ABSTRACT

Because concrete and mortar do not obey the assumptions of linear fracture mechanics, it is assumed that a fracture process zone preceeds the development of a macroscopic traction free crack. In the second approach it is tried to isolate a fracture process zone and to study its behaviour under combined tensile and shear loadings (e.g. [3], [7], [10]). As a result constitutive equations should be derived (normal and shear stress versus crack opening and crack sliding displacement, see pp. 94-96 in [6]) for implementation in finite element codes. This last approach is in fact an extension of the fictitious crack model [4] and related models for mode I loading. The input parameters for the fictitious crack models must be derived by loading small specimens in a very stiff loading apparatus. However, recently researchers became aware of the fact that besides the stiffness of the machine, the stiffness of the specimen itself has a considerable influence on the measured response in tension.