VISCOELASTIC EFFECTS IN A POLYMER MICROFIBER DUE TO SURFACE CONTACT
Nicholas Cramer (University of California Santa), Mircea Teodorescu (UC Santa Cruz)
Contact Mechanics
Tue 2:40 - 4:00
Barus-Holley 161
The nanofibrillar array of a Gecko inspired Synthetic Adhesive (GSA) adheres to a surfaces when fibers undergo non-linear deformation of both the stems and the tip. The polymers used for manufacturing the fibers display plastic creep even at relatively low strain rates and stresses below plastic yield. Therefore, a suitable numerical solution, which predicts the optimal fiber geometry, must consider not only the initial shape of the fiber, but also the fiber progressive deformation (local and global) and the influence this has on the local mechanical properties (elastic, viscoelastic, strain hardening/softening and plastic flow). The localized mechanical properties are difficult to calculate using traditional methods because of the nonlinearities associated with viscoelastic effects, the large deformations, and the variable boundary conditions. The variable boundary conditions make a mesh free modeling method ideal. Smooth Particle Hydrodynamics (SPH) is the most prominent mesh free Lagrange method, which takes a set particle area and uses particle kinematics, density gradients, and material properties to determine the interaction between particles. Due to the lack of grid structure, SPH is capable of predicting large deformations, removal of material, and material properties varying within the simulationeasier than the FEM does. The current paper presents SPH as a valid alternative to FEM for the simulation and analysis of polymer microfibers. The paper focuses on the modeling of a single polymer micro fiber, which is subjected to similar conditions to what it would see as part of an array. It was found that the SPH method was able to appropriately model the effect of various scenarios on the mechanical deformation. Further more the force required for fiber deformation, the friction force for the fiber on glass and fiber tip to glass and stem profiles are predicted.