Fatigue Tests and Design of Offshore Tubular Joints

1983 ◽  
Vol 105 (2) ◽  
pp. 189-194
Author(s):  
D. Dutta ◽  
F. Mang
Keyword(s):  
Stress Ratio ◽  
Design Method ◽  
Fatigue Behavior ◽  
Load Cycle ◽  
Fatigue Tests ◽  
Post Weld Heat Treatment ◽  
Small Scale ◽  
Plate Test ◽  
Tubular Joints ◽  
Stress Load

The AWS-X “hotspot stress-load cycle” curve used at present for designing tubular joints is based mainly on the fillet-welded plate test data and some more data from small-scale tests on tubular joints, which were available in the early 1970s. A review of further tests carried out in the recent years, including those by the authors, leads to the conclusion that the influence of the diameter and thickness of the tubes plays a significant role in the joint fatigue behavior. Hence, they must be taken into consideration while designing tubular joints accurately and more economically. A modified design method is proposed here with design curves for four diameter values. Further, the results of fatigue tests on K-type joints investigating the effect of stress ratio R and of post-weld heat treatment on the joint fatigue strength are described in this paper.

Enhanced Portland Cement Concrete Fatigue Model for StreetPave

2005 ◽  
Vol 1919 (1) ◽  
pp. 29-37 ◽  
Author(s):  
Leslie Titus-Glover ◽  
Jagannath Mallela ◽  
Michael I. Darter ◽  
Gerald Voigt ◽  
Steve Waalkes
Keyword(s):  
Portland Cement ◽  
Stress Ratio ◽  
Design Method ◽  
High Volume ◽  
Fatigue Tests ◽  
Slab Thickness ◽  
Portland Cement Concrete ◽  
Cement Concrete ◽  
Fatigue Model ◽  
Pavement Thickness

The Portland Cement Association (PCA) pavement thickness design method for jointed concrete pavements is mechanistically based and consists of both fatigue and erosion analyses. It determines the minimum slab thickness required for a given set of site and design conditions on the basis of both fatigue and erosion criteria. At the heart of the fatigue analysis is the fatigue model, which establishes the number of allowable load repetitions for a given stress ratio [ratio of flexural edge stress caused by the application of wheel loads to the portland cement concrete (PCC) slab flexural strength]. The PCA fatigue model is based on data derived from beam fatigue tests conducted in the early 1950s and 1960s. The model estimates the conservative lower-bound estimate of the allowable number of load applications at a given stress ratio (i.e., it incorporates a high degree of reliability–-approximately 90% or higher). Although this may be desirable for high-volume, high-traffic pavements, it is too conservative for low-volume roads or street pavements. The PCA pavement thickness design method currently is being used in the American Concrete Pavement Association (ACPA) pavement design software, StreetPave. StreetPave incorporates the PCA's pavement thickness design methodology in a Windows-based user platform. ACPA commissioned a study to expand, improve, and broaden the current PCA fatigue model by including reliability as a parameter for predicting PCC fatigue damage and by calibrating the enhanced model with additional fatigue data from recently completed studies. An enhanced fatigue model was then developed.

Effects of Residual Stresses on the High Cycle Fatigue Behavior of Ti-6Al-4V

2010 ◽  
Author(s):  
Yu-Jia Li ◽  
Fu-Zhen Xuan ◽  
Zheng-Dong Wang ◽  
Shan-Tung Tu
Keyword(s):  
Residual Stress ◽  
Fatigue Limit ◽  
Stress Ratio ◽  
Fatigue Behavior ◽  
Fatigue Tests ◽  
X Ray Diffraction ◽  
Surface Residual Stress ◽  
Manufacturing Techniques ◽  
Stress Ratios ◽  
Effect Of Surface

Axial force-controlled fatigue tests are conducted at various stress ratios (R) on Ti-6Al-4V specimens prepared by two different manufacturing techniques (hard turning plus polishing with and without vacuum stress relieve anneal carried out after polishing). Residual stress is measured by using X-ray diffraction. Results indicate that the surface compressive residual stress lead to an increase of fatigue limit at a given life and stress ratio. This effect decreases with increasing stress ratio R. At R = 0.6, the effect of surface residual stress on fatigue limit fades away. In addition, the location of crack initiation shifts from surface to interior when the stress ratio changes from −1 to 0.6.

