Showing papers in "Journal of Strain Analysis for Engineering Design in 2015"
TL;DR: In this paper, a modified stress function approach is developed for reconstruction of residual stress and eigenstrain fields from limited experimental measurements, which is successfully applied to three experimental case studies where residual stresses are introduced by surface peening.
Abstract: A modified stress function approach is developed for reconstruction of residual stress and eigenstrain fields from limited experimental measurements. The modified approach is successfully applied to three experimental case studies where residual stresses are introduced by surface peening. The smooth reconstructed residual fields not only minimize the deviation of measurements from its approximation but also satisfy all continuum mechanics requirements. Furthermore, a comprehensive discussion is performed on regularity of the solution in Tikhonov scheme and the regularization parameter is then determined utilizing Morozov discrepancy principle. Newton iterative method is also shown to have an excellent fast convergence to the regularization parameter while effectively reduces the computational cost.
47 citations
TL;DR: In this article, a multiview framework is proposed to perform stereocorrelation by resorting to isogeometric descriptions of the observed 3D surfaces, where the three-dimensional surface is represented by a 3D polygon.
Abstract: It is proposed to develop a multiview framework to perform stereocorrelation by resorting to isogeometric descriptions of the observed three-dimensional surfaces. Once the three-dimensional surface...
43 citations
TL;DR: In this article, the micro-scale ring-core focused ion beam-digital image correlation technique is used for quantifying absolute in-plane residual stresses, which can provide great improvements in understanding the complex interactions between microstructure, mechanical state, mode(s) of failure and structural integrity.
Abstract: Quantification of residual stress gradients can provide great improvements in understanding the complex interactions between microstructure, mechanical state, mode(s) of failure and structural integrity. Highly focused local probe non-destructive techniques such as X-ray diffraction, electron diffraction or Raman spectroscopy have an established track record in determining spatial variations in the relative changes in residual stress with respect to a reference state for many structural materials. However, the interpretation of these measurements in terms of absolute stress values requires a strain-free sample often difficult to obtain due to the influence of chemistry, microstructure or processing route. With the increasing availability of focused ion beam instruments, a new approach has been developed which is known as the micro-scale ring-core focused ion beam-digital image correlation technique. This technique is becoming the principal tool for quantifying absolute in-plane residual stresses. It can b...
43 citations
TL;DR: In this paper, a comprehensive theoretical and numerical study on the cyclic elastic-plastic notch stress and strain distributions is carried out, where the incremental cyclic plasticity theory is extended to the study of three-dimensional effects at the tip of rounded notches in plates of finite thickness.
Abstract: In this work, a comprehensive theoretical and numerical study on the cyclic elastic–plastic notch stress and strain distributions is carried out. In more detail, the incremental cyclic plasticity theory, already proposed by other authors to determine the actual stress and strain state arising in two-dimensional or axisymmetric notched components, is extended to the study of three-dimensional effects at the tip of rounded notches in plates of finite thickness. The analytical frame is initially validated considering a number of plane problems and later modified to consider three-dimensional effects. Different notch geometries are investigated, such as plane specimens with finite thickness weakened by circular holes, U-notches and rounded V-notches subjected to cyclic mode-I loading. Theoretical results based on the incremental cyclic plasticity theory are compared with time-consuming elastic–plastic finite element analyses carried out with a commercial finite element code showing a very satisfactory agreement. Finally, a link between the averaged strain energy density criterion and the area subtended by the hysteresis loops tied to the different stress and strain components acting at the notch tip has been investigated.
31 citations
TL;DR: In this article, a new understanding on the deformation mechanics of flexible roll forming and the occurrence of flange wrinkling was presented, based on the experimental and numerical simulation of flexible-roll forming.
