دانلود رایگان مقاله انگلیسی مدل تخریب UV برای پلیمرها و کامپوزیت های ماتریکس پلیمری - الزویر 2018

abstract

We are proposing in this work a new model of ultraviolet (UV) damage for polymers and Polymer Matrix Composites (PMCs). Flat and sinusoidal polymer surfaces were numerically simulated for their UV damage as a function of UV intensity, surface topography, and exposure time. Experimentally determined UV degradation rates for a unidirectional glass/epoxy composite were used to predict numerically the local rates of material degradation on sinusoidal epoxy surfaces subjected to UV. This allowed us to show that UV damage on uneven polymer surfaces reduces their surface roughness making them planar and that the degradation rates are the largest at the tips of the local heights of the surfaces. This was subsequently verified experimentally by exposing neat epoxy specimens to UV in air at 80
C for 1000 h and by precisely monitoring their surface topography as a function of time. It was found that the surface roughness of the epoxy was reduced by about 12.5% and that UV affected the local peaks on the surfaces of the specimens more than the valleys.

6. Summary observations and conclusions

It has been found in this work that UV degradation of polymeric surfaces is strongly dependent on UV wavelength, intensity and exposure time. It is also shown that UV intensity and inclinations determine the local degradation rates of the material which can be numerically simulated from the global degradation rates for a material determined experimentally. The finite difference method was successfully applied in the UV radiation simulation to study the evolution of the sinusoidal surface due to the material degradation under UV exposure. The simulation parameters were appropriately defined to avoid numerical instabilities in the solution. Through the numerical simulations it is concluded that the initial irregular, sinusoidal surface of the material will be eventually degraded to a flat surface under a long period of exposure to UV radiation regardless of the irradiation angle. Although the simulations were performed in the setting of sinusoidal surfaces, the methodology is equally applicable to any irregular surfaces. The UV planarization effect on irregular polymeric surfaces observed numerically was finally experimentally verified in this work by the UV testing of neat epoxy specimens at elevated temperature. The surface roughness of the specimens was reduced by about 12.5% after 1000 h of UV exposure.