PSI - Issue 13

ScienceDirect Available online at www.sciencedirect.com Av ilable o line at www.sciencedire t.com cienceDirect Structural Integrity Procedia 00 (2016) 000 – 000 Procedia Structu al Integrity 13 (2018) 735–74 Available online at www.sciencedirect.com Scie c Dire t Structural Integrity Procedia 00 (2018) 000–000 Available online at www.sciencedirect.com Sci nceDirect Structural Integrity Procedia 00 (2018) 000–000

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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. ECF22 - Loading and Environmental effects on Structural Integrity Crack path stability in brittle fracture under pure mode I loading M.R. Ayatollahi a, *, S.M.J. Razavi b , F. Berto b a Fatigue and Fracture Lab., Centre of Excellence in Experimental Solid Mechanic and Dynamics, School of Mechanical Engineering, Iran University of Science and Technology, Narmak, 16846, Tehran, Iran. b Department of Mechanical and Industrial Engineering, Norwegian University of Science and Technology (NTNU), Richard Birkelands vei 2b, 7491 Trondheim, Norway. Abstract The crack growth path is expected to be along the initial crack line when the pre-cracked components possess symmetric geometry and loading conditions relative to the crack line. However, it has been previously shown that in some mode I specimens the path of crack growth is not stable and deviates from its initial line after some stages of crack growth. The aim of this paper is to develop an energy-based theoretical model for predicting the instability in the pat of rack rowth. The theoretical m del takes into account both the singular term of stress ahead of the crack tip and the first non-singular term known as the T-stress. The corresponding two-term stresses are replaced in the energy relation around the crack tip and a model is extracted for predicting instability of crack path under mode I loading. The results obtained from the energy-based criterion was then compared to the results obtained from the well-known Generalized Maximum Tangential Stress (GMTS) criterion, which is a two parameter stress-based fracture criterion that considers the effect of T-stress. To validate the theoretical model, the experimental results published recently from fracture test on several mode I cracked specimens are used. Very good prediction is provided for the path of crack growth in these specimens. It is shown the crack path instability is significantly geometry dependent and can be prevented by modifying the specimen geometry or loading type. The results obtained in this research are important because an appropriate knowledge about the stability of crack path and fracture trajectory can play a key role on the extent of damage that occurs in a cracked structure when it experiences mode I brittle fracture. © 2018 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the ECF22 organizers. Keywords: Brittle Fracture; Crack Growth Instability; Crack Growth Path; Strain Energy Density. 1. Introduction Cracks can be generated in engineering components and structures during their service life or due to manufacturing deficiencies. The component then loses its initial load bearing capacity and fails at much lower external loads. In particular, brittle materials like ceramics, rocks, brittle polymers, etc. are vulnerable against mechanical or thermal loads when a crack is present in their structure. If the geometry and loading conditions in a cracked component are symmetric relative to the crack line, the component experiences pure mode I loading. Due to symmetry, it is expected that a mode I crack in isotropic brittle materials extends and progresses along the initial crack line. However, it has been previously shown that in some mode I specimens the path of crack growth is not stable and deviates from its initial line after some stages of crack growth (Cotterell, 1966; Smith et al., 2001; Liu and Chao, 2003). The deviation of the crack path from its initial direction is due to high geometry constraints, which is also demonstrated by T-stress value. In order to be able to consider the geometry effect in the fracture prediction of brittle materials, one can use two-parameter fracture criteria considering both the first singular term and second non-singular term of stress in Williams’ series expansion. © 2018 he uthors. Published by lsevier . . Peer-re ie er res onsi ilit f t e r anizers. ECF22 - Loading and Environ ental effects on Structural Integrity rac at sta ilit i rittle fract re er re e I l a i M.R. Ayatollahi a, *, S.M.J. Razavi b , F. Berto b a Fatigue and Fracture Lab., Centre of Excellence in Experimental Solid Mechanic and Dynamics, School of Mechanical Engineering, Iran University of Science an Technology, Narmak, 16846, Te ran, Iran. b Department of Mechanical and Industrial Engineering, Norwegian University of Science and Technology (NTNU), Richard Birkelands vei 2b, 7491 Trondheim, Norway. Abstract The crack growth path is expected to be along the initial crack line when the pre-cracked components possess symmetric geometry and loading conditions relative to the crack line. However, it has been previously shown that in some mode I specimens the path of crack growth is not stable and deviates from its initial line after some stages of crack growth. The aim of this paper is to develop an energy-based theoretical model for predicting the instability in the path of crack growth. The theoretical model takes into account both the singular term of stress ahead of the crack tip and the first non-singular term known as the T-stress. The corresponding two-term stresses are replaced in the energy relation around the crack tip and a model is extracted for predicting instability of crack path under mode I loading. The results obtained from the energy-based criterion was then compared to the results obtained from the well-known Generalized Maximum Tangential Stress (GMTS) criterion, which is a two parameter stress-based fracture criterion that considers the effect of T-stress. To validate the theoretical model, the experimental results published recently from fracture test on several mode I cracked specimens are used. Very good prediction is provided for the path of crack growth in these specimens. It is shown the crack path instability is significantly geometry dependent and can be prevented by modifying the specimen geometry or loading type. The results obtained in this research are important because an appropriate knowledge about the stability of crack path and fracture trajectory can play a key role on the extent of damage that occurs in a cracked structure when it experiences mode I brittle fracture. 2018 he uthors. Published by lsevi r . . er-re ie er r s onsi ilit f t e r a i rs. Keywords: Brittle Fracture; Crack Growth Instability; Crack Gr wt Path; Strain Energy Density. 1. Introduction Cracks can be generated in engineering components and structures during their service life or due to manufacturing deficiencies. The component th n lo es its initial load beari g capacity and fails at much lower external loads. In particular, brittle materials like ceramics, rocks, brittle polymers, etc. are vulnerable against mechanical or thermal loads when a crack is present in their structure. If the geometry and loading conditions in a cracked co ponent are symmetric relative to the crack line, the component experiences pure mode I loading. Due to symmetry, it is expected that a mode I crack in isotropic brittle materials extends and progresses along the initial crack line. However, it has been previously shown that in some mode I specimens the path of crack growth is not stable and deviates from its initial line after some stages of crack growth (Cotterell, 1966; Smith et al., 2001; Liu and Chao, 2003). The deviation of the crack path from its initial direction is due to high geometry constraints, which is also demonstrated by T-stress value. In order to be able to consider the geometry effect in the fracture prediction of brittle materials, one can use two-parameter fracture criteria considering both the first singular term and second non-singular term of stress in illiams’ series expansion. © 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.

* Corresponding author. Tel.: +351 218419991. E-mail address: amd@tecnico.ulisboa.pt * Corresponding author. Tel.: +98-21-77240201; fax: +98-21-77240488. E-mail address: m.ayat@iust.ac.ir * Corresponding author. Tel.: +98-21-77240201; fax: +98-21-77240488. E-mail address: m.ayat@iust.ac.ir

2452-3216 © 2016 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Scientific Committee of PCF 2016. 2452-3 16 © 2018 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the ECF22 organizers. 2452-3216 © 2018 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the ECF22 organizers.

2452-3216  2018 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the ECF22 organizers. 10.1016/j.prostr.2018.12.122