[Research on thorax impact injury of children at different ages based on finite element models].

The pediatric cadaver impact experiments were reconstructed using the validated finite element(FE) models of the 3-year-old and 6-year-old children. The effect of parameters, such as hammer size, material parameters and thorax anatomical structure characteristics, on the impact mechanical responses of 3-year-old and 6-year-old pediatric thorax was discussed by designing reasonable finite element simulation experiments. The research results showed that the variation of thorax contact peak force for 3-year-old group was far larger than that of 6-year-old group when the child was impacted by hammers with different size, which meant that 3-year-old child was more sensitive to hammer size. The mechanical properties of thoracic organs had little influence on the thorax injury because of the small difference between 3-year-old and 6-year-old child in this research. During the impact, rib deformation led to different impact location and deformation of internal organs because the 3-year-old and 6-year-old children had different geometrical anatomical structures, such as different size of internal organs. Therefore, the injury of internal organs in the two groups was obviously different. It is of great significance to develop children finite element models with high biofidelity according to its real anatomical structures.

[Effect of muscle biofidelity on thoracic impact biomechanical response of a six-year-old child using finite element method].

Finite element(FE) model of thorax with high biofidelity is one of the most important methods to investigate thoracic injury mechanism because of the absence of pediatric cadaver experiments. Based on the validated thorax finite element model, the FE models with equivalent muscles and real geometric muscles were developed respectively, and the effect of muscle biofidelity on thoracic injury was analyzed with reconstructing pediatric cadaver thorax impact experiments. The simulation results showed that the thoracic impact force, the maximum displacement and the maximum von-Mises stress of FE models with equivalent muscles were slightly greater than those from FE models with real geometric muscles, and the maximum principal strains of heart and lung were a little lower. And the correlation coefficient between cadaver corridor and FE model with real muscles was also greater than that between cadaver corridor and FE model with equivalent muscles. As a conclusion, the FE models with real geometric muscles can accurately reflect the biomechanical response of thorax during the impact.

[Effects of Geometrical Dimensions and Material Properties on the Rotation Characteristics of Head].

The validated finite element head model(FEHM)of a 3-year-old child,a 6-year-old child and a 50 th percentile adult were used to investigate the effects of head dimension and material parameters of brain tissues on the head rotational responses based on experimental design.Results showed that the effects of head dimension and directions of rotation on the head rotational responses were not significant under the same rotational loading condition,and the same results appeared in the viscoelastic material parameters of brain tissues.However,the head rotational responses were most sensitive to the shear modulus(G)of brain tissues relative to decay constant(ß)and bulk modulus(K).Therefore,the selection of material parameters of brain tissues is most important to the accuracy of simulation results,especially in the study of brain injury criterion under the rotational loading conditions.

Brain pressure responses in translational head impact: a dimensional analysis and a further computational study.

Brain pressure responses resulting from translational head impact are typically related to focal injuries at the coup and contrecoup sites. Despite significant efforts characterizing brain pressure responses using experimental and modeling approaches, a thorough investigation of the key controlling parameters appears lacking. In this study, we identified three parameters specific and important for brain pressure responses induced by isolated linear acceleration a(lin) via a dimensional analysis: a(lin) itself (magnitude and directionality), brain size and shape. These findings were verified using our recently developed Dartmouth Head Injury Model (DHIM). Applying a(lin) to the rigid skull, we found that the temporal profile of the given a(lin) directly determined that of pressure. Brain pressure was also found to be linearly proportional to brain size and dependent on impact direction. In addition, we investigated perturbations to brain pressure responses as a result of non-rigid skull deformation. Finally, DHIM pressure responses were quantitatively validated against two representative cadaveric head impacts (categorized as "good" to "excellent" in performance). These results suggest that both the magnitude and directionality of a(lin) as well as brain size and shape should be considered when interpreting brain pressure responses. Further, a model validated against pressure responses alone is not sufficient to ensure its fidelity in strain-related responses. These findings provide important insights into brain pressure responses in translational head impact and the resulting risk of pressure-induced injury. In addition, they establish the feasibility of creating a pre-computed atlas for real-time tissue-level pressure responses without a direct simulation in the future.

