FEA simulations revealed that the friction between the sample
and the loading platens causes bulging (or barreling) of the
sample under compression loading, which then leads to inhomogeneity in the stress and strain distributions in the sample.
The degree of stress and strain inhomogeneity in the sample
depended upon its aspect ratio. Formation of friction cone (or
hill) may be responsible for an increase in the stress bearing
capacity of PDMS with a decrease in aspect ratio of the sample.
Increased apparent stiffness of the sample with a decrease in
aspect ratio is also responsible for a relative increase in the
stress-relaxation with a decrease in aspect ratio