Showing papers in "Journal of Strain Analysis for Engineering Design in 2005"
TL;DR: In this paper, the authors established a framework for predictive modeling of residual stress states due to surface peening and simulated uniform deformation of the surface layer taking place during shot peening of a thin plate.
Abstract: The beneficial effect of surface peening (including shot peening, laser shock peening, low plasticity burnishing, etc.) on fatigue resistance of structural alloys is well documented and widely used in industry to improve component life. It is perhaps the most widely used technique that relies on the introduction of residual stresses into the component by direct mechanical means. The resulting stress states are usually evaluated experimentally by X-ray diffraction or other stress measurement techniques. In order for shot peening operations to be effective and reliable, the process of introducing residual stresses and strains into peened components must not only be controlled but also be predictable and quantifiable.The present paper establishes a framework for predictive modelling of the residual stress states due to surface peening. Firstly, uniform (within planes parallel to the surface) plastic deformation of the surface layer taking place during shot peening of a thin plate is simulated using the conce...
81 citations
TL;DR: In this paper, the displacement field is determined by using digital image correlation based on images taken at different stages of the mechanical tests, which reveals strain heterogeneities and further localisation in compression tests well below the peak stress.
Abstract: Mechanical compression and tearing tests are carried out on crimped glass wool samples. The displacement field is determined by using digital image correlation based on images taken at different stages of the mechanical tests. A multiscale algorithm is used to resolve accurately fine details of the displacement field. This technique reveals strain heterogeneities and further localisation in compression tests well below the peak stress. Crack formations are identified in tearing tests. Reliability and resolution of the displacement and strain fields are validated by using different window sizes in the correlation analysis.
68 citations
TL;DR: In this paper, a simplified finite element simulation of the out-of-plane distortion caused by fusion butt welding is presented, which is applied to a non-linear elastic finite element model to provide predictions of the final angular and overall deformations of the butt-welded plates.
Abstract: The main aim of the work was to investigate a simplified finite element simulation of the out-of-plane distortion caused by fusion butt welding. The thermal transient part of the simulation made use of a finite element analysis of the two-dimensional cross-section of the weld joint and the thermoelastic-plastic treatment was based on analytical algorithms describing transverse and longitudinal deformations, leading to predictions of transverse angular deformation and longitudinal contraction force. These results were then applied to a non-linear elastic finite element model to provide predictions of the final angular and overall deformations of the butt-welded plates. The validity of the simulation was investigated via full-scale tests on 4m x 1.4m x 5 mm steel plates, butt welded using a flux-cored Ar-CO2 metal-inert gas process. Thermography and thermocouple arrays were used to validate the thermal transient computations and out-of-plane deformations were measured using displacement transducers for transient deformations and a laser scanning system to measure the profiles of the whole plates before and after welding. The results of six full-scale tests are given and comparison with the simulations shows that the procedure provides good prediction of the angular and overall out-of-plane deformations. Prediction accuracy requires account to be taken of initial shape, gravity loading, and support conditions.
66 citations
TL;DR: In this article, a novel microscopic strain mapping technique has been developed based on the analysis of surface topography using digital image correlation (DIC) software, which uses topographic features (such as surface slip traces) found in these images as the input.
Abstract: Measuring the distribution of local strain at the microscopic level is a challenging problem, especially for materials subjected to large overall strain. In the present study, a novel microscopic strain mapping technique has been developed based on the analysis of surface topography using digital image correlation (DIC) software. The input is a series of scanning electron microscopy (SEM) images. The method uses topographic features (such as surface slip traces) found in these images as the input. A commercially available optical strain measurement system (ARAMIS®, which is a trade name of the equipment from GOM mbH, Braunschweig, Germany) that utilizes the DIC methodology is used for this purpose. It was found that the best results were obtained using an incremental approach in which DIC is used to map the local strain increments following a modest amount of macroscopic deformation. This is essential when using topographic features such as slip traces that are not static. The accuracy and scale of the me...
