3D Roughness Parameters as Factors in Determining the Evolution of Effective Stress Concentration Factors in Fatigue Processes

2012 ◽  
Vol 248 ◽  
pp. 504-510 ◽  
Author(s):  
Valentin Mereuta ◽  
Mihaela Buciumeanu ◽  
Liviu Palaghian
Keyword(s):  
Surface Roughness ◽  
Fatigue Life ◽  
Stress Concentration ◽  
Effective Stress ◽  
Roughness Parameters ◽  
Machined Surface ◽  
Machined Surface Roughness ◽  
Concentration Factors ◽  
Stress Concentration Factors ◽  
Effective Stress Concentration Factor

The influence of machined surface roughness on the fatigue life of S355JR steel has been investigated. The specimen have been machined with three roughness levels and tested under plane fatigue. The surface roughness parameters were used to estimate the effective stress concentration factors Kt using the Arola-Ramulu model and Neuber model. In this paper it is proposed a modification for both models. Based on the experimental results was obtained the evolution of the effective stress concentration factor for the original Arola-Ramulu and Neuber models and also for the modified ones.

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.

scholarly journals The influence of vibrations on surface roughness formed during precision boring

2017 ◽  
Vol 37 (1) ◽  
pp. 1-5
Author(s):  
Dariusz Korzeniewski ◽  
Natalia Znojkiewicz
Keyword(s):  
Surface Roughness ◽  
Rotational Speed ◽  
Piezoelectric Sensor ◽  
Stability Loss ◽  
Vibration Level ◽  
Roughness Parameters ◽  
Machined Surface ◽  
Boring Tool ◽  
Machined Surface Roughness ◽  
Conventional Tool

AbstractIn this paper, the analysis of vibrations on surface roughness generated during boring with the application of the conventional boring tool and one with the damper is presented. The experiments included the measurement of vibration accelerations carried out with the piezoelectric sensor, as well as the evaluation of surface roughness parameters after each machining pass. The obtained results reveal that in the investigated range, no stability loss was found. Furthermore, the growth of the rotational speed induces the increase of vibration level, as well as the growth of the differences between the vibration values generated during boring with the conventional tool and one equipped with damper. Vibrations have also the direct influence on the machined surface roughness. In case of the tool equipped with the damper, the tool’s overhang L had more intense influence than rotational speed n. However, for the conventional boring tool this dependency was unequivocal.

A Multidimensional FEA Approach for Determination of Hot Spot Stresses in Offshore Jacket Structures

2021 ◽  
Author(s):  
Kris Hectors ◽  
Hasan Saeed ◽  
Wim De Waele
Keyword(s):  
Fatigue Life ◽  
Stress Concentration ◽  
Hot Spot ◽  
Wave Spectrum ◽  
Wave Direction ◽  
Tubular Joints ◽  
Jacket Structures ◽  
Concentration Factors ◽  
Stress Concentration Factors

Abstract A new fatigue lifetime assessment approach for offshore jacket structures is presented. It combines a previously developed numerical framework for automated determination of stress concentration factors in tubular joints and a multidimensional finite element modelling approach. The approach is explained based on a case study of an OC4 type offshore jacket. To determine the fatigue life, a directional wave spectrum is combined with the JONSWAP spectrum. The fatigue life of the jacket is assessed for two different sea states. Based on the fatigue analysis the most fatigue critical wave direction is identified. The hot spot stresses in one of the most critical joints are determined and compared to stresses obtained with the Efthymiou equations. The shortcomings of these equations are highlighted and it is shown how the numerical framework can be used to improve the current fatigue design philosophy for offshore jackets which relies on the Efthymiou equations for stress concentration factors in the welded tubular joints.

Surface Texture, Fatigue, and the Reduction in Stiffness of Fiber Reinforced Plastics

2002 ◽  
Vol 124 (2) ◽  
pp. 160-166 ◽  
Author(s):  
D. Arola ◽  
C. L. Williams
Keyword(s):  
Surface Roughness ◽  
Stress Concentration ◽  
Surface Texture ◽  
Fatigue Loading ◽  
Machined Surface ◽  
Flexural Fatigue ◽  
Reinforced Plastics ◽  
Fiber Reinforced Plastics ◽  
Stress Concentration Factors ◽  
Machined Surfaces

