JournalTOCs

Glass Structures & Engineering
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Hybrid journal (It can contain Open Access articles)
ISSN (Print) 2363-5142 - ISSN (Online) 2363-5150
Published by Springer-Verlag

[2626 journals]

The effects of high strain-rate and in-plane restraint on quasi-statically
loaded laminated glass: a theoretical study with applications to blast
enhancement
- Abstract: Abstract Laminated glass panels are increasingly used to improve the blast resilience of glazed facades, as part of efforts to mitigate the threat posed to buildings and their occupants by terrorist attacks. The blast response of these ductile panels is still only partially understood, with an evident knowledge gap between fundamental behaviour at the material level and observations from full-scale blast tests. To enhance our understanding, and help bridge this gap, this paper adopts a ‘first principles’ approach to investigate the effects of high strain-rate, associated with blast loading, and the in-plane restraint offered by blast-resistant frames. These are studied by developing simplified analytical beam models, for all stages of deformation, that account for the enhanced properties of both the glass and the interlayer at high strain-rates. The increased shear modulus of the interlayer results in a composite bending response of the un-fractured laminated glass. This also enhances the residual post-fracture bending moment capacity, arising from the combined action of the glass fragments in compression and the interlayer in tension, which is considered negligible under low strain-rates. The post-fracture resistance is significantly improved by the introduction of in-plane restraint, due to the membrane action associated with panel stretching under large deflections. This is demonstrated by developing a yield condition that accounts for the relative contributions of bending and membrane action, and applying the upper bound theorem of plasticity, assuming a tearing failure of the interlayer. Future work aims to complete the theoretical framework by including the assessment of plate-action and inertia effects.
  PubDate: 2019-09-21
Cut edge of annealed float glass: crack system and possibilities to
increase the edge strength by adjusting the cutting process
- Abstract: Abstract The edge strength of annealed float glass is an essential aspect in engineering design. A common problem in engineering applications is the failure of the edge due to thermally induced stresses. The edge strength of annealed glass is affected by cutting, further processing and handling. Thermally treated glass exhibits higher edge strengths, but may show optically negative effects such as anisotropy and roller waves. In case of covered edges, e.g. insulating glass covered by framing, an enhanced strength of the cut edge is desirable. This paper presents results showing that enhanced strength of the cut edge is feasible and reproducible using regular cutting technology. A large part of this contribution deals with the crack system resulting from the cutting process. A deep understanding of this is essential for the relationship between cutting parameters, damage and edge strength. In addition to optical microscopic analyses, confocal microscopy and indentation tests have been carried out. The influence of different cutting process parameters on the edge strength was investigated within the scope of extensive analyses by the Fachverband Konstruktiver Glasbau e.V. This allowed to adjust selected process parameters so that the edge strength could be reproducibly enhanced. In this contribution the latest results of these investigations are presented. In addition, the correlation between microscopic optical characteristics and the mechanical strength as expressed by the macroscopic fracture stress is described.
  PubDate: 2019-09-14
Load-bearing behaviour of innovative lightweight
glass–plastic-composite panels
- Abstract: Abstract The trend towards large glass façades and the urge to reduce the material to a minimum requires further evolution in high performance transparent as well as lightweight structures. Therefore, a combination of polymeric interlayer core, chemically connected to cover layers of thin glass to reduce self-weight and to utilize the high durability of glass at the same time, is under development. The novel glass–plastic-composite panels behave as a unit and ensure a sufficient and high-performance load-bearing behaviour. The first studies, including four-point bending tests according to EN 1288-3 (2000), showed a nearly equivalent load-bearing behaviour to monolithic glass panes with the same nominal thickness. However, the composite load-bearing behaviour is significantly influenced by time- and temperature-dependent stiffness of the polymer interlayer material, as well as the shear connection between the interlayer core and glass cover layers. Hence, an extended experimental study on the load-bearing behaviour of the innovative composite panels was performed. This paper presents the new product with possible applications for the building industry and introduces the ongoing development and investigation process for the novel glass–plastic-composite panels. Afterwards, the test methods and results for the conducted short- and long-term four-point bending tests are given. Subsequently, the behaviour of the composite panels is compared to conventional glass, and the insights are discussed. This also includes a study on potential material models and analytical simulations to extend the results to large-scale application. The high structural performance and lower self-weight at the same time paves the way for high transparent glass construction with slender substructures.
