Effect of additional holes on crack propagation and arrest in gas turbine casing (original) (raw)
Related papers
2017
Gas turbines casings are susceptible to cracking at the edge of the eccentric pin hole. This paper describes the improvement of the transient thermal fatigue life of gas turbines casings through the application of pins. The repair technology under consideration involved drilling a number of holes in the gas turbines casing along the crack and inserting pins into them. The crack position and direction were determined using non-destructive tests. A series of finite element models were developed and tested in AStM-A395 elastic-perfectly plastic ductile cast iron. In some specimens, holes were drilled near the crack tips. Pins were inserted into the holes in some cases. Abaqus software finite element package and Zencrack fracture mechanics code were used for modeling. The efficiency of crack repair by the installation of pins was investigated along with the effect of the number of pins on crack repair efficiency. The result shows that the insertion of pins into holes drilled in the vicinity of the crack tips is an effective method of retarding crack growth in a gas turbine casing.
LCF Initiated - HCF Propagated Crack Life Estimation of Gas Turbine Bolts
2018
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 mids...
A numerical finite fracture mechanics approach on asymmetric cracks in open-hole plates
Procedia Structural Integrity, 2016
During their operation, modern aircraft engine components are subjected to increasingly demanding operating conditions, especially the high pressure turbine (HPT) blades. Such conditions cause these parts to undergo different types of time-dependent degradation, one of which is creep. A model using the finite element method (FEM) was developed, in order to be able to predict the creep behaviour of HPT blades. Flight data records (FDR) for a specific aircraft, provided by a commercial aviation company, were used to obtain thermal and mechanical data for three different flight cycles. In order to create the 3D model needed for the FEM analysis, a HPT blade scrap was scanned, and its chemical composition and material properties were obtained. The data that was gathered was fed into the FEM model and different simulations were run, first with a simplified 3D rectangular block shape, in order to better establish the model, and then with the real 3D mesh obtained from the blade scrap. The overall expected behaviour in terms of displacement was observed, in particular at the trailing edge of the blade. Therefore such a model can be useful in the goal of predicting turbine blade life, given a set of FDR data.
Engineering Failure Analysis, 2020
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Computer simulation of fatigue, creep and thermal-fatigue cracks propagation in gas-turbine blades
2012
Methods and computational algorithms for determining the growth rate of fatigue creep and thermal-fatigue cracks are considered. The rate of crack growth is dependent on the stress-intensity factor (or J-integral) for fatigue, on the C*-integral for creep and on the stress-intensity factor (or J-integral) and C*-integral for thermal fatigue. Simulations of the crack propagation under fatigue, creep and thermal fatigue at the edge of the blade of a gas turbine are carried out and discussed.
Crack Initiation in 14% Cr Low Pressure Turbine Blade Steel
Journal of Engineering for Gas Turbines and Power, 2014
The impact of multiple erosion pits and crack initiation was investigated for a 500 megawatt (MW) steam turbine unit with three low pressure (LP) rotors on the steam end and generator end of the stage L0 blades. These units have been subjected to two-shifting operation and have been retrofitted with new high pressure (HP) turbine units over the life history of the turbines. Droplet erosion damage was exacerbated by operating conditions causing multiple crack initiation sites concentrated above the root platform. A method of accumulated damage was employed using pit counting and the number of cycles referenced back to turbine revolutions in line with the accumulated damage model developed from the damage function analysis and Palmgren–Miner approaches. The number of rotational cycles were calculated from the starts and running hours for pre- and post-retrofit scenarios and compared and correlated to the number of pits formed during the completed cycles. The macro crack size represent...
Cracks path growth in turbine blades with TBC under thermo – mechanical cyclic.PDF
Blades of combustion turbines are extremely loaded turbojet elements, which transmit operative energy onto a rotor. Experiences of many years indicate, that cracks initiation and propagation in the blades during the operation time can cause destruction not only of the engine, but sometimes an airplane. In high temperature one of the most often occuring interactions in the turbine engine are time variable force fields, caused by non-stationary flowing of an exhaust gas and aerodynamical interaction of the engine elements. The extremal thermo-mechanical loadings initiate gradual degradation process of the blades as a result of fatigue and material creep. More often Thermal Barrier Coatings (TBCs) are applied on the turbine blade surface to provide protection not only against the high temperature but also against aggressive environment. The paper presents the advantages of applying of the TBC layers for increase of the cracks resistance to gradual degradation of the turbine blades. The level of save values of thermo-mechanical loading was estimated. Analysis of critical values of loading leading to crack initiation, further growth and the final blade fragmentation was performed. The most efforted places of the turbine blades were selected and crack paths due to thermo-mechanical cyclic loading were determined.
Finite Element Analyses of Turbine Disc with Surface Cracks
2017
In Aircrafts, Gas turbine discs are critical engine components, which must endure substantial mechanical and thermal loading, such air facts will be in trouble if an induced cracks develop and may gradually affect the whole engine function and leads to failure. In order to overcome the problem turbine life span has to be predicted using the approximate methods of evaluation (Ansys workbench software). There are a number of investigations devoted to both failure analyses and life assessment of turbine discs. Therefore, it is important to get approximate life of the turbine disc by simulating the fatigue damage of crack growth rate, and are essential in determining either the likely failure modes or the component replacement intervals to prevent failures under normal operating conditions.
Cracks path growth in turbine blades with TBC under thermo – mechanical cyclic loadings
Frattura ed Integrità Strutturale, 2015
Blades of combustion turbines are extremely loaded turbojet elements, which transmit operative energy onto a rotor. Experiences of many years indicate, that cracks initiation and propagation in the blades during the operation time can cause destruction not only of the engine, but sometimes an airplane. In high temperature one of the most often occuring interactions in the turbine engine are time variable force fields, caused by non-stationary flowing of an exhaust gas and aerodynamical interaction of the engine elements. The extremal thermo-mechanical loadings initiate gradual degradation process of the blades as a result of fatigue and material creep. More often Thermal Barrier Coatings (TBCs) are applied on the turbine blade surface to provide protection not only against the high temperature but also against aggressive environment. The paper presents the advantages of applying of the TBC layers for increase of the cracks resistance to gradual degradation of the turbine blades. The level of save values of thermo-mechanical loading was estimated. Analysis of critical values of loading leading to crack initiation, further growth and the final blade fragmentation was performed. The most efforted places of the turbine blades were selected and crack paths due to thermo-mechanical cyclic loading were determined.