Experimental studies to determine strain concentration factors for space tubular joints

1987 ◽  
Vol 22 (4) ◽  
pp. 237-245 ◽  
Author(s):  
R Sundaravadivelu ◽  
C G Nandakumar ◽  
S K Srivastava ◽  
C Ganapathy
Keyword(s):  
Stress Concentration ◽  
Stress Concentration Factor ◽  
Concentration Factor ◽  
Experimental Studies ◽  
Offshore Structures ◽  
Strain Concentration ◽  
Tubular Joints ◽  
Orthogonal Plane ◽  
Concentration Factors ◽  
Semi Empirical

This paper presents studies carried out on grouted and ungrouted space tubular joints, with K in one plane and T in the orthogonal plane. Three models have been tested for different load cases adopting T, K, and both T and K (STK) configurations. The tubular joints used in offshore structures, especially in jacket platforms, are multiplanar and some are grouted and hence their study is essential. The stress concentration factor, SCF, as determined using the semi-empirical formulae which are applicable for planar joints are not appropriate for space, grouted joints. The results of the present study indicates that the SCF as determined by formulae for simple joints is unsafe in the plane of K and conservative in the plane of T for the space joint. The effect of the grout is to reduce the stress concentration.

Computation of Stress Concentration Factors for Tubular Joints

2013 ◽  
Author(s):  
Philippe Thibaux ◽  
Steven Cooreman
Keyword(s):  
Stress Concentration ◽  
Stress Concentration Factor ◽  
Concentration Factor ◽  
Tubular Joints ◽  
Element Size ◽  
Out Of Plane ◽  
Weld Toe ◽  
Concentration Factors ◽  
Stress Concentration Factors ◽  
Bending Modes

Stress concentration factors for tubular joints were computed using solid quadratic elements. The results of the computations are compared with experiments reported in the literature and with expressions reported in the literature and in design codes. An influence of element size and element type was observed, which leads to recommendations regarding element size of four quadratic elements in thickness, which is finer than in different published recommendations. A parametric study was performed, showing that stress concentration factors from the literature are not always conservative, particularly at the crown toe of the chord, while they tend to be overconservative at the chord saddle. The stress concentration factor for the inside of the member was also computed; it is found that it can be close to the stress concentration factor at the weld toe for both the in plane or out of plane bending modes.

Investigation of Critical Stress Concentration Factor in Analytical Stress Based Forming Limit Criterion

2009 ◽  
Author(s):  
Kyle R. McLaughlin ◽  
Tugce Kasikci ◽  
Igor Tsukrov ◽  
Brad L. Kinsey
Keyword(s):  
Stress Concentration ◽  
Stress Concentration Factor ◽  
Failure Criterion ◽  
Concentration Factor ◽  
Critical Stress ◽  
Strain Path ◽  
Path Dependence ◽  
Forming Limit ◽  
Concentration Factors ◽  
Stress Concentration Factors

Tearing concerns in sheet metal forming have traditionally been predicted by comparing the strain state imposed on a material to its associated strain based Forming Limit Diagram. A shortcoming of this strain based failure criterion is that the Forming Limit Curves exhibit strain path dependence. Alternatively, a stress based failure criterion was introduced and shown analytically and numerically to exhibit less strain path dependence. In our past research, an analytical model was created to predict the stress based Forming Limit Curve. Inputs into the model include a material constitutive relationship, anisotropic yield criterion and a critical stress concentration factor, defined as the ratio of the effective stress in the base material to the effective stress in the necking region. This stress concentration factor is thought to be a material parameter, which characterizes a material’s ability to work harden and prevent the concentration of stress which produces the necking condition. In this paper, the critical stress concentration factors for steel and aluminum alloys were determined by comparing analytical model predictions and experimental data and found to be significantly different. A setup is then proposed to experimentally measure the critical stress concentration factors and initial results are presented.

Stress Concentration Factors Calculation: Analytical and Numerical Approaches for Welded Tubular Joints

2020 ◽  
Author(s):  
Nathalia Paruolo ◽  
Thalita Mello ◽  
Paula Teixeira ◽  
Marco Pérez
Keyword(s):  
Stress Concentration ◽  
Oil And Gas ◽  
Hot Spot ◽  
Experimental Tests ◽  
Oil And Gas Industry ◽  
Offshore Structures ◽  
Gas Industry ◽  
Tubular Joints ◽  
Concentration Factors ◽  
Stress Concentration Factors

