Glass is being increasingly used as a structural material. In particular, its favorable aesthetic qualities have made it popular with modern designers. The most recent developments have seen glass being used as major structural elements such as beams and columns. From the engineering viewpoint these new applications present a series of design problems which need to be addressed before a coherent and safe design philosophy can be achieved.
To date there has been much work on out-of-plane loading of glass, and in-plane loading of traditional materials is well described. However, there is little published advice on design for long term, in-plane loading of glass. In reality engineers have been borrowing design concepts from the two former areas to try and satisfy the latter. In this thesis it is demonstrated that this is not satisfactory, and a new “Crack Size Design” method is proposed.
Novel contact and fracture mechanics techniques are developed in the course of this thesis, which may also be applied to more general engineering problems. Of particular interest is the evaluation of the stress intensity factors for closed edge cracks in a half plane, and a description of their growth in a bulk compressible stress field. These techniques are used in an investigation of contact loading. Contact stresses are particularly important to glass design as glass is unable to flow plastic-ally to relieve high local stresses.
Hence “soft” inter layers are often inserted between the glass and the contacting material to facilitate stress redistribution. The problem of a rigid, square-ended punch loading glass via a perfectly linear elastic or rigid plastic inter layer is analyzed. The results for an edge crack under such loading conditions are then investigated and incorporated into the newly derived Crack Size Design philosophy.
Source: University of Oxford
Author: Mark Porter