PSI - Issue 13

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XV Portuguese Conference on Fracture, PCF 2016, 10-12 February 2016, Paço de Arcos, Portugal Thermo-mechanical modeling of a high pressure turbine blade of an airplane gas turbine engine P. Brandão a , V. Infante b , A.M. Deus c * a Department of Mechanical Engineering, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1, 1049-001 Lisboa, Portugal b IDMEC, Department of Mechanical Engineering, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1, 1049-001 Lisboa, Portugal c CeFEMA, Department of Mechanical Engineering, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1, 1049-001 Lisboa, Portugal Abstract 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. © 2018 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the ECF22 organizers. ECF22 - Loading and Environmental e ff ects on Structural Integrity E ff ect of Gradient Plasticity on Crack Initiation and Propagation in the Ductile-Brittle Transition Region of Ferritic Steel Giang, N.A. ∗ , Kuna, M., Hütter, G. Institute of Mechanics and Fluid Dynamics (IMFD), TU Freiberg, 09599 Freiberg, Germany Abstract Micro-crack initiation in ductile-brittle transition region of ferritic steel is often observed through cracking of carbides near or at ferritic grain boundary. The main reason is that the dislocation pile-up at a grain boundary induces high stre ses in the carbide. This mechanism cannot be modelled by classical plasticity. In the present study, the e ff ective gradient plasticity (scalar gradient plasticity) together with cohesive zone models is employed in a unit cell model to adress this mechanism at the microscale. c 2018 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the ECF22 organizers. Keywords: Ferritic steel; Gradient plasticity; Cell model; Cracking of carbide particle. 1. Introduction Table 3 Representative values of cementite thickness, grain size and yield stress at room temperature [21]. Symbol 10LL 10LM 10LS Cementite particle thickness ( l m) Average 0.55 0.30 0.19 0.28 Max 2.02 1.10 0.66 0.93 Average aspect ratio of cementite particle 2.29 2.89 4.99 4.55 Ferrite grain diameter ( l m) Average 75 85 78 45 Max 218 226 229 104 Yield stress at room temperature (MPa) 161 170 171 215 Fig. 4. Configuration of circumferential notched round bar specimen [21]. 0.1 0.4 0.3 0.2 Max. principal plastic 0.1 0.2 0.3 +800 +700 +600 +500 +400 +300 +200 +100 0 Symmetry plane Symmetry axis strain 166 K. Shibanuma et al. / Engineering Fracture Mechanics 151 (2016) 161–180 Ferritic steels contain a nu ber of carbides including Fe 3 C, Mo 2 C, M 7 C 3 , M 23 C 7 and carbo-nitrides. Among them, cementite Fe 3 C is a relatively coarse c r bide and it is often firstly fractured or debonded from the ferritic matrix under working conditions. Experimental obs rvations indicate that iron carbides Fe 3 C (cementite) play a critical role for cleavage initiation in ductile–brittle transition of ferritic steel (Lee et al., 2002; Tanguy et al., 2005). Micro-cracks often initiate from carbides near or at a grain boundary as illustrated in Fig. 1. Consequently, car bide particles have a strong influence on fracture toughness of these steels. Kroon and Faleskog (2005) proposed a micro-mechanics unit-cell approach considering potential cleavage of the ferrite and debonding of the carbide. However, using clas sical J 2 plasticity for the ferrite matrix, this model cannot account for the pile-up of dislocations. The present study employs a gradient-enhanced plasticity theory to model the dislocation pile-up at grain boundaries in order to explore the interaction with initiation of micro-cracks. ECF22 - Loading and Environmental e ff ects on Structural Integrity E ff ect of Gradient Plasticity on Crack Initiation and Propagation in th Ductile-Brittle Transition Region of Ferritic Steel Giang, N.A. ∗ , Kuna, M., Hütter, G. Institute of Mechanics and Fluid Dynamics (IMFD), TU Freiberg, 09599 Freiberg, Germany Abstract Micro-crack initiati n in ductile-brittle t a sition region of ferritic steel s often observed through cracking of carbides near or at ferritic grain boundary. The main reason is that the dislocation pile-up at a grain boundary induces high stresses in the carbide. This mechanism cannot be modelled by classical plasticity. In the present study, the e ff ective gradient plasticity (scalar gradient plasticity) together with cohesive zone models is employed in a unit cell model to adress this mechanism at the microscale. c 2018 The Authors. Published by Elsevier B.V. P r-review unde responsibility of the ECF22 organizers. Keywords: Ferritic steel; Gradient plasticity; Cell model; Cracking of carbide particle. 