Ballistic Gelatin Characterization and Constitutive Modeling

Abstract

Ballistic gelatin is widely used as a soft tissue simulant for non-penetrating and penetrating, and the mechanical properties of gelatin are known to be highly sensitive to strain rate and temperature. Mechanical compression testing was undertaken across a range of strain rates at constant temperature to evaluate the material response. The material strength and stiffness increased with increasing strain rate, while the strain to failure was relatively constant across a wide range strain rates. The mechanical test data was implemented in two constitutive models: a quasi-linear viscoelastic model, commonly available in explicit finite element codes, and a tabulated hyperelasticity model. The implementations were verified using simulations of the experimental tests and it was found that the quasi-linear viscoelasticity model did not adequately capture the low and high strain rate response across the range of data. The tabulated hyperelasticity model was found to provide accurate representation of the material across the range of strain rates considered, and included a damage function to predict material failure.

Characterization of real and substitute birds through experimental and numerical analysis of momentum, average impact force and residual energy in bird strike on three rigid targets: A flat plate, a wedge and a splitter

“…Force or momentum can be measured using multiple set-ups such as a ballistic pendulum [18], a Hopkinson bar [1,3,19], a spring in the form of calibrated beams [8], load cells [20][21][22][23][24][25][26][27][28], etc, all having their advantages and disadvantages. The actual shock behaviour and constitutive modelling of ballistic gelatine can be investigated using more fundamental set-ups such as the Hopkinson bar [29][30][31].…”

A constitutive model for ballistic gelatin at surgical strain rates

“…Characterisation at lower speeds, similar to here, was considered in (Cronin and Falzon (2011);Cronin (2011)). Both finite strain behaviour and strain rate-dependence were studied.…”

“…Such models, however, are unable to capture strain rate-dependence, and it was therefore separately fit to the data for each strain rate. Improved models aimed at addressing this deficiency were proposed in (Cronin (2011)) in the form of quasi-linear viscoelasticity and tabulated hyperelasticity, both of which are able to capture strain rate-dependence, though using quite different approaches. Viscoelastic models are formulated in terms of a convolution integral that imbues a dependence on the entire strain history of the material, naturally including, for example, temporal patterns of strain magnitude and rate.…”

“…Many important physical manifestations of these mechanisms, such as stress relaxation, creep and rate-dependence therefore naturally emerge from such models. In contrast, tabulated models, which were favoured in (Cronin (2011)), simply incorporate an ensemble of elastic response curves at different strain rates, and provide a numerical mechanism for switching between them according to the imposed loading characteristics (Kolling et al (2007)). The approach is general in the sense that quite varied phenomena can be included (for example, a wide range of loading speeds was considered in (Cronin (2011)), as well as material damage), but it relies on provision of a sufficiently rich set of constituent curves to cover the desired range of loading conditions.…”

“…In contrast, tabulated models, which were favoured in (Cronin (2011)), simply incorporate an ensemble of elastic response curves at different strain rates, and provide a numerical mechanism for switching between them according to the imposed loading characteristics (Kolling et al (2007)). The approach is general in the sense that quite varied phenomena can be included (for example, a wide range of loading speeds was considered in (Cronin (2011)), as well as material damage), but it relies on provision of a sufficiently rich set of constituent curves to cover the desired range of loading conditions. Instabilities may also be introduced when transitioning between certain loading regimes, meaning additional care must be taken in those regions (Kolling et al (2007)).…”