Stress analysis of local blisters coupling Raman spectroscopy and X-ray diffraction. Correlation between experimental results and continuous damage modelling for buckling in an iron oxide/phosphated iron system

In this present work, local stress development in the iron oxide layers growing on phosphated α-Fe at 400 °C in ambient air is investigated by Raman spectroscopy. Coupled with X-ray diffraction it enables to obtain directly local stresses' maps in the oxide layers. Use of Raman spectroscopy allows obtaining better accuracy on mechanical behaviour at local scale. This characterisation technique is very useful to study systems developing mechanical heterogeneities on surface, especially in case of buckling phenomenon. Investigations on particular local blisters have been done to measure some characteristic lengths at local scale. From local measurements, we are able to evaluate general effect of buckling from simplified scale transition. So, a macroscopic approach has been performed to calculate global stress evolution of the oxide layer, based on continuous damage mechanics. Consequently, it leads to good comparison between modelling and experimental values (global stresses versus oxidation time) in α-Fe2O3 oxide.