61 citations
TL;DR: A review of recent advances in acoustic emission (AE) studies, primarily on mechanisms and modelling, can be found in this article, where the authors summarized the current status and new goals are discussed in conjunction with analytical, experimental, and electronic tools now available.
Abstract: This article reviews recent advances in acoustic emission (AE) studies, primarily on mechanisms and modelling. Methods of signal analysis used in acoustic emission have improved significantly, allowing various AE signals to be evaluated critically. The understanding of AE from materials during fracture has advanced greatly, but that due to deformation processes remains elusive. Current status is summarized and new goals are discussed in conjunction with analytical, experimental, and electronic tools now available.
56 citations
TL;DR: In this article, a general autofrettage model that incorporates the material strain-hardening relationship and the Bauschinger effect, based upon the actual tensile-compressive stress-strain curve of a material is proposed.
Abstract: The basic autofrettage theory assumes elastic-perfectly plastic behaviour. Because of the Bauschinger effect and strain-hardening, most materials do not display elastic-perfectly plastic properties and consequently various autofrettage models are based on different simplified material strain-hardening models, which assume linear strain-hardening or power strain-hardening or a combination of these strain-hardening models. This approach gives a more accurate prediction than the elastic-perfectly plastic model and is suitable for different strain-hardening materials. In this paper, a general autofrettage model that incorporates the material strain-hardening relationship and the Bauschinger effect, based upon the actual tensile-compressive stress-strain curve of a material is proposed. The model incorporates the von Mises yield criterion, an incompressible material, and the plane strain condition. Analytic expressions for the residual stress distribution have been derived.Experimental results show that the pr...
56 citations
TL;DR: In this paper, the local reinforcement effect in tension is studied by using a simple theoretical model by considering a strain gauge mounted on a semi-infinite plate having the same width of the strain gauge and subjected to a uniaxial tension load.
Abstract: The reinforcement effect of electrical resistance strain gauges is well documented in the technical literature. In this paper the local reinforcement effect in tension is studied by using a simple theoretical model by considering a strain gauge mounted on a semi-infinite plate having the same width of the strain gauge and subjected to a uniaxial tension load. Neglecting the effect of the adhesive layer and considering the interface shear stress as an exponential distribution, the proposed model gives a closed-form solution. In detail, this model permits a simple formula to be obtained which allows the user to correct the local reinforcement effect provided that a proper calibration is performed by installing a strain gauge, of the same type as that used on the structure, on a low modulus material. Experimental evidence of the proposed method is shown. Experimental proof of the positive effect of large grid lengths on the local reinforcement effect is also reported.
55 citations
TL;DR: In this article, the results of an experimental investigation on the effect of subcritical damage on the residual strength properties of notched composite laminates are presented, based on a procedure based on the procedure described in this paper.
Abstract: In this paper the results of an experimental investigation on the effect of subcritical damage on the residual strength properties of notched composite laminates are presented. A procedure based on...
45 citations
TL;DR: In this paper, the application of acoustic emission (AE) for monitoring internal combustion (IC) engines is reviewed, with reference to the development of AE data handling and analysis approaches for engines.
Abstract: The application of acoustic emission (AE) for monitoring internal combustion (IC) engines is reviewed in this paper. Recent developments in monitoring mechanical events and processes using AE are discussed. The high spatial and temporal fidelity of the AE signals acquired from engines in service make it possible to focus monitoring strategies on individual events and processes. This gives AE the advantages of earlier fault diagnosis and source location whereas other techniques generally monitor symptoms of faults. Monitoring of engine speed, event timing, and reconstitution of processes such as injection and combustion are also possible. These capabilities of AE monitoring are discussed with reference to the development of AE data handling and analysis approaches for engines.
38 citations
TL;DR: Unit cell models have been proposed to predict the constitutive law and failure of ductile materials with complex microstructures, such as ferritic nodular cast iron and particulate metal matrix as discussed by the authors.
