Glass Plies Research Articles

Buckling behaviour of laminated glass panel in compression

There is a significant increase in the application of laminated glass panel in the modern and innovative construction industry. Glass element is frequently used as a structural component because of its aesthetic and allows abundance of daylight shining in through in which leads to energy saving. The glazing consists of two thin glass plates bonded together by a thin core material called polyvinyl-butyral (PVB). A laminated glass panel is typically brittle and slender, thus frequently subjected to buckling. This paper focuses on the load-carrying behaviour of laminated glass panel supported merely along four edges subjected to compressive force. A 1 m x 1 m laminated glass panel with glass plies of 8 mm thick and the interlayer thickness of 1.52 mm is modeled and analyzed through nonlinear static analysis by using ABAQUS finite element (FE) analysis software. The behaviour of the laminated glass panel under buckling and post-buckling analysis was presented. Analytical approach by Zenkert’s formulation based on the theory of sandwich is utilized to validate the technique used to build the FE model of the glass panel. Essentially, the critical buckling load and the load-displacement relationship are in a good agreement with the analytical formulation and the empirical study respectively. In addition, the significant effect of the interlayer and the slenderness aspect of the panel are also studied. This involves parametric analysis of the configuration of the different interlayer stiffness and the aspect ratio length to width (a/b) of the glass panel. It was found that the rate of decrement of buckling load is indirectly proportionate to the rate of increment of (a/b) ratio. This study also shows that the buckling load of a laminated glass panel depended very much on the slenderness aspect of the structure.

Experimental determination of failure strength in automotive windscreens using acoustic emission and fractography

This paper presents a methodology to determine failure stresses from components consisting of laminated safety glass. For this purpose, automotive windscreens were tested under quasi-static loading by a head impactor for pedestrian protection. Automotive windscreens consist of two glass ply connected by a polyvinyl butyral interlayer. During the experiment, the failure origin was determined by acoustic emission localisation. The computed failure origins were examined for fracture marks, particularly for the fracture mirror. Fracture mirrors have a direct relation to failure stresses by a material constant, which can be used to determine the failure stresses of brittle materials. It is shown, that the measured stress samples fit best to a two parameter Weibull distribution. The experimentally obtained failure stresses are compared to numerical results obtained by finite element analysis. Furthermore, observations on fracture marks confirm the conclusion, that the glass ply both failed at the interior side. It could also be shown, that in eleven of twenty experiments, the interior ply failed first. With the gained failure stresses and the fracture toughness, conclusions were drawn for critical flaw sizes and their statistical distribution.

Laminated Glass Cantilevered Plates under Static and Impact Loading

The structural performance of cantilevered laminated glass plates for different glass thicknesses and interlayers is considered in this paper. Heat-strengthened and tempered glass plies and two different interlayer films were utilized. The response of laminated glass specimens is then evaluated under low-velocity hard and semirigid impacts. Experimental findings were simulated and discussed by means of finite element analyses. In particular, this discussion includes the evaluation of the influence that the fixed edge clamping technique (number of clamps, their size, and their stiffness) has on the stress distribution in the specimens.

Advanced 3D and 2D damage assessment of low velocity impact response of glass and Kevlar fiber reinforced epoxy hybrid composites

This work focuses on quasi-static mechanical (tensile, flexural, indentation), low velocity impact (LVI) and viscoelastic behaviour of different stacking sequences and ] of 16 layers woven roving Kevlar-E-glass/epoxy interply hybrid composites. The outermost layers are Kevlar and remaining 14 E-glass layers are placed as interior for making these hybrid laminates. The viscoelastic properties are measured over the temperature range from 25 °C (room temperature) to 180 °C at three different frequencies (1, 10 and 50 Hz) by using the dynamic mechanical analyzer (DMA). The LVI results indicated that Kevlar-glass/epoxy hybrid laminates exhibit the highest damage threshold load (DTL) whereas laminates possess the higher peak load and threshold and maximum energies. Advanced non-destructive testing techniques (NDT) such as X-ray computed tomography (X-CT) and ultrasonic C-scan are employed to evaluate the micro and macro damage mechanisms of LVI tested specimens, respectively. Detailed observations have been made on the onset and growth of cracks in 30°, 45° and 0° plies using X-CT scan imaging. These images show that the bottommost plies subjected to more impact than the topmost plies, the outer Kevlar plies protect the inner 0° glass plies and delays the delamination propagation. ‘C’ scan images indicate that laminates spread the damage to more area. The scanning electron microscopy (SEM) is used for examining the failure mechanisms of indentation specimens.

