Modeling of static and kinetic friction in rubber-pad forming process
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Date
2009
Authors
Ramezani, Maziar
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Abstract
The frictional behaviour in sheet metal forming simulations is often taken into
account by using a constant coefficient of friction (Coulomb model). This thesis
develops static and kinetic friction models which are based on local contact
conditions and consider the effect of pressure, velocity, surface roughness and
lubricant viscosity on coefficient of friction. The surface asperities were modeled
using statistical Gaussian distribution and the behavior of rubber asperities was
assumed to be viscoelastic. In lubricated contact surface between die and sheet, the
total normal load was assumed to share by the hydrodynamic lifting force and the
asperity interacting force. According to developed friction models, at low normal
loads the static friction coefficient decreases sharply with increasing normal load and
reaches a quite stable level at higher loads. The coefficient of kinetic friction
decreases with increasing the sliding velocity and normal load. It was shown
theoretically that the coefficient of friction is larger for rougher surfaces, and by
increasing the lubricant viscosity, the coefficient of kinetic friction decreases.
Furthermore, rubber-pad forming experiments and simulations were performed. The
calculated friction curves using the new friction models were implemented in the
finite element code ABAQUS/Standard. From the results of simulations it was found
that the new friction models have better correlation with experimental results
compared to traditional Coulomb friction model, in terms of punch load-stroke curve
and thinning prediction. The FE prediction error for maximum punch load is 8%
using Coulomb friction model and 5.6% using the kinetic friction model. The error
decreases to 4.8% using the static friction model.
Description
Keywords
Kinetic fiction , Forming process