Photoelastic Study and Fatigue Tests of a Contoured, Integrally Reinforced Branch Connection

1971 ◽  
Vol 93 (4) ◽  
pp. 1021-1029
Author(s):  
R. W. Schneider ◽  
W. M. Jackson ◽  
W. R. Nicolls
Keyword(s):  
Stress Concentration ◽  
Internal Pressure ◽  
Fatigue Behavior ◽  
Three Dimensional ◽  
Bending Moment ◽  
Fatigue Tests ◽  
Extensive Study ◽  
Cylindrical Pressure Vessel ◽  
Concentration Factors ◽  
Stress Concentration Factors

The paper describes the results of an extensive study of a contoured, integrally reinforced branch connection in a cylindrical pressure vessel (or run pipe). Three epoxy models were tested by means of three-dimensional photoelasticity using the stress-freezing and slicing technique. Loads applied were internal pressure, a longitudinal moment on the branch, and a transverse bending moment on the branch; one model was required for each mode of loading. Stress distribution curves are given. In addition, thirteen geometrically similar steel headers were fatigue tested by longitudinal and transverse forces cyclically applied to the branch pipes. Tests were conducted over a range of nominal stress in the branch. Stress concentration factors or stress indices from the photoelastic tests for bending and stress intensification factors from the bending fatigue tests are compared. Stress concentration factors for internal pressure loading, as derived from the photoelastic tests, are presented. Since stress intensification factors are not used to describe fatigue behavior under pulsating pressure, a similar comparison is not possible. Owing to the amount of data accumulated, only the most pertinent are presented; in every instance this includes the area of maximum stress.

Studies in Three-Dimensional Photoelasticity: Stresses in Bent Circular Shafts With Transverse Holes—Correlation With Results From Fatigue and Strain Measurements

1944 ◽  
Vol 11 (1) ◽  
pp. A10-A16
Author(s):  
M. M. Frocht
Keyword(s):  
Stress Concentration ◽  
Three Dimensional ◽  
Fatigue Tests ◽  
Pure Bending ◽  
Simple Method ◽  
Strain Measurements ◽  
Concentration Factors ◽  
Stress Concentration Factors ◽  
Considerable Work ◽  
Maximum Stresses

Abstract Bent circular shafts with holes in the plane of bending are of frequent occurrence in modern machines. They often form a part of the lubricating system as, for example, in the crankshafts of aircraft engines. Considerable work has been done to determine the maximum stresses and the factors of stress concentration in such shafts. The author presents a simple method of calculating such stresses for transverse holes in pure bending. Experimental photoelastic evidence that led to this method is given. A comparison of the stress-concentration factors obtained by it is made with the published results from fatigue tests and strain measurements from large steel shafts, which were performed a number of years ago at the Westinghouse Research Laboratories.

Derivation of Stress Intensification Factors for a Special, Contoured, Integrally Reinforced Branch Connection

1973 ◽  
Vol 95 (1) ◽  
pp. 106-112
Author(s):  
R. W. Schneider ◽  
E. C. Rodabaugh
Keyword(s):  
Three Dimensional ◽  
Fatigue Tests ◽  
Stress Indices ◽  
Cylindrical Pressure Vessel ◽  
Out Of Plane ◽  
Stress Intensification Factor ◽  
Concentration Factors ◽  
Stress Concentration Factors ◽  
Fitting In ◽  
Standard Weight

The results of an extensive experimental investigation of a contoured, integrally reinforced branch connection in a cylindrical pressure vessel (or run pipe) have been reported [1]. One size model, specifically a 12 in. (0.375) × 6 in. (0.280) standard weight header was studied by three-dimensional photoelasticity using the stress-freezing and slicing technique. Loads applied were internal pressure, plus in-plane and out-of-plane bending moments on the branch; one model was used for each mode of loading. In addition, carbon steel headers were fatigue tested by longitudinal and transverse moments cyclically applied to the branch pipes. A model was required for each mode of loading for each level of amplitude of applied nominal stress. Stress concentration factors (stress indices) were derived from the photoelastic tests, whereas, the fatigue tests produced stress intensification factors. The stress indices and stress intensification factors derived from the tests apply only to 12 × 6 standard weight headers, or geometrically identical headers, with the particular type of branch connection. This paper describes how generalized stress intensification factor equations were derived to cover a broad range of sizes and thicknesses of headers incorporating the same type of branch fitting. In this paper the term “header” applies to a single branch connection in a pipe remote from all other discontinuities.

