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Fatigue performance of welded joints made of high-strength steel under variable amplitude loading conditions and varying mean stress

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WELDING IN THE WORLD 2025年 1-16页

作者： Gronlund, Kiia Ahola, Antti Lipiainen, Kalle Pesonen, Tero Bjork, Timo Moshtaghi, Masoud Lappeenranta Lahti Univ Technol LUT Lab Steel Struct POB 20 Lappeenranta 53851 Finland

The study experimentally and analytically investigates the effects of variable amplitude (VA) load sequence and varying mean stress on the fatigue strength of welded joints made of high-strength steel. The variable amplitude load spectra were constructed according to a Gaussian normal distribution, and the test series of increasing mean stress (constant maximum stress of the VA load) and decreasing mean stress (constant minimum stress) with identical equivalent stresses were implemented. The applied load spectra incorporated a high peak stress in the beginning of the block to further study the overload and residual stress relaxation effects. In addition, a notch-based fatigue assessment approach, the 4R method, was applied to these load cases. Analyses were conducted with the 4R method to analytically compute local elastic-plastic behavior, and the sequential effect of VA load cycles were considered in the mean stress correction. The fatigue test results showed that the mean stress had a significant impact on the fatigue strength of the welded joints in spite of identical equivalent loads. The difference between the mean fatigue strengths (Delta sigma c,50% = 130 MPa and Delta sigma c,50% = 80 MPa) of the two-test series was approximately 63% with the higher fatigue strength corresponding to low mean stress loading conditions.

关键词： Fatigue strength High-strength steel variable amplitude loading Welded joints 4R method

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A novel experimental method to evaluate the fatigue behaviour and damage evolution of bi-directional composites under variable amplitude loading

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INTERNATIONAL JOURNAL OF FATIGUE 2025年 198卷

作者： Khan, Ateeb Ahmad Singh, Indra Vir Mishra, Bhanu Kumar Chennamsetti, Ramadas IIT Roorkee Dept Mech & Ind Engn Roorkee India Aligarh Muslim Univ Dept Mech Engn Aligarh India DRDO Composites Res Ctr R&DE E Pune India

This study presents a novel experimental approach to evaluate the fatigue performance of bi-directional glass fiber-reinforced polymer (GFRP) composites under variable amplitude sequential block loading conditions. The proposed method incorporates advanced loading protocols to simulate realistic service conditions, capturing the complex nonlinear stress interactions and damage progression unique to composite materials. The experimental setup ensures precise control over load sequences and stress blocks, facilitating a comprehensive understanding of fatigue performance and failure mechanisms based on fatigue life, stiffness degradation and thermal response. Results demonstrate a significant influence of load sequence, cycle mixing and stress level on fatigue behaviour, providing critical insights into material performance and damage evolution. Key findings highlight the pronounced effect of high-to-low (H-L) compared to low-to-high (L-H) loading regimes on fatigue performance, showing up to 38 % reduced fatigue life. The study also demonstrates the influence of crack initiation and propagation rates on fatigue performance under both loading regimes. A load sequence sensitive damage law has been proposed to capture the nonlinear damage accumulation under variable loading conditions. This work provides a robust framework for improving the design and reliability of GFRP composites subjected to variable amplitude loading in engineering applications.

关键词： variable amplitude loading Bi-directional composites Stiffness Degradation Damage Mechanism Modified Miner's Rule

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variable amplitude loading in the very high-cycle fatigue regime

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FATIGUE & FRACTURE OF ENGINEERING MATERIALS & STRUCTURES 2002年第8-9期25卷 887-896页

作者： Stanzl-Tschegg, SE Mayer, H Stich, A Univ Agr Sci Inst Meteorol & Phys Vienna Austria AUDI AG D-85045 Ingolstadt Germany

Ultrasonic fatigue testing is appropriate to perform random loading tests in the regime of very high numbers of cycles. It has been shown that neither an endurance limit nor a threshold stress intensity exists under loading with randomly varying amplitudes even for materials that do show these limits under constant amplitude loading conditions. The technical features of the ultrasonic testing technique in order to perform random fatigue tests are shortly described. Endurance tests were performed on smooth specimens of AlSi7Mg (A356.0) aluminium alloy and on notched AISI 4142 and C45 steel specimens. The previous studies of crack propagation and threshold behaviour on AISI 420 ferritic chromium steel and GGG 100-B cast iron are included. Experimental results on lifetime and fatigue crack growth measurements under randomly varying amplitudes, as well as lifetime predictions, based on constant amplitude measurements and damage accumulation calculations are reported.

