Nonlocal continuum damage and measurement of characteristic length

Damage such as cracking or void formation is in many materials distributed and localizes only to a limited extent. The macroscopic treatment of such materials calls for a continuum description of damage, and this in turn necessitates a nonlocal definition of damage. Reasons for the nonlocal approach are briefly reviewed and the nonlocal damage model is summarized. Detailed attention is then focused on the experimental determination of the characteristic length which enters the spatial weighting function and characterizes the nonlocal properties of the material. The basic idea is to compare the response of two types of specimens, one in which the tensile softening damage remains distributed and one in which it localizes. The latter type of specimen is an edge-notched tensile fracture specimen, and the former type of specimen is of the same shape but without notches.