Showing papers in "Journal of Strain Analysis for Engineering Design in 2007"
TL;DR: In this article, the concept of effective structural size in titanium alloys and its importance with respect to material production routes and component lifing/design is introduced and reviewed in the context of industrial application.
Abstract: This paper introduces the concept of effective structural size in titanium alloys and its importance with respect to material production routes and component lifing/design. Traditionally, process route optimization has relied on optical microscopy, which may be misleading when predicting mechanical properties. Similarly, continuum mechanics and current lifing methods are based on empirical data analysis. The advent of advanced material characterization techniques, e.g. EBSD combined with crystal plasticity modelling, has the potential to provide the next generation of mechanistically sound methods that more accurately predict material behaviour in complex loading regimes. These benefits are reviewed in the context of industrial application. Crystal plasticity modelling techniques are presented and a particular structural unit - termed a rogue grain - in a model single-phase titanium alloy is considered. Cold dwell under both strain and stress control is then assessed in the structural unit.
98 citations
TL;DR: In this paper, the problem of fretting contact between a functionally graded coated half-space and a rigid cylindrical punch is considered for the case where, first, a constant normal load is applied, and then a cyclically varying tangential load, which is less than that necessary to cause complete sliding, is applied.
Abstract: Fretting is a major cause of surface damage, with fretting fatigue crack initiation at the contact surface subjected to a small-scale oscillatory tangential motion. In the present paper, which is part 2 of the series, the fretting contact between a functionally graded coated half-space and a rigid cylindrical punch is considered for the case where, first, a constant normal load is applied, and then a cyclically varying tangential load, which is less than that necessary to cause complete sliding, is applied. The functionally graded coated half-space is under conditions of plane strain deformation. The whole contact region is composed of an inner stick region and two outer slip regions in which Coulomb's friction law is assumed to apply. Owing to the mismatch in material constants of the punch and half-space, the problem is fully coupled and can be reduced to two coupled Cauchy singular integral equations. Based on the analyses of normal loading in part 1, contact tractions and in-plane stresses associated ...
46 citations
TL;DR: In this paper, the creep behaviour of a functionally graded cylinder is considered under both internal and external pressures, and an asymptotic solution can be derived on the basis of a Taylor expansion series.
Abstract: In this paper the creep behaviour of a functionally graded cylinder is considered under both internal and external pressures. When the properties of the graded material are axisymmetric and dependent on the radial coordinate, an asymptotic solution can be derived on the basis of a Taylor expansion series. The approximate solutions calculated from different higher-order terms are compared with the results of finite element (FE) analysis using ABAQUS software. It is shown that, although the use of higher-order terms may help to obtain a more accurate result for the time-dependent behaviour of the cylinder, a fifth-order form has been sufficiently accurate to calculate the creep stress distribution with satisfactory approximation.
42 citations
TL;DR: In this paper, an analytical solution of the elastic field of a deep stiffened cantilever beam of orthotropic composite material is presented, which reduces the problem to the solution of a single fourth-order partial differential equation of equilibrium and is capable of dealing with mixed modes of boundary conditions appropriately.
Abstract: An analytical solution of the elastic field of a deep stiffened cantilever beam of orthotropic composite material is presented in the paper. The cantilever beam is subjected to a parabolic shear loading at its free lateral end and the two opposing longitudinal edges are stiffened. Unidirectional fibre-reinforced composite is considered for the present analysis where the fibres are assumed to be directed along the beam length. Following a new development, the present mixed-boundary-value elastic problem is formulated in terms of a single potential function defined in terms of the associated displacement components. This formulation reduces the problem to the solution of a single fourth-order partial differential equation of equilibrium and is capable of dealing with mixed modes of boundary conditions appropriately. The solution is obtained in the form of an infinite series. Results of different stress and displacement components at different sections of the composite beam are presented numerically in the f...
28 citations
TL;DR: In this article, the magnitudes of the PZS in the investigated specimens have been compared using a new reference standard J/aσy where a is crack length and σy is yield stress of the material.
