Structural integrity assessment of rigid polyurethane

Available online at www.sciencedirect.com Available online at www.sciencedirect.com

ScienceDirect ScienceDirect

Available online www.sciencedirect.com Available online at at www.sciencedirect.com Structural Integrity Procedia 00 (2018) 000–000 Structural Integrity Procedia 00 (2018) 000–000

ScienceDirect ScienceDirect

Procedia Structural Integrity 13 00 (2018) 1595–1599 Structural Integrity Procedia (2016) 000–000

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

www.elsevier.com/locate/procedia

ECF22 - Loading and Environmental effects on Structural Integrity ECF22 - Loading and Environmental effects on Structural Integrity

Structural Structural integrity integrity assessment assessment of of rigid rigid polyurethane polyurethane components components XV Portuguese Conference on Fracture, PCF 2016,methods 10-12 February 2016, Paço de Arcos, Portugal using energy using energy methods a* a a a a G.Lesiuk A.De pressure Jesusb , B.Babiarczuk Thermo-mechanical modeling of abb,,high turbine blade of an a*, K.Junika, M.Smolnick a, J.Correia a, K.Otczyk a G.Lesiuk , K.Junik , M.Smolnick , J.Correia A.De Jesusb , B.Babiarczuk , K.Otczyk Department of Mechanics, Materials Science and Engineering, Wrocław University of Science and Technology, 50-370 Wrocław, Poland airplane gas turbine engine Department of Mechanics, Materials Science andUniversity Engineering, Wrocław of Science and Technology, 50-370 Wrocław, Poland INEGI/Faculty of Engineering, of Porto, RuaUniversity Dr. Roberto Frias, 4200-465 Porto, Portugal a a

b b

INEGI/Faculty of Engineering, University of Porto, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal

P. Brandãoa, V. Infanteb, A.M. Deusc*

Abstract a Department of Mechanical Engineering, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1, 1049-001 Lisboa, Abstract Portugal

In the b paper, the experimental results of the mechanical investigation have been presented. The main attention was paid to fracture Department of Mechanical Engineering, Institutoinvestigation Superior Técnico, de Lisboa, Av. Rovisco Pais, 1, 1049-001 Lisboa, In theIDMEC, paper,tearing the experimental results of the mechanical haveUniversidade been presented. Theelastomers main attention was paid fracture toughness, resistance and fatigue crack growth rate characterization of polyurethane in terms of twotodifferent Portugal toughness, tearing resistance and and fatigue crackThe growth rate characterization of polyurethane elastomers in terms twocyclic) different c hardness configurations; 90ShA. impact of material hardness on thedefracture properties (static and is CeFEMA, Department of80ShA Mechanical Engineering, Instituto Superior Técnico, Universidade Lisboa, Av. Rovisco Pais, 1,of1049-001 Lisboa, hardness configurations; 80ShA and 90ShA. The impact of material hardness on the fracture properties (static and cyclic) is Portugal reflected in experimental results. For fracture toughness characterization, the EWF (essential work of fracture) method was reflected experimental results. For80ShA fractureand toughness characterization, the EWF (essential workbehavior of fracture) was involved. in It has been shown, that the 90ShA materials demonstrate completely different undermethod high stress involved. It has been shown, the 80ShA and 90ShA materials demonstrate high in stress concentration condition. Fromthat the perspective of usefulness of fracture mechanics,completely the energydifferent approachbehavior seems tounder be crucial the Abstract concentration condition. From the perspective of usefulness of fracture mechanics, the energy approach seems to be crucial in the context of the real operating conditions of the bushing in suspension system of vehicles. For this purpose the fatigue crack growth context of the real operating conditions of the bushing in suspension system of vehicles. For this purpose the fatigue crack growth rate test was performed on planar specimens PS (Pure Shear). Based on the experimental results, it can be concluded that fatigue During their modern aircraft was engine components areinon subjected to toincreasingly demanding operatingthat conditions, rate test was performed on planar specimens PS significantly (Pure Shear).higher Based the experimental results,PUR it canelastomer. be concluded fatigue crack growth rateoperation, in 90ShA PUR elastomer comparison the 80ShA especially pressure turbine (HPT)was blades. Such conditions these parts to undergo different types of time-dependent crack growththe ratehigh in 90ShA PUR elastomer significantly higher incause comparison to the 80ShA PUR elastomer. degradation, one of which is creep. A model using the finite element method (FEM) was developed, in order to be able to predict © 2018 2018The TheAuthors. Authors. Published by Elsevier B.V. © Published by Elsevier B.V. the behaviour of HPT blades. Flight © 2018creep The Authors. Published by Elsevier B.V.data records (FDR) for a specific aircraft, provided by a commercial aviation Peer-review under responsibility of the ECF22 Peer-review under responsibility of the ECF22 organizers. company, under were used to obtainofthermal and organizers. mechanical data for three different flight cycles. In order to create the 3D model Peer-review responsibility the ECF22 organizers. needed for the FEM analysis, a HPT blade scrap was scanned, and its chemical composition and material properties were Keywords: elastomers; static properties; energy; rate; obtained.polyurethane The data that was gathered was fed tearing into the FEMfatigue modelcrack and growth different simulations were run, first with a simplified 3D Keywords: polyurethane elastomers; static properties; tearing energy; fatigue crack growth rate; 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 1.model Introduction can be useful in the goal of predicting turbine blade life, given a set of FDR data.