  PubDate: 2019-09-13
Stress whitening effects in transparent structural silicone adhesives
- Abstract: Abstract Stress whitening is a common effect in polymers where an increase in brightness or an increased opacity of the material can be observed under mechanical loading. Investigating the stress whitening effect for the transparent structural silicone adhesive (TSSA), this effect occurs in different forms depending on the applied deformation. The intensity and appearance of whitening in TSSA depends decisively on the type of loading, i.e. under isochoric deformation a spot-wise whitening can be observed, whereas under volumetric loading a very dense, cloud-like whitening becomes visible. In order to clarify why the stress whitening effect occurs at all, experimental investigations are carried out on uniaxial cyclic tensile tests and constrained tensile tests. The special feature of the uniaxial cyclic tensile tests is that they are performed in a miniature tensile testing machine, which is positioned under a light microscope. This makes it possible to observe stress whitening during cyclic deformation at a micro-scale. Furthermore, for the observation of whitening during constrained tensile tests, so-called pancake test are investigated and compared with the results of the uniaxial cyclic tensile tests. Since the whitening effect in the pancake test is in clear contrast to the uniaxial tensile tests, differences of both results are presented. Finally, the causes of both forms of whitening are defined and characterized.
  PubDate: 2019-08-29
Pseudo-elastic cavitation model—part II: extension to cyclic behavior of
transparent silicone adhesives
- Abstract: Abstract This study investigates the cyclic structural behaviour of adhesive joints of glass and metal using thin, structural silicone adhesives in heavily constrained applications. Based on cyclic uniaxial tensile tests on dog-bone and pancake test samples, the pseudo-elastic cavitation model from part I of this publication will be extended to describe two phenomenons: stress softening due to Mullins effect, as well as a mechanical hysteresis occurring under hydrostatic loading of rubber-like materials. This mechanical hysteresis under hydrostatic loading is associated with the growth and shrinkage of microscopic voids in the materials structure, and shows distinctive differences to the mechanical hysteresis known from isochoric test samples. In order to transfer the already presented pseudo-elastic cavitation model to describe the cyclic material behaviour, the isochoric part of the cavitation model is extended according to the classical theory of pseudo-elasticity to numerically describe stress softening under isochoric deformations. In addition, the volumetric part is provided with a special material formulation so that it can numerically reproduce the void growth hysteresis under cyclic volumetric tests, e.g. pancake tests. For validation, three-dimensional simulations of both cyclic tensile tests (dog-bone and pancake tests) are carried out.
  PubDate: 2019-08-27
Impact of glass technology on future electrical individual transportation:
the Pop.Up case study
- Abstract: Abstract Low driving range is one of the main obstacles for a larger market penetration of future autonomous Electric Vehicles (EV). Heating, Ventilation and Air Conditioning (HVAC) system size and consumption can lower the range of an EV from 5 to 50%, depending on the outside weather conditions, vehicle size, vehicle envelope characteristics and driving style. The present paper investigates the impact of vehicle transparent envelope design and characteristics on vehicle performance, that is EV driving range or HVAC size for internal combustion vehicles, considering traditional glazing solutions as well as switchable glazing technologies. Sensitivity analysis on vehicle transparent envelope properties was carried out by means of a lumped thermal model, tested in pull-down test and static summer conditions. The results show that by optimizing transparent envelope characteristics, the size of the HVAC system can be largely reduced (up to 25%) by maintaining even higher comfortable level inside the vehicle (maximum perceived temperature reduced by 10% and higher surface temperatures reduced by 55%). Air conditioning load reduction can impact the driving range for EV between 5 and 10%, depending on battery capacity and vehicle average consumption. Larger improvement could be achieved by optimizing the opaque part of the vehicle envelope as well. This result is particularly important for material and component manufacturer supplying the automotive industry, and could positively impact on a deeper penetration of EV in the mass market.
