Interpreting the spectral reflectance of advanced high strength steels using the Davies’ model

Abstract

This study investigates the relationship between surface roughness and spectral reflectivity of DP980, an advanced high strength steel (AHSS) alloy. Five surface states were considered: as-received, polished, roughened, and two coupons annealed in a reducing atmosphere. Radiative properties were measured using a UV–Vis-NIR spectrophotometer and two FTIR spectrometers for directional-hemispherical and specular reflectance measurements, while surface roughness is determined using an optical profilometer. These measurements were interpreted in the context of a theoretical relationship derived from Davies’ model for specular reflectance. The reflectance of the polished coupon most closely matches this theory, and the remaining coupons become more aligned with this relationship after large-scale roughness has been removed from the profilograms using a wavelet filter. The results show that directional-hemispherical reflectance can be predicted using Davies’ model with local scale roughness as opposed to macroscopic artifacts, although this model is intended to capture the variation of specular reflectance with respect to wavelength.