General Concepts and Definitions
· Strength The ability to sustain load.
· Stiffness Push per move; the ratio of deformation to associated load level.
· Stability The ability of a structure to maintain position and geometry. Instability involves collapse that is not initiated by material failure. External stability concerns the ability of a structure's supports to keep the structure in place; internal stability concerns a structure's ability to maintain its shape.
· Ductility The amount of inelastic deformation before failure, often expressed relative to the amount of elastic deformation.
Strength Material strength is measured by a stress level at which there is a permanent and significant change in the material's load carrying ability. For example, the yield stress, or the ultimate stress.
Stiffness Material stiffness is most commonly expressed in terms of the modulus of elasticity: the ratio of stress to strain in the linear elastic range of material behavior.
Stability As it is most commonly defined, the concept of stability applies to structural elements and systems, but does not apply to materials, since instability is defined as a loss of load carrying ability that is not initiated by material failure.
Ductility Material ductility can be measured by the amount of inelastic strain before failure compared to the amount of elastic strain. It is commonly expressed as a ratio of the maximum strain at failure divided by the yield strain.