scholarly journals Effects of variable amplitude loading on fatigue life

2015 ◽  
Vol 6 (3) ◽  
pp. 10 ◽  
Author(s):  
Niels Laseure ◽  
Ingmar Schepens ◽  
Nahuel Micone ◽  
Wim De Waele
Keyword(s):  
Offshore Structures ◽  
Fatigue Tests ◽  
Variable Amplitude Loading ◽  
Variable Amplitude ◽  
Industrial Sectors ◽  
Closure Mechanism ◽  
Physical Phenomena ◽  
Published Research ◽  
Variable Amplitude Fatigue ◽  
Plasticity Induced Crack Closure

This paper is a review of published research on variable amplitude loading of steels. The use of service spectra for different industrial sectors and specifically for offshore applications is first considered. Constant amplitude fatigue failure models are not representative for these applications. The JONSWAP spectrum shows potential to be used as service spectrum for offshore structures. Further investigation of variable amplitude fatigue is needed to get insight in the various phenomena linked to the variable amplitude. Observed trends in fatigue crack growth rate in variable amplitude fatigue tests on steels, such as the effects of overloads and underloads (occurring as single events, sequential events or block loadings), are discussed. Furthermore, suggestions of the underlying physical phenomena behind the load interaction effects due to variable amplitude loading are presented. It can be concluded that the plasticity induced crack closure mechanism is the most profound explanation for the acceleration effect in overloads and the retardation effect observed in underloads.

Application of the Strip Yield Model to Crack Growth Predictions for Structural Steel

2010 ◽  
Vol 57 (1) ◽  
pp. 1-20
Author(s):  
Małgorzata Skorupa ◽  
Tomasz Machniewicz
Keyword(s):  
Structural Steel ◽  
Crack Growth ◽  
Model Calibration ◽  
Load History ◽  
Yield Model ◽  
Variable Amplitude Loading ◽  
Variable Amplitude ◽  
Constraint Factors ◽  
Strip Yield Model ◽  
Closure Mechanism

Application of the Strip Yield Model to Crack Growth Predictions for Structural SteelA strip yield model implementation by the present authors is applied to predict fatigue crack growth observed in structural steel specimens under various constant and variable amplitude loading conditions. Attention is paid to the model calibration using the constraint factors in view of the dependence of both the crack closure mechanism and the material stress-strain response on the load history. Prediction capabilities of the model are considered in the context of the incompatibility between the crack growth resistance for constant and variable amplitude loading.

Fatigue of Stabilized SS and 316 NG Alloy in PWR Environment

2006 ◽  
Author(s):  
Jussi P. Solin
Keyword(s):  
Stainless Steels ◽  
Fatigue Tests ◽  
Test Results ◽  
Constant Amplitude ◽  
Low Oxygen ◽  
Variable Amplitude ◽  
Variable Amplitude Fatigue ◽  
Reduction Factors

Strain controlled constant and variable amplitude fatigue tests for 316NG and Titanium stabilized stainless steels in low oxygen PWR waters were performed. The stabilized steel has been plant aged for 100 000 hours. Constant amplitude test results at 0,01 Hz sinusoidal straining comply with predicted lives according to the Fen approach for both materials. Spectrum straining both in air and in environment caused predicted life reduction factors (about 3) for the stabilized steel, but for the 316NG steel spectrum straining in environment resulted to a larger reduction in life.

Fractographic Study on the Use of Rainflow Counting for Small and Long Cracks in AA7050

2014 ◽  
Vol 891-892 ◽  
pp. 687-692 ◽  
Author(s):  
Paul White ◽  
David S. Mongru
Keyword(s):  
Crack Growth ◽  
Fatigue Loading ◽  
Variable Amplitude Loading ◽  
Variable Amplitude ◽  
Counting Technique ◽  
Rainflow Cycle Counting ◽  
Small Cracks ◽  
The Individual ◽  
Rainflow Counting ◽  
Variable Amplitude Fatigue

Using ada/dNequation to predict fatigue crack growth for a variable amplitude loading sequence, requires converting the sequence into an equivalent series of constant amplitude cycles, which is sometimes achieved using the rainflow cycle counting technique. Rainflow counting views small intermediate cycles as an interruption to a larger cycle, in effect, the crack tip remembers the state of the larger cycle. This has been shown to be an effective technique in predicting fatigue growth rates for long cracks, but has not been extensively investigated for use in predicting the growth of small cracks. An investigation was made into the applicability of rainflow cycle counting for predicting the crack growth of small and long cracks created with variable amplitude fatigue loading in AA7050-T7451 plate, a common modern aircraft material. A series of coupons were tested with a number of different variable amplitude loading sequences which had distinct marker bands inserted to separate the individual segments of loading and enable them to be identified fractographically. For the sequences examined, which covered varying numbers of interrupted cycles and a staircase of three steps, the baseline and the rainflow loading segments within each sequence showed effectively the same rate of growth for the same stress intensity range in both the small and long crack coupons, demonstrating that rainflow cycle counting was a suitable cycle counting technique for both small and long cracks.

