scholarly journals Study on Creep Damage of Ni-Based Superalloy Caused by Variable Load Conditions at Elevated Temperatures

Materials ◽  
2021 ◽  
Vol 14 (22) ◽  
pp. 6971
Author(s):  
Sunguk Wee ◽  
Keekeun Kim ◽  
Kibum Park ◽  
Changsung Seok
Keyword(s):  
Gas Turbines ◽  
Elevated Temperatures ◽  
Low Cycle Fatigue ◽  
Creep Damage ◽  
Fatigue Tests ◽  
Variable Load ◽  
Test Results ◽  
Nickel Based Superalloy ◽  
Essential Properties ◽  
Load Conditions

Higher fatigue and creep resistance at high temperatures are the essential properties for materials such as those used in gas turbines for power generation and aircraft turbines. Therefore, the nickel-based superalloy CMSX-4 was developed through single-crystal casting to satisfy these requirements. In this study, the CMSX-4 creep test results reported by previous researchers were used to mathematically derive an equation to estimate the amount of creep damage occurring under variable load conditions. In addition, low-cycle fatigue tests were performed, and the effect of creep damage occurring during fatigue on material failure was described.

Coupled Thermo-Mechanical Fatigue Tests for Simulating Load Conditions in Cooled Turbine Parts

2011 ◽  
Author(s):  
Roland Mu¨cke ◽  
Klaus Rau
Keyword(s):  
Gas Turbine ◽  
Gas Turbines ◽  
Mechanical Load ◽  
Fatigue Tests ◽  
Temperature Fields ◽  
Hot Gas ◽  
Mechanical Fatigue ◽  
Numerical Predictions ◽  
Temperature Capability ◽  
Load Conditions

Modern heavy-duty gas turbines operate under hot gas temperatures that are much higher than the temperature capability of nickel superalloys. For that reason, advanced cooling technology is applied for reducing the metal temperature to an acceptable level. Highly cooled components, however, are characterised by large thermal gradients resulting in inhomogeneous temperature fields and complex thermo-mechanical load conditions. In particular, the different rates of stress relaxation due to the different metal temperatures on hot gas and cooling air exposed surfaces lead to load redistributions in cooled structures, which have to be considered in the lifetime prediction methodology. In this context, the paper describes Coupled Thermo-Mechanical Fatigue (CTMF) tests for simultaneously simulating load conditions on hot and cold surfaces of cooled turbine parts, Refs [1, 2]. In contrary to standard Thermo-Mechanical Fatigue (TMF) testing methods, CTMF tests involve the interaction between hot and cold regions of the parts and thus more closely simulates the material behaviour in cooled gas turbine structures. The paper describes the methodology of CTMF tests and their application to typical load conditions in cooled gas turbine parts. Experimental results are compared with numerical predictions showing the advantages of the proposed testing method.

Experimental Investigation on the Creep and Low Cycle Fatigue Behaviors of a Serviced Turbine Blade

2019 ◽  
Author(s):  
Zhenlei Li ◽  
Duoqi Shi ◽  
Xiaoguang Yang ◽  
Nina Li
Keyword(s):  
Turbine Blade ◽  
Low Cycle Fatigue ◽  
Test System ◽  
Fatigue Tests ◽  
Test Results ◽  
Cycle Fatigue ◽  
Hold Period ◽  
Low Pressure Turbine ◽  
Creep Fatigue ◽  
Crack Initiation Life

Abstract This paper experimentally investigated the creep and fatigue behaviors of a low-pressure turbine (LPT) blade with 600 hours of service using a novel test system. Pure low cycle fatigue (LCF), pure creep and creep-fatigue interaction (CFI) experiments on the full-scale serviced blades were conducted respectively. Test results showed that the increasing of deformation amplitude was divided into three stages under both pure LCF and creep-fatigue loadings. The deformation of each blade increased rapidly until failure when the test cycle exceeded the 80% of their overall life under the pure LCF and CFI condition. The hold period in creep-fatigue tests shortens the first stage of whole life and has no influence on the proportion of crack initiation life to overall life. The fractures in pure LCF, pure creep and creep-fatigue tests emerged transgranular, intergranular and both transgranular and intergranular behaviors respectively. The crack initiated and propagated in a specific zone of the blade under all the experimental loadings, which limited its creep-fatigue resistance. At last, the remaining life of turbine blade was estimated conservatively by introducing the safety limit into a statistical method.

scholarly journals Stationary gas turbines: an exergetic approach to part load operation