Abstract: Unit cell models have been proposed to predict the constitutive law and failure of ductile materials with complex microstructures, such as ferritic nodular cast iron and particulate metal matrix co...
37 citations
TL;DR: The use of acoustic emission in orthopaedics, in particular for the evaluation of hip replacement constructs, is reviewed in this article, where three case studies undertaken at the University of Southampton are presented, in which acoustic emission on-line monitoring has been used to evaluate the performance of simulated artificial hip replacement construct and their constituents during static and fatigue testing.
Abstract: Traditionally, orthopaedic research has focused upon the assessment of individual components in an implanted construct. A great deal of research has investigated the durability of the metallic stem, even though this is the most robust component in the implanted system. Standards have been developed for the structural assessment of the implant and even the bone cement which holds the implant in place in the bone. However, the construct as a whole, and its short- and long-term structural integrity, are rarely assessed, and few methods have been established to monitor and predict the mechanisms leading to failure. These are necessary to ensure that any new implants entering the market will perform satisfactorily and prevent premature revision surgery. The acoustic emission (AE) technique offers the capability of monitoring structural degradation passively and in real time, and can distinguish failure mechanisms and their location through the analysis of AE parameters. In the present paper, the use of acoustic emission in orthopaedics, in particular for the evaluation of hip replacement constructs, is reviewed. Following this, three case studies undertaken at the University of Southampton are presented, in which acoustic emission on-line monitoring has been used to evaluate the performance of simulated artificial hip replacement constructs and their constituents during static and fatigue testing. In Case Study 1, the fatigue behaviour of bone cement is characterized; in Case Study 2, the residual stresses induced in the construct as a result of bone cement cure are investigated; in Case Study 3, the mechanisms leading to failure of a carbon fibre reinforced plastic hip stem during fatigue testing are characterized.
TL;DR: The implication of selecting different contact algorithms in solving a contact problem by a submodeling approach is highlighted using the example of a partial slip Cattaneo-Mindlin problem.
Abstract: The implication of selecting different contact algorithms in solving a contact problem by a submodelling approach is highlighted using the example of a partial slip Cattaneo-Mindlin problem. It is ...
TL;DR: In this paper, a finite element creep continuum damage mechanics (CDM) analysis of thin-section butt-welded, internally pressurized pipes, and of uniaxial cross welded tension testpieces made of Cr-Mo-V steels is presented.
Abstract: The paper reports the finite element creep continuum damage mechanics (CDM) analysis of the creep rupture behaviour of thin-section butt-welded, internally pressurized pipes, and of uniaxial cross-welded tension testpieces made of Cr-Mo-V steels. The CDM analyses are shown to predict accurately lifetimes and failure mechanisms observed from metallographic analyses of sectioned components.The paper then addresses the lifetime prediction of components by comparing predictions made using British Standards BSi PD 5500 with the results of the experiments. Predictions have been based on uniaxial plain bar data for both parent and Type IV materials; both of these have been obtained by integration of constitutive equations. Comparison of predicted and experimental weldment lifetimes has been made using a weld strength reduction factor. It is found that the required factors are very dependent on temperature and the ratio of axial to hoop pipe stresses.Finally, the paper examines the British Energy Generation Limit...
TL;DR: In this paper, a displacement discontinuity method with crack-tip elements was used to deal with the microdefect-finite main crack linear elastic interaction by means of a displacement-discrepancy method.
Abstract: This paper deals with the microdefect-finite main crack linear elastic interaction by means of a displacement discontinuity method with crack-tip elements. It consists of the non-singular displacement discontinuity element presented by Crouch and Starfield and the crack-tip displacement discontinuity elements presented by the author. Two models are used: one is ‘a finite main crack interaction with a collinear elliptical microdefect (hole)’ in an infinite medium; the other is ‘a finite main crack interaction with a pair of symmetric collinear elliptical microdefects (holes)’ in an infinite medium. In numerical computations, the ratio of the elliptical horizontal axis length to the main crack length is varied from 0.05 to 0.4 and the elliptical aspect ratio is taken as 0.0, 0.5, and 1.0. Thus, the present numerical results reveal the effect that the relative size of the elliptical microdefect (hole) to the main crack has on the microdefect-finite main crack interaction.
