An Energy-Based Approach to Determine the Fatigue Strength and Ductility Parameters for Life Assessment of Turbine Materials

2015 ◽  
Vol 137 (7) ◽  
Author(s):  
M.-H. Shen ◽  
Sajedur R. Akanda
Keyword(s):  
Experimental Data ◽  
Fatigue Strength ◽  
High Cycle Fatigue ◽  
Low Cycle Fatigue ◽  
Turbine Rotor ◽  
Life Assessment ◽  
Cycle Fatigue ◽  
Strength Parameters ◽  
Strength And Ductility ◽  
Good Agreement

An energy-based framework is developed to determine the fatigue strength parameters of the Basquin equation and the fatigue ductility parameters of the Manson–Coffin equation to predict high cycle fatigue (HCF) and low cycle fatigue (LCF) life of a steam turbine rotor base and weld materials. The proposed framework is based on assessing the complete energy necessary to cause fatigue failure of a material. This energy is considered as a fundamental material property and is known as the fatigue toughness. From the fatigue toughness and the experimentally determined fatigue lives at two different stress amplitudes, the cyclic parameters of the Ramberg–Osgood constitutive equation that describes the hysteresis stress–strain loop of a cycle are determined. Next, the coefficients and the exponents of the Basquin and the Manson–Coffin equations are computed from the fatigue toughness and the cyclic parameters of a material. The predicted fatigue life obtained from the present energy-based framework is found to be in a good agreement with the experimental data.

An Energy-Based Framework to Determine the Fatigue Strength and Fatigue Ductility Parameters for LCF/HCF Life Assessment of Turbine Materials

2014 ◽  
Author(s):  
M.-H. Herman Shen ◽  
Sajedur Akanda
Keyword(s):  
Experimental Data ◽  
Fatigue Life ◽  
Fatigue Strength ◽  
Weld Metal ◽  
Weld Joint ◽  
Turbine Rotor ◽  
Life Assessment ◽  
Strength Parameters ◽  
First Approximation ◽  
Good Agreement

An energy-based framework is developed to determine the fatigue strength parameters of Basquin equation and the fatigue ductility parameters of Manson-Coffin equation to predict fatigue life of a steam turbine material. The proposed framework is based on assessing the complete energy necessary to cause fatigue failure of a material. This energy is considered as a fundamental material property and is known as fatigue toughness. As a first approximation, the fatigue toughness is equivalent to the monotonic tension energy of a material. This assumption was experimentally verified for weld metal of a weld joint constituent of a turbine rotor and for aluminum 6061-T6. However, in case of base metal of the weld joint constituent, the fatigue toughness was found to be higher than the monotonic energy. From the fatigue toughness and the experimentally determined fatigue life at two different stress levels, the cyclic parameters of Ramberg-Osgood constitutive relation that describes the hysteresis stress-strain loop were calculated. Next, the coefficients and exponents of Basquin and Manson-Coffin equations were expressed as functions of fatigue toughness and cyclic parameters of a material. The predicted fatigue life obtained from the present energy-based framework was found to be in a good agreement with the experimental data.

Transition From Low Cycle to High Cycle in Uniaxial Fatigue

2013 ◽  
Author(s):  
Mohamed E. M. El-Sayed
Keyword(s):  
Fatigue Life ◽  
High Cycle Fatigue ◽  
Low Cycle Fatigue ◽  
Fatigue Behavior ◽  
Uniaxial Stress ◽  
Life Assessment ◽  
Elastic Behavior ◽  
Cycle Fatigue ◽  
Fatigue Life Assessment ◽  
Component Development

Fatigue is the most critical failure mode of many mechanical component. Therefore, fatigue life assessment under fluctuating loads during component development is essential. The most important requirement for any fatigue life assessment is knowledge of the relationships between stresses, strains, and fatigue life for the material under consideration. These relationships, for any given material, are mostly unique and dependent on its fatigue behavior. Since the work of Wöhler in the 1850’s, the uniaxial stress versus cycles to fatigue failure, which is known as the S-N curve, is typically utilized for high-cycle fatigue. In general, high cycle fatigue implies linear elastic behavior and causes failure after more than 104 or 105 cycles. However. the transition from low cycle fatigue to high cycle fatigue, which is unique for each material based on its properties, has not been well examined. In this paper, this transition is studied and a material dependent number of cycles for the transition is derived based on the material properties. Some implications of this derivation, on assessing and approximating the crack initiation fatigue life, are also discussed.