High-Cycle Fatigue Behavior of Type 4340 Steel Pressurized Blocks Including Mean Stress Effect

2019 ◽  
Author(s):  
Elie A. Badr ◽  
Joanne Ishak
Keyword(s):  
Stress Ratio ◽  
Fatigue Behavior ◽  
Fatigue Loading ◽  
Fatigue Tests ◽  
Ultimate Stress ◽  
Stress Effect ◽  
Mean Stress ◽  
Test Results ◽  
Linear Correction ◽  
The Mean

Abstract Mean stress effects in pressurized steel blocks were examined under constant amplitude fatigue loading. The tests were performed to provide experimental data needed to study the effect of mean stress on fatigue lives of subject specimen, and to substantiate the use of analytical expressions to account for the mean stress. The mean stress was the result of subjecting the specimens to an autofrettage pressure which induced compressive residual stresses at the crossbore intersection of the specimens. Fatigue tests were carried out under both tensile and compressive mean stress levels. Test results were compared to several mean stress accounting relationships such as the Smith-Watson Topper, Bergmann and Seeger, modified Goodman, Gerber and Soderberg. Test results indicated that the modified Goodman equation is favorable in accounting for the effect of both tensile and compressive mean stresses on fatigue life (up to a compressive mean stress to ultimate stress ratio of −0.2). The behavior under compressive mean stress to ultimate stress ratio of less than −0.2 indicated that a linear correction relationship was required.

Effects of chromic acid anodizing on fatigue behavior of 7050 T7451 aluminum alloy

2021 ◽  
Vol 63 (9) ◽  
pp. 805-810
Author(s):  
Çağrı İlhan ◽  
Rıza Gürbüz
Keyword(s):  
Aluminum Alloy ◽  
Stress Ratio ◽  
Chromic Acid ◽  
Fatigue Behavior ◽  
Fatigue Tests ◽  
Constant Amplitude ◽  
Aluminum Oxide Layer ◽  
Fatigue Life Reduction ◽  
Selection Of ◽  
Scanning Electron

Abstract The effect of chromic acid anodizing (CAA) surface treatment on 7050 T7451 aluminum alloy was presented in this study in terms of fatigue behavior. CAA is a treatment against corrosion by producing aluminum oxide layer (Al2O3) at the surface. However, fatigue performance of 7050 T7451 is affected by the coating. In this study, eight different CAA processes were examined with regard to etching stage of pre-treatments by using an alkaline etchant and/or acid etchants with various immersion times. Optical microscopic examinations were applied in order to determine pitting characteristics for the selection of CAA process parameters before fatigue tests. A CAA process was selected among eight processes in terms of pitting characteristics in order to apply fatigue specimens. Four fatigue test groups were determined to investigate bare condition of 7050 T7451 and sub-stages of the CAA particularly. Constant amplitude axial fatigue tests were conducted on specimens at 91 Hz at stress ratio (R) -1 until run-out criteria, which was 106 cycles. Fatigue life reduction was determined due to pretreatments of CAA. Fracture surfaces of the specimens were examined by scanning electron microscope (SEM) to investigate morphology and crack initiation sites.

Orientation Dependence on Fatigue Fracture Behavior of Pure Mg Single Crystals

2018 ◽  
Vol 941 ◽  
pp. 1507-1510
Author(s):  
Yuta Kido ◽  
Akinobu Nakamura ◽  
Masayuki Tsushida ◽  
Hiromoto Kitahara ◽  
Shinji Ando
Keyword(s):  
Single Crystals ◽  
Fracture Behavior ◽  
Room Temperature ◽  
Stress Ratio ◽  
Stress Amplitude ◽  
Fatigue Behavior ◽  
Orientation Dependence ◽  
Fatigue Tests ◽  
Crystal Orientations ◽  
Fatigue Fracture Behavior

It is well known that magnesium (Mg) shows anisotropic fatigue behavior. However, the fatigue mechanisms have yet to be elucidated. The relationships between crystal orientations and crack initiation behavior in Mg single crystals were investigated by uniaxial tension-compression fatigue tests. Three types of round-bar specimens were prepared. The lording direction of AD, BC and EF specimen were [110], [100] and [0001], respectively. Fatigue tests were carried out with the stress ratio R=-1 and the frequency of 10Hz at room temperature in laboratory air. At stress amplitude (σa) over 40 MPa, fatigue lives of BC specimen and EF specimen were the longest and shortest. However, at σa =20 MPa, the fatigue life of all specimens were almost the same. It was found that fatigue lives of Mg single crystals strongly depend on crystal orientations and stress.

