribution in the layered structures. [ABSTRACT FROM AUTHOR]

In this paper, the simultaneous identification of the Poisson ratio, the shear modulus and a circular cavity embedded in an isotropic linear elastic material from boundary measurements is investigated. The numerical method proposed is based on the least-squares minimisation of the errors between the measured and the calculated tractions on the outer boundary using the boundary element method (BEM). [ABSTRACT FROM AUTHOR]

This paper describes a numerical approach to the optimization of effective properties of periodic perforations in an infinite body, in the frameworks of heat conduction and of linear elasticity. We implement a special finite element mesh in order to deal with the periodic nature of the problem. We compute the gradient of the functional to be minimized. We describe the process of mesh deformation and mesh regeneration. We give several numerical examples, some of them having practical relevance. [ABSTRACT FROM AUTHOR]

The strength of materials at high strain levels has been determined using the so-called Continuous-Bending-under-Tension (CBT) test. This is a modified tensile test where the specimen is subjected to repetitive bending at the same time. This test enables to create high levels of uniform strain. A wide variety of materials has been tested this way. The strength of the material after CBT testing has been measured in different ways: by secondary tensile tests, by interrupted CBT tests, and directly from the fracture in the CBT test. All methods yield similar results: the strength is largely unaffected by the cyclic pre-deformation and mainly depends on the overall increase in length. Only for multi-phase materials the strength shows a minor influence of CBT test conditions. The hardening follows the extrapolated hardening observed in a conventional tensile test, except for brass. This test method can potentially be used for measuring hardening curves at high strain levels. [ABSTRACT FROM AUTHOR]

n energy dissipation rate concept is employed in conjunction with the J-integral to calculate crack growth resistance of elastic-plastic fracture. Different from Rice's J-integral, the free energy density is employed in place of the stress working density to define an energy-momentum tensor, which yields that the slightly changed J-integral is path dependent regardless of incremental plasticity and deformational plasticity. The J-integral over the remote contour is split into the plastic influence term and the J-integral over the fracture process zone which is an appropriate estimate of the separation work of fracture. Finite element simulations are carried out to predict the plane strain mode I crack growth behavior by an embedded fracture process zone. It can be concluded that J-integral characterization is in essence a stress intensity-based fracture resistance similar to the K criterion of linear elastic fracture, and energy dissipation rate fracture resistance can be taken as an extension of the Griffith criterion to the elastic-plastic fracture. [ABSTRACT FROM AUTHOR]

The asymptotic problem of a semi-infinite interface crack between dissimilar electrostrictive materials that are subjected to electric loading is numerically analyzed by using the finite element method. Numerical results of electric displacement fields are obtained on the basis of the mathematical equivalence of the mode III problem and an electrostatic problem. The shape and the size of saturation zones are explored as a function of the ratio of the saturated electric displacements of dissimilar electrostrictive materials. In contrast with conventional wisdom, the ratio of the permittivities is shown to exert a negligibly small influence on electric displacement fields. For various combinations of the material properties of dissimilar electrostrictive materials, stress fields and stress intensity factors are systemically calculated by using the numerical results of electric displacement fields. The effects of the electric, elastic, and electrostrictive properties on stress intensity factors are demonstrated. [ABSTRACT FROM AUTHOR]

This research is concerned with the fracture mechanics of a laminated composite medium, which contains a central layer sandwiched by two outer layers. There is a periodic array of cracks in the central layer along the central axis of the medium. Fourier transform is used to reduce the problem to the solution of a system of dual integral equations, which are solved by the singular integral equation technique. Rigorous fracture mechanics analysis, which exactly satisfies all boundary conditions of the problem, is conducted. Numerical solutions for the crack tip field and the stress in the medium are obtained for various values such as crack length, crack spacing and layer thickness. Results are also given for the reduction of the equivalent Young’s modulus of the laminate due to multiple cracking. The cases of axial extension and residual temperature change of the composite medium are accounted for. [ABSTRACT FROM AUTHOR]

