Deformation behavior of agar gel on a soft substrate during instrumental compression and its computer simulation

Deformation behavior of agar gel on a hard or soft substrate was investigated during instrumental compression at a crosshead speed of 10 mm/s, and its computer simulation was performed. Silicone rubbers of different consistencies were used as a soft substrate, and linear stress–strain response upon instrumental compression was confirmed in a range of 10%–30% nominal strain for each silicone rubber at the same crosshead speed. All agar gels of different consistencies tested fractured upon instrumental compression on hard aluminum stage at a nominal strain of av. 58.4% and showed high linearity in a range of 15%–30% nominal strain. Some agar gels fractured upon instrumental compression on the soft substrate at a smaller nominal strain of av. 41.9%, depending on the combination of both entities. Computer simulation based on a finite element model used the linear isotropic elastic moduli of both agar gel and silicone rubber as parameters for the linear static analysis. The simulation recreated well the reality of instrumental compression tests of agar gel on each substrate. The maximum equivalent strain for an element of agar gel was approx. 75% at the fracture point regardless of the substrate, where local strain-concentration occurred at the middle to lower part of the gel, working as a trigger of fracture.