Fatigue Life Analysis of Polyurethane Bending Stiffeners

2005 ◽  
Author(s):  
Fre´de´ric Demanze ◽  
Didier Hanonge ◽  
Alain Chalumeau ◽  
Olivier Leclerc
Keyword(s):  
Fatigue Life ◽  
Effective Strain ◽  
Fatigue Behaviour ◽  
Life Assessment ◽  
Test Results ◽  
Critical Areas ◽  
Fatigue Life Assessment ◽  
Fatigue Data ◽  
Life Analysis ◽  
Fatigue Life Analysis

Following some experiences of bending stiffeners fatigue failures during full scale tests performed at Flexi France on flexible pipe and stiffener assemblies, Technip decided to launch in 1999 a major research program on fatigue life analysis of bending stiffeners made of Polyurethane material. This fatigue life assessment is now systematically performed by Technip for all new design of flexible riser bending stiffeners. This totally innovative method comprises a number of features as follows: Firstly fatigue behaviour of polyurethane material is described. The theoretical background, based on effective strain intensity factor, is detailed, together with experimental results on laboratory notched samples, solicited under strain control for various strain ratios, to obtain fatigue data. These fatigue data are well fitted by a power law defining the total number of cycles at break as a function of the effective strain intensity factor. The notion of fatigue threshold, below which no propagation is observed, is also demonstrated. Secondly the design used by Technip for its bending stiffeners, and most of all the critical areas regarding fatigue for these massive polyurethane structures are presented. Thirdly the methodology for fatigue life assessment of bending stiffeners in the critical areas defined above is discussed. Calibration of the strain calculation principle is presented versus finite element analysis. Based on all fatigue test results, the size of the equivalent notch to be considered at design stage, in the same critical areas, is discussed. Finally, a comprehensive calibration of the methodology according to full and middle scale test results is presented. The present paper is therefore a step forward in the knowledge of fatigue behaviour of massive polyurethane bending stiffener structures, which are critical items for flexible risers integrity, and widely used in the offshore industry. The confidence in bending stiffeners reliability is greatly enhanced by the introduction of this innovative methodology developed by Technip.

Fatigue Life Analysis of an Automotive Tensioner Through Strain-Life Approach

2015 ◽  
Author(s):  
Maryam Talimi ◽  
Jean W. Zu
Keyword(s):  
Fatigue Life ◽  
Stress Analysis ◽  
Drive System ◽  
Life Assessment ◽  
Fatigue Properties ◽  
Fatigue Life Assessment ◽  
Front End ◽  
Life Analysis ◽  
Fatigue Life Analysis ◽  
Prediction Approach

In this paper, fatigue life assessment of a tensioner is studied through dynamic load analysis, stress analysis, and stress-life fatigue analysis approach. Tensioner is a critical part of an automotive front end accessory drive system, providing pre-tension to the belt. The front end accessory drive systems are responsible for transmitting power from the crankshaft to the accessory components. Due to the engine pulsation, components of the accessory drive including the tensioner are subjected to dynamic loads leading to fatigue failure. The fatigue life assessment of a mechanical component highly depends on loading, geometry, and material properties. In addition, the dynamic behavior of the front end accessory drive is complicated due to coupling between several modes of vibrations in belt, pulleys, and the tensioner arm. Duo to the complexity of the parameters involved and complicated dynamics, the fatigue life analysis of FEAD components is a challenging task. This paper includes three main parts, namely stress analysis, fatigue properties prediction, and life estimation. The dynamic analysis of a generic front end accessory drive system is performed in order to obtain effective loads on the tensioner. Stress state for the tensioner in case of different applied loading conditions is performed via a series of Finite Element (FE) analyses, and the critical region of the part is determined. Finally, fatigue life is estimated through strain-life approach. Modest work has been found in this area providing a comprehensive solution to the fatigue life investigation of power train components. The present study offers a comprehensive modeling approach which predicts the automative tensioner lifetime. The lifetime of any FEAD system components can be determined using the developed fatigue life prediction approach.

Proposal for a Total Fatigue Life Assessment Methodology That Predicts Fatigue Life From Defect Initiation to Through Wall Leak

2020 ◽  
Author(s):  
Joseph Batten ◽  
Chris Currie ◽  
Jonathan Mann ◽  
Andrew Morley
Keyword(s):  
Fatigue Life ◽  
Effective Strain ◽  
Strain Range ◽  
Assessment Methods ◽  
Life Assessment ◽  
Assessment Methodology ◽  
Traditional Assessment ◽  
Fatigue Life Assessment ◽  
Definition Of

