Fused Filament Fabrication (FFF) is nowadays one of the most widespread and promising additive manufacturing techniques. However, the presence of process-related defects, such as inclusions and pores, decreases the strength and toughness of FFF parts and represents the greatest obstacle for structural applications. Understanding the complex mechanical behavior of FFF printed parts is essential to consider this approach as a valid alternative to conventional manufacturing methods. Extremely critical is the incomplete layers and filaments adhesion due to the material cooling during deposition which inhibits the molecular diffusion and thus creates weak interfaces. From a durability perspective, it has been found that failure usually occurs in correspondence with these interlayer and cross-layer interfaces for FFF parts under loading. Characterization techniques capturing the failure of FFF interfaces are essential not only to understand the fracture behavior of such parts but also to develop predictive constitutive models. In this work, we present a full characterization procedure to study the interlayer and cross-layer interface failure of polylactic acid specimens manufactured by FFF. We monitor the microscale mechanical behaviour of FFF interfaces undergoing mode I failure by means of stereoscopic Digital Image Correlation. Full-field displacement and strain measurements are performed in the vicinity of the specimens mid-plane interface undergoing damage.