Numerical Analysis of Contact Stresses Between Mooring Chain Links and Potential Consequences for Fatigue Damage

2013 ◽  
Author(s):  
Philippe Bastid ◽  
Simon D. Smith
Keyword(s):  
Finite Element ◽  
Residual Stresses ◽  
Contact Zone ◽  
Fatigue Damage ◽  
Contact Region ◽  
High Stress ◽  
Breaking Load ◽  
High Stress Concentration ◽  
Cyclic Stresses ◽  
Chain Links

Design codes for offshore mooring systems recommend proof loading chain links to around 70% of the specified breaking load of the chain (API RP 2FP1, Lloyd’s Register). This is primarily to check that the chain will safely resist the service loads and will not excessively elongate. It is assumed that the proof load also generates compressive residual stresses at the interlink contact region and also at the point of the intrados (KT point) where a high stress concentration occurs during tensile loading. Tests have shown that proof loading improves the fatigue performance of chain under cyclic axial loads. Elastic-plastic finite element analyses of the proof loading have been performed. These analyses have shown that the proof loading also generates very high tensile residual stresses in the region surrounding the interlink contact zone. This region also experiences significant in-service cyclic stresses under cyclic tension or out-of-plane bending. The combination of the cyclic stresses and high tensile residual stress is of concern and it is proposed that the periphery of the interlink contact zone should be carefully reviewed. It is understood that chain link fatigue at present is only based on the risk of fatigue damage at the KT point. This paper presents and discusses results of finite element stress analyses of studless chains of different sizes and grades, and show the relative fatigue sensitivity of the KT and contact regions. The chain grade, dimensions and loading regime are shown to be important.

Finite Element Analysis of Residual Stresses in Threaded End Closures

1991 ◽  
Vol 113 (3) ◽  
pp. 398-401 ◽  
Author(s):  
A. Chaaban ◽  
U. Muzzo
Keyword(s):  
Finite Element ◽  
Residual Stresses ◽  
Bauschinger Effect ◽  
High Stress ◽  
Empirical Method ◽  
Pressure Vessels ◽  
Element Analysis ◽  
High Stress Concentration ◽  
Proof Testing ◽  
Pressure Cycle

Due to the high stress concentration at the root of the first active thread in threaded end closures of high pressure vessels, yielding may occur in this region during the application of the first pressure cycle or proof testing. This overstraining introduces residual stresses that influence the fatigue performance of the vessel. This paper presents a parametric analysis of threaded end closures using elastic and elasto-plastic finite element solutions. The results are used to discuss the influence of these residuals on the estimated fatigue life when the vessel is subjected to repeated internal pressure. A simple empirical method to allow for the Bauschinger effect of the material is also proposed.

On the Axisymmetric Response of a Damaged Flexible Pipe

2014 ◽  
Author(s):  
José Renato M. de Sousa ◽  
Carlos Magluta ◽  
Ney Roitman ◽  
George C. Campello
Keyword(s):  
Finite Element ◽  
Analytical Model ◽  
Load Capacity ◽  
High Stress ◽  
Experimental Tests ◽  
Theoretical Models ◽  
Experimental Measurements ◽  
Fe Model ◽  
Flexible Pipe ◽  
High Stress Concentration

This work focuses on the structural analysis of a damaged 9.13″ flexible pipe to pure and combined axisymmetric loads. A set of experimental tests was carried out considering one up to ten broken wires in the outer tensile armor of the pipe and the results obtained are compared to those provided by a previously presented finite element (FE) model and a traditional analytical model. In the experimental tests, the pipe was firstly subjected to pure tension and, then, the responses to clockwise and anti-clockwise torsion superimposed with tension were investigated. In these tests, the induced strains in the outer armor were measured. Moreover, the axial elongation of the pipe was monitored when the pipe is subjected to tension, whilst the twist of the pipe was measured when torsion is imposed. The experimental results pointed to a slight decrease in the stiffness of the pipe with the increasing number of broken wires and, furthermore, a redistribution of forces among the intact wires of the damaged layer with high stress concentration in the wires close to the damaged ones. Both theoretical models captured these features, but, while the results obtained with the FE model agreed well with the experimental measurements, the traditional analytical model presented non-conservative results. Finally, the results obtained are employed to estimate the load capacity of the pipe.

