Long-term laminated glass four point bending test with PVB, EVA and SG interlayers at different temperatures

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1 Delft University of Technology Long-term laminated glass four point bending test with PVB, EVA and SG interlayers at different temperatures Serafinavicius, Tomas; Lebet, Jean-Paul; Louter, Christian; Lenkimas, Tomas; Kuranovas, Artiomas DOI /j.proeng Publication date 2013 Document Version Final published version Published in 11th International Conference on Modern Building Materials, Structures and Techniques, MBMST 2013 Citation (APA) Serafinavicius, T., Lebet, J-P., Louter, C., Lenkimas, T., & Kuranovas, A. (2013). Long-term laminated glass four point bending test with PVB, EVA and SG interlayers at different temperatures. In 11th International Conference on Modern Building Materials, Structures and Techniques, MBMST (pp ). DOI: /j.proeng Important note To cite this publication, please use the final published version (if applicable). Please check the document version above. Copyright Other than for strictly personal use, it is not permitted to download, forward or distribute the text or part of it, without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license such as Creative Commons. Takedown policy Please contact us and provide details if you believe this document breaches copyrights. We will remove access to the work immediately and investigate your claim. This work is downloaded from Delft University of Technology. For technical reasons the number of authors shown on this cover page is limited to a maximum of 10.

2 Available online at Procedia Engineering 57 (2013 ) th International Conference on Modern Building Materials, Structures and Techniques, MBMST 2013 Long-term laminated glass four point bending test with PVB, EVA and SG interlayers at different temperatures Tomas Serafinavičius a,b *, Jean-Paul Lebet a, Christian Louter a, Tomas Lenkimas c, Artiomas Kuranovas b a Steel Structures Laboratory, School of Architecture, Civil and Environmental Engineering, École polytechnique fédérale de Lausanne, Station st. 18, CH-1015 Lausanne, Switzerland b Department of Steel and Timber Structures, Faculty of Civil Engineering, Vilnius Gediminas Technical University, Saulėtekio ave. 11, LT Vilnius, Lithuania c Glassbel Baltic, Pramones str. 11, LT Klaipėda, Lithuania, Abstract This paper presents the results of long term experiments of four point bending test with structural laminated glass plates. For experiments 6 mm thick annealed Soda-Lime-Silica Glass and three different interlayer laminates were used: Polyvinyl butyral (PVB), Ethylene vinyl acetate (EVA), DuPont s SentryGlas (SG). These types of laminates were chosen because there is a wide range of their possible practical application in buildings constructions. Bending creep tests were carried out by applying the four point bending test model. Applied dimensions of the laminated glass plates and loading scheme are from the standard EN Three specimens were tested with the same interlayer laminated glass plates. Tests were successively carried out at three temperatures: C, C, C. Every test took 24 hours interval at each temperature, so in total one full experiment took 72 hours with one type of interlayer. The deflections at the middle of specimens, volatile displacement between two glass sheets and longitudinal strains at the middle of the laminated plate were measured. In the paper the comparisons of the experimental results between the glass panels with various laminates and at different temperatures are presented The Authors. Published by Elsevier Ltd The Authors. Published by Elsevier Ltd. Open access under CC BY-NC-ND license. Selection Selection and and peer-review peer-review under under responsibility responsibility of the of Vilnius the Vilnius Gediminas Gediminas Technical Technical University University.. Keywords: long-term test; four point bending test; laminated glass; temperature conditions; creep test; PVB, EVA, SG. Nomenclature PVB Polyvinyl butyral EVA Ethylene vinyl acetate SG DuPont s SentryGlas Subscripts t loading time T temperature * Corresponding author. Tel.: ; fax: address: tomas.serafinavicius@epfl.ch The Authors. Published by Elsevier Ltd. Open access under CC BY-NC-ND license. Selection and peer-review under responsibility of the Vilnius Gediminas Technical University doi: /j.proeng

