PSI - Issue 3

Volume 3 • 2017

ISSN 2452-3216

ELSEVIER

XXIV Italian Group of Fracture Conference, 1-3 March 2017, Urbino, Italy

Guest Editors: Francesco I acoviello L uca Susmel

D onato Firrao Giuse pp e Ferro

Available online al www.sciencedirect.com ScienceDirect

ScienceDirect Available online at www.sciencedirect.com Av ilable o line at ww.sciencedire t.com ScienceDirect Structural Integrity Procedia 00 (2016) 000 – 000 Procedia S ructural Int grity 3 ( 7) 1–2 Structural Integrity Procedia 00 (2017) 000–000 Available o line at www.sciencedirect.com ScienceDirect Structural Integrity Procedia 00 (2017) 000–000 ScienceDirect Structural Integrity Procedia 00 (2017) 000–000

www.elsevier.com/locate/procedia

www.elsevier.com/locate/procedia www.elsevier.com/locate/procedia

www.elsevier.com/locate/procedia 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. XXIV Italian Group of Fracture Conference, 1-3 March 2017, Urbino, Italy Editorial Franc sc Iacovi llo a *, Luca Susmel b , Donato Firrao c , Giuseppe Ferro c a Università di Cassino e del Lazio Meridionale, via G. Di Biasio 43, 03043 Cassino (FR) Italy b University of Sheffield, Mappin Street, Sheffield, S1 3JD, UK c Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129, Torino, Italy © 2017 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Scientific Committee of IGF Ex-Co. According to its Statutes, Gruppo Italiano Frattura (the Italian Group of Fracture, IGF) is a cultural association that is devoted to:  spreading and promoting the results from those research activities specifically focussed on fracture phenomena, with this being done also with the support of ad hoc workgroups;  promoting activities aiming to develop material/structure testing standards;  cooperating with foreign associations operating in the the fracture field (International Congress on Fracture, ICF; European Structural Integrity Society, ESIS; etc.);  organizing meetings, workshops, conferences and courses about fracture phen mena  publishing meeting/wo kshops/conferen e proceedings, news, journal et .;  implementing those activities that are aligned with the association’s aims and scopes. Since 1981, the IGF conferences are among the most important scientific/technical meetings focussing on “fracture” and “structural integrity” that are organized in Italy every year. The topics of the presentations being delivered range from concrete to stainless steels and from stones to polymers. By considering different loading or environmental conditions, they tackle the fracture is ue from d fferent angles (analytical, numerical, experimental, etc.), investigating the phenomena of int rest from a micro-level up to a “full scale” level. The fact that the IGF covers such a wide area of interest makes it difficult for the “typical” IGF member to be described… a metallurgist or a materials scientist? A civil XXIV Italian Group of Fracture Conference, 1-3 March 2017, Urbino, Italy Editorial Francesco Iacoviello a *, Luca Susmel b , Donato Firrao c , Giuseppe Ferro c a Università di Cassino e del Lazio Meridionale, via G. Di Biasio 43, 03043 Cassino (FR) Italy b University of Sheffield, Mappin Street, Sheffield, S1 3JD, UK c Politecnic di Torino, Corso Duca degli Abruzzi 24, 10129, T rino, Italy © 2017 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Scientific Committee of IGF Ex-Co. According to its Statutes, Gruppo Italiano Frattura (the Italian Group of Fracture, IGF) is a cultural association that is devoted to:  spreading and promoting the results from those research activities specifically focussed on frac ure phenomena, with this being done also with the support of ad hoc workgroups;  promoting activities aiming to develop material/structure testing standards; cooperating with f reig associations operating in the th fracture field (Int rnational C ngr ss Fracture, ICF; European Structural Integrity S cie y, ESIS; etc.); o ganiz ng meeting , workshops, conferences and courses about fracture phenomena publishing meeting/workshops/conference proceedings, news, journa etc.;  implementing those activities that are aligned with the association’s aims and scopes. Since 1981, the IGF conferences are mong t most imp tant scientific/technical meeti gs focussing on “fracture” and “structural integrity” that ar organ zed in Italy every year. T topics of the presentations b ing delivered range from concrete to stainless steels and from stones to polymers. By considering different loading or environmental conditions, they tackle the fracture issu from different angle (analy ical, numerical, experimental, et .), nvestigating the phenomena of rest from micro-lev l up o a “full scale” level. The act that the IGF covers such a wide area of interes makes it difficult for the “typical” IGF memb r to be described… a metallurgist or a mate ials scientist? A civil XXIV Italian Group of Fracture Conference, 1-3 March 2017, Urbino, Italy Editorial Francesco Iacoviello a *, Luca Susmel b , Donato Firrao c , Giuseppe Ferro c a Università di Cassino e del Lazio Meridionale, via G. Di Biasio 43, 03043 Cassino (FR) Italy b University of Sheffield, Mappin Street, Sheffield, S1 3JD, UK c Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129, Torino, Italy © 2017 Th Authors. Published by Elsevier B.V. Peer-review under responsibility of the Scientific Committee of IGF Ex-Co. Accor ing to its Statutes, Gruppo Italia o Frattura (the Italian Group f Fracture, IGF) is a cultural association that is devoted to:  spreading and promoting the results from those research activities specifically focussed on fracture henomena, with this bei g done also with the supp rt of ad hoc workgroups;  r moting activities aiming to develop material/structure testing standards; co p rating with for ign associations operating in th th fracture field (International Congress on Fractur , ICF; European Structural Inte rity Society, ESIS; etc.); organizi ti gs, workshops, conferences and courses about fracture phenomena publishing meeting/workshops/conference proceedings, news, j urnal etc.;  implementing those activities that are aligned with the association’s aims and scopes. Since 1981, th IGF c nferences ar among th most importa t scientific/t c nical meetings focussing on “fr cture” a d “structural integrity” th t ar rganized in Italy ev ry year. The topics of the presentations being deliver d range from concrete to stainless teels and from ton s to polymers. By considering different loading or environmental conditions, they tackle the fracture issue from different angles (analytical, numerical, experimental, etc.), investigating the ph nomena of interest from a micro-level up to a “full scale” level. The fact that the IGF covers such a wide area of interest makes it difficult for the “typical” IGF member to be described… a metallurgist or a materials scientist? A civil © 2016 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Scientific Committee of PCF 2016. Copyright © 2017 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the Scientific Committee of IGF Ex-Co. Keywords: High Pressure Turbine Blade; Creep; Finite Element Method; 3D Model; Simulation. * Corresponding author. Tel.: +39.07762993681; fax: +39.07762993781. E-mail address: iacoviello@unicas.it