Abstract: In this investigation the nature of the plastic zone ahead of a crack-tip in centrecracked tension, double-edge-notched tension, single-edge-notched tension, compact tension, extended compact tension, and single-edge-notched bend specimens have been assessed by elastic-plastic finite element analyses at different applied load levels (J integral). The magnitudes of the plastic zone size (PZS) in the investigated specimens have been compared using a new reference standard J/aσy where a is crack length and σy is yield stress of the material. The results demonstrate that the PZS is almost invariant with respect to specimen geometry up to a critical value of J/aσy at a specific a/W ratio. However, beyond this critical value, the magnitudes of the PZS are found to depend on the specimen geometry, which has been attributed to the varying in-plane constraints at the crack tip in various specimens.
26 citations
TL;DR: In this article, the authors used the crack compliance method for the determination of residual stresses in beams subjected to prior straining before the introduction of residual stress through bending, and introduced a support system that allows free movement of specimens during cutting by electric discharge machining.
Abstract: This work used the crack compliance method for the determination of residual stresses in beams subjected to prior straining before the introduction of residual stresses through bending. The paper also introduces a support system that allows free movement of specimens during cutting by electric discharge machining. The experimental testing and verification procedure considered factors such as different materials and strain hardening levels. The results obtained provide a quantitative demonstration of the effect of prior strain hardening on residual stress distribution in beams.
24 citations
TL;DR: In this article, an engineering design formula for the torsion stiffness of a filled rubber bushing in the frequency domain, including the amplitude dependence, was presented by applying a novel sep...
Abstract: An engineering design formula for the torsion stiffness of a filled rubber bushing in the frequency domain, including the amplitude dependence, is presented. It is developed by applying a novel sep ...
24 citations
TL;DR: In this article, a dual-time-scale finite element model is developed for simulating cyclic deformation in polycrystalline alloys, which is characterized by crystal plasticity constitutive relations.
Abstract: A dual-time-scale finite element model is developed in this paper for simulating cyclic deformation in polycrystalline alloys. The material is characterized by crystal plasticity constitutive relations. The finite element formulation of the initial boundary-value problems with cyclic loading involves decoupling the governing equations into two sets of problems corresponding to two different time-scales. One is a long-time-scale (low-frequency) problem characterizing a cycle-averaged solution, while the other is a short-time-scale (high-frequency) problem for a remaining oscillatory portion. Cyclic averaging together with asymptotic expansion of the variables in the time domain forms the basis of the multitime-scaling. The crystal plasticity equations at the two scales are used to study cyclic deformation of a titanium alloy Ti-6Al. This model is intended to study the fatigue response of a material by simulating a large number of cycles to initiation.
24 citations
TL;DR: The difference between the stress value calculated by a two-dimensional finite element model of spur gears and those obtained by the rules in ISO 6336 was evaluated in this paper, where the difference was less than 2.5 per cent.
Abstract: The difference between the stress value calculated by a two-dimensional finite element model of spur gears and those obtained by the rules in ISO 6336 was evaluated. Hertz theory, which provides information on the extension of the contact area and the maximum value of the contact pressure, was used to choose the dimensions of the elements. The mesh was created using the stress analytical solution relative to a model consisting of two cylinders in contact.Analogous optimization was executed for the mesh of the teeth feet; a mesh of 15 elements was considered optimum, because it minimized the difference to 0.5 per cent in the bending stress calculation. Stress values, obtained using the finite element method (FEM), are generally lower than those obtained with the ISO rules. Hence, this approach yields a conservative determination of the effective material strength. In all the examined cases, the difference was less than 2.5 per cent.The set FEM technique gives a result accuracy of better than 1 per cent; th...
23 citations
TL;DR: In this article, a micromechanical finite element model is established and used to model the damage evolution process of a free-cutting steel bloom, where the inclusions are associated with a lead tail and the damage growth is directly related to the inclusion size and spacing.
