Shear Wave Measurements of a Gelatin’s Young’s Modulus

Abstract

Gelatin is a commonly used material for analog experiments in geophysics, investigating fluid-filled fracture propagation (e.g., magmatic dikes), as well as fault slip. Quantification of its physical properties, such as the Young's modulus, is important for scaling experimental results to nature. Traditional methods to do so are either time consuming or destructive and cannot be performed in situ. We present an optical measurement technique, using shear waves. Polarizing filters enable visualization of the deviatoric stresses in a block of gelatin, so shear wave propagation can be observed. We demonstrate how the wave velocity can be measured and related to the Young's modulus, show how the results are comparable to another methodology and discuss processing techniques that maximize the measurement precision. This methodology is useful for experimentalist, as it is simple to implement into a laboratory setting, can make precise, time-efficient estimates of the material strength and additionally is non-destructive and can be performed in situ.

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

“…Slightly smaller Poisson's ratio with values around 0.45 for gelatin concentration greater than 3 wt % were measured by van Otterloo and Cruden [15] but the values they obtained for smaller concentration were unrealistic [15]. Pansino and Taisne 2 [20] inferred a value larger than 0.47 with a 2.7 wt % concentration. Because these values are very close to 0.5, we will further consider gelatin as an incompressible medium.…”

“…This method can be thought of as the equivalent of crustal Young's modulus estimations from seismic waves. The results were compared with estimations made using the static loading method and showed to be in good agreement [20]. In addition, Pansino and Taisne [20] proposed that the shear wave method could potentially be used to quantify any variations of the Young's modulus inside the tank.…”

“…In order to estimate the gelatin Young's modulus by measuring the shearwaves propagation velocity, we added polarizing filters on both the front and back sides of the tank. Following Pansino and Taisne [39,20], we excited the gelatin surface with a spoon, and we recorded the shear wave propagation with the front camera. Using the open source software TRACKER [12], we measured the propagation velocity (Fig.…”

“…An alternative method for non-destructive and in-situ measurements of Young's modulus has been proposed recently by Pansino and Taisne [39,20].…”

“…More recently, Pansino and Taisne [39,20] proposed to derive the Young's modulus from the propagation velocity of shear waves. They took advantage of gelatin being a birefringent photo-elastic material.…”