scholarly journals A Finite Element Study of the Residual Stress and Deformation in Hemispherical Contacts

2005 ◽  
Vol 127 (3) ◽  
pp. 484-493 ◽  
Author(s):  
Robert Jackson ◽  
Itti Chusoipin ◽  
Itzhak Green
Keyword(s):  
Residual Stress ◽  
Finite Element ◽  
Residual Stresses ◽  
Yield Criterion ◽  
Contact Region ◽  
Element Model ◽  
Von Mises Stress ◽  
Contact Radius ◽  
Perfectly Plastic ◽  
Von Mises

This work presents a finite element model (FEM) of the residual stresses and strains that are formed after an elastoplastic hemispherical contact is unloaded. The material is modeled as elastic perfectly plastic and follows the von Mises yield criterion. The FEM produces contours for the normalized axial and radial displacements as functions of the removed interference depth and location on the surface of the hemisphere. Contour plots of the von Mises stress and other stress components are also presented to show the formation of the residual stress distribution with increasing plastic deformation. This work shows that high residual von Mises stresses appear in the material pileup near the edge of the contact area after complete unloading. Values are defined for the minimum normalized interference, that when removed, results in plastic residual stresses. This work also defines an interference at which the maximum residual stress transitions from a location below the contact region and along the axis of symmetry to one near to the surface at the edge of the contact radius (within the pileup).

Acoustic Vibration Induced Fatigue in Pipe Joints

2015 ◽  
Author(s):  
Ajay Prakash ◽  
Philip Diwakar ◽  
Dan Lin ◽  
Paul Deane ◽  
Yuqing Liu ◽  
...  
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Sound Pressure ◽  
High Stress ◽  
Acoustic Vibration ◽  
Acoustic Energy ◽  
Piping System ◽  
Element Analysis ◽  
High Stress Concentration ◽  
Pipe Joints

High acoustic energy has the potential to cause severe acoustic induced vibration (AIV) that can lead to fatigue failure at high stress concentration locations (discontinuities) in a piping system. AIV at pipe junctions (Lateral, Tee, and Wye) and welded support attachments (trunnions and shoes) is evaluated using Finite Element Analysis. At different size pipe junctions, branch and header pipe shells may be subjected to different sound pressure. Also, inertia associated with different wall thickness(s) can lead to very different dynamic response of the two shell walls. The effect of these differences on AIV response is analyzed. Resulting response for different junction reinforcement designs is evaluated and compared to an unreinforced ‘stub-on’ configuration to assess the designs.

Failure Analysis of Full Delamination on the Stacked Die Leaded Packages

2003 ◽  
Vol 125 (3) ◽  
pp. 392-399 ◽  
Author(s):  
T. Y. Lin ◽  
Z. P. Xiong ◽  
Y. F. Yao ◽  
Lane Tok ◽  
Z. Y. Yu ◽  
...  
Keyword(s):  
Finite Element ◽  
Adhesion Strength ◽  
High Stress ◽  
Consumer Products ◽  
Lead Frame ◽  
Element Analysis ◽  
Factors Affecting ◽  
Temperature Cycles ◽  
High Stress Concentration ◽  
Die Attach

There has been significant demand for stacked die technology during the past few years. The stacked die devices are mainly used in portable consumer products. This kind of silicon integration technology provides flexibility in space reduction, weight savings, and excellent electrical functionality. In this article, the stacked die construction was built into the leaded package. It was found that the test vehicles had full delamination at the lead-frame paddle/mold compound interface after 100 temperature cycles (−65°C to 150°C) with moisture preconditioning at level 3 (60°C at 60% relative humidity for 40 h) although the electrical test passed 1000 temperature cycles. The fishbone diagram was used to identify the possible failure root causes. The material, process, and design factors were extensively evaluated by the experiments and finite element analysis. The evaluation results showed that die attach paste voids were major factors affecting the package integrity and could produce the delamination initiation at the edge of the die attach paste and propagate down to the lead-frame paddle/mold compound interface due to high stress concentration and weak adhesion strength. The finite element analyses were implemented to address the stress distribution in the stacked die package and verified by the scanning acoustic microscope. It demonstrated that excellent package integrity could be obtained by applying the void-free die attach paste and improving the adhesion strength at the lead-frame paddle level.