Abstract: The spatial variations in the inclusion size and distribution are examined for a free-cutting steel bloom. Chemical analysis has been carried out on the inclusions using energy-dispersive X-ray analysis and the main findings are reported. It has been observed that inclusions are often associated with a lead tail. Thus an assumption is made that the lead layer becomes liquid or gaseous at hot-forming temperatures. Based on this assumption, a micromechanical finite element model is established and used to model the damage evolution process. Microstructure examinations of hot-tensile-tested specimens are used to compare experimentally the observed inclusion shape and void growth features with those obtained from the micromechanical finite element method. It is concluded that there is no significant inclusion debonding process for the material deformed under hot-forming conditions. The damage growth is directly related to the inclusion size and spacing.
23 citations
TL;DR: In this paper, a combination of experimental and modelling techniques that involves microstructural investigation, diffraction measurement of residual elastic strains, and finite element simulation of residual stress distributions is investigated.
Abstract: Most engineering components made from wrought metallic alloys undergo complex sequences of manufacturing operations. These processing steps frequently include extrusion, forging, or rolling, followed by machining and heat treatment. Since such components will be subjected to service loading as part of engineering assemblies, their durability must be assessed using suitably reliable life prediction models. The present study is aimed at the investigation of a combination of experimental and modelling techniques that involves microstructural investigation, diffraction measurement of residual elastic strains, and finite element simulation of residual stress distributions.Eigenstrain-based modelling approach to the analysis of processing-induced residual stresses has been previously presented in the two-dimensional approximation, i.e. under the assumption that the equivalent permanent plastic strain field induced by processing is equibiaxial. Several different formulations were considered and compared, includi...
TL;DR: In this paper, the authors developed analytical theories for industry to predict the relations between the punch stroke, flaring ratio, tube thickness, and flaring forming limit in the tube flaring process.
Abstract: The aim of the current paper is to develop analytical theories for industry to predict the relations between the punch stroke, flaring ratio, tube thickness, and flaring forming limit in the tube flaring process. The volume incompressible condition, Levy-Mises equation, and explicit die profile description are combined to derive the analytical expressions relating the flaring ratio to the punch stroke and velocity in the tube flaring process. Then, according to the stress equilibrium state of a small tube element, the relation of the tube-end thickness ratio to the flaring ratio is developed on the basis of Tresca's criterion. Combining these two analytical theories and the fractured thickness at the tube end, the flaring forming limit can be determined. An elastoplastic finite element method based on the updated Lagrangian formulation is also developed to verify the analytical theories. A flaring experiment, using a 30° semi-cone angle to describe the conical die, is conducted to validate the analytical ...
TL;DR: In this article, the authors explore the use of both macroscale and microscale modelling for the analysis of extrusion of an AA2009 + 25%SiCp metal matrix composite (MMC).
Abstract: This paper explores the use of both macroscale and microscale modelling for the analysis of extrusion of an AA2009 + 25%SiCp metal matrix composite (MMC). The performance of a micromechanical model...
TL;DR: In this article, an investigation of the stress concentration around a spherical cavity in a cubic medium is conducted by means of the equivalent inclusion method, where cases of uniformly applied tensile, shear, and hydrostatic stresses are analysed and examined.
Abstract: An investigation of the stress concentration around a spherical cavity in a cubic medium is conducted by means of the equivalent inclusion method. Cases of uniformly applied tensile, shear, and hydrostatic (spherical) stresses are analysed and examined. Theoretical formulation and computational procedures are described in detail. Numerical results for some representative cubic crystals (niobium, molybdenum, nickel, and copper) are presented for illustration and important features of the ensuing stress concentration are discussed.
TL;DR: In this article, the authors used a numerical model of the disc test to predict failure times over a wide range of test conditions, and the resulting response surface was then approximated using a polynomial.
