Mean Stress Effect on Fatigue of Welded Joint in FPSOs

2006 ◽  
Author(s):  
Bin Zhang ◽  
Torgeir Moan
Keyword(s):  
Fatigue Life ◽  
Fatigue Strength ◽  
Residual Stresses ◽  
Stress Effect ◽  
Mean Stress ◽  
Initial Condition ◽  
Mean Stress Effect ◽  
Structural Details ◽  
The Mean ◽  
Mean Stresses

This paper deals with the mean stress effect on the fatigue life of welded joints in FPSOs. Mean stresses in structural details of FPSOs are composed of residual stresses and mean stresses induced by external service loading conditions. Mean stresses, both the residual stresses and those induced by external load, affect on the fatigue life of structural details. Fatigue strength decreases as tensile mean stress increases. Under compressive mean stresses, fatigue lives are increased. Different fatigue analysis procedures to account for mean stress effect, i.e. JBP, JTP, DNV CN30.7 and IIW procedure, are used to compare the fatigue test data of different specimens representing different typical welded connections in ship-shaped structures from HHI in Korea. In this paper these procedures are compared and an improved procedure explicitly considering of the mean stress effect is also proposed. The fatigue strength of welded joints of FPSO is affected by the initial condition as well as possible redistribution (shake-down) of the residual stresses. The initial condition of welding residual stress and its re-distribution by static preload and cyclic load in the small scale specimens are evaluated with FE analyses and analytical equations, also compared with the test results obtained from measurement based on ordinary sectioning method.

scholarly journals Application of the S-N Curve Mean Stress Correction Model in Terms of Fatigue Life Estimation for Random Torsional Loading for Selected Aluminum Alloys

Materials ◽  
2020 ◽  
Vol 13 (13) ◽  
pp. 2985
Author(s):  
Michał Böhm ◽  
Krzysztof Kluger ◽  
Sławomir Pochwała ◽  
Mariusz Kupina
Keyword(s):  
Fatigue Life ◽  
Fatigue Strength ◽  
Stress Effect ◽  
Mean Stress ◽  
Torsional Loading ◽  
Correction Model ◽  
Life Estimation ◽  
Mean Stress Effect ◽  
Fatigue Life Estimation ◽  
The Mean

The paper presents the experimental fatigue test results for cyclic constant amplitude loading conditions for the case of the torsion of the PA4 (AW-6082-T6), PA6 (AW-2017A-T4) and PA7 (AW-2024-T3) aluminum alloy for a drilled diabolo type test specimen. The tests have been performed for the stress asymmetry ratios R = −1, R = −0.7, R = −0.5 and R = −0.3. The experimental results have been used in the process of a fatigue life estimation performed for a random generated narrowband stress signal with a zero and a non-zero global mean stress value. The calculations have been performed within the time domain with the use of the rainflow cycle counting method and the Palmgren−Miner damage hypothesis. The mean stress compensation has been performed with the S-N curve mean stress model proposed by Niesłony and Böhm. The model has been modified in terms of torsional loading conditions. In order to obtain an appropriate R = 0 ratio S-N curve fatigue strength amplitude, the Smith−Watson−Topper model was used and compared with literature fatigue strength amplitudes. The presented solution extends the use of the correction model in terms of the torsional loading condition in order to obtain new S-N curves for other R values on the basis of the R = −1 results. The work includes the computational results for new fatigue curves with and without the mean stress effect correction. The results of the computations show that the mean stress effect plays a major role in the fatigue life assessment of the tested aluminum alloys and that the method can be used to assess the fatigue life under random conditions.

S–N curves for fatigue life estimation of friction stir welded 19501 aluminum alloy T-joint

2018 ◽  
Vol 233 (2) ◽  
pp. 664-674
Author(s):  
Prakash Chandra Gope ◽  
Harshit Kumar ◽  
Himanshu Purohit ◽  
Manish Dayal
Keyword(s):  
Aluminum Alloy ◽  
Fatigue Life ◽  
Fatigue Strength ◽  
Weld Zone ◽  
Stress Effect ◽  
Mean Stress ◽  
Friction Stir ◽  
Fracture Surfaces ◽  
Mean Stress Effect ◽  
Metallic Bonding