3 Tomas Serafi navičius et al. / Procedia Engineering 57 ( 2013 ) Introduction In modern architecture the trend to seek high levels of transparency has resulted in the recent construction of many remarkable buildings with glass envelopes. In order to increase this level of transparency even further, the idea has been proposed that part of the primary structure can be made from structural glass as well. To allow this approach, the glass must be able to act as a load-bearing structural element capable providing adequate levels of safety, stability and durability. The structural behaviour of laminated glass is different from that usually used in design by engineers for structural member made from other building materials. Existing theories used for other types of structures cannot be directly applied to glass structures due to the peculiar properties of this material [1]. The understanding of the structural performance of laminated glass has made great advances over the past decade. In view of the increasing use of glass as a load-bearing structural element, questions concerning the safety of such structures and the need for the development of procedures to facilitate their safe and economic design have arisen. During the last twenty years numbers of experiments were performed in Europe technical universities, the review on some of those is given in [2]. There were usually investigated the behaviour problems of a single type of structural glass specimens under short term loading [3]. The most of experiments were carried out to ensure continuous production of single glass or single laminates and as well too less result are representing [4] the needs of laminated structural design generalization in different temperatures under long term loading with three glass construction market most used interlayers. The purpose of this research is to investigate the durability aspects of laminated glass in the framework of long-term tests under different temperatures. The formation of this goal was influenced by approaches of laminated glass supporting conditions that now dominates in engineering practice. Therefore, in Steel Structures Laboratory (ICOM) of École polytechnique fédérale de Lausanne (EPFL) the attempts to investigate the long term behaviour of structural glass plates with different laminates and at different temperatures were made. All specimens were manufactured by professionals using modern glass laminating equipment at Glassbel Baltic Company. 2. Materials Used in Research Test specimens were produced from two 6 mm thick annealed Soda-Lime-Silica glasses; it is the most prevalent type of glass used for windows. The glass panels were laminated each to other with three different interlayer materials: Polyvinyl butyral (PVB), Ethylene vinyl acetate (EVA), and DuPont s SentryGlas (SG). Typical specimen before test is presented in Figure 1. The specimen dimensions are: length 1100 mm, width 360 mm and lamination film thickness 1.52 mm. In this research 3 specimens each with 3 laminates (PVB, EVA and SG), totally 9 specimens were tested. Fig. 1. View on one of laminated glass plate during preparation for testing

4 998 Tomas Serafi navičius et al. / Procedia Engineering 57 ( 2013 ) Laminated Glass Panels with PVB Interlayer PVB Poly(vinyl butyral) / Poly[(2-propyl-1,3-dioxane-4,6-diyl)methylene]. Molecular formula (C8H14O2)n. Non chlorinated vinyl was invented in 1930 s and is formed by reaction of polyvinyl alcohol with butyraldehyde with further is conducted under heat and pressure. Manufacturing of laminated safety glass panels is one of the main PVB appliances in attempts to achieve strong binding between glasses, optical clarity, toughness and flexibility. Furthermore, PVB has excellent adhesion with many materials such as glass. As well PVB is widely used as a film sandwiched in a safety glass. In this research project Kuraray Europe GmbH (Germany) Trosifol brand PVB type interlayer [5] was used Laminated Glass Panels with EVA Interlayer EVA Ethylene vinyl acetate the copolymer consisting of ethylene and vinyl acetate monomers. The material possesses the characteristics of high tensile strength, excellent transparency, sufficient cohesion, low-temperature toughness, stress-crack resistance, hot-melt adhesive, water proof properties and resistance to UV radiation that allows it to use in the photovoltaic industry as an encapsulation material for silicon cells [6]. One of the major applications of EVA film is making laminated glass panels requiring safety and also moisture and UV radiation resistance. This lamination film is especially used for decorative glasses when some painted pictures or pattern should be put on it. EVA can be used as a substitute in many applications. For this research study the Bridgestone Corporation (Japan) EVASAFE brand EVA type interlayer was used Laminated Glass Panels with SG Interlayer SentryGlas (SG) interlayer is a semi-crystalline thermoplastic polymer (ionoplast) sheet material that has been developed by DuPont Company for hurricane, bomb blast, vandalism and burglary resistant laminated glass. This lamination material improves strength and stiffness of laminated glasses for both in the un-fractured and the fractured state of laminated glass compared with usual used interlayer materials [7]. Technical datasheets of ionoplast interlayer [8] show up the five times greater strength and up to 100 time s greater stiffness properties, and better creep resistance under load and environment action than ordinary laminating polymers such as PVB and EVA. This allows greater safety of bolted connections and free standing glass structures such as balustrades, canopies, glass fins and structural glazed envelopes using all possible fixation methods and technologies. 3. Test Methods Long term tests were carried out with the specimens under four-point bending according to European standard [9]. Tests have not been carried out until failure. Deflections at the middle of span, the volatile displacement between glass sheets with different types of interlayer laminates and longitudinal strains were measured. All tests were carried out in a climatic chamber, see Figure 2. Fig. 2. Climatic chamber

