Showing papers in "Journal of Strain Analysis for Engineering Design in 2003"

A review of the general theory of thermoelastic stress analysis

Abstract: Thermoelastic stress analysis (TSA) is now a well-known experimental technique providing information on the surface stress field in structures. Many studies have assessed the potential of the technique for a number of applications and some useful and detailed reviews of these investigations are available, focusing mainly on the experimental aspects related to the measurement of the thermoelastic signal. In this work, instead, a complete and detailed insight into the origins of the various forms of the equations describing the thermoelastic effect is given with reference to the concepts of the thermodynamic theory of a continuum. A discussion on the theory leading to the thermoelastic effect law is intended to give a useful overview of the applications and real limitations of TSA.

A self-powered damage detection sensor:

Abstract: All existing methods of embedded damage-detecting sensors require an external power source and a means of transmitting the data to a central processor This paper presents a novel self-powered strain sensor capable of transmitting data wirelessly to a remote receiver This paper illustrates the performance of the sensor through the theoretical and experimental analysis of a simple damaged beam The results show that a sensor powered through the conversion of mechanical to electrical energy is viable for detecting damage The potential benefits of this sensor include ease of implementation during manufacture of the structure, and the use of an environmentally safe and renewable power source

Fatigue design in the presence of stress concentrations

Abstract: This paper reports a comparative study of some recent methods developed for the estimation of high-cycle fatigue behaviour of components containing stress concentrations. It begins by reviewing some existing methods for the prediction of fatigue limits: the stress-life method, linear elastic fracture mechanics, the Kitagawa-Takahashi and Atzori-Lazzarin approaches and the method of Smith and Miller. Two new methods are described which have been developed during the last few years: the crack modelling method (CMM) and the critical distance method (CDM). These methods were tested by comparing their predictions with experimental data using a large database of 88 different notch geometries and materials. Notches were divided into three types: blunt, sharp and short. The CDM was found to be very successful for all types of notch, giving predictions within 20 per cent of experimental values in the great majority of cases. The CMM encountered difficulties with short notches; correction factors were developed to ...

Experimental determination of impact tensile properties of adhesive butt joints with the split Hopkinson bar

Abstract: The tensile strength and energy absorption of adhesive butt joints at high rates of loading are determined with a tensile split Hopkinson bar using a cylindrical specimen. A commercially available single-component cyanoacrylate adhesive (instantaneous adhesive) and two different adherend materials are used in the adhesion tests. The impact tensile strength of the cyanoacrylate adhesive butt joints is determined from the applied tensile stress history at failure initiation. The impact absorbed energy is obtained by numerical integration of dynamic tensile load-adhesive deformation data. Comparative tension tests at low and intermediate rates of loading are performed on an Instron testing machine. An axisymmetric finite element analysis is carried out to investigate the stress distributions in the adhesive layer of the cyanoacrylate adhesive butt joints. The effects of loading rate, adherend material and adhesive layer thickness on the tensile strength and energy absorption of the cyanoacrylate adhesive but...

Creep analysis of pressurized circumferential pipe weldments—a review:

Abstract: This paper reviews work related to the high-temperature creep analysis of pressurized circumferential pipe weldments. It is important to define the problem and thus metallurgical features correctly; the identification of material microstructural-property variations within the heat-affected zone (HAZ) and the failure modes of welds are briefly included, as well as in-service experience of pipe welds. Experimental methods, including model and full-size component testing, are summarized and examples of typical tests results are described. Material constitutive equations, which can be used in describing the creep deformation of and failure mechanisms in welds, are briefly described. Numerical modelling using finite element (FE) methods, covering a range of approaches and analyses, taking account of the effects of material properties, pipe geometry, weld dimensions and system loading, on the stresses and failure behaviour of pipe weldments, are summarized. Typical results are presented to illustrate the potent...

