Polypropylene numerical photoageing simulation by dose - response functions with respect to irradiation and temperature

The aim of the joint project ViPQuali (Virtual Product Qualification) was to describe a component's ageing behaviour in a given environment, by numerical simulation. Having chosen polypropylene (PP) as the material, which does not show sensitivity to moisture, the relevant weathering parameters of the dose-response functions could be limited to spectral irradiance and temperature. In artificial irradiation tests, for PP plates of varied stabiliser content, spectral sensitivity as well as temperature dependence of irradiation-caused crack formation was quantified. For that purpose, samples were exposed both to artificial weathering tests at various constant temperatures and to spectrally resolved irradiation. The temperature dependence could be modelled by an Arrhenius fit. For fitting the spectral sensitivity, a plateau function was chosen. Subsequently, the stabiliser content was parameterised and extrapolated. The formed dose-response functions were incorporated into a Computational Fluid Dynamics (CFD) software program, simulating the environment of a sample within a Phoenix-exposed IP/DP (Instrument Panel/Door Panel box) box, based on sun position and weather conditions, including radiation interactions. Observed local effects as well as the general ageing advance of PP hats are compared with respect to simulation and experiment. Resulting from this project, for this most simple example of PP of varied stabiliser content, the time to failure can be estimated for each weathering exposure environment with known time-resolved irradiance and temperature conditions.