Fracture mechanics in design and service: ‘living with defects’ - Fracture mechanics of non-metallic materials

Abstract

An outline of linear elastic fracture mechanics (l.e.f.m.) is given with an emphasis on those aspects most relevant to non-metallic materials. Provided that the nonlinear zone of energy absorption surrounding the crack tip is small compared with other dimensions, then a K e or G e value may be used. A simple extension of this concept can include elastically nonlinear materials such as rubber. Examples of the use of this method are then given for polymers, rubber and wood, and include some discussion of the difficulties involving plane strain-plane stress transitions. The role of K e as a characterizing parameter in time-dependent, fatigue and environmental behaviour is then described with several examples, and it is concluded that plane strain fractures may be achieved with a wide range of values for any material. The consequences of this in choosing a design criterion are then discussed.

The toughness of hygrothermally modified wood

“…Both energy and force-based failure criteria have been developed for materials exhibiting brittle or quasi-brittle behaviour ( Knott 1973 ;Parton 1992 ). Primarily developed for metals, linear elastic fracture mechanics (LEFM) has nonetheless been applied to nonmetallic materials including wood (e.g., Williams 1981 ;Patton-Mallory and Cramer 1987 ;Stanzl-Tschegg et al 1994, 1996 as well as to other plant materials ( Lucas et al 1991( Lucas et al , 1995( Lucas et al , 1997.…”