* Corresponding author. Tel.: +351 218419991. E-mail address: amd@tecnico.ulisboa.pt 2452-3216 © 2017 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Scientific Committee of IGF Ex-Co. 2452-3216 © 2017 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Scientific Committee of IGF Ex-Co. * Corresponding author. Tel.: +39.07762993681; fax: +39.07762993781. E-mail address: iacoviello@unicas.it * Corresponding author. Tel.: +39.07762993681; fax: +39.07762993781. E-mail address: iacoviello@unicas.it 2452-3216 © 2017 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Scientific Committee of IGF Ex-Co.

2452-3216 © 2016 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Scientific Committee of PCF 2016. Copyright © 2017 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ ). Peer-review under responsibility of the Scientific Committee of IGF Ex-Co. 10.1016/j.prostr.2017.04.001

Francesco Iacoviello et al. / Procedia Structural Integrity 3 (2017) 1–2 Author name / Structural Integrity Procedia 00 (2017) 000–000

2

2

or a mechanical engineer? A “pc addicted” or a “lab rat”? Well, during the IGF events you can meet all of them and, during the IGF events, a multidisciplinary approach to fracture and structural problems is always offered. In 2015, the 23 rd edition of the IGF Conference was the first one organized as an international event. It was held in Favignana, a wonderful Sicilian island, and the proceedings were published in Procedia Engineering. The present issue of Procedia Structural Integrity groups together those technical articles that were presented at the 24 th IGF Conference (Urbino, March 1-3, 2017), the second organized as an international event. This issue is opened by the invited lecture that was given by Professor Jesús Toribio from the University of Salamanca. During his lecture, Professor Toribio focused his attention on the structural integrity of progressively cold-drawn pearlitic steels. Inside this issue, the reader will find an exhaustive overview of the research work that is being carried out in Italy on fracture and structural integrity related issues as well as many contributions coming from different countries (such as: Greece, Moroc, Ukraine etc). For the first time, IGFXXIV was also broadcasted “live” via the IGF Facebook page. Further, according to the IGF tradition, many presentations are now available in the IGF YouTube channel at https://www.youtube.com/c/IGFTube. We hope you will enjoy both the technical articles and the presentations. Finally, the present volume was possible thanks to the work done by all the members of the IGF Ex-Co… maybe the best Ex-Co that the IGF has ever had, i.e.: Vittorio Di Cocco (Università di Cassino e del Lazio Meridionale) Giuseppe Ferro (Politecnico di Torino, VicePresident) Angelo Finelli (Treasurer) Donato Firrao (Politecnico di Torino, VicePresident) Francesco Iacoviello (Università di Cassino e del Lazio Meridionale, President)

Carmine Maletta (Università della Calabria) Giacomo Risitano (Università di Messina) Andrea Spagnoli (Università di Parma) Luca Susmel (University of Sheffield, Secretary)

Available online at www.sciencedirect.com

Available online at www.sciencedirect.com

ScienceDirect

ScienceDirect Available online at www.sciencedirect.com Av ilable o line at ww.sciencedire t.com Sci ceDirect Structural Integrity Procedia 00 (2016) 000 – 000 Procedia Structu al Integrity 3 (2017) 168–171 ScienceDirect Structural Integrity Procedia 00 (2017) 000–000 Structural Integrity Procedia 00 (2017) 000–000

www.elsevier.com/locate/procedia

www.elsevier.com/locate/procedia

www.elsevier.com/locate/procedia

XXIV Italian Group of Fracture Conference, 1-3 March 2017, Urbino, Italy XXIV Italian Group of Fracture Conference, 1-3 March 2017, Urbino, Italy

