Stresses In Welded Structures Research Articles

Tuning residual stresses in welded structures by exploiting bio‐inspired suture interfaces

AbstractNature offers a valuable source of inspiration when designing optimized structures. For instance, when two or more shells are joined during growth processes, Nature prefers to exploit interlocking paradigms to enhance the strength of the bond—cranial sutures are one example. Mimicking this distinctive characteristic when welding thin metallic elements may offer some structural benefits. The present study theoretically investigates the possibility of mitigating the detrimental tensile residual stress that always originated by welding processes, by exploiting Computational Welding Mechanics. Specifically, two plates joined by laser welding following sinusoidal paths (i.e., wave‐like), alongside a linear one, will be studied and compared. Thanks to the distinctive temporal and spatial heat distributions of sinusoidal welding, both welding stress and strain develop in dissimilar ways compared with linear path welding—this is reflected to the resulting weldment distortion too. The results show that geometrically optimized sinusoidal welding can effectively reduce residual stress magnitudes compared with the linear configuration counterpart. The implications of these findings are of particular interest when dealing with the structural performance of welded structures, especially in fatigue contexts.

Prediction of residual stresses in welded structures based on neural network: a review

Prediction of residual stresses in welded structures based on neural network: a review

Combined experimental/theoretical approach to residual stresses within multiplicative elasto-plasticity

The study is devoted to geometrically non-linear modelling of viscoplastic structures with residual stresses. We advocate and develop a special approach to residual stresses based on the transition between reference configurations. The finite strain kinematics of the viscoplastic material is modelled by the multiplicative decomposition of the deformation gradient tensor. Numerical algorithms originally developed for unstressed materials are extended to materials with pre-stresses. Owing to the weak invariance of constitutive equations, the incorporation of pre-stresses happens without additional costs. Thus, the advocated approach is especially efficient. A novel experimental/theoretical method for assessment of residual stresses in welded structures is presented; the method combines advantages of purely experimental and theoretical approaches. To demonstrate the applicability of the proposed procedure, we simulate plate welding. As an example we show that the procedure allows extrapolation of the field of residual stresses away from the measurement points. As another example, we address the reduction of weldment-related residual stresses by mechanical treatment.

Comparative analysis of methods for reducing residual stresses in welded structures made of austenitic steels

In this article, the authors conducted a comparative analysis of methods for removing residual stresses in welded structures. The reasons for the formation of residual stresses and methods of their removal are given.

Multiaxial fatigue assessment of welded joints using a principal component-based measure for non-proportionality

Non-proportional multiaxial stresses in welded structures cause higher fatigue damage than proportional stresses. In this paper, a new approach based on principal component analysis for quantifying the level of non-proportionality in stress signals is developed. The quantifier is developed for large-scale structures (civil and offshore structures), where the influence of mean stresses is negligible. The proposed quantifier is compared and validated with other approaches from literature with the relevant fatigue criteria and experimental data. The results show that the proposed principal component-based quantifier can capture the level of non-proportionality accurately, which can be used for accurate fatigue life estimations.

Eksperimentalno određivanje zaostalih napona u konstrukciji metodom bušenja rupe

A very important segment, which occurs as a result of welding, is the occurrence of residual stresses in welded structures. The effects of residual stresses can be beneficial or harmful to the structure, depending on their size, sign, and stress distribution in relation to the stresses caused by the external load itself. Therefore, the examination of residual stresses is very important because they significantly affect the formation and growth of cracks, the appearance of brittle fractures, material fatigue, etc. The paper presents the test procedure for measuring residual stresses by the method of "hole drilling" and the possibility of practical application of knowledge about residual stresses in order to improve the quality of machine parts and the structure itself.

Vibration stress relief of DH 36 rectangle welded plates

Vibration stress relief (VSR) is widely used in reducing residual stress in welded structures. However, the effectiveness of this method is still instable in some circumstance. In this study, a covert negative treatment phenomenon was investigated, i.e. natural frequency of welded structures decreased after VSR but residual stress in one direction increased. When the alteration of natural frequency after VSR is significant, the residual stresses in both the longitudinal and transversal directions shall decrease. Otherwise, residual stresses may increase on one direction. Thus, sufficient power shall be applied to the welded structures to avoid negative results.

Acoustic Emission Detection during Welding Residual Stresses Release in 2.25Cr1Mo0.25V Steel Welds

The main goal of this study is acoustic emission (AE) measuring of residual stresses in welded structures. The welding residual stresses release in three 2.25Cr1Mo0.25V welded specimens with different heat treatment conditions were detected and evaluated during the hole drilling strain gauge measurement by AE technique. AE signals from residual stresses release were detected and analyzed for the first time. The results showed that the waveform of residual stress release signal is in a burst type and the spectral energy has the peak frequency at 147 kHz. Furthermore, the AE hits of as-welded specimen are much more than those of specimens after heat treatment due to the higher welding residual stresses. This indicates that AE is sensitive to residual stresses and could be used as a tool to monitor residual stresses release and to make evaluations on residual stresses qualitatively in the future.

