Statistical Analysis of Fatigue Test Data

2017 ◽  
Author(s):  
Carol Johnston
Keyword(s):  
Statistical Analysis ◽  
Fatigue Strength ◽  
Cyclic Loading ◽  
Fatigue Test ◽  
Test Data ◽  
Fatigue Tests ◽  
Fatigue Performance ◽  
Test Results ◽  
Girth Welds ◽  
New Procedures

The offshore environment contains many sources of cyclic loading. Standard design S-N curves, such as those in DNVGL-RP-C203, are usually assigned to ensure a particular design life can be achieved for a particular set of anticipated loading conditions. Girth welds are often the ‘weak link’ in terms of fatigue strength and so it is important to show that girth welds made using new procedures for new projects that are intended to be used in fatigue sensitive risers or flowlines do indeed have the required fatigue performance. Alternatively, designers of new subsea connectors, used for example in tendons for tension leg platforms, mooring applications or well-heads which will experience cyclic loading in service, also wish to verify the fatigue performance of their new designs. Often operators require contractors to carry out resonance fatigue tests on representative girth welds in order to show that girth welds made using new procedures qualify to the required design S-N curve. Operators and contractors must then interpret the results, which is not necessarily straightforward if the fatigue lives are lower than expected. Many factors influence a component’s fatigue strength so there is usually scatter in results obtained when a number of fatigue tests are carried out on real, production standard components. This scatter means that it is important first to carry out the right number of tests in order to obtain a reasonable understanding of the component’s fatigue strength, and then to interpret the fatigue test results properly. A working knowledge of statistics is necessary for both specifying the test programme and interpreting the test results and there is often confusion over various aspects of test specification and interpretation. This paper describes relevant statistical concepts in a way that is accessible to non-experts and that can be used, practically, by designers. The paper illustrates the statistical analysis of test data with examples of the ‘target life’ approach (that is now included in BS7608:2014 + A1) and the equivalent approach in DNVGL-RP-C203, which uses the stress modification factor. It gives practical examples to designers of a pragmatic method that can be used when specifying test programmes and interpreting the results obtained from tests carried out during qualification programmes, which for example, aim to determine whether girth welds made using a new procedure qualify to a particular design curve. It will help designers who are tasked with specifying test programmes to choose a reasonable number of test specimens and stress ranges, and to understand the outcome when results have been obtained.

Fatigue Performance of Concrete with Pre-Cracks in Tension-Compression Cycles

2014 ◽  
Vol 584-586 ◽  
pp. 1054-1061
Author(s):  
Jian Shen ◽  
Xiao Yun Liu ◽  
Lang Wu
Keyword(s):  
Fatigue Life ◽  
Fatigue Strength ◽  
Cyclic Loading ◽  
Fatigue Test ◽  
Stress Ratio ◽  
Fatigue Property ◽  
Fatigue Performance ◽  
Cycle Fatigue ◽  
Fatigue Load ◽  
Compression Cycle

A tension-compression cycle fatigue test was performed in order to study the fatigue property of C50 concrete with pre-cracks in cyclic loading. The stress ratio was-1 and the amplitude was 0.2 MPa ~1.30 MPa. The results show that the modified coefficient of fatigue strength is 0.198~0.265 and the infinite life fatigue strength is below 0.45MPa. While the log value of fatigue life is approximately linear with the amplitude of fatigue load stress, the discreteness of fatigue life, the particularity of concrete, has little to do with the amplitude. The S-N, P-N fatigue life curves and the constant fatigue life diagram of pre-crack concrete are obtained.