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. Copyright © 2017 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the Scientific Committee of IGF Ex-Co. A c mbin d experimental-numerical investigation of the failure mode of thin metal foils Gabriella Bolzon a *, Mahdieh Shahmardani a , Rui Liu b , Emanuele Zappa b a Department of Civil and Environmental Engineering, Politecnico di Milano, piazza Leonardo da Vinci 32, 20133 Milano, Italy b Department of Mechanical Engineering, Politecnico di Milano, via La Masa 1, 20156 Milano, Italy Abstract A combined experimental and numerical analysis of the mechanical response of the thin aluminum foils employed in beverage packaging has been performed using 3D digital image correlation and non-linear finite element techniques. The present contribution focuses on the significant amount of out-of-plane displacements that develop in tensile tests as fracture propagates across the investigated specimens. The influence of this phenomenon on the actual failure mode of the considered metal samples is further discussed. © 2017 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Scientific Committee of IGF Ex-Co. Keywords: pipeline steel; material aging; mechan cal characteristics; indentation 1. Introduction Thin metal foils are employed in several technological fields related to the production of micro-devices, flexible electronics and beverage packaging (Read and Volinski, 2007; Wong and Salleo, 2009; Bolzon et al., 2015). In these applications, the metal thickness is of the order of a few microns or even less. The foil properties are influenced by the lamination proc sses and di fer from those of he corresponding bulk materials. In particular, the apparent material brittleness increases as the thickness is reduced. At the same time, thin samples are difficult to handle and their mechanical response is sensitive to local imperfections, size and geometric effects (Klein et al., 2001; Hu, 2003; Wang et al., 2003). Thus, for instance, the overall load versus displacement output recorded during uniaxial A combined experimental-numerical investigation of the failure mode of thin metal foils Gabriella Bolzon a *, Mah ieh Shahmardani a , Rui Liu b , Emanuele Zappa b a Department of Civil and Environmental Engineering, Politecnico di Milano, piazza Leonardo da Vinci 32, 20133 Milano, Italy b Department of Mechanical Engineering, Politecnico di Milano, via La Masa 1, 20156 Milano, Italy Abstract A combined experimental and numerical analysis of the mechanical response of the thin aluminum foils employed in beverage packaging has been performed using 3D digital image correlation and non-lin ar finite element techniques. The pr sent contribution focus s on the significa t amount of out-of-plane displacements that d velop in t nsil tests as fracture pro agates across the i vestigated specime s. The influe ce of this phe omenon on the actual failure mod of the considered m tal sampl is further discu sed. © 2017 The Authors. Published by Elsevier B.V. Peer-review under espons bility of the Scientific Committee of IGF Ex-Co. Keywo ds: p peline steel; material aging; mechanica characteristics; indentation 1. Introduction Thin metal foils are employed in several technological fields related to the production of micro-devices, flexible electro ics and beverag packaging (Read and Volinski, 2007; Wong and Salleo, 2009; Bolzon et al., 2015). In thes applicat ons, the m t l thickness is of the or er f a few microns or even less. The foil properties are influenced by the lam nation pr cesses and differ from those of the corresponding bulk mat rials. In particular, the apparent mat rial brittleness incr ases as th thi k ess i reduc d. At the same time, thin samples are difficult to handle a d their mechanical response i sensitive to local imperfections, size and g ometric eff cts (Klein et al., 2001; Hu, 2003; Wang et al., 2003). Thus, for ins ance, the ov rall l ad versus displacement output recorded during uniaxial © 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 © 2017 The Authors. Published by Elsevier B.V. Peer-review und r responsibility of the Scientific Committee of IGF Ex-Co. 2452-3216 © 2017 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Scientific Committee of IGF Ex-Co. * Corresponding author. Tel.: +39-02-2399-4319; fax: +39-02-2399-4300. E-mail address: gabriella.bolzon@polimi.it * Corresponding author. Tel.: +39-02-2399-4319; fax: +39-02-2399-4300. E-mail address: gabriella.bolzon@polimi.it

2452-3216 © 2016 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Scientific Committee of PCF 2016. Copyright © 2017 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ ). Peer-review under responsibility of the Scientific Committee of IGF Ex-Co. 10.1016/j.prostr.2017.04.030

Gabriella Bolzon et al. / Procedia Structural Integrity 3 (2017) 168–171 Author name / Structural Integrity Procedia 00 (2017) 000–000

