Characterization of 10% Ballistic Gelatin to Evaluate Temperature, Aging and Strain Rate Effects

Ballistic gelatin is widely used as a soft tissue simulant in physical surrogates for the human body to evaluate penetrating impacts and, more recently to evaluate blunt impact and blast loading effects on soft tissues. It is known that the properties of gelatin are sensitive to temperature and aging time, but this has not previously been quantified. The mechanical properties of 10% ballistic gelatin were measured using a compression test apparatus with temperature controlled platens to maintain the sample temperature at a fixed level. Penetration testing was undertaken using a standard BB impact test to assess the effect of aging. The gelatin was found to be within calibration after 3 days (72 h of aging), based on the standard penetration test. The material properties were evaluated using the stress at failure, strain at failure and material stiffness as characterized by the Neo-Hookean constitutive model. The stress at failure and material stiffness increased with decreasing temperature and increasing strain rate, as expected, while the strain at failure remained relatively constant for the test conditions considered (1 to 23°C, strain rate from 0.01 to 1.0 s⁻¹). The study showed that the penetration resistance was consistent after 72 h of aging, while the mechanical study demonstrated increasing failure stress and stiffness with decreasing failure strain at longer aging times, suggesting that these effects offset one another so that the penetration resistance remains relatively constant. The primary contribution of this study was to show the importance of temperature and aging time, through mechanical and penetration testing, to achieve appropriate and consistent response from ballistic gelatin.