ABSTRACT
Automotive legislations request a monitoring system on wheel’s pressure for safety reasons. Those systems are called TPMS (Tire Pressure Monitoring System) and are attached to the rear of the valve inside the tire. For high speed application, the centrifugal force generated by the wheel rotation causes high stress located in the rubber element and may lead to cracks. A dedicated bench test replicates the mechanical profile of vehicle accelerations and decelerations. The results obtained on the latter show a large dispersion when valve lifespan characterization results are analyzed.The aim of this work is first to understand cracks initiation on rubber valves and then, to characterize the standard deviation. Fracture study has been carried out using field emission gun combining with CT-scans analysis. Results attest that initiation occurs on surface to the contact with the rim thanks to striations observed on valves features. CT-scan experiment also exhibits the presence of decohesion near carbon black agglomerates while analyses indicate high thermo-oxidative phenomenon.Finally, rubber fatigue variability has been investigated on laboratory specimen to counter variability related to test bench equipment. Test parameters and amplitudes have been set by numerical calculation using Hencky invariants calculated via a FE model of the valve. The main interest was to determine which mechanical loading type (shearing, tension or compression) predominates among rubber valves and then to re-apply an equivalent one on specific specimens during low cycles fatigue tests campaign. Experimental fatigue results on specimens are compared with experimental tests ran on valves, mechanically representative of the industrial conditions.
