Correlation Between Mechanical Properties Degradation and Discoloration of Epoxy Polymer by Solar Radiation Exposure

Many materials used for industrial, architectural or logistics systems are exposed to various environmental factors such as temperature, humidity and solar radiation. In particular, solar radiation is a primary concern regardless of weather or season. It causes changes in mechanical properties, the generation of cracks in concrete, color fading in clothing and plastic, and so on. This paper demonstrates some of these effects. To do this, the authors used an artificial solar radiation test apparatus to examine epoxy polymer specimens. The apparatus included a number of metal halide and infrared lamps, which simulated natural solar radiation as per US military testing standards (MIL-STD-810G). 18 specimens were manufactured based on the ASTM-D638 testing method. They were then divided into three groups with six specimens each. Each group was exposed to artificial solar radiation for 28days, 56days and 84days, respectively. To identify the color shift in each specimen, digital images for each specimen group before and after the solar radiation test were obtained prior to the tensile test. The R, G and B values were subsequently extracted from these digital images using MATLAB and used to calculate the total color shift between the two specimen states (before and after the solar radiation test) following linear and non-linear formulas. Finally, the authors proposed a method of predicting the extent of the decline in maximum tensile strength. This method employed four mathematical correlation relationships between the maximum tensile strength and the total color shift.