Longitudinal bonded joints of timber beams using plywood and LVL plates

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2nd International Conference on Structural Integrity, ICSI 2017, 4-7 September 2017, Funchal, Madeira, Portugal

Longitudinal bonded joints PCF of timber beams using and XV Portuguese Conference on Fracture, 2016, 10-12 February 2016,plywood Paço de Arcos, Portugal LVL plates Thermo-mechanical modeling of a high pressure turbine blade of an Antonin Lokaja,a,gas *, Kristyna Vavrusova airplane turbine engineaa a aVŠB

Depatment of Building Structures, Ludvika VŠB –– Technical Technical University University of of Ostrava, Ostrava, Faculty Faculty of of Civil Civil Engineering, Engineering, Depatment Ludvika Podeste Podeste 11 875, 875, Ostrava Ostrava a b of Building Structures, c Poruba, Poruba, 708 708 33, 33, Czech Czech Republic Republic

P. Brandão , V. Infante , A.M. Deus *

a

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

The The content content of of this this article article is is to to analyze analyze destructive destructive testing testing results results of of longitudinal longitudinal solid solid wood wood joints joints of of structural structural size size beams beams with with external external glued glued wood-based wood-based panels panels (plywood, (plywood, laminated laminated veneer veneer lumber lumber –– LVL) LVL) stressed stressed in in bending. bending. The aim Abstract The aim of of this this article article is is to to compare compare the the carrying carrying capacity capacity and and the the real real joint joint behaviour behaviour under under load load with with values values obtained obtained using using numerical numerical modelling modelling and and calculation calculation according according to to valid valid standards. standards. © 2017 The Authors. Published by During their operation, modern aircraft B.V. engine components are subjected to increasingly demanding operating conditions, © 2017The The Authors. Published by Elsevier Elsevier © especially 2017 Authors. Published Elsevier B.V. B.V. the high pressurebyturbine (HPT) blades. Such conditions cause these parts to undergo different types of time-dependent Peer-review under responsibility of the Scientific Committee of ICSI Peer-review under responsibility of the Scientific Committee ICSI 2017. 2017. Peer-review under responsibility of the Scientific Committee of ICSIof2017 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 LVL data records (FDR) for a specific aircraft, provided by a commercial aviation Keywords: timber; joint; capacity; plywood; Keywords: timber; joint; carrying carrying capacity; plywood; LVL 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 The data that was gathered was fed into the FEM model and different simulations were run, first with a simplified 3D 1. obtained. Introduction 1. Introduction 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 The of in the building industry brings only The growth growth of timber timber use in of thepredicting buildingturbine industry brings new trends, not only to the the field field of of innovative innovative wood-based wood-based model can be useful in theuse goal blade life, new giventrends, a set ofnot FDR data.to

materials, materials, but but also also to to the the joining joining of of the the timber timber structure structure elements. elements. Besides Besides already already well well normatively normatively described described and and laboratory tested joints with glued-in elements, © 2016 The Authors. by Elsevier laboratory tested jointsPublished with steel steel glued-inB.V. elements, most most commonly commonly rods rods or or plates, plates, glued glued timber-timber timber-timber joints, joints, used used of the Scientific Committee in furniture the building are as the building in Peer-review furniture or orunder the responsibility building industry industry are created created as well. well.ofIn InPCF the2016. building industry industry it it is is possible possible to to use use glued glued joints joints especially especially for for the the reconstruction reconstruction of of timber timber structure structure elements elements – – for for its its strengthening strengthening or or for for the the replacement replacement of of damaged damaged Keywords: High Pressure Turbine Blade; Creep; Finite Element Method; 3D Model; Simulation.

** Corresponding Corresponding author. author. Tel.: Tel.: +420 +420 597 597 321 321 302; 302; fax: fax: +420 +420 597 597 321 321 377. 377. E-mail E-mail address: address: [email protected] [email protected] 2452-3216 2452-3216 © © 2017 2017 The The Authors. Authors. Published Published by by Elsevier Elsevier B.V. B.V. Peer-review under responsibility the * Corresponding Tel.: +351of Peer-review underauthor. responsibility of218419991. the Scientific Scientific Committee Committee of of ICSI ICSI 2017. 2017. 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  2017 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Scientific Committee of ICSI 2017 10.1016/j.prostr.2017.07.199