Post-failure behavior of laminated glass beams using different interlayers

An experimental investigation is presented on the mechanical response of progressively damaged Laminated Glass (LG) beams assembled with modified polyvinyl butyral (PVB)-based interlayers (DG41). While it is known that ionoplast interlayers significantly improve the load-bearing capacity and residual strength of damaged LG elements, limited experimental data are available on recently developed compounds such as DG41. The role of interlayers increases with the damage level within LG elements: when glass plies break, LG stiffness and strength depend on the ability of the interlayer to couple intact glass plies and fragments of shattered ones. For damaged LG beams, the consequences of the increases in volume of a broken tempered glass plies are discussed. In particular, the interlayer activates two competing effects on the undamaged glass plies affecting the residual carrying capacity: a positive “tension-stiffening” over time and the tendency of tempered glass to expand when fractured that triggers “negative” stress/strain fields in undamaged glass plies.

Structural Performance of Double Laminated Glass Panels with EVA and PVB Interlayer in Four-Point Bending Tests

Many examples of glass loadbearing structures such as handrails, panes, beams and columns can be found in modern architecture. Most of these elements are made of laminated glass panels. There is a general lack of knowledge about the transfer of shear forces between the glass plies in perpendicularly-loaded laminated panels. This transfer depends significantly on the stiffness of the polymeric interlayer, which is time-dependent and temperature-dependent. There are several computational methods for the design of laminated glass that take the shear coupling of the glass plies into account, e.g. analytical methods, numerical modeling and also the draft of European code. These methods need to be verified experimentally. This paper reports on rectangular double-laminated glass panels in a shortterm displacement controlled four-point bending test with an EVA and with a PVB interlayer under a constant temperature. These tests were performed at CTU in Prague. Our experimental results show that panels with an EVA interlayer had greater bending stiffness than panels laminated with PVB and achieved higher ultimate load values. The experimental data were further compared with simplified analytical methods, such as the European draft prEN 16612 and the Enhanced Effective Thickness approach and also a numerical FEM model. Numerical and EET methods results were in good agreement with the experimental data. The way in which the specimens broke was a characteristic feature of laminated glass. The shards remained attached to the interlayer, proving that laminated glass panels can be used safely above the heads of users of the structure. Simplified methods and numerical models validated by experimental tests on perpendicularly-loaded laminated glass panels enable these structures to be designed safely and economically for practical uses.

Viscoelastic Behavior of Cellulose Coated Glass/Kevlar Epoxy Composite Laminates using Dynamic Mechanical Analyzer

The dynamic behaviour of fiber reinforced composites plays a significant role on the performance of the laminated composite materials. In the present study the dynamic characteristics of cellulose Glass Epoxy Composites (CGEC) and Cellulose Kevlar epoxy composites (CKEC) were investigated and compared with pristine glass epoxy (GE) and Kevlar Epoxy (KE) composites using Dynamic Mechanical Analyzer (DMA). Cellulose particles were liquefied in organic solvents such as Acetone, Dimethylformamide (DMF), Ethanol and Sodium Hydroxide (NaOH) to inspect the settling time and it was found that cellulose particles settled in short interval of time in solvents and hence NaOH was used to make solution as better dispersion with high settling time was observed with NaOH. The Glass and Carbon plies were coated with Cellulose using semi automated coating technique. The DMA test was conducted in accordance with ASTM 1867-13. The tests results revealed that initially all the samples exhibited high storage modulus but there was a small drop in storage modulus in the temperature range of 50-70˚C and considerable drop in storage modulus was observed in the temperature range of 70-90˚C and also it was found that composite laminates changed in state from solid to elastic beyond glass transition temperature (Tg)

