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[en] With the two key controlling parameters identified and their effectiveness demonstrated in Part I of this study series for constructing a continuous residual stress profile at weld region, a classical shell theory based model is proposed in this paper (Part II) for describing through-thickness residual stress distributions of both axial and hoop components at any axial location beyond weld region. The shell theory based model is analytically constructed through an assembly of two parts: One represents weld region and the other represents the remaining component section away from weld. The final assembly of the two parts leads to a closed form solution to both axial and hoop residual stress components as a function of axial distance from weld toe position. The effectiveness of the full-field residual stress estimation scheme is demonstrated by comparing with a series of finite element modeling results over a broad range of pipe weld geometries and welding conditions. The present development should provide a consistent and effective means for estimating through-thickness residual stress profile as a continuous function of pipe geometry, welding heat input, as well as material characteristics. - Highlights: • A shell theory based two-part assembly model is developed for generalizing residual stress distributions. • A full-field estimation of through-thickness residual stress profiles can be achieved. • The proposed estimation scheme offers both consistency and mechanics basis in residual stress profile generation. • An estimation scheme for welding-induced plastic zone size is proposed and validated. • The shell theory based estimation scheme can also provide a reasonable estimate on distortion in radial direction
[en] Highlights: • The reference stress (RS) solutions for plates with embedded elliptical cracks are derived. • The RS solution conservatism due to assuming rectangular cracks are discussed. • The J solutions for the plates are proposed via the reference stress J scheme. • The FE J can be well predicted by the RS solutions under small loads values. • Ignoring side surface stress may result in non-conservative or conservative J evaluation. - Abstract: The reference stress solutions for plates with embedded off-set elliptical cracks under combined biaxial forces and cross-thickness bending are derived based on the Mises yield criterion and net-section collapse principle. The newly developed reference stress solutions are compared with the reference stresses of plates with embedded rectangular cracks evaluated using the available limit load solutions. The developed reference stress solutions have been used to predict J via the reference stress J scheme. Elastic-plastic 3-D finite element (FE) analyses are used to calculate J values along the crack front and the results are compared with the reference stress predictions. The results show that the estimated J values based on the reference stress method with the reference stress solutions developed in this paper are very close to the FE J values, but the predictions may be non-conservative. However, the non-conservatism could be removed by simply applying a constant factor less than 1 to the reference stress solutions when they are used in the reference stress J scheme.
[en] Highlights: • The receptance method can easily deal with the dynamic response of real complex piping systems at various fluid velocities. • The presented method has the advantage of simulating arbitrary supports to pipe systems. • For the same pipe element, the cut-off frequency based on the receptance method is higher than that based on theFEM. - Abstract: In this paper, a new set of six-variable linear partial differential equations of motion of fluid-conveying pipes with general boundary conditions are derived using the Hamilton principle and these equations are solved by the receptance method. The frequencies of the straight pipes conveying fluid with or without elastic supports are determined and the results are compared with experimental ones. Then a fluid-conveying, semi-circular pipe and complex piping system with different kinds of boundary conditions are studied. These pipes are divided into some straight pipe units and are assembled using the receptance method. The numerical results show that the receptance method is efficient for pipes with arbitrary geometrical layouts and support types, and once the dynamic receptance of the elastic support of a piping system is obtained via experiment, its dynamic stability at different fluid velocities can be analysed by the receptance method.
[en] This paper focuses on the development of a simplified analytical scheme for the elastic-plastic Fracture Mechanics Assessment of large nozzle corners. Within that frame, following the specific numerical effort performed for the definition of a Stress Intensity Factor compendium, complementary elastic-plastic developments are proposed here for the consideration of the thermal shock loading in the elastic-plastic domain: this type of loading is a major loading for massive structures such as nozzle corners of large components. Thus, an important numerical was performed in order to extend the applicability domain of existing analytical schemes to those complex geometries. The final formulation is a simple one, applicable to a large variety of materials and geometrical configurations as long as the structure is large and the defect remains small in comparison to the internal radius of the nozzle. - Highlights: • Fracture Mechanics Assessment of large nozzle corners. • Elastic-plastic Stress Intensity Factor determination under thermal shock loading. • Semi-analytical schemes for J calculation.
[en] Fracture studies were carried out on 170 mm OD welded straight pipes having circumferential through-wall crack in the weld under quasi-cyclic loading. The specimens were made of Type 304 LN stainless steel and welded using conventional Shielded Metal Arc (SMA) welding or Narrow Gap (NG) welding. The specimens were subjected to different amplitudes of load/displacement, which was decided based on the monotonic load carrying capacity of the specimens. It was found that the failure load reduces to 78.5% and 74.0% of the monotonic failure load for resisting 50 and 100 loading cycles, respectively in the case of NG welded pipes. The NG welded specimens showed more energy absorbing capability and crack growth resistance, when compared with SMA welded specimens. Crack growth was more stable in the case of specimens tested under displacement control; whereas the same was unstable in the case of load-controlled experiments and specimens failed by sudden collapse. - Graphical abstract: Crack Growth during Quasi-cyclic Loading under Load Control. - Highlights: • Cyclic fracture behaviour of through-wall cracked welded straight pipes was studied. • Cyclic failure load reduced to 78.5% of the monotonic failure load for resisting 50 loading cycles. • NG welded specimens showed more energy absorbing capability and crack growth resistance. • Crack growth under load-control was unstable and specimens failed by sudden collapse.