1. Introduction

©Polyurethane 2016 The Authors. Published by is Elsevier B.V. (PUR) material a commonly used material, as a rubber replacement, in suspension system of Polyurethane materialof is commonly usedcyclic material, as a rubber in suspension system of Peer-review responsibility theaabout Scientific Committee of PCF 2016. vehicles (Fig.under 1).(PUR) The knowledge static and behavior of thisreplacement, materials with consideration of the vehicles (Fig. 1). The knowledge about static and cyclic behavior of this materials with consideration of the manufacturing discontinuities or fatigue cracks behavior is limited. The classical fracture toughness tests are not Keywords: High discontinuities Pressure Turbine Blade; Creep; Finite Element Method; 3D Model; Simulation. manufacturing or fatigue cracks behavior limited. The classical fracture toughness tests are not suitable to the nonlinear and visco-elastic behavior of suchisa type materials like rubber or rubber-similar elastomers. suitable to the nonlinear and visco-elastic behavior of such a type materials like rubber or rubber-similar elastomers. However, the J-integral approach will be the most useful in many engineering tasks. On the other hand, its However, the J-integral approach be the most useful in many engineering tasks. On the other hand, its implementation could be not simple will in engineering practice. implementation could be not simple in engineering practice.

2452-3216 © 2018 The Authors. Published by Elsevier B.V. 2452-3216 © 2018 Authors. Published Elsevier B.V. Peer-review underThe responsibility of theby ECF22 organizers. Peer-review underauthor. responsibility the ECF22 organizers. * Corresponding Tel.: +351of 218419991. E-mail address: [email protected]

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.2018.12.336

G. Lesiuk et al. / Procedia Structural Integrity 13 (2018) 1595–1599 Author name / Structural Integrity Procedia 00 (2018) 000–000

1596 2

Fig. 1. Typical PUR elastomers in vehicles parts

In a last decades, the Essential Work of Fracture (EWF) is a promising substitution and alternative in a polymer testing by several researchers; Mehmood et al. (2012), Gamez-Perez et al. (2009), Arkhireyeva, A., and S. Hashemi (2001) and ESIS (European Structural Integrity Society) recommendations: Clutton (2001) It should be underlined that, the physical explanation and relation with J-integral approach are well documented in work of Arkhireyeva, A., and S. Hashemi (2001). The main fundamentals of energy approach EWF for PUR elastomers (Lesiuk et al. (2016)) can be shortly represented by the W-specific total work of fracture referred to the non-fractured ligament L area (divided by the Lt, t-thickness of specimen):

W  We  Wp ,

(1)

where We represents essential specific work of the fracture referred to the non-fractured ligament area (divided by Lt, t-thickness of specimen) and Wp-non-essential – plastically dissipated energy work of fracture referred to the non-fractured ligament area (divided by the Lt, t-thickness of specimen). -factor is a scalar, non-dimensional factor associated with geometric shape of deformation zone. 2. Fracture susceptibility and fatigue crack growth in PUR elastomers According to the American Standards ASTM D412-16 (DIE C specimen type), ASTM 624-00 (DIE C specimen type), basic static mechanical properties were determined. The main results are collected in Table 1. Table 1. Basic mechanical properties of tested PUR materials (static tensile test, tear resistance test) Property Ultimate Tensile Strength UTS (MPa) Critical strain at rupture u (%) Tear Resistance T (N/mm) 100% (MPa) 200% (MPa) 300% (MPa)

PUR80ShA 31.8 419 93.7 3.7 5.4 7.0

PUR90ShA 41.8 422 134.0 7.4 11.1 15.1

2.1. Essential Work of Fracture In order to evaluate the critical essential work of fracture, the two types of specimens were prepared. According to the literature standardization of the EWF test method, the 40-DENT specimens were fabricated from molded plates 2 mm thick. The moulding process was performed with accordance of the material manufacturer DOW Company using Hyperflex 101 material. Two type of hardness in specimen were obtained; 80 and 90 ShA. During the experiments, the force, displacement and temperature were measured (with additional channel from thermovision camera). According to the numerical procedure prepared in HP VEE environment all energy quantities, responsible for fracture process were solved. All the mechanical tests were performed with a constant cross-head of displacement speed level – 50mm/min using the MTS 810 machine with 5kN load cell. The cracks were prepared using a surgical knife. As it was expected, a


1597 3

significant difference was observed due to the differences in hardness of polyurethane elastomers. According to the EWF method, the We – specific, essential work of fracture were evaluated; for 80ShA – 26.8kJ/m2, for 90ShA – 52.3kJ/m2. Exemplary load-displacement results for different crack lengths are presented in Fig. 2.

