Glass Belis, Bos & Louter (Eds.) Conference on Architectural and Structural Applications, Ghent University, September 2020. Copyright © Author. all rights reserved. ISBN 978-94-6366-296-3, https://doi.org/10.7480/cgc.7.4491

David Antolinc-Faculty of Civil and Geodesy Engineering, University of Ljubljana, Slovenia

This article introduces the experimental results of a three-point bending test on laminated glass at high temperatures in an environmental test chamber. The focus of this research is that the bending stiffness of laminated glass decreases with increasing temperature. The test sample is made of two fully tempered glass panels and bonded with EVA and PVB interlayers.

For each type of laminated glass and set temperature, we prepared and tested 5 samples. Before performing the experiment in the environmental chamber, pre-condition each sample to a set temperature. After the sample reaches the specified contact temperature, it is tested at 23°C, 35°C and 60°C. During the test, the mid-span deflection, the mid-span longitudinal deformation and the mid-span force were recorded.

Finally, based on the measured mid-span deflection, deformation and stiffness degradation, the behavior of two different types of laminated glass panels was compared. According to the results, it can be seen that compared with the samples with PVB interlayer, the laminated glass with EVA interlayer exhibits higher stiffness, and the stiffness degradation is almost linear and slower.

Structural glass in the form of laminated glass may have different interlayers as bonding materials. Generally, PVB, EVA, and isomers that have been commercially labeled as Sentry Glass (SG) intermediate layers in recent years are used. Although quite extensive research has been conducted on the behavior of laminated glass with PVB and SG interlayers at different temperatures, more research is needed for laminated glass with EVA interlayers manufactured by different manufacturers, which is also ( Serafinavičius et al. 2013) mentioned recently in (Martin et al. 2019) and (Sable et al. 2017).

(Sable et al., 2017) clearly shows that the mechanical properties of laminated glass with EVA interlayer are greatly affected by interlayer temperature and curing time. Due to the limited experimental data recorded on EVA laminated glass, we decided to conduct experimental research on this subject.

Krüger (1998) studied the effect of temperature on the mechanical properties of laminated glass under bending load. He studied laminated glass with only PVB interlayer and proved that the interlayer provides very good adhesion between glass plates at temperatures above 40°C. The coupling is little or no coupling.

Pankhardt (2010) studied the comparison between PVB and EVA laminated glass subjected to short-term bending loads at temperatures of -20°C, 23°C and 60°C. This study once again proves that the bending stiffness of laminated glass is greatly affected by the ambient temperature and decreases with the increase of temperature. There is a large temperature step between 23°C and 60°C, which is why we decided to investigate and compare the behavior at at least one temperature at 35°C in our research, which will be explained later. 

Serafinavičius et al. conducted another important research and experimental analysis on laminated glass and PVB, EVA and SG laminated glass exposed to 20°C, 30°C and 40°C and subjected to long-term four-point bending load. Al. (2013). They concluded that the samples with EVA and SG interlayers provided relatively similar stability and rigidity compared to samples with PVB interlayers that recorded the maximum deflection and tensile strain across the bottom surface of the laminated glass.

The EVA interlayer used in the study was from Bridgestone and was named EVASAFE. Since there are several manufacturers on the market, the author made a comment in the conclusion. In further research, we should also test other manufacturers' EVA interlayers. This encourages us to use the EVA interlayer film with the brand name of the manufacturer Glaast as DayLight EV200. Limited company

Based on previous experimental analysis of laminated glass under bending load at different temperatures by other authors, and according to the capacity of our environmental chamber, we decided to perform three-point bending load on the short laminated glass sample. One of the main motivations for conducting this research is the lack of experimental results available in the literature, and to clarify the failure mechanism of laminated glass exposed to high temperature under short-term load, which can easily occur in the case of sandwich bridge decks or on hot summer days. Use railings, as shown in Figure 1.

Two laminated glass samples were prepared for the three-point bending test, one using PVB and the other using EVA DayLight EV200 brand interlayer film. The sample was assembled from two heat-strengthened soda lime silicate glass plates 350 mm long and 100 inches wide, each 5 mm thick, with polished edges. The thickness of the polymer interlayer for both interlayer types (PVB or EVA) is 0.76 mm.

The overall size of the sample is limited to the size of the environmental chamber. A set of five samples was prepared and tested for each type of sample and each ambient temperature level of 23°C, 35°C, and 60°C. Therefore, a total of 15 samples with EVA and 15 samples with PVB interlayer were prepared and tested. The bottom surface of each sample is equipped with strain gauges in the middle of the span and 30 mm from the lateral edge, and is oriented longitudinally to measure the maximum tensile deformation during the test. Figure 2a) shows a set of specimens, while Figure 2b) shows the location of the longitudinal strain gauges in the mid-span.