169

2

tensile tests may not be directly correlated with the local stress-strain response. The interpretation of the results can be enhanced by full-field monitoring techniques complemented by simulation models of the experiment (Avril et al., 2008; Bolzon, 2014). This approach has been applied to the case of thin aluminum foils employed in beverage packaging. A three-dimensional digital image correlation (3D-DIC) technique has been exploited to measure the displacement distribution and the configuration changes of non-conventional metal samples subjected to tensile load. The performed measurements evidence the significant amount of out-of-plane displacements that develop as fracture propagates across the investigated specimens. The influence of this phenomenon on the actual failure mode of the considered metal samples is discussed in this contribution with the aid of non-linear finite element models of the experiment validated in former investigations (Bolzon et al., 2015). Tensile tests have been performed on notched specimens cut from thin aluminum foils (9 µm nominal thickness). The considered material configurations are shown in Fig. 1. The sample dimensions are approximately 250 mm length and 100 mm width, comparable with those considered in former investigations (Andreasson et al., 2014). The deformation of the specimens and the crack propagation has been followed by a 3D-DIC technique. The resolution achievable with 3D-DIC permits to detect phenomena like material separation and crack propagation at early stage, well in advance with respect to visual inspection (Mathieu et al., 2012). The measurement accuracy of DIC depends on the experimental conditions (Zappa et al., 2014): it can be optimized by the specimen preparation and by image pre-processing (Mazzoleni et al., 2015). In the considered experimental set-up, a stereo camera system mounted on a tripod points the specimen, which is connected with the loading machine by clamps. Two LED-based lighting devices are mounted nearby. The light intensity and projection angle with respect to the metal sample are tuned in order to avoid specular reflection and to get the optimal quality of the image observed in a monitor. An external trigger is used to synchronize the two cameras. The image acquisition frequency is 1Hz. The stereoscopic vision system allows to detect the spatial deformation of the foil under the increasing applied load. The dimensions of the field of view are set to 220x160 mm in order to acquire images of the full area of the specimen. A pair of GX3300 cameras equipped with 50 mm focal length optics (Zeiss Makro Planar T 2/50) are used to acquire the images for DIC. The full resolution thus achieved is 3296×2472 pixels (px), with about 15px/mm in the camera field of view. 2. Experimental investigation

Fig. 1. Snapshots of the notched material specimens subjected to tensile test and DIC reconstruction of the displacement distribution in the loading direction (vertical in the images).

Gabriella Bolzon et al. / Procedia Structural Integrity 3 (2017) 168–171 Author name / Structural Integrity Procedia 00 (2017) 000–000

170

3

Fig. 2. Maximum and minimum out-of-plane displacement during the test.

The surface of the specimen is prepared with a random speckle obtained with black spray paint. The accuracy of the DIC measurement is strongly related to the characteristics of the speckle generated on the monitored surface; the optimal size of the speckle is around 4-5px on average, corresponding in this application to approximately 0.3mm. The contrast of the speckles with the background is increased and the negative effect of the reflection light is reduced by painting the specimen surface white first. The speckle is then generated by means of an airbrush, changing the nozzle and the air pressure to control the size of the black paint particles and to obtain their optimal average size. The full-field deformation of the investigated material samples is recovered during the test. The extreme values of the out-of-plane displacements measured in the case of a plain metal foil are reported in the graph of Fig. 2. Notably, the amplitudes are magnified in the last (softening) phase of the experiment, during material separation. The tensile tests performed on the thin aluminum foils considered in the present investigation have been reproduced in a finite element context (Abaqus, 2015), considering both material and geometric non-linearity. The classical elastic-plastic constitutive law based on Hencky-Huber-von Mises criterion with isotropic hardening rule represents the constitutive metal response in the numerical model. Material parameters coincide with those employed in former investigations (Andreasson et al., 2014; Bolzon et al., 2015). The simulations evidence that a significant compressive state arises orthogonally to the loading direction and in the proximity of the notches, as shown for instance by the contour plots drawn in Fig. 3. 3. Numerical analysis

Fig. 3. Distribution of the stress components arising from the uniaxial tensile test, acting orthogonally (S11, left) and in parallel (S22, right) to the loading direction (vertical in the graphs).

Gabriella Bolzon et al. / Procedia Structural Integrity 3 (2017) 168–171 Author name / Structural Integrity Procedia 00 (2017) 000–000

171

4

4. Discussion

The full-field monitoring of the performed tensile tests detects a significant amount of displacements developing in the direction orthogonal to the specimen surface. The observed deformation is a likely consequence of the geometric instability induced by the compressive stresses evidenced by the numerical simulation. The out-of-plane deformation (warping) is enhanced in the crack propagation phase. Thus, different interacting non-linear phenomena influence the overall response of the sample, that can be fully captured only in a three-dimensional modelling space. The analyses performed so far rest on the elastic-plastic idealization of the metal response. This assumption is motivated by former studies (Bolzon et al., 2014; Bolzon and Shahmardani, 2017), which suggest that failure of thin free-standing aluminum foils and laminates is mainly induced by strain localization and necking. The possibility of introducing displacement discontinuities in order to account for material separation explicitly represents a still open issue, also due to the uncertainties associated to the definition of a specific traction-separation law (Tallinen and Mahadevan, 2011; Pfaff et al., 2014).

5. Closing remarks

The in-plane deformation of the thin aluminum foils subjected to the tensile tests considered in this investigation is accompanied by warping, already documented by Kao-Walter (2004). Numerical simulations permit to understand the origin of this phenomenon. The computational results gathered so far present a fair qualitative agreement with the experimental observations, while quantitative matching requires additional efforts. Further analyses shall also consider the influence of imperfections on the load-displacement output usually exploited to material characterization purposes.

