Monolithic and laminated glass under extreme loading conditions: Experiments, modelling and simulations
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Design of glass components has become more challenging over the past few decades, owing to the increased use of glass as a structural material. When a structure is required to withstand extreme loading, such as blast or impact, the design process becomes all the more difficult. The work of this thesis aims to facilitate more predictive glass design, and focuses on the development of numerical tools that can predict the structural capacity of glass components under various loading conditions. Glass components designed against extreme loading are often made from laminated glass, i.e., a sandwich structure including a polymeric interlayer. Thus, the work of this thesis also considers laminated glass, as well as regular monolithic (non-laminated) glass. Glass is a brittle material that fails in a sudden manner, and has a highly stochastic fracture behaviour. Fracture initiation in monolithic glass typically induces complete failure, but laminated glass is able to maintain some structural integrity also after glass fracture due to properties of the polymeric interlayer. Thus, the numerical work is divided into two parts. The first part aims to predict the fracture initiation of glass, with special emphasis on the probabilistic fracture strength of glass components. In the second part, we investigate the possibility of describing the post-fracture behaviour in finite element (FE) simulations. In an effort to validate the numerical tools, we perform an extensive experimental study using different setups and loading rates, including various geometries of the glass specimens. In this study, the glass and polymer material is limited to annealed soda-lime-silica float glass and polyvinyl butyral (PVB), respectively. The thesis consists of four individual parts in the form of journal articles, in addition to a synopsis. The synopsis includes the motivation and background of the thesis, the objectives and scope, along with a summary of the four parts, and an overall conclusion and suggestions for further work. Part 1 of the thesis presents a strength prediction model (SPM), which aims to predict the probabilistic fracture strength of glass under various loading conditions. The SPM is based on the notion of microscopic surface flaws, in which fracture in glass typically initiates. Three different experimental test series were performed for validation of the SPM, including quasi-static four point bending tests, quasi-static pressure tests and blast-pressure tests on monolithic glass. The blast-pressure tests were performed in the SIMLab Shock Tube Facility. The experiments demonstrated the stochastic fracture behaviour of glass by means of a varying fracture strength and position of fracture initiation. In addition, the fracture strength proved to be dependent on the experimental setup and the geometry of the glass specimens. The SPM was able to recreate many of the trends from the four-point bending tests, and managed to reproduce the fracture behaviour of the pressure tests reasonably well. However, further studies on loading rate dependency on the fracture strength were deemed necessary. Part 2 presents an experimental study on the response of laminated glass exposed to fragment impact before blast loading. The blast pressure was produced in the SIMLab Shock Tube Facility, while fragment impact was mimicked by 7.62 mm armour-piercing bullets or drilled holes. Blast tests on laminated glass excluding fragment impact were also performed as a reference. It was found that the safety and structural integrity of the laminated glass against blast loading are significantly reduced if the glass is damaged by fragments beforehand. Part 3 presents a numerical study on the post-fracture behaviour of blast-loaded monolithic and laminated glass using non-linear explicit FE simulations. The simulations applied novel numerical techniques, such as higher-order elements and node splitting. The simulations were compared to blast experiments conducted in the SIMLab Shock Tube Facility. The experiments on laminated glass demonstrated a progressive failure response, which depends on the fracture initiation in the glass. The simulations of both monolithic and laminated were in good agreement with the blast tests, revealing the potential of the employed numerical techniques. Part 4 deals with the probabilistic fracture strength of glass through an experimental and numerical study. In the numerical part, we propose an extension of the SPM, in which the loading-rate dependency of the fracture strength of glass is considered. To validate the rate-dependent SPM, we performed an extensive experimental study including quasi-static punch tests and low-velocity impact tests on monolithic and laminated glass. The experimental work demonstrated again the stochastic fracture behaviour of glass by a variation in fracture load and position of fracture initiation. The predictions obtained with the rate-dependent SPM were in general in good agreement with the experiments, and provided a realistic rate enhancement of the fracture strength.
Has partsPaper 1: Osnes, Karoline; Børvik, Tore; Hopperstad, Odd Sture. Testing and modelling of annealed float glass under quasi-static and dynamic loading. Engineering Fracture Mechanics 2018 ;Volum 201. s. 107-129 https://doi.org/10.1016/j.engfracmech.2018.05.031
Paper 2: Osnes, Karoline; Dey, Sumita; Hopperstad, Odd Sture; Børvik, Tore. On the dynamic response of laminated glass exposed to impact before blast loading. Experimental mechanics 2019 ;Volum 59.(7) s. 1033-1046 - Springer US, Published in cooperation with SEM, © Society for Experimental Mechanics 2019 https://doi.org/10.1007/s11340-019-00496-1
Paper 3: Osnes, Karoline; Holmen, Jens Kristian; Hopperstad, Odd Sture; Børvik, Tore. Fracture and fragmentation of blast-loaded laminated glass: An experimental and numerical study. International Journal of Impact Engineering 2019 ;Volum 132. s. 1-17 - Attribution 4.0 International (CC BY 4.0) https://doi.org/10.1016/j.ijimpeng.2019.103334
Paper 4: Osnes, K., Hopperstad, O.S., Børvik, T. (2019). Rate dependent failure of monolithic and laminated glass: an experimental and numerical study