Effect of Novel Thermo-Chemical Treatment on Bending Strength of Laminated Glass

The science of thermal and chemical treatment of glass is well documented. The Laminated Glass (LG) is usually not treated as either treated glass is used during production or lower melting temperature of interlayer does not allow the treatment. The present work reports the novel methods of thermo-chemical treatment of LG having annealed soda lime glass plies. Five thermo-chemical treatments were performed on LG using different salts (Potassium Nitrate Carbohydrazide, Lithium Nitride), via clay coating (saturated with salts), using fused silica wafer coated with a thin graphene layer and utilizing the microwave heating. The bending strength is measured before and after thermo-chemical treatment using Q-set coupled bending tester (following the ASTM D790-03). The linear elastic model is utilized for obtaining normal stress and deformation at fracture load using ANSYS 14.5. The bending strength of thermo-chemical treated LG sample was found significantly higher than untreated LG in the most cases. The fracture pattern of the treated LG was also modified compared to the untreated LG as impurities and defects were reduced during treatment. The mechanics of increased bending strength and modified fracture is also discussed with reference to the effects of thermo-chemical treatment of LG, however, the need of a specialized numerical method that can effectively model the implications of treatment on LG and multiple fractures experienced by the LG during testing are suggested as future work.

Numerical and Experimental Investigation on I-type Damage Evolution in Glass Fiber Reinforced Laminates Subjected to Quasi Static Loading

Glass fiber reinforced polymer composites has become more popular material used in aerospace and marine structural applications due to their specific strength and anti-corrosion properties. The present work discusses the numerical and experimental investigation on I-type damage evaluation in glass fiber reinforced laminates under quasi-static loading is presented. Three volume fraction of glass and resin (40/60, 50/50 and 60/40) plies were selected for both numerical and experimental damage analysis. The damage analysis was conducted for double cantilever beam as per ASTM standard using a universal testing machine. The J-integral method of numerical investigation carried out by virtual crack closure technique and cohesive zone modelling. The fracture toughness has increased with the resin content and dependent on the ductility caused at the crack tip due to the plastic zone around the crack tip. The numerical results were found to possess good agreement with the experimental values. Cite this Article Nikhil Rangaswamy, Shivakumar S, Kallol Anupama N. Numerical and Experimental Investigation on I-Type Damage Evolution in Glass Fiber Reinforced Laminates Subjected to Quasi Static Loading. Emerging Trends in Chemical Engineering. 2017; 4(3): 27–33p.

Temperature effects on laminated glass at high rate

The load bearing capacity of a laminated glass pane changes with temperature. In blast protection, laminated glass panes with a Polyvinyl Butyral (PVB) interlayer are usually employed. The post-crack response of the laminated pane is determined by the interlayer material response and its bond to the glass plies. An experimental study has been performed to determine the effects of temperature on the post cracked response of laminated glass at a test rate of 1 m/s for PVB thicknesses of 0.76 mm, 1.52 mm and 2.28 mm. Tensile tests were carried out on single cracked and randomly cracked samples in a temperature range of 0 °C–60 °C. Photoelasticity observation and high speed video recording were used to capture the delamination in the single cracked tests. Competing mechanisms of PVB compliance and the adhesion between the glass and PVB, were revealed. The adhesion showed an increase at lower temperatures, but the compliance of the PVB interlayer was reduced. Based on the interlayer thickness range tested, the post-crack response of laminated glass is shown to be thickness dependent.

Ultrasonic detection and sizing of compressed cracks in glass- and carbon-fibre reinforced plastic composites

Nondestructive evaluation of compressed cracks is a major challenge. A quantitative study of the effect of crack-tip closure on the pulse-echo ultrasonic sizing of delaminations in fibre-reinforced polymer-matrix composites (FRP) is presented. In particular, this study focuses on the interaction of ultrasound with a closed crack or kissing disbond, and their effect on the ultrasonic inspectability of FRP laminates consisting of carbon and glass plies. The compression of laminar cracks in these two different laminate types is clearly detectable via both pulse-echo and through-transmission ultrasonic measurements, but the reflected ultrasonic pulses in the two material types exhibit markedly different behaviour. The glass-fibre laminates show a drop in the reflected signal for crack openings up to approximately half the crack growth load, whereas the corresponding carbon-fibre laminates show the expected increase in the reflected signal as the crack opens. The origins of the observed effect of crack closure on the reflection and transmission of ultrasound are analysed in detail to ascertain possible mechanisms responsible for these effects.