Finite Element Residual Stress Analysis Applied to Offshore Studless Chain Links

2004 ◽  
Author(s):  
Pedro M. Calas Lopes Pacheco ◽  
Paulo Pedro Kenedi ◽  
Jorge Carlos Ferreira Jorge ◽  
Marcelo Amorim Savi ◽  
Hugo Gama dos Santos
Keyword(s):  
Finite Element ◽  
Residual Stresses ◽  
Structural Integrity ◽  
Wind Waves ◽  
Mooring Line ◽  
Single Element ◽  
Finite Element Models ◽  
Waves And Currents ◽  
Fatigue Life Analysis ◽  
Chain Links

The increasing expansion of deepwater petroleum activities has resulted in new challenges to the design of mooring systems. The complex mooring systems load history, which consists in a combination of wind, waves and currents, could induce nucleation and propagation of cracks in mooring line components. The failure of a single element in a mooring line of an offshore oil exploitation platform can produce incalculable environment damage as well as human and material losses. Offshore mooring line components like chain links must be submitted to a mandatory proof test, dictated by offshore standards, where loads higher than operational loads are applied to the mechanical component, resulting in high levels of residual stresses. Nevertheless, its presence is not considered in traditional design methodologies. Therefore, it is fundamental to develop new and more precise methodologies for assessing the structural integrity of mooring components. In this article, a comparative study is developed considering different approaches: two bidimensional finite element models, two tridimensional finite element models and an analytic model. These analyses establish the drawbacks and goals of using simpler models in the prediction of studless chain links stress distributions and in their fatigue lives. The four finite element models consider large displacements, plasticity and contact phenomena. Moreover, a simple fatigue life analysis is presented, based on SN curve, considering the effect of residual stresses in studless chain links before operation, that is, with loads caused by the proof test.

Fatigue Life Investigation of a High Pressure Inner Casing Under In-Service Conditions

2016 ◽  
Author(s):  
Hui Hong ◽  
Weizhe Wang ◽  
Zhenwei Cai
Keyword(s):  
Finite Element ◽  
High Pressure ◽  
Fatigue Life ◽  
Fatigue Damage ◽  
High Stress ◽  
Element Model ◽  
Steam Pressure ◽  
Strain Behavior ◽  
Service Conditions ◽  
High Stress Level

The fatigue life of a specific inner casing of an ultra-supercritical steam turbine was investigated under a half year in-service conditions. The Ramberg-Osgood model and Manson-Coffin-Basquin strain-life equation were used to describe the stress-strain behavior and calculate the fatigue damage. A temperature comparison was performed to validate the reliability of finite element model. The results showed that fluctuating steam pressure rather than temperature had more significant effect on the variation of stress in the casing. Locations with high stress level were prone to cause larger fatigue damage. Statistical analysis was carried out to reveal that over half fluctuations of steam pressure could cause damage.

Analysis and validation of femur bone data using finite element method under static load condition

2019 ◽  
Vol 233 (16) ◽  
pp. 5547-5555 ◽  
Author(s):  
S Mathukumar ◽  
VA Nagarajan ◽  
A Radhakrishnan
Keyword(s):  
Finite Element ◽  
Stress Concentration ◽  
Static Load ◽  
High Stress ◽  
Load Condition ◽  
Computational Method ◽  
Medical Attention ◽  
Element Analysis ◽  
High Stress Concentration ◽  
Femur Bone

Humans face bone fracture when they unfortunately met an accident, which requires timely medical attention for healing and repairing the fractured bone; otherwise that paralyzes their life. 3D modeling technique with computational method is very helpful at the side of doctors for healing and repairing the damaged bones. Fractional bone healing is one of the natural processes, which regain the mechanical reliability of the bone to a limited level of failures. The relationship between the biology and mechanics has introduced a new branch namely biomechanics. Various biomechanics models were used to identify the fracture for different patients and helps in the fracture treatment. The aim of this work is to find out the high stress concentration area of the femur bone, which has been extracted as image from computer tomography scanner. The retrieved noise-free femur bone image is tested by the static load condition with the help of the finite element analysis. The result obtained from the testing of different loads has been compared with the existing literature. It is found that the femur bone has tensile and compressive stress, and the neck area of the femur is at a very high stress concentration. The outcome of this work is much supportive to orthopedic surgeons in femur surgery and bone prosthesis by avoiding experiments on femur bone.