The time-harmonic dynamical stress field in a system comprising a pre-stressed orthotropic layer and orthotropic half-plane is studied within the scope of the piecewise homogeneous body model utilizing the three-dimensional linearized theory of elastic waves in an initially stressed body. The main focus is on the influence of the mechanical properties of the constituent materials and the initial stresses present on the “resonance” values of the normal stress acting on the interface plane and on the “resonance” values of the frequency of the external point-located force. The numerical results are presented and discussed. In particular, it is shown that the values of the normal stress decrease with a decrease in the modulus of elasticity of the materials along the thickness of the covering layer. [ABSTRACT FROM AUTHOR]

A new microscale uniaxial tension experimental method was developed to investigate the strain rate dependent mechanical behavior of freestanding metallic thin films for MEMS. The method allows for highly repeatable mechanical testing of thin films for over eight orders of magnitude of strain rate. Its repeatability stems from the direct and full-field displacement measurements obtained from optical images with at least 25 nm displacement resolution. The method is demonstrated with micron-scale, 400-nm thick, freestanding nanocrystalline Pt specimens, with 25 nm grain size. The experiments were conducted in situ under an optical microscope, equipped with a digital high-speed camera, in the nominal strain rate range 10−6–101 s−1. Full field displacements were computed by digital image correlation using a random speckle pattern generated onto the freestanding specimens. The elastic modulus of Pt, E = 182 ± 8 GPa, derived from uniaxial stress vs. strain curves, was independent of strain rate, while its Poisson’s ratio was v = 0.41 ± 0.01. Although the nanocrystalline Pt films had the elastic properties of bulk Pt, their inelastic property values were much higher than bulk and were rate-sensitive over the range of loading rates. For example, the elastic limit increased by more than 110% with increasing strain rate, and was 2–5 times higher than bulk Pt reaching 1.37 GPa at 101 s−1. [ABSTRACT FROM AUTHOR]

We will solve a fracture-mechanics problem for an elastic material with cracks subject to a polyharmonic load created by longitudinal waves with different wavelengths propagating through the material. The frictionless contact between the edges of a finite-length plane crack under the action of two normal harmonic tension/compression waves with different frequencies is studied. The forces of contact interaction and displacement discontinuity are analyzed. The effect of the wave frequency on the stress intensity factor is examined for different normalized wave numbers. [ABSTRACT FROM AUTHOR]

We consider the problem of determining the stability boundary of an elastic rod clamped at both ends and loaded by a compressive force and a couple. The constitutive equations of the rod are such that both shear of the cross section and compressibility of the rod axis are considered. The stability boundary is given by the bifurcation points of a system of eight nonlinear first-order differential equations, obtained by using the first integrals. Depending on the parameter values the type of bifurcation is determined. The post-critical shape of the rod is obtained by the numerical integration of a system of 12 nonlinear first-order differential equations. [ABSTRACT FROM AUTHOR]

Failure during sheared edge stretching of sheet steels is a serious concern, especially in advanced high-strength steel (AHSS) grades. The shearing process produces a shear face and a zone of deformation behind the shear face, which is the shear-affected zone (SAZ). A failure during sheared edge stretching depends on prior deformation in the sheet, the shearing process, and the subsequent strain path in the SAZ during stretching. Data from laboratory hole expansion tests and hole extrusion tests for multiple lots of fourteen grades of steel were analyzed. The forming limit curve (FLC), regression equations, measurement uncertainty calculations, and difference calculations were used in the analyses. From these analyses, an assessment of the primary factors that contribute to the fracture during sheared edge stretching was made. It was found that the forming limit strain with consideration of strain path in the SAZ is a major factor that contributes to the failure of a sheared edge during stretching. Although metallurgical factors are important, they appear to play a somewhat lesser role. [ABSTRACT FROM AUTHOR]