Abstract: This article presents a new understanding on the deformation mechanics of flexible roll forming and is focused on the occurrence of flange wrinkling. The presentation draws from the experimental and numerical simulation of flexible roll forming to the determination of the wrinkling limits by means of a new theoretical and experimental methodology based on the utilization of rectangular test specimens loaded in axial compression. This research work is performed in mild steel sheets and the results show that the combined evolution of the effective strain with stress triaxiality obtained from finite element modelling of flexible roll forming and from the rectangular test specimens loaded in axial compression can be successfully utilized to predict the occurrence of flange wrinkling in variable cross-sectional profiles produced by flexible roll forming. The proposed methodology can, therefore, be considered an alternative to existing approaches based on simplified analytical and numerical procedures.
30 citations
TL;DR: Strain field evolution on the surface of aluminum sheet D16 and 2024-T3 alloys has been analyzed during static deformation and during specific high-speed impact and oscillation loading as mentioned in this paper.
Abstract: Strain field evolution on the surface of aluminum sheet D16 and 2024-T3 alloys has been analyzed during static deformation and during specific high-speed impact and oscillation loading—dynamical non-equilibrium process. Experiments have been conducted using an original mechanical testing technique and a specially developed software solution for non-contact study of strain field using digital image correlation fitted with a high-speed camera. It has been established that deformation process kinetics for tested aluminum alloys after a dynamical non-equilibrium process during further static deformation changes as compared with a process of static deformation mainly manifests itself in the increase in general alloy ductility and delay in “neck formation.” It has been shown that strain field is an important indicator for deformation band structure formation in the tested materials.
29 citations
TL;DR: In this paper, a novel noncontact strain measurement technology for smart skin is proposed, in which the sensors are single-walled carbon nanotubes, and the method exploits the characteristic short-wave infrared fluorescence signatures of semiconducting single-Walled carbon-nanotubes and the systematic shifts of their fluorescence wavelengths when the nanots are axially strained.
Abstract: Progress is reported in the development of a novel non-contact strain measurement technology in which the sensors are single-walled carbon nanotubes. This approach exploits the characteristic short-wave infrared fluorescence signatures of semiconducting single-walled carbon nanotubes and the systematic shifts of their fluorescence wavelengths when the nanotubes are axially strained. A strain-sensing smart skin is prepared by coating the surface to be monitored with a thin film of a composite containing well-dispersed single-walled carbon nanotubes embedded in a urethane varnish host. Strain in the surface transfers through the host polymer to the embedded nanotubes. The nanotube strains are then quantitatively monitored by exciting the region of interest with a visible laser beam and capturing and analyzing the resulting single-walled carbon nanotube fluorescence spectrum. High-quality spectra are shown for strain-sensing smart skin films in which the nanotubes were pre-processed by selective extraction w...
27 citations
TL;DR: In this article, the roller straightening as the fin of a railway train was shown to have a significant influence on the rail functional properties and reliability in service life, and the residual stresses in railway rails were analyzed.
Abstract: Residual stresses in railway rails have a significant influence on the rail functional properties and reliability in service life. Already during the production, the roller straightening as the fin...
20 citations
TL;DR: In this article, the analysis involved subjecting DP 500 steel to prefatigue loads, and then tension at high strain rates using Hopkinson bar, and a digital image correlation method was used to investigate how the pre-fatigue load affected the performance of the steel.
Abstract: The analysis involved subjecting DP 500 steel to pre-fatigue loads, and then tension at high strain rates using Hopkinson bar. Digital image correlation method was used to investigate how the pre-f...
19 citations
TL;DR: The true stress-strain curve has a significant role in the analysis of deformation in theoretical plasticity and numerical simulations as discussed by the authors, and it has been used extensively in deformation analysis.
Abstract: The true stress–strain curve has a significant role in the analysis of deformation in theoretical plasticity and numerical simulations. Because of the triaxial state of stress in the neck zone, the...
18 citations
TL;DR: In this paper, a new prediction model of stress relaxation from creep data in terms of average creep rate was established and an incremental calculation procedure was further established to obtain stress relaxa...