Strength and Fatigue Analysis of VIM Suppression Strakes for Large Diameter Spars

2007 ◽  
Author(s):  
Sudhakar Tallavajhula ◽  
Jim Wang ◽  
Inge Solberg
Keyword(s):  
Finite Element ◽  
Stress Analysis ◽  
Fatigue Damage ◽  
Global Analysis ◽  
Large Diameter ◽  
High Stress ◽  
Hydrodynamic Pressure ◽  
Frequency Domain Analysis ◽  
Unit Load ◽  
Principal Stresses

The efficiency of spar vortex induced motion (VIM) suppression strakes has been found to be dependent upon the height of the strakes, the number of strakes in the helix, the pitch of the helix and the extent of strake coverage. As spars have increased in diameter, the height of the VIM suppression strakes has grown to maintain strake efficiency. This has introduced new challenges to the structural design of the strakes as a result of the increased hydrodynamic pressure loads on the strakes and the effect of global bending of the spar hull. The connection of the strakes to the hard tank outer shell often has high stress concentration, which in combination with the cyclic hydrodynamic loading, tends to result in fatigue considerations governing the design of these connections. As a result, finite element models, both global and local, are required to perform detailed stress analysis for the structural strength and fatigue assessment of the strakes and surrounding hard tank structures. This paper will use a generic, large diameter truss spar as an example to outline the methodology and key elements used for strength and fatigue analyses of the strakes. In particular, an efficient unit load method will be presented, which has been used to de-couple the finite element stress analysis and the actual hydrodynamic pressure load analysis for fatigue damage calculation. This method incorporates a time domain global analysis of spar hull global bending loads, and a frequency domain analysis of wave induced hydrodynamic pressure loads on the strakes. Final fatigue damage is calculated based on combined principal stresses using the spectral method. Analysis results and findings are presented for both the in-place condition and the wet tow condition. By applying this procedure, Technip has been able to repeatedly design robust and reliable VIM suppression strakes in a cost efficient process, within the constraints of tight fabrication schedules.

Localized Autofrettage as a Design Tool for the Fatigue Improvement of Cross-Bored Cylinders

1998 ◽  
Vol 120 (4) ◽  
pp. 393-397 ◽  
Author(s):  
A. E. Segall ◽  
C. Tricou ◽  
M. Evanko ◽  
J. C. Conway
Keyword(s):  
Fatigue Life ◽  
Residual Stresses ◽  
High Stress ◽  
Circular Crack ◽  
Design Tool ◽  
Element Analysis ◽  
High Stress Concentration ◽  
Significant Extension ◽  
The Cross ◽  
Machining Operations

An investigation was launched into the feasibility of improving the fatigue life of thick-walled cylinders with cross-bores by using a localized autofrettage technique. This technique utilized the high stress concentration at the cross-bore to induce localized residual stresses using relatively low internal pressures. An elastic-plastic finite-element analysis indicated that the resulting residual stresses in the vicinity of the cross-bore were predominately compressive and not sufficient in magnitude to induce reverse plasticity. When the resulting residual stresses were used with an elastic fracture-mechanics assessment of a quarter-circular crack at the intersection of the cylinder and cross-bore inner diameter, a significant extension of fatigue life was shown to be possible. In addition to prolonging the useful life of the cylinder, the localized residual stresses were shown to be possible at pressures below the yield threshold for the thick-walled cylinder. Thus, reverse plasticity, permanent deformations, and the need for post-autofrettage machining operations that could inadvertently lessen the beneficial results of a traditional autofrettage were avoided.

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