Abstract In the oil and gas industry, fixed platforms are commonly applied in shallow water production. In-place environmental conditions generates cyclic loads on the structure that might lead to structural degradation due to fatigue damage. Fatigue is one of the most common failure modes of offshore structures and is typically estimated when dimensioning of the structure during design phase. However, in times when life extension of existing offshore structures is being a topic in high demand by industry, mature fields may represent an interesting investment, especially for small companies. Concerning fixed platforms, composed mainly by welded tubular joints, the assessment of hot spot stresses is considered to predict structure fatigue. The estimation of welded joint hot spot stresses is based on the stress concentration factors (SCFs), which are given by parametric formulae, finite element analysis (FEA) or experimental tests. Parametric formulae may be defined as a fast and low-cost method, meanwhile finite elements analysis may be time consuming and experimental tests associated with higher costs. Given these different characteristics, each method is applied according to the study case, which will rely on the joint geometry and associated loads. Considering simple joint geometries several sets of parametric equations found in the literature may be applied. On the other hand, the SCFs calculation of non-studied yet complex joints consider known formulae adapted according to the under load joint behavior and geometry. Previous analysis shows that this adaptation may furnish different results compared to those obtained by FEA. Furthermore, it is observed that even for simple joints the results derived from the different methods may differ. Given their importance for the oil and gas industry, since they are the basis for the assessment of the fatigue life of welded tubular joints which may impact on additional costs related to maintenance and inspection campaigns, the estimation of SCFs must be the most accurate as possible. Therefore, this paper intends to investigate the differences between results derived from parametric formulae and different FEA studies.

Stress-Concentration Factors at a Doubly-Symmetric Hole

1966 ◽  
Vol 17 (2) ◽  
pp. 177-186 ◽  
Author(s):  
L. H. Mitchell
Keyword(s):  
Stress Concentration ◽  
Stress Concentration Factor ◽  
Concentration Factor ◽  
Infinite Plate ◽  
Concentration Factors ◽  
Stress Concentration Factors

SummaryThe stress-concentration factor is calculated for an infinite plate in tension containing a doubly-symmetrical hole whose boundary consists of parts of three intersecting circles. A suggestion is made for modifying the results to apply to a strip.

Stress Concentration Factors From Overlapping Stress Fields in Uniaxial Tension

1976 ◽  
Vol 98 (1) ◽  
pp. 332-339 ◽  
Author(s):  
H. T. Gencsoy ◽  
J. F. Hamilton ◽  
C. C. Yang
Keyword(s):  
Stress Concentration ◽  
Uniaxial Tension ◽  
Stress Concentration Factor ◽  
Concentration Factor ◽  
Substantial Effect ◽  
Stress Fields ◽  
Concentration Factors ◽  
Stress Concentration Factors ◽  
Stress Raisers ◽  
Resultant Stress

Standard transmission photoelastic techniques were used to determine the resultant stress concentration factors produced by multiple stress raisers in flat, rectangular bars under uniaxial tension. Observations were made on the overlapping stress fields due to various combinations and orientations of holes and semicircular grooves. Two cases of directly superposed discontinuities were also investigated. The results of this investigation indicate that the sizes and relative positions of the discontinuities had a substantial effect on the resultant stress concentration factor. In some cases the stress concentration factor would be decreased while in other cases it would be increased. In the case of superposed stress raisers considered in this investigation, the resultant stress concentration factor can be taken as the product of the individual stress concentration factors; this is in agreement with the results of other investigators. However, for other cases, much judgment and experience will be required to decide when this can be done. And even then this product should be considered only as the probable upper limit of the actual stress concentration factor.

The Interaction of Holes on Stress and Strain Concentrations in Uniaxially Loaded Tensile Plates

2012 ◽  
Vol 268-270 ◽  
pp. 767-771
Author(s):  
Zheng Yang
Keyword(s):  
Stress Concentration ◽  
Stress Concentration Factor ◽  
Concentration Factor ◽  
Thickness Effect ◽  
Central Hole ◽  
Stress And Strain ◽  
Strain Concentration ◽  
Minimum Value ◽  
R Ratio ◽  
Stress Concentration Region

Abstract. The elastic stress and strain fields of plates containing one central hole and two auxiliary holes subjected to uniaxial tension are examined using finite element method. The interaction between holes and the thickness effect on stress and strain concentration factors are investigated. It is shown that the distributions of strain concentration factor and stress concentration factor are different near central hole and auxiliary hole, and both of them depend on the hole radii and the distance between central hole and auxiliary hole. There is a minimum value of Kε/Kσ in stress concentration region and the quantity and location of this minimum value in plane stress state depend on the r/R ratio and d/R ratio of the plate. There are some specific distances between central hole and auxiliary hole corresponding to the radii of auxiliary hole to make the stress concentration factor in the plate minimum.