Residual stresses in components formed by the laserengineered net shaping (LENS®) process

Abstract: The residual stress distributions in two laser-engineered net shaping (LENS®) samples were mapped by neutron diffraction. The samples took the form of a thin wall and a pillar of square cross-section. Stresses were measured in the three orthogonal symmetry directions of the parts, parallel and perpendicular to the growth direction. Surprisingly, over most of the bulk of the samples the stress was uniaxial and directed along the growth axis, with compression in the centre of the samples and tension at the edges. The magnitudes of the maximum residual stresses were significant fractions (50 and 80 per cent for the thin wall and pillar respectively) of the 0.2 per cent yield point. The origin of the residual stress distributions is discussed qualitatively in terms of the thermal histories of the samples.

Measurement of residual stresses in T-plate weldments

Abstract: Tensile welding residual stresses can, in combination with operating stresses, lead to premature failure of components by fatigue and/or fracture It is therefore important that welding residual st

Stress analysis of V-notches with and without cracks, with application to foreign object damage

Abstract: Gas turbine engines can be subject to ingestion of small hard particles, leading to foreign object damage. This can take the form of sharp V-notches in the leading edge of blades and there is a need to predict the initiation and propagation behaviour of fatigue cracks growing from the base of the notch. The notch geometry is quite extreme and is not normally covered in standard references for notch stress concentration factors. Similarly, stress intensity factor solutions for this geometry are not widely available. This paper uses the dislocation density approach to solve the two-dimensional elastic problem of a V-notch with a radiused root. Stress concentration factors are found for the notch itself, and stress intensity factors are determined for cracks growing away from the notch for cases of applied and residual stress distributions. Comparisons are made with existing notch solutions from the literature.

Neuber prediction of elastic-plastic strain concentration in notched tensile specimens under large-scale yielding:

Abstract: A general version of Neuber's rule, applicable to large-scale yielding, is presented. It is applied to a variety of notched tensile specimens made of power-hardening elastic-plastic material. Neuber's rule predictions of notch stress and strain are compared with finite element results. The best agreement is obtained for shallow mild notches. Models of more limited applicability, based on the invariance of the total strain energy density and the strain energy density at the root of the notch, have been applied to some of the specimens.

Boundary element analysis of finite domains under thermal and mechanical shock with the Lord-Shulman theory:

Abstract: A boundary element method based on the Laplace transform technique is developed for transient coupled thermoelasticity problems with relaxation times in a two-dimensional finite domain. The dynamic thermoelastic model of Lord and Shulman (LS) is selected to show how mechanical and thermal energy conversion takes place in a coupled field. The Laplace transform method is applied to the time domain and the resulting equations in the transformed field are discretized using the boundary element method. The nodal dimensionless temperature and displacements in the transformed domain are inverted to obtain the actual physical quantities, using the numerical inversion of the Laplace transform method. The creation and propagation of elastic and thermoelastic waves in a finite domain and their effects on each other are investigated for the first time in this paper. Different relaxation times are chosen to show briefly the events that take place in temperature, displacement and stress fields considering the LS theory...

Improved data reduction for the deep-hole method of residual stress measurement

Abstract: This paper describes an improved data reduction scheme for the deep-hole method of residual stress measurement. The deep-hole method uses the changes in diameter of a reference hole, drilled through the thickness of a component, to determine residual stress. The diameter changes result from the removal of a cylindrical core from the component, where the core is larger than and concentric with the reference hole. The new data reduction seeks to determine the unknown eigenstrain distribution that gives rise to the residual stress state and to the reference hole deformations; once the eigenstrain distribution is found, it is input to an elastic finite element analysis to provide the residual stress distribution in the original component. The new data reduction relies on expressing the unknown eigenstrain field in a polynomial basis, and finding the unknown basis function amplitudes from the measured reference hole diameter changes. The new data reduction is compared with the current technique, and it is shown that the proposed scheme offers several advantages to the current method of data reduction.

An investigation for control of residual stress in roller-straightened rails

Abstract: The cold roller straightening operation is the most critical process for the development of residual stress in rails during manufacturing. Knowledge of the residual stress in ‘as-manufactured’ rails is important for evaluation of the fatigue behaviour of rails during actual use. While experimental investigations have been reported on the induced residual stress in rails, the formulation of an appropriate simulated model for computation of the residual stress generated during the roller straightening process is still in the developmental stage. In the present investigation, an attempt has been made to develop a simulated model using the finite element (FE) method to evaluate the residual stress and to reduce its magnitude by controlling the relevant parameters of the straightening operation. The straightness of the finished rail has also been examined, and a suitable procedure for examination of the straightness of finished rails is indicated. Process parameters are recommended for reducing the residual st...

