Blunt force impact to the head using a teeball bat: systematic comparison of physical and finite element modeling

Blunt head trauma secondary to violent actions with various weapons is frequently a cause of injury in forensic casework; differing striking tools have varying degrees of injury capacity. The systematic approach used to examine a 19-year-old student who was beaten with a wooden teeball bat will be described. The assailant stopped beating the student when the teeball bat broke into two pieces. The surviving victim sustained bruises and a forehead laceration. The State's Attorney assigned a forensic expert to examine whether the forces exerted on the victim's head (leading to the fracture of the bat) were potentially life threatening (e.g. causing cranial bone fractures). Physical modeling was conducted using a pigskin-covered polyethylene end cap cushioned by cellulose that was connected to a piezoelectric force gauge. Experiments with teeball bats weighing 295-485 g demonstrated that 12-20 kN forces were necessary to cause a comparable bat fracture. In addition to physical testing, a computer-aided simulation was conducted, utilizing a finite-element (FE) method. In the FE approach, after selecting for wood properties, a virtual bat was swung against a hemisphere comprising two layers that represented bone and soft tissue. Employing this model, a 17.6 kN force was calculated, with the highest fracture probability points resembling the fracture patterns of the physically tested bats.