Structural analysis of failure behavior of laminated glass

Abstract The use of laminated glass is increasing since it is able to guarantee robustness requirements so by improving the post-breaking characteristics of the glass. Due to the brittle nature of glass the reason for employing such composite materials are related to their ability to avoid cracks propagation, retain the glass fragments and present a post-cracking phase. Since the behavior of laminated glass depends on the constituent materials and especially on the type of interlayer, this research deals with the structural behavior of laminated glass plates made with different types of interlayer materials: PVB, SGP, EVA and XLAB. Twenty-four specimens were constructed with two annealed glass plies and transparent interlayer and were subjected to four point bending tests with the aim to study their structural behavior in both elastic and post-breaking phases. Laboratory outcomes highlight the enhanced initial-breakage strength of the XLAB plates, as well as the influence of the laminate type on the post-failure safety, since the use of thicker (double or triple ply) and/or stiffer (such as SGP and XLAB) interlayers seemed not to improve the residual load-carrying capacity. Finally, a 3-dimensional FE model is also presented for reproducing the structural behavior of the glass plates. The ability of the numerical model to reproduce experimental results for the load–deflection curves is validated promoting a deeper understanding and knowledge of the capabilities of the different types of interlayers in the context of the laminated glass design.

Investigation on flexural buckling of laminated glass columns under axial compression

Due to its relatively good safety performance and aesthetic benefits, laminated glass (LG) is increasingly being used as load-carrying members in modern buildings. This paper presents a study into one application scenario of structural LG subjected to axial compression. The aim of the study is to reveal the flexural buckling behavior of the LG columns made up of multi-layered annealed glass plies. The LG specimens respectively consisted of two, three and four plies of annealed glass, bonded together by two prominent types of adhesives. To reach the research aim, both full-scale tests and nonlinear numerical simulations were carried out. Based on the test and numerical results, the influences of interlayer type, laminate number, load duration and ambient temperature on the buckling resistance of the LG columns were studied in detail. In addition, the applicability of the so-called Southwell plot method for LG columns was examined and discussed. Subsequently a characteristic initial geometrical imperfection for LG columns made of annealed glass was suggested. Finally design buckling curves were proposed for LG columns carrying axial loads with the various durations in various ambient temperatures. The results obtained are expected to provide supplementary information that is currently lacking in existing literature.

Experimental investigation of multi-layered laminated glass beams under in-plane bending

Due to its relatively good safety performance and aesthetic benefits, laminated glass (LG) is increasingly being used as load-carrying members in modern buildings. This paper presents an experimental study into one applicational scenario of structural LG subjected to in-plane bending. The aim of the study is to reveal the in-plane behaviors of the LG beams made up of multi-layered glass sheets. The LG specimens respectively consisted of two, three and four plies of glass, bonded together by two prominent adhesives. A total of 26 tests were carried out. From these tests, the structural behaviors in terms of flexural stiffness, load resistance and post-breakage strength were studied in detail, whilst considering the influence of interlayer type, cross-sectional interlayer percentage and presence of shear forces. Based on the test results, analytical suggestions were made, failure modes were identified, corresponding failure mechanisms were discussed, and a rational engineering model was proposed to predict the post-breakage strength of the LG beams. The results obtained are expected to provide useful information for academic and engineering professionals in the analysis and design of LG beams bending in-plane.

A homogenized analysis à la Hashin for cracked laminates under equi-biaxial stress. Applications to laminated glass

Abstract We extend, to the case of equibiaxial states of stress, the variational approach originally proposed by Hashin for the analysis of cracked three-layer laminates under uniaxial tensile loading. The type of damage considered here is complementary to that analyzed by Hashin, in the fact that the external plies of the laminate, rather than the inner layer, are those that are supposed to break, now according to a regular 2D crack pattern. This renders the model particularly suitable for the post-breakage response of laminated glass, composed by a polymeric interlayer sandwiched by two brittle glass plies: the resulting shards partially delaminate but remain attached to the polymer, so to impart to the system a residual load bearing capacity. Within a class of admissible stress systems that verify the equilibrium equations, variational minimization of the complementary energy functional is used to find the optimal approximation, which represents a lower bound for the stiffness. The major complication here consists in the definition of such class, which must take into account the biaxial nature of the problem. Comparisons with numerical experiments confirm the very good accuracy of the proposed approach, at least when applied to laminated glass.

