Development of a finite element model of the human body

A finite element human model, THUMS (Total HUman Model for Safety), was developed in order to study human body responses to impact loads. This paper briefly describes the structure of the human model, as well as some of the results of the simulations conducted to validate the model. Crash/Safety (1) 7th International LS-DYNA Users Conference 3-38 INTRODUCTION A finite element model of the whole human body, THUMS (Total HUman Model for Safety), has been developed. The purpose of the THUMS model is for the LS-DYNA users to simulate responses of the human body sustaining impact loads. This paper briefly describes the structure of the human model, as well as some results of the simulations conducted to validate the model. Finally, we describe further development plan of the model. OVERVIEW OF THE THUMS MODEL The THUMS model represents 50 percentile American adult male in a seating posture. Figure 1 shows the whole structure of the THUMS model with some soft tissues removed to expose the skeletal structure. The model contains about sixty thousand nodes and eighty thousand elements that include thirty thousand solid elements, fifty thousand shell elements and three thousand bar or beam elements. Figure 1. The THUMS Model with Some Soft Tissues Removed to Expose the Skeletal Structure 7th International LS-DYNA Users Conference Crash/Safety (1) 3-39 Whole skeletal structures are modeled in the THUMS model. Each bone consists of solid elements and shell elements; the solid elements represent the cancellous bone while the shell elements represent the cortical bone. In the joints of the THUMS model, ligaments that connect the bones are modeled by using shell elements or beam elements and sliding interfaces are defined on the contacting surfaces of these bones. In the thoracic cavity, the lung and heart are modeled as a single continuum body with solid elements. Abdominal organs are also modeled as continuum bodies. Skins and muscles that cover the bones are modeled with solid elements. The material properties of the tissues have been taken from Yamada (1970). VALIDATION OF THE THUMS MODEL Thoracic Frontal Impact Simulation We have simulated the published cadaver impact tests conducted by Kroell et al. (1971 and 1974) to validate the response of the THUMS model to thoracic frontal impact. Figure 2 shows the set-up of the THUMS model and the pendulum. Though all the soft tissues are included in the simulation, the right half of the soft tissues is removed to expose the skeletal structure in the Figure 2. The arrow in the figure shows the direction of the pendulum’s motion. In this simulation the mass and initial velocity of the pendulum are 23.4kg and 6.9m/s, respectively. Thoracic Side Impact Simulation The thoracic side impact simulation is discussed in this section. We have simulated the cadaver impact test conducted by Bouquet et al. (1994). Figure 3 shows the configuration of the THUMS model and the pendulum. In this simulation the mass and initial velocity of the pendulum are 23.4kg and 5.9m/s, respectively. We show the direction of the pendulum’s motion by the arrow in the figure. Figure 2. The Set-up of the Thoracic Frontal Impact Simulation Figure 3. The Set-up of the Thoracic Side Impact Simulation Crash/Safety (1) 7th International LS-DYNA Users Conference 3-40 Pelvic Side Impact Simulation In this section the pelvic side impact simulation is discussed. We have simulated the cadaver impact experiment reported by Viano (1989). Figure 4 shows the set-up of the THUMS model and the pendulum. In this simulation the mass and initial velocity of the pendulum are 23.4kg and 9.5m/s, respectively. The arrow in the figure indicates the direction of the pendulum’s motion. Abdominal Frontal Impact Simulation In this section the abdominal frontal impact simulation is described. We simulated the cadaver impact tests conducted by Nusholtz et al. (1988). Figure 5 shows the THUMS model and the pendulum that simulates a lower half of a steering wheel. In this simulation the mass and initial velocity of the pendulum are 18kg and 10m/s, respectively. The arrow in the figure indicates the direction of the pendulum’s motion. Figure 4. The Set-up of the Pelvic Side Impact Simulation Figure 5. The Set-up of the Abdominal Frontal Impact Simulation 7th International LS-DYNA Users Conference Crash/Safety (1) 3-41 RESULTS AND DISCUSSION Thoracic Frontal Impact Simulation Figure 6 shows the relation between the chest deflection in the antero-posterior direction and the impact force sustained by the chest. The solid line shows the simulation result, while the dashed lines show the upper and lower limits of the corridor obtained by Kroell et al. (1971 and 1974). The simulation result shows a good agreement with the experimental data. Figure 7 shows the deformation of the model at 0, 20, 40, and 60msec. The right half of the soft tissues are not shown in this figure to expose the skeletal structure. Although the overall force-deflection response of the model shows a good agreement with the experimental corridor, the unloading path of the model response deviates from the corridor. Therefore, we may add more energy-absorbing capabilities to the materials of the thoracic tissues so that the unloading path of the model response can be more accurate. Figure 6. Force-deflection curve obtained from the thoracic frontal impact simulation and the cadaver test conducted by Kroell et al (1971, 1974) Crash/Safety (1) 7th International LS-DYNA Users Conference 3-42 Figure 7. Deformation of the body obtained from the thoracic frontal impact 0msec 20msec