Current state and progress of research on forensic biomechanics in China

[Mathematical modeling using finite element analysis in forensic medical examination]

The purpose of the work is to develop methods of mathematical modeling using finite element analysis in forensic medical examination. The stages of the methodology for solving problems of deformable body mechanics in forensic medicine are considered, which allows to reliably establish the possibility of formation and morphology of damage under specific conditions and circumstances, to focus the researcher's attention on problem points when creating and evaluating the model. The use of simplified models of the human body makes the expert's conclusion more reasonable, which increases the confidence of law enforcement agencies in the activities of the forensic medical expert service and allows for a new look at solving the problems of forensic medicine and forensic medical examination.

Multiobjective optimization algorithm for accurate MADYMO reconstruction of vehicle-pedestrian accidents

In vehicle-pedestrian accidents, the preimpact conditions of pedestrians and vehicles are frequently uncertain. The incident data for a crash, such as vehicle deformation, injury of the victim, distance of initial position and rest position of accident participants, are useful for verification in MAthematical DYnamic MOdels (MADYMO) simulations. The purpose of this study is to explore the use of an improved optimization algorithm combined with MADYMO multibody simulations and crash data to conduct accurate reconstructions of vehicle-pedestrian accidents. The objective function of the optimization problem was defined as the Euclidean distance between the known vehicle, human and ground contact points, and multiobjective optimization algorithms were employed to obtain the local minima of the objective function. Three common multiobjective optimization algorithms-nondominated sorting genetic algorithm-II (NSGA-II), neighbourhood cultivation genetic algorithm (NCGA), and multiobjective particle swarm optimization (MOPSO)-were compared. The effect of the number of objective functions, the choice of different objective functions and the optimal number of iterations were also considered. The final reconstructed results were compared with the process of a real accident. Based on the results of the reconstruction of a real-world accident, the present study indicated that NSGA-II had better convergence and generated more noninferior solutions and better final solutions than NCGA and MOPSO. In addition, when all vehicle-pedestrian-ground contacts were considered, the results showed a better match in terms of kinematic response. NSGA-II converged within 100 generations. This study indicated that multibody simulations coupled with optimization algorithms can be used to accurately reconstruct vehicle-pedestrian collisions.

Effects of Loading Conditions on the Pelvic Fracture Biomechanism and Discrimination of Forensic Injury Manners of Impact and Run-Over Using the Finite Element Pelvic Model

This study aimed to systematically simulate the responses of pelvic fracture under impact and run-over to clarify the effects of boundary and loading conditions on the pelvic fracture mechanism and provide complementary quantitative evidence for forensic practice. Based on the THUMS finite element model, we have validated the simulation performance of the model by a real postmortem human pelvis side impact experiment. A total of 54 simulations with two injury manners (impact and run-over), seven loading directions (0°, 30°, 60°, 90°, 270°, 300°, 330°), and six loading velocities (10, 20, 30, 40, 50, and 60 km/h) were conducted. Criteria of effective strain, Von-Mises stress, contact force, and self-designed normalized eccentricity were used to evaluate the biomechanism of pelvic fracture. Based on our simulation results, it’s challenging to distinguish impact from run-over only rely on certain characteristic fractures. Loads on the front and back were less likely to cause pelvic fractures. In the 30°, 60°, 300° load directions, the overall deformation caused a “diagonal” pelvic fracture. The higher is the velocity (kinetic energy), the more severe is the pelvic fracture. The contact force will predict the risk of fracture. In addition, our self-designed eccentricity will distinguish the injury manner of impact and run-over under the 90° loads. The “biomechanical fingerprints” based on logistic regression of all biomechanical variables have an AUC of 0.941 in discriminating the injury manners. Our study may provide simulation evidence and new methods for the forensic community to improve the forensic identification ability of injury manners.