References

Abaqus 6.10, 2015. Dassault Systèmes Simulia Corp. Andreasson, E., Kao-Walter, S., Ståhle, P., 2014. Micro-mechanisms of a laminated packaging material during fracture. Engineering Fracture Mechanics 127, 313–326. Avril, S., Bonnet, M., Bretelle, A.S., Grediac, M., Hild, F., Ienny, P., Latourte, F., Lemosse, D., Pagano, S., Pagnacco, E., 2008. Overview of identification methods of mechanical parameters based on full-filed measurements. Experimental Mechanics 48, 381-402. Bolzon, G., 2014. Advances in experimental mechanics by the synergetic combination of full-field measurement techniques and computational tools. Measurement 54, 159–165. Bolzon G., Cornaggia G., Shahmardani M., Giampieri A., Mameli A., 2015. Aluminum laminates in beverage packaging: Models and experiences. Beverages 1, 183–193. Bolzon G., Shahmardani M., 2017. Macroscopic response and decohesion models of metal-polymer laminates. Engineering Transactions 65, in press (pre-print available on line). Hu, W., 2003. Characterised behaviours and corresponding yield criterion of anisotropic sheet metals. Materials Science and Engineering A 345, 139–144. Kao-Walter, S., 2004. On the Fracture of Thin Laminates. Dissertation Series No. 2004:07, Blekinge Institute of Technology, Karlskrona, Sweden. Klein, M., Hardboletz, A., Weiss, B., Khatibi, G. 2001. The ‘size effect’ on the stress–strain, fatigue and fracture properties of thin metallic foils. Materials Science and Engineering A 319, 924–928. Mathieu, F., Hild, F., Roux, S., 2012. Identification of a crack propagation law by digital image correlation. Journal of Fatigue 36, 146-154. Mazzoleni, P., Matta, F., Zappa, E., Sutton, M.A., Cigada, A., 2015. Gaussian pre-filtering for uncertainty minimization in digital image correlation using numerically-designed speckle patterns. Optics and Lasers in Engineering 66, 19–33. Pfaff, T., Narain, R., de Joya, J.M., O’Brien, J. F., 2014. Adaptive tearing and cracking of thin sheets. ACM Transactions on Graphics 33(4), 110: 1–9. Read, D.T., Volinski, A.A., 2007. Thin films for microelectronics and photonics: Physics, mechanics, characterization, and reliability. Ch. 4 in: Micro- and Opto-Electronic Materials and Structures: Physics, Mechanics, Characterization, Reliability, Packaging (Suhir, E.L., Lee, Y.C., Wong, C.P., Eds.), Springer, New York, pp. 135-180. Tallinen, T, Mahadevan, L., 2011. Forced tearing of ductile and brittle thin sheets. Physical Review Letters 107 (245502), 1–5. Wang, H.W., Kang, Y.L., Zhang, Z.F., Qin, Q.H, 2003. Size effect on the fracture toughness of metallic foil. International Journal of Fracture 123, 177–185. Wong, W.S., Salleo, A. (Eds.), 2009. Flexible Electronics (Materials and Applications). Springer, New York. Zappa, E., Mazzoleni, P., Matinmanesh, A., 2014. Uncertainty assessment of digital image correlation method in dynamic applications. Optics and Lasers in Engineering 56, 140–151.

ScienceDirect Available online at www.sciencedirect.com Av ilable online at ww.sciencedire t.com ScienceDirect Structural Integrity Procedia 00 (2016) 000 – 000 Procedia Structu al Integrity 3 (2017) 362–369 Available online at www.sciencedirect.com ScienceD rect Structural Integrity Procedia 00 (2017) 000–000 Available online at www.sciencedirect.com ScienceDirect Structural Integrity Procedia 00 (2017) 000–000