Abstract: A new prediction model of stress relaxation from creep data in terms of average creep rate was established. An incremental calculation procedure has been further established to obtain stress relaxa...
TL;DR: The use of single-colour image for determining the fringe orders in digital photoelasticity has gained importance in recent years, and in this, the fringe order are obtained by comparing the colou
Abstract: The use of single-colour image for determining the fringe orders in digital photoelasticity has gained importance in recent years, and in this, the fringe orders are obtained by comparing the colou
TL;DR: In the transient regime, for geometries where the contact area cannot be a... as mentioned in this paper, contact problems with wear are often modelled according to the Reye-Archard law that applies locally to the wearing parts.
Abstract: Contact problems with wear are often modelled according to the Reye–Archard law that applies locally to the wearing parts. In the transient regime, for geometries where the contact area cannot be a...
TL;DR: In this paper, a review of different methods for residual stress mapping at the micron scale highlighting their relative merits and limitations with the aim of guiding the user towards the most appropriate techniques for a given application.
Abstract: The advent of dual-beam focused ion beam - field emission gun scanning electron microscope (FIB-SEM) imaging and milling systems in combination with digital image correlation (DIC) analysis has made it possible to make very fine excisions and to record the resulting displacements with nanometre precision. This has led to novel implementations of macroscale residual stress measurement methods to the microscale, for example, micro-slotting, micro-hole drilling and so on. This review article outlines the different methods for residual stress mapping at the micron scale highlighting their relative merits and limitations with the aim of guiding the user towards the most appropriate techniques for a given application. These open new possibilities for residual stress measurement not just at the continuum scale but even for mapping stresses within grains. In addition, recent advances in milling throughput promised by new dual-beam plasma focused ion beam systems promise to help bridge the gap between the conventi...
TL;DR: In this paper, a fractography study revealed that in the case of axial feed, the nature of fracture was ductile; whereas in the fixed condition, some brittle characteristics were seen.
Abstract: Tube hydroforming is an advanced manufacturing process in which a tube is placed inside a die cavity and plastically deformed under hydraulic pressure, so that it takes the shape of the die. This process is commonly applied in the automotive and aerospace sectors. Welded tubes are commonly used in the hydroforming process. In this work, therefore, the entire study is carried out on resistance-welded tubes. Forming limit diagram is a measure of formability of any forming process; and in the case of the tube hydroforming process, it was obtained by deforming the tubes under different strain paths. A simulation of the hydroforming process was carried out using the finite element–based commercial software, PAM-STAMP 2G. The forming limit diagram obtained through experiments was predicted using this simulation. A fractography study revealed that in the case of axial feed, the nature of fracture was ductile; whereas in the fixed condition, some brittle characteristics were seen. In these experiments, it was obs...
TL;DR: In this paper, the main aim of the paper is to understand whether biaxial stress fields have a significant impact on the rate of growth of fatigue cracks in engineered products.
Abstract: The main aim of this article is to understand whether biaxial stress fields have a significant impact on the rate of growth of fatigue cracks. Many components in engineered products are subjected t...
TL;DR: A new version of the well-known Brazilian disk specimen weakened by a dumbbell-shaped slit with two key-shaped ends, called keyhole notched Brazilian disk, made of polymethylmethacrylate, was proposed in this paper.
Abstract: A new version of the well-known Brazilian disk specimen weakened by a dumbbell-shaped slit with two key-shaped ends, called key-hole notched Brazilian disk specimen, made of polymethylmethacrylate,...
TL;DR: In this article, the authors used the contour method and finite element models together with knowledge of the surface deformation resulted from the stress relaxation along a newly cut-plane to construct the residual stresses in commercially available float glass and showed that the residual stress depth profile of float glass is parabolic.
