Feasibility study of structural systems made from ceramics

The objective of this paper is to investigate the feasibility of making structural systems from ceramics. Segmental and composite systems are quantitatively studied, partial application of ceramics to traditional systems is considered, and the special application of a lunar base is studied. The quantitative and qualitative studies made indicate both advantages and disadvantages for ceramics in structural systems. However, the structural systems proposed may stimulate further studies to eliminate the disadvantages. In a previous paper the authors 1 made a qualitative analysis of the applicability of advanced ceramics to construction based on a set of criteria; the results indicated both advantages and disadvantages in their use. To understand clearly and quantitively the performance of advanced ceramics for construction, it was suggested that structural systems in which the unique properties of advanced ceramics could be optimally utilized should be developed. In this paper feasible structural systems for ceramics are investigated and the future utilization and mechanical performance of ceramics in construction are considered. Candidate materials The mechanical properties of typical ceramics are given in Table 12. Examples 1 and 2 represent high-performance ceramics: lithium aluminosilicate and silicon carbide, respectively. This table shows the considerable advantages of certain properties of ceramics over those of concrete and steel, indicating the potential of structural systems made from ceramics. However, the mechanical properties of monolithic ceramics are not adequate for use in structural systems because monolithics are brittle materials that usually fail abruptly without giving much warning in advance. Moreover, owing to their brittleness, the strength of ceramics is very sensitive to the flaw size in the material. Ceramic parts made from the same matedal may thus have very different strengths, making ceramics materials of low reliability. So ceramic toughness must be improved for structural systems. There are several ways of improving ceramic toughness, but fibre reinforcement is by far the most effective means 3. It has been shown that continuous-fibre reinforcements can greatly improve the reliability of ceramics because the sensitivity of first-cracking strength to flaw size is significantly reduced '~ (first-cracking strength is the applied tensile stress at which an inherent flaw will propagate unstably across the whole section of the material). After first-cracking, the bridging of the crack by fibres allows the material to take further load. With increased loading, multiple cracks form, producing a pseudo-strain-hardening affect similar to that in metals 4. 5. 7 This quasi-ductility provides a warning before final failure and also allows for strsss rsdiadbution to less severely loaded parts. While continuous-fibra-reinforced ceramics have been shown to possess the desirable properties described, their use has been limited to parts of relatively simple geometric shape because it is very difficult and costly to construct continuous-fibre-rainforcing mesh for complex shapes. However, short fibres can be mixed with ceramic powders and formed into any shape by traditional POwder compaction techniques. * Department of Civil Engineering, MIT, Cambridge, MA 02139, USA. (On leave from Shimizu Corporation, Tokyo, Japan) ** Department of Civil Engineering, University of Michigan, Ann Arbor, MI 48109-2125, USA Table 1 Mechan ica l proper t ies Ceramics" Example Example Concrete Steel 1 2 Density,P 2.2 2.3 7.9 (Mg m -3) Compressive 130