Abstract  Three fixtures for conducting laboratory fretting fatigue tests are described and their respective testing methods and the results of the analysis are compared. Each of these fixtures has been used to investigate the effects of various parameters of interest in fretting fatigue. These fixtures include a unique apparatus in which all load applied to the specimen is transferred to the fretting pads, an apparatus similar to many found in the literature where partial load transfer occurs across the pads, and a simplified dovetail fixture in which the clamping load, P, and the shear load, Q, are varied in phase. Select test conditions from prior experiments performed on identical material and resulting in similar lives ranging from one to ten million cycles from these fixtures are identified. The various testing conditions were used to compute the unique stress field for each case. The resulting contact stresses were used to calculate crack initiation based criteria, and to calculate stress intensity factors. The three fixtures were shown to be able to accommodate a range of loads, fretting pad contours, and specimen geometries that produced a variety of stress fields. A crack-initiation-based criterion was shown to predict the failure lives of thinner specimens accurately. The stress intensity factor calculations showed the possibility of a crack arresting for a stress field that decays rapidly and the possibility of a local minimum for K as a function of depth. The fixtures are shown to be complementary in generating data for development of robust fretting fatigue models that use these criteria. [ABSTRACT FROM AUTHOR]

The axisymmetric problem of a functionally graded, transversely isotropic, annular plate subject to a uniform transverse load is considered. A direct displacement method is developed that the non-zero displacement components are expressed in terms of suitable combinations of power and logarithmic functions of r, the radial coordinate, with coefficients being undetermined functions of z, the axial coordinate. The governing equations as well as the corresponding boundary conditions for the undetermined functions are deduced from the equilibrium equations and the boundary conditions of the annular plate, respectively. Through a step-by-step integration scheme along with the consideration of boundary conditions at the upper and lower surfaces, the z-dependent functions are determined in explicit form, and certain integral constants are then determined completely from the remaining boundary conditions. Thus, analytical elasticity solutions for the plate with different cylindrical boundary conditions are presented. As a promising feature, the developed method is applicable when the five material constants of a transversely isotropic material vary along the thickness arbitrarily and independently. A numerical example is finally given to show the effect of the material inhomogeneity on the elastic field in the annular plate. [ABSTRACT FROM AUTHOR]

In this contribution the effective material behaviour of thin structures like membranes and plates consisting of heterogeneities is investigated. The diameter of typical inclusions can be in the order of magnitude of the thickness of the membrane or plate. Thus, the prerequisite for a standard homogenization procedure using representative volume elements is not fulfilled anymore, since the required size of an RVE would be larger than the thickness of the structure itself. Additionally the assumption of uniformity of the boundary conditions on the RVE would be violated especially for plates since in general the predominant deformation of such structures is bending. However, it can be shown that the effective behaviour of such heterogeneous thin structures subjected to finite deformations is still in good agreement to the results obtained for homogenized materials. [ABSTRACT FROM AUTHOR]

A simple deformation field associated with an exact torsion-like solution of the equilibrium equations of linear elasticity is shown to provide a good approximation of the deformation field in interior elements of a mesh that models pure torsion of a right cylindrical bar with rectangular cross-section. Using this solution, modified torsion coefficients are proposed for a 3-D brick Cosserat point element (CPE) which are shown to improve convergence properties for solutions of pure torsion. [ABSTRACT FROM AUTHOR]

Abstract  In a dynamic experiment to obtain the high-rate stress–strain response of a ductile specimen, it takes a finite amount of time for the strain rate in the specimen to increase from zero to a desired level. The strain in the specimen accumulates during this strain-rate ramping time. If the desired strain rate is high, the specimen may yield before the desired rate is attained. In this case, the strain rates at yielding and early plastic flow are lower than the desired value, leading to inaccurate determination of the yield strength. Through experimentation and analysis, we examined the validity and accuracy of the flow stresses for ductile materials in a split Hopkinson pressure (SHPB) bar experiment. The upper strain-rate limit for determining the dynamic yield strength of ductile materials with a SHPB is identified. [ABSTRACT FROM AUTHOR]

