Post-breakage Behaviour Research Articles

Adhesion Properties of Polyvinyl-Butyral-Laminated Glass under High-Speed Loading

Laminated glass has been widely used as safety glass for decades owing to its remarkable post-breakage load-bearing capacity. The post-breakage behaviour of laminated glass is mainly affected by several key factors such as the interlayer property, the adhesion property of the glass-interlayer interface, and the size of glass fragments. In this study, the adhesion properties of polyvinyl butyral (PVB) laminated glass under high-speed uniaxial tension were studied by through-cracked tensile (TCT) tests. Two adhesion grades (i.e., BG-R15 medium adhesion grade and BG-R20 high adhesion grade) PVB-laminated glass and three loading rates (i.e., 0.1m/s, 0.5m/s, and 5m/s) were considered in the tests. The delamination behaviour of PVB-laminated glass was modelled using a numerical cohesive zone model (CZM) to accurately calibrate the interfacial adhesion properties. It was found that BG-R15 PVB-laminated glass exhibits a progressive delamination behaviour under high-speed loading, which results in a stable but low post-cracking force, whereas the delamination was significantly constrained for BG-R20 PVB-laminated glass, which leads to a higher post-cracking force but very poor deformability. The deformability of high adhesion grade laminated glass increases with the crack number since more PVB participates into the stretching of cracked laminated glass. The interfacial adhesion property shows a significant rate effect, with the bonding strength and energy release rate of BG-R15 PVB-laminated glass increase by nearly 25% and 50%, respectively, as the loading rate increases from 0.1m/s to 5m/s. In general, the energy dissipation capacity of the BG-R15 PVB-laminated glass is much higher than that of the BG-R20 PVB-laminated glass. This study can provide a valuable reference for the design of laminated glass under blast or impact loads.

Prediction of Pre- and Post-Breakage Behavior of Laminated Glass Using a Phase-Field Damage Model

Laminated glass composed of several layers of glass plies bonded to a polymer interlayer enjoys ever growing interest in modern architecture. Being often used in impact protection designs requires understanding of both pre- and post-breakage behavior of these structures. This paper contributes to this subject by examining an application of an explicit phase field dynamic model to the description of fracture in a laminated glass subjected to a low velocity impact. The achieved results indicate the ability of the proposed model to successfully describe the onset of damage and subsequent crack propagation. It has, however, been observed that a relatively fine mesh is needed to interpolate a sharp discontinuity accurately, which makes this approach computationally demanding. The model is first validated against experimental results obtained for a single-layer float glass. Next, the usability of the phase-field damage model as a crack predictor in individual layers of the composite is investigated. The dependence of the results on residual stiffness, element type, and initial tensile strength is examined and discussed.

Post-failure behavior of 2-ply laminated glass plates with different interlayers

Modern design codes, such as the new Eurocode on the design of structural glass components, consider the prediction of the post-failure behavior of these elements of paramount importance for a proper and safe design. In this view, an experimental investigation is presented in the paper, on the mechanical response of undamaged and damaged 2-ply Laminated Glass (LG) under quasi-static loads, with different interlayers, namely polyvinyl butyral (PVB), SentryGlas (SG) and a plasticized version of PVB, Saflex DG41 (DG41). Firstly, undamaged specimens (UDLG) were tested in simply supported configuration (configuration 0) with a vertical load in the middle increased up to the failure of the bottom glass ply. damaged LG specimens (PDLG) were then tested into two different configurations: configuration I, with broken ply below (bottom ply) and configuration II, with broken ply above (top ply). All the presented tests were performed under displacement control. For both configurations, the interlayers influence on the post-breakage behavior was discussed. It is underlined that the global response of the two configurations was completely different: configuration II, which was characterized by a deformed shape opposite to the load direction, showed a good residual stiffness and reached high failure loads. On the contrary, in configuration I, the response was characterized by a low stiffness and load carrying capacity. In addition, also the influence of different glass types was discussed, focusing attention on tempered and toughened glass. The results showed that the contribution of the fractured layer cannot be disregarded in the evaluation of the global stiffness of a PDLG and its contribution is strictly related to the interlayer and glass typologies.

Phase-field damage of laminated glass in explicit dynamics

Laminated glass is aesthetic but also functional modern material, which has spread from the automotive industry to the civil engineering in the form of design as well as structural elements. Proper design of this material requires understanding not only its intact phase, but also its post-breakage behavior. To describe crack initiation and propagation the phase field damage model seems to be suitable tool despite the fact that this approach requires a fine mesh to sufficiently interpolate sharp discontinuity. In this contribution we investigate possibilities of explicit phase field dynamic model with specific use on glass plates, especially applied for dynamic impact load. The dependence of the result on residual stiffness term is examined and incorrect crack speed is observed. Usability of phase-field model is still uncertain.