Fretting fatigue analysis of aluminium conductor wires near the suspension clamp: Metallurgical and fracture mechanics analysis:

Abstract: Fretting fatigue is the main phenomenon inducing reduction of fatigue strength in overhead transmission conductor lines which are subjected to aeolian vibrations. Using the Bersfort ACSR 48/7 conductor, fatigue tests were conducted under several traction forces and relative vibration amplitudes. By metallographic examinations it has been observed that fretting induces microcracks which are mainly located between the keeper edge (KE) and the last point of the contact (LPC) of the conductor at the mouth of the suspension clamp.Under the fatigue tests conditions, several cross-sections of wires in the external layer of the conductor were instrumented using strain gauges. Wire strains recorded near to the suspension clamp show that the alternating strains were predominantly traction strains near the KE and that bending alternating strains become significant near the LPC.On the basis of fatigue tests results and assuming some simplified hypothesis, stress intensity factors were computed at the tip of cracks. T...

Elastoplastic strain concentration factors in finite thickness plates

Abstract: The paper presents a comparison of a detailed finite element modelling of elastoplastic strains at a notch root with experimental Moire interferometric data. The three-dimensional nature of the local constraint at a notch root for elastic or elastoplastic material behaviour is confirmed. The elastoplastic analysis shows that the stress concentration factor ratio from the mid-plane and the surface is practically insensitive to the actual σ—e. relationship when the nominal stress achieves the yield stress.

Experimental study of double cold expansion of holes

Abstract: This paper examines experimentally the effect of double cold expansion on the residual stress field and fatigue behaviour of fastener holes in plates. Measurements of the hoop strain generated by the progressive drawing of the mandrel through the hole, of the retained expansion and of the surface residual stresses were performed on both cold and double cold expanded specimens. Fatigue testing and a fracture surface examination were also carried out for all specimens. It was found that double cold expansion reduces the through-thickness variation of the residual stress field generated and improves the behaviour of fastener holes under fatigue loading.

The effect of high compressive loading on residual stresses and fatigue crack growth at cold expanded holes

Abstract: The effect of monotonic compressive loading on the residual stresses developed at cold expanded fastener holes has been investigated using the neutron and X-ray diffraction techniques. Monotonic loading models the effect of the peak of a fatigue loading sequence experienced before a crack is initiated. It was found that the compressive loading significantly affected the residual stress distribution. A low load relaxed only the stresses near to the bore of the hole, whereas a larger load affected the stress distribution over a greater area. Residual stresses measured at the mandrel entrance face were more affected by the compressive loading than the residual stresses measured at the other segments of thickness. The comparison between the X-ray and neutron diffraction results showed that the techniques complemented each other well, enabling a three-dimensional residual stress distribution to be derived. This distribution was used for modelling the effect of compressive loading on fatigue crack growth, using a linear elastic fracture mechanics approach and assuming a stabilized residual stress field.

Computational modelling of shot-peening effects on crack propagation under fretting fatigue:

Abstract: Recent experimental studies have demonstrated fretting fatigue life enhancement of titanium alloy Ti-6A1–4V specimens after treatment by shot-peening. Because of complexities in tracking crack growth under fretting conditions experimentally, the present work describes computational modelling for crack propagation behaviour in specimens with and without shot-peening. A crack growth model is combined with a finite element submodelling technique to assess the crack trajectory and crack propagation life in the specimens under fretting fatigue. A parametric numerical analysis has been performed to investigate crack trajectories and stress intensity factors along the crack path under different loading conditions. Obtained results revealed the features of the crack growth trajectory and stress intensity factors in the presence of residual stresses from shotpeening. These results also demonstrated a significant (2–3 times) increase in the crack propagation life of shot-peened specimens relative to virgin specimen...

