In this research, we demonstrate the effect of ultraviolet-C (UV-C) irradiation of Polyamide 6/carbon-fiber (PA6/CF) composites. The PA6 and PA6/CF composites were fabricated using a fused deposition modeling type 3D printer with a single spool. These specimens were exposed for 0, 1, 3, 5, and 7 days under UV-C light irradiation. After exposure, the specimens were observed and characterized with contact angle measurements, Fourier transform infrared analysis, 3D fluorescence spectroscopy analysis, tensile tests, and scanning electron microscopy. As a result, PA6 was found to be more photo-oxidative degraded than PA6/CF. Furthermore, the 3D fluorescence images and emission spectra were shown to successfully coincide with the results of the photo-oxidative degradation reactions of PA6 and PA6/CF. In addition, the tensile test results showed a dramatic decrease in PA6 while PA6/CF did not decrease much, indicating that CF is useful not only as a reinforcement of the composite but also for UV protection.

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This paper explores quasi-static flexural properties and fracture behavior of a pultruded glass fiber/unsaturated polyester square pipe for automotive structural applications. Three-point flexural testing is performed in an Instron Universal Testing Machine with steel jigs supporting the top and bottom surfaces of the pipe. Acoustic emission (AE) measurements are recorded during flexural testing to evaluate initial fracture in the pipe structure. After final fracture, five cross-sections of the pipe are cut at 50-mm intervals along the longitudinal axis, with the first cut located at the mid-span of the pipe. Cross-sections of a pipe from an interrupted test where initial fracture is detected from the AE method are also prepared. Damage locations and behavior on each cross-section are observed. The flexural testing results show that the cumulative AE counts increase rapidly from 2.5 kN, that final failure occurs at a maximum load of approximately 13 kN, and that corresponding initial and final failure occurs in the two corner regions on the compressive side of flexural loading. Failure initiates by stress concentrations due to the upper jig on the top surface during bending. The cross-sectional observations also reveal clear deformation behavior of the pipe where failure is present, marked by inward bending of the top surface and upper corners located on the compressive side, near the jig. The locations of maximum stresses and deformations obtained from finite element analysis of this pipe structure are in very good agreement with the experimental observations.

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