Overall response of 2-ply laminated glass plates under out-of-plane loading

The results of an experimental and numerical investigation on the mechanical response of undamaged and damaged 2-ply Laminated Glass (LG) plates with different interlayers are presented in the paper. Three different interlayers, polyvinyl butyral (PVB), SentryGlas (SG) and Saflex DG41 (DG41) characterized by different rheological properties and fully tempered glass plates were considered. Simply supported plates under out of plane loads were tested in three different configurations: configuration 0, undamaged; configuration I, partially damaged, with a broken ply below (bottom ply) and configuration II, partially damaged, with a broken ply above (top ply). In the three configurations the top ply is always subjected to compression while the bottom one is in tension. The main aspects and the different response of each configuration were discussed and compared. Experimental results highlighted the influence of the interlayer properties on both the pre- and post-breakage behavior. Moreover, numerical models were developed to reproduce the experimental results. For the post-breakage response two different strategies were developed: a) the equivalent temperature variation and b) elastic-brittle constitutive law. Differences and advantages associated with both solutions are discussed. Finally, extensive parametric numerical analyses are proposed to underline the influence on the mechanical response of different parameters: i) plate geometry (size effect); ii) interlayer thickness; iii) glass thickness; iv) additional glass ply (3-ply LG plate). It is underlined that the size effect plays an important role on the mechanical response of LG plates and it should be always considered in the design. The numerical findings were used to define a critical length from which the plates behave as monolithic, independently of the stiffness of the interlayer.

Phase Field Simulation of Laminated Glass Beam.

The complex failure mechanisms of glass laminates under in-plane loading conditions is modelled within the framework of phase-field strategy. Laminated glass is widely used for structural purposes due to its safe post-glass-breakage response. In fact, the combination of several glass plies bonded together with polymeric interlayers allows overcoming the brittleness of the glass and to reach a pseudo-ductile response. Moreover, the post-breakage behaviour of the laminate is strictly correlated by the mechanical properties of the constituents. Ruptures may appear as cracks within the layers or delamination of the bonding interface. The global response of a glass laminate, validated against experimental results taken from the literature, is carried out by investigating a simplified layup of two glass plies connected by cohesive interfaces through an interlayer. Delamination of the adhesive interface is described, and crack patterns within the materials are fully described. Finally, the proposed approach put the basis for future comparisons with results of experimental campaign and real-life applications.

Viscoelastic properties of EVA interlayer used in laminated glass structures

Laminated glass is getting used more extensively in a current architecture due to its transparency, aesthetic impression, and post-breakage behaviour. Examples of such structures are balustrades, stairs, or facade panels. These are usually loaded in bending. Polymeric interlayer embedded between glass plies has no flexural stiffness, but it can itself transfer shear stress. The rate of this transfer depends on the shear stiffness of interlayer which is time and temperature dependent parameter. Producers of interlayers often do not specify this quantity thus engineers rather neglect the shear interaction of glass plies in perpendicularly loaded laminated glass panels. This paper provides the values of shear stiffness modulus of common interlayer EVASAFE® by BridgestoneTM in time and temperature domain. This shear stiffness is expressed through Maxwell model whose parameters are based on the series of Dynamic mechanical thermal analysis (DMTA) performed on single lap small-scale specimens in Klokner institute CTU in Prague. Results show that shear stiffness of this interlayer is able to provide significant shear coupling of glass plies in broad temperature range of short-term perpendicularly loaded laminated glass structures.

Experimental investigation into the post-breakage performance of pre-cracked laminated glass plates

SentryGlas® (SG) laminated glass (LG) is commonly used as a load bearing material in structural applications. Like other conventional structural materials, SG LG plates are expected to have adequate stiffness and resistance to breakage so that they can withstand loads from either external action or their self-weight. This paper reports an experimental study of the post-breakage behaviour of SG LG plates. In the study, a weight-drop impact load was first applied to crack glass plates to create a crack pattern under hard-body impact. These cracked glass plates were subsequently subjected to a continuous static load until collapse. The applied load and the deflections at seven reference points on the specimens were recorded and examined. Two key parameters, the initial stiffness and the peak post-breakage resistance, were identified to evaluate the post-breakage performance of seven groups of specimens. The effects of glass make-up and the support condition were observed and are discussed. It was found that the support condition determines the load transfer path and further influences the ‘yield line’ pattern and post-breakage resistance. It was also observed that the different crack patterns created various load bearing mechanisms and the glass make-up also played an important role in the post-breakage resistance and the failure mode. Experimental results reveal that the annealed glass (ANG) sheet yields the highest initial stiffness and resistance in the post-breakage phase. With an increasing number of SG interlayers, the LG plate is more likely to be penetrated before the ‘yield lines’ completely form. Finally, a comparison study was carried out to investigate the post-breakage performance. Results indicate that in comparing ANG and the fully tempered glass (FTG) plates, the former exhibits a better ability in retaining the post-breakage capacity.