In order to evaluate the effect of temperature on the bending stiffness and strength of the considered laminated glass specimens, we performed a three-point bending test using the dimensions and equipment shown in Figures 3 and 4. The span between the brackets is 300 mm. The deflection in the sample span is captured by LVDT. The vertical load F is applied to the middle of the span at a loading rate of 4.8 mm/min until the specimen is completely destroyed.

As mentioned above, three levels of ambient temperature are set for testing, 23°C, 35°C and 60°C. We set a temperature of 60°C as the highest temperature that can be expected under harsh environmental conditions in actual civil engineering applications. For the future, it is recommended to conduct experiments at a temperature level of 80°C according to the ETAG 002 guideline and the research conducted by Santarsiero et al. (2017).

The size of the sample is limited by the size and capacity of the environmental chamber. Therefore, the maximum length of the specimen is 350 mm. For the experiment at room temperature of 23°C, we did not use the environmental box, as shown in Figure 4. The working range of the environmental chamber is between -150°C and 600°C, which allows us to set the required elevated temperature to 35°C and 60°C.

For each required temperature, we preheat the chamber and sample to a set temperature level. To this end, we put the specimens in a separate heating chamber for 24 hours to preheat to the desired temperature, and then move them to the preheated environmental chamber for a three-point bending test. The thermocouple is used to check the contact temperature of the sample.

One of the main characteristics of laminated glass is its ability to hold the broken glass fragments together after exceeding the tensile strength of the glass, thereby providing improved post-breaking behavior, keeping the broken laminated glass sheet in place. The samples with PVB interlayer in our research show that PVB has the ability to connect broken glass fragments at an ambient temperature of 60°C. Figure 6a) and b) show the failure modes of PVB laminated glass at 35°C and 60°C, respectively.

Obviously, the viscosity of PVB drops significantly at 60°C because the stiffness after bending and fracture is very low and may represent potentially dangerous behavior. The samples with EVA interlayer showed similar failure modes, except that at an ambient temperature of 60°C, all samples were divided into two pieces, as shown in Figure 6c), which is very problematic in the case of overhead glass. Because it may fall on the occupants. 

Based on the measured value of mid-span deflection and the corresponding applied force, Figure 7 shows the bending stiffness of laminated glass samples with PVB and EVA interlayers at ambient temperatures of 23°C, 35°C, and 60°C. In all the graphs below, the blue curve represents the results of the samples with EVA, and the red curve represents the samples with the PVB intermediate layer.

Compared with samples with PVB interlayer, samples with EVA interlayer generally exhibit higher stiffness at most ambient temperatures, and are very close at 60°C. The glass transition temperature Tg of polymer materials plays an important role in the temperature-dependent behavior of EVA and PVB interlayers, as it indicates the temperature range in which the stiffness of the material is significantly reduced (Kuntsche et al., 2019).

However, the average stiffness of the sample with EVA interlayer at room temperature is 0.5 kN/mm, and as the ambient temperature increases, it almost linearly decreases to 0.29 kN/mm. This behavior corresponds to the almost linear stiffness degradation of the EVA interlayer in the temperature range from the glass transition temperature Tg of -28°C to the crystal melting temperature Tm of 70°C.

At the same time, the largest proportion of the stiffness degradation of the samples with PVB interlayer, which is related to the viscosity of the interlayer, occurred in the temperature range of 23°C and 35°C, and dropped from 0.34 kN/mm to 0.27 kN/mm, respectively. In the temperature range of 35°C to 60°C, only a small degradation of stiffness as low as 0.25 kN/mm was recorded. This behavior corresponds to the fact that the glass transition temperature Tg of the PVB intermediate layer is 38°C.

This is very close to the temperature of 35°C, at which we tested our sample, and the greatest share of stiffness degradation occurred on our sample. We can conclude that due to the different viscoelastic properties at the considered ambient temperature, the interlayer has different behaviors, and the stiffness values ​​of EVA and PVB laminated glass are very close at 60°C.

Figure 8 shows the tensile stress evaluated on the bottom surface of the specimen, which is the result of the applied mid-span bending load F=2.45 kN. This is the average failure load of samples with PVB interlayer at an ambient temperature of 60°C. Since this is the lowest average load-bearing capacity of all the considered samples, we use it as the reference force for other samples at all ambient temperatures.