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sections of wood. The stiffness and load bearing capacity of glued joints is influenced by several aspects (type of wood species, moisture, thickness of glued line, quality of gluing process, etc.). Glued wood-steel joints, mainly in the form of threaded rods, are already an established practice in the construction industry with normative described values of bearing capacity (Eurocode 5, 2006; CSN 73 1702, 2007) along with and perpendicular to grains supported by many laboratory experiments and scientific works. Some specialists from all around the world (Gustafsson et al. 2001; Aicher et al. 1992; Gaun 1998) and also from the Czech Republic (Vašek and Mikeš 1998; Lokaj and Klajmonova 2014) are dedicated to the issue of carrying capacity and the performance of joints of timber structures with glued-in steel rods and plates. These joints are used both for new buildings and for restoration and redevelopment in locally damaged elements of timber structures, where there is no need of total replacement, but only the local repair of damaged parts. The load bearing capacity and deformation of glued wood-wood joints is influenced by considerably more factors than in the case of steel-wood joints. They are mainly: the type of wood species, adhesive properties, glued line thickness, moisture and geometry. A number of influences affecting the behaviour therefore offer a wide range of questions that need to be answered in this issue. Worldwide, research inquiries and the testing of these joints, focusing on various influences and their combinations affecting their bearing capacity, are already in progress. For example (Serrano 2002) is devoted to the mechanical behaviour of these joints. Other works are mainly devoted to the carrying capacity of adhesives in combination with various aspects (Noguchi and Komatsu 2006), (Cameron and Pizzi 1985) and (Stoeckel 2013) and the thickness of the glued lines (Pizzio et al, 2003). 2. Material and methods 2.1. Test specimens For testing, sets of test specimens with structural dimensions1402001400 mm were assembled. The test specimens were made of solid spruce wood with a strength class of C24. For the outside glued element were used plywood of beech veneers D40 with dimensions of 27140280 mm and laminated veneer lumber (LVL) with dimensions of 39140280 mm. The bio component epoxy adhesive with low viscosity and high wetting power was used for gluing. The test samples were conditioned prior to destructive testing in a standard ambient temperature of 202°C and relative humidity of 655%. To determine the moisture of test samples, a moisture detector was used. 2.2. Laboratory testing The testing was proceeded on a EU100 pressure machine at the laboratories of the Faculty of Civil Engineering, VSB-TU Ostrava, while the force was increased gradually (Fig. 1 and 2). The chosen rate of the press seems to be optimal, because the failure of all the tested samples appeared in a time-boundary of 300120 sec, which corresponds to the interval of laboratory tests for short–time strength according to the current European standards for timber structures – Eurocode 5 (2006).

Fig. 1. Laboratory testing scheme



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Fig. 2. Laboratory testing

2.3. Numerical modelling Numerical model in ANSYS was calculated as the volume using the finite element SOLID45 and auxiliary member elements BEAM189. Using volume elements were modelled studied parts of the structure and joint. Using beam elements, the head of the press and its transfer to steel distribution plates were simulated. The numerical model was calculated taking into account the construction (contact task), geometrical and physical nonlinearity. Physical nonlinearity was considered in material models of the individual parts of construction joints. 2.4. Calculation according to standards The calculation of the tested joints bearing capacity has been proceeded according to the rules provided in (Eurocode 5, 2006; CSN 73 1702, 2007), with input material data taken from (CSN EN 338). The minimal value of bearing capacity is for tested samples in the glued line. The value shall be calculated according to the following expression (CSN 73 1702, 2007).

Ft ,c  k mod

f k , 2,k Atc

M

where: kmod fk,2,k Atc

M

- modification factor for duration of load and moisture content, - strength of glued surface, - effective glued area, - partial factor for material properties.

(1)

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3. Results 3.1. Laboratory testing of glued joints During the destructive laboratory testing of glued joints occurred the damage in most of test specimens in first internal layer of plywood or LVL. Only in minimum test specimens occurred the damage in the solid wood middle element. In figures 3 and 4 are shown typical damages in first layers of LVL and plywood after the joint collapse.

Fig. 3. Typical damage of test specimens – LVL (a) side view; (b) detail

Fig. 4. Typical damage of test specimens – plywood (a) side view; (b) detail



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The average value of the vertical force on the carrying capacity limit of joints with glued internal plywood (loaded according to Figure 1) is 46.43 kN with corresponds with the bending moment of the value 9.29 kNm. In joints with glued LVL boards is the average value of vertical force 33.59 kN, which corresponds with the value 6,72 kNm. Figure 5 shows the average deformation curves (relation: vertical force – joint deflection) on the specimens set with glued plywood and LVL.

