Mechanical Properties of Ballistic Gelatin at High Deformation Rates

Abstract

The characterization of soft or low impedance materials is of increasing importance since these materials are commonly used in impact and energy absorbing applications. The increasing role of numerical modeling in understanding impact events requires high-rate material properties, where the mode of loading is predominantly compressive and large deformations may occur at high rates of deformation. The primary challenge in measuring the mechanical properties of soft materials is balancing the competing effects of material impedance, specimen size, and rate of loading. The traditional Split Hopkinson Pressure Bar approach has been enhanced through the implementation of polymeric bars to allow for improved signal to noise ratios and a longer pulse onset to ensure uniform specimen deformation. The Polymeric Split Hopkinson Pressure Bar approach, including the required viscoelastic bar analysis, has been validated using independent measurement techniques including bar-end displacement measurement and high speed video. High deformation rate characterization of 10% and 20% ballistic gelatin, commonly used as a soft tissue simulant, has been undertaken at nominal strain rates ranging from 1,000 to 4,000/s. The mechanical properties of both formulations of gelatin exhibited significant strain rate dependency. The results for 20% gelatin are in good agreement with previously reported values at lower strain rates, and provide important mechanical properties required for this material.

High Strain Rate Mechanics of Polymers: A Review

“…titanium, magnesium alloy or aluminum, or a polymer, e.g. polymethylmethacrylate (PMMA), PC, or nylon [77][78][79][80][81][82][83][84][85][86][87][88]. Low impedance metallic bars do not require any changes to the experimental apparatus or data reduction.…”

Robotic burrowing in brain parenchyma tissue

“…To obtain the right boundary conditions, we calculated the elastic constant and the viscosity of the gelatine running a simulation to match the data shown in (Salisbury and Cronin, 2009) using a linear Maxwell model, for 20% and 10% gelatine concentration. A simulation was run to fit the data for all the frequencies shown in (Salisbury and Cronin, 2009) (from 350Hz up to 4000Hz), focusing on the measured resonant frequencies of the stripe actuator, i.e.…”

“…Therefore, gelatine is a good material for obtaining preliminary results on the burrowing properties of such a microrobot. Even if the gelatine properties are well known at low frequencies, there is only one paper describing viscoelastic behaviour of gelatine at high frequencies (Salisbury and Cronin, 2009). By using these results we extracted the viscoelastic parameters of the gelatine assuming a Maxwell model and running the simulation of the experiment detailed in the Salisbury article (Salisbury and Cronin, 2009).…”

“…Even if the gelatine properties are well known at low frequencies, there is only one paper describing viscoelastic behaviour of gelatine at high frequencies (Salisbury and Cronin, 2009). By using these results we extracted the viscoelastic parameters of the gelatine assuming a Maxwell model and running the simulation of the experiment detailed in the Salisbury article (Salisbury and Cronin, 2009). In this paper, preliminary evaluation of the commercial actuator's ability to advance in the measured materials is shown and the performances of a microsystem that can be embedded in the brain is evaluated.…”

A constitutive model for ballistic gelatin at surgical strain rates

“…The majority of past studies have focused on characterisation at 'dynamic' (∼ 1000 − 3000s −1 ) strain rates, reflecting its primary application area (Kwon and Subhash (2010); Subhash et al (2012); Salisbury and Cronin (2009)). Test configurations such as Hopkinson bar impact (Cronin and Falzon (2009)), uniaxial tension (Moy et al (2008)), indentation (Juliano et al (2006)), and others have been used for this purpose.…”