On the use of local strain fields for the determination of the intrinsic length scale

Spatially nonlocal regularization techniques invariably introduce one or mo re material length parameters. A major difficulty resides in the experiment al determination of such intrinsic length scales. Several indirect techniqu es have been proposed in the past years which are based on the observation of macroscopic mechanical effects which ensue from the process zone, e.g. t he size effect. The present contribution uses a different approach by explo iting local measurements which were carried out in and around the process z one. Using an appropriate experimental technique, displacement and strain f ields have been determined during the damage and fracture process in a CT-t est of a composite material. The unknown length scale is extracted by compa rison of the experimental results with the numerical simulations which have been obtained with a transient gradient damage model. The necessity and th e importance of such a local comparison is motivated and discussed. A param eter estimation based on the global mechanical response of one experiment o nly, may lead to an erroneous and deluding determination of the intrinsic l ength scale.