Corrosion Fatigue of AZ91E-T6 Cast Magnesium Alloy in a 3.5 Percent NaCl Aqueous Environment

1995 ◽  
Vol 117 (3) ◽  
pp. 293-298 ◽  
Author(s):  
R. I. Stephens ◽  
C. D. Schrader ◽  
K. B. Lease
Keyword(s):  
Fatigue Life ◽  
Magnesium Alloy ◽  
Fatigue Behavior ◽  
Fatigue Tests ◽  
Mean Stress ◽  
Constant Amplitude ◽  
Variable Amplitude ◽  
Cast Magnesium Alloy ◽  
Cast Magnesium ◽  
Variable Amplitude Fatigue

The objective of this research was to obtain and compare constant and variable amplitude fatigue behavior of AZ91E-T6 cast magnesium alloy in both an air and 3.5 percent NaCl aqueous corrosive environment. An additional objective was to determine if commonly used models that describe fatigue behavior and fatigue life are applicable to this material and test environment. Fatigue tests included constant amplitude strain-controlled low cycle fatigue with strain ratio, R, equal to 0, −1 and −2, Region II constant amplitude fatigue crack growth with load ratio, R, equal to 0.05 and 0.5 and variable amplitude fatigue tests using keyhole notched specimens. In all fatigue tests, the corrosion environment was significantly detrimental relative to the air environment. Mean strains influenced fatigue life only if accompanied by significant mean stress. The Morrow and Smith, Watson, and Topper mean stress models provided both accurate and inaccurate fatigue life calculations. Likewise, variable amplitude fatigue life calculations using the local strain approach and based upon the formation ofal mm crack at the keyhole notch were both accurate and fairly inaccurate depending on the specific model used.

Influence of Load Signal Form and Variable Amplitude Loading on the Corrosion Fatigue Behaviour of Aluminium Alloys

2014 ◽  
Vol 891-892 ◽  
pp. 217-223 ◽  
Author(s):  
Kathrin Bauer-Trossmann ◽  
Liu Hao Yu ◽  
Tobias Melz ◽  
Matthias Oechsner ◽  
Heinz Kaufmann
Keyword(s):  
Corrosion Fatigue ◽  
Aluminium Alloys ◽  
Magnesium Content ◽  
Fatigue Behaviour ◽  
Thermal Ageing ◽  
Fatigue Tests ◽  
Electrochemical Characteristics ◽  
Variable Amplitude Loading ◽  
Variable Amplitude ◽  
The Impact

Aluminium alloys are used for a large variety of safety relevant applications for example in the automotive and aviation industries. With the introduction of high strength but possibly less corrosion resistant alloys it is essential to determine if an enhanced sensitisation against corrosion comes into effect under simultaneous mechanical and corrosive loading. Within this work corrosion fatigue tests under constant and variable amplitude loading were carried out on aluminium alloys established for chassis applications such as EN AW-5018 with slightly elevated magnesium content (AlMg3.5Mn), EN AW-6082-T6, EN AW-6110A-T6 and EN AC‑42100-T6 as well as alloys sensitised to corrosion. Sensitisation was obtained by a borderline (17 h at 130 °C) and an excessive (500 h at 130 °C) thermal ageing treatment and elevated copper contents for the forged and cast alloys. Aforementioned alloys and material conditions were assessed concerning the impact of mechanical loading conditions such as load signal type (sinusoidal and square-wave signal), strain rate and load spectra on the damaging process and on corrosion fatigue life. Fatigue tests were complemented by simultaneous determination of electrochemical characteristics as well as the type of corrosion by metallographic investigations.