www.elsevier.com/locate/procedia www.elsevier.com/locate/procedia

www.elsevier.com/locate/procedia

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. Copyright © 2017 The Authors. Published by Elsevier B.V. This is an open access rticl under the CC BY-NC-ND license (http://creativecommons. rg/lice ses/by-nc- /4.0/). Peer-review under responsibility of the Scientific Committee of IGF Ex-Co. XXIV Italian Group of Fracture Conference, 1-3 March 2017, Urbino, Italy A coupled ALE-Cohesive formulation for layered structural systems Marco Francesco Funari a , Fabrizio Greco a , Paolo Lonetti a * a Department of Civil Engineering, University of Calabria, Via P. Bucci, Cubo39B, 87030, Rende, Cosenza, Italy. Abstract A computational formulation able to simulate crack initiation and growth in layered structural systems is proposed. In order to identify the position of the onset interfacial defects and their dynamic debonding mechanisms, a moving mesh strategy, based on Arbitrary Lagrangian-Eulerian (ALE) approach, is combined with a cohesive interface methodology, in which weak based moving connections are implemented by using the finite element formulation. Contrarily to the xisting models a ailable from the literature, the proposed approach appears to be able to describe dynamic debonding processes with a relatively low number of computational elements also in specimens without a pre-existing interfacial crack. The numerical formulation has been implemented by means separate steps, concerned, at first, to identify the correct position of the onset cracks and, subsequently, their growth by changing the computational geometry of the interfaces. In order to verify the accuracy and to validate the proposed methodology, comparisons with experimental and numerical results are developed. In particular, the results, in terms of location and speed of the debonding front, obtained by the proposed model, are compared with the ones arising from the literature. Moreover, a parametric study in terms of geometrical characteristics of the layered structure are developed. The investigation reveals the impact of the stiffening of the reinforced strip and of adhesive thickness on the dynamic debonding mechanisms. © 2017 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Scientific Committee of IGF Ex-Co. Keywords: debonding; ALE; dynamic delamination; FEM; crack onset; layered structures. 1. Introduction During the last decades, la ered structures in the form of laminates or thin films have employed extensively in many engineering fields, ranging from nano to macro scale applications. Typically, such materials are formed by strong layers and weak interfaces, in which internal material discontinuities may evolve, producing relevant loss of stiffness (Barbero (2010)). Moreover, the crack evolution is strongly affected by the time rate of the external loading, XXIV Italian Group of Fracture Conference, 1-3 March 2017, Urbino, Italy A coupled ALE-Cohesive formulation for layered structural systems Marco Francesco Funari a , Fabrizio Greco a , Paolo Lonetti a * a Department of Civil Engineering, University of Calabria, Via P. Bucci, Cubo39B, 87030, Rende, Cosenza, Italy. Abstract A computational formulation able to simulate crack initiation and growth in layered structural systems is proposed. In order to identify the position of the onset in erfacia defects and he r dy amic debonding m chanisms, a moving mesh strategy, based on Arbi rary Lagrangian-Eul rian (ALE) approach, is combin d with a cohesive interface methodology, in which weak based moving connections a e implemented by using the finite element formula ion. Contrarily to the exis ing m dels available from the literature, the prop sed approach app ars to be abl to describe dynamic deb ding processes with a relatively low number f computational el ments also in spe imens with ut pre-existing interf cial crack. The num rical formulation has bee i plemented by means separate steps, concerned, at f rst, to identify the corr ct position of the o set c acks and, subsequently, their growth by changi g the computational geometry of the inter aces. In order to verify the accuracy and to validate the proposed methodology, comparisons with experimental and num ical results are developed. In parti l r, the results, in terms of locati n and spee of the debond ng front, obtained by the propos d mod l, are compared with the ones ising from the literature. Moreover, a arame ric study in terms of geom trical cha acteristics of the layered structure ar developed. The inv stigation reveals th im ct of the iffen g of the reinforced strip and of adhe ive ickness on he dynamic ebonding mechanisms. © 2017 The Authors. Publi hed by Elsevier B.V. Peer-review under espons bility of the Scientific Committee of IGF Ex-Co. Keywords: debonding; ALE; dynamic delamination; FEM; crack onset; layered structures. 1. Introduction During the last decades, layered structures in the form of laminates or thin films have employed extensively in many en ineering fi lds, ranging from nano to macro scale appl c ions. Typically, such aterials are formed by strong layers and weak interfaces, in which intern l material discontinuities may evolve, producing rel vant loss of stiffness (Barbero (2010)). Moreover, the crack evolution is strongly affected by the time rate of the external loading, © 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 © 2017 The Authors. Published by Elsevier B.V. Peer-review und r responsibil ty of the Scientific Committee of IGF Ex-Co. 2452-3216 © 2017 The Authors. Published by Elsevier B.V. Peer review under r sponsibility of the Scientific Committee of IGF Ex-Co. * Corresponding author. Tel.: +39-0984-496917; fax: +39-0948-496917. E-mail address: lonetti@unical.it * Corresponding author. Tel.: +39-0984-496917; fax: +39-0948-496917. E-mail address: lonetti@unical.it

2452-3216 © 2016 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Scientific Committee of PCF 2016. Copyright © 2017 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ ). Peer-review under responsibility of the Scientific Committee of IGF Ex-Co. 10.1016/j.prostr.2017.04.035

Marco Francesco Funari et al. / Procedia Structural Integrity 3 (2017) 362–369 Marco Francesco Funari et al./ Structural Integrity Procedia 00 (2017) 000–000