TL;DR: In this article, the incremental blind hole-drilling and X-ray diffraction methods were used to measure the residual stress field introduced by shot peening in aluminium alloy 6082-T5 plates.
Abstract: The incremental blind hole-drilling and the X-ray diffraction methods were used to measure the residual stress field introduced by shot peening in aluminium alloy 6082-T5 plates. Two peening treatm...
TL;DR: In this article, the Neuber method was adapted and extended for predicting creep equivalent notch stresses and strains, based on a time-stepping integration scheme, and a linear interpolation method was used for predicting elastic-plastic equivalent stresses and strain.
Abstract: This paper describes general techniques for predicting multiaxial notch stresses and strains under elastic-plastic and creep conditions. The Neuber method, which is often used in elastic-plastic analysis, has been adapted and extended for predicting creep equivalent notch stresses and strains, based on a time-stepping integration scheme. A linear interpolation method, often used in creep analysis, is adapted and extended for predicting elastic-plastic equivalent stresses and strains. Then notch principal stresses and strains are obtained by applying plasticity theory in combination with assumptions concerning the ratios of the stress or strain components. The accuracy of the predicted equivalent and principal stress and strain values are assessed by comparing predictions based on them with results obtained from finite element analyses.
TL;DR: In this article, the multi-parameter stress field equations of Deng are simplified for use by experimentalists to evaluate the stress field parameters by digital photoelasticity using an overdeterministic least-squares technique.
Abstract: Photoelastic evaluation of the stress intensity factor (SIF) for a crack in a bimaterial tangential to the interface is hitherto confined to the use of only a singular stress field equation. In this paper, the multi-parameter stress field equations of Deng are simplified for use by experimentalists to evaluate the stress field parameters by digital photoelasticity using an overdeterministic least-squares technique. A bimaterial Brazillian disc with a central interface crack is selected as the model for study as different mode mixities could be easily simulated by changing the crack orientation angle. The use of SIF evaluation based on a singular stress field equation is found to be inadequate for the problems considered. On the other hand, the use of a multi-parameter stress field equation is quite successful in evaluating the stress field for various mode mixities and for two values of bimaterial constant. It is shown that the new procedure allows data collection from a larger zone, which helps to simpli...
TL;DR: In this article, a full three-dimensional (3D) thermo-mechanical finite element (FE) model has been developed to simulate the step-by-step multipass welding process.
Abstract: A full three-dimensional (3D) thermo-mechanical finite element (FE) model has been developed to simulate the step-by-step multipass welding process. Non-linearities associated with welding, such as a moving heat source, material deposition, temperature-dependent material properties, latent heat, and large deformations, were taken into account. The model was applied to multipass butt-welded mild steel plate and girth butt-welded stainless steel pipe for validation. The simulation results were compared with independently obtained experimental data and numerical predictions from two-dimensional (2D) generalized plane strain and axisymmetric models. Good agreements between the 3D predictions and experimental data have been obtained. The computational model has the potential to be applied to multipass welded complex geometries for residual stress prediction.
TL;DR: In this article, the optimal ratio between the inside and outside diameters of the hub is calculated, which maximizes the load transmitted by the joint, regardless of the frictional coefficient (up to 1), of the kind of loading (torsional or axial), and of the material response (brittle or ductile).
Abstract: The stress state in frictional interference fits under torsional and axial loading is examined. The optimal ratio between the inside and outside diameters of the hub is calculated, which maximizes the load transmitted by the joint. Design formulae and charts are provided, giving the most efficient aspect ratio of the hub for all practical situations. It is found that the maximum load capacity is achieved for an aspect ratio in the range from 0.5 to 0.7, regardless of the frictional coefficient (up to 1), of the kind of loading (torsional or axial), and of the material response (brittle or ductile).
