PSI - Issue 13

ScienceDirect Available online at www.sciencedirect.com Av ilable o line at ww.sciencedire t.com ienceDirect Structural Integrity Procedia 00 (2016) 000 – 000 Procedia Structu al Integrity 13 (2018) 813–818 Available online at www.sciencedirect.com ScienceDirect Structural Integrity Procedia 00 (2018) 000 – 000 Available online at www.sciencedirect.com ScienceDirect Structural Int grity 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 A discussion about multi-axial fatigue criteria for NiTinol cardiovascular devices Francesca Berti a , Lorenza Petrini b *, Andrea Spagnoli c a Department of Chemistry, Materials and Chemical Engineering “Giulio Natta”, Politecnico di Milano, 20133 Milano (Italy) b Department of Civil and Environmental Engineering, Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133 Milano (Italy) c Department of Engineering and Architecture, Università di Parma, Parco Area delle Scienze, 181/A - 43124 Parma (Italy) Abstract Nickel-Titanium (NiTinol) alloys exploit a typical super-elastic behavior which makes them suitable for many biomedical applications, among which peripheral stenting, requiring the device being subjected to the high mobility of the lower limbs. Unfortunately, this complex environment can lead to the device fati ue fracture with likely other more sever complications, e.g. re tenosis. Standards require to experimentally verify stent fatigue life behavior, without giving indications on how to select the loads to be applied for resembling most critical in-vivo conditions. Moreover, different multi-axial fatigue criteria have been originally developed for standard metals to predict the behavior under cyclic loads, but none of them is specifically formulated for NiTinol. This paper presents a numerical study having two aims: i) understanding how non-proportional loading conditions due to combination of axial compression, bending and torsion induced at each patient gait on the femoro-popliteal artery affects the implanted stent stress/strain distribution; ii) understanding how stent fatigue life prediction may be affected by the choice of the fatigue criteria. Accordingly, two different peripheral stent geometries, resembling commercial ones, were analysed under different sets of loading conditions. The cyclic deformations induced over the device structure by macroscopic loads are interpreted through four different fatigue approaches recently used in Nitinol fatigue analyses: Von Mises, Fatemi-Socie, Brown-Miller and Smith-Watson-Topper. The comparison between the outputs highlights that they are strongly influenced by the loading path, recognizing the major role in fatigue due to the combined torsional and bending actions. On the other hand, the choice of the fatigue criterion impacts on the fatigue life prediction. © 2018 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the ECF22 organizers. Keywords: shape memory alloys; multi-axial fatigue; NiTinol; peripheral stents elastic modulus for the austenite phase , empirical material constant accounting for the coupling of shear/bending fatigue limit © 2018 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the ECF22 organizers. ECF22 - Loading and Environmental effects on Structural Integrity A discussion about multi-axial fatigue criteria for NiTinol cardiovascular devices Francesca Berti a , Lorenza Petrini b *, Andrea Spagnoli c a Department of Chemistry, Materials and Chemical Engineering “Giulio Natta”, Politecnico di Milano, 20133 Milano (Italy) b Department of Civil and Environmental Engin ering, Pol tecn co di Mi ano, Pi zza Leonard a V nci 32, 201 3 Milano (Italy) c Department of Engineering a d Architectur , U iversità di Parma, P rco Area delle Scienze, 181/A - 43124 Parm (Italy) Abstract Nickel-Titanium (NiTinol) alloys exploit a typical super-elastic behavior which makes them suitable for many biomedical applications, among which peripheral stenting, requiring the device being subjected to the high mobility of the lower limbs. Unfortunately, this complex environment can lead to the device fatigue fracture with lik ly ther more severe c mplications, e.g. resten sis. Standard requir to experi e tally v rify stent fatigu l fe behavior, with ut giv ng indications on how to select the load to be applie f r sembling most critic l in-vivo conditions. Moreover, different multi-axial fatigue criteria have been originally developed for standard metals to predict the beha ior under cyclic l ads, but non of them is specifically formulated for NiTinol. This paper presents a numerical stu y having two aims: i) understanding how -proportional loading conditions due to combination of axi l compression, bending and torsion i duced at each pati nt gait on the femoro-popliteal artery affects the implanted stent stress/str in distribution; ii) understanding how stent fatigu life pr diction may b affected by the choice of the fatigue criteria. Accordingly, two different peripheral stent geometries, resembling commercial ones, w re analysed under different s ts of loading co ditions. The cyclic d formations i duced over the device structure by m cr scopic loads are interpret d through four dif erent fatigue approaches re ently used in Nitinol fatigue analyses: Von Mises, Fatemi-Socie, Brown-Miller and Smith-Watson-Topper. The comparison between the outputs highlights that they are strongly influenc d by th loading path, ecognizing the major role in fatigue due t the combined torsional and bending actions. On the other hand, the choice of the fatigue criterion i pacts on the fatigue life prediction. © 2018 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the ECF22 organizers. Keywords: shape memory alloys; multi-axial fatigue; NiTinol; peripheral stents elastic m dulus for t austenite phase , empirical material constant accounting for the coupling of shear/bending fatigue limit © 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 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 r sponsibility of the ECF22 o ganizers. * Corresponding author. Tel.: +39 02 2399 4307; fax: +39 02 2399 4286. E-mail address: lorenza.petrini@polimi.it * Corresponding author. Tel.: +39 02 2399 4307; fax: +39 02 2399 4286. E-mail ad ress: lorenza.petrini@polimi.it

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

2452-3216  2018 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the ECF22 organizers. 10.1016/j.prostr.2018.12.156