The student Asier Iglesias Sanchez obtained an 'OUTSTANDING' qualification

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The student Asier Iglesias Sanchez obtained an 'OUTSTANDING' qualification

THESIS

The student Asier Iglesias Sanchez obtained an 'OUTSTANDING' qualification

2022·04·11

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Thesis title: Methodology for assessing the in-service behavior of glass plates considering the effect of residual stresses.

Court:

  • Chairmanship: Eugenio Giner Maravilla (Universidad Politécnica de Valencia)
  • Vocal:Antti Aronen (Glaston Finland)
  • Vocal:Miguel Muñiz Calvente (Universidad de Oviedo)
  • Vocal: Joanes Berasategi Arostegi (Mondragon Unibertsitatea)
  • Secretary:Iñigo Llavori Osa (Mondragon Unibertsitatea)

Abstract:

The structural performance of glass mainly depends on the surface quality and the residual stress state. Surface damage produced during the manufacturing process or subsequent handling, might lead to the presence of microscopic flaws on the surface. The opening or propagation of these microscopic flaws reduce the strength of glass. For this reason, glass is most often tempered before being employed as a structural material. Tempering techniques bring about non-uniform heat transfer rates, which lead to non-homogeneous residual stresses, having a direct impact on the structural behaviour of components. Moreover, once glass is ready to use, its fracture behaviour tends to present significant differences between measured strength values. This results in the need for extensive experimental work, especially if non-uniform residual stresses need to be considered. Thus, this thesis presents a numerical methodology to predict the in-service behaviour of glass plates subjected to bending loads considering the residual stresses developed as a result of non-uniform cooling processes.

First, a numerical methodology based on a Fluid-Structure Interaction (FSI) one-way approach is proposed to consider the influence of non-uniform cooling techniques on the residual stress development during the thermal tempering process. Results show that local flow phenomena during heat treatment process play a vital role in residual stress development in glass plates. In line with this approach, efforts were made to reduce the computational time of the involved calculations. For this purpose, the influence of volumetric radiation and the viscoelastic behaviour of glass were analysed. As a result, a decrease of around 87\% of the computational time with respect to the initially proposed procedure was achieved. The results were in good agreement with both, experimental measurements in laboratory case studies and an industrial tempering case study published in the literature.

Secondly, a statistical-numerical procedure to predict the failure probability of structural glass components is presented. To this end, statistical assessment based on the Generalised Local Model (GLM) was carried out. Bending loads, which may result from the effect of wind, snow or the weight of pedestrians, are considered the main loads acting on structural glass plates. Therefore, plates exhibiting different residual stress conditions subjected to bending loads were analysed. The most striking observation to emerge from the analysis was the transferability between the failure cumulative functions of annealed and tempered glass, with the latter exhibiting different residual stress patterns. A master Primary Failure Cumulative Damage Function (PFCDF) was also calculated by jointly assessing the results of the experimental tests. This enables a more reliable prediction of the fracture behaviour of annealed and tempered glass. Overall, average relative differences between the predicted and experimental data were below 10\%. Finally, particularly noteworthy was the scatter band of the experimental results. Given this spread, statistical evaluation can be considered essential for designing or assessing structural pre-stressed components.