Effects of Pre-Damage on HCF Behaviors of Ti-6Al-4V Alloy

2003 ◽  
Vol 17 (08n09) ◽  
pp. 1994-2000
Author(s):  
Taewon Park ◽  
Shankar Mall ◽  
Thedore Nicholas
Keyword(s):  
Fatigue Strength ◽  
High Cycle Fatigue ◽  
Low Cycle Fatigue ◽  
Cycle Fatigue ◽  
Loading Test ◽  
Progressive Change ◽  
Loading Method ◽  
Step Loading ◽  
Damage Condition

The effects of pre-damage on the fatigue strength of Ti-6Al-4V were investigated by applying the low cycle fatigue(LCF) as a pre-damage prior to high cycle fatigue(HCF) test. The fatigue strengths were obtained by means of step-loading method. The pre-damage condition was decided as 900MPa, 0.5R, 50,000 cycles through LCF test, and was introduced before step-loading test. The fatigue strength of Ti-6Al-4V alloy derived from step-loading test without pre-damage was about 639MPa. The introduction of pre-damage deteriorates the fatigue strength about 6%. Progressive change in elongation with increasing cycles was observed. The strain accumulated by pre-damage varies the displacement in the next loading step, but afterward this doesn't change the displacement any more. The strain formed by pre-damage is thought to result in earlier failure and lower fatigue strength.

LCF Initiated - HCF Propagated Crack Life Estimation of Gas Turbine Bolts

2018 ◽  
Author(s):  
Amit K. Paspulati ◽  
Krishna Veluru ◽  
Kashinath Akki ◽  
Rohit Khattar ◽  
Sudeep Bosu ◽  
...  
Keyword(s):  
Crack Propagation ◽  
Gas Turbine ◽  
High Cycle Fatigue ◽  
Low Cycle Fatigue ◽  
Evaluation Studies ◽  
Three Dimensional ◽  
Fatigue Loading ◽  
Turbine Rotor ◽  
Cycle Fatigue ◽  
Compressor Rotor

This paper discusses the methodology to calculate high cycle fatigue (HCF) crack propagation life of gas turbine bolts and compares two dimensional (2D) HCF crack propagation life to three dimensional (3D) HCF crack propagation life. Gas turbine bolts when exposed to fatigue loading are prone to crack initiation and propagation (structural failure) during operation. In such cases cracks mostly are initiated by low cycle fatigue (LCF) and propagated by HCF. Therefore in current illustration the authors have evaluated crack propagation primarily initiated by low cycle fatigue and propagated by high cycle fatigue. 2D and 3D fracture methodology approaches had been used for analytical evaluation. The authors conclude on the efficacy of both the methods based on the data from the field. The coupling joint bolts located in the engine mid-section, which are used to join compressor rotor with turbine rotor are being considered for crack evaluation studies. The coupling bolts located in mid-section are primarily loaded by high axial bolt pre-loads needed to keep the joint intact, as well as loaded in bending due to rotor gravity sag. The crack propagation life is evaluated and validated with field data using cracked bolt specimen from the field.

Fatigue Performance of Low Rigidity Titanium Alloy for Biomedical Applications

2004 ◽  
Vol 449-452 ◽  
pp. 1265-1268
Author(s):  
Toshikazu Akahori ◽  
Mitsuo Niinomi ◽  
Hisao Fukui ◽  
Akihiro Suzuki
Keyword(s):  
Fatigue Life ◽  
Fatigue Strength ◽  
Fatigue Limit ◽  
High Cycle Fatigue ◽  
Low Cycle Fatigue ◽  
Tangential Force ◽  
Solution Treatment ◽  
Beta Phase ◽  
Fretting Fatigue ◽  
Cycle Fatigue

Microstructures of Ti-29Nb-13Ta-4.6Zr (TNTZ) aged at temperatures between 573 and 723 K after solution treatment at 1063 K have super fine omega phase, or􀀂 both super fine alpha and omega phases, respectively in beta phase with an average grain diameter of 20 µm. Plain fatigue strength of TNTZ aged after solution treatment is much greater than that of as-solutionized TNTZ in both low cycle fatigue and high cycle fatigue life regions. This is due to the improvement of the balance of strength and ductility by the precipitation of alpha phase. Fretting fatigue strength of TNTZ conducted with various heat treatments decreases dramatically as compared with their plain fatigue strength in both low cycle fatigue and high cycle fatigue life regions. In this case, the decreasing ratio of fretting fatigue life increases with increasing the small crack propagation area where both the tangential force and frictional force at the contact plane of pad exist. In fretting fatigue in air, the ratio of fretting damage (Pf/Ff), where Pf and Ff stand for plain fatigue limit and fretting fatigue limit, respectively, increases with increasing elastic modulus. In fretting fatigue in Ringer’s solution, the passive film on specimen surface is broken by fretting action in TNTZ, which have excellent corrosion resistance, and, as a result, corrosion pits that lead to decreasing fretting fatigue strength especially in high cycle fatigue life region, are formed on its surface.

