A Shoulder Injury Criterion for the EuroSID-2re Applicable in a Large Loading Condition Spectrum of the Military Domain.

The EuroSID-2re (ES-2re) is an Anthropometric Test Device (ATD) from the automotive domain designed for lateral impact. Since the 2000's, it has also been used by NATO armies to assess the risk of injury to armored vehicles occupants submitted to an Improvised Explosive Device (IED) attack. The resulting loading conditions from an explosion can vary a lot in term of impact velocity and duration. They range from high velocity impacts (~28 m/s), characterized by a short duration (~10 ms) corresponding to cases where the panel deforms under an explosion, to low velocity impacts (~4 m/s), ch aracterized by a long duration (~50 ms) similar to the automotive domain. The goal of the study is to develop a shoulder injury criterion for the EuroSID- 2re that is relevant over the whole loading conditions spectrum of the military domain. For that purpose, thirty-three laboratory ES-2re tests are conducted to replicate four PMHS shoulder impactor test series from the literature. Each test series corresponds to a different loading condition in term of impact velocity and duration: [28 m/s, 3 ms], [14 m/s, 9 ms], [7 m/s, 30 ms], [4 m/s, 50 ms]. The injury result (AIS 2015 scale) of each PMHS test is paired with the shoulder sensor force response signal of the corresponding ES-2re test, resulting in a sample of 75 paired-data. The proposed injury criterion resulting from the sample analysis is the straightened peak force Fs, which is an estimate of the peak of the external force applied to the shoulder. This criterion combines two metrics from the response signal of the shoulder force sensor Y-axis of the ES-2re ATD: the initial slope (S) and the peak (Fmax). The threshold value for a given injury risk depends on the duration of the impact: it is higher for the shorter duration. Thus, a third metric should be extracted from the ES-2re shoulder load cell: the duration of the force T. The present study proposes three force-duration threshold curves Fs=f(T) for low, medium, and high risks of shoulder AI2+ injury.

Human Shoulder Response to Lateral Impact in Intermediate Loading Conditions Between High-Velocity, Short-Duration and Low-Velocity, Long-Duration.

The EuroSID-2re (ES-2re) Anthropomorphic Test Device (ATD) commonly known as the crash test dummy is also used in the military domain to assess the risk of injury of armored vehicles occupants from lateral impact. The loading conditions range from low velocity - long duration impacts (4 m/s - 50 ms) similar to the automotive domain, to high velocity - short duration impacts (28 m/s - 3 ms) corresponding to cases where the panel deforms under an explosion. The human shoulder response to lateral impact was investigated at bounds of the loading condition spectrum previously mentioned, and also at intermediate conditions (14 m/s - 9 ms) in previous studies. The aim of the current study is to provide additional insight at the intermediate loading conditions which are not found in the literature. Eight pure lateral shoulder impact tests were performed on Post Mortem Human Subjects (PMHS) using an 8.1 kg rigid impactor at velocities ranging from 3.3 m/s to 8.8 m/s with the duration ranging from 25 ms to 35 ms. The PMHS were instrumented with accelerometers attached to the sternum, and the upper thoracic spine (T1 vertebra). Strain gages were glued onto the right and left clavicles and ribs 2 to 6. The shoulder force was measured at the interface with the impactor and the impact was filmed by high speed cameras (5000 fps) to track the YZ displacements of the impactor, T1 vertebra, and sternum in the laboratory frame. Three shoulders out of the eight sustained AIS 2 injuries which included a clavicle fracture. The impactor forces ranged from 1200 to 4600 N. The PMHS accelerations ranged from 44 to 163 g at the sternum, and from 17 to 60 g at the T1 vertebra. The analysis of the strain gage signals revealed that the clavicle fractures occurred at the beginning of the impact and coincided with a peak force. An estimate of the acromion-to-shoulder compression (Cmax) was computed. It ranged from 0% to 15% for the non-injured shoulders, and from 19% to 28% for the injured shoulders. This new PMHS test series will be used in a future work to develop a shoulder injury criterion for the ES-2re ATD that is relevant for the whole loading conditions spectrum of the military domain.

Human Shoulder Response to High Velocity Lateral Impact.

The armies of the North Atlantic Treaty Organization need a shoulder injury criterion for the EuroSID-2re dummy that must be reliable over a large range of loading conditions, from high velocity, short duration impacts (28 m/s - 3 ms) to low velocity long, duration impacts (4 m/s - 50 ms). In the literature, the human shoulder response to lateral impact was investigated at bounds of the loading condition spectrum as previously mentioned. For the low velocities, the injuries were mainly clavicle fractures and the maximum compression between the acromion and the sternum (Cmax) was proposed as an injury criterion. For the high velocities, the typical injury was humerus fractures, including a crushed humeral head. The present study investigates the human shoulder response at an intermediate loading condition (14 m/s - 9 ms). Six lateral shoulder impact tests have been performed with three Post Mortem Human Subjects using a rigid impactor. The duration of the impact was controlled by means of an aluminum honeycomb that decelerated the impactor during the impact. The shoulder external deflection (impactor-to-sternum) ranged between 40 to 64 mm and the applied forces ranged from 4.3 kN to 8 kN. Four shoulders out of six sustained AIS2 injuries. Two acromio-clavicular joint dislocations, one clavicle fracture, and one scapula fracture were observed. Though the shoulder force responses were closer to those induced by the high velocity, short duration impacts, the injury patterns resembled those observed for low velocity, long duration loading conditions. Furthermore, the estimated acromion-to-sternum deflection values were not inconsistent with the prediction of the shoulder injury risk curve of the literature. Despite the relatively high-velocity impact (14.3 m/s), the shoulder injury mechanism appeared to be similar to those observed in the automotive field.