This work is part of a global experimental approach aiming at studying the damage and rupture of 3D
carbon/epoxy composites and based on multiinstrumented experiments. It focuses on the use of digital
image correlation (DIC) in order to detect the development of local non-linearities corresponding to damage
(with no other non-linearities) and is limited to small deformation. To that purpose, the strain field is
required, hence derived from the measured displacement field, through a diffuse approximation algorithm.
This approach is detailed and studied in terms of filtering and some criteria are proposed to choose
the filtering parameters. A pragmatic approach based on the evolution of the linear approximation of the
strain is proposed in order to detect local non-linearities leading to a local damage indicator. The effect of
the filtering on the damage detection is then discussed.