An Approximate Model for an Elastic-Plastic Pipe Element Under Combined Loading

1975 ◽  
Vol 97 (1) ◽  
pp. 22-28 ◽  
Author(s):  
L. D. Larson ◽  
W. F. Stokey ◽  
W. E. Franzen
Keyword(s):  
Strain Hardening ◽  
Axial Load ◽  
Analytical Approach ◽  
Limit Load ◽  
Approximate Model ◽  
Experimental Results ◽  
Combined Loading ◽  
Elastic Plastic ◽  
Plastic Pipe ◽  
Plastic Analysis

An approximate model for the elastic-plastic analysis of a pipe element under combined loading is developed. The model is obtained by generalizing a limit load solution for combined pressure, bending, torsion and axial load to include strain hardening. For various combinations of loading of tubes, curvatures and twist angles are predicted and compared with experimental results and those predicted by a more rigorous analytical approach. The comparison shows that good results are obtained from the approximate model.

A Comparison of Design by Analysis Techniques for Evaluating Nozzle-to-Shell Junctions per ASME Section VIII Division 2

2015 ◽  
Author(s):  
Phillip E. Prueter ◽  
Robert G. Brown
Keyword(s):  
Stress Analysis ◽  
Failure Modes ◽  
Elastic Stress ◽  
Limit Load ◽  
Plastic Collapse ◽  
Elastic Plastic ◽  
Plastic Analysis ◽  
Non Linear ◽  
Section Viii ◽  
Division 2

Part 5 of ASME Section VIII Division 2 offers several design by analysis (DBA) techniques for evaluating pressure retaining equipment for Code compliance using detailed computational stress analysis results. These procedures can be used to check components for protection against multiple failure modes, including plastic collapse, local failure, buckling, and cyclic loading. Furthermore, these procedures provide guidance for establishing consistent loading conditions, selecting material properties, developing post-processing techniques, and comparing analysis results to the appropriate acceptance criteria for a given failure mode. In particular, this study investigates the use of these methods for evaluating nozzle-to-shell junctions subjected to internal pressure and nozzle end loads. Specifically, elastic stress analysis, limit load analysis, and elastic-plastic stress analysis are utilized to check for protection against plastic collapse, and computational results for a given load case are compared. Additionally, the twice elastic slope method for evaluating protection against plastic collapse is utilized as an alternate failure criterion to supplement elastic-plastic analysis results. The goal of these comparisons is to highlight the difference between elastic stress checks and the non-linear analysis methodologies outlined in ASME Section VIII Division 2; particularly, the conservatism associated with employing the elastic stress criterion for nozzle end loads compared to limit load and elastic-plastic analysis methodologies is discussed. Finally, commentary on the applicability of performing the Code-mandated check for protection against ratcheting for vessels that do not operate in cyclic service is provided. The intent of this paper is to provide a broad comparison of the available DBA techniques for evaluating the acceptability of nozzle-to-shell junctions subjected to different types of loading for protection against plastic collapse. Predicted deformations and stresses are quantified for each technique using linear and non-linear, three-dimensional finite element analysis (FEA) methodologies.

scholarly journals Analysis by FEMof elasto-plastic deformation of beams with associated plate

2020 ◽  
Author(s):  
A.И. Притыкин
Keyword(s):  
Plastic Deformation ◽  
Strain Hardening ◽  
Load Capacity ◽  
Limit Load ◽  
Transverse Load ◽  
The Finite Element Method ◽  
Elastic Plastic ◽  
Hardening Modulus ◽  
Analytical Relations ◽  
Symmetric Profile