关键词： fatigue limit lifetime prediction random fatigue threshold ultrasonic fatigue variable amplitude loading

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variable amplitude loading in En8 (080M40) steel: A detailed experimental study of crack growth

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FATIGUE & FRACTURE OF ENGINEERING MATERIALS & STRUCTURES 1996年第2-3期19卷 207-216页

作者： Nganga, SP James, MN School of Process and Materials Engineering University of the Witwatersrand Private Bag 3 WITS 2050 Johannesburg South Africa

The load interaction effects that occur under variable amplitude loading conditions following single peak overloads, low-high blocks and high-low blocks have been investigated on a commonly used structural steel. A detailed investigation has been carried out on long cracks which aims at developing and assessing the efficacy of a simple predictive model based on closure and plastic zone effects. The material was tested in a quenched and tempered condition. All the tests were carried out in the four point bending mode, in both the Paris regime and near the threshold, with overloads ranging from 10% to 100%. An attempt to relate crack closure to crack growth rates in the transient growth rate region (which follows a load change) was made. The trends observed for a wide range of loading parameters are presented.

关键词： variable amplitude loading crack closure medium carbon (En8) steel

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variable amplitude loading of small fatigue cracks in 6261-T6 aluminium alloy

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FATIGUE & FRACTURE OF ENGINEERING MATERIALS & STRUCTURES 1996年第4期19卷 413-426页

作者： James, MN delosRios, ER UNIV SHEFFIELD DEPT MECH & PROC ENGNSHEFFIELD S1 3JDS YORKSHIREENGLAND

Constant and variable amplitude (VA) loading fatigue studies were carried out on a 6261 aluminium alloy using cylindrical plain hour-glass specimens. Crack growth was monitored via surface replication using cellulose acetate. Crack growth results at constant amplitude loading show the typical intermittent high and low periods of growth rate associated with crack-microstructure interactions. Acceleration in growth rate during an overload block depends on crack length and stress amplitude ratio. It appears to pass through a maximum at a crack length corresponding to the first microstructural barrier. Microstructural-based modelling is therefore required for small fatigue cracks, rather than solely closure-based modelling. The Navarro-de los Rios model of short fatigue crack growth appears able to provide good indications of crack growth rates under VA block loading, and gives reasonable life predictions. For short cracks (surface length < 80 mu m) and a small overload ratio (6.7%), crack growth may show severe retardation during the overload block. This is ascribed to crack tip blunting being more important than the increase in stresses when closure is low. It appears from a Miner's rule type exercise, that VA block loading has its major effect on growth at a surface crack length of 20 mu m. This means that the crack initiation period cannot be ignored in life prediction models for small fatigue cracks.

关键词： small fatigue cracks variable amplitude loading crack growth modelling 6261-T6 aluminium alloy

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variable amplitude loading of Al 2024-T351 at different load ratios using ultrasonic equipment

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INTERNATIONAL JOURNAL OF FATIGUE 2014年 60卷 34-42页

作者： Mayer, H. Fitzka, M. Schuller, R. BOKU Inst Phys & Mat Sci A-1190 Vienna Austria

Ultrasonic fatigue tests with variable amplitude are performed for the first time at positive load ratios. The method utilising ultrasonic equipment, a servo-hydraulic or electromechanical load frame and computer control is described. Aluminium alloy 2024-T351 is tested at approximately 20 kHz with variable amplitude in the high cycle fatigue (HCF) and very high cycle fatigue (VHCF) regime at load ratios R= -1,R= 0.1 and R= 0.5. Constant amplitude data are available and are used for Miner damage accumulation calculations. For load ratio R= -1, the mean damage sum decreases from 0.5 to 0.3 when lifetimes increase from the HCF regime to 10(9) cycles, and increases at higher numbers of cycles. For load ratio R = 0.1, the mean damage sum decreases from 1.1 to 0.2 when lifetimes increase from HCF to VHCF. At load ratio R= 0.5, the mean damage sum is approximately 0.1 in the VHCF regime. Cracks leading to VHCF failures start at broken constituent particles, probably Al7Cu2(Fe,Mn), or at agglomerations of fractured particles. Crack initiation occurs at the surface or less frequently in the interior. (C) 2013 Elsevier Ltd. All rights reserved.

关键词： Very high cycle fatigue variable amplitude loading 2024 Aluminium alloy Ultrasonic fatigue Damage accumulation

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Elastic-plastic fatigue crack growth analysis under variable amplitude loading spectra

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INTERNATIONAL JOURNAL OF FATIGUE 2009年第11-12期31卷 1828-1836页

作者： Mikheevskiy, S. Glinka, G. Univ Waterloo Dept Mech Engn Waterloo ON N2L 3G1 Canada

Most fatigue loaded components or structures experience a variety of stress histories under typical operating loading conditions. In the case of constant amplitude loading the fatigue crack growth depends only on the component geometry, applied loading and material properties. In the case of variable amplitude loading the fatigue crack growth depends also on the preceding cyclic loading history. Various load sequences may induce different load-interaction effects which can cause either acceleration or deceleration of fatigue crack growth. The recently modified two-parameter fatigue crack growth model based on the local stress-strain material behaviour at the crack tip [1,2] was used to account for the variable amplitude loading effects. The experimental verification of the proposed model was performed using 7075-T6 aluminum alloy, Ti-17 titanium alloy, and 350WT steel. The good agreement between theoretical and experimental data shows the ability of the model to predict the fatigue life under different types of variable amplitude loading spectra. (C) 2009 Elsevier Ltd. All rights reserved.