Fatigue Design Model Based on Damage Mechanisms Revealed by Acoustic Emission Measurements

1995 ◽  
Vol 117 (2) ◽  
pp. 200-208 ◽  
Author(s):  
D. Fang ◽  
A. Berkovits
Keyword(s):  
Acoustic Emission ◽  
Stress Ratio ◽  
Crack Nucleation ◽  
Load Cycle ◽  
Fatigue Tests ◽  
Damage Prediction ◽  
Fatigue Design ◽  
Final Failure ◽  
On Line ◽  
Selection Of

Integration of the microcomputer into acoustic emission instrumentation has brought AE monitoring of fatigue tests into the realm of practicality. On-line processing makes available a selection of software tools, enhancing classical techniques for eliminating the background noise which usually blanked out the desired data. Fatigue tests monitored for acoustic emission were carried out at room temperature on Incoloy 901 material specimens, over a stress-ratio range of −1 ≤ R ≤ .2. Valid AE data were obtained even when the load cycle passed through zero. The AE data permitted specific identification of the various phenomena occurring on the way to final failure. These included initial plasticity, crack nucleation and propagation phases. The AE findings were supported by microscopic examination. Based on the experimental data, a preliminary damage-prediction model was formulated.

scholarly journals Fatigue Analysis of Threaded Components with Cd and Zn-Ni Anticorrosive Coatings

Metals ◽  
2021 ◽  
Vol 11 (9) ◽  
pp. 1455
Author(s):  
Jefferson Rodrigo Marcelino dos Santos ◽  
Martin Ferreira Fernandes ◽  
Verônica Mara de Oliveira Velloso ◽  
Herman Jacobus Cornelis Voorwald
Keyword(s):  
Stress Concentration ◽  
Stress Ratio ◽  
Fatigue Behavior ◽  
Base Material ◽  
Experimental Tests ◽  
Fatigue Tests ◽  
Element Analysis ◽  
Aisi 4140 ◽  
Stress Concentration Effect ◽  
Zinc Nickel

The influence of the electrodeposition of cadmium and zinc-nickel and the stress concentration effect on the fatigue behavior of AISI 4140 steel threaded components were studied. Axial fatigue tests at room temperature with a stress ratio of R = 0.1 were performed using standard and threaded specimens with and without nut interface under base material, cadmium, and zinc-nickel-coated conditions. Finite element analysis (FEA) was used, considering both elastic and elastoplastic models, to quantify the stress distribution and strain for threaded specimens with and without a nut interface. The numeric results were correlated to the experimental fatigue data of threaded components with and without the nut interface, to allow the oil & gas companies to extrapolate the results for different thread dimensions, since the experimental tests are not feasible to be performed for all thread interfaces. Scanning electron microscopy (SEM) was used to analyze the fracture surfaces. The stress concentration factor had a greater influence on the fatigue performance of threaded components than the effect of the Cd and Zn-Ni coatings. The fatigue life of studs reduced by about 58% with the nut/stud interface, compared to threaded components without nuts. The elastoplastic FEA results showed that studs with a stud/nut interface had higher stress values than the threaded specimens without a nut interface. The FEA results showed that the cracks nucleated at the regions with higher strain, absorbed energy, and stress concentration. The substitution of Cd for a Zn-Ni coating was feasible regarding the fatigue strength for threaded and smooth components.

scholarly journals Seawater Effect on Fatigue Behaviour of Notched Carbon/Epoxy Laminates

2021 ◽  
Vol 11 (24) ◽  
pp. 11939
Author(s):  
Ricardo Branco ◽  
Paulo N. B. Reis ◽  
Maria A. Neto ◽  
José D. Costa ◽  
Ana M. Amaro
Keyword(s):  
Water Absorption ◽  
Stress Ratio ◽  
Stress Amplitude ◽  
Rectangular Cross Section ◽  
Fatigue Behavior ◽  
Failure Mechanisms ◽  
Fatigue Behaviour ◽  
Fatigue Tests ◽  
Artificial Seawater ◽  
Microscopy Technique