Abstract: Contour method–based finite element models together with knowledge of the surface deformation resulted from the stress relaxation along a newly cut-plane were used to construct the residual stresses in commercially available float glass. The results show that the residual stress depth profile of float glass is parabolic. The constructed residual stress profiles, validated to some extent against results of scattered light polariscope experiments, were then used to establish the misfit strains (i.e. eigenstrains) existed in the original glass specimens. It is shown that despite the modelling uncertainty of the contour method and the limitations associated with the scattered light polariscope measurements, the eigenstrain depth profile in a given float glass specimen can be determined to an acceptable accuracy. The article shows that once the underlying eigenstrain distribution in a given thickness of glass has been determined, the complete residual stress distribution can simply be determined by incorporati...
TL;DR: In this paper, the authors present the procedure to obtain constitutive equations to express the creep behavior of Araldite 2015 epoxy adhesive using the results of the uniaxial creep tests.
Abstract: This article presents the procedure to obtain constitutive equations to express the creep behavior of Araldite 2015 epoxy adhesive using the results of the uniaxial creep tests. The experimental da...
TL;DR: In this article, the authors considered the thermal contact between a magneto-electro-elastic material halfplane and a rigid flat punch, where the punch was assumed to be a perfect thermal insulator and electro-magnetic conductor.
Abstract: This article is concerned with the thermal contact between a magneto-electro-elastic material half-plane and a rigid flat punch. The punch is assumed to be a perfect thermal insulator and electro-magnetic conductor. The sliding speed of the punch over the surface of the magneto-electro-elastic material half-plane is a small constant far slower than the shear wave speed of the magneto-electro-elastic material half-plane, which generates the heat flux with its value proportional to the contact pressure, friction coefficient and sliding speed. The contact problem is reduced to Cauchy-type singular integral equations of the first and the second kinds, which are then solved numerically to obtain the contact stress, electric displacement, magnetic induction and surface temperature. Numerical results show that the friction coefficient and sliding speed can affect the magnitude of the surface temperature and magneto-electro-elastic fields.
TL;DR: In this paper, strain-controlled tests were conducted to study the cyclic behavior of oxygen-free high thermal conductivity pure copper at different strain ranges and each cycle of the hysteresis curve was divided into a tensile and a compressive half cycle.
Abstract: Although attempts have been devoted to consider the strain range effect in the material models, identification of material constants for accurate modeling the material response under cyclic loading within a wide range of strain amplitude is still a challenge. The experiments show that the cyclic stress–strain curves are severely dependent on the strain range for ductile metals. In most of the cyclic material models, only the stabilized cycle is considered to compute the constants of the models. Considering this strategy in the simulation of ductile metals subjected to cyclic loading may lead to erroneous results particularly for the initial cycles of the loading. In this study, strain-controlled tests were conducted to study the cyclic behavior of oxygen-free high thermal conductivity pure copper at different strain ranges. Each cycle of the hysteresis curve was divided into a tensile and a compressive half cycle. The yield stress and the constants of the four-rule Chaboche kinematic hardening model were ...
TL;DR: The mechanical properties of welded boiler tubes used in power plants can be significantly altered as a result of the fabrication history, such as pre-straining and heat treatment as mentioned in this paper.
Abstract: The mechanical properties of welded boiler tubes used in power plants can be significantly altered as a result of the fabrication history, such as pre-straining and heat treatment. The primary aim ...
TL;DR: In this paper, a semi-analytic method for elastic/plastic shrink-fit analysis and design is developed, which is assumed that the outer disc obeys the von Mises yield criterion and its associated flow rule.
Abstract: A semi-analytic method for elastic/plastic shrink-fit analysis and design is developed. In contrast to many available semi-analytic methods, it is assumed that the outer disc obeys the von Mises yield criterion and its associated flow rule. The inner component of the assembly is purely elastic. The complete solution consists of three principal steps. First, the elastic/plastic solution in the outer disc is outlined. The only output of this solution required for the next step is the circumferential strain at the inner radius. It is shown that this strain can be found without having the strain distribution in the plastic region of the disc. This significantly simplifies the design of shrink fits. Moreover, only two parameters related to the outer disc (Poisson’s ratio and the dimensionless inner radius) are involved in numerical part of the elastic/plastic solution in the outer disc. Second, the found circumferential strain at the inner radius is used in conjunction with an analytic solution in the inner co...
