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The objective of this work was to investigate and quantify damage mechanisms occurring in neat and hemp fiber-reinforced high-density polyethylene (HDPE) subjected to complex loading histories, including strain unloading, stress recovery, and cyclic tension / compression testing.To this end, we selected time-resolved small-angle x-ray scattering (SAXS) to have real-time information about voids scattering.An analysis methodology was assessed to extract, quantify, and interpret the voids scattering in neat and reinforced HDPE, and hence, to analysis damage mechanisms.For neat HDPE, stress unloading and strain recovery procedures caused a decrease of voids volume fraction compared to the loaded state.As a consequence, voids volume fraction was divided into a permanent component and a nonpermanent component.For cyclic tension/compression testing, the maximum voids volume fraction gradually increased with the number of cycles, while each compression stage reduced the void fraction to zero.These results were discussed on t he basis of the influence of undetectable residual nanometric voids.For the HDPE composite, tensile loading induced a fast increase of void scattering intensity until the breaking point due to marked fiber/matrix debonding mechanisms starting along fibers oriented perpendicular to tensile direction and at the tip of fibers oriented along tensile direction.The present work provides a novel knowledge about damage mechanisms in semi-crystalline polymer, which could be the basis of new damage modeling.