Abstract: The small-creep disc test is seen as a promising solution to the problem of sampling from in-service components for remanent life estimation. However, experimental studies have revealed substantial scatter in failure times resulting from variations in test and apparatus geometries. These studies therefore suggest that there exists a set of conditions that both minimizes the scatter and also maximizes the sensitivity of the disc test to the determination of remanent life, so enabling reliable estimates of the remaining life to be made. The objective of this paper is to identify such an optimum.The large scatter present in small-disc test data would make the identification of this optimum problematic and inconclusive using an experimental approach. Instead this paper uses a numerical model of the disc test to predict failure times over a wide range of test conditions. The resulting response surface is then approximated using a polynomial and from this model the optimum set of test conditions is identified. ...
TL;DR: In this paper, the most relevant multiscale models for predicting crystallographic textures formed during the primary static recrystallization of metals are discussed, and two main groups of approaches are presented, namely those which spatially discretize the grains and the interface motion associated with recrasing and those which treat these phenomena in an Avrami-type statistical fashion.
Abstract: This paper discusses the most relevant multiscale models for predicting crystallographic textures formed during the primary static recrystallization of metals. Two main groups of approaches are presented, namely those which spatially discretize the grains and the interface motion associated with recrystallization and those which treat these phenomena in an Avrami-type statistical fashion. The article gives a concise review of the methods, placing particular attention on their strengths and weaknesses in the context of process modelling, of conceptual aspects, and of the data sets required as input for practically applying the models to the prediction of crystallographic textures in the course of metallurgical processes.
TL;DR: Combined thermoelasticity-photo elasticity as mentioned in this paper integrates the use of reflection photo-lasticity to determine the difference in principal stresses with thermo-elastic stress analysis to evaluate the sum of the principal stresses, the advantage gained from this combination being the independent separation of principal stresses at all points in the field of view.
Abstract: Combined thermoelasticity-photoelasticity integrates the use of reflection photoelasticity to determine the difference in the principal stresses with thermoelastic stress analysis to evaluate the sum of the principal stresses, the advantage gained from this combination being the independent separation of the principal stresses at all points in the field of view. The principle has been established in prior research and suitable instrumentation designed and employed on classical test specimens. This work is extended here with the analysis of two more complex components, namely a composite panel subject to a biaxial strain field and a compressor blade excited at approximately 250 Hz. The methodology for applying combined thermoelasticity-photoelasticity under these conditions is described and the difficulties encountered highlighted and discussed. The results demonstrate that the technique and instrumentation are relatively robust and can be successfully used in these demanding applications.
TL;DR: In this paper, a parametric finite element analysis of stress concentration at radial crossholes in pressurized cylinders is presented in numerical and graphical form, and the analysis shows that the location of maximum stress does not generally occur at the junction between the bores, as is commonly supposed, but at some small distance up the crosshole from the junction.
Abstract: Results of a parametric finite element analysis investigation of stress concentration at radial crossholes in pressurized cylinders are presented in numerical and graphical form. The analysis shows that the location of maximum stress does not generally occur at the junction between the bores, as is commonly supposed, but at some small distance up the crosshole from the junction. Maximum stress concentration factors (SCFs) are defined on the basis of the maximum principal stress, von Mises equivalent stress, and stress intensity. Three-dimensional plots of the SCF against the cylinder radius ratio b/a and the crosshole-to-main-bore-radius ratio c/a are presented. The SCFs were found to vary across the range of geometries considered with local minima identified within the parameter range in most cases. The results therefore allow designers to select optimum b/a and c/a ratios to minimize stress concentration in real problems.
TL;DR: In this paper, edge welding and partial quenching are explored as two processes capable of generating well-defined residual stress fields in beam specimens, which allow the influence of pre-existing residual stresses on the fracture behaviour of metallic components under applied loads to be studied in a systematic manner.
Abstract: Edge welding and partial quenching are explored as two processes capable of generating well-defined residual stress fields in beam specimens. The purpose of introducing residual stress fields into test specimens is to allow the influence of pre-existing residual stresses on the fracture behaviour of metallic components under applied loads to be studied in a systematic manner. Three materials are considered in this paper: two stainless steels (type 316H and Esshete 1250) and one ferritic steel (A533B). The paper presents both numerical and experimental results. The numerical results were obtained using finite element analysis, and the experimental measurements made primarily with the neutron diffraction technique, and also with X-ray synchrotron diffraction and incremental centre hole drilling. There was, in many cases, good agreement between predictions and measurements; however, there were several instances where finite element predictions differed significantly from measurements. This difference was oft...
