Over the past decades, fatigue crack growth has been an area of active research aimed at guided fatigue design on one hand and, on the other, at failure prediction in engineering facilities once the fatigue crack sets in. The former is footed primarily on the empiric Paris law relating the crack growth rate to the stress intensity ahead of the crack tip in the linear elastic fracture mechanics approximation. The latter therefore suffers from all limitations imposed by the Paris law or any of its modifications. The complexity of the mechanisms that govern the fatigue crack propagation calls for development of new physical models that capture the underlying physical mechanisms and microstructure evolution in the plastic zone and yet are robust and user-friendly enough to be applicable in engineering praxis. Having this as a main mindset and a future goal, we present the novel in-situ approach towards experimental investigation of the thermodynamics and kinetics of deformation processes in the plastic zone of the propagating fatigue crack in situ. We describe an original experimental setup including the synergy from the combined high-resolution infrared imaging, optical microscopy with digital image correlation and acoustic emission technique, and provide examples of its successful application to a set of stainless steels including the conventional hot-rolled stable 316L steels and metastable high-alloyed CrMnNi TRIP and TWIP steels.