scholarly journals Stress Concentration Factor of Expanded Aluminum Tubes Using Finite Element Modeling

2013 ◽  
Vol 10 (1) ◽  
pp. 88
Author(s):  
L Mhamdi ◽  
AC Seibi ◽  
A Karrech ◽  
S El-Borgi ◽  
I Barsoum
Keyword(s):  
Finite Element ◽  
Stress Concentration ◽  
Stress Concentration Factor ◽  
Concentration Factor ◽  
Plastic Material ◽  
Structural Response ◽  
Perfectly Plastic ◽  
Empirical Relations ◽  
Aluminum Tubes ◽  
Semi Empirical

 This paper discusses the development of semi-empirical relations for the maximum stress concentration factor (SCF) around circular holes embedded in aluminum tubes under various expansion ratios and mandrel angles. Finite element models were developed to study the expansion of a typical aluminum tube with embedded holes of various sizes. An elastic perfectly-plastic material behaviour was used to describe the structural response of the tubes under expansion. Various hole-diameter-to-tubewall- thickness ratios, tube expansion ratios, and mandrel angles were considered to determine the stress state around the hole at zero and 90 degree locations from which the maximum SCF was determined. Semi-empirical relations for the maximum SCF using the Lagrange interpolation formulation were developed. The developed relations were found to predict the SCFs accurately. 

Engineering Procedure for Calculation of Elastic Stress Concentration Factors of Bearing Pad Fretting Flaws

2009 ◽  
Author(s):  
Bogdan S. Wasiluk ◽  
Douglas A. Scarth
Keyword(s):  
Finite Element ◽  
Stress Concentration ◽  
Crack Initiation ◽  
Stress Concentration Factor ◽  
Concentration Factor ◽  
Elastic Stress ◽  
Elliptical Hole ◽  
Flat Bottom ◽  
Concentration Factors ◽  
Stress Concentration Factors

Procedures to evaluate volumetric bearing pad fretting flaws for crack initiation are in the Canadian Standard N285.8 for in-service evaluation of CANDU® pressure tubes. The crack initiation evaluation procedures use equations for calculating the elastic stress concentration factors. Newly developed engineering procedure for calculation of the elastic stress concentration factor for bearing pad fretting flaws is presented. The procedure is based on adapting a theoretical equation for the elastic stress concentration factor for an elliptical hole to the geometry of a bearing pad fretting flaw, and fitting the equation to the results from elastic finite element stress analyses. Non-dimensional flaw parameters a/w, a/c and a/ρ were used to characterize the elastic stress concentration factor, where w is wall thickness of a pressure tube, a is depth, c is half axial length, and ρ is root radius of the bearing pad fretting flaw. The engineering equations for 3-D round and flat bottom bearing pad fretting flaws were examined by calculation of the elastic stress concentration factor for each case in the matrix of source finite element cases. For the round bottom bearing pad fretting flaw, the fitted equation for the elastic stress concentration factor agrees with the finite element results within ±3.7% over the valid range of flaw geometries. For the flat bottom bearing pad fretting flaw, the fitted equation agrees with the finite element results within ±4.0% over the valid range of flaw geometries. The equations for the elastic stress concentration factor have been verified over the valid range of flaw geometries to ensure accurate results with no anomalous behavior. This included comparison against results from independent finite element calculations.

Fatigue Life Properties of Circumferentially-Notched Bar of Austenitic Stainless Steel With Various Concentration Factors

2018 ◽  
Author(s):  
Naoaki Nagaishi ◽  
Michio Yoshikawa ◽  
Saburo Okazaki ◽  
Hisao Matsunaga ◽  
Junichiro Yamabe ◽  
...  
Keyword(s):  
Stainless Steel ◽  
Fatigue Life ◽  
Stress Concentration ◽  
Austenitic Stainless Steel ◽  
Stress Concentration Factor ◽  
Concentration Factor ◽  
Stress Ratio ◽  
Ambient Air ◽  
Fatigue Tests ◽  
Concentration Factors

Fatigue tests were performed using three types of round-bar specimens of Type 304, meta-stable, austenitic stainless steel. The specimens had circumferential notch with stress concentration factors, Kt, of 2, 3 or 6.6. Load controlled fatigue tests were conducted at stress ratio, R, of 0.1 and −1 in ambient air at room temperature. At R of 0.1, fatigue life was decreased with an increase in the stress concentration factor. Conversely, at R of −1, the stress concentration factor had little influence on the fatigue life. To understand the mechanism of the stress ratio effect, local deformation behavior at and beneath the notch root during the fatigue test was computed by means of finite element analysis considering that the plastic constitutive model describes the cyclic stress-strain response.

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