An energetic method to evaluate the macro and micro high-cycle fatigue behavior of the aluminum alloy

2017 ◽  
Vol 232 (8) ◽  
pp. 1456-1469 ◽  
Author(s):  
Junling Fan ◽  
Xinglin Guo ◽  
Yanguang Zhao
Keyword(s):  
Aluminum Alloy ◽  
Fatigue Life ◽  
Fatigue Strength ◽  
Energy Dissipation ◽  
High Cycle Fatigue ◽  
Fatigue Behavior ◽  
Cycle Fatigue ◽  
Thermal Signal ◽  
Dissipation Mechanism ◽  
Good Agreement

An energetic method is proposed to rapidly evaluate the macro- and microfatigue behavior of aluminum alloy in high-cycle fatigue. The theoretical correlation between the thermal signal and the energy dissipation during the fatigue process is established for the irreversible dissipation mechanism description. The energetic method is applied to predict the fatigue strength and the entire fatigue life of the aluminum alloy. Moreover, the energy dissipation is properly used to evaluate the microplastic behavior at the grain scale, which is responsible for the progressive movements of the internal microstructures. Experiments were carried out to validate the current energetic method, and good agreement was obtained between the predicted results and the traditional results. Thus, the current energetic method is confirmed to be promising for the macro and micro high-cycle fatigue behavior assessment.

Modification of the Equation for Description of Wöhler's Curves

2010 ◽  
Vol 27 (1) ◽  
pp. 99-104 ◽  
Author(s):  
Sylwester Kłysz ◽  
Janusz Lisiecki ◽  
Tomasz Bąkowski
Keyword(s):  
Experimental Data ◽  
High Cycle Fatigue ◽  
Low Cycle Fatigue ◽  
Fatigue Tests ◽  
Experimental Results ◽  
Fatigue Threshold ◽  
Cycle Fatigue ◽  
Exponential Equation ◽  
The Way

Modification of the Equation for Description of Wöhler's Curves The paper presents the way to modify the equation σ = f(2Nf) in order to improve the fit of experimental results from High Cycle Fatigue tests. In particular, the study deals with introduction of the 5-parameter exponential equation that enables better fit of the full Wöhler's curve to experimental data within the range of stress at the level of fatigue threshold as well as approximation to the quasi-static range and Low Cycle Fatigue tests for the highest stress values. It is illustrated how individual parameters affect the procedure and possibility to match the aforementioned equation to experimental data.

scholarly journals Elaboration of the Equipment and Technology for Cutting Rolled Round Bars and Pipes with the Cyclic Circular Bending Method

2021 ◽  
Vol 346 ◽  
pp. 01011
Author(s):  
Aleksej Antimonov ◽  
Sergej Poljanskij ◽  
Nadezhda Pushkareva
Keyword(s):  
Experimental Data ◽  
Low Cycle Fatigue ◽  
Continuous Process ◽  
Comparative Assessment ◽  
Strength Analysis ◽  
Cyclic Loads ◽  
Cycle Fatigue ◽  
Significant Difference ◽  
Theoretical Assessment ◽  
Good Agreement

A brief overview of methods for cutting round bars and pipes is presented, their main advantages, disadvantages and field of application are considered. It is proposed to use the effect of fatigue fracture for round bars and pipes breaking. The task is to study this process under the action of cyclic loads. The possibility of applying the known provisions of calculating theory of strength analysis for low-cycle fatigue for this process is tested. A comparative assessment of theoretical and experimental data is given and their significant difference is established. New calculated dependences are proposed, which are in good agreement with the experimental data. A theoretical assessment of the productivity of the process of round bars and pipes breaking by the method of cyclic circular bending was carried out using new results and various options for the design of a device for breaking were considered with an analysis of the features of their operation. Based on the results of the analysis, a variant of the device for the implementation of a continuous process of breaking the pointed ends of thick-walled fuel pipes during drawing in coils and a diagram of the mechanism for breaking the ends of the pipe with its supply from the coil were selected. Samples of pipes obtained by brittle cyclic bending are presented.

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