2020 ◽  
Vol 75 ◽  
pp. 10
Author(s):  
Michel Moliere ◽  
Jean-Noël Jaubert ◽  
Romain Privat ◽  
Thierry Schuhler
Keyword(s):  
Gas Turbine ◽  
Gas Turbines ◽  
Low Cycle Fatigue ◽  
Renewable Energy Sources ◽  
Air Flow ◽  
Plant Management ◽  
Variable Load ◽  
Spinning Reserve ◽  
Part Load ◽  
Equipment Lifetime

As renewables are progressively displacing thermal plants in the power generation scene worldwide, the vocation of stationary Gas Turbines (GT) is deeply evolving. In this irreversible move GT plants are called upon to become cycling units with increasingly variable load profiles. This is dictated by the need to compensate for the fluctuations of renewable energy sources and secure the spinning reserve that is indispensable for the stability of the grids. This new scenario creates a serious challenge for gas turbine designers and operators in terms of investment policy, plant management and equipment lifetime. Indeed, operating a gas turbine at part, variable load requires reducing its firing temperature and possibly its air flow. While part load operation entails efficiency losses with respect to the full load mode, load variations cause maintenance penalties due the premature component ageing tied namely with thermal and low cycle fatigue effects on machine materials. As far as efficiency is concerned, an exergy analysis of a contemporary, air-based Brayton cycle is useful for quantifying and comparing the losses incurred by the various engine components. Such study reveals the high sensitivity of compressor efficiency to load decreases. Among possible counter-measures, heating the air at the compressor intake represents a simple mitigation measure, as it enables reducing the air flow rate while preserving to some extent the efficiency of the compressor and consequently GT efficiency.

Buckling Restrained Brace With Inspection Windows

2015 ◽  
Author(s):  
C. S. Tsai ◽  
Yi Liu ◽  
B. Q. Liu
Keyword(s):  
Experimental Study ◽  
Energy Dissipation ◽  
Mechanical Behavior ◽  
Low Cycle Fatigue ◽  
Fatigue Tests ◽  
Test Results ◽  
Cycle Fatigue ◽  
Buckling Restrained Brace ◽  
Steel Core ◽  
Testing Protocols

The buckling restrained brace (BRB) has been worldwide recognized as an energy absorber to protect structures from earthquake damage. However, the traditional BRB is a fully close design, it is therefore impossible to detect the condition of the steel core during manufacturing and after earthquakes. This paper proposed a buckling restrained brace with inspection windows that allow inspecting the condition of the internal components of the BRB. Experimental study in selecting the sizes and locations of the inspection windows without affecting the functionality of the BRB has been carried out to search for an economically feasible BRB that is convenient for manufacturing and installation and meets testing protocols. Test results of the proposed BRBs under cyclic loadings showed that the mechanical behavior of the BRB with inspection windows on the buckling-restraining unit consisting of the constraining and lateral support elements was stable and that damage always occurred at the energy dissipation segments after low cycle fatigue tests. These test results indicate that the inspection windows opened on the proposed BRB have little influence on the strength of the device and that the proposed device can be considered as a stable energy dissipation device.

Influences of Cyclic Pre-Overload on Low Cycle Fatigue Behaviours of Elbow Pipe

2011 ◽  
Author(s):  
Kazuya Matsuo ◽  
Koji Takahashi ◽  
Kyohei Sato
Keyword(s):  
Low Cycle Fatigue ◽  
Three Dimensional ◽  
Preliminary Test ◽  
Growth Direction ◽  
Fatigue Tests ◽  
Test Results ◽  
Cycle Fatigue ◽  
Crack Penetration ◽  
Crack Growth Direction ◽  
Cumulative Fatigue Damage

Low cycle fatigue tests were conducted using sound elbows made of carbon steel (STPT410). The elbows were subjected to cyclic in-plane bending under displacement control with internal pressure of 9 MPa. The preliminary fatigue tests were conducted under constant cyclic displacements. Then, two test conditions were adopted to investigate the influence of cyclic pre-overload on low cycle behavior of elbow on the basis of the preliminary test results. The fatigue test results were evaluated by using the total usage factor UFTotal (= UFpre+UFpost), where the UFpre and UFpost correspond to usage factor for δpre and δpost, respectively. The fatigue lives of overloaded elbow pipes were estimated based on the cumulative fatigue damage rule basically from UFpre = 0.2 to UFpre = 0.6. In addition, three-dimensional elastic-plastic analyses were carried out using the finite element method. The crack penetration area and the crack growth direction were successfully predicted by the analyses.