  PubDate: 2019-08-26
A probability model for evaluating the effectiveness of the Heat Soak Test
- Abstract: Abstract The potential presence of Nickel Sulfide (NiS), which contaminates glass melt, can provoke “spontaneous” rupture even after years from installation. This is why most standards recommend that glass panels bearing a safety risk are subjected to the Heat Soak Test (HST): they are exposed to a certain temperature for a certain time so to destroy the glass panes affected by critical NiS inclusions before installation. A micro-mechanically motivated model for assessing the risk of spontaneous failure of thermally-treated glass is here proposed. This correlates the statistical expectation of finding a critical NiS inclusion with the breakage consequent to its volumetric expansion due to phase transformation. Three functions à la Weibull for the probability of spontaneous rupture during lifetime are derived for the case of no HST, short HST and long HST. This analysis may contribute to solve the long-standing problem of defining the risk of spontaneous breakage in glass due to NiS inclusions, by assessing the optimal holding time of the HST as a function of the risk reputed acceptable for the particular application of glass. A parametric analysis shows the potentiality of the proposed approach.
  PubDate: 2019-07-11
Post-breakage in-plane stiffness of laminated glass: an engineering
approach
- Abstract: Abstract In the post-breakage phase, laminated glass (LG) can maintain a residual load-bearing capacity due to the tension stiffening of the polymer through the adhesion with the shards, but the determination of the overall post-breakage stiffness presents formidable difficulties. A simple model is here proposed for the in-plane response of broken thermally treated LG, characterized by a fine cracking pattern. A simple formula for the effective post-breakage stiffness under in-plane loading is provided, which depends upon interlayer modulus and amount of delamination. Comparisons with numerical experiments confirm its accuracy for interpreting the response of representative portions of broken LG, composed by a large number of glass fragments, for different shapes of the glass shards and for different amount of delamination. The proposed model may represent an useful practical tool for evaluating the post-critical response of LG under in-plane loading, in particular under shear. This may be of crucial importance in view of possible applications of LG-based elements as structural shear-resistant transparent diaphragms for the seismic retrofitting of historical monuments. Glass-based bracings shall be designed to remain sound under moderate earthquakes; they can possibly break under the most severe seismic events, but always in a ductile manner while dissipating energy, thanks to the hysteretic response of broken LG consequent to progressive delamination.
  PubDate: 2019-07-10
Welcome to the world of glass!
- PubDate: 2019-07-01
Sustainable facade design for glazed buildings in a blast resilient urban
environment
- Abstract: Abstract In facade construction the glazed elements have always been considered the most critical components for the minimization of hazards during a blast event. In today’s blast events, terrorists have changed their mode of action and targets where the glass performance is weak have become even more of a concern. Therefore counter-terrorism offices (such as in the UK) have been introducing design guidelines for crowded places, making a compromise between safety and sustainability. This paper describes how it is possible to achieve a resilient urban environment, where glass is still the dominant element of the architectural scope making use of glazed facade systems with excellent blast protection performances. Novel façade systems have recently been developed by means of effective simulation techniques. The numerical tools recognize, enhance and balance the already existing façade capacity to resist the blast loads and take into account the fundamental dynamic interactions between all façade elements. In this way, innovative façade components (such as curtain walling brackets) have been developed which have the ability to upgrade conventional or lightly enhanced glass facade systems to higher blast protection levels.
  PubDate: 2019-07-01
Investigating the strength effects of drilling in tempered glass
- Abstract: Abstract The tempering process introduces a residual stress field to the glass that only allows a drilling depth of approximately \({20}{\%}\) of the thickness (compressive zone) before fragmentation will be initiated. The present paper investigates post-drilled holes in tempered glass that can be used for a novel assembling technique leading to an increased accuracy in the connection and avoiding custom made solutions with holes drilled prior to tempering. The partly drilling is first studied experimentally measuring the change in strains (stresses) on the surface close to the hole as function of drilling depth. These data are then further used to validate a finite element model capable of describing the redistribution of residual stresses around the hole for several geometric variations such as depth, diameter, rounding and inclination. Above all, the numerical study shows an increase in the apparent strength (The term “apparent strength” is used for the strength originating from both the material strength and the residual stress state) of the hole. Furthermore, it is seen that drilling into the compressive zone only, will not lead to any tensile stresses at the surface of the hole. As the drilling process will damage the glass around and inside the hole, hence decreasing the strength, an etching technique is finally given to post-improve the quality of the hole surface locally. After 6 h of local etching with ammonium hydrogen fluoride \((\hbox {NH}_{4}\hbox {HF}_2)\) , an increase in strength of about \({310}\,{\%}\) is observed. Increasing the etching time further, with the given acid and concentration, is shown not to yield any further (significant) increase in the strength.