5 Tomas Serafi navičius et al. / Procedia Engineering 57 ( 2013 ) The temperatures: C, C, C were selected based on the climatic chamber technical capabilities and were controlled automatically at the set level. Humidity inside the chamber was always automatically controlled at 50% level for all tests of this research. The loading model is presented at Figure 3. The specimens were under constant loading during all 72 h of testing time. The constant loading was kn for all glass plates the same, as well including the self-weight of the laminated glass. Length between the supporting stainless steel rolls is 1000 mm and the distance between upper loading rolls is 200 mm. To avoid stress concentration on glass between glass plate and supporting stainless steel rolls are provided by aluminum strips. As well, rubber strips was replaced to aluminum strips due to rubber deformation during long term loading and temperature effect. Four-point bending scheme was chosen due to pure bending zone at the middle in the plate instead of the three-point bending scheme where the maximum bending moment is a single point of peak. Fig. 3. Four point bending test model Three laminated glass plate specimens with the same interlayer materials were tested: PVB-1, PVB-2, PVB-3 first testing setup; EVA-1, EVA-2, EVA-3 second testing setup; SG-1, SG-2, SG-3 third testing setup. All these three tests setups were placed in the climatic chamber controlling and changing temperature successively every 24 hours. The typical view on the mentioned test setups is presented in Figure 4. Fig. 4. General view on the four point bending test setup in the climatic chamber during the test At the middle span of the plate deflections were measured during the all 72 h, see Figure 5. HBM deflection sensors with ± 0.01 mm tolerance were used for this research. For one plate two deflection sensors were used for more accurate data recording.

6 1000 Tomas Serafi navičius et al. / Procedia Engineering 57 ( 2013 ) Fig. 5. Setup of middle span deflection measurement As well, at the edges of laminated plate volatile displacement between the two glasses sheets were measured by HBM deflection sensors with ± mm tolerance, see Figure 6. Fig. 6. Setup of volatile displacement measurement at one side of plate Longitudinal strains at the middle of span were measured using special strain gauges for glass material. Strain gauge type: TML FLA-5-8-3LT. Length of gauge base 5 mm, produced by Tokyo Sokki Kenkyujo Co., Ltd (Japan), see Figure 7. Fig. 7. TML 5 mm base strain gauge for glass material testing All above mentioned testing measurement data were recorded by HBM UPM-100 data recording device. Above mentioned measuring technique recorder at the same time provides calculated average values.

