  Heterogeneous materials are often organized in a hierarchical manner, where a
basic unit is repeated over multiple scales.The structure then acquires a
self-similar pattern. Examples of such structure are found in various
biological and synthetic materials. The hierarchical structure can have
significant consequences for the failure strength and the mechanical response
of such systems. Here we consider a fiber bundle model with hierarchical
structure and study the effect of the self-similar arrangement on the avalanche
dynamics exhibited by the model during the approach to failure. We show that
the failure strength of the model generally decreases in a hierarchical
structure, as opposed to the situation where no such hierarchy exists. However,
we also report a special arrangement of the hierarchy for which the failure
threshold could be substantially above that of a non hierarchical reference
structure.