In this study, the mechanical properties and fatigue life of 19501 aluminum alloy friction stir welded T-joint is investigated. Tensile properties of friction stir welded joint show that there is a marginal reduction of about 5% in strength and ductility as compared to unwelded 19501 aluminum alloy. Fatigue test results of T-joint specimen at two stress ratios of 0 and -1 show that there is a reduction of 15% in fatigue strength due to change of stress ratio from -1 to 0. Also, higher variation is seen in fatigue strength in low cycle zone than the high cycle zone. Effect of mean stress on fatigue life is discussed on the basis of different mean stress effect models. Morrow’s mean stress effect model is found to be better than other models. Micrographs from the fracture surfaces of retreating side, mid weld zone, and advancing side of the T-joint indicates that fracture surfaces are cleavage fracture. Different sizes of inter-metallic bonding are seen in the micrographs, which indicate that fracture is initiated due to breaking of the brittle inter-metallic bonding.

Mean Stress Effect on Fatigue Properties of Type 316 Stainless Steel: Part II — In PWR Primary Water Environment

2017 ◽  
Author(s):  
Masayuki Kamaya
Keyword(s):  
Stainless Steel ◽  
Fatigue Life ◽  
Effective Strain ◽  
Strain Range ◽  
Stress Effect ◽  
Mean Stress ◽  
316 Stainless Steel ◽  
Mean Stress Effect ◽  
Primary Water ◽  
The Mean

The mean stress effect on the fatigue life of Type 316 stainless steel was investigated at 325°C in simulated PWR primary water. It was shown that, as shown in high-temperature air environment, the fatigue life was extended by applying the mean stress under the same stress amplitude. An increase in the maximum peak stress by applying the mean stress induced additional plastic strain and this hardened the material. On the other hand, the fatigue life was shortened by the mean stress for the same strain range. The ratcheting strain caused by applying mean stress accelerated crack mouth opening and reduced fatigue life. It was also shown that the fatigue life in the simulated PWR primary water was shorter than that in air even without the mean stress. The magnitude of the reduction depended on the strain range. The reduction in fatigue life was the maximum when the strain range was 0.6%. The environmental effect disappeared when the effective strain was less than 0.4%.

scholarly journals Thermoelastic Stress Analysis: An NDE Tool for Residual Stress Assessment of Metallic Alloys

2002 ◽  
Vol 124 (2) ◽  
pp. 383-387 ◽  
Author(s):  
A. L. Gyekenyesi
Keyword(s):  
Residual Stress ◽  
Second Harmonic ◽  
Temperature Response ◽  
Thermoelastic Stress ◽  
Stress Effect ◽  
Mean Stress ◽  
Thermoelastic Stress Analysis ◽  
Mean Stress Effect ◽  
The Mean ◽  
Mean Stresses

The primary objective of this report involves studying and developing various experimental techniques for accurate measurement of the mean stress effect in thermoelastic stress analysis (TSA, also recognized as SPATE: stress pattern analysis by thermal emission). The analysis of cyclic mean stresses at the coupon level directly relates to the measurement of residual stresses in structures. In a previous study by the authors, it was shown that cyclic mean stresses significantly influenced the TSA results for titanium and nickel-based alloys, although, difficulties were encountered concerning the quantification of the mean stress effect because of large test-to-test variations. This study continues the effort of accurate direct measurements of the mean stress effect by implementing various experimental modifications. In addition, a more in-depth analysis is included which involves analyzing the second harmonic of the temperature response. By obtaining the amplitudes of the first and second harmonics, the stress amplitude and the mean stress at a given point on a structure subjected to a cyclic load can be simultaneously obtained. The rather complex analysis of the temperature response involves obtaining the first and second harmonic amplitudes for 16384 infrared detectors (128×128 focal plane array). Upon establishing a protocol for mean stress measurements in the laboratory using the TSA technique, the next step is to utilize the method to assess residual stress states in complex structures during manufacturing and life.