Fatigue Life Prediction of Welded Joints for Offshore Structures Under Variable Amplitude Loading

1993 ◽  
Vol 115 (2) ◽  
pp. 123-130 ◽  
Author(s):  
R. Bell ◽  
O. Vosikovsky
Keyword(s):  
Fatigue Life ◽  
Welded Joints ◽  
Life Prediction ◽  
Experimental Tests ◽  
Offshore Structures ◽  
Multiple Cracks ◽  
Stress Range ◽  
Variable Amplitude Loading ◽  
Model Calculations ◽  
Variable Amplitude

This paper describes the development of a fracture mechanics model for the prediction of fatigue life of welded joints subjected to variable amplitude loading. The prediction program is based on the integration of the Paris equation. A novel feature of this program are relationships which account for the development, growth and coalescence of multiple cracks that occur at the weld toe. These relationships or forcing functions were developed from extensive monitoring of the initiation and crack shape development of multiple cracks during experimental tests. Data is also presented on a series of variable amplitude tests performed on welded T-plate joints loaded in 3-point bending using the common load sequence (COLOS) at a stress ratio of R=−1. These results are presented in terms of effective and root mean square stress ranges. The experimental data are used to validate the life prediction results from the growth model. A discussion is also included on the proportion of the compressive stress range to be included as an effective stress range in the prediction model calculations.

scholarly journals Experimental Study on Variable-Amplitude Fatigue of Welded Cross Plate-Hollow Sphere Joints in Grid Structures

2018 ◽  
Vol 2018 ◽  
pp. 1-15 ◽  
Author(s):  
Jin-Feng Jiao ◽  
Hong-Gang Lei ◽  
Y. Frank Chen
Keyword(s):  
Fatigue Life ◽  
Hollow Sphere ◽  
Fatigue Behavior ◽  
Fatigue Tests ◽  
Metallographic Analysis ◽  
Variable Load ◽  
Random Loading ◽  
Variable Amplitude ◽  
Different Types ◽  
Variable Amplitude Fatigue

The fatigue stress amplitude of the welded cross plate-hollow sphere joint (WCPHSJ) in a grid structure varies due to the random loading produced by suspending cranes. A total of 14 specimens considering three different types of WCPHSJs were prepared and tested using a specially designed test rig. Four typical loading conditions, “low-high,” “high-low,” “low-high-low,” and “high-low-high,” were first considered in the tests to investigate the fatigue behavior under variable load amplitudes, followed by metallographic analyses. The experimental and metallographic analysis results provide a fundamental understanding on the fatigue fracture form and fatigue mechanism of WCPHSJs. Based on the available data from constant-amplitude fatigue tests, the variable-amplitude fatigue life of the three types of WCPHSJs was estimated using the Miner rule and Corten-Dolan theory. Since both accumulative damage theories yield virtually same damaging results, the Miner rule is hence suggested to estimate the fatigue life of WCPHSJs.

Fatigue Modeling of 508 LAS Under Variable Amplitude Loading: A Mechanistic Based Analytical Approach

2017 ◽  
Author(s):  
Bipul Barua ◽  
Subhasish Mohanty ◽  
William K. Soppet ◽  
Saurindranath Majumdar ◽  
Krishnamurti Natesan
Keyword(s):  
Material Behavior ◽  
Time Dependent ◽  
Plastic Behavior ◽  
Pressurized Water ◽  
Material Models ◽  
Variable Amplitude Loading ◽  
Variable Amplitude ◽  
Water Reactor ◽  
Material Parameters ◽  
Variable Amplitude Fatigue

A Chaboche-based evolutionary cyclic plasticity model is proposed to model the elastic-plastic behavior of 508 Low Alloy Steel (LAS), a commonly used material for Light Water Reactor (LWR), under variable amplitude loading. A novel parameter estimation technique is developed to incorporate the amplitude dependency of the material behavior into the earlier developed time-dependent material models based on constant amplitude fatigue test data. The resulting new material model can be referred as time-dependent-amplitude-independent material models. Variable amplitude fatigue tests under different environmental conditions (in air and pressurized water reactor (PWR) coolant water at 300°C) are analytically/mechanistically modeled. The analytical modeling results show that the time-dependent-amplitude-independent material parameters are able to capture the stress-strain state under variable amplitude fatigue loading. The developed model and reported material parameters can be utilized for more accurate stress analysis of safety-critical reactor components under real-life loading scenarios with variable/random loading transients. Recently a report on related 508 LAS material characterization work has been published by Argonne National Laboratory [1]. In this work a summary of the related work is presented.

Sign in / Sign up

Export Citation Format

Share Document