Novel treatment methods for improving fatigue behavior of laminated glass

The use of laminated glasses (LG) is increasing day-by-day in the fatigue prone structures. In the present work, the pre- and post-breakage behavior of LG was improved for the fatigue loading via five novel thermo-chemical treatment methods. The fatigue life of LG samples was evaluated using the standard bending cyclic fatigue test. The prime goal of the treatment methods was to bring the surfaces of LG samples in the compressive state without causing melting or bubbling of interlayer having a melting temperature lesser than 150 °C. A comparison of treatment methods based on cyclic fatigue strength (CFS) of LG was reported. Further, a theoretical explanation for improved fatigue life was presented. The life of LG samples was increased by more than 40% by one of the treatment methods. The finite element (FE) model was developed to calculate the deformations and stresses for the corresponding number of cycles at which LG samples were fractured. Further, the FE model was extending to consider the residual stresses profile due to different treatments before modeling the effect of cyclic fatigue loading. The strain-life and stress-life relations were established using experimental and modeling results. The crack propagation and fracture of LGs were explained using previously established models and correlated with the effect of treatment. The statistical analysis was conducted for ensuring the validity of the results.

Dynamic response analysis for submerged floating tunnel with anchor-cables subjected to sudden cable breakage

Anchor-cables are critical bearing components of the submerged floating tunnel (SFT). As the accidental cable-breakage incident will seriously threaten the public safety, this paper investigates the global dynamic response of a SFT subjected to an abrupt anchor-cable failure by focusing on the post-breakage behavior. Firstly, an approximate theoretical approach is proposed, in which the analysis model of SFT is simplified and the alternate load path method (AP method) is adopted to simulate the cable-breakage process. Then, the differential equations of the SFT tube are established based on the Hamilton principle, and solved through the fourth order Runge-Kutta method. A finite element analysis in ABAQUS is also performed as a verification of the theoretical results, in which the VUSDFLD subroutine and ABAQUS/Aqua is employed to simulate the stiffness loss of the cable and apply the fluid loads respectively. A good agreement exists between the simplified theoretical model and FE simulation. Finally, the effects of some key parameters are discussed, such as the gravity-buoyance ratio and the damping ratio of the SFT, the breakage time and position of the broken cable, etc. The results show that the structural vibration is intensive after the sudden cable breakage. Also, the remaining anchor-cables close to the cable-loss position are most affected by the cable rupture. The change of gravity-buoyance ratio and damping ratio have notable effects on structural deformation. The SFT is most unfavorable when the cable breakage happens at the mid-span or near the two ends of the tunnel. The vibration amplitude attenuates significantly with the increase of the failure time of anchor-cable.

Glass fins with embedded titanium inserts for the façades of the new Medical School of Montpellier

The new Medical School of Montpellier, designed by Francois Fontes, is enclosed by several facades stiffened by the use of glass fins up to 12.71 m high. The main facade assures the monumentality of the institution with its length of more than 60 m. The facade glass panels, with a maximum size of $$3.8\times 2.8$$ m, are stacked transferring the dead load to the bottom panels through plastic setting blocks. The facade panels are fixed with patch-fittings bolted to titanium inserts embedded in the vertical glass fins. The structural system is designed to resist seismic actions and to accommodate the displacement of the main structure under an earthquake scenario. The stability to lateral buckling and under seismic loads is guaranteed by a system of cables and rods which transmits the in-plane forces to the main structure. The post-breakage behaviour of the multilaminate heat-strengthened glass panels and the design of the facade guarantee the stability even under very aggressive accidental scenarios. The paper contains the main issues about the fabrication of titanium inserts laminated with SentryGlas® interlayer. The verification methodology of the glass fin with embedded titanium connections in terms of strength and stability is described. In particular, non-linear buckling analysis and stability checks based on Eurocodes are proposed. The numerical analyses were completed with pull-out tests of aged specimens in order to determine the resistance of the adhesive connections. Finally, a full-scale glass fin was submitted to a three-point bending test to validate the design including the post-breakage behaviour. A brief description of the construction phase is also included.