Review on finite element analysis for estimation of residual stresses in welded structures

In this review various finite element analysis approaches available for estimation of residual stresses in welded structures are presented. FEA can effectively estimate residual stresses, especially the relaxation of residual stresses in weld region and region in close vicinity under repeated loading. The amount of the residual stress relaxation depends on the magnitude of applied repeated loading. Comparison revealed that rapid dumping approach have least computational time and shows qualitatively good agreement with experimental values for welding residual stresses whereas gradual weld bead deposition approach estimated more exact results as compared to experimental and various other approaches. Using substructuring approach computation is remarkably reduced without any loss to acceptable accuracy of predicted welding residual stresses. In this composition various assumptions required to carry out finite element analysis of welded structures are also explained. Conclusion indicates that it is important to include all weld sequences for accurate estimation of residual stresses in a structure but even before that it is required to analyze the weld sequences in critical area as a starting point in initial design stage.

Comparative Study of Heat Transfer Parameter Estimation Using Inverse Heat Transfer Models of a Trailing Liquid Nitrogen Jet in Welding

Welding induces distortions and stresses in welded structures. A heat sink trailing the weld arc is one among the methods used to reduce the stresses and distortions. Researchers have made use of cooling agents like atomized water and liquid nitrogen (LN2) jet as trailing heat sinks. As the inclusion of a heat sink alters the temperature distribution, estimation of heat removal due to cooling jet is a prerequisite for the study of the effects of the heat sink on stresses and distortions. Analytical methods for the estimation of heat transfer parameters are complicated due to nonuniform cooling by the impinging jet, boiling heat transfer of cooling jet, stray fluid particles on the work-piece surface, and the sharp localized temperature gradient on the work piece due to weld heat input. Therefore, an inverse heat transfer (IHT) method is adapted to estimate the heat transfer parameters due to heat sink. Experiments were conducted using automated tungsten inert gas welding apparatus on a low-carbon steel work piece with an LN2 trailing jet, and transient temperature history was recorded at select points. A finite-element method is used as a solution procedure for IHT method. The heat transfer parameters are estimated by comparing the temperature history at a point from the experiment with the temperature history of the same point in the finite-element model by an iterative method. The heat transfer coefficient, heat flux of LN2 jet, and effective radius of the jet are estimated using two-dimensional and three-dimensional models.

Investigation of fields of residual stresses in welded structures

The results of analysis of the principal methods of investigating the residual stresses in welded structures are presented. Special features of the welded joints, restricting the areas of application of the individual methods, are discussed. An efficient method, resulting in reliable data, is described.

Diagnostics of Structures by the Methods of Electron Shearography and Speckle-Interferometry

A procedure aimed at nondestructive quality testing and determination of the residual stresses in welded structures is developed on the basis of the methods of electron shearography and speckle-interferometry. We create compact shearographic and speckle interferometric measuring systems capable of the investigation of welded structures under the conditions of their manufacturing and operation and present the results of diagnostics of the quality and stress states of the elements of welded panels made of VT-20 high-strength titanium alloy and the technology used for the evaluation of the diameter of weld-spot nugget.

Residual stress evaluation in dissimilar welded joints using finite element simulation and the L CR ultrasonic wave

Subsurface stresses in welded structures increase the likelihood of fatigue cracks and environmental induced material degradation. The ability to evaluate stresses at the surface as well as in the interior of welded structural members would substantially increase the accuracy of structure life estimation. The longitudinal critically refracted (L CR) wave is a bulk longitudinal mode that travels within an effective depth underneath the surface. It may be used to detect in-plane subsurface stresses in the structures. This paper presents a three dimensional thermo-mechanical analysis to evaluate welding residual stresses in dissimilar plate-plate joint of AISI stainless steel 304 and Carbon Steel A106-B type. After finite element simulation, the residual stresses were evaluated by L CR ultrasonic waves. Finally the results of two methods were compared and verified by hole-drilling method. This paper introduces a combination of “Finite Element Welding Simulation” and “Ultrasonic Stress Measurement using the L CR Wave” which is called as “FEL CR”. The capabilities of FEL CR″. The capabilities of FEL CR in residual stress measurement are confirmed here. And also this paper evaluates residual stresses of dissimilar welded joints by LCR ultrasonic waves. It has been shown that predicted residual stress from three dimensional FE analyses is in reasonable agreement with measured residual stress from LCR method and also the results of both are verified with hole-drilling experimental measurements.

Analysis of welding conditions based on induced thermal irreversibilities in welded structures: Cases of welding sequences and preheating treatment

Preheating treatment and employing a proper welding sequence are introduced as two efficient approaches for reducing residual stresses in welding processes. Selecting a right welding sequence and a proper preheating temperature for a weld system are crucial tasks, since welding residual stresses are inevitably produced in a welded structure. However, obtaining residual stresses is very complex, and much time is needed in some cases, particularly for the modeling and prediction of residual stresses in welded structures. So in this work, we attempt to show that these stresses depend on generated entropy during the arc welding process. Thus by obtaining thermal irreversibility effects from temperature distribution, due to a variation of different welding parameters, selection of optimum factors to achieve minimum residual stress is not only possible, but easier to undertake. In the proposed method, it is not a necessity to obtain residual stress values, and one can predict the behavior of residual stress qualitatively. To do so, 3D numerical models are employed to study the similar behavior of created residual stresses and entropy due to a variation of different preheating temperatures and three common welding sequences.