Static and dynamic response of progressively damaged ionoplast laminated glass beams

This paper investigates the mechanical behaviour of progressively damaged laminated glass (LG) beams made with ionoplast interlayers. After the failure of one or more glass plies, the load-bearing capacity of LG beams depends on the capacity of the interlayer to provide coupling effect between broken and undamaged glass plies via adhesion and its own mechanical properties. Dynamic and static tests have been carried out on undamaged and progressively damaged LG beams. The comparison of experimental data with theoretical values obtained neglecting broken plies highlight that ionoplast interlayers assure the transmission of significant shear stresses between broken and unbroken plies, and glass fragments provide a “tension stiffening” effect to the interlayer. Further tests have been carried out on fully damaged LG beams to evaluate their residual load bearing capacity at the time of glass failure and after a five-month interval to assess effects of aging on the bond between ionoplast interlayers and glass fragments.

Water absorption behavior and residual strength assessment of glass/epoxy and glass-carbon/epoxy hybrid composite

Present investigation is aimed to study the water absorption behaviour and evaluation of residual strength of glass fibre/epoxy (GE) and alternate plies of glass- carbon/epoxy (GCE) hybrid composite. Both the composite systems were exposed to water at 70°C. Specimens were weighed after certain time periods to study the water uptake kinetic. Flexural tests were conducted after 4, 100 and 450 hours of ageing to evaluate the effect of hot water ageing on the mechanical properties of these potential materials. The water uptake kinetic was found to follow Fickian diffusion kinetic for GE as well as GCE hybrid composite but the rate of diffusion was higher for GE composite over GCE composite. The water content was also higher in GE composite over GCE composite after 450 hours of ageing. Significant decrement in flexural strength was observed with the increase in ageing time. Presence of water in the composite also imparted significant embrittlement to the matrix as reflected in the decrease in strain at peak for both the composite systems.

Low Velocity Impact Behaviors of a Laminated Glass

Dynamic behaviors of a laminated glass subjected to foreign object impact are studied by the use of the developed finite element program. A finite element simulation based on a higher-order beam finite element and a PVB interlayer model is applied to compute the dynamic responses of laminated glass panel. In this analysis, the glass plies and PVB interlayer are modeled as linear elastic. The results such as the histories of contact force and deflection, and the distribution for strains, stresses through the beam thickness during impact are obtained. The impact behaviors of laminated glass panel are compared with those of the monolithic glass of the same total thickness. It shows that PVB interlayer can be prevented inner glass ply of LG beam from damage by reducing the stress to zero. Specially, stress distribution through the thickness except PVB interlayer in impact analysis shows nearly linear unlike that of static analysis in spite of its discontinuity of the short time shear modulus of PVB in a laminated glass.

Structural behavior of window laminated glass plies using new interlayer materials

In most cases for the structural design of architectural glazing systems under a wide range of environmental conditions, the designers follow procedures provided by model building codes to design window glass. These codes commonly use design charts to determine design strength based on nominal glass thickness and aspect ratio. Glass plies are the principal components of laminated glass (LG) where a thin ply of elastomeric material Polyvinyl butyral (PVB) is used to bond glass plies (normally two plies) to form the LG. Because of the reduction in LG design strength by most building codes and design guidelines, designers avoid architectural LG applications, other than for safety consideration. In this research a higher order mathematical model based on Mindlin plate theory is presented. LG was modeled using finite element methodology with new interlayer (NI). It consists of two plies of PVB with a hard ply of film material in between. In the FEM, properties of PVB/film material can be easily controlled regardless of their thicknesses. The finite element model (FEM) was extended to account the design recommendations of ASTM (2012) to develop the design charts for LG with NI. The current FEM was verified and used to study the stresses transformation through NI. Design charts for samples of LG with NI were developed and presented. It has been found that using NI enhances the total behavior of LG and reflects on the design charts for this type of interlayer material.

Enhanced Effective Thickness (EET) of curved laminated glass

Approximate methods for calculating laminated glass (LG), a composite where thin polymeric layers are sandwiched by glass plies, are very useful in the design practice. The most common approach relies upon the definition of the effective thickness, i.e., the thickness of a glass monolith that, under the same boundary and load conditions, presents the same maximal stress or deflection of the laminate. Different alternative formulations have been proposed, but for flat glass only. Meeting the increasing interest for curved glazing in modern architecture, here the recent “Enhanced Effective Thickness” method is extended to the case of single-curvature LG panels. Under the assumption that the curvature is moderate, usually met in the practice, simple formulae for the effective thickness are proposed. A practical method is presented to calculate the relevant coefficients, which depend upon the geometry, load and boundary conditions. Comparison with numerical experiments in paradigmatic examples confirms the accuracy of the proposed approach.