Characterisation of the mechanical behaviour of annealed glass–GFRP hybrid beams

This paper presents the results of a combined experimental and numerical investigation on the mechanical behaviour of annealed glass–Glass Fibre Reinforced Polymer (GFRP) hybrid beams. The experimental results showed that an adhesively-bonded GFRP interlayer significantly improved the strength and ductility of annealed glass beams. The paper also presents the post-breakage behaviour and the response of damaged beams in unloading. The paper numerically investigates the degree to which the strength and stiffness of the hybrid beams can be modelled by using finite element (FE) analyses. The novelty of work also includes numerical modelling and validating the through-thickness stress profiles in the hybrid beams.

Comparative Study on Structural Performance of Different Laminated Glass Composites and Brick Wall

Laminated glass composites are structural glass members made by assembling thin laminated panels which are connected by structural adhesives called interlayer. Laminated glass composite is a safety and security glass which enables significant improvement in the post-breakage behaviour. The interlayer of laminated glass composites ensures the integrity of the glass by holding it together. In the field of modern and innovative architectural engineering, the applications of laminated glass composites are increasing due to its lighting, aesthetics and architectural advantages. This paper introduces the buckling and vibration characteristics of different laminated glass elements using ANSYS 16.2.

Impact Performance of Thin Glass-Polycarbonate Composite Panels

Safety glass is usually the proper designer choice when glazing may be subjected to the impact of a person. In order to avoid people injuries, glass products must comply with appropriate safety practices. Existing technical standards classify safety glass products by mode of breakage and post-breakage behavior. Critical demanding applications in terms of self-weight saving, like high efficiency elevator cars in buildings or aircrafts and other means of transportation interiors in aerospatial and automotive industries, are currently driving the innovation in the development of safety glass. In this framework, glass-polycarbonate composite panels offer a lightweight alternative which is at once able to preserve the aesthetic and safety aspects of traditional laminated safety glass. The aim of this paper is to present an experimental investigation on the performance under impact of thin glass layer with a cellular polycarbonate backing joined together by an auto-adhesive interlayer film. Different coatings (mirror and paint) at the glass-adhesive interface are also taken into account.

Structural Safety of Photovoltaic Modules in the Building Envelope

The mechanical performance of photovoltaic modules has not been adequately characterized for use as glazing product in the building envelope. As a result, the modules are subject to individual approval by the building authorities in many building-integrated applications. This paper presents experimental research on glass based photovoltaic modules, analyzing their mechanical properties in comparison with regulated construction products. The focus is on the influence of photovoltaic thin-film coatings on the bending strength of the float glass used as a substrate or superstrate and on the post-breakage behavior of glass-glass modules. The four-point bending test according to EN 1288-3 was modified in terms of specimen dimensions in order to test full-size photovoltaic glass panes. The modified set-up was verified as a suitable and simple test method to determine and confirm strength values. Edge ablation was found to reduce glass strength rather than the PV coating and cell scribing processes, but the reduction is less than 10 % and the minimum strength value of float glass can still be met. Residual strength testing of glass-glass photovoltaic modules in different load and temperature scenarios showed that the integration of crystalline silicon cells as well as thin-film solar cells improves the post-breakage behavior of glazings. A critical point may be mechanical failure within the layers of thin-film cells on glass associated with the potential danger of broken glass pieces falling down. Standard glass-glass module configurations appear to provide the same or higher residual strength performance as laminated safety glass, if the interlayer material is approved for use in laminated safety glass.

Experimental Investigation on Post-tensioned Spannglass Beams during Temperature Loads

Recent research work focused on material efficient and safe structural use of glass beams. Reinforcing and post-tensioning of those structures in the style of reinforced concrete are promising options. They allow for a safe post-breakage behaviour of load bearing glass constructions. Other ductile materials such as steel and high-grade cables strengthen the glass, which results in robust structures. However, hybrid structures are prone to temperature loads. Especially post-tensioned glass beams – Spannglass Beams – are vulnerable to lose part of their initial cable load caused by a different expansion of their parts. The thermal expansion coefficient of steel cables is about 70% larger than the value of glass. Therefore, a cable in a hybrid structure will expand much more during heating. This effect results in a loss in initial cable load of a post-tensioned reinforcement, and cannot be prevented. Hence, the temperature dependency needs to be considered during the design stage. Furthermore, a change in temperature influences the material properties of glass-contact materials and the interlayer. Thermoplastic blockings transfer the cable load into the laminated glass edge. Due to manufacturing tolerances, the interlayer material is stressed. Therefore, this will affect the reaction of the structure to a change in temperature. The non-destructive experimental study includes the results of a set of two Spannglass Beams with 8 mm post-tensioned cables. Adhesively bonded connectors redirect the cables according to the needs in a four-point bending set-up. Two-meter long beams were placed in a climate chamber to heat the specimens from ambient temperature to 60°C. We recorded the structural behaviour at alternating initial cable loads as well as different bending loads. Finally, the results led to a recommendation on how to consider a possible loss in cable load caused by a change in temperature. This will support the argumentation that post-tensioning glass beams is a feasible structural option.