In this study the influence of machined surface texture on the fatigue strength of a Graphite/Bismaleimide (Gr/Bmi) laminate was examined. Rectangular beam specimens were machined to achieve specific surface roughness 0.2⩽Ra⩽10.0 μm and then subjected to fully reversed four-point flexural fatigue. The surface texture resulting from machining was evaluated using contact profilometry and the standard surface roughness parameters were used in estimating the effective stress concentration K¯t and effective fatigue notch K¯f factors for the machined surfaces according to models reported in the open literature. Fully reversed flexural fatigue loading of the laminate was conducted at two separate maximum bend loads corresponding to Tsai-Hill ratios for first ply failure of 0.75 and 0.9. It was found that the reduction in stiffness of the Gr/Bmi laminate at both levels of fatigue loading increased with the magnitude of surface roughness. The apparent fatigue stress concentration factors Kf of the machined surfaces determined from experimental results ranged from 1.0 to 1.2. The effective fatigue notch factors estimated using the Arola-Ramulu model for the machined specimens were within 10% of the corresponding Kf determined from experiments.

Stress Concentration Factors for Stud-Less Mooring Chain Links in Fairleads

2004 ◽  
Author(s):  
Pedro M. Vargas ◽  
Teh-Min Hsu ◽  
Wai Kong Lee
Keyword(s):  
Fatigue Life ◽  
Stress Concentration ◽  
Fine Tuning ◽  
Mooring Line ◽  
Loop Current ◽  
Parametric Problem ◽  
Chain Link ◽  
Concentration Factors ◽  
Stress Concentration Factors ◽  
Mooring Chain

Mooring chains are critical components of off-shore installations. The fatigue assessment of these components often requires complex calculations to determine the loadings in the mooring chains. Traditionally the loadings can be converted into fatigue lives using S-N curves such as the DnV Posmoor curve, or the API RP2 SK curve. Deep water SPARs undergoing vortex-induced-motion (VIM) in loop current conditions may be subject to higher mean/cyclic loadings with considerably lower fatigue life estimates — compared with earlier installations in which fatigue life estimates were so large that fine tuning fatigue prediction methodologies was only of academic interest. In this case a more accurate evaluation of the fatigue performance of mooring chains is needed. In this study the stress concentration factors (SCFs) of a studless 5.25” (133mm) mooring chain were examined in a seven-pocket fairlead. The chain-fairlead system analyzed in this study had a very tight fit (i.e., was not designed for passing connector links), and the results of this study will, in general, not be applicable to other chain-fairlead combinations without additional study. The computed SCFs of the stud-less link interacting with the fairlead pocket were compared to the corresponding SCFs in a chain link away from the fairlead. The study shows that the maximum SCF ratio is 1.15, significantly less than the upper bound 2.5 value recommended by Det Norske Veritas in OS-E301 in lieu of detailed analyses. This has a significant impact, nearly an order of magnitude, on fatigue life prediction of the chain, justifying the analytical effort. The study also found that the SCF of the chain link in the fairlead is a function of the geometry of the chain and the fairlead. As a result some guidance is provided in this paper with respect to the implications of minimum SCFs on other link and fairlead geometries. This study combines computational efforts from NEL and ChevronTexaco in a two-pronged approach where: 1) NEL provided calculations addressing parametric variations of the chain link angles of the mooring line leaving the fairlead and the chain tension levels, and 2) ChevronTexaco validated simplified modelling assumptions done by NEL to make the parametric problem tractable.

Stress Concentration Factors of Damaged FPSO Side Panels Under Cyclic Loads

2013 ◽  
Author(s):  
Ilson Pasqualino ◽  
Bianca Pinheiro ◽  
Carolina Ferreira
Keyword(s):  
Fatigue Life ◽  
Stress Concentration ◽  
Fatigue Cracks ◽  
Mechanical Damage ◽  
Element Model ◽  
Compression Load ◽  
Life Study ◽  
Concentration Factors ◽  
Residual Fatigue ◽  
Stress Concentration Factors

FPSO (floating production, storage and offloading) units can be subjected to mechanical damage in their side panels caused by collision with supply vessels. Even if the ultimate strength of the panel is not significantly affected by small damage, the stress concentration in the collided region may lead to the initiation of fatigue cracks, considering the long period of operation undergone by these vessels. The aim of this work is to evaluate stress concentration factors (SCFs) in damaged FPSO side panels and estimate their effect on the fatigue life through a theoretical study. A finite element model is developed to reproduce a supply vessel collision and evaluate resulting SCFs under in-plane compression load. A parametric study is carried out considering different damage magnitudes and the results obtained are used to develop an analytical expression to provide SCFs as a function of dimensions of damage and panel. SCFs provided by this expression could be used in a theoretical fatigue life study that can estimate the residual fatigue life of collided FPSO side panels and help to forewarn a fatigue failure under the event of an accidental collision.

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.

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