Essais dynamiques hors équilibre et avec champs hétérogènes.
Résumé
Soft materials have the disadvantage of creating inhomogeneous strain fields under dynamic loading. Especially, the dynamic equilibrium is very difficult to achieve in high strain rate testing on gelatin-based materials, because of their very low mechanical wave speed and impedance. However, the motions of gelatin matter are important during the test, and a digital image correlation (DIC) technique is proposed to identify the displacement field. In this paper, an identification approach based on DIC technique is developed to deduce the acceleration fields in the longitudinal and transverse directions. Furthermore, stress, strain and strain rates histories are carried out in different specimen positions by this approach. The accuracy of estimated stress field is approved by the measurement of PVDF pressure sensors. The comparison results between axial and transverse stresses confirm the uni-axial stress state assumption in the specimen. The deduced stress-strain relations show the significant strain rate sensitivity at the tested rate range.