Fracture modelling has always been a direction of research in engineering, more specifically in
civil engineering. In this last quarter of century, the implementation of nonlocality in damage
models has been a direction of study for materials fracture, more specifically for quasi-brittle
materials such as concrete or rocks. This type of damage model allows a more accurately
characterization of the behavior of this type of materials and it has been seen that it is not
possible to accurately model the behavior of this materials without a nonlocal formulation,
because it characterizes the behavior of the material as a whole, weighting the value of a
variable of a point on its neighborhood.
This dissertation aims for an investigation on new models able to characterize the damage effect
on quasi-brittle materials. In this direction, this thesis focuses on models with a variable internal
length which sees its value reduced due to the increase on damage. Furthermore, two models
in this dissertation are presented on how to treat this internal length reduction.
One model presents an unbounded internal length reduction allowing a vanish of its value for
high damage values, whereas the other model do not allow a null value of the internal length,
even for high damage values, imposing a minimum value –threshold– for the internal length.
Finally, both models and an original model with a constant internal length –where these two
models are based from– are tested on a uniaxial strain and stress problem and its results and
parameters discussed.
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