This paper studies the effect of seawater immersion on the fatigue behavior of notched carbon/epoxy laminates. Rectangular cross-section specimens with a central hole were immersed in natural and artificial seawater for different immersion times (0, 30 and 60 days), being the water absorption rate evaluated over time. After that, fatigue tests were performed under uniaxial cyclic loading using a stress ratio equal to 0.1. After the tests, the optical microscopy technique allowed the examination of the failure micro-mechanisms at the fracture surfaces. The results showed that saturation appeared before 30 days of immersion and that water absorption rates were similar for natural and artificial seawater. The S–N curves showed that the seawater immersion affects the fatigue strength, but there were no relevant effects associated with the type of seawater. Moreover, it was also clear that fatigue life was similar for long lives, close to 1 million cycles, regardless of the immersion time or the type of seawater. On the contrary, for short lives, near 10 thousand cycles, the stress amplitude of dry laminates was 1.2 higher than those immersed in seawater. The failure mechanisms were similar for all conditions, evidencing the fracture of axially aligned fibres and longitudinal delamination between layers.

Aluminum Drill Pipes: Material and Design Developments

2008 ◽  
Author(s):  
Marcelo Igor Lourenc¸o ◽  
Theodoro A. Netto ◽  
Joa˜o Carlos Ribeiro Pla´cido
Keyword(s):  
Mechanical Design ◽  
Fatigue Behavior ◽  
Axial Stress ◽  
Drill Pipe ◽  
Element Model ◽  
Fatigue Tests ◽  
Small Scale ◽  
Physical Experiments ◽  
Drill Pipes ◽  
Tool Joint

An extensive research program on the structural strength of aluminum drill-pipes is being conducted at COPPE/UFRJ. The main objective is to improve the fatigue performance of these components by selecting the appropriate aluminum alloy and by enhancing the mechanical design of the threaded steel connector. This paper presents the experimental test program and numerical analyses conducted on a drill-pipe of different materials (Al-Zn-Mg alloy) and geometries from those previously presented [1,2]. Small-scale specimens were tested to determine its uni-axial stress-strain and fatigue behavior. Full-scale fatigue test results are also presented. A finite element model of the drill pipe, including the tool-joint region, was developed. The model simulates, through different load steps, the tool-joint hot assembly, and then reproduces the physical experiments numerically in order to obtain the actual stress distribution. The correlation between full and small-scale fatigue tests is performed via multi-axial fatigue models. The weak points of the current practice design are highlighted for further development.

Flexural Fatigue of PVC Foams

2001 ◽  
Author(s):  
Krishnan Kanny ◽  
Hassan Mahfuz ◽  
Leif A. Carlsson ◽  
Tonnia Thomas ◽  
Shaik Jeelani
Keyword(s):  
Stress Ratio ◽  
Fatigue Behavior ◽  
Damping Ratio ◽  
Fatigue Tests ◽  
Foam Density ◽  
Flexural Fatigue ◽  
Viscoelastic Parameters ◽  
Final Failure ◽  
Failure Event ◽  
Sem Analyses

Abstract Flexural fatigue tests were performed on cross-linked PVC foams of densities in the range from 75 to 300 kg/m3 at a frequency of 3Hz and at a stress ratio, R = 0.1. S-N diagrams were generated, and the failure mechanisms were examined. The fatigue behavior was found to be similar to structural materials with a fatigue strength that decreased with increased stress and increased with increased foam density. The final failure event was catastrophic due to crack propagation initiating at the tension side of the beam. SEM analyses of unfailed and failed 300kg/m3 density foam specimens revealed cell wall cracking and densification of the foam. The densification contributed to stiffening of foam specimens. Viscoelastic parameters of the foams were determined at room temperature using a Dynamic Mechanical Analyzer (DMA) over a frequency range of 1–10Hz. For the virgin specimens it was found that the viscoelastic moduli and damping ratio were quite independent of frequency over this range of frequencies. Except for the lowest density foam (75kg/m3), the damping ratio was quite independent of foam density.

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