TL;DR: In this paper, the design, manufacturing, testing, and finite element analysis (FEA) of glass-fibre-reinforced polyester leaf springs for rail freight vehicles are summarized.
Abstract: This paper summarizes the design, manufacturing, testing, and finite element analysis (FEA) of glass-fibre-reinforced polyester leaf springs for rail freight vehicles. FEA predictions of load-deflection curves under static loading are presented, together with comparisons with test results. Bending stress distribution at typical load conditions is plotted for the springs. The springs have been mounted on a real wagon and drop tests at tare and full load have been carried out on a purpose-built shaker rig. The transient response of the springs from tests and FEA is presented and discussed.
TL;DR: In this article, a set of multiaxial mechanism-based unified viscoplastic-damage constitutive equations is presented, which models the evolution of grain boundary (intragranular) and plasticity-induced (intergranular) damage for a free-cutting steel tested over a range of temperatures and strain rates on a Gleeble thermomechanical simulator.
Abstract: During axisymmetric hot tensile testing, necking normally takes place due to the thermal gradient and the accumulation of microdamage. This paper introduces an integrated technique to predict the damage and necking evolution behaviour. Firstly, a set of multiaxial mechanism-based unified viscoplastic-damage constitutive equations is presented. This equation set, which models the evolution of grain boundary (intragranular) and plasticity-induced (intergranular) damage, is determined for a free-cutting steel tested over a range of temperatures and strain rates on a Gleeble thermomechanical simulator. This model has been implemented using the CREEP subroutine of the commercial finite element (FE) solver ABAQUS. Numerical procedures to simulate axisymmetric hot tensile deformation are developed with consideration of the thermal gradient along the axis of the tensile testpiece. FE simulations are carried out to reproduce the necking phenomenon and the evolution of plasticity-induced and grain boundary damage. ...
TL;DR: In this paper, an efficient and accurate semi-analytical method is developed to calculate the elastodynamic field produced by localized dynamic loads in a relatively thick composite plate, where two types of loads are considered: a pencil lead break source located on the surface and a localized shear delamination within the interior of the plate.
Abstract: In this paper, an efficient and accurate semi-analytical method is developed to calculate the elastodynamic field produced by localized dynamic loads in a relatively thick composite plate. Two types of loads are considered: a pencil lead break source located on the surface and a localized shear delamination within the interior of the plate. In the case of the pencil lead break source, the calculated results for the surface motion are compared with those obtained in laboratory experiments on a 4.4mm thick 32 layered cross-ply graphite/ epoxy using high-fidelity broadband transducers. The waveforms consist of both flexural and extensional modes; the amplitude variations of these modes are found to be strongly dependent on their propagation direction. For the delamination source, the results from the exact calculation are compared with those from an approximate laminate theory with a shear correction factor and 'moment tensor' representation of the source. The results obtained by the two methods are shown to have excellent agreement in the low-frequency ranges. Although the motion due to the delamination is dominated by flexural waves of lower frequency in both thin and thick plates, the presence of extensional waves are observed in thicker laminates.
TL;DR: In this article, a half-plane covered with a prestretched layer is assumed to be subjected to a uniformly distributed harmonic load acting on a strip extending to infinity in the x3 direction, which is perpendicular to the x1-x2 plane and is of width 2a in the 1 direction.
Abstract: Within the framework of the piecewise homogeneous body model, by employing the three-dimensional linearized theory of elastic waves in initially stressed bodies the dynamical problem of the stress distribution in a half-plane covered with a prestretched layer is investigated. It is assumed that the free face plane of the covered layer is subjected to a uniformly distributed harmonic load acting on a strip extending to infinity in the x3 direction, which is perpendicular to the x1-x2 plane and is of width 2a in the x1 direction. The plane-strain state in the x1-x2 plane is analysed.The corresponding boundary-value problems are investigated by employing the exponential Fourier integral transformation. The numerical results regarding the interface normal stress distribution are presented. The influences of the problem parameters and pre-stretching of the covered layer on this distribution are analysed. Practical engineering application fields of the results are suggested.