[Response of a finite element model of the pelvis to different side impact loads].

The pelvis is one of the most likely affected areas of the human body in case of side impact, especially while people suffer from motor vehicle crashes. With the investigation of pelvis injury on side impact, the injury biomechanical behavior of pelvis can be found, and the data can help design the vehicle security devices to keep the safety of the occupants. In this study, a finite element (FE) model of an isolated human pelvis was used to study the pelvic dynamic response under different side impact conditions. Fracture threshold was established by applying lateral loads of 1000, 2000, 3000, 4000 and 5000 N, respectively, to the articular surface of the right acetabulum. It was observed that the smaller the lateral loads were, the smaller the von Mises stress and the displacement in the direction of impact were. It was also found that the failure threshold load was near 3000 N, based on the fact that the peak stress would not exceed the average compressive strength of the cortical bone. It could well be concluded that with better design of car-door and hip-pad so that the side impact force was brought down to 3000 N or lower, the pelvis would not be injured.

[Effects of head dimensions on intracranial responses based on finite element model].

A validated 5th and 95th percentile Chinese head model was used to investigate the influence of head dimensions on the biomechanical responses by comparing acceleration, intracranial pressure and shear stress of the heads with different dimensions under the same impact energy. Moreover, the reasonability of scaling method used in the research considering head dimensions was discussed by respectively scaling the small head to a big one and scaling the big head to a small one. It therefore more scientifically provides a newer and more scientific reference for the assessment of head injury.

[Development and validation of a finite element model of human knee joint for dynamic analysis].

Based on the biomechanical response of human knee joint to a front impact in occupants accidents, a finite element (FE) model of human knee joint was developed by using computer simulation technique for impacting. The model consists of human anatomical structure, including femoral condyle, tibia condyle, fibular small head, patellar, cartilage, meniscus and primary ligament. By comparing the results of the FE model with experiments of the knee joint in axial load conditions, the validation of the model was verified. Furthermore, this study provides data for the mechanical of human knee joint injury, and is helpful for the design and optimization of the vehicle protective devices.

[The measurement and analyses of symmetry characteristic of human skull based on CT images].

Two kinds of algorithm have been set forth to estimate the symmetry characteristic of live human skull on CT image. These CT images were treated with a series of processes such as coding into programs, formatting originals, binary coding, rectifying image deviation, detecting boundary edge, and quantitatively measuring the skull symmetry. The statistical analyses of measuring 3000 live human skull images have worked out the ratio and the distribution of the skull symmetry, so that dependable data are provided for establishing the human head injury biomechanics model. The results are of great practical value in the fields of anatomy, clinical medicine, biomechanies study, head injury analysis, etc.

[The thickness measurement of alive human skull based on CT image].

This study sought to measure accurately the thickness of the frontal, parietal and occipital bones of the alive human skull based on CT images. The images were treated with a series of processes by coding into a program: image segmentation and binary coding; eliminating edge interference; rectifying image deviation and clarifying boundary edge; redrawing the boundary and reference point fixing; and finally thickness measurement. The new method can measure not only the different points in one CT image but also the same point in massive CT images. The measurement results are of great practical value in the fields of anatomy, clinical medicine, biomechanics study, head injury analysis, etc.

[A new exploration of the applicability of the head injury criterion].

Head injury criterion (HIC) is a widely accepted injury criterion in assessing the injury potential of the human head under external loads. It has been used in vehicle safety regulations worldwide and helmet design. However, controversy about its applicability exists. In this study, two human head models of different size and mass were created to explore the applicability of HIC. Under three different impact loadings, the principal stresses of the two brains of the two different head models were calculated and compared with the corresponding HIC values. The influences on the application of HIC in head injury assessment were investigated. This study provides some new insights and leads new conclusions towards human head injury assessment.