Experimental and Numerical Peeling Investigation on Aged Multi-Layer Anti-Shatter Safety Films (ASFs) for Structural Glass Retrofit

Anti-shatter safety films (ASFs) are often used for structural glass applications. The goal is to improve the response of monolithic elements and prevent fragments from shattering. Thus, the main reason behind their use is the possibility to upgrade safety levels against the brittle failure of glass and minimize the number of possible injuries. However, the impact response of glass elements bonded with Polyethylene terephthalate (PET)-films and pressure sensitive adhesives (PSAs) still represents a research topic of open discussion. Major challenges derive from material characterization and asymmetrical variability under design loads and ageing. In particular, the measurement of interface mechanical characteristics for the adhesive layer in contact with glass is a primary parameter for the ASF choice optimization. For this reason, the present paper presents an experimental campaign aimed at calibrating some basic mechanical parameters that provide the characterization of constitutive models, such as tensile properties (yielding stress and Young modulus) for PET-film and adhesive properties for PSA (energy fracture and peel force). In doing so, both tensile tests for PET-films and peeling specimens are taken into account for a commercially available ASF, given that the peeling test protocol is one of most common methods for the definition of adhesion properties. Moreover, an extensive calibration of the Finite Element (FE) model is performed in order to conduct a parametric numerical analysis of ASF bonded glass solutions. Furthermore, a Kinloch approach typically used to determine the fracture energy of a given tape by considering a variable peel angle, is also adopted to compare the outcomes of calibration analyses and FE investigations on the tested specimens. Finally, a study of the effect of multiple aspects is also presented. The results of the experimental program and the following considerations confirm the rate dependence and ageing dependence in peel tests.

Remote Facial Expression and Heart Rate Measurements to Assess Human Reactions in Glass Structures

In engineering applications, human comfort fulfillment is challenging because it depends on several aspects that can be mathematically controlled and optimized, like in case of structural, energy, or thermal issues, and others. Major troubles can indeed derive from combined human reactions, which are related to a multitude of aspects. The so-called “emotional architecture” and its nervous feelings are part of the issue. The interaction of objective and subjective parameters can thus make the “optimal” building design complex. This paper presents a pilot experimental investigation developed remotely to quantify the reactions and nervous states of 10 volunteers exposed to structural glass environments. As known, intrinsic material features (transparency, brittleness, etc.) require specific engineering knowledge for safe mechanical design but can in any case evoke severe subjective feelings for customers, thus affecting their psychological comfort and hence behaviour and movements. This study takes advantage of static/dynamic Virtual Reality (VR) environments and facial expression analyses, with Artificial Intelligence tools that are used to measure both Action Units (AUs) of facial microexpressions and optical heart rate (HR) acquisitions of volunteers exposed to VR scenarios. As shown, within the limits of collected records, the postprocessing analysis of measured signals proves that a rather good correlation can be found for measured AUs, HR data trends, and emotions under various glazing stimuli. Such a remote experimental approach could be thus exploited to support the early design stage of structural glass members and assemblies in buildings.

On the Use of Cloud Analysis for Structural Glass Members under Seismic Events

Current standards for seismic-resistant buildings provide recommendations for various structural systems, but no specific provisions are given for structural glass. As such, the seismic design of joints and members could result in improper sizing and non-efficient solutions, or even non-efficient calculation procedures. An open issue is represented by the lack of reliable and generalized performance limit indicators (or “engineering demand parameters”, EDPs) for glass structures, which represent the basic input for seismic analyses or q-factor estimates. In this paper, special care is given to the q-factor assessment for glass frames under in-plane seismic loads. Major advantage is taken from efficient finite element (FE) numerical simulations to support the local/global analysis of mechanical behaviors. From extensive non-linear dynamic parametric calculations, numerical outcomes are discussed based on three different approaches that are deeply consolidated for ordinary structural systems. Among others, the cloud analysis is characterized by high computational efficiency, but requires the definition of specific EDPs, as well as the choice of reliable input seismic signals. In this regard, a comparative parametric study is carried out with the support of the incremental dynamic analysis (IDA) approach for the herein called “dynamic” (M1) and “mixed” (M2) procedures, towards the linear regression of cloud analysis data (M3). Potential and limits of selected calculation methods are hence discussed, with a focus on sample size, computational cost, estimated mechanical phenomena, and predicted q-factor estimates for a case study glass frame.

Spin glass behavior and magnetic boson peak in a structural glass of a magnetic ionic liquid

Glassy magnetic behavior has been observed in a wide range of crystalline magnetic materials called spin glass. Here, we report spin glass behavior in a structural glass of a magnetic ionic liquid, C4mimFeCl4. Magnetization measurements demonstrate that an antiferromagnetic ordering occurs at TN = 2.3 K in the crystalline state, while a spin glass transition occurs at TSG = 0.4 K in the structural glass state. In addition, localized magnetic excitations were found in the spin glass state by inelastic neutron scattering, in contrast to spin-wave excitations in the ordered phase of the crystalline sample. The localized excitation was scaled by the Bose population factor below TSG and gradually disappeared above TSG. This feature is highly reminiscent of boson peaks commonly observed in structural glasses. We suggest the “magnetic” boson peak to be one of the inherent dynamics of a spin glass state.

Novel Studies on Thermo-Mechanical Properties of Structural Glass with and without Lamination

The attractiveness of glass is something that occupied the world market with a unique claim. It has many applications that go beyond the provision of visual aesthetics, which includes a view of the inside and out. Due to extreme levels of clarity, structural glazing may be so transparent that it may go unnoticed by design or make a strong visual impact such as the focal point of a building. This paper focused on structural glass with various laminated/laminated conditions that were used to investigate the Dynamic Mechanical Properties. The storage modulus (G'), loss modulus (G'') and damping factor (tan delta) were determined at various levels, ranging from room temperature to elevated temperatures (250 °C) to understand the behavior of glass structure with and without laminated glass over a range of temperatures. The G' & G'' were tested to understand the effect of bonding, fracture behavior between the pure glass and laminated glass to observe the response with respect to temperature. Results are found that G' and G'' improve over a range of temperatures for laminated glass with enlightening fracture behavior. Laminated glass also has a major influence on the damping factor, but it also depends on the laminated thickness and materials. Thermo-Mechanical Properties of laminated glass are more improved, without affecting the transferability of glass.

Simplified Lateral Torsional Buckling (LTB) Analysis of Glass Fins with Continuous Lateral Restraints at the Tensioned Edge

Within multiple design challenges, the lateral torsional buckling (LTB) analysis and stability check of structural glass members is a well-known issue for design. Typical examples can be found not only in glass slabs with slender bracing members but also in facades and walls, where glass fins are used to brace the vertical panels against input pressures. Design loads such as wind suction give place to possible LTB of fins with LR at the tensioned edge and thus require dedicated tools. In the present investigation, the LTB analysis of structural glass fins that are intended to act as bracers for facade panels and restrained via continuous, flexible joints acting as lateral restraints (LRs) is addressed. Geometrically simplified but refined numerical models developed in Abaqus are used to perform a wide parametric study and validate the proposed analytical formulations. Special care is spent for the prediction of the elastic critical buckling moment with LRs, given that it represents the first fundamental parameter for buckling design. However, the LR stiffness and resistance on the one side and the geometrical/mechanical features of the LR glass members on the other side are mutually affected in the final LTB prediction. In the case of laminated glass (LG) members composed of two or more glass panels, moreover, further design challenges arise from the bonding level of the constituent layers. A simplified but rational analytical procedure is thus presented in this paper to support the development of a conservative and standardized LTB stability check for glass fins with LR at the tensioned edge.