Objective To explore the influence of child head injury under different impact angles by applying the finite element model of six-year-old child pedestrian as specified in the European New Car Assessment Programme (Euro NCAP). Methods Based on the finite element model of 6-year-old pedestrian with detailed anatomical structure as specified by the Euro NCAP (TB024), four groups of simulation experiments were set up to explore the mechanism of head injury in children under different impact angles. The initial position for head mass center was on the longitudinal center line of the car. The initial speed of the car was 40 km/h. The car contacted with the model from the direction of the right (0°), the front (90°), the left (180°) and the back (270°). The kinematics differences and head impact responses were compared, and injuries of the facial bone and skull were analyzed. Results Through the analysis of head contact force, acceleration of head mass center, resultant velocity of head mass center with the vehicle, head injury criterion (HIC15), facial bone fracture and skull stress distribution, it was found that the risk of head fracture and brain contusion under back impact and front impact was higher than that under side impact. The risk of head fracture and brain contusion was highest under back impact, while the lowest under side impact. Conclusions Child pedestrian head injury was the largest under back impact. The results have important application values for the assessment and development of car-pedestrian collision protection device.

Objective To study the influence of skull thickness on intracranial biomechanical parameters by finite element method. Methods The female head at 5th percentile was selected for CT scanning to construct finite element model of the head with high biofidelity,and the model was verified by reconstructed cadaver test. The finite element model of the head with different skull thickness was established, and multiple groups of tests were carried out to compare the intracranial mechanical parameters. Results The negative value of intracranial pressure was significantly affected by the decrease in skull thickness under the same head size, while the negative value of intracranial pressure was slightly affected, with an increasing trend. The shear stress and von Mises stress of brain tissues were significantly increased with skull thickness increasing. Conclusions Under the same head size, the skull thickness will affect head injury to a certain extent, and people with small skull thickness are more likely to be injured than those with large skull thickness.

Objective To study the constitutive model of adipose tissue at medium strain rate and its parameter inversion. Methods Based on experiments of adipose tissue mechanical properties, the compression experiment of adipose tissues was reconstructed by finite element method, and the parameters for characterizing constitutive models of adipose tissues were screened. Combined with the method of feasible direction (MFD) in optimization method, the reverse calculation for parameters of fat tissue constitutive model at medium strain rate was conducted. ResultsCompared with Ogden constitutive model, the viscoelastic constitutive model was more suitable for characterizing the mechanical response at medium strain rate (260 s-1). The parameters of the constitutive model suitable for simulation were obtained using the reverse method. Conclusions The viscoelastic constitutive model was more suitable for characterizing the mechanical response at medium strain rate. The results provide references for studying the influence of human adipose tissues on body injury in finite element simulation of vehicle collisions.

Objective To study influencing factors of renal blunt impact injury by using finite element (FE) method. Methods Based on CT images of the kidney, the kidney FE models for different age groups were constructed. The renal blunt impact test was reconstructed, and the influence of kidney material constitutive parameters, kidney tissue structure, kidney size, impact position and impact velocity on injury severity were analyzed. Results Under the same impact condition, the stress of renal cortex decreased with the kidney mass increasing, and increased with the impact velocity of the hammer increasing. The renal capsule had a certain energy absorption effect, so as to reduce the kidney stress. When the kidney was impacted, the stress of renal cortex under side impact was significantly higher than that under frontal impact. Conclusions Compared with viscoelastic constitutive model, Mooney Rivlin material constitutive model is more suitable for FE evaluation on renal injury severity. The renal injury decreases with the kidney mass increasing. The increase of impact velocity will intensify the renal injury severity. Renal capsule will reduce renal injury to a certain extent, so the existence of renal capsule structure must be considered in FE modeling of the kidney. Compared with frontal and rear impact, the renal injury severity is greater when the kidney is impacted from the lateral side.