Experimental Study on Fatigue Strength of Small-Diameter Socket-Welded Pipe Joints

1998 ◽  
Vol 120 (2) ◽  
pp. 149-156 ◽  
Author(s):  
M. Higuchi ◽  
A. Nakagawa ◽  
K. Iida ◽  
M. Hayashi ◽  
T. Yamauchi ◽  
...  
Keyword(s):  
Fatigue Life ◽  
Fatigue Strength ◽  
Fatigue Test ◽  
Welded Joints ◽  
Fatigue Tests ◽  
Defect Size ◽  
Test Results ◽  
Pipe Surface ◽  
Bending Fatigue ◽  
Nominal Diameter

The authors conducted fully reversed four-point bending fatigue tests on socket-welded joints 20 to 50 mm in nominal diameter, and rotating bending fatigue tests on socket-welded joints 20 mm in nominal diameter. S-N curves for 33 series of different types of specimens were obtained. Examination was made of the effects of various parameters listed in the forthcoming on fatigue strength such as steel types (carbon and stainless steels), diameter, pipe thickness (Sch), fillet shape, slip-on gap, and root defects. Bending fatigue test results indicated fatigue strength for socket-welded joints to be less for longer life regions than reported in the literature by Markl and George (1950). Fatigue strength for socket joints of 50 mm nominal diameter at 107 cycles of fatigue life was 46 MPa for carbon steel and 60 MPa for stainless steel with nominal bending stress on the pipe surface. Cracks generally originated from the toe when stress amplitude was high with shorter fatigue life and from the root when amplitude was small with longer life. Fatigue strength was greater for smaller diameter, larger Sch (thicker pipe wall), final welding pass on the toe of pipe side, and in the absence of a slip-on gap. From fatigue test results of socket joints with weld defects at the roots, an empirical equation for the relation of defect size with decrease in fatigue strength was established. Fatigue strength was found to decrease to 60 percent the original level for defect size 25 percent of leg length.

An Empirical Approach to the Fatigue-Strength Analysis of Structures

1946 ◽  
Vol 13 (3) ◽  
pp. A201-A206
Author(s):  
Henry W. Foster ◽  
Victor Seliger
Keyword(s):  
Experimental Data ◽  
Aluminum Alloy ◽  
Fatigue Strength ◽  
Fatigue Test ◽  
Test Data ◽  
Empirical Approach ◽  
Strength Analysis ◽  
Test Results ◽  
Structural Fatigue ◽  
Actual Test

Abstract A method of fatigue-strength analysis for fabricated structures, based on laboratory fatigue-test data, is proposed in this paper. To this end the nature of structural fatigue strength is discussed with the view of defining the necessary correlating assumptions and the type of experimental data needed. An example of this method is presented for structures fabricated from Alclad 24S-T aluminum alloy and analysis results are compared with actual test results.

scholarly journals Analysis of the Correlation between the Static and Fatigue Test Results of the Interlayer Bondings of Asphalt Layers

2016 ◽  
Vol 62 (1) ◽  
pp. 83-98 ◽  
Author(s):  
A. Szydło ◽  
K. Malicki
Keyword(s):  
Fatigue Life ◽  
Fatigue Test ◽  
Asphalt Mixture ◽  
Fatigue Tests ◽  
Test Results ◽  
Static Tests ◽  
Bonding State ◽  
Road Pavement ◽  
The Future ◽  
Pavement Structure

Abstract The bonding state of the asphalt layers in a road pavement structure significantly affects its fatigue life. These bondings, therefore, require detailed tests and optimization. In this paper, the analyses of the correlation between the results of laboratory static tests and the results of fatigue tests of asphalt mixture interlayer bondings were performed. The existence of the relationships between selected parameters was confirmed. In the future, the results of these analyses may allow for assessment of interlayer bondings’ fatigue life based on the results of quick and relatively easy static tests.

