Research On Mechanical Characteristic Of Visco-elastic Materials By Nano-indentation And FEM

Visco-elastic materials have wide application in the field of microelectronics, nanotechnology and micro-electromechanical systems(MEMS), for example, visco-elastic materials can be used in micro-nano structures and micro-devices, making the research on mechanical characteristic of visco-elastic materials very important. In this paper, mechanical characteristic of visco-elastic materials and effect mechanism of contact morphology on indentation test are studied by nano-indentation and finite element method (FEM). Finite element analysis software is used to simulate the measuring process of visco-elastic materials by using nanoindentor, and the effect of tip radius as well as surface roughness on indentation test are further analyzed.Firstly, nano-indentation is implemented on polrvinyl chloride(PVC), and displacement-load curves including elastic modulus and hardness are acquired. Finite element analysis software ANSYS is used to simulate the nano-indentation experiment on the basis of references and experiment data. Then Displacement Vector Sum, Von Mises Stress, displacement-load curves and hardness are calculated. The data of FEM and nano-indentation experiment are analyzed and compared. The result demonstrates that FEM simulating nano-indentation experiment into visco-elastic material to investigate the mechanical properties is feasible.Secondly, four contact modules of conical-indenters with different tip radius interacting with the surface of specimen are built.2-D rotational symmetry FEM models are used to simulate nano-indentation experiment. The simulation results indicate that hardness rises with the increase of tip radius and the decrease of indention depth. With the decline of indention depth, the influence of tip radius becomes more obvious.Finally, Indenter size index is introduced. Two 3-D FEM modules are established by two situations:surface roughness shares the same order of magnitude with Indenter size index or is far beyond Indenter size index. Simulation results indicate that the measured hardness is respectively undervalued or overvalued as the point of surface contact is on summit or on bottom, and the deviation of hardness increases with the augment of roughness distance and maximum height of the profile.