TL;DR: In this paper, various stress-raising features have been analyzed using the finite element method to determine the stress concentration factor, and it is shown that Poisson's ratio can have a significant effect on the SCF.
Abstract: In design, it is common to use values for stress concentration factors (SCFs) obtained from textbooks. These textbook values have generally been obtained from photoelastic experiments for which Poisson's ratio will probably have a value greater than 0.3 and for frozen stress analysis a value approaching 0.5. However, when designing machine parts made from other isotropic materials, e.g. metals and structural ceramics, Poisson's ratio will probably have a lower value, which will affect the value of the SCF.In this paper, various stress-raising features have been analysed using the finite element method to determine the stress concentration factor. It is shown that Poisson's ratio can have a significant effect on the SCF.
TL;DR: In this paper, the coupled torsional-lateral model of the rotor system is set up and governing equations are derived using the Lagrange approach with six degrees of freedom.
Abstract: The coupled torsional-lateral model of the rotor system is set up and governing equations are derived using the Lagrange approach with six degrees of freedom. The gyroscopic effect and gravity are ...
TL;DR: In this article, Damper rings of a soft material were used to absorb the impact energy by deforming plastically, and the influence of the dimensions of damper rings on the stress waves and also the ability of the system to support the interruption of the deformation process were considered in numerical analyses and verified by the experimental results.
Abstract: The damage evolution in a material during quasi-static and dynamic tests can be studied by interrupting the test at predetermined elongation values and post-mortem analyses of the specimens. While it is straightforward to interrupt quasi-static tests at a predetermined level of elongation, this interruption presents difficulties at high-strain-rate conditions. In the present work, tests at high strain rate using a split Hopkinson tensile bar have been interrupted by an interruption mechanism as a modification of this device. This interruption mechanism is based on the use of two rings of a soft material that absorb the impact energy by deforming plastically. The influence of the dimensions of damper rings on the stress waves and also the ability of the system to support the interruption of the deformation process were considered in the numerical analyses and verified by the experimental results. The relationship between the recommended ring thickness and maximum reached strain for aluminium alloy A16082 w...
TL;DR: In this paper, the authors deal with the application of such relations in an opposite way, to deduce the local fields from the macroscopic ones, and their improvement when some basic hypotheses of the homogenization technique are no longer valid.
Abstract: Usually the homogenization process used to determine the macroscopic mechanical fields from knowledge of the microscale geometry and the corresponding local fields is based on the development of localization (sometimes also called concentration) relations. The aim of this paper is to deal with the application of such relations in an opposite way, to deduce the local fields from the macroscopic ones, and their improvement when some basic hypotheses of the homogenization technique are no longer valid.
TL;DR: In this paper, the Berger equation is used to obtain solutions for deformation of thin elastic plates, and is solved by applying the charge simulation method, and the general solution for the deflection is first obtained by a combination of two kinds of series of Green's functions.
Abstract: The non-linear Berger equation is used to obtain solutions for deformation of thin elastic plates, and is solved by applying the charge simulation method. The general solution for the deflection is first obtained by a combination of two kinds of series of Green's functions. Satisfying the boundary conditions at the collocation points, the unknown constants in the general solution are determined, and the deflection of the plate is calculated. Numerical results are presented in dimensionless graphical form for rectangular and isosceles triangular plates.
TL;DR: In this paper, the authors investigated the validity of stationary models when the applied contact conditions are subjected to rapid changes, with the objective of deducing the effects of the evolution of the instationary process on the contact parameters.
