Abstract
The structural integrity and reliability of glass components are key issues for concentrated solar power (CSP) systems. For example, the glass windows in a solar furnace may suffer catastrophic fracture due to thermal and structural loadings, including reaction chamber pressure cycling. Predicting design strength provides the basis for which the optical components and mounting assembly can be designed so that failure does not occur over the operational lifetime of a given CSP system. The fracture strength of brittle materials is dependent on the size and distribution of cracks or surface flaws. Due to the inherent brittleness of glass resulting in catastrophic failure, conservative design approaches are currently used for the development of optical components made of glass, which generally neglect the specific glass composition as well as subcritical crack growth, surface area under stress, and nature of the load – either static or cyclic – phenomena. In this paper, several methods to characterize the strength of glass are discussed to aid engineers in predicting a design strength for a given surface finish, glass type, and environment. Based on the Weibull statistical approach and experimental data available on testing silica glass rod specimens, a theoretical model is developed for estimating their fracture strength under typical loading conditions. Then, an integrated assessment procedure for structural glass elements is further developed based on fracture mechanics and the theory of probability, which is based on the probabilistic modelling of the complex behaviour of glass fracture but avoids the complexity for calculation in applications. As an example, the design strength of a glass window suitable for a solar furnace reaction chamber is highlighted.
Highlights
I mprovements in production and refining technologies such as tempering and the production of laminated glass enabled glass to carry more substantial superimposed loads and achieve a more ‘structural’ role [1]
Based on the Weibull statistics and experimental data obtained from testing silica glass rod specimens with diameters between 0.5 and 1 mm [14], a theoretical model was developed for estimating their fracture strength under different loading conditions [15]
In 2001, Porter [6] proposed the Crack Size Design method (CSD); and in 2006 Haldimann [4] developed the Lifetime Prediction Model (LPM) where he calculated directly the failure probability of a glass element starting from the probability distribution of its defects and from the deterministic knowledge of loading time-history [4]
Summary
I mprovements in production and refining technologies such as tempering and the production of laminated glass enabled glass to carry more substantial superimposed loads and achieve a more ‘structural’ role [1]. Based on the Weibull statistics and experimental data obtained from testing silica glass rod specimens with diameters between 0.5 and 1 mm [14], a theoretical model was developed for estimating their fracture strength under different loading conditions [15]. For engineering applications, the complexity of calculation procedures needs to be simplified reasonably The motivation for this present work is to develop an integrated approach for analyzing the crack problem of the glass components in the CSP industry, to incorporate the probabilistic modelling, the principles of fracture mechanics and the details of the specific design in question. One design strength diagram may be created from the above procedures and the time-to-failure versus equivalent stress curves as a function of the survivability probability (or reliability) can be shown in the diagram, which will be very helpful for the design processes as presented
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