Mechanical characterization of elastic/viscoplastic response of polymeric materials using depth sensing nano-indentation

L. SANCHEZ FELLAY; FASCE, LAURA; MARINA CZENER; PATRICIA M FRONTINI

Congreso; CONGRESO INTERNACIONAL DE METALURGIA Y MATERIALES SAM-CONAMET/IBEROMAT/MATERIA 20141; 2014

Several investigations have been carried out to extract both the elastic and plastic response of materials using nano-indentation tests. While this achievement is very important, it is widely known that polymers also exhibit a strong time dependent mechanical behavior. This dependence can be observed in depth sensing indentation (DSI) tests. For example, the displacement of the punch in DSI increases while the force remains constant (creep). In this work, a numerical strategy is proposed to calibrate parameters of the Arruda-Boyce constitutive model from DSI data. A virtual Arruda-Boyce material is used and three-step load cases are designed in order to uncouple the elastic, plastic and viscous behavior. Using an inverse analysis technique, the mechanical response is deconvoluted by matching the experimental curve with the ones computed by finite element modeling. The first step is loading, performed at different velocities; after that, a constant-load step is used, varying the holding time; and finally the unload step is carried out at the same velocity than the load step. The elastic parameters are obtained from the unload step, using the completely elastic unload hypothesis. The second step (constant load) is used to recover the parameters related to the creep behavior. All remaining parameters are obtained from the load step. Keywords: Nano indentation, viscoplasticity, inverse analysis, polymers