Temperature-dependent reflectance of plated metals and composite materialsunder laser irradiation

Experiments were performed to investigate laser-heating-induced changes in the surface properties of metals and composite structural materials commonl y used in aerospace applications. The objective of this test series was to determine the effect of surface heating on the 1,3-mu m-wavelength laser re flectance of these materials. Reflectance measurements were made using a un ique hemiellipsoidal reflectometer. Polished metals, plated metals, and com posite materials were tested to determine their temperature-dependent refle ctance characteristics in vacuum and air environments. This experiment seri es produced temperature-dependent, 1.3-mu m laser reflectance curves for us e in surface degradation analyses. All of the finishes investigated on dupl ex stainless-steel substrates increase the low-temperature, 1.3-mu m reflec tance compared to the unpolished steel. However, the reflectance decreases dramatically at elevated temperatures when the surfaces discolor. The large reflectance transition observed for the polished and plated steel coupons in air also occur in vacuum. The polished aluminum alloys had a higher 1.3- mu m reflectance than the plated aluminum samples throughout the temperatur e range. The elevated temperature reflectance of S-glass epoxy is irradianc e dependent. Low irradiance creates a black char. A higher irradiance can i gnite the char and form a lighter, more reflective surface.