Effect of Body-Borne Equipment on Injuries in Helicopter Crashes and Land Blasts
thesis
posted on 2016-12-14, 01:59 authored by Daniel Eugene AggromitoThis thesis investigates the effect of equipment mass and
attachment on occupant injury in short vertical loading using anthropomorphic test
devices. The investigation includes analytical, numerical and experimental methods to
simulate an occupant in a helicopter crash and a land blast. The results
further shed light and explanation into the use of the Dynamic Response Index in a
land blast.
To investigate the effects of increasing equipment mass during a helicopter crash on injury, a linear mass-spring-damper model was developed to simulate an occupant wearing body-borne equipment on a crashworthy helicopter seat. To examine the effects of equipment attachment types, the mass bodies representing the equipment are attached with a spring and damper, with low and high stiffness values indicating loose and tight attachment respectively. The results demonstrate that increasing the equipment mass reduces the seat's capability to absorb the total impact energy at higher initial impact velocities. The safe velocity, the velocity that prevents bottoming out, reduces. The results show that increasing equipment mass significantly increases the potential for injury at the lumbar, upper torso and head.
How distribution of equipment on the body affects injury potential during a helicopter crash is investigated. A finite element model representing a helicopter seat with a fully deformable 50th percentile Hybrid III carrying equipment was developed. The model was subjected to a standard military certification crash test. Various equipment configurations were investigated and analysed to determine its influence on the risk of injury. It was found that placing the equipment low on the torso, near the thighs, not only reduces the likelihood of injury in the lumbar, spinal region but also provides favourable results in neck and head injury risk when compared to other configurations investigated. In contrast, placing equipment high on the torso, close to the chin, increases the lumbar load and implicitly, the risk of head injury. A statistical analysis was carried out using the Wilcoxon Signed Rank Test to deliver probability of loads experienced within a certain interval. An equipment configuration that improves survivability for an occupant seated on a fixed load energy absorbing seat which is subjected to Military Standard 58095A Test 4 was delivered.
In land blasts, neither the effect of body-borne equipment (BBE) on the ATD response nor the dynamic response index (DRI) is well understood. An experimental study was carried out using a drop tower test rig, with a rigid seat mounted on a carriage table undergoing accelerations similar to those experienced in a land blast. Various lumbar spine assemblies available for a Hybrid III ATD were investigated. 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. The results showed that the straight lumbar spine assemblies produced similar peak vertical loads and therefore either straight lumbar spine assembly can be used in experiments simulating blast tests. The maximum relative displacement of the lumbar spine occurred after the peak loading event, suggesting that the DRI is not suitable for assessing injury when the impact duration is short and an ATD is seated on a rigid seat on a drop tower. The peak vertical lumbar loads did not change with increasing body-borne equipment mass because the equipment mass effects did not become a factor during the peak loading event.
The study was concluded through the development of a numerical model to investigate additional acceleration pulses. The numerical model developed used VPS software, with a pulse and initial velocity taken from the experimental tests to compare. The model used two Hybrid III ATDs including the curved spine Hybrid III and the FAA Hybrid III. Simulations showed that an acceleration pulse of 81 g is required to surpass the FAA lumbar load threshold when an ATD is seated on a rigid seat in a drop tower to simulate a blast event.
The work in this thesis contributes to the body of knowledge in injury assessment during helicopter crashes and land blasts. The thesis presents a guideline on how to attach and place equipment to lessen injury in helicopter crashes. The thesis also provides a recommendation on which ATD to use in land blasts and why equipment is not a factor in land blasts. A detailed explanation on why the DRI is not suitable as an injury assessment criteria in land blast is given.
To investigate the effects of increasing equipment mass during a helicopter crash on injury, a linear mass-spring-damper model was developed to simulate an occupant wearing body-borne equipment on a crashworthy helicopter seat. To examine the effects of equipment attachment types, the mass bodies representing the equipment are attached with a spring and damper, with low and high stiffness values indicating loose and tight attachment respectively. The results demonstrate that increasing the equipment mass reduces the seat's capability to absorb the total impact energy at higher initial impact velocities. The safe velocity, the velocity that prevents bottoming out, reduces. The results show that increasing equipment mass significantly increases the potential for injury at the lumbar, upper torso and head.
How distribution of equipment on the body affects injury potential during a helicopter crash is investigated. A finite element model representing a helicopter seat with a fully deformable 50th percentile Hybrid III carrying equipment was developed. The model was subjected to a standard military certification crash test. Various equipment configurations were investigated and analysed to determine its influence on the risk of injury. It was found that placing the equipment low on the torso, near the thighs, not only reduces the likelihood of injury in the lumbar, spinal region but also provides favourable results in neck and head injury risk when compared to other configurations investigated. In contrast, placing equipment high on the torso, close to the chin, increases the lumbar load and implicitly, the risk of head injury. A statistical analysis was carried out using the Wilcoxon Signed Rank Test to deliver probability of loads experienced within a certain interval. An equipment configuration that improves survivability for an occupant seated on a fixed load energy absorbing seat which is subjected to Military Standard 58095A Test 4 was delivered.
In land blasts, neither the effect of body-borne equipment (BBE) on the ATD response nor the dynamic response index (DRI) is well understood. An experimental study was carried out using a drop tower test rig, with a rigid seat mounted on a carriage table undergoing accelerations similar to those experienced in a land blast. Various lumbar spine assemblies available for a Hybrid III ATD were investigated. 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. The results showed that the straight lumbar spine assemblies produced similar peak vertical loads and therefore either straight lumbar spine assembly can be used in experiments simulating blast tests. The maximum relative displacement of the lumbar spine occurred after the peak loading event, suggesting that the DRI is not suitable for assessing injury when the impact duration is short and an ATD is seated on a rigid seat on a drop tower. The peak vertical lumbar loads did not change with increasing body-borne equipment mass because the equipment mass effects did not become a factor during the peak loading event.
The study was concluded through the development of a numerical model to investigate additional acceleration pulses. The numerical model developed used VPS software, with a pulse and initial velocity taken from the experimental tests to compare. The model used two Hybrid III ATDs including the curved spine Hybrid III and the FAA Hybrid III. Simulations showed that an acceleration pulse of 81 g is required to surpass the FAA lumbar load threshold when an ATD is seated on a rigid seat in a drop tower to simulate a blast event.
The work in this thesis contributes to the body of knowledge in injury assessment during helicopter crashes and land blasts. The thesis presents a guideline on how to attach and place equipment to lessen injury in helicopter crashes. The thesis also provides a recommendation on which ATD to use in land blasts and why equipment is not a factor in land blasts. A detailed explanation on why the DRI is not suitable as an injury assessment criteria in land blast is given.