  PubDate: 2019-07-01
Experimental determination of failure strength in automotive windscreens
using acoustic emission and fractography
- Abstract: Abstract 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.
  PubDate: 2019-07-01
An experimental investigation of the flexural strength of
soda–lime–silica glass at high loading rates
- Abstract: Abstract A novel ring-on-ring test setup was developed for investigating the biaxial flexural strength of small circular soda–lime–silica glass specimens at high loading rates in a high-speed test rig. Such rate effects becomes important when designing for extreme events such as impact and blast, which are highly relevant for glass used in e.g. façades. The investigation focused on two groups of specimens with different surface conditions: as-received and pre-damaged with a well-defined flaw. A total of 151 specimens were tested in order to evaluate the influence of loading rate and surface condition on the flexural strength. Quasi-static and dynamic experiments were performed at loading rates ranging between 2 and \(5.6\times 10^6\hbox { MPa/s}\) . An 85% increase in strength with loading rate was observed for the ‘as-received’ specimens and 52% for the ‘pre-damaged’.
  PubDate: 2019-07-01
The flexural response of large scale steel-framed composite glazing panels
- Abstract: Abstract Novel composite glazing panels provide an opportunity to significantly reduce the weight and depth of glazed facades and simultaneously minimize the visual and spatial bulkiness of conventional facade framing systems. However the mechanical response of these novel composite glazing panels is poorly understood and there is no published data on the flexural response of large scale panels. In this research, medium scale (700-mm long and 300-mm wide) and large scale (3500-mm long and 1500-mm wide) composite glazing panels were fabricated and tested in bending up to failure. Recently developed analytical model for composite sandwich panels was also implemented on the medium and large scale panels. The experimental test data shows that shear-lag effects can be significant in large scale panels and can reduce their effective widths by about 40%. The analytical model provided a good fit of experimental results when the effective width was reduced according to strain gauge measurements. Neglecting shear-lag effect is unsafe and would underestimate deflections and stresses by approximately 40%. Further research is required to quantify the shear-lag effects, and the corresponding variation of effective widths, along the length of composite glazing panels and the influence of load distribution and boundary conditions on the effective thickness of the glass panels.
  PubDate: 2019-07-01
Subdivided switchable sun protection glazing
- Abstract: Abstract The façade, as an interface between the interior and the exterior environment, performs multiple tasks. On one hand it has to ensure the highest possible comfort for building occupants, on the other hand it should contribute to minimizing the energy demand of the building. The detailed requirements on a façade depend on its orientation, local climatic conditions and the building use. Since surrounding conditions vary, an invariant façade system cannot react properly to this variability. In order to overcome this limitation, the authors are developing a switchable glazing unit with adjustable light and energy transmission properties. The functional principle is based on the use of liquid crystal materials. The main component of the switchable glazing is a thin switchable cell which is embedded in an insulating glazing unit. The cell area can be substructured into independently tintable pixels. This ensures maximum utility of the glazing. Currently, a prototype glazing is investigated under real conditions. A floor-to-ceiling glazing is assembled using small sized cells (310 mm \(\times \) 286 mm) arranged in nine rows and six columns. The cell size is currently limited by the restrictions of the available production capabilities. However, cell integration in other insulating glazing units is possible as well. An effective daylight and shading control can be provided within these glazing units. In order to enhance the effectiveness of the system, the authors are developing different control strategies. The switchable glazing system and its simulation-based performance analysis will be presented in the paper.
  PubDate: 2019-07-01
Relationship between strain energy and fracture pattern morphology of
thermally tempered glass for the prediction of the 2D macro-scale
fragmentation of glass
- Abstract: Abstract This work deals with the prediction of glass breakage. A theoretical method based on linear elastic fracture mechanics (LEFM) merged with approaches from stochastic geometry is used to predict the 2D-macro-scale fragmentation of glass. In order to predict the fragmentation of glass the 2D Voronoi tesselation of distributed points based on spatial point processes is used. However, for the distribution of the points influence parameters of the fracture structure are determined. The approach is based on two influencing parameters of fragment size \(\delta \) and fracture intensity \(\lambda \) , which are described in this paper. The Fragment Size Parameter describes the minimum distance between the points and thus the size of a fragment. It is derived from the range of influence of the remaining elastic strain energy in a single fragment taking into account the LEFM based on the energy criterion of Griffith. It considers the extent of the initial elastic strain energy \(U_0\) before fragmentation obtained from the residual stress as well as a ratio of the released energy \(\eta \) due to fragmentation. The Fracture Intensity Parameter describes the intensity of the fragment distribution, and thus the empirical reality of a fracture pattern. It can be obtained by statistical evaluation of the fracture pattern. In this work, the fracture intensity is determined from the experimental data of fracture tests. The intensity of a fracture is the quotient of the number of fragments in an observation field and its area and is assumed to be constant in the observation filed. The fracture intensity and the correlation between a constant intensity and the Fragment Size Parameter was determined. The presented methodology can also generally be used for the prediction of fracture patterns in brittle materials using a Voronoi tesselation over random fields.
