The simulation process has gained importance over the last decades for the cost-effective and reliable development of vehicle safety systems. The use of updated Human Body Models (HBMs) is key in the development process in order to deliver trustworthy simulations so that impact protection can be improved. One of the main objectives of the SENIORS project is to investigate and develop HBMs representative for older car occupants.
In the event of a car crash, elderly people tend to suffer more injuries in the thoracic area than other car occupants. For this reason, the improvements developed in SENIORS are focused on the thoracic rib cage for the car occupants, especially on the particularities on rib geometry of elderly people.
The main changes in the body of elderly and overweight people regarding the thorax anatomy are specific geometrical and material property changes. The figure below shows the ribcage geometry for a 35-year-old (blue), the original HBM (green) and a 75-year-old (red).
We used one of the most broadly used HBMs in the automotive industry, the THUMS TUC occupant model, to implement age-related material changes and rib cage geometry modifications. For the latter, we used almost 1,000 medical computer tomography scans from ICAM that generated 2D and 3D parameters for a better fitted geometry and consequently more accurate representation of elderly HBM.
Once the HBM was improved, it was time to assess the impact of these changes on the HBM. Using a simplified test condition (table-top seat-belt loading) and sled simulations with the aged model, we found a low effect on stiffness response, but we demonstrated an effect on rib peak strain, which is the most important predictor for rib fractures. Based on this finding, the improved HBM was adopted for further investigations related to rib fracture risk within the subsequent tasks of the SENIORS project.
Shortly before a crash, people tend to have a muscular reaction by pushing their arms against the steering wheel. This phenomenon, known as bracing, can have an effect on injury probability. HBMs can also be used to study this effect. To improve the HBMs in this area, in some cases the low-speed volunteers test was used to predict the response of elderly occupants during braking events (similar to what happens after the activation of an AEB system). We then compared these results with the outcome of simulations with HBMs. The correlation of the model output against the experiment was successful, although there is still some room for improvement.
As people age, often their BMI tends to increase (their weight increases), therefore overweight people is also a specific area of interest in SENIORS. The analysed particularities of overweight people are the lower rib angle, the rotation of ribs towards a more horizontal configuration and the tendency to have “rounder” ribs. The figure below shows the shape of the ribs for different weights, from 40 kg (in dark blue) to 175 kg (in red).
To study the effect this geometrical change has on potential injuries in car crashes, we compared a simulation of an average female occupant model with a modified overweight female occupant. We used the female occupant as it is more representative of elderly people. The results showed that, for the same seat position, the distance between the head and the instrumental panel for the overweight occupant was less than for the standard occupant and thus increased the risk of injuries in case of bottoming-out the airbag. Moreover, we also found higher neck forces and moments.
All these findings point in the same direction: the diversity of car occupants needs to be considered to improve their safety and HBMs can support this work greatly.