Cycle-Dependent and Time-Dependent Bone Fracture With Repeated Loading

1983 ◽  
Vol 105 (2) ◽  
pp. 166-170 ◽  
Author(s):  
D. R. Carter ◽  
W. E. Caler
Keyword(s):  
Low Cycle Fatigue ◽  
Strain Range ◽  
Creep Damage ◽  
Cyclic Strain ◽  
Fatigue Tests ◽  
Time Dependent ◽  
Tensile Creep ◽  
Repeated Loading ◽  
Time To Failure ◽  
Creep Fracture

Fatigue tests of human cortical bone (up to 1.74 × 106 cycles) were conducted under tension-compression (T-C) and zero-tension (O-T) modes with a 2Hz, stress controlled, sinusoidal loading history. Tensile creep-fracture tests at constant stress levels were also performed. The relationship between the initial cyclic strain range and cycles to failure with the T-C specimens were consistent with that derived previously in low-cycle fatigue under strain control. Using a time-dependent failure model, the creep-fracture data was found to be consistent with previous studies of the influence of strain rate on the monotonic tensile strength of bone. The model also predicted quite well the time to failure for the O-T fatigue specimens, suggesting that creep damage plays an important role in O-T fatigue specimens.

Experimental Study of All-Steel Buckling Restrained Brace With Windowed Lateral Support Elements

2014 ◽  
Author(s):  
Chong-Shien Tsai ◽  
Yan-Ming Wang
Keyword(s):  
Energy Dissipation ◽  
Structural Control ◽  
Low Cycle Fatigue ◽  
Control Device ◽  
Fatigue Tests ◽  
Test Machine ◽  
Test Results ◽  
Buckling Restrained Brace ◽  
Steel Core ◽  
The Difference

The buckling restrained brace (BRB) that has been worldwide adopted as a structural control device possesses excellent energy dissipation mechanism and can overcome the disadvantages of the traditional brace. However, the traditional BRB is a fully close design, it is therefore impossible to inspect the condition of the internal components during manufacturing and after earthquakes. This study proposed an all-steel buckling restrained brace with windowed lateral support elements that allow inspecting the internal condition of the BRB. We also studied the optimization in selecting the sizes and positions of the windows in the internal components without affecting its strength to provide an economically feasible all-steel BRB that is convenient for manufacturing and installation and meets the rigorous testing protocols. The all-steel BRB consists of the steel core, lateral support and constraining elements. In this study, scaled all-steel BRBs were tested under cyclic loadings by using an MTS 250 kN test machine. Test results showed that the mechanical behavior of the BRB with windows on the sides of lateral support elements is stable and that damage always occurred at the energy dissipation sections after low cycle fatigue tests. The difference between tensile and compressive forces was small under identical strain, and the accumulated inelastic deformation exceeded the requirement of test protocols. These test results confirm that the windows opened on the proposed BRB have insignificant effects on the strength of the device and that the proposed device meets the design requirement and is thus considered as a stable energy dissipative apparatus.

Low-Cycle Fatigue Behavior of Small Slice Specimens of Zircaloy-4 at Elevated Temperature

2006 ◽  
Vol 324-325 ◽  
pp. 1241-1244 ◽  
Author(s):  
Li Xun Cai ◽  
Yu Ming Ye
Keyword(s):  
Elevated Temperature ◽  
Low Cycle Fatigue ◽  
Fatigue Behavior ◽  
Cyclic Hardening ◽  
Cyclic Softening ◽  
Fatigue Tests ◽  
Uniaxial Strain ◽  
Transverse Strain ◽  
Test Results ◽  
Element Analysis

A series of strain fatigue tests were carried out on small bugle-like slice-specimens of Zr-4 alloy at 20 and 400. According to Elastic and Plastic Finite Element Analysis and assumption of local damage equivalence, a strain formula was given to transform transverse strain of the specimen to uniaxial strain. Based on the test results of the alloy and the strain transform formula, M-C (Manson-Coffin) models to be used for estimating uniaxial fatigue life of Zr-4 alloy were obtained. The results show that, the alloy mainly behaves as cyclic softening at 20 and as cyclic hardening at 400, and the elevated temperature can lead serious additional fatigue damage of the alloy and the effect of the elevated temperature impairs gradually with increasing of amplitude strain. A conclusion is helpful that prediction life by using M-C model based on traditional strain transform equation is quite conservative when uniaxial strain amplitude is less than 0.5%.

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