PROcess influence on the Fatigue of Elastomeric Materials – PROFEM

The use of elastomeric parts is today very widespread in all industrial markets to fulfil very different requirements (static or dynamic tightness, damping of vibrations or shocks, high chemical resistance…). If the design of static or dynamic requirements is today well mastered, the field experience underlines that the two main failure mechanisms are related to fatigue and ageing. For a dozen years, coupled studies of industrials and academic partners allowed to propose several phenomenological criteria to evaluate the fatigue lifetime of elastomeric structures. But the requirements for higher durability under even more severe conditions lead now to overcome the next difficulty, which is the coupling between the process and the fatigue properties. Indeed, fatigue of elastomeric materials is strongly driven by the process. This comes from the heterogeneous nature of these materials (for a wide range of matrix and fillers and with crucial influence of compounding) and from the huge influence of a complex two steps process (mixing, and injection) on the microstructure. It is therefore crucial to understand the couplings between process and microstructure, on the one hand, and between the microstructure and the fatigue properties on the other hand.
To understand these links, it is mandatory to answer three main questions, associated to the three different scales:
1.What are the basic damage and dissipation mechanisms?
2.What is the damage scenario for a given matrix and inclusions distribution (in size and space) and how can it be used to understand and to evaluate quickly the fatigue properties?
3.What are the influences of the injection process on the microstructure of injected samples and are the previous answers relevant to understand the fatigue phenomenon observed on massive samples with a heterogeneous microstructure?

These are precisely the answers aimed at by the PROFEM project, which will take profit of several tools used and developed in very recent preliminary studies:
-Association of X-Ray Computed tomography and infrared measurements thanks to an energy-based criterion, in order to quickly evaluate the fatigue properties of elastomeric materials;
-Micromechanical modelling using a complex morphological pattern which takes into accounts occluded rubber, carbon black, bound rubber and a percolating network. These specific features give the opportunity to extend the model to the dissipation and damage mechanisms for local relevant scales.

The scientific and technical outcomes are very numerous leading to answer not yet understood issues of the field of elastomers fatigue. It is aimed:
1.To understand and to model the initiation and growth mechanisms (coupling several scales observations and micromechanical modelling) ;
2.To validate a way to evaluate quickly the fatigue properties for several kind of matrix and fillers, and to extend it to the prediction of lifetime dispersion;
3.To understand the influences of mixing and injection on the fatigue properties, for healthy zone as well as sensible zones (parting line, injection point).

These achievements will greatly help manufacturers to reduce the parts weight and time development and to meet environmental requirements.

The scientific originality of the PROFEM project also stands in two specific aspects:
-­The use of mechanical modelling to couple two experimental techniques (X-Ray CT and thermal measurements) which allow overcoming their specific limitations
­-The strong dialog between a phenomenological approach (based on energy criterion) and a micromechanical modelling, with are usually seen as diverging ways rather than partners ones.

It should be underlined that the goals of this study are very challenging and require a very wide skills range. Mixing industrial and academic partners, the PROFEM partners propose extensive technical and scientific complementarities that are relevant to achieve efficiently this project challenges.