Investigation of a relationship between external force to shoulder and chest injury of WorldSID and THUMS in 32 km/h oblique pole side impact.

Objective: This article describes the chest injury risk reduction effect of shoulder restraints using finite element (FE) models of the worldwide harmonized side impact dummy (WorldSID) and Total Human Model for Safety (THUMS) in an FE model 32 km/h oblique pole side impact.

Methods: This research used an FE model of a mid-sized vehicle equipped with various combinations of curtain shield air bags, torso air bags, and shoulder restraint air bags. As occupant models, AM50 WorldSID and THUMS AM50 Version 4 were used for comparison.

Results: The research investigated the effect of shoulder restraint air bag on chest injury by comparing cases with and without a shoulder side air bag. The maximum external force to the chest was reduced by shoulder restraint air bag in both WorldSID and THUMS, reducing chest injury risk as measured by the amount of rib deflection, number of the rib fractures, and rib deflection ratio. However, it was also determined that the external force to shoulder should be limited to the chest injury threshold because the external shoulder force transmits to the chest via the arm in the case of WorldSID and via the scapula in the case of THUMS. Because these results show the shoulder restraint air bag effect on chest injury risk, the vent hole size of the shoulder restraint air bag was changed for varying reaction forces to investigate the relationship between the external force to the shoulder and the risk of chest injury. In the case of THUMS, an external shoulder force of 1.8 kN and more force from the shoulder restraint air bag was necessary to help prevent rib fracture. Increasing external force applied to shoulder up to 6.2 kN (the maximum force used in this study) did not induce any rib or clavicle fractures in the THUMS. When the shoulder restraint air bag generated external force to the shoulder from 1.8 to 6.2 kN in THUMS, which were applied to the WorldSID, the shoulder deflection ranged from 35 to 68 mm, and the shoulder force ranged from 1.8 to 2.3 kN.

Conclusions: In the test configuration used, a shoulder restraint using the air bag helps reduce chest injury risk by lowering the maximum magnitude of external force to the shoulder and chest. To help reduce rib fracture risk in the THUMS, the shoulder restraint air bag was expected to generate a force of 3.7 kN with a minimum rib deflection ratio. This corresponds to a shoulder rib deflection of 60 mm and a shoulder load of 2.2 kN in WorldSID. Supplemental materials are available for this article. Go to the publisher's online edition of Traffic Injury Prevention to view the supplemental file.