  PubDate: 2019-07-01
Engineering design of laminated safety glass considering the shear
coupling: a review
- Abstract: Abstract The use of glass and, in particular, laminated glass (LG) in the building industry is a continuously rising trend. Thus, in order ensure a safe fracture and a post-breakage load bearing capacity but still be economical, the consideration of the shear transfer by the polymeric interlayer between the glass panes is gaining importance in the structural design. This also relates to future European harmonised product and design standards in glass construction. In addition to simple models using particular shear modulus values for certain load situations and temperatures, linear viscoelastic material models for the interlayer can be applied for more complex design situations. We present the basics of mechanical modelling of the time- and temperature dependent material behaviour of polymers used in LG. The procedure for the experimental determination of the material parameters is explained for the most common product polyvinyl butyral. For practical application in glass design, different standards (national and international) and other building regulations are compared. The analysis of the compliant composite shows that already low shear modulus values lead to a significant reduction in glass stresses. Finally, a comparative example shows the design of laminated glass considering the shear transfer with different methods.
  PubDate: 2019-07-01
Experimental investigations on the creep behaviour of PVB under different
temperatures and humidity conditions
- Abstract: Abstract The use of structural glass applications with requirements on post-fracture performance has so far only been possible under consideration of large-scale tests. The development of a design concept for fractured laminated glass is the subject of current research in structural glass engineering. This requires material models for the respected components (glass and polymer interlayer). Since moisture can reach the polymer interlayer in the fractured state via the cracks in the glass, investigations on the mechanical behaviour of the interlayer at different air humidity levels are necessary. In order to obtain the first systematically recorded parameters for the material behaviour of the most common polymeric interlayer used in laminated glass, standard Polyvinylbutyral (PVB), a test set up was developed for carrying out creep tests at different levels of load, humidity and temperatures. Subsequently, tests were conducted which were evaluated with the help of Digital Image Correlation. The results show that the stiffness of the interlayer decreases significantly with increasing relative humidity and temperature. Based on the data obtained, material models can be developed which take into account the influence of the interlayer moisture on the post fracture performance of laminated glass. Analogously to the time temperature superposition principle it can be shown, that the application of a time humidity superposition principle is possible and standard PVB is approximately a moisture rheological simple material.
  PubDate: 2019-06-03
Glass is all around us!
- PubDate: 2019-01-01
Experimental investigation of mortar mechanical properties for glass brick
masonry
- Abstract: Abstract The main advantage of solid bricks over hollow blocks is substantially higher compressive strength. On the other hand, solid bricks have much higher thermal conductivity, which would lead to major heat loss when used for exterior walls. Masonry pillars and walls are usually loaded in compression and/or bending resulting from the eccentricity of vertical load or wind load. In case of solid glass bricks, compressive strength is about ten times higher than tension strength therefore the limiting factor of the glass masonry is tensile stress resulting from the bending. Whether compared to ceramic or concrete bricks masonry, the glass bricks have a smooth and non-absorbent surface and the adhesion of the mortar to the glass surface is the critical parameter. Presented paper is focused on the experimental investigation of mortar applicable for glass brick masonry with regard to use for load bearing brick walls or columns. Shear, compression and tension tests have been recently performed. Shear and tension resistance and failure modes of brick bed joint were determined during series of tests using various mortar composition, two types of surface treatment and different thickness of the mortar joint. Significant influence of the joint thickness on the resistance was found. The compression tests were performed on two small pillars to determine the compression resistance and failure mode of glass bricks walls and pillars. In parallel to these tests, several small-scale tests have been performed to determine flexural and compressive strength of hardened mortar.
  PubDate: 2019-01-01