Abstract: The rapid convergence of the tangential rolling contact parameters to their stationary values, combined with the high computational cost associated with calculations using instationary models, has meant that stationary models are usually employed in railway dynamics. However, the validity of stationary models when the applied contact conditions are subjected to rapid changes has not been sufficiently investigated. With the objective of deducing the effects of the evolution of the instationary process on the contact parameters, the tangential contact problem is solved for a set of reference conditions. For this purpose a calculation model is adapted, from which it is possible to analyse the evolution of the contact parameters when the forces exerted between rail and wheel are subjected to rapid changes. From the calculations made, situations impossible to simulate by means of stationary theories are obtained according to the frequency of variation in the forces, such as slip zones in the leading edge of th...
TL;DR: In this article, the pure rolling contact stresses in conical rollers under normal loading were studied and the existing analytical expression for the contact pressure in uniform cross-section c was derived.
Abstract: In this paper, the pure rolling contact stresses in conical rollers under normal loading are studied The existing analytical expression for pure rolling contact pressure in uniform cross-section c
TL;DR: In this article, the elastic stresses in the vicinity of the unreinforced intersection of a single 90° mitred bend, subjected to an in-plane bending moment, were investigated and compared with adaptive-p thin-shell finite element results.
Abstract: The experimental investigation reported provides elastic stresses in the vicinity of the unreinforced intersection of a single 90° mitred bend, subjected to an in-plane bending moment. The specimen was extensively strain gauged on the outer surface. A small number of rosettes were also laid on the inside surface close to the welded intersection. The procedures used for the successful installation of the inside surface gauges are discussed. In the experiment, consideration was also given to deflections and rotations. Satisfactory comparisons with adaptive-p thin-shell finite element results were obtained in general and differences are explained in terms of the known experimental variables and finite element approximations. The nature of the stresses at such intersections is discussed and various methods of obtaining fatigue 'hot-spot' stresses are considered.
TL;DR: In this article, the effects of orthotropy ratio and plate length on the stress concentration factor for orthotropic plates with a centred circular opening under the action of uniaxial tension loads are investigated by use of the finite element method.
Abstract: In this study, the effects of orthotropy ratio and plate length on the stress concentration factor for orthotropic plates with a centred circular opening under the action of uniaxial tension loads are investigated by use of the finite element method. This work demonstrates that the stress concentration factor depends on the length of the member in addition to other established geometric parameters. The value of the transition length between long and short plates is computed and reported as well. This study has shown that Tan's equation for a finite width orthotropic plate is accurate for a ratio of the opening radius to plate semiwidth of less than 0.35 for orthotropy ratios less than 50. A new concept is introduced, namely the transition ratio.
TL;DR: In this article, limit analyses of cylindrical shells with a circular opening under the action of combined axial force and bending moment at the ends are carried out using both finite element methods and the approximate analytical lower-bound limit load of the weakest section of the cylinder.
Abstract: In this paper, limit analyses of cylindrical shells with a circular opening under the action of combined axial force and bending moment at the ends are carried out using both finite element methods and the approximate analytical lower-bound limit load of the weakest section of the cylinder. The finite element calculations consist of elastic-plastic and elastic compensation methods using an ANSYS suite of programs. The results obtained by the finite element methods are then compared with the approximate analytical lower-bound limit load of the cylinder, and the correlation between them is discussed.
TL;DR: In this article, the authors investigated stress wave effects in the high-rate tensile testing apparatus known as the "Flying Wedge" and found that the results for small and low-strength specimens were significantly affected by the stress waves that propagate through the parts of the testing machine following the impact.
Abstract: Stress wave effects in the high-rate tensile testing apparatus known as the ‘Flying Wedge’ have been investigated using both experimental and numerical approaches. The experiments were conducted on R2000 glass/epoxy composites and iron specimens at strain rates up to 103/s. Numerical simulations were carried out using the LS-DYNA hydro code. Both the numerical and the experimental results showed that the results for small and low-strength specimens were significantly affected by the stress waves that propagate through the parts of the testing machine following the impact. The time period of the resulting load oscillations was found to be similar to that calculated from one-dimensional stress wave theory for different load paths in the apparatus. Therefore, it is concluded that stress wave effects play a dominant role in the Flying Wedge for small and low-strength specimens and consequently this machine is not a suitable choice for dynamic testing of such specimens.