Quadrilateral finite elements for multilayer sandwich plates

Abstract: The bending behaviour of isotropic and laminated composite and sandwich plates has been analysed using two new C° assumed strain quadrilateral finite element formulations based on a refined form of Reddy's higher-order theory. The assumed strain approach ensures that there are no parasitic spurious zero energy modes and no shear locking. The element performances are evaluated on some standard plate tests involving closed-form solutions and experimental results. All results indicate that the present elements have satisfactory convergence properties, accuracy in the results and freedom from any major defects.

Delamination modelling of a curved composite beam subjected to an opening bending moment

Abstract: A theoretical approach is developed for the case of delamination of a curved composite beam under an opening bending moment. This is based on linear curved beam theory coupled with fracture mechanics concepts. The general solution is applied to analyse a specific case of delamination occurring at the mid-plane. The effects of the arc angle of delamination crack and the radius of curvature of the beam on the critical load are also studied.

Simple determination of the axial stiffness for largediameter independent wire rope core or fibre core wire ropes

Abstract: Raoof and Kraincanic recently developed two somewhat different theoretical models for analysing large-diameter wire ropes with either an independent wire rope core (IWRC) or a fibre core. Most importantly, unlike all of the previously available theories (with their often very lengthy mathematical formulations), very encouraging correlations have been found between Raoof and Kraincanic's theoretical predictions of wire rope axial stiffnesses and a fairly large body of experimental data from other sources, hence providing ample support for the reliability of both theoretical models. Raoof and Kraincanic's original models were, however, computer based and involved certain iterative procedures. This potential drawback for practical applications (in an area where, by tradition, the rule of thumb reigns supreme) is overcome in the present paper, which reports details of some simplified (but still accurate) procedures for predicting the no-slip and/or full-slip axial stiffnesses of wire ropes with either an independent wire rope core or a fibre core, with the proposed formulations being amenable to simple hand calculations using a pocket calculator, which is of value to busy practising engineers.

Shape optimization of two-dimensional anisotropic structures using the boundary element method:

Abstract: A shape optimization procedure is developed, using the boundary element method, for two-dimensional anisotropic structures to minimize weight while satisfying certain constraints upon stresses and geometry. A directly differentiated form of boundary integral equation with respect to geometric design variables is used to calculate shape design sensitivities of anisotropic materials. The boundary element method is very suitable for shape optimization and in comparison with the finite element method needs much fewer data, related only to the boundary of the structure being considered. Because a directly differentiated form of the boundary integral equation can be used to determine the derivatives of the objective and constraint functions, the accuracy of computation is very high. Because of the non-linear nature of weight and stresses, the numerical optimization method used in the program is the feasible direction approach, together with the golden section method for the one-dimensional search. Three example...

Evaluation of plastic limit load of piping branch junctions subjected to out-of-plane moment loadings:

Abstract: Under out-of-plane moment loadings, the piping branch junctions (also called tees in engineering) exhibit three kinds of failure mode, namely collapse failure of the branch pipe, global collapse of the intersection due to plastic hinges forming along the intersection line and local instability of the main pipe at the flank. In this work, the common piping branch junctions utilized in petrochemical and power industries with a failure mode of global collapse were investigated, and a new approximate formula for an out-of-plane plastic limit moment was presented. The formula was built on the following process: firstly, an equation between the out-of-plane limit moment and internal force of the branch pipe along the intersection is set up on the basis of the force equilibrium condition. Regarding this internal force as an external load for the main pipe shell, the internal force and moment along the intersection of the main pipe, under the plastic limit state, are then obtained. Finally, referring to the von Mises yield criterion, the approximate plastic limit load of the piping branch junctions subjected to the out-of-plane moment is derived. The accuracy of the new formula is validated by comparison with finite element analysis and experimental results.

Design of a defence hole system for a shear-loaded plate:

Abstract: Stress concentrations associated with circular holes in pure shear-loaded plates can be reduced by up to 13.5 per cent by introducing elliptical auxiliary holes along the principal stress directions. These holes are introduced in the areas of low stresses near the main circular hole in order to smooth the principal stress trajectories.A systematic study based on univariate search optimization method is undertaken by using finite element analysis (FEA) to determine the optimum size and location for an auxiliary defence hole system. The results are validated using RGB (red-green-blue) photoelasticity.