Для оценки несущей способности балок судовых конструкций надо определять их предельную нагрузку. Существующие расчетные зависимости, приводимые в справочных изданиях, далеко не всегда дают верные рекомендации, когда речь идет о балках с присоединенным пояском обшивки, который может намного превосходить размер свободного пояска. В работе проведен сравнительный анализ оценки предельной нагрузки, определяемой аналитически и путем упругопластического расчета методом конечных элементов с варьированием ширины присоединенного пояска. Рассматривался вариант упругопластического нагружения с линейным упрочнением. Полученные результаты показали, что приводимая в справочнике по СМК, зависимость для оценки предельной нагрузки балок с асимметричным профилем не совсем корректна из-за неполного включения присоединенного пояска в работу. Это дает завышенные значения предельной нагрузки. Проверены были также рекомендации по оценке прогибов балок в предельном состоянии, показавшие, что рекомендации справочника по СМК приводят к заниженным значениям прогибов. Для балок симметричного профиля расчетные зависимости справочника дают вполне удовлетворительные результаты. Отмечено, что если поперечная нагрузка вызывает текучесть стенки балки от сдвига, то влияние ширины присоединенного пояска практически не сказывается на ее несущей способности. Проанализировано также влияние величины секущего модуля на предельную нагрузку балки. For estimation of load capacity of the ship beams it is necessary to determine their limit load. Existing analytical relations, indicated in different manuals, not always give true recommendations when talk is about beams with associated plate many times exceeding dimensions of free flange. In this paper fulfilled comparative analysis of limit load, determined with analytical and elastic-plastic calculation by the finite element method. It was considered case of elastic-plastic deformation with lineal strain-hardening. Obtained results show that indicated in manual on the ship structural mechanics, relation for estimation of limit load of non-symmetric I-beams is not quite correct because of not complete inclusion of associated plate to the beam deformation. This lead to overestimation of limit loads. It was also shown that recommendations on evaluation of the deflections of beams in elastic-plastic deformations according to mentioned manual lead to much lower values of deflections. For beam with symmetric profile the relations of manual give quite satisfactory results. It was noticed, that if transverse load produces the yielding of web due to shear the influence of width of associated plate has no influence on the load capacity of beam. It was also analyzed influence of value of the strain-hardening modulus on limit load of beam.

Plastic Buckling of Torispherical and Ellipsoidal Shells Subjected to Internal Pressure

1981 ◽  
Vol 195 (1) ◽  
pp. 329-345 ◽  
Author(s):  
G D Galletly
Keyword(s):  
Stainless Steel ◽  
Internal Pressure ◽  
Strain Hardening ◽  
Design Procedure ◽  
Experimental Results ◽  
Elastic Plastic ◽  
Theoretical Predictions ◽  
The Usa ◽  
Simplifying Assumptions ◽  
The Uk

Thin metallic torispherical shells are used frequently in many industries as end closures on cylinders subjected to internal pressure and, for those torispheres which have diameter/thickness ratios greater than 400, elastic-plastic internal pressure buckling may occur. As yet, however, code rules to assist the designer with this buckling problem are not available in either the UK or the USA and one of the aims of this paper is to help to correct this situation. Elastic-plastic internal buckling pressures, for a range of perfect torispherical geometries and obtained with the aid of a sophisticated computer program, are given in the first part of the paper. These pcr's are then utilized (a) to develop a relatively simple equation for predicting the internal buckling pressures of torispherical shells and (b) to assess the accuracy of another, even simpler, approximate buckling equation which was suggested recently (1). Next, the correlation between the theoretical predictions of pcr and the experimental results is considered. The tests taken into account were (a) 5 in diameter machined model torispherical shells, (b) 20 in diameter spun ellipsoidal shells, and (c) 54 in diameter pressed and spun torispherical shells. The shells in (b) and (c) were not stress-relieved and a number of them were made from strain-hardening materials. The agreement between theory and experiment was good for the machined models and fairly satisfactory for the spun models. For the ellipsoidal shells there was also reasonably good agreement between the predictions of two simple design equations and the experimental results. The problems associated with the prediction of the internal buckling pressures of spun torispherical shells made from strain-hardening materials (e.g. stainless steel) are considered in the last section of the paper. Taking the results of the previous sections of the paper into account, and making some simplifying assumptions, a tentative design procedure for predicting the pcr's of these ‘as-manufactured’ spun torispherical shells is proposed. This procedure is then checked by comparing its predictions with experimental buckling pressures found for eleven spun stainless steel heads and six crown and segment ones. The agreement between experiment and theory was quite satisfactory and it is hoped that the suggested procedure might become the first step towards the development of experimentally validated code rules for preventing the occurrence of buckling in these dished ends.

