  An in-situ Dynamic Mechanical Analysis (DMA) method for soft matter developed
by our group [Wu. et.al. 2022] encounters the problem of irregular samples,
which significantly vary in shape and size in practice, therefore a standard
sample "large enough" to ignore the boundary and size effects is necessary to
determine the baseline of test and build the correspondence between this new
method to classical mechanical tests. In this work, we use finite element
analysis to approach the optimal size of a brick sample where the stress on the
boundaries in three spatial directions are ignorable, and certified the results
by testing a series of silicone gel samples on the in-situ DMA device. The
stress-strain of tensile and compression are characterized. The material
properties of gel are chosen to be close to the biological soft tissue. The
size of 40mm(L)*40mm(W)*20mm(H) is determined to be the optimal result.