7 Tomas Serafi navičius et al. / Procedia Engineering 57 ( 2013 ) General Results This paragraph presents the general test results using three different measurement methods mentioned above and with three types of interlayers: PVB, EVA and SG at three different temperatures: C, C, C for 24 h for each temperature, with 72 h in total loading time. A limited loading time was chosen taking into account the duration of this research project. In Figures 8 10 indicates the recorded data of three laminated glass specimens on the same time of the same interlayer are given Results of Measured Middle Span Deflections Experimental data of middle span deflection recorded for laminated glass plates under constant long-term four points bending (0.1 knm) are presented in Figure 8. Fig. 8. Results of middle span deflection measurements Increase of deflection of laminated PVB glass plate was observed from the first second of the plate loading. With each higher temperature step the deflection values of glass plate were increasing from average 7 mm at C up to 8 mm at C. Glass plate with EVA laminate at C almost not deflected and at C very small difference in deflection was recorded. The maximum deflection values are recorded at C and equal to 3.5 mm. Laminated glass plates with SG interlayer at C and C showed very limited deflections during the 48 hours period. Deflection jump for glass plate laminated with SG interlayer is fixed at C and the maximum value obtained was 2.5 mm after 72 hours of loading time Results of Measured Volatile Displacements The curves of volatile displacements which values are measured at one side of laminated glass plate s edge are given in Figure 9. As it is seen, the PVB interlayer starts to slip immediately at constant temperature and constant loading in time from 0 h till 24 h. The displacement average values were increased from 0.12 mm at C until 0.15 mm at C. Behaviour of EVA and SG interlayers is very close to each other and some slight differences reveal when it reached C. Laminated glass with EVA interlayer slightly slips during temperature changes. Behaviour of SG interlayer is the same, but at C there is no at all any slip at the load duration of 24 hours. It starts slip at C temperature and the value is less than mm. The highest slip is possible to see at C temperature and the value not more than mm.

8 1002 Tomas Serafi navičius et al. / Procedia Engineering 57 ( 2013 ) Results of Measured Longitudinal Strains Fig. 9. Results of volatile displacement measurement of one plate edge Using recorded longitudinal strain results the tensile stresses using glass Young s modulus value 73 GPa obtained from previous research [10] were calculated. The curves of tensile stresses for the glass plates with PVB, EVA and SG interlayers are given in Figure 10. Using different measurement methods the highest values are obtained with the PVB laminated glass. As well, there are small jumps during the temperature changes and the average values of tensile stresses are from 17 MPa at C temperature until 20 MPa at C temperature. The EVA and SG laminated glass curves of tensile stresses are parallel at C and C temperatures. The tensile stresses values for laminated glass plates with EVA are about: 12 MPa at C; 13 MPa at C; 14 MPa at C. As follows tensile stresses of SG laminated glass plates are: 9 MPa at C; 10 MPa at C; 11 MPa at C temperature. Fig. 10. Tensile stresses defined due to recorded values of longitudinal strains of laminated glass plates under constant long-term loading Simultaneously three of one type laminated glass plates were tested, but the several tests lasted occasionally longer than 28 h at C. For this reason all three interlayers do not match on time, but it does not change the character of curve s behaviour then the temperature is changed.

9 Tomas Serafi navičius et al. / Procedia Engineering 57 ( 2013 ) Comparisons In Table 1 are given average values taken from curves given in figures 8 10 for average loading time at three different temperatures. Table 1. Comparison of the recorded measurement data for laminated glass plates with three types of interlayers Interlayer Measurement definition C C C PVB Deflections [mm] EVA SG PVB Volatile displacements EVA [mm] SG PVB Tensile stresses [MPa] EVA determinate according to the values of recorded SG longitudinal strains The comparative differences are calculated between interlayers: PVB EVA, PVB SG and EVA SG. The percentage deflection differences between PVB and EVA are 57%. Differences between PVB and SG are about 71%. As well, deflection differences between EVA and SG are about 31%. Volatile displacement differences between PVB and EVA glass plates are 92%. Displacement differences between PVB and SG are about 99%. As well, volatile displacement differences percentage results between EVA and SG interlayers are about 87%. Tensile stresses differences between PVB and EVA are 31%. The percentage tensile stress differences between PVB and SG are 46%. Between EVA and SG differences of tensile stress are about 22%. 6. Discussion The resistance of the laminated glass depends on environmental and loading conditions. The durability of the mechanical properties against environmental influences is also important ensuring the suitability of laminated glass for safe practical design purposes [11]. For the further experimental researches it could be valuable to carry out the long-term tests which it will be possible to take into account the influence of environmental conditions (high temperature, humidity and UV radiation) as it is regulated by standards [12]. As well, the testing methods presented in this paper for this purpose could be used too. 7. Conclusions 1. From compared the three laminated glass types Polyvinyl butyric (PVB), Ethylene vinyl acetate (EVA), DuPont s SentryGlas (SG) under long-term loading, only the glass plates with SG interlayer showed the least values of middle span deflections, volatile displacements and longitudinal strains under different temperature conditions. 2. The difference of endurance properties between the EVA and SG interlayers is very small. 3. Measured parameters differences obtained with the PVB interlayer at the C temperature; with EVA at C and with SG at C. 4. The highest values of middle span deflection, volatile displacements and longitudinal strains are obtained with a PVB laminated glass plates. 5. In view relatively good results with EVA interlayer it would be appropriate to conduct further research experiments with other manufacturers' materials. 6. The presented test methodology of measurements (middle span deflections, volatile displacements and longitudinal strains) is appropriate for testing the laminated glass plates affected by the environment conditions.