Broken tempered laminated glass: Non-linear discrete element modeling

The research presented herein aimed to simulate the structural behavior of laminated glass with all the glass layers broken, by means of the discrete element modeling. This paper focuses on laminated glass composed of two layers made of tempered glass and an interlayer made of either a totally compliant or a relatively stiff material.The paper demonstrates that discrete element modeling is a viable tool to predict the load–deflection curve from the cracking up to the collapse of laminated glass members, and, hence, to assess the collapse limit states of structural glass. In fact, discrete element modeling may simulate the non-linear composite behavior that the polymeric interlayer and the glass fragments provide a member with, considering the crack patterns of the broken glass, the visco-elasticity of the interlayer, and the structural conditions of the member. The validity of the method is also confirmed through comparisons with other sources — namely, some experiments performed by the authors and an empirical model.The paper presents the method and the results from its application to typical laminated glass members used for structural glass. Those results provide insight into the effects of the design choices on the post-breakage behavior; emphasis is placed on the role played by the type of interlayer.

Critical assessment of the post-breakage performance of blast loaded laminated glazing: Experiments and simulations

Glass windows are the most vulnerable building components when impacted by an air blast wave. For safety requirements, the customary choice for the window glazing is laminated glass, where two or more glass plies are bonded with a polymer interlayer to retain glass fragments upon breakage. With proper choice of interlayer material, the window can keep functioning as a shield to the blast wave even when fractured. Numerical simulation of the post-breakage response of a laminated glass panel can be a valuable tool for optimisation of the interlayer material and the glass panel configuration.This article presents the results of a blast testing campaign for laminated glazing, according to a standardised procedure, and subsequent numerical simulation thereof. The experiments show that laminated glass using a soft polyvinyl-butyral (PVB) interlayer with low adhesion properties achieves the best safety performance at higher loads with no interlayer tearing, while still efficiently retaining glass fragments. The numerical simulation of these experiments attempts to capture the fracture and post-breakage behaviour of laminated glass under the blast load. In the finite element model, glass elements are deleted upon reaching a fracture criterion. The model can globally reproduce crack formation and post-fracture deformation, but lacks prediction of ultimate failure, mainly because of a strong dependency on the element size for both glass and interlayer parts.

Quasi-Static Performance of Interlayer Systems for Laminated Glass

AbstractTo be able to accurately predict the static resistance function of laminated glass subjected to blast loads using engineering analysis methods, it is critical to evaluate the static behavior of the polymer interlayer before and after breakage of the glass layers. Therefore, the main objective of this research is to experimentally evaluate the constitutive behavior of polymeric glass interlayers under quasi-static loading. Constitutive relation of virgin and extracted polyvinyl butyral (PVB) and UVEKOL-S extracted from laminated glass panels were evaluated, including the energy absorption capabilities for each material. Also, the postbreakage behavior of laminated glass was investigated. The experimental results of scored tensile samples carried out on UVEKOL-S glass laminates using different numbers of scores are presented, discussed, and compared with the results of the PVB glass laminates. The energy absorption of the PVB glass interlayer was found to be larger than that of the UVEKOL-S interlay...

Glass - steel hybrid elements under four point bending test

Problems evolving from the brittleness of structural glass result in need of innovative solutions which will improve the post-breakage behaviour of the elements in the structure. As the need of the glass performance gets higher, the fully tempered glass gets in the focus and its usage becomes greater. But although this type of glass gives great performance with its tensile strength and deflection capaciy, it has no residual strength. Due to its breakage pattern into small pieces the collapse of the element may be instant even in laminated glass elements. Thus, increasing the post breakage behaviour is crucial in order to keep the integrity of the tempered glass element. This can be done either by changing the interlayer properties, or including kind of reinforcement in the element structure. This paper presents experimental testing of the performances of steel plate reinforced hybrid glass element under four point bending test. As a result, it shows the improvement in mechanical behaviour of the described hybrid structure concept compared to a monolithic glass element with same dimensions, by means of stress distribution and reinforcement capacity.