The three-dimensional stress state of a transversely isotropic plate with a nearly circular cylindrical cavity is examined. The cavity surface is subject to normal and tangential stresses and the plate is subject at infinity to tensile and shear forces. The problem is solved by expanding unknown functions into Fourier-Legendre series in the thickness coordinate and using the boundary-shape perturbation method. The equations and recurrence formulas needed to solve the problem in an arbitrary approximation are presented [ABSTRACT FROM AUTHOR]

New representations of the stress tensor in the linear theory of elasticity and thermoelasticity are proposed. These representations satisfy the equilibrium equations and the strain compatibility equation. The stress tensor is expressed in terms of a harmonic tensor or a harmonic vector. The second boundary-value problem for an elastic half-space and an elastic layer is solved as an example [ABSTRACT FROM AUTHOR]

The contact interaction of a pneumatic tire with a roadbed is studied. The discrepancy between the Gim-Nikravesh analytic model and experimental data is established to be due to the one-dimensionality of the model and the assumption that the pressure of the wheel on the roadbed is symmetric [ABSTRACT FROM AUTHOR]

In this study, mechanical properties such as tensile, flexural and impact strengths of hemp/phenol formaldehyde (PF), basalt/PF and hemp/basalt hybrid PF composites have been investigated as a function of fibre loading. Hemp fibre reinforced PF composites and basalt fibre reinforced composites were fabricated with varying fibre loading i.e. 20, 32, 40, 48, 56 and 63 vol%. The hybrid effect of hemp fibre and basalt fibre on the tensile, flexural and impact strengths was also investigated for various ratio of hemp/basalt fibre loading such as 1:0, 0.95:0.05, 0.82:0.18, 0.68:0.32, 0.52:0.48, 0.35:0.65, 0.18:0.82 and 0:1. Total fibre loading of the hybrid composites was 40 vol%. The results showed that the tensile strength and elongation at break increase with increasing fibre loading up to 40 vol% and decrease above this value for hemp fibre reinforced PF composite. Similar trend was observed for flexural strength and the maximum value was obtained for 48 vol% hemp fibre loading. Impact strength of hemp/PF composite showed a regular trend of increase with increasing fibre loading up to 63 vol%. Tensile strength, flexural strength and impact strength values of basalt/PF composites were found to be lower compared to hemp/PF composites. The tensile strength and elongation at break of basalt/PF composite increased by incorparation of basalt fibre up to 32 vol% and decreased beyond this value. Flexural strength of basalt/PF composite decreased linearly with fibre loading. However, the maximum impact strength was obtained for 48 vol% basalt fibre loading. For hemp/basalt hybrid PF composite, the tensile strength decreased with increasing basalt fibre loading. On the other hand, the flexural and impact strengths showed large scatter. The maximum flexural strength value was obtained for 0.52:0.48 hemp/basalt ratio. Corresponding value for impact strength was obtained for 0.68:0.32 hemp/basalt fibre ratio. [ABSTRACT FROM AUTHOR]

The tear resistance of polyethylene terephthalate film is characterized by the essential work of fracture method in mode I as a function of test speed and temperature. Attempts to extrapolate tearing resistance found by the method of essential work to commercial slitting processes are discussed. Limitations of the essential work of fracture method with regards to specimen size are evaluated. Based on the findings modifications to the test protocol are suggested. [ABSTRACT FROM AUTHOR]

Based on the refined plate theory, a refined theory of rectangular beams is derived by using the Papkovich-Neuber solution and Lur’e method without ad hoc assumptions. It is shown that the displacements and stresses of the beam can be represented by the angle of rotation and the deflection of the neutral surface. The solutions based on the new theory are the same as the exact solutions of elasticity theory. In three examples it is shown that the new theory provides as good or better results than Levinson’s beam theory when compared to those obtained from the linear theory of elasticity. [ABSTRACT FROM AUTHOR]

