The use of laminated glass in structural glass construction has become increasingly important in recent decades. By combining glass layers with a polymer interlayer, the glass fragments remain connected to the interlayer in case of breakage and a certain residual load-bearing capacity is available. Knowledge of the material behaviour of the interlayer is of elementary importance both in the intact and fractured state. Currently, polyvinylbutyral (PVB) is the most common type of interlayer and is the subject of the investigations carried out here.
The investigation of the intact state of a laminated glass is the subject of the first part of this thesis. In the intact state, the determination of the time- and temperature-dependent shear modulus of the polymer interlayer is the essential parameter to be investigated for the design. For this purpose, experiments can be performed on the pure interlayer, which have to be validated by large scale tests on laminated glass. A test and evaluation methodology for the execution of such large scale tests as bending and torsion tests is described and discussed in detail. The influence of measurement errors is also discussed and it is shown that the influence is not linear over the shear modulus range. The results can be used for a future calibration of a partial safety factor for PVB.
In the second part of this thesis the fractured state of a laminated glass is investigated in more detail. Here, the number of factors influencing the load-bearing behaviour increases. The deformation of the glass structure can become so large that the strain in the interlayer exceed the linear viscoelastic range. By means of relaxation tests at large strains it can be shown that the time dependence stays linear even for large strains. Only the individual spring stiffnesses in the generalized Maxwell model have to be adjusted outside the linear range.
Furthermore, moisture can reach the interlayer via cracks in the glass. Since PVB is a hygroscopic material, moisture is absorbed, which leads to changes in the stiffness behaviour. Creep tests at different humidity levels indicate that PVB has a moisture rheological simple material behaviour. Analogous to the time-temperature superposition principle (TTSP), a time-humidity superposition principle is introduced for PVB. Comparable to an increase in temperature, increased humidity leads to a significant reduction in the stiffness of PVB.
In addition to these investigations on the pure interlayer, the post-fractured state is investigated by means of tests on laminated glass. For this purpose, a holistic test approach is pursued, in which various tests are carried out on the same test specimen. Through-Crack-Bending (TCB) tests clarify the influence of the adhesion of the interlayer, the temperature, the load level and the glass thickness. Depending on the crack pattern in the laminated glass, it can be shown that both too high and too low adhesion can have a negative effect on the post-fracture performance. Furthermore, it can be shown that in the offset between two cracks, delamination phenomena occur due to a pure shear stress state. This observation can be validated by shear tests on specimens taken from the TCB specimens. In addition, pummel tests are performed on the TCB specimens with the aim of quantifying the post-fracture performance of a laminated glass by means of a simple test. Overall, the results of the three tests correlate only conditionally with regards to the failure duration in the TCB test, maximum adhesive shear strength in the shear a laminated glass via one of the tests is difficult to realise. However, the results can be used to develop an explicit numerical model of a broken laminated glass and illustrate the complexity of this topic.
In addition to these tests for the evaluation of broken laminated glass made of float or heat strengthened glass, uniaxial tensile tests are carried out on broken laminated glass made of fully-tempered safety glass. It can be shown that the glass fragments lead to stiffening effects of the system and should not be neglected in the design of broken laminated glass made of toughened safety glass. The characterisation of this material behaviour can be simplified by a trilinear material model.
Finally, the results are discussed in relation to current standards and suggestions for revising and supplementing the standardization are provided. «
The use of laminated glass in structural glass construction has become increasingly important in recent decades. By combining glass layers with a polymer interlayer, the glass fragments remain connected to the interlayer in case of breakage and a certain residual load-bearing capacity is available. Knowledge of the material behaviour of the interlayer is of elementary importance both in the intact and fractured state. Currently, polyvinylbutyral (PVB) is the most common type of interlayer and is... »
Fakultät für Bauingenieurwesen und Umweltwissenschaften