Fatigue Life Analysis of Steel Pipelines With Plain Dents Under Cyclic Internal Pressure

2008 ◽  
Author(s):  
Bianca de Carvalho Pinheiro ◽  
Ilson Paranhos Pasqualino ◽  
Se´rgio Barros da Cunha
Keyword(s):  
Finite Element ◽  
Fatigue Life ◽  
Stress Concentration ◽  
Internal Pressure ◽  
Fatigue Tests ◽  
Small Scale ◽  
Concentration Factors ◽  
Life Analysis ◽  
Fatigue Life Analysis ◽  
Stress Concentration Factors

This work is within an ongoing study, which aims to propose a new methodology for fatigue life analysis of steel pipelines with plain dents under cyclic internal pressure. This methodology follows the current high cycle fatigue theory and employs stress concentration factors induced by plain dents to modify standard S-N curves. A previously developed and validated finite element model is extended to generate stress concentration factors for longitudinal and transverse dents, in addition to spherical dents. Several finite element analyses are carried out in a parametric study to evaluate stress concentration factors induced by the three dent types studied: spherical, longitudinal and transverse dents. Analytical expressions are developed to estimate stress concentration factors for these three dent types as function of pipe and dent geometric parameters. Small-scale fatigue tests are conducted to evaluate the finite life behavior of dented steel pipes under cyclic internal pressure. The methodology is validated in view of the fatigue tests results. Including expressions to estimate stress concentration factors for three different dent types (spherical, longitudinal and transverse dents), the proposed methodology can then be used for fatigue life analysis of dented steel pipelines under cyclic internal pressure.

Fatigue Assessment of Dented Rigid Risers

2019 ◽  
Author(s):  
Elvis J. O. Santander ◽  
Bianca Pinheiro ◽  
Carlos Magluta ◽  
Ney Roitman
Keyword(s):  
Stress Concentration ◽  
Structural Integrity ◽  
Three Dimensional ◽  
Element Model ◽  
Oil Fields ◽  
Dimensional Finite Element ◽  
Concentration Factors ◽  
Stress Concentration Factors ◽  
Three Dimensional Finite Element ◽  
Remaining Fatigue Life

Abstract In the development of oil fields, submarine pipelines are used in various applications. These pipelines and risers are subject to accidents that may occur during operation, such as shocks between risers or shocks between a riser and an anchor, rock, or any equipment or heavy object, which may cause mechanical failure, such as dents. The objective of this work is to study of the effect of the introduction of plain dents on the structural integrity of rigid risers under fully reversed bending. A three dimensional finite element model was developed to estimate the stress concentration on dented risers under bending. Several numerical simulations were carried out to evaluate stress concentration factors (SCFs) for varying dimensions of dents and risers, in a parametric study. These SCFs can be used in the prediction of the remaining fatigue life of dented rigid risers.

Fatigue Assessment of Damaged Pipelines After Glass Fiber and Epoxy Matrix Laminate Repairs

2017 ◽  
Author(s):  
Sabrina Regalla ◽  
Bianca Pinheiro ◽  
Ilson Pasqualino ◽  
Luiz Daniel Lana ◽  
Valber Perrut
Keyword(s):  
Stress Concentration ◽  
Internal Pressure ◽  
Epoxy Matrix ◽  
Glass Fibers ◽  
Before And After ◽  
Repair Procedure ◽  
Concentration Factors ◽  
Residual Fatigue ◽  
Stress Concentration Factors ◽  
Fatigue Life Enhancement

The aim of this work is to evaluate the residual fatigue life enhancement of damaged pipelines after the execution of composite material repairs made of laminates of epoxy matrix reinforced with glass fibers. In view of structural performance and cost concerns, the more suitable repair thickness should be proposed. The work comprises a numerical and experimental study on the stress concentration of damaged pipes under internal pressure before and after repair. A numerical model is developed, based on the finite element method, to provide stress concentration factors of damaged pipes (plain dent defect), under cyclic internal pressure, before and after applying glass fiber and epoxy matrix laminate repairs with varying thicknesses. Small-scale steel pipe samples are submitted to denting and the resulting stress concentration in the damaged region is estimated under cyclic internal pressure, before and after repair execution. From correlation between numerical and experimental results, the finite element model is calibrated and validated. A parametric study is carried out to evaluate stress concentration factors of dented pipes repaired with varying laminate thickness. Stress concentration factors of dented pipes under internal pressure after repair can be used in a fatigue assessment methodology from correction of S-N curves. The effect of repair thickness on the reduction of stress concentration factors is evaluated in view of the residual fatigue life enhancement of damaged pipes, beside repair procedure costs. Based on results of the parametric study, recommendations about the repair procedure using laminates of epoxy matrix reinforced with glass fibers will be proposed, comprising indications of the more suitable repair thickness, as a function of pipe and damage dimensions, in view of fatigue performance and cost concerns.

