Geometrical and Mechanical Characterization of the Abdominal Fold of Obese Post Mortem Human Subjects for Use in Human Body Modelling.

Abstract

Obese vehicle occupants sustain specific injury patterns in case of accidents in which the interaction between the seat belt and the abdomen may play a role. This study aimed to collect geometrical characteristics and to investigate the mechanical responses of the abdomen of obese subjects. Four Post Mortem Human Subjects (PMHS) with BMI ranging from 31 to 46 kg/m² were collected. CT-scans performed in the seated position revealed that the antero-posterior depth of the abdominal fold (from the inguinal region to the most anterior point of the abdominal surface) was much greater (170 mm max., 127 mm average) than the thickness of subcutaneous adipose tissues (85 max., 38 mm in average). Each PMHS was subjected to three infra-injurious antero-posterior belt pulls in a seated posture with a lap belt positioned (C1) superior to the umbilicus, (C2) inferior to the umbilicus, (C3) inside the abdominal fold between the abdomen and the thigh. During the C1 and C2 tests, the belt moved cranially, and the abdominal fold opened widely especially in C2. Forces remained below 1800 N, for maximum applied displacements ranging from 89 to 151 mm for C1 and C2, and 37 to 66 mm for C3. Finally, sled tests were conducted on two PMHS seated on a semi-rigid seat and restrained by a three-point belt equipped with pretensioners and a 3.5 kN force limitation at the shoulder. The first PMHS (BMI 39 kg/m²) was tested at 49 km/h (39 g peak) and sustained severe injuries (AIS 4 pelvis dislocation, AIS 3 bilateral femur fractures) attributed to the combined loading of the seat and lap belt force (about 11 kN and 7 kN, respectively). The second PMHS (BMI 46 kg/m²) was subjected to a 29 km/h test (8 g plateau) and sustained no injury. The lap belt slid inside the abdominal fold in the first case and deformed the lower abdomen in the second, providing limited restraint forces during that interaction and leading to a large body excursion for the first test. The results highlight the possible relevance of the abdominal fold at the abdomen thigh junction to model and study the restraint conditions of obese occupants using Human Body Models (HBM).