Critical Factors Influencing Lap Belt-Pelvis Interaction and Submarining Occurrence for Occupants in Frontal Crashes

Submarining is defined as the mechanism in which the lap belt, initially positioned superficial to the anterior superior iliac spines (ASIS), fails to engage the bony pelvis during occupant forward excursion, and translates superior and posterior relative to the ASIS, loading the abdominal soft tissue. The goal of this dissertation was to evaluate the effects of parameters pertaining to the vehicle environment (extrinsic) and occupant (intrinsic) on lap belt-pelvis interaction and submarining occurrence through experiments using post- mortem human surrogates (PMHS) and simulations using computational human body models (HBMs).
A comprehensive literature review was performed to identify the intrinsic and extrinsic factors that have been hypothesized to affect lap belt-pelvis interaction, particularly submarining. Of these factors, investigating the effects of a reclined torso angle and the angle of the lap belt relative to the pelvis required additional experimental research and HBM validation. This finding informed the design of the experimental and computational studies of this dissertation. As no experimental data existed to understand how a reclined seating posture affected lap belt-pelvis interaction and submarining occurrence, an innovative methodology was developed to investigate this through experimental sled tests using PMHS. One subject (of five) submarined, and exhibited a large lap belt-pelvis angle, indicating a shallow lap belt angle relative to the horizontal and/or a pelvis pitched rearward, relative to the other subjects. This prompted the need for further experimental study to identify a submarining threshold through variation of this lap belt-pelvis angle. This parameter was further investigated in belt pull experiments through systematic variation of lap belt and torso angle, which identified a submarining threshold. Finally, a parametric study, in which the effects of extrinsic and intrinsic factors on lap belt-pelvis interaction and submarining were quantified, was conducted using a computational HBM, validated in the aforementioned test conditions. The simulations were sampled to best approximate for the full design space and used to develop, train, and test a neural network (NN) metamodel which predicted submarining occurrence based on these varied input parameters. From the NN metamodel’s predictions, fore-aft lap belt angle and recline angle were identified as the dominating factors (out of nine) that affected submarining occurrence.
This dissertation provides the automotive safety community with a wealth of data to inform restraint system design for current and future vehicles. Specifically, this research improves the automotive safety field’s understanding of the fundamental characteristics that influence lap belt-pelvis interaction and submarining. This research also identifies limitations of current safety standards for a restraint system equipped with modern technologies, and for a reclined seating posture. Finally, this research shows that lap belt angle and recline angle are the dominant parameters affecting submarining risk, and thus need to be prioritized in further research with varying boundary conditions, HBM formulations, and anthropometries.