  Oscillatory shear tests are widely used in rheology to characterize the
linear and non-linear mechanical response of complex fluids, including the
yielding transition. There is an increasing urge to acquire detailed knowledge
of the deformation field that is effectively present across the sample during
these tests; at the same time, there is mounting evidence that the macroscopic
rheological response depends on the elusive microscopic behavior of the
material constituents. Here we employ a strain-controlled shear-cell with
transparent walls to visualize and quantify the dynamics of tracers embedded in
various cyclically sheared complex fluids, ranging from almost-ideal elastic to
yield stress fluids. For each sample, we use image correlation processing to
measure the macroscopic deformation field, and echo-Differential Dynamic
Microscopy to probe the microscopic irreversible sample dynamics in reciprocal
space; finally, we devise a simple scheme to spatially map the rearrangements
in the sheared sample, once again without tracking the tracers. For the yield
stress sample, we obtain a wave-vector dependent characterization of
shear-induced diffusion across the yielding transition, which is accompanied by
a three-order-of-magnitude speed-up of the dynamics and by a transition from
localized, intermittent rearrangements to a more spatially homogeneous and
temporally uniform activity. Our tracking free approach is intrinsically
multi-scale, can successfully discriminate between different types of dynamics,
and can be automated to minimize user intervention. Applications are many, as
it can be translated to other imaging modes, including fluorescence, and can be
used with sub-resolution tracers and even without tracers, for samples that
provide intrinsic optical contrast.
