In link with the thermal degradation of polymers during the process, and the use of polymer and composites in very demanding industrial areas (nuclear energy, aeronautic and aerospace….) where they are submitted to severe stresses (temperature, radiation, oxygen, ultrafast mechanical stresses), our group has also a strong research activity in the field of polymer durability.  Our aim is to establish multiscale and multiphysics models based on the study of polymer degradation at various scales:

 

                                                                                                   

                                                                                                                      Multiscale approach of ageing.

 

1. At molecular scale : characterization of the degradation pathway and kinetic modeling for predicting the rate of ageing of polymer submitted to its environment:

- in the case of chemical ageing: hydrolytic, photo-, thermal and radiolytical ageing so as to predict for example the rrate of chain scissions or crosslinking for each kinds of mechanisms. We are in particular speciliazed in establishing kinetic schemes able to simulate the degradation rate as a function of environmental stresses. 

                                                                             

                                                                                           Example of chain scission mechanisms in polymers.

 

- in the case of physical processes such as water (or any other chemicals) on polymer, or when those diffusion processes are coupled with cheicals reactions (for example diffusion-reaction coupling for oxygen leading o the appearance of degraded layers, or diffusion/evaporation/reaction coupling for antioxidants). .

                                                                             

                                                                         Correlation between water diffusivity and solubility in polymers (case on non Fickian diffusion).

 

2. At macromolecular scale: establishing structure-properties relationships allowing to predict the changes in mechanical properties (rubber elasticity in elastomer networks, toughness and plastic deformation in linear polymers and networks…) from the molecular changes (chain scissions or crosslinking) that can be predicted from kinetic modeling.

 

Some example of network degradation : Degelation dose of PMMA based networks as a function of length of elastically active chains (a), decrease of rubber elasticity in polyester-urethane networks with various scenario of autocatalysis by carboxylic acids (expressed by A value) (b) and effect of stress induced crystallization on fracture properties of CPE elastomer. (c)

 

3. At macroscopic scale, we study of mechanical damage and ultimate behavior of polymers and composites :  

- for example the cracking in thermoset networks:

                                                                                      

                                                                                          Prediction of maximum principal stress in thermally aged epoxy/diamine system                           

 

- Multiscale modeling of damage in composites materials submitted to various loadings so as to take into account the local phenomena in the establishment of behavior laws and limit criteria allowing to predict the response of material depending on the local microstructure. Damages occurence are studied under fast or repeated loadings. The study of interrupted tests (performed at rates varying from  10^-4 to 400 s^-1 allows to identify the nature of the damage (matrix micro cracking, delamination) and to use the resulting behaviour law in industrial computational codes.

                                                                       

                                                                                      Multiscale study of damages in SMC composites.