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Aim- To perform the Head Impact Simulation and calculate the Head Impact Criterion (HIC) value for the following cases. Objective- To perform head impact analysis and calculate the HIC (Head injury criteria/coefficient) value for the following cases: Case1: Simple head model and rigid wall Case2: Child head-foam…
Tribhuvankumar Pandit
updated on 29 Jul 2022
Aim-
To perform the Head Impact Simulation and calculate the Head Impact Criterion (HIC) value for the following cases.
Objective-
To perform head impact analysis and calculate the HIC (Head injury criteria/coefficient) value for the following cases:
Basic Introduction-
Head Impact :
Fig: Head Impact Test
About 14% of all road fatalities in Europe & rest of world are pedestrians, with children and the elderly being at greatest risk. Pedestrians comprise one of the main categories of vulnerable road users, which also include cyclists and motorcyclists.
Most pedestrian accidents occur within city areas where speeds are moderate. The head, the lower body and the legs are amongst the most frequently injured body regions. To estimate the potential risk of head injury in the event of a vehicle striking an adult or a child, a series of impact tests is carried out at 40 km/h using an adult or child head form impactor. Impact sites are then assessed and the protection offered is rated as good, adequate, marginal, weak or poor.
The procedure promotes energy absorbing structures, deformation clearance and deployable protection systems such as pop-up bonnets and external airbags.
Child Head Impact:
Car-pedestrian accidents account for a considerable number of automobile accidents in industrialized countries. Head injury continues to be more concerned with Automobile impacts. Because the head is the most seriously injured part in many collisions including in pedestrian automobile collisions. To reduce the severity of such injuries international safety committee have proposed subsystem tests in which head foam impactors are impacted upon the car hood
Currently in India, Automotive Indian Standard (AIS) 100, Amendment 1 is used to evaluate the performance of vehicles against pedestrian safety. This standard has been harmonized from the international evaluation standard Global Technical Regulation No. 9 (GTR 9), whose purpose is to bring about an improvement in the construction of the fronts of vehicles and, in particular, those areas which have been most frequently identified as causing injury when in collision with a pedestrian or other vulnerable road user. The tests required are focused on those elements of the child and adult body most frequently identified as sustaining an injury, i.e. the adult head and leg and the child's head. To achieve the required improvements in the construction of vehicles, the tests are designed in such a way that they will represent the rear world accident scenario.
Fig: Pedestrian Protection Test Procedures as per AIS 100
The different impactors used in predicting the performance against pedestrian safety are the lower leg form and upper leg form impactors (representative of the adult leg) and the adult and child head form impactors (representative of the adult head and child's head). Head injury is a more life-threatening and most common cause of pedestrian deaths in pedestrian to vehicle collision; it was decided to focus on these impactors and test procedures as a part of this study.
Wrap Around Distance (WAD):
When a car crashes on the pedestrian, the whole human body wraps around the front shape of the car, and the head impacts on the bonnet or the windscreen. The distance at which the head impacts on the car from the ground is mentioned as Wrap Around Distance (WAD).
To be specific the Wrap Around Distance is a measurement of the distance from the ground to the head impact zone over the outer surface of the car. The wrap-around distance is measured longitudinally in the center of the vehicle from the ground.
The severity of the injury caused by the frontal crash depends on the type and shape of the vehicle, the speed of the vehicle, and the movement of the pedestrian relative to the vehicle. In addition to these parameters, the wrap-around distance plays a major role in the safety measures of a pedestrian
During the crash analysis, based on the Wrap Around Distance(WAD), two test areas will be created namely the Child head impact zone and the Adult head impact zone. The child head impact zone is between 1000 to 1700 mm WAD and the adult head impact zone ranges between 1700 to 2100 mm WAD.
Fig: WAD zone
Head injury criteria (HIC)
The head injury criterion (HIC) is a measure of the likelihood of head injury arising from an impact. ... At a HIC of 1000, there is an 18% probability of a severe head injury, a 55% probability of a serious injury and a 90% probability of a moderate head injury to the average adult.
The head foam impactors are used to test the behavior on vehicle structures such as the hood. In a pedestrian-vehicle impact, the kinematics and severity of pedestrian injuries are affected by the impact locations on the vehicle and body velocities after impact. The objective of this project is to analyze the pedestrian kinematics in a Pedestrian-Car accident scenario and determine the Head Injury Criteria (HIC) from the head resultant acceleration, for head impacts on the vehicle hood
The equation used for the measurements of the head injury of the whole model for the pedestrian head impact was head injury criteria (HIC). It has been used to predict the risk of engine hood to a pedestrian during the collision.
