New evaluations for multiaxial-stress properties of ceramic materials

This paper suggests some new evaluations for multiaxial-stress properties of ceramic materials. These evaluations include some that have been used for other kinds of materials, as well as others which have not been previously employed. In some cases, these methods represent modifications of existing evaluations. The paper is confined to macroscopic behavior based upon bulk laboratory specimens. The influences of volume, stress gradients and localized behavior are not considered here since considerable attention has recently been devoted to these questions. The important problem of fracture strength will not be considered since this property appears to be considerably influenced by localized microscopic behavior. However, new evaluations of remaining mechanical properties for states of combined stresses will be presented. These include elastic and plastic strength, stiffness, ductility, resilience and toughness. Emphasis on combined-stress properties was selected since recent critical reviews indicate the need for for such an evaluation. Part A of this paper outlines new experiments that are needed to evaluate the mechanical properties and to confirm theories proposed in Part B. In Part B of this paper, new macroscopic engineering-type theories for combined-stress behavior are presented for the first time. These theories attempt to predict combined-stress behavior from uniaxial tension and compression (or pure bending and compression) behavior. These theories provide for materials such as ceramics with different properties in tension and compression. A final section of this presentation is devoted to improvements in the evaluations of other mechanical properties of materials as related to high-temperature creep and fatigue properties.