Flat glass is used in many applications such as window glazing, whereas curved and bent glass is rising in its applications nowadays as well. Innovative ways of bending glass have been further developed in the past 25 years, and bending glass by laser-induced heat has been developed and discovered in 2017. This technique allows, at this moment in time, for bending glass around corners of up to 90 degrees with radii less than 10mm and is able to sag various forms out of plane. The structural properties, such as the stiffness, strength, and failure mechanisms of this laser-formed glass, have not been investigated thoroughly yet. This results in the product still being in the development phase, instead of already being available on the market and applicable in construction projects.
In the search for the use of sustainable and less raw materials in buildings, laser-forming might directly impact the latest goal. Flat geometries are structurally unfavourable, so the hypothesis states that laser-forming flat glass increases the inertia. This thesis aims to confirm the assumption of creating stiffer glass by using laser-forming techniques, the opportunity to reduce material, and to be able to predict the behaviour of laser-formed glass in Finite Element Method (FEM) programmes. Both lab-experiments and numerical analyses were performed to obtain results on these objectives.
The thesis starts with a parameter study on the influence of different cross-sectional parameters on the stiffness. The second moment of area (inertia) relates to the stiffness of the cross-section and four different parameters have been checked by its influence. The thickness of the web is directly related to the total height of the sample, as a deeper elevation induces larger necking of the web, resulting in thinner glass. The influence of this necking phenomenon is, therefore, investigated and described.
Subsequently, a design for a two-sided supported glass panel is manufactured with an implemented laser-formed elevation to perform an experimental study. By implementing this laser-forming technique, the total height of the samples went from 4mm to a maximum of 12mm, while retaining the same amount of material. The laser-formed glass panels were tested in a four-point bending test setup. Four flat samples were first tested to obtain reference values for the stiffness of the glass. Subsequently, the laser-formed sample sets were tested.
A numerical research is performed to simulate and predict the behaviour of the laser-formed glass. FEM-models have been used to compare the numerically derived deformations and therefore the stiffness of the panels, with the results of the four-point bending tests. In addition, the FEM-models were used to obtain numerically derived stresses at the points of failure. Individual and nominal models have been created to obtain insight into the need for individual models.
The results of this research conclude that the increase in stiffness shows nearly the same behaviour as the increase in cross-sectional inertia. The effect of laser-forming is therefore immediately visible in the stiffness properties of the glass. The laser-forming process of glass is able to convert the stiffness properties of an originally 3.87mm panel to meeting the properties of an equivalent thickness of 8.3mm thick flat glass panel. The stiffness showed predictable behaviour in the FEM-models, whereas the (failure) stresses showed a harder predictability. The presence of necking showed to be an influence in predicting the failure behaviour and needs to be taken into account when designing with laser-formed glass. Individual models are needed in order to visualise the different failure mechanisms in the FEM-models.
A comparison-study is performed to theoretically increase the size of a laser-formed glass panel and the stiffness properties and the bending stresses are checked. The stiffness and stresses are compared to regular flat glass panels. For stiffness properties, the laser-formed glass panels are able to reduce the material use by 46%. Laser-formed glass is able to decrease a required equivalent flat thickness of 23.6mm to a laser-formed glass thickness of 14.5mm, when observing the bending stresses. A material reduction of 39%.