Biomechanics as support for forensic expert reports in/after pedestrian-car collisions

This paper systematically explores the mechanical properties of facial and cranial bones, aiming to contribute to the understanding of brain and cervical spine injuries from a mechanical/biomechanical perspective. The research also seeks to provide insights applicable in forensic practice, bridging the gap for engineering professionals not typically involved in forensic medicine. Strength and stiffness parameters of facial and cranial bones were utilized to analyze forces leading to fractures, proposing a simple analytical approach for determining head velocity upon striking a car windshield. Experimental testing was conducted to examine defects on the windshield resulting from an impactor's crash, simulating head impacts at varying velocities. Two approaches for determining head impact velocity during pedestrian-car collisions were explored. The first, neglecting body deformation effects, assumes that the manikin's center of gravity moves at the same speed as the impacting vehicle, resulting in an impact velocity that is approximately twice the car's speed. The second, a more realistic scenario, considers slower movement of the body's center of gravity, yielding an impact velocity that is about one and a half times the car's speed, with a specific angle relative to the X-axis. Calculation reveals that head impact velocity decreases with reduced windshield inclination at constant vehicle speed. Experimental testing with an adult head impactor monitored impact velocity, acceleration, contact time, and puncture diameter and depth on the vehicle glass. Results align closely with published data, emphasizing higher injury risk near the location of fixation of the windshield to the frame of the vehicle. In forensic investigations, the research findings, including newly measured or calculated parameters, offer practical applications. Acknowledging simulation limitations, the study emphasizes the reliance on experimental data for a more realistic understanding. Application of knowledge in expert opinions for car crashes with injuries involves considering windshield defect dimensions in relation to speed, minimizing the need for revision by expert opinions. This comprehensive exploration contributes to understanding biomechanical factors influencing injuries, particularly in vehicular accidents, and underscores the importance of empirical data in forensic practice. The proposed analytical approach and experimental insights provide valuable tools for forensic professionals and contribute to the broader understanding of injury mechanisms.