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Final Project “Investigation of Head Impact during an Inverted Drop Test” ME 272 12/18/06 Luke Gibbons

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Problem Statement Inverted 8 foot drop test of 2000+ lb auto with 250+ lb dummy Inverted 8 foot drop test of 2000+ lb auto with 250+ lb dummy Focus our attention upon determining the pressure experienced by the skull during impact Focus our attention upon determining the pressure experienced by the skull during impact We will use Nastran 4-d’s Finite Element Analysis (FEA) to determine the von Mises stress (psi) experienced during impact We will use Nastran 4-d’s Finite Element Analysis (FEA) to determine the von Mises stress (psi) experienced during impact We will also use Nastran to determine the location and direction of the force experienced by the skull We will also use Nastran to determine the location and direction of the force experienced by the skull Finally, we will compare the results with documented tolerance limits of the human brain and the Severity Index (SI) Finally, we will compare the results with documented tolerance limits of the human brain and the Severity Index (SI)

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Problem Setup [1] [1] A lifelike dummy will be modeled using standard dummy dimensions A lifelike dummy will be modeled using standard dummy dimensions The head and body will be modeled with material representing cortical, or dense, skull bone The head and body will be modeled with material representing cortical, or dense, skull bone The use of cortical bone to represent the entire body will act as a safety factor because the body will now weigh more than an average human for the given volume The use of cortical bone to represent the entire body will act as a safety factor because the body will now weigh more than an average human for the given volume

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Problem Setup The dummy’s body will be joined in Nastran 4-d using revolute joints for all joints except the head-neck connection The dummy’s body will be joined in Nastran 4-d using revolute joints for all joints except the head-neck connection The dummy’s head will be connected to the neck by means of a spherical joint The dummy’s head will be connected to the neck by means of a spherical joint We assume the Coefficient of Restitution is 0.3 We assume the Coefficient of Restitution is 0.3 We will mesh the head using a 0.5 inch mesh size We will mesh the head using a 0.5 inch mesh size

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Problem Setup A restraint system was added to model a lap and chest seatbelt A restraint system was added to model a lap and chest seatbelt The restraint system was modeled as two spring/damper systems anchored to the auto in the same location and attached to the dummy at the center of the upper and lower back The restraint system was modeled as two spring/damper systems anchored to the auto in the same location and attached to the dummy at the center of the upper and lower back The standard value of 9.81 m/s² for gravity was implemented The standard value of 9.81 m/s² for gravity was implemented

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Problem Setup We will also look at the Gadd Severity Index (SI) We will also look at the Gadd Severity Index (SI) According to Gadd, a SI value above 1,000 is considered “dangerous to life” According to Gadd, a SI value above 1,000 is considered “dangerous to life” The Severity Index is calculated by: The Severity Index is calculated by: where a is the acceleration of the head and t is the impact duration [2]

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Results Results [1] [1] The maximum von Mises stress the brain can withstand The maximum von Mises stress the brain can withstand before neurological lesions occur is 18 kPa At the present height above the ground, the car takes At the present height above the ground, the car takes 0.61 seconds to contact the ground while the dummy’s head takes 0.62 seconds to initially contact the roof of the auto and 0.63 seconds until the maximum impact point The green arrows show pressure applied to the skull The green arrows show pressure applied to the skull

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Results: 0.60 seconds Results: 0.60 seconds Before Impact Before Impact

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Results: 0.62 seconds Results: 0.62 seconds Initial Impact Initial Impact

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Results: 0.63 seconds Results: 0.63 seconds Full Impact Full Impact

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Results: 0.64 seconds Results: 0.64 seconds Whiplash Effect Whiplash Effect

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Results: Stress vs. Time

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Results: Stress During Impact

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Results: Stress Distribution at Maximum Impact

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Conclusion The brain cannot withstand the fall with the present restraining system The brain cannot withstand the fall with the present restraining system The head experiences von Misses stress of over 152 MPa, which is significantly larger than the critical von Mises stress the brain can withstand (18 kPa) [1] The head experiences von Misses stress of over 152 MPa, which is significantly larger than the critical von Mises stress the brain can withstand (18 kPa) [1] The point where the head connects to the neck receives a tremendous force at maximum impact even after the head absorbs a portion of the force The point where the head connects to the neck receives a tremendous force at maximum impact even after the head absorbs a portion of the force The head experiences the greatest acceleration during whiplash The head experiences the greatest acceleration during whiplash The whiplash effect is prevalent, and according to Gadd [2], with a head acceleration of 386 m/s² and assuming an impact duration of 0.001 seconds, the Severity Index value is almost 3,000, 3 times greater than Gadd’s “dangerous to life value” of 1,000 The whiplash effect is prevalent, and according to Gadd [2], with a head acceleration of 386 m/s² and assuming an impact duration of 0.001 seconds, the Severity Index value is almost 3,000, 3 times greater than Gadd’s “dangerous to life value” of 1,000

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Reference [1] Raul, J., Baumgarter, D., Willinger, R., Ludes, B. “Finite Element Modeling of Human Head Injuries caused by a Fall”. International Journal of Legal Medicine. Published online 03 July, 2005 [1] Raul, J., Baumgarter, D., Willinger, R., Ludes, B. “Finite Element Modeling of Human Head Injuries caused by a Fall”. International Journal of Legal Medicine. Published online 03 July, 2005 [2] Gadd, C.M. “Use of a Weighted Impulse Criterion for Estimating Injury Hazard”. Proceedings of the 10 th Stapp Car Crash Confrence, Society of Automotive Engineers, New York NY, pp. 164-174, 1966 [2] Gadd, C.M. “Use of a Weighted Impulse Criterion for Estimating Injury Hazard”. Proceedings of the 10 th Stapp Car Crash Confrence, Society of Automotive Engineers, New York NY, pp. 164-174, 1966

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