摘要：The cohesive surface methodology is probably the most used in recent
Fracture Mechanics researches (see Needleman, A., A continuum model for void
nucleation by inclusion debonding, J. Appl. Mech., 54:525- 531, 1987). This
methodology is characterized by two parameters, the energy fracture and a
characteristic length (or maximum stress at crack tip), and has been used to
model fragile and ductile material satisfactorily. On the other side,
quasi-fragile materials (as concrete) also need two fracture parameters to be
characterized, depending on the used methodology. Then concrete seems to be a
material that can be model by the above mentioned methodology. However,
concrete is a strong heterogeneous material and its behavior depends on
mortar properties and aggregate size and shape. Also, a factor that
complicates the analysis of this material is the fact that the fracture
process is accompanied by intense micro-cracking and bridging of main cracks.
Recent numerical applications to concrete show that not only these two
parameters are sufficient to correctly model its fracture process, but also
other parameters as the shape of crack tip stress - crack opening
function. In this paper a discussion about the relations among all the above
mentioned parameters is introduced and suggestions are raised on how to
capture the quasi-fragile behavior with the cohesive surface methodology.
The effect of micro-cracking is addressed as well as the effect of the shape
of the stress-opening interface curve. A three-point bending beam is used as
a numerical experimentation and compared to experimental results. The results
show that micro-cracking and unloading shape of the stress-opening interface
curve are variables as important as maximum stress at crack tip. Also it is
shown that the original shape proposed by Needleman can not be used in
quasi-fragile material when micro-cracking is considered. However, the
methodology works quite well when only one main crack is considered, at least
for the material and boundary conditions tested here.