The relationship between the Dang Van criterion and the traditional bulk fatigue criteria

Abstract: A formal relationship is established between the traditional bulk fatigue criteria such as the Goodman rule and the Sines criterion, and the recent crack initiation criterion of Dang Van. The constants implied by the Dang Van procedure may be formally connected to the fatigue limit and mean stress dependence given by the Goodman rule, under conditions of uniaxial loading. The biaxial fatigue criterion of Sines is also compared with the Dang Van procedure. The similarity in the approaches may be further extended to permit finite initiation times to be estimated by the Dang Van criterion when the fatigue limit is exceeded.

On the press fit of a crankpin into a circular web in pressed-up crankshafts

Abstract: The contact stresses induced by press-fitting a crankpin into a crankweb bore in pressed-up crankshafts are analysed for crankwebs possessing a circular geometry. The three-dimensional nature of this problem is reduced to a plane model, where the crankweb is described in terms of an eccentrically bored disc of uniform thickness, while the crankpin is idealized as an annular ring. Two different approaches are employed. Firstly, an elastic plane finite element analysis is carried out for this contact problem. Secondly, based upon the results of the numerical study, three variously approximated plane analytical models are developed. The contact pressure and the circumferential stress by the web bore are investigated, as well as the transmissible torque, where normalized diagrams are provided exploring a variety of disc-type crankweb geometries. Finally, selected three-dimensional finite element results are discussed, which highlight the limits of a plane model.

Study on the transient response and wavelet time—frequency feature of a cracked rotor passage through a subcritical speed

Abstract: The dynamic model in dimensionless form of the transient response of a cracked rotor system is derived, which is based on the simple hinge crack model. By numerical simulation, the transient responses of the uncracked rotor and the cracked rotor are obtained and the subharmonic resonance of the cracked rotor is analysed. The influence of the unbalance, the inhabiting angle and the stiffness variation on the transient response is investigated. The wavelet time-frequency features of the cracked rotor and the uncracked rotor are studied, and the difference between them is discussed. The numerical simulation demonstrates that the wavelet analysis algorithm is valid for the identification of cracked rotor.

On the analysis of singular stress fields Part 2: Application to complete slipping contacts

Abstract: The stress state adjacent to the edge of a complete slipping contact has an implied elastic singularity. Using an asymptotic approach the order of this singularity, and hence the spatial distribution of the local stress field, may be found. The region over which it characterizes the full field solution is found by defining a generalized stress intensity factor K*. In practice, this requires a finite element (FE) analysis. However, the use of isoparametric elements leads to convergence problems which may be circumvented by using special singular elements which incorporate the required shape function. Here, these elements are applied to a complete contact problem for which there is an analytical solution, for comparison purposes, i.e. a rigid square-ended punch sliding along an elastic half-plane. It is shown that the singular elements are able to reproduce the singular field accurately, and that they significantly accelerate convergence when compared with a conventional mesh of isoparametric elements. Addi...

A technique for the determination of post-yield material properties from the small punch test

Abstract: The aim of the present work was to determine post-yield material properties from small punch test results, i.e. from the force-displacement curve obtained in such a test. This determination was mad...

Determination of creep curves from multiple hardening-relaxation testing

Abstract: Multiple hardening and relaxation tests have been carried out on a nickel-based superalloy at 650°C The stress relaxation curves were obtained at selected strain levels, from which the plastic strain rates spanning three decades were obtained Creep curves were simulated from the relaxation test results and compared reasonably well with those obtained from the creep tests This method may be useful in the assessment of creep resistance, particularly during the material development stage

Computation of stresses and deformations for a two-dimensional sliding contact between an elastic layer and a rigid indenter with a rounded profile

Abstract: The two-dimensional indentation problem of an elastic layer by either a wedge with a rounded tip or a flat punch with rounded corners in the presence of friction is investigated numerically. Contact stresses and deformations are presented when the layer is either bonded or resting without friction on a rigid foundation. Moreover, a set of asymptotic solutions for the contact pressure is obtained for an unbonded thin layer (the contact width is significantly larger than the layer thickness). The effects of several parameters on the results are examined.