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Title: The influence of the body on the response of the helmeted head during impact
Author: Ghajari, Mazdak
ISNI:       0000 0004 2695 9463
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2011
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According to helmet standards, the absorption capacity of helmets is assessed through impact of a headform fitted with the helmet onto an anvil. It implies that the effect of the rest of the body on impact outputs has been assumed to be negligible. The purpose of this work was to investigate this effect. Full-body and detached-head impacts were simulated using the Finite Element (FE) method. A detailed FE model of a composite-shell helmet was developed and validated against experimental data. It was coupled with an FE model of the Hybrid III dummy. To validate the full-body impact model, a new test method was designed to drop test helmeted dummies. As a consequence of the presence of the body, the crushing distance of the helmet liner was drastically increased. This evidence indicated that the effect of the body should be included in impact absorption tests in order to provide conditions that are more realistic to real world accidents and more stringent. The solution to an analytical model proposed for helmeted headform impacts revealed that the influence of increasing the headform mass on impact outputs, particularly the liner crushing distance, is the same as the influence of the body. The added mass was calculated for various impact configurations by using a detailed FE model of the human body. Finally, an added mass of 20% together with a 9% reduction in the limit of head linear acceleration were proposed. Full-body and detached-head oblique impacts were also simulated. The results indicated that the body had a noticeable influence on head rotational acceleration. Modifying the inertia matrix of the head to include this effect in the detached-head drop tests was proposed. By using an FE model of the human head, intracranial injury predictors were also evaluated in oblique impacts considering the complete kinematics of the head.
Supervisor: Galvanetto, Ugo ; Iannucci, Lorenzo Sponsor: Marie Curie Fellowship
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral