Characterization of Residual Stresses in Composite Parts Manufactured by Material Extrusion Technology Using Reflection Photoelasticity

Residual stresses are a persistent challenge in the additive manufacturing of composite parts by FFF (Fused Filament Fabrication) and can impair dimensional accuracy and mechanical performance. This article evaluates reflection photoelasticity (PhotoStress) as a full-field optical technique to visualize and compare residual-stress relaxation in ASA (Acrylonitrile Styrene Acrylate) reinforced with aramid fibers. The approach combines a controlled AWJ (Abrasive Water Jet) relief cut to induce local stress release with subsequent optical recording of isochromatic fringe fields using a reflection polariscope. Samples with thicknesses of 2–10 mm were manufactured and evaluated in two conditions: non-annealed and after annealing (80 °C/5 h). Under identical optical settings, no discernible isochromatic fringes were detected for 2–6 mm (Nmaxlobal < 0.60 in both conditions), whereas resolvable fringe patterns were observed for 8–10 mm. For 8 mm, the response was localized near the relief cut, with Nmax,global = 1.0 in the non-annealed condition and Nmax,global < 0.60 after annealing. For 10 mm, the response was more spatially extensive, and annealing reduced the global maximum from Nmax,global = 1.2 to 0.9. Taken together, these results demonstrate that reflection photoelasticity supports comparative full-field visualization of residual-stress relaxation in FFF composite specimens under fixed measurement conditions. In addition, an AWJ relief cut constitutes a practical and repeatable stress-release feature with limited additional thermal influence in the present configuration.