On the relationship between ceramic strength and the requirements for mechanical design |
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Affiliation: | 1. Institut für Struktur- und Funktionskeramik, Montanuniversität Leoben, A-8700 Leoben, Austria;2. Materials Center Leoben, A-8700 Leoben, Austria;1. Nanjing Research Institute of Electronics Technology, No.8 Guorui Road, Nanjing 210039, China;2. School of Materials Science and Engineering, Harbin Institute of Technology, 92 West Da-Zhi Street, Harbin 150001, China;1. Institut für Struktur- und Funktionskeramik, Montanuniversitaet Leoben, Peter-Tunner Strasse 5, A-8700 Leoben, Austria;2. Materials Center Leoben Forschung GmbH, Roseggerstrasse 12, A-8700 Leoben, Austria;3. National Physical Laboratory, Teddington, Middlesex, TW11 0LW, United Kingdom;1. Institut für Struktur- und Funktionskeramik (ISFK), Montanuniversität Leoben, Peter Tunner Strasse 5, A-8700 Leoben, Austria;2. National Physical Laboratory, Teddington, Middlesex TW11 0LW, United Kingdom;1. Institute of Physics, Johannes Gutenberg University Mainz, Staudingerweg 7, 55128, Mainz, Germany;2. Department of Physics, Humboldt University of Berlin, Newtonstraße 15, 12489, Berlin, Germany;3. Institute of Quantum Optics, University of Hanover, Welfengarten 1, 30167, Hannover, Germany;4. Ferdinand-Braun-Institut, Leibniz-Institut für Höchstfrequenztechnik, Gustav-Kirchhoff-Str. 4, 12489, Berlin, Germany;5. The Center of Applied Space Technology and Microgravity (ZARM), University of Bremen, Am Fallturm 2, 28359, Bremen, Germany;6. Institute of Laser Physics, Universität Hamburg, Luruper Chaussee 149, 22761, Hamburg, Germany |
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Abstract: | During the last fifty years the mechanical properties of ceramic materials have been greatly improved, their toughness and strength have been increased and the scatter of strength decreased. Adequate statistical design procedures for brittle materials exist but cracking and brittle fracture of ceramic components still occur very often.In this review the theory of brittle fracture and the underlying assumptions are critically discussed and the measurement procedures of strength are reviewed. It is shown that the strength of materials, the strength of specimens and the strength of components are often quite different properties. Three main factors are identified which – in order to avoid unexpected failure of components – have to be considered much more than in the past: (i) hidden stresses, i.e. stresses caused by thermal strain mismatch, by contact (for example in joints) and internal stresses, (ii) the quality of the component's surfaces and edges and (iii) proper handling of ceramic materials and components.It can clearly be stated that the mechanical properties of many ceramic materials are appropriate even for applications under severe loading conditions but bad or incomplete mechanical design, insufficient surface finish and mishandling are the main reasons for unexpected failure of ceramic components. |
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Keywords: | Mechanical reliability Strength Brittle fracture Fracture statistics Tensile stresses |
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