Approximate Elastic-Plastic J Estimate of Cylinders With Off-Centered Circumferential Through-Wall Cracks

2003 ◽  
Author(s):  
Do-Jun Shim ◽  
Nam-Su Huh ◽  
Yun-Jae Kim ◽  
Young-Jin Kim
Keyword(s):  
Fracture Mechanics ◽  
Strain Hardening ◽  
Combined Loading ◽  
Influence Functions ◽  
Elastic Plastic ◽  
Crack Geometry ◽  
Reference Stress ◽  
Plastic Influence Functions ◽  
Reference Stress Approach

This paper provides approximate J estimates for off-centred, circumferential through-wall cracks in cylinders under bending and under combined tension and bending. The proposed method is based on the reference stress approach, where the dependence of elastic and plastic influence functions of J on the cylinder/crack geometry, the off-centred angle and strain hardening is minimised through the use of a proper normalising load. Based on published limited FE results for off-centred, circumferential through-wall cracks under bending, such normalising load is found, based on which the reference stress based J estimates are proposed for more general cases, such as for a different cylinder geometry and for combined loading. Comparison of the estimated J with extensive FE J results shows overall good agreements for different crack/cylinder geometries and for combined tension and bending, which provides sufficient confidence in the use of the proposed method to fracture mechanics analyses of off-centred circumferential cracks. Furthermore, the proposed method is simple to use, giving significant merits in practice.

TUEV NORD Concept Loop: Lifetime Optimisation of Pipelines

2014 ◽  
Author(s):  
Ralf Trieglaff ◽  
Christian Schrandt ◽  
Axel Schulz ◽  
Mayk Schulz
Keyword(s):  
Finite Element ◽  
Limit Load ◽  
Burst Pressure ◽  
Unique Element ◽  
Assessment Procedure ◽  
Elastic Plastic ◽  
Geometry Model ◽  
Finite Element Software ◽  
Plastic Analysis ◽  
Pressure Test

LOOP is a concept to evaluate corroded or damaged pipelines based on detailed data from UT-pigging. The procedure of LOOP delivers a 3D-model generated from the data of a commercial in-line inspection tools (ultrasonic, magnetic flux). This makes it possible to use the full functionalities of the relevant finite element software like evaluation of wall-thinning (LOOP 1) and fracture mechanics analysis to evaluate cracks in the wall (LOOP 2). In this paper is given the basic ideas of the LOOP concept, where the main focus is directed to the LOOP 1 assessment procedure. Based on a real example of a corroded pipeline is demonstrated the assessment procedure, which is based on an elastic-plastic analysis of a real inner contour of the corroded surface transferred in the finite element geometry model. The unique element is that the surface data of the UT-pigging is used directly to generate the geometry model in the FE-software ANSYS. The assessment procedure is validated by a burst pressure test of a corroded pipeline. The result of the burst pressure test is compared with the calculated limit load from an elastic-plastic analysis based on measured material properties. Additionally, the assessment procedure is compared with the results of a limit load analysis based on DIN EN 13445-3 and with the results of the standard assessment procedure. At the end the assessment procedure is compared with the procedure given in API 579-1 standard.

Bifurcation in Elastic-Plastic Rotating Shells Under Combined Loading

1985 ◽  
Vol 9 (4) ◽  
pp. 181-191 ◽  
Author(s):  
P. Tugcu
Keyword(s):  
Axial Load ◽  
Lateral Pressure ◽  
Cylindrical Shells ◽  
Combined Loading ◽  
Inertial Forces ◽  
Elastic Plastic

The buckling of elastic-plastic cylindrical shells under combined axial load, lateral pressure and torsion is examined. The effects of inertial forces due to rotation are also investigated. Results for flow and deformation theories of plasticity are compared. Some simple expressions are given for the case of axisymmetric bifurcations.

Bifurcation Buckling Versus Limit Load Instabilities of Elastic-Plastic Tubes Under Bending and External Pressure

1991 ◽  
Vol 113 (1) ◽  
pp. 43-52 ◽  
Author(s):  
G. T. Ju ◽  
S. Kyriakides
Keyword(s):  
Limit Load ◽  
External Pressure ◽  
Experimental Results ◽  
Offshore Pipelines ◽  
Elastic Plastic ◽  
Combined Loads ◽  
Bifurcation Buckling ◽  
Load Types ◽  
T Values

Commonly used procedures for installing offshore pipelines can induce substantial bending to the line in the presence of external pressure. These combined loads can lead to catastrophic collapse of the structure. For typically used steels and higher diameter-to-thickness ratios (D/t), bending is limited by a bifurcation type of instability; for lower D/t values, the structures exhibit limit load types of instabilities. Similar distinctions can be made for bending in the presence of external pressure. Previous work (Corona and Kyriakides, 1988) addressed primarily the limit load types of instabilities. In this paper, this analysis is extended to include bifurcation instabilities. The predictions from the two types of analyses are critically compared to experimental results and recommendations about the regime of applicability of each are made.

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