HIC is calculated according to the below Equation
Where
Note :
For example, At HIC=650,
90% probability of level 1,
55% of level 2,
20% of level 3,
5% of level 4.
Abbreviated Injury Scale (AIS):
Level 1: Slight damage to the brain with headache, dizziness, no loss of consciousness, confusion.
Level 2: Concussion with or without skull fracture, less than 15 minutes of unconsciousness, detached retina, face, and nose fracture.
Level 3: Concussion with or without skull fracture for more than 15 minutes of unconsciousness without severe neurological damage, multiple skull fractures, loss of vision, multiple facial fractures, cervical fracture without damage to the spine.
Level 4: Multiple skull fractures with severe neurological damage.
Procedure-
Note: Kg/mm/ms unit system is used throughout the analysis.
Case-1- Simple head Model
The output request in ASCII format, The following keyword are activated
Results & Plots-
Effective Stress (V-M)-
Resultant Acceleration-
Energy Plot-
The above plot depicts the energy plot for a simple head impact on rigid wall simulation. It is visible that the kinetic energy decreases and internal energy increases at the instant of impact and they both meet at around 1.9 ms. This is due to the reduction of the velocity during impact. The simple head geometry being elastic material bounces back without major loss of energy and attains velocity in other direction. This causes again an increase in kinetic energy and a decrease in internal energy further and again they meet at around 2.1 ms. The internal energy and Kinetic energy remain constant and the hourglass energy is also under desired limits.
Head Injury Criteria (HIC)-
Manual calculation of HIC value:
The expression to calculate HIC value is,
From the plot,
The average value of acceleration for the time interval of t1=1.8 ms and t2=10 ms,
From the above graph we can take time span = t2 - t1
= 10-1.8
= 8.2 ms
So, the average acceleration from the graph is taken as around 3000.
HIC = [(1/8.2)*3000*8.2]^2.5*[8.2/1000]
= 4.042e+06, which is nearly equal to the value that we got from solver.
Note: Why HIC-15 used here rather than HIC-36?
This is because the simulation span that we have taken into consideration is very minimal so that we need to go with the HIC-15 rather than HIC-36. Here both the terms will try to capture the time span of a specific peak acceleration area in the graph. So selected this way!
Animations-
Effective Stress (V-M)-
Resultant Acceleration-
Case-2-Child head-form and rigid wall
The test setup as per AIS 100. The release angle was 55⁰ for the Child head foam. The head-foam velocity at impact was 11.1mm/ms (40 km/h) for head foam. Here in this case impact point on the Rigidwall instead of a car hood.
Note: While adding keywords to main file, ensure the Subsys: is set to the main file .k extension.
The output request in ASCII format, The following keyword are activated
Results & Plots-
Effective Stress (V-M)-
Effective Plastic Strain-
Plots-
Manual calculation of HIC value:
The expression to calculate HIC value is,
From the plot,
The average value of acceleration for the time interval of t1=4.3 ms and t2=5.4 ms,
From the above graph we can take time span = t2 - t1
= 5.4-4.3
= 1.1 ms
So, the average acceleration from the graph is taken as around 486.
HIC = [(1/1.1)*486*1.1]^2.5*[1.1/1000]
= 5727.74, which is nearly equal to the value that we got from solver.
Animations-
Effective Stress (V-M)-
Effective Plastic Strain-
Case3 : Child head-form and bonnet/hood
The Initial Velocity is defined along X and Z direction to the Head foam to impact on the car hood. An initial velocity of 11.11mm/ms is with which the Head impacts the rigid wall but here it will be a resultant direction. So, the component motion in the negative x and negative z-direction has to be calculated.
Reslts & Plots-
Effective Stress (V-M)-
Effective Plastic Strain-
Plots-
Manual calculation of HIC value:
The expression to calculate HIC value is,
From the plot,
The average value of acceleration for the time interval of t1=2.6 ms and t2=10 ms,
From the above graph we can take time span = t2 - t1
= 10-2.3
= 7.7 ms
So, the average acceleration from the graph is taken as around 64.8.
HIC = [(1/7.7)*64.8*7.7]^2.5*[7.7/1000]
= 260.272, which is nearly equal to the value that we got from solver.
Animations-
Effective Stress (V-M)-
Effective Plastic Strain-
Conclusion-
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