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Feature | MEEA Lumber Spine
Effect of Lumbar Spine Assemblies and Body-Borne Equipment Mass on Anthropomorphic
Test Device Responses During
Drop Tests
Daniel Aggromito1,2, Wenyi Yan1 1Monash University
ABSTRACT
When simulating or conducting land mine blast tests on armoured vehicles to assess potential occupant injury, the preference is to use the Hybrid III anthropomorphic test device (ATD). In land blast events, the effect of body- borne equipment (BBE) on the ATD response is not well understood. An experimental study was carried out using a drop tower test rig, with a rigid seat mounted on a carriage table undergoing average accelerations of 161 g and 232 g over 3 ms. A key aspect of the work looked at the various lumbar spine assemblies available for a Hybrid III ATD. These can
result in different load cell orientations for
the ATD which in turn can affect the load measurement in the vertical and horizontal planes. Thirty-two tests were carried out using two BBE mass conditions and three variations of ATDs. The three ATDs investigated were the Hybrid III with the curved (conventional) spine, the Hybrid III with the pedestrian (straight) spine, and the Federal Aviation Administration (FAA) Hybrid III (straight spine). The results showed that the straight lumbar spine assemblies produced similar ATD responses. In contrast the curved lumbar spine generated lower pelvis accelerations and a higher lumbar load than the straight lumbar spine assemblies. An accelerometer was attached to a magazine mass to assess the loading of the equipment compared to the loading of the ATD. The peak vertical lumbar loads did not change with increasing BBE because the mass effects did not become a factor during the peak loading event.
INTRODUCTION
In recent history, land vehicle occupant injuries and deaths caused by improvised explosive devices (IED) have increased substantially [1-2]. IEDs require relatively little skill and technology to construct and allow devastating attacks for a relatively small investment. This makes them ideal for small terrorist groups [3-4]. To compound the issue, IEDs are easily hidden and difficult to detect. Like land mines, they can also be buried under a road. Blast events can cause traumatic injury to the lower limbs and spinal column of military vehicle occupants as they can inflict
22 | June 2018
an acceleration which is in excess of 200 g in less than 10 ms to the vehicle floor [5-10].
Military personnel are required to wear a
vast amount of equipment during combat to provide adequate support for any situation that may arise. The majority of equipment carried by personnel is generally placed in
a vest, which is worn over the top of the clothing. The vest includes a location for body armour and an ability to affix equipment pouches in various positions on the vest. How equipment affects occupant injury potential during a land blast is not well understood. Using LS-Dyna, Zhang et al [11] found that
the BBE mass may have a large effect at a later stage of the spine deformation under low pelvis accelerations between 20 g to 100 g over a 40 ms time period. However, that paper used finite element analysis and no experimental validation.
Apart from modelling, a practical and inexpensive experimental method for predicting occupant injury potential utilises
a drop tower, and is commonly used for simulating helicopter and aircraft heavy landings. Although this approach may not completely simulate a land blast event, the total absolute change in velocity during the drop tower experiment is similar to the change in velocity experienced in a real blast situation [12]. For the drop test, an ATD is configured in a seated posture on a seat. A number of load cells and accelerometers are installed within the ATD to measure various parameters such as lumbar compression loads, acceleration
of the pelvis, chest and head. At present, the most commonly used ATDs are the Hybrid III series used for automotive vehicle crash.
This paper presents the results of an experimental investigation into the effects of lumbar spine assemblies and body-borne equipment mass on ATD responses during a simulated blast event.
EXPERIMENT
Set Up
The experimental apparatus used to test the ATD with BBE was a drop tower. The drop tower, as shown in Figure 1, consists of a carriage table guided by four vertical shafts