Fatigue Capacity of Stiffener to Web Frame Connections

2009 ◽  
Author(s):  
Torbjo̸rn Lindemark ◽  
Inge Lotsberg ◽  
Joong-Kyoo Kang ◽  
Kwang-Seok Kim ◽  
Narve Oma
Keyword(s):  
Fatigue Test ◽  
Test Data ◽  
Large Scale ◽  
Fatigue Tests ◽  
Life Assessment ◽  
Shear Stresses ◽  
Test Model ◽  
The Difference ◽  
Marine Engineering ◽  
Plate Connections

Daewoo Shipbuilding & Marine Engineering Co., Ltd. (DSME), StatoilHydro and DNV established a common project to investigate the reason for the difference between calculated fatigue lives and the in-service experience and to assess the fatigue capacity of stiffener web connections subjected mainly to web frame shear stresses. The main objective of the work was to establish fatigue test data and perform numerical analysis of collar plate connections in order to provide improved confidence in analysis methodology for fatigue life assessment. Large scale fatigue tests of different types of connections were carried out to obtain fatigue test data of collar plate connections. Finite element analyses were carried out for comparison with fatigue test data and with measured stresses on the test model. Based on this work recommendations on fatigue design analysis of connections between stiffeners and web frames have been derived. The background for this is presented in this paper.

The effect on the fatigue strength of bone cement of adding sodium fluoride

2001 ◽  
Vol 215 (2) ◽  
pp. 251-253 ◽  
Author(s):  
C Minari ◽  
M Baleanil ◽  
L Cristofolini ◽  
F Baruffaldi
Keyword(s):  
Fatigue Strength ◽  
Bone Cement ◽  
Sodium Fluoride ◽  
Biomedical Applications ◽  
Cement Mantle ◽  
Fatigue Tests ◽  
Fatigue Performance ◽  
Bone Cements ◽  
The Novel ◽  
Pmma Bone Cement

New bone cements that include several additives are currently being investigated and tested. One such additive is sodium fluoride (NaF), which promotes bone formation, facilitating implant integration and success. The influence of NaF on the fatigue performance of the cement as used in biomedical applications was tested in this paper. In fact fatigue failure of the cement mantle is a major factor limiting the longevity of a cemented implant. An experimental bone cement with added NaF (12wt%) was investigated. The fatigue strength of the novel bone cement was evaluated in comparison with the cement without additives; fatigue tests were conducted according to current standards. The load levels were arranged based on a validated, statistically based optimization algorithm. The curve of stress against number of load cycles and the endurance limit were obtained and compared for both formulations. The results showed that the addition of NaF (12 wt %) to polymethylmethacrylate (PMMA) bone cement does not affect the fatigue resistance of the material. Sodium fluoride can safely be added to the bone cement without altering the fatigue performance of the PMMA bone cement.

scholarly journals Effects of thermomechanical history and environment on the fatigue behavior of (β)-Ti-Nb implant alloys

2018 ◽  
Vol 165 ◽  
pp. 06001 ◽  
Author(s):  
André Reck ◽  
Stefan Pilz ◽  
Ulrich Thormann ◽  
Volker Alt ◽  
Annett Gebert ◽  
...  
Keyword(s):  
Fatigue Strength ◽  
Cyclic Loading ◽  
Fatigue Behavior ◽  
Fatigue Tests ◽  
Grain Structure ◽  
Fatigue Properties ◽  
Β Phase ◽  
Α Phase ◽  
Nb Content ◽  
Implant Alloys

This study examined the fatigue properties of a newly developed cast and thermomechanical processed (β)-Ti-40Nb alloy for a possible application as biomedical alloy due to exceptional low Young’s modulus (64-73 GPa), high corrosion resistance and ductility (20-26%). Focusing on the influence of two microstructural states with fully recrystallized β-grain structure as well as an aged condition with nanometer-sized ω-precipitates, tension-compression fatigue tests (R=-1) were carried out under lab-air and showed significant differences depending on the β-phase stability under cyclic loading. Present ω- precipitates stabilized the β-phase against martensitic α’’ phase transformations leading to an increased fatigue limit of 288 MPa compared to the recrystallized state (225 MPa), where mechanical polishing and subsequent cyclic loading led to formation of α’’-phase due to the metastability of the β-phase. Additional studied commercially available (β)-Ti-45Nb alloy revealed slightly higher fatigue strength (300 MPa) and suggest a change in the dominating cyclic deformation mechanisms according to the sensitive dependence on the Nb-content. Further tests in simulated body fluid (SBF) at 37°C showed no decrease in fatigue strength due to the effect of corrosion and prove the excellent corrosion fatigue resistance of this alloy type under given test conditions.