A two-level fracture model of composites with cracks under compression is proposed. Fiber-reinforced laminated panels with a hole are considered. The panels are compressed along the fibers so that two cracks propagate from the hole boundary at a right angle to the loading direction. The fracture mechanism is analyzed at two levels. The first level is the compression-induced stress concentration at the tip of a finite-thickness crack filled with a fractured material. At this level, the theory of elasticity of linear orthotropic body is used. The second level is compression fracture at the crack tip. The analysis performed at this level involves the three-dimensional linearized theory of stability of solids, considering microcracks in the interface between the fractured and intact materials, and the exact solution describing the compression-induced instability of the cracked interface. The second level is where results obtained by the author are used. Thus, the approach proposed employs the theory of elasticity of linear orthotropic body and the three-dimensional linearized theory of stability of solids to analyze a specific mechanism of fracture [ABSTRACT FROM AUTHOR]

The structural theory of short-term damage is generalized to the case where the undamaged components of anN-component laminar composite deform nonlinearly. The basis for this generalization is the stochastic elasticity equations for anN-component laminar composite with porous components whose skeleton deforms nonlinearly. Microvolumes of the composite components meet the Huber-Mises failure criterion. Damaged microvolume balance equations are derived for the physically nonlinear materials of the composite components. Together with the equations relating macrostresses and macrostrains of the laminar composite with porous nonlinear components, they constitute a closed-form system. This system describes the coupled processes of physically nonlinear deformation and microdamage. For a two-component laminar composite, algorithms for calculating the microdamage-macrostrain relationship and plotting deformation curves are proposed. Uniaxial tension curves are plotted for the case where microdamages occur in the linearly hardening component and do not in the linearly elastic component [ABSTRACT FROM AUTHOR]

Internal parameters, eigenstrains, or eigenstresses, arise in functionally graded materials, which are typically present in particulate, layered, or rock bodies. These parameters may be realized in different ways, e.g., by prestressing, temperature changes, effects of wetting, swelling, they may also represent inelastic strains, etc. In order to clarify the use of eigenparameters (eigenstrains or eigenstresses) in physical description, the classical formulation of elasticity is presented, and the two most important Lagrange's and Castigliano's variational principles are formulated in the sequel. Then the classical Hashin-Shtrikman principles are recalled and the involvement of eigenparameters is studied in more detail. [ABSTRACT FROM AUTHOR]

Precise estimation of local stress profiles in individual phases of a fiber reinforced metal matrix composite is a crucial concern for design of composites. Stress profiles are significantly affected by plastic relaxation of soft matrix. In this work, an analytical model was developed to compute local stress profiles in individual phases of fibrous metal matrix composites. To this end, embedded cell cylindrical composite model was applied in which a layered concentric cylinder consisting of a fiber-, matrix- and homogenized composite layers was used. Mean field micromechanics was integrated into the conventional elasticity solution process so that micro-macro dual scale analysis could be performed. The algorithm was formulated in an iterative incremental structure which was able to perform plastic analysis. This also allows temperature dependence of flow stress to be considered. Taking copper-SiC system as a reference composite, stress profiles were obtained for mechanical and thermal loading cases. For comparison, independent finite element analyses were carried out for two different unit cell models. Excellent agreement between analytical and numerical solutions was found for the mechanical loading case even for plastic range. In the case of thermal loading, however, plastic solutions revealed notable difference in quantity, especially for the axial stress component. [ABSTRACT FROM AUTHOR]

The joint strength and fracture surfaces of Sn-Pb and Au stud bumps for photodiode packages after isothermal aging were studied experimentally. Aluminum/gold stud bumps and Cu/Sn-Pb solders were adopted and aged for up to 900 h to analyze the effect of intermetallic compound (IMC) formation. The joint strength decreased with aging time. The diffraction patterns of Cu6Sn5, scallop-shaped IMCs, and planar-shaped Cu3Sn were characterized by transmission electron microscopy (TEM). The IMCs between Au stud bumps and A1 pads was identified as AlAu2. The formation of Kirkendall voids and the growth of IMCs at the solder joint were found to be a possible mechanism for joint strength reduction. [ABSTRACT FROM AUTHOR]