关键词： UniGrow variable amplitude loading Residual stress

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Strip yield modelling of fatigue crack under variable amplitude loading

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JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY 2011年第12期25卷 3025-3036页

作者： Singh, Konjengbam Darunkumar Xu, Yigeng Sinclair, Ian Indian Inst Technol Guwahati Dept Civil Engn Gauhati India Univ Hertfordshire Sch Aerosp Automot & Design Engn Hatfield AL10 9AB Herts England Univ Southampton Mat Res Grp Sch Engn Sci Southampton Hants England

The results from 'strip yield' approach of the FASTRAN type models of plasticity induced crack closure effects of fatigue cracks subjected to variable amplitude loadings are presented. The strip yield results are compared with authors' finite element (FE) and experimental results. It has been observed that the strip yield model is seen to be fundamentally limited by choice of alpha (constraint factor) and corresponding to treat baseline closure effects. Double overload closure behavior is functionally similar for both strip yield and FE models. Under multiple overloads, an important functional difference is seen between FE and strip yield models. This has been linked to the absence of in-plane constraint in the strip yield model, which is seen to have a distinct decreasing influence on on-going closure effects.

关键词： Fatigue variable amplitude loading Strip yield modelling Finite element modelling

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The influence of variable amplitude loading on crack closure and notch fatigue behaviour

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INTERNATIONAL JOURNAL OF FATIGUE 1997年第5期19卷 389-400页

作者： MacDougall, C Topper, TH Department of Civil Engineering University of Waterloo Waterloo Ontario Canada

Smooth and notched 1045 steel specimens were tested under constant amplitude, R = -1 loading and under a variable amplitude load history consisting of periodic overloads followed by high R-ratio small cycles. The notched specimens exhibited a notch size effect under constant amplitude loading, but the effect was reduced in the long life region (defined as a fatigue life > 10(7) cycles) under the variable amplitude load history. A crack growth model that followed crack closure changes on a cycle-by-cycle basis adequately predicted fatigue life for the periodically overloaded notched specimens. (C) 1997 Elsevier Science Ltd.

关键词： fatigue notch fatigue crack closure variable amplitude loading crack growth

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Corrosion fatigue crack growth behavior of pipeline steel under underload-type variable amplitude loading schemes

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ACTA MATERIALIA 2015年 96卷 159-169页

作者： Yu, Mengshan Xing, Xiao Zhang, Hao Zhao, Jiaxi Eadie, Reg Chen, Weixing Been, Jenny Van Boven, Greg Kania, Richard Univ Alberta Dept Chem & Mat Engn Edmonton AB T6G 2G6 Canada TransCanada Pipelines Ltd Calgary AB T2P 5H1 Canada Spectra Energy Transmiss Vancouver BC V6E 3P3 Canada

This investigation attempts to rationalize various near-neutral pH corrosion fatigue (CF) failure scenarios found during pipeline operations, which continues to be a major consideration in pipeline integrity. The phenomenon is often referred to as stress corrosion cracking (SCC) but as will be discussed is more properly considered as CF. Existing CF (SCC) models predict a service life of more than 100 years for gas pipelines, as compared with the 20-30 years typically seen in the field when these mechanisms are operative. It has been identified from analyzing pressure fluctuations recorded in the field that the underload-type variable amplitude loading schemes often found within 30 km downstream of a compressor station are the most prone to crack growth, and these locations comprise more than 70% of all-service and hydrostatic-test failures attributed to stress cracking. In this investigation, underload-type variable amplitude loading schemes were designed and used for crack growth measurements in pipeline steel in near-neutral pH environments. Crack growth enhancement by a factor of 10 was found under the underload-type variable amplitude cyclic loading, as compared with the constant amplitude cyclic loading. There also exist two distinct regimes of crack growth behavior over the range of loading frequency from 5.0 x 10(-1) Hz to 10(-5) Hz under such variable amplitude fatigue. Crack growth rate was found to increase with decreasing loading frequency down to 10(-5) Hz, while it remained constant below 10(-3) Hz. This critical loading frequency was successfully modeled based on the crack growth mechanisms identified. The outcome of the investigation agrees well with the failures experienced in the field. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

关键词： Corrosion fatigue Crack growth rate Steel Hydrogen embrittlement variable amplitude loading

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