363

2

which typically produces high amplifications of the fracture parameters. As a matter of fact, the measured crack tip speeds, during crack propagation, are relatively high, ranging also close to the Rayleigh wave speed of the material (Bruno et al. (2005); Greco and Lonetti (2009)). Therefore, in order to predict the interfacial crack growth, models developed also in a dynamic framework are much required. In order to simulate debonding phenomena in layered structures, several approaches have been proposed in the literature. However, among the most important ones, Fracture Mechanics (FM) and Cohesive Zone Model (CZM) are widely utilized in practice (Rabinovitch (2008)). In FM, the total energy release rate and its individual mode components need to be evaluated, in order to predict delamination growth. For general configurations energy release rates can be computed by using a very accurate mesh of solid finite elements and the Virtual Crack Closure Method (VCCM) (Camacho and Ortiz (1996)). Such models calculate the energy release rate as the work performed by the internal traction forces at the crack faces during a virtual crack advance of the tip. Moreover, in dynamic Fracture Mechanics, the VCCM is applied by using the modified form, in which the ERR, during the time evolution, is evaluated by the product between the reaction forces and the relative displacements at the crack tip and at the nodes closer to the crack tip front, respectively, (Bruno et al. (2005)). The prediction of the energy release rate is strictly dependent on the mesh discretization of the crack tip. However, the resulting model is affected by computational complexities, because of the high number of variables and nonlinearities involved along the interfaces. Contrarily, CZM are based on damage formulation making use of interface cohesive elements between each layers, reproducing material interfaces. In this framework, strain softening interface elements with a damaged constitutive relationship are introduced between the crack faces. Cohesive models represent an alternative way to take into account for dynamic crack propagation, since the crack growth is predicted by releasing interfacial constraints, which reproduce displacements continuity between cracked faces. In order to avoid such problems, combined formulations based on fracture and moving mesh methodologies are proposed (Funari et al. (2016)). In particular, the former is able to evaluate the variables, which govern the conditions concerning the crack initiation and growth, whereas the latter is utilized to simulate the evolution of the crack growth by means of ALE formulation (Bruno et al. (2013)). It is worth noting that the use of moving mesh method, combined with regularization and smoothing techniques, appears to be quite efficient to reproduce the evolution of moving discontinuities. However, existing models based on ALE and Fracture mechanics are based on a full coupling of the governing equations arising in both structural and ALE domain. In this framework, material and mesh points in the structural domain produce convective contributions and thus nonstandard terms in both inertial and internal forces. In the proposed formulation, the use of a weak discontinuity approach avoids the modification of the governing equations arising from the structural model and thus a lower complexity in the governing equations and the numerical computation is expected. Despite exiting numerical methodologies based on pure CZM, the present approach reduces the nonlinearities involved in the governing equations to a small region containing the process zone, leading to a quite stable and efficient procedure to identify the actual solution in terms of both crack initiation and evolution. In order to verify the consistency of the proposed model, comparisons with existing formulations for several cases involving single and multiple delaminations are developed. The outline of the paper is as follows. Section 2 presents the theoretical and the numerical aspect of the implementation, in which crack initiation and evolution conditions are discussed. In Section 3, numerical comparisons with existing formulations are proposed and a parametric study is carried out to investigate the dynamic characteristics of the debonding phenomena. 2. Theoretical and numerical implementation The proposed model is presented in the framework of the layered structures, in which thin layers are connected through adhesive elements. The theoretical formulation is based on a multilayered shear deformable beam and a moving interface approach (Fig.1). The former is able to reproduce 2D solution by introducing a low number of finite elements along the thickness of the structure, whereas the latter is able to simulate the crack tip motion on the basis of the adopted growth criterion (Bruno et al. (2008)).

3

Marco Francesco Funari et al. / Procedia Structural Integrity 3 (2017) 362–369 Marco Francesco Funari et al./ Structural Integrity Procedia 00 (2017) 000–000

364

Fig. 1. Multilayered laminate structure: general representations of geometry, interface and TSL.

The mathematical description of the moving mesh modeling is defined by a mapping operator, which relies a particle in a fixed Referential Frame and the one in current material coordinate system. The mesh motion in terms of displacement field, at the k-th interface, is described as the difference between material 1 k X and the referential coordinates ( ) x : ( ) ( ) ( ) ( ) 1 1 , k k k k k k X X t t t t on x x x D = - =F - W (1) where k k B h W = ´ represent the region in which the debonding mechanisms are produced. In order to reduce mesh distortions, produced by the mesh movements, rezoning or smoothing equations are introduced to simulate the grid motion consistently to Laplace based equation which is, in the case of one dimensional domain for both Static (S) and Dynamic (D) cases, defined on the basis of the following relationships (Lonetti (2010)):

( ) , t x

( ) , t x

2 ¶ F

3 ¶ F

k

k



(2)

, k X D = xx

k X D =

,

,

rr

2

2

t ¶ ¶

¶

x

x

The crack onset definition is described by means of a mixed crack growth, which is a function of the fracture variables, coinciding with the ratio between ERR mode components and corresponding critical values, as follows:

r

r

( ) 1 k

( ) 1 k

æ ç ç ç ç ç è

2 ö æ ÷ ç ÷ ç + ÷ ç ÷ ç ÷ ç ø è ÷

ö ÷ ÷ ÷ ÷ ÷ ÷ ø

G X

II G X

2

( ) 1 k

I

1

k g X T

(3)

=

-

G

G

IC

IIC

where k represents the generic k -th interface in which debonding phenomena may occur, r is the constant utilized to describe fracture in different material and ( ) , IC IIC G G are the total area under the traction separation law, whereas

c n

c t

( ) n n G T d D I

( ) t t G T d D II

n = D D ò and

t = D D ò . For

( ) , I II G G are the individual energy release rates calculated as

0

0

Marco Francesco Funari et al. / Procedia Structural Integrity 3 (2017) 362–369 Marco Francesco Funari et al./ Structural Integrity Procedia 00 (2017) 000–000

