Issue 30

L. Guerra Rosa et alii, Frattura ed Integrità Strutturale, 30 (2014) 438-445; DOI: 10.3221/IGF-ESIS.30.53 438 Focussed on: Fracture and Structural Integrity related Issues Integrated assessment procedure for determining the fracture strength of glass components in CSP systems L. Guerra Rosa, J. Cruz Fernandes, B. Li ICEMS & Dept. of Mechanical Engineering, Instituto Superior Tecnico Universidade de Lisboa, Av. Rovisco Pais, 1049-001 Lisboa, Portugal luisguerra@ist.utl.pt , cruz.fernandes@ist.utl.pt , bli@ist.utl.pt A BSTRACT . 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. K EYWORDS Probabilistic model; Fracture strength; Structural glass; Reliability; Concentrated solar power (CSP). I NTRODUCTION mprovements in production and refining technologies such as tempering and the production of laminated glass enabled glass to carry more substantial superimposed loads and therefore achieve a more ‘structural’ role [1]. Especially, the glass components play important role in some new energy industries such as the concentrated solar power (CSP) systems, etc. This gives impetus to studies on the mechanical behaviour of these materials and, in particular on their ability to resist fracture. I