TL;DR: In this paper, a frictionless theory was proposed to predict the resultant torque and lift in the links as non-dimensionalized functions of the angle of twist and axial load.
Abstract: Chain in both its forms - common (or stud-less) and stud-link - has many engineering applications. It is widely used as a component in the moorings of offshore floating systems, where its ruggedness and corrosion resistance make it an attractive choice. Chain exhibits some interesting behaviour in that when straight and subject to an axial load it does not twist or generate any torque, but if twisted or loaded when in a twisted condition it behaves in a highly non-linear manner, with the torque dependent upon the level of twist and axial load. Clearly an understanding of the way in which chains may behave and interact with other mooring components (such as wire rope, which also exhibits coupling between axial load and generated torque) when they are in service is essential. However, the sizes of chain that are in use in offshore moorings (typical bar diameters are 75 mm and greater) are too large to allow easy testing. This paper, which is in two parts, aims to address the issues and considerations relevant to torque in mooring chain. The first part introduces a frictionless theory that predicts the resultant torques and 'lift' in the links as non-dimensionalized functions of the angle of twist. Fortran code is presented in an Appendix, which allows the reader to make use of the analysis. The second part of the paper presents results from experimental work on both stud-less (41 mm) and stud-link (20.5 and 56 mm) chains. Torsional data are presented in both 'constant twist' and 'constant load' forms, as well as considering the lift between the links.
TL;DR: In this paper, the theoretical consideration of the caustics and the photoelasticity due to a concentrated load applied at a point of the straight boundary of the semi-infinite plate was studied.
Abstract: In this paper the theoretical consideration of the caustics and the photoelasticity due to a concentrated load applied at a point of the straight boundary of the semi-infinite plate was studied. Then, the load distribution in a roller bearing was experimentally determined in terms of caustics and photoelasticity.
TL;DR: In this paper, the effect of phase transformation on the residual stresses generated by the quenching process was analyzed in two different models: complete (thermoelastoplastic model with austenite-martensite phase transformation) and without phase transformation.
Abstract: The determination of residual stresses is an important task in the analysis of the quenching process. Nevertheless, because of the complexity of the phenomenon, many simplifications are usually adopted in the prediction of these stresses for engineering purposes. One of these simplifications is the effect of phase transformation. Many studies analyse residual stresses generated by the quenching process considering a thermoelasto- plastic approach, neglecting phase transformation. The present study analyses the effect of austenite-martensite phase transformation during quenching in the determination of residual stresses, comparing two different models: complete (thermoelastoplastic model with austenite-martensite phase transformation) and without phase transformation (thermoelasto- plastic model without phase transformation). The finite element method is employed for spatial discretization together with a constitutive model that represents the thermomechanical behaviour of the quenching process. Progressive induction hardening of steel cylinders with semicircular notches is of concern. Numerical simulations show situations where great discrepancies are introduced in the predicted residual stresses if phase transformation is neglected.
TL;DR: In this paper, an approach to select the tube wall thickness distribution of streamlined tubes intended for use in heat exchangers is developed, where the goal is to retain a streamlined outer profile (resist deformation) and to prevent strain failure due to the applied internal pressure.
Abstract: An approach to select the tube wall thickness distribution of streamlined tubes intended for use in heat exchangers is developed. The goal is to retain a streamlined outer profile (resist deformation) and to prevent strain failure due to the applied internal pressure. The effect of the tube wall thickness distribution on heat transfer is also considered. The strain is calculated as a function of several dimensionless geometric ratios and the ratio of the internal pressure to material modulus. Using the finite element method, a set of dimensionless design curves is created for elliptical tube geometries. From these curves, a range of possible materials and tube geometries can be selected that meet a specific strain limit. To illustrate the approach, structure-satisfied elliptical designs are selected and their thermal performance is evaluated for an automotive radiator and an automotive charge air cooler made of polymeric materials. The same method can be extended to tubes of other shapes and materials.