TL;DR: In this paper, a roll bending process is selected as a case study which can create residual stress in manufactured parts, and the slitting method is employed to determine the residual stresses in a roll-bent stainless steel 314 sample.
Abstract: Slitting method or crack compliance method is used widely for residual stress measurement in different geometries, materials and processes. In this article, roll bending process is selected as a case study which can create residual stress in manufactured parts. The slitting method is employed to determine the residual stresses in a roll-bent stainless steel 314 sample. The series expansion approach is used for residual stress calculation. The compliance matrix is determined by finite element analysis. The uncertainty analysis and average strain misfit are used as two criteria for selecting the best order of expansion. The results show that nine terms of Legendre basis function (L2–L10) can calculate residual stress profile accurately. It is observed that a maximum of 117 MPa residual stress magnitude is induced to the sample. The sample was manufactured with 1.078 m curvature radius by three-roll bending process. The sample thickness was 10 mm. The average uncertainty for residual stress distribution thro...
TL;DR: In this paper, an energy-based fatigue life prediction method was developed to accurately predict lifetimes of coupon specimens in excess of 105 cycles, based on empirically determined room temperature high-cycle fatigue data for both Al 6061-T6 and Ti-6Al-4V in uniaxial, bending, and shear at various stress ratios (R).
Abstract: An energy-based fatigue life prediction method has been developed to accurately predict lifetimes of coupon specimens in excess of 105 cycles. The method has been shown to agree with empirically determined room temperature high-cycle fatigue data for both Al 6061-T6 and Ti-6Al-4V in uniaxial, bending, and shear at various stress ratios (R). As with any life prediction method, using a testing scheme to accurately predict fatigue performance from a reduced data set greatly reduces test time and material costs. For gas turbine engine components, this can account for a large portion of development costs, making the use of reduced order models very attractive. The stress state of these components can be difficult to characterize and simulate, as they are subjected to both low-cycle fatigue and high-cycle fatigue from both mechanical and vibrational loading. Mechanical loading is generally within the low-cycle fatigue regime and attributed to throttle excursions of various flight maneuvers or engine start-up/sh...
TL;DR: In this article, the influence of the dimensions of the damping rings used for interrupting a dynamic tension experiment on the results of a modified split Hopkinson tension bar was discussed.
Abstract: This article discusses the influence of the dimensions of the damping rings used for interrupting a dynamic tension experiment on the results of a modified split Hopkinson tension bar. The damping ...
TL;DR: In this paper, a shear localization model for simulating the shear band formation process uniquely associated with friction stir welding is presented, by introducing a thermal and plastic deformation model.
Abstract: This article presents a shear localization model for simulating the shear band formation process uniquely associated with friction stir welding. By introducing a thermal and plastic deformation bou...
TL;DR: It is reasonable to conclude that when the intended use of models in material science is ‘to provide insight and understanding in material properties and failure modes’, then it is sufficient to demonstrate that the model reliably reproduces the appropriate phenomena or behaviour observed in the real world.