Residual Stresses Measurement of Butt-welded Aluminium Alloy Plates by X-ray

X-ray diffraction(XRD) method is used to determine the distribution of surface residual stress on the butt-welded aluminium alloy LD10 plates. Two methods of determining peak positions, i.e. half-width and parabola methods, are adopted and compared in the experiment, the distribution of residual stresses is obtained, and the distribution results of residual stresses are explained. The test shows that the results of the two methods are similar, and stress distribution curve of parabola method is largely lower than that of half-width method, which is on the low side of tensile stress and on the high side of compressive stress. At the same time, the experimental results reveal that the half-width method is better in consistency, stability, adaptability and accuracy than parabola, and the distribution data of the residual stresses surveyed by XRD method is reliable,and XRD is a valid method to measure residual stresses in welded structures. All these results contribute reference to the distribution of residual stresses on welded aluminium alloy LD10 plates.

Advances in Residual Stress Modeling and Measurement for the Structural Integrity Assessment of Welded Thermal Power Plant

The safe operation of both thermal and nuclear power plant is increasingly dependent upon structural integrity assessment of pressure vessels and piping. Furthermore, structural failures most commonly occur at welds so the accurate design and remnant life assessment of welded plant is critical. The residual stress distribution assumed in defect assessments often has a deciding influence on the analysis outcome, and in the absence of accurate and reliable knowledge of the weld residual stresses, the design codes and procedures use assumptions that yield very conservative assessments that can severely limit the economic life of some plant. However, recent advances in both the modeling and measurement of residual stresses in welded structures and components open up the possibility of characterising weld residual stresses in operating plant using state-of–the–art fully validated Finite Element simulations. This paper describes research undertaken to predict residual stresses in stainless steel welds in order to provide validated reliable, accurate Structural Integrity assessment of nuclear power plant components

Residual stresses in welded structures

The nature of residual stresses in welded structures is discussed in terms of their magnitude, directionality, spatial distribution, range and variability. The effects of the following factors on the residual stresses are considered: material properties, material manufacture, structural geometry, fabrication procedure, welding procedure, post-weld treatments and service conditions. Examples are given of residual stress distributions in plate butt welds, circumferential butt welds and weld cladding. These illustrate the different magnitudes and distributions of residual stress that can be found in different joint geometries, and demonstrate the effects of the mechanical, thermal and metallurgical properties of the constituent materials and the sensitivity of residual stresses to pass sequence and to the restraints applied during welding. Further examples for the common case of circumferential butt welds in pipes and pressure vessels are used to illustrate the extent of residual stresses as a function of distance from the weld and the effects of post-weld heat treatment. Measurements or analytical predictions of residual stresses are often subject to significant scatter or variability. This scatter may be due to systematic factors such as variability in measurement location or material properties, or to experimental error in measured data, erroneous assumptions in analytical modelling or unknown factors such as pre-existing residual stresses, inadequately documented welding or fabrication procedures or unrecorded local repairs. Improved prediction and reduction of uncertainty of residual stresses will require better recording of the whole manufacturing and service history of the welded structure and its component materials and better understanding and analysis of the many processes that may affect the residual stresses.

An Integrated Approach to the Determination and Consequences of Residual Stress on the Fatigue Performance of Welded Aircraft Structures

Abstract Although residual stress in welded structures and components has long been known to have an effect on their fatigue performance, access to reliable, spatially accurate residual stress field data has been limited. Recent advances in neutron and synchrotron X-ray diffraction allow a far more detailed picture of weld residual stress fields to be obtained that permits the development and use of predictive models that can be used for accurate design against fatigue in aircraft structures. This paper describes a fully integrated study of the three-dimensional residual stress distribution accompanying state-of-the-art fusion welds in 2024-T4 aluminum alloy, and how it is affected by subsequent machining and service loading. A particular feature of this work has been the development of techniques allowing the nondestructive evaluation of the residual stress field in the full range of specimens used to provide the design data required for welded aircraft structures and the integration of this information into all aspects of damage tolerant design.

Approximate evaluation of the efficiency of operations of reducing residual stresses in welded structures

Approximate evaluation of the efficiency of operations of reducing residual stresses in welded structures

Diagnostics of Residual Stressed State of Welded Structures Using the Methods of Holographic Interferometry and Electron Speckle-Interferometry

To determine the residual stresses in welded structures it is suggested to use the methods of holographic interferometry and electron speckle-interferometry which make it possible to determine the components of a space vector of displacements and to calculate the residual stresses. The residual stresses in welded structure elements, which are used in machine-building and aircraft industries, were determined using the above-mentioned methods. Compact instruments and devices for the holographic and electron speckle-interferometry methods of determination of residual stresses are described. The problems of prospects for use of the offered technology in industry are discussed.