Response and Vulnerability of the Upper Arm Through Side Air Bag Deployment 973323

The number of passenger cars equipped with side air bags is steadily increasing. With the aim of investigating the mechanical responses and the injuries of the arm under the influence of a side air bag, tests in probably higher injury risk configurations with dummies and cadavers were performed.

The air bag was installed at the outer side of the seat back, with the subject seated in the driver or front passenger seat of a passenger car. During the inflation of the air bag, the left or right forearm of the subject was positioned on the arm rest while the upper arm made contact with the seat back edge. The volume of the thorax air bag was 15 litres and for the thorax-head air bag 28 litres. The dummy was instrumented at the thorax c.g. shoulder, elbow and wrist with triaxial accelerometers. In the cadaver, triaxial accelerations in three orthogonal directions were measured at the upper and the lower humerus, the upper radius and the lower radius and the first thoracic vertebrae. Bending tests on three humeri was performed to characterise the mechanical properties of the bone.

Two high speed cameras with a frame rate of 1000 or 2000 frames/secs were used in order to record the deployment phase as well as the arm movement.

During the post test film review it was determined, that the interaction of the Hybrid III dummy with the Side Air Bag (SAB) was different from that of the cadaver. In all of the dummy tests, a clockwise rotation of the forearm between 20° and 90° occurred with a simultaneous slip-through of the air bag between the arm and the vehicle B-pillar/door trim. The general motion of the cadaver's arm was different to the dummy due to the different behaviour of the airbag.

The duration of the time-histories for the resultant accelerations varied between 10 and 15 ms. For the cadavers, the highest acceleration values were measured at the humerus with a maxima between 193 and 334 g, the lowest accelerations were measured at the Th1 with a maximum between 13 and 26 g. The dummies showed the highest values at the elbow and the wrist. In cadaver tests acceleration values were clearly than in the dummy tests.

The maximum bending moments for the three humeri were between 130 and 148 Nm. In only one case did the exposed humerus fracture, due to cushion fabric failure and the brittle condition of the bone. In a second case, a front rupture of the shoulder joint capsule with subluxation of the joint (arthritic joint) was observed.

The results indicate that even old people can endure the inflation of a side air bag without suffering humerus fractures.