Characterizing the physical properties of gelatin, a classic analog for the brittle elastic crust, insight from numerical modeling

Precise characterization of the mechanical properties of gelatin, a classic analog of the elastic crust, is necessary
for scaling the mechanical models of the Earth's crust behavior in laboratory experiments. Here we reassess how
to accurately calculate the Young modulus (E) of gelatin contained in experimental tanks. By means of dedicated
analog experiments and finite element simulations, we estimate the bias introduced by using equations appro­
priate for a half-space to interpret the subsidence due to a cylindrical surface load applied on the gelatin. In the
case of a standard experimental setup with gelatin adhering to the tank wall, we find E is overestimated by at
least 5% for a box with lateral size smaller than 20 times the cylinder diameter. In addition, we deduce a
correction factor to be applied when using an analytical formula. We confirm that measuring the shear velocity
leads to accurate estimates for the rigidity of gelatin. We also propose a new method for in situ Young's modulus
estimation, relying on the length of air-filled propagating crack. Indeed, for a given injected volume, this length
depends only on the density contrast between air and gelatin and on the Young's modulus of the gelatin. The
fracture toughness of the gelatin is estimated independently. Direct comparison between fracture toughness and
Young's modulus shows that for a given Young's modulus, salted gelatin has a higher fracture toughness than
unsalted gelatin.