DEFORMATION CURVES

50 45 40 35 30

FORCE (kN)

25 20 15 10 5 0

0

2

4

6

DEFORMATION (mm) LVL

8

PLYWOOD

Fig. 5. Average deformation curves of tested joints

3.2. Numerical modelling Figure 6 shows shear stresses in outer layers of plywood and LVL. The stress reaches the maximal value of 6.01 MPa for plywood and 5.17 MPa for LVL.

Fig. 6. Shear stress in the outer layer of the (a) plywood; (b) LVL

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Figure 7 shows shear stresses in the plane of loading in solid timber element. The stress reaches the maximal value of 5.17 MPa in joints with plywood and 3.93 MPa with LVL.

Fig. 7. Shear stress in the timber element in connection with (a) plywood; (b) LVL

3.3. Calculation according to standards With calculation of the bearing capacity using bending moment of loaded joint according to standards (Eurocode 5, 2004; CSN 73 1702, 2007) it is possible to determine the maximal value of vertical force in the glued line of value 4.25 kN for given loading mechanism, where the uniform distribution of shear stress is not ensured. This force corresponds the value of bending moment in the joint 0.85 kNm. If a uniform distribution of the shear stress in the glued joint is ensured, then the minimal carrying capacity will be given with a failure in the inner layer of the glued element and the vertical force value will be 6.80 kN for the given load mechanism according to Fig. 1, which corresponds with the bending moment of 1.36 kNm. 4. Conclusions The average value of the joint carrying capacity with the flexural bindings found by the laboratory tests is much higher than the value determined conservatively according to the relevant standards. It is evident from Figure 6 that the deformation response of the glued joints to the load is linear over the entire loading time. Once the bonding capacity is reached, an immediate fragile fracture occurs. The low ductility of glued joints is one of causes of the relatively conservative values of the carrying capacity of these joints determined according to the applicable standards for the design of timber structures. To increase the safety of these glued joints, it would be desirable to add joints with plastic bonding possibility. Acknowledgements This outcome has been achieved with funds of Conceptual development of science, research and innovation assigned to VSB - Technical University of Ostrava by Ministry of Education Youth and Sports of the Czech Republic in 2017.



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References Aicher, S., Gustafsson, P.J., Wolf, M., Load displacement and bond strength of glued-in rods in timber influenced by adhesive, wood density, rod slenderness and diameter, In Proceedings 1st RILEM Symposium on timber engineering, Stockholm, 1999, pp. 369-378. Cameron, F.A., Pizzi, A., 1985: Effects of excessive pretreatment of pine timber with CCA wood preservatives on the bond quality of PRF and TRF wood adhesives. Holz als Roh- und Werkstoff, 43:149-151. CSN 73 1702, 2007: Design of timber structures – General rules for buildings. CSN EN 338, 2010: Structural timber – Strength classes. Eurocode 5, 2006: Design of timber structures – Part 1-1: General – Common rules and rules for buildings. Guan, Z. W., 1998: Structural behavior of glued bolt joints using FRP, WCTE 98(1): 265-272. Presses Polytechniques et Universitaires Romandes, Lousanne. Gustafsson J., Serrano E., Aicher S. and Johansson C.J., 2001: Strength design equation for glued-in rods, International RILEM Symposium Joints in timber structures, Stuttgart, Pp 323-332. Noguchi M, Komatsu, K., 2006: Estimation of stiffness and strength in timber knee joints with adhesive and verification by experiment. J Wood Sci : 411-421. Lokaj, A., Klajmonová, K., 2014: Round timber joints exposed to static and dynamic loading, Wood research, 59 (3): 439-448. Pizzio, B., Lavisci, P., Misani, C., Triboulot, P., 2003: The compatibility of structural adhesives with wood, Holz als Roh- und Werkstoff 61: 288290. Serrano, E., 2002: On the mechanical behavior of test specimens for wood-adhesive bonds, Report TVSM-3063. Division of Structural Mechanics, Lund University, Sweden. Stoeckel, F., Konnerth, J., Gindl-Altmutter W., 2013, Mechanical properties of adhesives for bonding wood-A review, International Journal od Adhesion & Adhesives 45: 32-41. Vašek, M., Mikeš, K., 1998: The metal joints for the space timber structures, the non-linear behavior, In 5th World Conference on Timber Engineering, Montreux, Pp. 822-823.