Modeling crash dynamic responses of high energy absorbing materials by multi-body, non-linear finite element, and optimization methods.

摘要

In this dissertation, the problem of contact/impact force optimization or minimization of damage is investigated. Existing contact force models are extended and their applications to multibody impacts are presented. A parameter optimization methodology is then developed for minimizing the peak contact force by searching for the optimal parameters in the force model such as the stiffness and the damping coefficients. A single degree-of-freedom vibro-impact model is used for two impacting bodies and shown to be an effective representation of the multibody system for the duration of impact. In addition to the initial conditions such as impact velocity, the optimization methodology takes a given maximum indentation, a required crash depth as its constraint. The optimal parameter searching is realized by using the method of modified feasible direction for constrained minimization. Since these parameters reflect the material properties and geometry configurations of the two bodies in contact, the optimal parameters provide useful guidelines for the selection of proper impact resistant materials. Mechanisms of energy absorbing during an impact are investigated based upon the information on the optimal parameters. In order to describe the impact characteristics of high energy absorbing materials, a contact force model is proposed, and its capability in describing impact energy dissipation is explored by comparing the analytical results to those from given experiments.; The developed methodologies are then applied to the study of gross motion behavior of human body and the potential injuries in various crash environment. Specifically, the problem of reducing the head injuries to an occupant as a result of a head contact with the surrounding, (bulkhead, instrument panel, and interior wall for aircraft; or windshield, and front panels for ground vehicles), is considered. Multibody model of the occupant from SOM-LA/TA (Seat/Occupant Model for Light/Transportation Aircraft) is used in conjunction with a created front panel model adopting the developed contact/impact force model. This environment can simulate the head impact of the occupant on energy absorbing padding materials. By using the nesting technique in design of experiment, a numerical statistical test is performed and it is shown that the single degree-of-freedom vibro-impact system can represent the multibody occupant model during the head impact. The concept of effective mass is used in the form of impact/contact force and maximum indentation in the evaluation of vibro-impact system. Parameter optimization of this system shows that the system described by the new model and having optimal parameters displays good energy absorbing capability. Substructuring technique is also used to simulate the head impact on the energy absorbing materials with the help of finite element method. Required padding thickness is obtained for securing the safety of the passengers in the crash environment.