[en] The present work aims to study residual stresses caused by circumferentially welding of two similar API X46 steel pipes by means of finite element modeling. Considering the metallurgical phase transformations and through thermal-mechanical uncoupled analysis, the 3D modeling was carried out by SYSWELD software. Materialistic thermal and mechanical properties of all phases were defined in terms of temperature as well as phase transformation properties. Residual stress was measured through hole-drilling method. The obtained results were used to verify the finite element model. By means of full factorial experiment designing method, effects of heat input and radius to pipe thickness ratio on maximum values of hoop and axial residual stresses were investigated. The effect of each factor was studied in 3 levels and by 9 experiments. Results of statistical analysis revealed that increase in heat input and radius-thickness ratio would lead to higher values of maximum hoop and axial residual stresses. However, interactions of high level of heat input and a low level of radius-thickness ratio increased inter-pass temperature and consequently caused a sudden raise in maximum values of residual stresses. - Highlights: • A FEM model was developed to simulate welding considering phase transformations. • The obtained residual stresses were validated by experiments. • Effect of heat input and radius-to-thickness ratio on residual stress were investigated. • Increasing heat input for 100% caused increasing hoop and axial residual stress until 200%. • Interaction of high heat input and low R/t causes a sudden increase in axial residual stresses.
[en] The current work presents an investigation of the effects of expansion rate on plasticity and structural integrity of down-hole solid tubular. Down-hole tubular has proven itself to be a promising technology in oil well applications by providing optimum solutions for many issues. One of the challenges still facing researchers and field engineers in implementing and making down-hole tubular technology cost effective is to conserve structural integrity of tubular. Cold expansion affects mechanical properties and induces residual stresses in tubular, hence reduces its collapse, burst, and fatigue ratings. The knowledge of properties variation is required in correctly predicting life span of tubular under given operational conditions. In present work, cold expansion of tubular under down-hole conditions is experimentally and numerically investigated at different strain rates. Strain rates are varied by changing the velocity of mandrel that is used to expand the tubular. Firstly, different tubular expansion experiments are performed to achieve 16%, 20%, and 24% expansion ratio. Secondly, finite element model of tubular expansion is developed in commercial finite element software ABAQUS. Simulation results are found to be in good agreement with experimental observations. Finally, further simulations are performed to thoroughly analyze the effects of expansion rate on the deformation behavior of tubular. It is found that there is variation in contact pressure at tubular-mandrel interface, effective stress, equivalent plastic strain, and thickness reduction during expansion process. These variations ultimately influence post-expansion properties of tubular particularly collapse and burst strengths, and hence its structural integrity. However, length shortening has marginally affected by expansion rates.
[en] The setting round process for the pipe-end of LSAW (Longitudinal Submerged Arc Weld) pipes is one of the most important processes to assure the pipe quality. The process is a local elastic–plastic deformation process. Therefore, it is difficult to provide a quantificational analysis because of the influence of its rigid part. However, the springback law of the circle–oval process for the whole pipe can be easily predicted. First, the equivalence relation between the setting round process and the circle–oval process, and the similarity relation in the circle–oval process between the pipe-end and the short pipe are studied. Then the quantitative analysis of the circle–oval process of short pipe and its springback process is given, and experimental results match with the theoretical results. Finally, the two-step control strategy of pipe-end setting round process is established, and experimental studies show this strategy can control the residual ovality within 0.5%. - Highlights: • A quantificationally analytical method for the circle–oval process is built. • The meshing idea in the finite element theory is used in the analytical method. • A two-step control strategy is built, which can control the ovality within 0.5%. • An equivalence relation and a similarity relation are given to support the strategy
[en] A simple and clear method of evaluating stress and strain ranges under non-proportional multiaxial loading where principal directions of stress and strain are changed during a cycle is needed for assessing multiaxial fatigue. This paper proposes a simple method of determining the principal stress and strain ranges and the severity of non-proportional loading with defining the rotation angles of the maximum principal stress and strain in a three dimensional stress and strain space. This study also discusses properties of multiaxial low cycle fatigue lives for various materials fatigued under non-proportional loadings and shows an applicability of a parameter proposed by author for multiaxial low cycle fatigue life evaluation
[en] The ratchet boundaries and ratchet strains are derived for the Bree problem and an elastic-perfectly plastic material with different yield stresses on-load and off-load. The Bree problem consists of a constant uniaxial primary membrane stress and a cycling thermal bending stress. The ratchet problem with differing yield stresses is also solved for a modified loading in which both the primary membrane and thermal bending stresses cycle in-phase. The analytic solutions for the ratchet boundaries are compared with the results of deploying the linear matching method (LMM) and excellent agreement is found. Whilst these results are of potential utility for purely elastic–plastic behaviour, since yield stresses will often differ at the two ends of the cycle, the solution is also proposed as a means of assessing creep ratcheting via a creep ductility exhaustion approach. -- Highlights: • The Bree problem is solved for differing yield stresses on and off load. • The modified Bree problem with cycling primary load is also solved. • These solutions can be applied to creep ratcheting using a pseudo-yield stress