Mean Stress Effect on Fatigue Properties of Type 316 Stainless Steel in Pressurized Water Reactors Primary Water Environment

2019 ◽  
Vol 141 (5) ◽  
Author(s):  
Masayuki Kamaya
Keyword(s):  
Stainless Steel ◽  
Fatigue Life ◽  
Water Environment ◽  
Stress Effect ◽  
Mean Stress ◽  
Pressurized Water ◽  
316 Stainless Steel ◽  
Mean Stress Effect ◽  
Primary Water ◽  
The Mean

The mean stress effect on the fatigue life of type 316 stainless steel was investigated in simulated pressurized water reactor (PWR) primary water and air at 325 °C. The tests in air environment have revealed that the fatigue life was increased with application of the positive mean stress for the same stress amplitude because the strain range was decreased by hardening of material caused by increased maximum peak stress. On the other hand, it has been shown that the fatigue life obtained in simulated PWR primary water was decreased compared with that obtained in air environment even without the mean stress. In this study, type 316 stainless steel specimens were subjected to the fatigue test with and without application of the positive mean stress in high-temperature air and PWR water environments. First, the mean stress effect was discussed for high-temperature air environment. Then, the change in fatigue life in the PWR water environment was evaluated. It was revealed that the change in the fatigue life due to application of the mean stress in the PWR water environment could be explained in the same way as for the air environment. No additional factor was induced by applying the mean stress in the PWR water environment.

scholarly journals Mean Stress Effect on the Fatigue Life of 304L Austenitic Steel in Air and PWR Environments Determined with Strain- and Load-Controlled Experiments

Metals ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 221 ◽  
Author(s):  
Philippe Spätig ◽  
Jean-Christophe Le Roux ◽  
Matthias Bruchhausen ◽  
Kevin Mottershead
Keyword(s):  
Fatigue Life ◽  
Austenitic Steel ◽  
Strain Amplitude ◽  
Synergistic Effects ◽  
Stress Effect ◽  
Mean Stress ◽  
Controlled Experiments ◽  
Pressurized Water ◽  
Mean Stress Effect ◽  
The Mean

The mean stress effect on the fatigue life of 304L austenitic steel was evaluated at 300 °C in air and pressurized water reactor (PWR) environments. Uniaxial tests were performed in strain-control and load-control modes, with zero mean stress and a positive mean stress of 50 MPa. A specific procedure was used for the strain-controlled experiments to maintain the strain amplitude and mean stress constant. The strain-controlled data indicate that the application of positive mean stress decreases the fatigue life for a given strain amplitude in air and PWR environments. The data also show that the life reduction is independent of the environments, suggesting that no synergistic effects between the mean stress and the LWR environment occur. The load-controlled experiments confirm that the application of positive mean stress increases fatigue due to cyclic hardening processes. This observation is much less pronounced in the PWR environment. All data were analyzed using the Smith–Watson–Topper (SWT) stress–strain function, which was shown to correlate well with all strain- and load-controlled data with and without mean stress in each environment. In the SWT–life curve representation, the life reduction in the PWR environment was found fully consistent with the NUREG-CR6909 predictions.

scholarly journals The effect of mean stress on the fatigue behaviour of overhead conductor function of the H/w parameter

2018 ◽  
Vol 165 ◽  
pp. 11001
Author(s):  
Remy Badibanga ◽  
Thiago Miranda ◽  
Pedro Rocha ◽  
Jorge Ferreira ◽  
Cosme da Silva ◽  
...  
Keyword(s):  
Fatigue Life ◽  
Fatigue Behaviour ◽  
Fatigue Tests ◽  
Experimental Results ◽  
Stress Effect ◽  
Mean Stress ◽  
Stress Effects ◽  
Mean Stress Effect ◽  
The Mean

The objective of this work is to evaluate the effects of mean stress on the fatigue behaviour of an All Aluminium Conductor (AAC Orchid), Aluminium Conductor Steel Reinforced (ACSR Tern), and an Aluminium Conductor Alloy Reinforced (ACAR 750 MCM). In this sense, 72 fatigue tests on overhead conductors were performed using different values of H/w parameter. Based on the experimental results, the parameters which describe the fatigue behaviour of the conductors were determined after generating theirs S-N curves. In the assessment of the mean stress effects on the fatigue life, Goodman and Gerber’s relations were fitted to evaluate the use of such models for the conductors. It was observed that the evaluation of the mean stress effect on the overhead conductor could be made by using the fatigue relations.

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