TL;DR: In this paper, the effect of the tube curvature is considered and a new weight function for longitudinal cracks in thin pipes is derived for the deepest point of a semi-elliptical surface crack.
Abstract: Owing to the complex geometry and non-uniform stress distribution, it is extremely difficult to obtain an accurate value for the analytical stress intensity factor (SIF) solution for a surface crack in a tubular welded joint. It is usually predicted using three-dimensional T-butt SIF solutions in conjunction with appropriate load-shedding models. The problem with this approach is that the effect of the tube curvature is ignored. Thus it may not represent the accurate stress intensity at the tip of the crack and stress redistribution resulting from the reduction of member stiffness with crack growth. Assuming that the relative influence of the weld toe for the deepest point SIF of a semi-elliptical surface crack in a thin pipe is the same as that for an edge crack of the same depth in a flat plate under the same stress distribution and using the weight function for longitudinal cracks in thin pipes as the reference solution, a new weight function in a closed form has been derived for the deepest point of a...
TL;DR: In this paper, the authors presented the application of the weight function method for the calculation of elastic T-stress for semi-elliptical surface cracks in finite-thickness plates.
Abstract: This paper presents the application of the weight function method for the calculation of elastic T-stress for semi-elliptical surface cracks. First, the weight function method for the calculation of T-stress previously developed for two-dimensional crack problems was extended for the T-stress calculation for three-dimensional crack problems. Then, the T-stress weight functions for the deepest point (corresponding to the parametric angle ϕ = 90°) and for any general point (5° ≤ ϕ < 90°) along the crack front of semi-elliptical surface cracks in finite-thickness plates for wide ranges of crack aspect ratios a/c and relative depths a/t were derived. The resulting weight functions were validated using available finite element results for non-linear stress fields and remote tension and bending cases, and very good agreement was achieved. The weight functions are suitable for the calculation of the T-stress under complex loading conditions for any general point (5° ≤ ϕ ≤ 90°) of surface cracks with wide ranges ...
TL;DR: In this paper, a modified Neuber method, using an appropriate scaling function, has been proposed to determine the maximum principal stress in the plane of the crack from the equivalent (von Mises) stress predicted by the Neuber approach.
Abstract: Under linear elastic and elastic-plastic conditions the K field and the HRR (Hutchinson-Rice-Rosengren) field respectively are expected to provide an accurate representation of the stress field close to the crack tip in an elastic-plastic material. It has recently been proposed in French and UK defect assessment procedures that the Neuber method, originally developed for sharply curved notches, provides an alternative approach to estimate both notch and crack-tip stress fields, for use in conjunction with the sigma-d (� d) method to predict creep crack initiation times. In this work, the crack-tip stress fields under plane strain conditions, predicted from the Neuber approach, are compared with the HRR and K fields as well as those obtained from full-field finite element calculations. A compact tension and a single edge notched tension specimen have been examined; the material model used is the Ramberg-Osgood, power law plasticity model. As expected, the K field and HRR field have been found to provide a good representation of the near-tip fields at low and high loads respectively. Satisfactory solutions have also been obtained through the use of the reference stress to estimate the amplitude of the crack-tip stress in conjunction with the HRR field. The Neuber approach provides a good estimate of the equivalent (von Mises) stresses over the full range of load levels. However, but the use of the Neuber approach directly to predict the maximum principal stress in the plane of the crack provides a non-conservative prediction. A modified Neuber method, using an appropriate scaling function, has been proposed to determine the maximum principal stress in the plane of the crack from the equivalent (von Mises) stress predicted by the Neuber approach. Using the proposed method, a significantly improved estimate of the crack-tip stresses is obtained.