10 1004 Tomas Serafi navičius et al. / Procedia Engineering 57 ( 2013 ) Acknowledgements Special acknowledgements are expressed to Scientific Exchange Program Sciex-NMSch The Swiss contribution to EU enlargement for funding internship at École polytechnique fédérale de Lausanne. Acknowledgements are expressed to Valdas Virbalas CEO at GLASSBEL Baltic for production of all glass specimens for this research project. As well, acknowledgements are expressed to COST Action TU0905 Structural Glass Novel design methods and next generation product for target information and valuable networking. Also acknowledgements are expressed to Sylvain Demierre technical coordinator at Steel Structures Laboratory for the valuable technical assistance during the whole execution of the experiments. References [1] Haldiman, M., Luible, A., Overend, M., Structural Use of Glass, International Association for Bridge and Structural Engineering - ETH Zürich. Switzerland, p [2] Serafinavičius, T., Kvedaras, A. K., Rewiew of study on structural glass and structures. In Proc. 10th International Conference Modern Building Materials, Structures and Techniques: selected papers, Vol. 2. May 19-21, 2010, pp [3] Serafinavičius, T., Kvedaras, A. K., Challenges to structural glass: what have been already done. Engineering Structures and Technologies, pp [4] Chmykhova, N. A., Chesnokov, A. G., Chesnokov, S. A., Investigation of strength properties of laminated glass with different bonding materials, in Proc of the International Conference on Architectural and Automotive Glass (Glass Performance Days). Tampere, Finland, pp [5] Kuraray Europe GmbH. Architecture The Future of Safety in Glass. Germany, 2012, p. 12. [6] Katzer, M., EVASAFE Smart Opportunities in Glass. Conference Glass Performance Days South America, 6-7 May Brazil, Sao Paulo. [7] Stelzer, I., High performance interlayer enables cost efficient glazing, Proceedings of the International Conference on Architectural and Automotive Glass (Glass Performance Days). Tampere, Finland, pp [8] DuPont Company. Technical Bulletin Strength characteristics and post-glass breakage performance. United States, [9] EN :2000. Glass in building. Determination of the bending strength of glass. Part 3: Test with specimen supported at two points (four point bending). European Committee for Standardization CEN. Brussels, 2000, p. 12. [10] Serafinavičius, T, Kvedaras, A. K., Šaučiuvėnas, G., Bending behaviour of structural glass with different interlayer laminate, Proceedings Mechanics of composite materials: Seventeenth International Conference, May 28-June 1, 2012, Riga, Latvia: book of abstracts. Riga, Institute of Polymer Mechanics, University of Latvia.. [11] Serafinavičius, T., Environmental Impact on the Structural Glass Elements. Recent, Current & Near Future Research on Structural Glass, COST Action TU0905, Ghent, Belgium, pp [12] EN ISO :2011. Glass in building - Laminated glass and laminated safety glass. Part 4: Test methods for durability. European Committee for Standardization CEN. Brussels, 2011, p. 14.