Fig.2. a) Exemplary diagram with the registered differences in load-displacement curves for PU80ShA and PU90ShA (L=14mm), b) Exemplary diagram with the registered differences in load-displacement curves for PU80ShA and PU90ShA (L=8mm)

2.2. Fatigue crack growth rate test For fatigue crack growth characterization, the PS – Pure Shear, cracked specimens were involved. Typical PS specimen is presented in Fig. 3. In experimental campaign, the main dimensions of the PS specimen were following: h0=20 mm, c0-initial crack length = 24.mm, W (specimen width) = 160 mm.

Fig. 3. PS (Pure Shear) planar specimen scheme with crack subjected to fatigue test; Thor (2012)

Fig. 4. Measurement stand; 1 – digital microscope with illumination system, 2 – gripping system, 3 – upper grip MTS with load cell, 4 - specimen

Initial notch was prepared by surgical blade in order to obtain sharp notch – similar to a fatigue crack. All specimens were gripped in additional fixture and the clamping force was controlled by bolts system in order to avoid slipping of the specimen during fatigue test. The measurement stand used in experimental campaign is presented in Fig. 4: 1 – digital microscope with low magnification and lightening system, 2 – grips, 3- load cell and 4 – specimen. During experiment, the crack length was monitored using microscopic system and image-data processing. Exemplary views on fatigue cracks (in different phases of fatigue crack growth) are presented in Fig. 5. The specimens were loaded with sinusoidal waveform under displacement mode control with keeping strain ratio R=0 and constant total strain on the level =15%. In order to avoid thermal effects, during experiments the frequency f was kept on constant level f=1Hz. During tests, the temperature was monitored using thermo-vision camera. The fatigue lives of the specimens; 80 ShA and 90ShA are presented in Fig. 6.


1598 4 a)

b)

c)

d)

Fig. 5. Measured crack length at different stages of fatigue crack growth of PUR elastomers: a) initial crack (80ShA), b) 45 mm crack length (80ShA), c) initial crack (90ShA) , d ) 51 mm crack length (90ShA)

Fig. 6. Fatigue crack growth curves for 80ShA and 90ShA (total strain =15%)

3. Conclusions The following conclusions from the test results of PUR elastomers can be drawn:  Static tensile properties (in each point of tests) were higher for 90ShA hardness level,  Fracture toughness equivalent – EWF energy was higher for 90ShA material in comparison with 80 ShA,  Increase of the precritical fatigue crack growth period is dependent from hardness level; fatigue crack growth rate was higher for 90ShA material in comparison with 80ShA.


1599 5

Acknowledgements This work was financial supported (in part) by the Wroclaw University of Science and Technology – Department of Mechanics, Materials Science and Engineering internal, fundamental research program - 0401/0029/17. The publication has been prepared as a part of the Support Programme of the Partnership between Higher Education and Science and Business Activity Sector financed by City of Wroclaw. References N. Mehmood, T. Mao, G. Bhupati, „Fracture Mechanical Trouser Tear Testing In Thin Polymer Films”, Department of Mechanical Engineering Blekinge Institute of Technology, Karlskrona, Sweden 2012, Str. 12-17. J. Gamez-Perez, M. Sanchez-Soto, J. Ignacio Velasco, M. LI. Maspoch, The Essential Work of Fracture (EWF) method – Analyzing the Post – Yielding Fracture Mechanics of polymers, Engineering Failure Analysis, December 2009. Arkhireyeva, A., and S. Hashemi. "Determination of fracture toughness of poly (ethylene terephthalate) film by essential work of fracture and J integral measurements." Plastics, rubber and composites 30.7 (2001): 337-350. Clutton, E. (2001). Essential work of fracture. In European Structural Integrity Society (Vol. 28, pp. 177-195). Elsevier. Lesiuk, G., Myszka, W., Snowacki, K., & Junik, K. (2016). Badania wytrzymałościowe elastomerów poliuretanowych stosowanych w przemyśle motoryzacyjnym z wykorzystaniem metod mechaniki pękania. Autobusy: technika, eksploatacja, systemy transportowe, 17. Thor Thorup, Characterisation of Fatigue Crack Growth in Silicone for DeapTechnology, Polymer Testing, Proceedings of International Mechanical Engineering Congress & Exposition, 2012, vol. 3, s. 627-634.