Three Ways of Sampling and Fatigue Test Results of Steel P92

2014 ◽  
Vol 891-892 ◽  
pp. 273-277
Author(s):  
Josef Volák ◽  
Zbynek Bunda
Keyword(s):  
Mechanical Properties ◽  
Power Plant ◽  
Fatigue Test ◽  
Fatigue Tests ◽  
Energy Industry ◽  
Fatigue Properties ◽  
Test Results ◽  
Steam Turbines ◽  
Standard Samples ◽  
Energy Component

This paper describes the fatigue properties of the steel P92. This material is widely used in the energy industry, especially for pipes and pipe bends of supercritical steam turbines. Steel P92 is alloyed with 2 % of tungsten compared to steel P91. This increases a creep strenght of the material. It is possible to reduce wall thickness of the P92 pipe up to about 20%. Fatigue tests were carried out on standard samples and compared with SFT samples (Small Fatigue Test). Using the device SSam 2 made by company Rolce Royce, it is possible to gently remove a samples from energy component without power plant shutdowns. Consider these correlations, i tis possible to determine mechanical properties of the material from small amount of removed experimental material.

Fatigue Strength Reduction Factors for Welded Joints: Another View

2007 ◽  
Author(s):  
Arturs Kalnins
Keyword(s):  
Standard Deviation ◽  
Fatigue Strength ◽  
Fatigue Test ◽  
Test Data ◽  
Welded Joints ◽  
Welded Joint ◽  
Fatigue Curve ◽  
Strength Reduction ◽  
Initial Estimate ◽  
Curve Fit

The paper distinguishes between FSRFs that are used for two different purposes. One is to serve as a guideline for an initial estimate of the fatigue strength of a welded joint. That is the purpose of the FSRFs that are given in the ASME B&PV Code and various accompanying documents. If that estimate renders the fatigue strength inadequate, an FSRF can be sought that is limited to the joint under consideration. The paper shows how such FSRFs can be determined from fatigue test data. In order to make it possible to read the allowable cycles from the same design fatigue curve as that used for the FSRFs of the guidelines, a Langer curve [defined by equation (2) in the paper] is used to curve fit the data. The appropriate FSRF is obtained by minimizing the standard deviation between this curve and the data. The procedure is illustrated for girth butt-welded pipes. The illustration shows that for the data used in the analysis, a constant FSRF is applicable to less than one million cycles but not to the high-cycle regime.

Comparison Between ASME Code-Case N-761, NUREG/CR-6909 and Stainless Steel Component Fatigue Test Results

2014 ◽  
Author(s):  
H. T. Harrison ◽  
Robert Gurdal
Keyword(s):  
Stainless Steel ◽  
Fatigue Test ◽  
Fatigue Tests ◽  
Test Series ◽  
Test Results ◽  
Actual Number ◽  
Steel Component ◽  
Class 1 ◽  
Asme Code ◽  
Number Of Cycles

For Class 1 components, the consideration of the environmental effects on fatigue has been suggested to be evaluated through two different methodologies: either NUREG/CR-6909 from March 2007 or ASME-Code Case N-761 from August 2010. The purpose of this technical paper is to compare these two methods. In addition, the equations from Revision 1 of the NUREG/CR-6909 will be evaluated. For these comparisons, two stainless steel component fatigue test series with documented results are considered. These two fatigue test series are completely different from each other (applied cyclic displacements vs. insurge/outsurge types of transients). Therefore, they are producing an appropriate foundation for these comparisons. In general, the severities of the two methods are compared, where the severity is defined as the actual number of cycles from the fatigue tests, including an evaluation of the scatter, divided by the number of design cycles from the two methods. Also, how stable the methods are is being evaluated through the calculation of the coefficient of variation for each method.

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