1. Introduction Table 3 Representative values of cementite thickness, grain size and yield stress at room temperature [21]. Symbol 10LL 10LM 10LS Ce entite particle thickness ( l m) Average 0.55 0.30 0.19 0.28 Max 2.02 1.10 0.66 0.93 Average aspect ratio of cementite particle .29 2.89 4.99 4.55 Ferrite grain diameter ( l m) Average 75 85 78 5 Max 218 226 229 104 Yield stress at room temperature (MPa) 161 170 171 215 Fig. 4. Configuration of circumferential notched round bar specimen [21]. 0.1 0.4 0.3 0.2 Max. principal plastic 0.1 0.2 0.3 7 6 5 4 3 2 1 Symmetry plane Symmetry axis strain 1μm ferrite ferrite cementite crack crack cementite Fig. 6. SEM image of cracked cementite particles [21]. 166 K. Shibanuma et al. / Engineering Fracture Mechanics 151 (2016) 161–180 Fig. 1: SEM image of cracked car bide particle (Shibanuma et al., 2016) Ferritic steels contain a number of car des including Fe 3 C, Mo 2 C, M 7 C 3 , M 23 C 7 and carbo-nitrides. Among them, cementite Fe 3 C is a relatively coarse car bide and it is often firstly fractured or debonded from the ferritic matrix under working conditions. Experimental observations indicate that iron carbides Fe 3 C (cementite) play a critical role for cleavage initiation in ductile–brittle transition of ferritic steel (Lee et al., 2002; Tanguy et al., 2005). Micro-cracks often initiate from carbides near or at a grain boundary as illustrated in Fig. 1. Consequently, car bide particles have a strong influence on fracture toughness of these steels. Kroon and Faleskog (2005) proposed a micro-mechanics unit-cell approach considering potential cleavage of the ferrite and debonding of the carbide. However, using clas sical J 2 plasticity for the ferrite matrix, this model cannot account for the pile-up of dislocations. The present study employs a gradient-enhanced plasticity theory to model the dislocation pile-up at grain boundaries in order to explore the interaction with initiation of micro-cracks. © 2016 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Scientific Committee of PCF 2016. Keywords: High Pressure Turbine Blade; Creep; Finite Element Method; 3D Model; Simulation. 1μm ferrite ferrite cementite crack crack cementite Fig. 6. SEM image of cracked cementite particles [21]. Fig. 1: SEM image of cracked car bide particle (Shibanuma et al., 2016)

10MM 10SS 10MM 10SS 0.15

0.15 0.49 0.49 3.02 3.02 19 19 47 47 247 247

Maximum Principal Stress [MPa] Maximum Principal Stress [MPa] +800

Fig. 5. Strain and stress distributions obtained by finite element analysis in the circumferential notched specimen, 10LM, Fig. 5. Strain and stress distributions obtained by finite element analysis in the circumferential notched specimen, 10LM,

2452-3216 © 2016 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Scientific Committee of PCF 2016. ∗ Corresponding author. Tel.: + 49-373-139-3313 ; fax: + 49-373-139-3455. E-mail address: Ngoc-Anh.Giang@imfd.tu-freiberg.de 2210-7843 c 2018 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the ECF22 organizers. ∗ Corresponding author. Tel.: + 49-373-139-3313 ; fax: + 49-373-139-3455. E-mail address: Ngoc-Anh.Giang@imfd.tu-freiberg.de 2210-7843 c 2018 The Authors. Published by Elsevier B.V. Peer-revi w under responsibility of the ECF22 organizers. * Corresponding author. Tel.: +351 218419991. E-mail address: amd@tecnico.ulisboa.pt 2452-3216  2018 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the ECF22 organizers. 10.1016/j.prostr.2018.12.008