EXPERIMENTAL-COMPUTATIONAL ESTIMATION OF ROUGH FRACTURE SURFACE-CONTACT STRESSES

This paper presents the preliminary results of a technique for estimat ing the contact stress distribution on the rough surfaces of cracks wh ich are partially closed and loaded in shear. Phase shifted speckle in terferrometric measurements of the crack face opening and sliding disp lacements of a crack in a four-point-bend mixed-mode fracture specimen under quasi-static cyclic loading are used as the initial data. An it erative computational process determines acceptable fits of the initia l displacement data and the corresponding crack face contact stresses, which are found from a numerical model of the specimen and loading. C ontact stress results are presented from one specimen at two load incr ements which suggest that the roughness causes an increase in the cont act length compared to flat and smooth surfaces. More importantly, as the extent of sliding increases, the effective frictional resistance b ecomes localized and is a strong function of position along the contac t. This cannot be modeled by Coulomb friction with a single value of t he coefficient of friction. These are the first results of their kind ever presented for the local displacement and contact stress distribut ions across rough interacting fracture surfaces. (C) 1998 Published by Elsevier Science S.A. All rights reserved.