365

4

each mode components, the Traction Separation Law (TSL) is assumed to be described by the critical cohesive stresses, ( ) , c c t n T T , the critical and initial opening or transverse relative displacements, namely ( ) 0 , c n n D D and ( ) 0 , c t t D D . The numerical implementation of the proposed model is developed by using a finite element approach, in which the layered structure is modelled by the combination of shear deformable beam elements connected through the moving mesh interfaces. A Lagrange cubic approximation is adopted to describe both displacement and rotation fields, whereas linear interpolation functions are adopted for the axial displacements. Moreover, for the variables concerning moving mesh equations, quadratic interpolation functions are assumed to describe the mesh position of the computational nodes. The proposed approach takes the form of a set of nonlinear differential equations, whose solution is obtained by using a customized version of the finite element package Comsol Multiphysics combined with MATLAB script files (COMSOL (2014)). The model can be solved in both static and dynamic framework, taking into account the time dependent effects produced by the inertial characteristics of the structure and the boundary motion involved by debonding phenomena. In both cases, since the governing equations are essentially nonlinear, an incremental-iterative procedure is needed to evaluate the solution (Funari et al. (2016)). In the case of static analysis, the resulting equations are solved by using a nonlinear methodology based on Newton-Raphson or Arch length integration procedures. In the framework of a dynamic analysis, the algebraic equations are solved by using an implicit time integration scheme based on a variable step-size backward differentiation formula (BDF). 3. Results In this section, results are developed with the purpose to verify the consistency and the reliability of the proposed model. At first, a layered structured formed by four mathematical layers and three intact interfaces are investigated in static framework. The main aim of the present analysis is to validate the proposed procedure to predict the onset conditions and the crack growth for a case involving multiple debonding mechanisms. Subsequently in order to validate the procedure to describe the crack front speed, the dynamic debonding mechanisms produced on a steel beam specimen have been investigated by means comparisons with numerical results arising from the literature.

Fig. 2. (a) Laminate configuration and loading scheme; (b) Steel beam configuration and loading scheme.

Marco Francesco Funari et al. / Procedia Structural Integrity 3 (2017) 362–369 Marco Francesco Funari et al./ Structural Integrity Procedia 00 (2017) 000–000

366

5

Table 1. Geometrical, mechanical and interface properties of the laminate. 1 E [GPa] 12 G [GPa] L c [mm] B c [mm] h [mm] H [mm]

e [mm]

 [Kg/mc]

130

6

200

20

2

12

20

1500

IC G [N/mm]

c n T [ MPa ]

IIC G [N/mm]

c t T [ MPa ]

0 n  [mm]

0 t  [mm]

c n  [mm]

c t  [mm]

0.26

30

0.00173

0.0173

1.02

60

0.00334

0.0334

Table 2. Geometrical, mechanical and interface properties of the steel specimen.

1 s E [GPa]

12 s G [GPa]

s L [mm]

1 s L [mm]

2 s L [mm]

c [mm]

a [mm]

s B [mm]

s H [mm]

s  [Kg/mc]

190

79.3

280

30

20

35

105

50

20

7500

1 adh E [GPa]

12 adh G [GPa]

adh L [mm]

adh B [mm]

adh h [mm]

adh  [Kg/mc]

ab  [N/mm]

ab n  [mm]

-

-

5

0.350

160

50

3

2000

0.350

0.01

-

-

1 frp E [GPa]

12 frp G [GPa]

frp L [mm]

frp B [mm]

frp h [mm]

frp  [Kg/mc]

af  [N/mm]

af n  [mm]

-

-

165

60

160

50

1.2

2000

0.350

0.01

-

-

3.1. Layered Structure – Multiple debonding mechanisms The loading scheme, reported in Fig. 2a, is based on clamped end conditions and concentrated untisymmetric opening forces. Moreover, the mechanical properties assumed for the laminate and the interfaces as well as the ones required by the cohesive zone constitutive model are reported in Tab.1. The numerical model is discretized along the thickness by using one mathematical layer for each sublaminate, whereas, for the interfaces, three ALE elements are introduced between the sublayers, in which the crack initiation could be potentially activated. The analysis is developed under a displacement control mode, to ensure a stable crack propagation. In order to verify the stability and accuracy of the solution, several mesh discretizations, ranging from a coarse uniform distribution to a refined one, are considered. In particular, for the proposed model, the following numerical cases are analyzed:  uniform discretization of the mesh with a characteristic element mesh equal  D/L=2/200 (M1) with 1841 DOFs;  uniform discretization of the mesh with a characteristic element mesh equal  D/L=1/200 (M2) with 3633 DOFs; In addition, in order to verify the consistency of the proposed approach, a model based on Pure Cohesive approach, namely PC1, in which a uniform discretization of the mesh with a length equal  D/L=0.2/200 involving in 12012 DOFs is adopted. In Fig. 3a, results in terms of resistance curve are reported. The loading curve obtained by the proposed model is in agreement with the results obtained by using refined CZM approach. Moreover, in the case of a very low mesh element number (M1), the prediction in terms of resistance curve is not affected by a divergent behavior, but it is always very close to enriched one, namely PC1. In Fig. 3b, the evolution between crack tip and applied displacements for two different mesh discretizations are considered. The results show that the proposed model is quite stable, since the predictions in terms of crack tip displacements coincide with that of the PC1 solution. However, it should be noted that in the case of a pure cohesive approach, the crack tip position is taken as the point where the fracture function of the cohesive interface tends to zero, whereas, in the proposed model, an explicit movement of ALE region is identified, since it corresponds to a variable which enters in the computation.