Experimental impacts of less lethal rubber spheres on a skin-fat-muscle model

Effectiveness and safety assessment for kinetic energy (KE) bullets is of importance, considering numerous reports about excessive damage cases of KE bullets in recent years. Early study of KE impacting targets mainly focused on threshold penetration issue, but did not involve cavity evolution of target and energy transfer. The paper aimed at analyzing cavity evolution and energy transfer during rubber bullet impacting skin-fat-muscle model.

In the ballistic experiment, skin-fat-muscle model was built including cowhide, paraffin gel and gelatin, respectively simulating skin, fat and muscle. 16 mm spherical rubber bullets were fired at a range of velocities (71 m/s-134 m/s) to skin-fat-muscle model. There were totally 7 valid impacts. Cavity evolution and cowhide deformation were captured by a high-speed camera.

Experiment result indicates that cavity shape evolution can be divided into 3 stages: parabola stage, arc stage, and bowl stage. The cavity shape evolution at different velocities follows a similar changing rule. Cavity depth firstly increases and then decreases with time. Cavity width gradually increases with time and the rate at which the cavity width grows decreases with time. The maximum cavity depth and cavity width at the same moment increase linearly with impacting velocity. When bullet impacts on the model, deformation occurs on the cowhide, paraffin gel and gelatin. Kinetic energy of bullet gradually transfers into kinetic energy of cowhide, strain energy of cowhide, absorbing energy of soft tissue (paraffin gel and gelatin). Energy transfer analysis result of 134 m/s demonstrates rubber bullet kinetic energy mainly transfers into cowhide strain energy and absorbing energy of paraffin gel and gelatin. Moreover, cowhide strain energy firstly increases and then decreases with time.