Creep rupture assessment by a robust creep data interpolation using the Linear Matching Method

2018

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A 90° back-to-back pipe bend structure subjected to cyclic in-plane bending moment and steady internal pressures is analysed by means of the Linear Matching Method (LMM) in order to create the limit, shakedown, and ratchet boundaries. The analyses performed in this work demonstrate that the cyclic moment has a more significant impact upon the structural integrity of the pipe bend than the constant pressure. Full cyclic incremental analyses are used to verify the structural responses either side of each boundary and confirm correct responses. In addition, the shakedown boundary produced by the LMM is compared to another shakedown boundary of an identical pipe bend computed by the simplified technique and it is shown that the LMM calculates results more accurately. Parametric studies involving a change of geometry of the pipe bends and loading type are carried out. From the studies of the geometry, two semi-empirical equations are derived from correlations of the reverse plasticity limit and the limit pressure with the bend characteristic. Finally, the results presented in this paper provide a comprehensive understanding of post-yield behaviours of the 90° back-to-back pipe structure under the combined loading as well as offering essential points to be concerned for the life assessment of the piping system.

Section: Iterative Elastic Techniques Are a Typical Approach Of Direcmentioning

confidence: 99%

Shakedown, ratchet, and limit analyses of 90° back-to-back pipe bends under cyclic in-plane opening bending and steady internal pressure

Cho

2018

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“…For industrial application, some simplified structural analysis methods, which are based upon the limit analysis and shakedown concepts and make full use of the creep rupture data, are utilised in integrity assessment procedure R5 (Ainsworth, 2003) and ASME NH (ASME, 2013). Such methods are able to directly simulate the creep rupture phenomenon without needing the development of detailed constitutive descriptions but a small number of material parameters, and can provide simple but reasonable assessment results (Barbera and Chen, 2015;Chen et al, 2003;Chen et al, 2006).…”

Section: Introductionmentioning

confidence: 99%

“…The linear matching method (LMM) (Chen and Ponter, 2001), matching the nonlinear material behavior to a linear one, was originally proposed for evaluation of plastic limit and shakedown limit loads of elastoplastic structures. For the sake of evaluating the maximum permissible load or predicting the creep rupture life of creeping structures, Chen et al (2003) extended the LMM to include the creep rupture effect via combining the shakedown analysis procedure with creep rupture data (Barbera and Chen, 2015;Chen et al, 2006), achieving the same function but with more accurate results as these simplified methods in integrity assessment procedure R5 (Ainsworth, 2003). In this way, the assessment of creep rupture limit was essentially translated into a shakedown analysis with a revised yield strength.…”

Section: Introductionmentioning

confidence: 99%

Numerical schemes based on the stress compensation method framework for creep rupture assessment

Peng

Liu

2020

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Evaluation of creep rupture limit and prediction of creep rupture life are two significant issues for high-temperature devices under the action of cyclic thermo-mechanical loadings. In this paper, the shakedown solution procedure proposed recently by the authors, so-called stress compensation method (SCM), is extended for creep rupture assessment via an extended shakedown theory including creep.Two distinct numerical schemes based on the SCM framework are presented, where Scheme 1 is utilised for evaluation of creep rupture limit and Scheme 2 is utilised for prediction of creep rupture life. Instead of using the detailed creep constitutive equations, the present methods just need to know several material parameters including the creep rupture data. A holed plate is provided as a typical example to validate the reliability of two numerical schemes. Detailed cycle-by-cycle analyses are carried out to illustrate the good accuracy of these calculated creep rupture limits and reveal the failure mechanisms of the structure under different combinations of loads. A numerical study on a pipe junction is also conducted to show the engineering application of the methods. As a result, the two numerical schemes are proved to be effective and reliable for solving practical industrial problems.

“…When a real complex engineering component is considered, these shakedown analyses are translated into the tremendous optimization problems which are hard to solve. Besides the mathematic programming methods, there are still some other direct methods, such as the elastic compensation method (ECM) (Ponter and Carter, 1997a, b;Ponter and Engelhardt, 2000), the linear matching method (LMM) (Chen and Ponter, 2001;Chen, 2010;Barbera and Chen, 2015;Barbera et al, 2017) and the stress compensation method (SCM) (Peng et al, 2018), which go around the difficulty of the optimization problem and are more suitable for practical engineering applications. The LMM simulates the plastic behavior via a series of full elastic solutions with variable moduli in time and space to evaluate shakedown limit.…”

Section: Introductionmentioning

confidence: 99%

Shakedown analysis of elastic-plastic structures considering the effect of temperature on yield strength: Theory, method and applications

Peng

Liu

2019

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According to the extended Melan's static theorem, theoretical and numerical aspects of the stress compensation method (SCM) are presented to perform shakedown analysis of elastic-plastic structures considering the effect of temperature on yield strength. Instead of constructing a mathematical programming formulation, this developed method consists of the two-level iterative scheme. The inner loop constructs the statically admissible self-equilibrating stress field, while the outer loop evaluates a sequence of decreasing load factors to approach to the shakedown limit multiplier. The yield strength considering temperature effect is updated based on the current temperature at each outer iteration, and the yield conditions are checked at all Gauss points. The numerical procedure is well incorporated into ABAQUS finite element code and used for calculating the shakedown limits of structures considering yield strengths as different functions of temperature under complex thermomechanical loading system. The method is validated by some plane stress and axisymmetric numerical examples with theoretical and numerical solutions, and subsequently applied to solve the practical shakedown problem of a pipe with oblique nozzle. The results demonstrate that the developed method is stable, accurate and efficient, and can effectively evaluate the shakedown limit of an elastic-plastic structure where the yield strength of material varies with temperature.