The Influence of Corrosion Pits and Cold Expanded Fastener Holes on the Fatigue Life Aluminium 7075-T651

2014 ◽  
Vol 891-892 ◽  
pp. 87-92 ◽  
Author(s):  
Benjamin Withy ◽  
Stephen Campbell ◽  
Glenn Stephen
Keyword(s):  
Fatigue Crack ◽  
Fatigue Life ◽  
Stress Concentration ◽  
Air Force ◽  
Fatigue Tests ◽  
Expansion Process ◽  
Cold Expansion ◽  
Concentration Factors ◽  
Stress Concentration Factors ◽  
Corrosion Pits

The Royal New Zealand Air Force (RNZAF) utilised the split sleeve cold expansion process to increase the fatigue life of fastener holes in the wings of the C130 transport fleet. As part of the validation of the fatigue improvements offered by the process the Defence Technology Agency conducted a series of fatigue tests on cold expanded fastener holes in aluminium 7075-T651, including specimens with corrosion induced after the cold expansion process had been performed. This research conducted an analysis of fatigue crack origins and modelled the stress concentration factors generated as a result of the corrosion pits. These results were used to explain the differing fatigue life and s-n curves produced by corroded and non-corroded fatigue specimens and the location of crack initiation sites around corroded cold expanded fastener holes.

Stress Concentration Factors of Dented Pipelines

2006 ◽  
Author(s):  
Bianca de Carvalho Pinheiro ◽  
Ilson Paranhos Pasqualino ◽  
Se´rgio Barros da Cunha
Keyword(s):  
Finite Element ◽  
Stress Concentration ◽  
Numerical Model ◽  
Finite Element Model ◽  
Internal Pressure ◽  
Element Model ◽  
Small Strain ◽  
Small Scale ◽  
Concentration Factors ◽  
Stress Concentration Factors

A nonlinear finite element model was developed to assess stress concentration factors induced by plain dents on steel pipelines subjected to cyclic internal pressure. The numerical model comprised small strain plasticity and large rotations. Six small-scale experimental tests were carried out to determine the strain behavior of steel pipe models during denting simulation followed by the application of cyclic internal pressure. The finite element model developed was validated through a correlation between numerical and experimental results. A parametric study was accomplished, with the aid of the numerical model, to evaluate stress concentration factors as function of the pipe and dent geometries. Finally, an analytical formulation to estimate stress concentration factors of dented pipelines under internal pressure was proposed. These stress concentration factors can be used in a high cycle fatigue evaluation through S-N curves.

Stress Concentration Factors in Shouldered Shafts Subjected to Combinations of Flexure and Torsion

1968 ◽  
Vol 90 (2) ◽  
pp. 301-307 ◽  
Author(s):  
H. G. Rylander ◽  
P. M. A. daRocha ◽  
L. F. Kreisle ◽  
G. J. Vaughn
Keyword(s):  
Stress Concentration ◽  
Maximum Stress ◽  
Small Diameter ◽  
Bending Moment ◽  
Pure Bending ◽  
Principal Stresses ◽  
Torsional Loads ◽  
Concentration Factors ◽  
Stress Concentration Factors ◽  
Experimental Values

Geometric stress concentration factors were determined experimentally for shouldered aluminum shafts subjected to combinations of flexural and torsional loads. Diameter ratios were varied from 0.42 to 0.83, and fillet radius to small diameter ratios were varied from 0.1 to 0.7 with bending moment to torque ratios varying over a range from 1:4 to 4:1. Experimental values for the stress concentration factors were obtained by using birefringent coatings and a reflection polariscope. Strain gage measurements and torsional relaxation solutions were used to verify some of the polariscope data. For the cases considered, the static geometric stress concentration factor was between 1.11 and 1:50 for pure torsion, between 1.08 and 1.46 for pure bending, and between 1.09 and 1.50 for combined torsion and bending. The directions of the principal stresses on the surface of the shouldered shafts do not change due to the presence of the discontinuity for a particular specimen and type of loading. Also, the location of the maximum stress in the fillet of a particular specimen under a certain type of loading does not change as the magnitude of the load is varied, but it does vary with the type of loading.

The Prediction of Three-Dimensional Stress Concentration Factors

1959 ◽  
Vol 63 (585) ◽  
pp. 549-551 ◽  
Author(s):  
I. M. Allison
Keyword(s):  
Stress Concentration ◽  
Mathematical Analysis ◽  
Three Dimensional ◽  
Stress Raiser ◽  
Two Dimensions ◽  
Two Dimensional ◽  
Torsional Loading ◽  
Loading System ◽  
Concentration Factors ◽  
Stress Concentration Factors

Two-Dimensional Stress concentration factors may be obtained more quickly and simply than the corresponding three-dimensional factors, either by experiment or mathematical analysis. It would be convenient to obtain information, for varying geometry in the two-dimensional case of a particular type of stress raiser, e.g. a shoulder, groove or hole, and use this either to predict the three-dimensional stress concentration factors or to extend the range of existing three-dimensional results. Clearly a comparison is only possible if the three-dimensional stress raiser embodies a plane of symmetry (which gives the geometry of the similar two-dimensional stress raiser), and if the loading conditions can be reproduced in both the two- and three-dimensional cases. The latter requirement restricts the correlation to the stress concentration factors obtained in tension and in bending. The three-dimensional torsional loading system has no plane of symmetry which can be simulated in two dimensions.

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