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Recent field data showed that lumbar spine fractures occurred more frequently in late model vehicles than early ones in frontal crashes. However, the lumbar spine designs of the current crash test dummies are not accurate in human anatomy and have not been validated against any human/cadaver impact responses. In addition, the lumbar spines of finite element (FE) human models, including GHBMC and THUMS, have never been validated previously against cadaver tests. Therefore, this study developed a detailed FE lumbar spine model and validated it against cadaveric tests. To investigate the mechanism of lumbar spine injury in frontal crashes, effects of changing the coefficient of friction (COF), impact velocity, cushion thickness and stiffness, and cushion angle on the risk of lumbar spine injuries were analyzed based on a Taguchi array of design of experiments. The results showed that impact velocity is the most important factor in determining the risk of lumbar spine fracture (P = 0.009). After controlling the impact velocity, increases in the cushion thickness can effectively reduce the risk of lumbar spine fracture (P = 0.039).

In autonomous vehicles, passengers often recline their seatbacks for a more comfortable posture. Such a reclined posture greatly increases risk of submarining and other injury concerns due to the unfavourable geometrical configuration of occupant, seat and seatbelt. In this paper, numerous simulations with a modified computational dummy model are proposed to analyse effects of various occupant restraint systems in frontal impact, including seatbelt, pretensioner, load limiter, locking tongue, airbag, knee bolster and so on. After the sensitivity analyses, four concepts for designing anti-submarining countermeasures are proposed: (1) increase the lap belt-topelvis friction coefficient; (2) reduce the shoulder belt force along with the use of the locking tongue; (3) increase the lap belt angle; (4) reduce the H point forward and downward displacement. Sled tests with anti-submarining countermeasures were conducted to verify the effectiveness of the anti-submarining concepts for reclining seats. Four anti-submarining countermeasures are suggested to prevent the submarining with no other auxiliary hurts: load limiter plus locking tongue, anchor pretensioners plus antisubmarining bar, seat cushion airbag, and retractor plus buckle pretensioner. This paper could give better understanding of submarining mechanism and eligible vehicle design.

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