The tensile stress is evaluated based on the tensile deformation measured at the mid-span of the loaded specimen, as shown in Figure 9. Obviously, compared with laminated glass, the tensile stress of the sample with PVB interlayer at 60°C is the same with zero interlayer stiffness, which is indicated by the black dashed line in Figure 8.

This means that the PVB interlayer almost completely loses its shear stiffness at an ambient temperature of 60°C. On the other hand, the residual shear stiffness of the EVA interlayer at 60°C can still achieve the coupling effect between the glass sheets. Therefore, the average tensile stress is reduced by approximately 15% compared to the stress obtained on the specimen with PVB interlayer.

We can also see that in the temperature range between 23°C and 35°C at room temperature, the tensile stress evaluated for the sample with EVA interlayer does not change significantly, which means that in this temperature range, the EVA interlayer The viscosity has changed. Essentially it will not change. However, the sample with PVB interlayer shows that as the temperature increases from room temperature to 35°C, the shear stiffness (shear modulus) of the interlayer also changes, so the tensile stress of the bottom glass plate also occurs Variety.

Figure 10 and Figure 11 respectively show the average load-bearing capacity and corresponding mid-span deflection of laminated glass samples at different temperatures. Compare again the samples with PVB (red curve) in the EVA (blue curve) interlayer. The average load-bearing capacity of the samples with EVA interlayer in the whole test environment temperature range is higher, and it decreases almost linearly with the increase of the environment temperature.

However, in the temperature range of 23°C to 35°C, the load-bearing capacity of the samples with PVB interlayer decreased from 2.8 kN to 2.57 kN. It is also obvious that the load-bearing capacity remains almost unchanged at a higher temperature of 60°C, reaching an average of 2.54 kN.

The graph in Figure 11 shows the mid-span deflection corresponding to the average load-bearing capacity of the specimen under consideration. Since the specimens with EVA interlayer have higher stiffness, the deflection of these specimens is smaller throughout the elevated temperature range. The deflection increases almost linearly with increasing temperature, which also corresponds to the stiffness diagram in Figure 7.

A similar correlation was developed with respect to the stiffness of the temperature level channel, so it was done for samples with PVB interlayers. At a temperature level of 35°C, the deflection of w=10.2mm remains almost the same as when the temperature rises to 60°C, where it increases to w=10.45 mm, which is again consistent with the bending stiffness of the specimen. The PVB sandwich is shown in Figure 7. Shown.

Based on a literature review, limited choices of information about the behavior of laminated glass at elevated ambient temperatures are available. Unlike the current research, most of them have studied the effect of temperature on the behavior of laminated glass under long-term load, or comparison of behavior under short-term load at high temperature.

The lack of experimental research and comparison of the behavior of laminated glass with PVB and EVA interlayers at elevated ambient temperatures encourages us to prepare this research and experimental analysis. A three-point bending test was carried out on PVB and EVA laminated glass at room temperature and two heating conditions, and the following conclusions were drawn:

-Laminated glass with an EVA interlayer is easily broken and divided into two separate parts at an ambient temperature of 60°C, which exhibits unfavorable behavior compared with the sample with a PVB interlayer. The specimen with PVB interlayer loses the bending stiffness after fracture, but it is still one piece.

-The stiffness degradation of laminated glass with EVA interlayer has a linear relationship with temperature increase on average. However, the main change in the shear stiffness of PVB interlayers related to room temperature occurred at 35°C, and there was no significant further change at the higher temperature of 60°C. This behavior of laminated glass also corresponds to the glass transition temperature Tg (38°C) of the PVB interlayer, at which the material stiffness will decrease significantly.

-The overall stiffness of the sample with EVA interlayer at room temperature and 35°C is approximately 35% higher. At the highest test ambient temperature of 60°C, the stiffness of the two sample types are very close. Compared with the EVA interlayer sample, the stiffness of the PVB interlayer sample is only 7% lower.

-As expected, compared with the samples with EVA interlayer, the average tensile stress at the mid-span of the bottom glass plate is higher for the samples with PVB interlayer due to the lower coupling effect between the glass plates. The tensile stress of the sample with PVB interlayer at an ambient temperature of 60°C is actually the same as that of a laminate with a zero-stiffness interlayer.

-The load-bearing capacity of samples with EVA interlayers decreases linearly with increasing temperature. Compared with the sample with EVA interlayer, the load-bearing capacity of the sample with PVB interlayer is reduced by 16% and 19% at 23°C and 35°C, respectively. Since the stiffness of the two types of laminates at 60°C is very similar, there is not much difference in load-bearing capacity.