Abstract: Is there a difference in purpose between modelling in material science and in engineering? The scope of the Journal of Strain Analysis (JSA) embraces material behaviour, to quote the journal’s scope: ‘studies in the mechanics of any material system (metal, polymer, ceramic, composite or other) at one or more length scales which provide insight and understanding in material properties and failure modes are welcome’. The scope also includes ‘measurement and analysis of strain’ and the use of strain ‘data in understanding nature; in engineering decision-making and in the design of industrial processes, structural components, or systems’. So my opening question is pertinent when considering the importance and relevance of articles describing modelling that are submitted for publication. In some disciplines, the primary value of models is seen to be heuristic. They are representations that are valuable for guiding further investigation. Whether or not a model is absolutely correct is not the key question, but instead a model needs to be useful and functional in providing relevant insights. This has been paraphrased as ‘validation of phenomena’ and may be appropriate in pure science. However, the role of models in engineering is distinctly different because models are used to inform decisions that have economic and human consequences. Consequently, it is important to ascertain the degree to which a model is ‘an effective surrogate for reality’. To someone about to trust their life to a machine, it might not be reassuring to know the model used to optimise its design was only tested to establish that it was an ‘effective surrogate for reality’, perhaps what they should really be interested in is ‘the degree to which the model was an accurate representation of the real world’. This implies a level of quantification of the validity of the model that goes beyond establishing that phenomena are appropriately embodied in the model and involves establishing credibility in the model, that is, the willingness of people to make decisions based on data from the model. In practice, the people making the decisions will be those who will be held to account when the machine or structure fails. Hence, it would be reasonable to conclude that when the intended use of models in material science is ‘to provide insight and understanding in material properties and failure modes’, then it is sufficient to demonstrate that the model reliably reproduces the appropriate phenomena or behaviour observed in the real-world. However, when models are intended to support ‘engineering decision-making’ or ‘the design of industrial processes, structural components, or systems’, then a higher level of evaluation is necessary that would usually include a quantitative comparison to the real world. In other words, models can be divided into two classes: informative and predictive, with the latter requiring a more rigorous demonstration of their fidelity. Tegmark identified an epistemological boundary between physics in which a theory is testable and metaphysics where theories are not testable. Perhaps there is a similar boundary between computation models that are essentially concerned with retrodiction or post-diction, that is, generating data that describe phenomena which have happened already or for which it is relatively easy to conduct an experiment, and engineering meta-models that predict future events for which no real-world data are available. In many scenarios, engineers are not very concerned about meta-models because they can build and test prototypes in order to provide data for validation. However, there are fields of engineering, such as the design of engineering devices for nuclear fusion reactors and planetary exploration probes, in which computational models have been created that it is impossible to test comprehensively using real-world data, i.e. meta-models. This separation between engineering models and engineering meta-models is illustrated schematically by the two boxes on the left in Figure 1 with an epistemological boundary between them (horizontal line in Figure 1). It is tempting to make the right-hand edge of the boxes the epistemological boundary between physics and metaphysics, that is, testable and not testable laws of nature. However, this is beyond the realm of analysis for engineering design and engineering in general. It is more instructive to use the right-hand edge as the boundary between known and unknown physics, whereby unknown physics includes those phenomena
TL;DR: In this article, the residual stress distributions in a welded thin Ti-6Al-4V T-joint were measured by the newly developed SScanSS program with synchrotron X-ray diffraction technique.
Abstract: To improve the manufacturing quality of welded structures, to prevent failures at weld joints and to predict their lifetime, measurements of the residual stresses generated by welding in the structures are extremely useful. The residual stresses may reduce the component life due to phenomena that occur at low applied stresses such as brittle fracture, fatigue and stress corrosion cracking. Welded thin Ti-6Al-4V panel components are commonly found in aero-engine assemblies and the weld integrity and reliability are critical. In this work, the residual stress distributions in a welded thin Ti-6Al-4V T-joint were measured by the newly developed SScanSS program with synchrotron X-ray diffraction technique. The measurement performed in this study, which included a large number of measurement points, has mapped a complete stress field in a thin sheet T-joint weld. It has not only provided improved understanding of residual stress in such a joint but also filled the missing link between the residual stress obtained by numerical modelling and their validation. The results have shown that the longitudinal stresses play the most important role in the residual stress distribution over the flange and high tensile stresses appear in the region near the weld zone. The measured results were compared with numerically predicted results and these showed good agreement.