Abstract Even with improvements to remove excessive conservatisms, current fatigue assessment approaches can result in high Cumulative Usage Factors (CUFs) for some analyses. In order to improve plant availability from these assessments and mitigate future changes to design codes, an improvement in understanding in this area is desirable. Hence the proposal for a Life Assessment Methodology (LAM) was created. The LAM is a concept for an approach based on modelling each stage of fatigue life to predict total fatigue life, as a means of minimising conservatism in an assessment, where necessary. It should also be capable of incorporating statistical methods to assign reliability figures to calculated plant lives. This paper describes the proposed definition of the LAM and how a proof of concept version of the LAM was developed to assess the Bettis Bechtel Stepped Pipe (BBSP) test. The results were presented with two seeded cases (fixed inputs) and a range of lives corresponding to associated Target Reliabilities (TRs). The Best Estimate (BE) and TR associated lives produced were based on using the latest methods available for calculating Fatigue Initiation (FI) and Fatigue Crack Growth (FCG), whereas the seeded Effective Strain Range (ESR) comparison case used current deterministic assessment methods. The results for the case study concluded that there is a benefit to pursuing the development of the LAM when compared to traditional assessment methods. It highlighted and quantified the conservatism present in traditional assessment methods for these cases as well as the need to understand the required TR for a specific component as this can have a large effect on the predicted life. With further refinements to the method, a more realistic and robust output of the total fatigue life distribution (for specific cases) would be obtained, which in turn would allow us to better quantify the conservatism associated with a TR.

Probabilistic Fatigue Life Assessment of a Titanium Alloy Impeller for Turbo Shaft Engine Application

2015 ◽  
Author(s):  
Esakki Muthu Shanmugam ◽  
Raghu V. Prakash ◽  
Sakthivel Ammaiappan
Keyword(s):  
Titanium Alloy ◽  
Fatigue Life ◽  
Equivalent Strain ◽  
Life Assessment ◽  
Centrifugal Impeller ◽  
Test Results ◽  
Distribution Method ◽  
Reliability Improvement ◽  
Fatigue Life Assessment ◽  
Strain Method

The fatigue life of the titanium alloy centrifugal impeller is estimated based on strain life method. a) Equivalent Strain Method and b) Smith Watson Topper Method are used. The probabilistic analysis of fatigue life is carried out by Weibull distribution method. The fatigue life of the impeller is assessed through cyclic spin test. The results are compared. The Equivalent Strain Method is found non conservative. The average fatigue life of the impeller is estimated as 12000 cycles by SWT method, which is found more closer to test results. The reliability improvement from 95% to 99% reduces the fatigue life around 18%.

Fatigue Life Analysis of Al 8090 Helicopter Fuselage Panels

2007 ◽  
Vol 348-349 ◽  
pp. 637-640
Author(s):  
Marco Giglio ◽  
Andrea Manes ◽  
Massimo Fossati
Keyword(s):  
Fatigue Life ◽  
Crack Growth ◽  
High Stress ◽  
Experimental Tests ◽  
Life Assessment ◽  
Fatigue Crack Growth Resistance ◽  
Anisotropic Mechanical Properties ◽  
High Crack ◽  
Life Analysis ◽  
Fatigue Life Analysis

Considering the aerospace structures, the advantages of Al-Li alloys in comparison with conventional aluminium alloys comprise relatively low densities, high elastic modulus, excellent fatigue and toughness properties, and superior fatigue crack growth resistance. Unfortunately, these alloys have some disadvantages due to highly anisotropic mechanical properties and due to a very high crack growth rate for microstructurally short cracks. This could mean relatively early cracking in high stress regions such as rivet holes in helicopter fuselage panels. Consequently a more accurate approach in fatigue life analysis is requested. Considering that the 8090 T81 aluminium alloy has been widely used in an helicopter structure, in particular in the bolted connection between the stringers and the modular joint frame in the rear of the fuselage, it is extremely important to found a reliable procedure for the fatigue life assessment of the component. Thus, using the results of experimental tests made on panel specimens, a FE general model and two submodels of the critical zone (involved in fatigue damage during the tests) have been modelled in order to investigate the complex state of stress near the rivets holes. These stress values obtained have been elaborated for a fatigue assessment.

scholarly journals Unified Principal S–N Equation for Friction Stir Welding of 5083 and 6061 Aluminum Alloys

2021 ◽  
Vol 34 (1) ◽  
Author(s):  
Xiangwei Li ◽  
Ji Fang ◽  
Xiaoli Guan
Keyword(s):  
Aluminum Alloy ◽  
Fatigue Life ◽  
Friction Stir Welding ◽  
Test Data ◽  
Fatigue Tests ◽  
Life Assessment ◽  
Test Results ◽  
Friction Stir ◽  
Fatigue Life Assessment ◽  
Curve Equation

AbstractWith the popularization of friction stir welding (FSW), 5083-H321 and 6061-T6 aluminum alloy materials are widely used during the FSW process. In this study, the fatigue life of friction stir welding with two materials, i.e., 5083-H321 and 6061-T6 aluminum alloy, are studied. Fatigue tests were carried out on the base metal of these two materials as well as on the butt joints and overlapping FSW samples. The principle of the equivalent structural stress method is used to analyze the FSW test data of these two materials. The fatigue resistances of these two materials were compared and a unified principal S–N curve equation was fitted. Two key parameters of the unified principal S–N curve obtained by fitting, Cd is 4222.5, and h is 0.2693. A new method for an FSW fatigue life assessment was developed in this study and can be used to calculate the fatigue life of different welding forms with a single S–N curve. Two main fatigue tests of bending and tension were used to verify the unified principal S–N curve equation. The results show that the fatigue life calculated by the unified mean 50% master S–N curve parameters are the closest to the fatigue test results. The reliability, practicability, and generality of the master S–N curve fitting parameters were verified using the test data. The unified principal S–N curve acquired in this study can not only be used in aluminum alloy materials but can also be applied to other materials.

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