Compared with the samples with PVB interlayer, the laminated glass with EVA interlayer shows more favorable overall performance at high temperature. The only disadvantage of EVA interlayer is that it will tear at a temperature of 60°C. It is recommended to further study the bending of laminated glass with smaller temperature steps, and the bending of laminated glass at temperatures below room temperature and below zero.

The current experimental research on the influence of temperature on the behavior of laminated glass is carried out under the guidance of the author. The title of the thesis is "The Behavior of Laminated Glass at High Temperature". The thesis was presided over and prepared by the graduate candidate Ms. Maksi Podobnik (Podobnik 2019). Her contribution to this research has been greatly recognized.

ETAG 002-Structural Sealed Glass Window System (SSGS) European Technical Certification Guide Part 1: Supported and unsupported systems. European Technical Certification Organization (2012) Brackin, S., M.: Development of a program for evaluating the shear modulus of laminated glass. Thesis. Texas A&M University, Civil Engineering (2010) Haldimann, M., Luible, A., Overend, M.: Structural use of glass. IABSE, Zürich (2008) Krüger, G.: The influence of temperature on the structural behavior of laminated safety glass. Autograph Magazine. roll. 9, 153-163 (1998) Kuntsche, J., Schuster, M., Schneider, J.: Engineering design of laminated safety glass considering shear coupling: a review. Glass structure engineering (2019). doi:10.1007//s40940-019-00097-3 Martin, M., Centelles, X., Solé, A., Barreneche, C., Fernández, A., I.: Polymeric interlayer materials for laminated glass: an overview. Constr.Build.Mater. (2019). doi:10.1016/j.conbuildmat.2019.116897 Pankhardt, K.: Temperature-dependent bending stiffness of load-bearing laminated glass panels. Periodica Polytechnica Civil Engineering (2010). doi:10.3311/pp.ci.2010-2.07 Pankhardz, K., Balázs, G., L.: Temperature-dependent load-bearing capacity of laminated glass panels. Periodica Polytechnica Civil Engineering (2010). doi:10.3311/pp.ci.2010-1.02 Podobnik, M.: The behavior of sandwich glass at high temperature. Graduation thesis. Faculty of Civil and Geodesy Engineering, University of Ljubljana (2019) Sable, L., Skukis, E., Japins, G., Kalnins, K.: The difference between numerical value and experimental test of laminated glass plate with viscoelastic interlayer Correlation. Procedia Eng. 172, pp. 945-952. Elsevier (2017) Santarsiero, M., Louter, C., Nussbaumer, A.: Laminated connection under tensile load at different temperatures and strain rates. Int.J.Adhes.Adhes. (2017). doi:10.1016/j.ijadhadh.2017.09.002 Serafinavičius, T., Lebet, P., J., Louter, C., Lenkimas, T., Kuranovas, A.: PVB long-term laminated glass four-point bending test, EVA and The SG sandwich is at different temperatures. Procedia Eng. 57, pages 996-1004. Elsevier (2013) Serafinavičius, T., Kvedaras, A., K., Sauciuvenas, G.: The bending behavior of different laminated laminated glass. mechanical. Compos.Mater. (​​2013). doi: 10/1007/s11029-013-9360-4

779 Washington Street Buffalo, NY 14203 United States

Via del Lavoro, 1 22036 Erba CO Italy

Ismail Horse. D-100 Karayolu CAD. No:44A, 34947 Tuzla, /İstanbul Turkey

Via Molare 23/c 15076 Ovada AL Italy

Industrijska zona RZ R29 51223 Kukuljanovo Croatia

Boll. Ind. Penapurreira Parcela C4-B, 15320 As Pontes de García Rodríguez A Coruña Spain

Polígono Industrial El Bayo, parela I, 19 24492 Cubillos del Sil León Spain

Carrer del Pla, 108-110, Pol. Ind. El Pla 08980 Sant Feliu de Llobregat Barcelona Spain

19, rue du Puits Romain, L-8070 8070 Bertrange Luxembourg

Via Fieramonti 1 04012 Cisterna di Latina LT Italy

3196 Thompson Road Fenton, MI 48430 United States

carat. Km from Estacion. 15.8 44415 Rubielos de Mora Teruel Spain

Via Marcatutto 7, (Milano) Italy 20080 Albairate MI Italy

Runów, ul. Solidarności 1 05-504 Złotokłos Poland

No. 160, Yichuan Road, Jiaonan City, Qingdao City, Shandong Province 266000

Building 8, SIRIM Complex, No. 1, Persiaran Dato' Menteri, Section 2, PO Box 7035, Darul Ehsan, 40700 Shah Alam Selangor Malaysia

Log in or register to post a comment