Zhiqing Cheng

Experiences in reverse-engineering of a finite element automobile crash model

The experiences encountered during the development, modification, and refinement of a finite element model of a four-door sedan are described. A single model is developed that can be successfully used in computational simulations of full frontal, offset frontal, side, and oblique car-to-car impacts. The simulation results are validated with test data of actual vehicles. The validation and computational simulations using the model show it to be computationally stable, reliable, repeatable, and useful as a crash partner for other vehicles.

LIMITING PERFORMANCE OF SEAT BELT SYSTEMS FOR THE PREVENTION OF THORACIC INJURIES

Abstract The theoretically optimal performance of seat belt systems for occupants in automobile frontal crashes is investigated based on a two-mass injury model of the thorax. The performance is measured by thoracic injury criteria which include the maximum chest acceleration, compression and viscous response. The relationship between the best possible performance (limiting performance) of the seat belt system and the distance between the occupant and the interior components of the vehicle is displayed in the form of trade-off curves, which can be used for the evaluation of seat belt performance. The characteristics of the optimal seat belt force and the kinematics of the system are illustrated. The results indicate that the optimal seat belt force is not constant during an impact and that an initial impulse is required. However, constant seat belt force can provide thoracic restraint that is close to the optimal solution.

Wave dispersion and attenuation in viscoelastic split Hopkinson pressure bar

A viscoelastic split Hopkinson pressure bar intended for testing soft materials with low acoustic impedance is studied. Using one-dimensional linear viscoelastic wave propagation theory, the basic equations have been established for the determination of the stress‐strain‐strain rate relationship for the tested material. A method, based on the spectral analysis of wave motion and using measured wave signals along the split Hopkinson pressure bar, is developed for the correction of the dispersion and attenuation of viscoelastic waves. Computational simulations are performed to show the feasibility of the method.

Limiting Performance of Helmets for the Prevention of Head Injury

This is a study of the theoretical optimal (limiting) performance of helmets for the prevention of head injury. A rigid head injury model and a two-mass translational head injury model are employed. Several head injury criteria are utilized, including head acceleration, the head injury criterion (HIC), the energy imparted to the brain which is related to brain injury, and the power developed in the skull that is associated with skull fracture. A helmeted head hitting a rigid surface and a helmeted head hit by a moving object such as a ball are considered. The optimal characteristics of helmets and the impact responses of the helmeted head are investigated computationally. An experiment is conducted on an ensemble of bicycle helmets. Computational results are compared with the experimental results.

Limiting performance analysis of toepan padding for mitigating lower limb injuries

Abstract The potential application of using toepan padding for the prevention and reduction of lower limb injuries is investigated computationally in this paper. A two-mass lower limb injury model is developed on the basis of impact tests using post-mortem human surrogates. A limiting performance analysis is used to find the best possible physical performance and characteristics of passive and active padding for the minimization of peak tibia force. Computational results indicate that, for the prevention and reduction of lower limb injuries, the active padding is superior to the passive padding.

Wavelet-based limiting performance analysis of mechanical systems subject to transient disturbances

Wavelets are used as the basis functions for control forces in the limiting performance analysis of a mechanical system subject to transient loading. The limiting performance problem, an open-loop control problem, can then be treated as a mathematical programming problem. A numerical example is presented to illustrate the effectiveness of using wavelets. Conventional approximate representations of the control function are interpreted in terms of the scaling function and multiresolution.

Optimization of Biomechanical Systems for Crashworthiness and Safety

The optimal performance of a safety device for crashworthiness and safety is studied in this paper. The problem is treated as the optimal control and optimization of a biomechanical system consisting of the safety device and occupant. The performance of this system is usually measured by certain injury criteria. The limiting performance analysis is implemented to find the best possible performance for the system. The parametric optimization is introduced for the optimal design of a safety device. Computational modeling and simulation of biomechanical systems is discussed with a brief description of various modeling techniques. The use of an Articulated Total Body model in the limiting performance analysis and parametric optimization is addressed in detail. The optimization of the safety performance of a type of ejection seat cushion is studied.

Optimal Occupant Kinematics and Crash Pulse for Automobile Frontal Impact

Based on a lumped-parameter model of the occupant-vehicle system, optimal kinematics of the occupant in frontal impact are investigated. It is found that for the minimization of the peak occupant deceleration, the optimal kinematics move the occupant at a constant deceleration. Based on this the optimal vehicle crash pulse is investigated. The optimal crash pulse for passive restraint systems is found to be: a positive impulse at the onset, an immediate plunge followed by a gradual rebound, and finally a positive level period. The relation of the peak occupant deceleration to the impact speed, crash deformation, and vehicle interior rattlespace is established. The optimal crash pulse for active and pre-acting restraint systems is discussed.

Optimal Restraint Characteristics for Minimization of Peak Occupant Deceleration in Frontal Impact

Abstract : In automobile frontal impact, given the vehicle motion and the interior free space for the occupants excursion, what are the optimal characteristics of restraint systems for the minimization of the peak occupant deceleration? In this paper, the problem is treated as the optimal protection from impact based on a lumped-parameter model of the occupant-vehicle system. The optimal kinematics of the occupant in frontal impact is studied. The optimal characteristics of passive restraint systems are investigated in detail for three types of vehicle crash pulses: optimal pulse, constant deceleration pulse, and half-sine pulse. Optimization of the characteristics of active and pre-acting restraint systems is addressed. It is found that the optimal kinematics of the occupant in frontal impact is such that the occupant moves at a constant deceleration. Passive restraint systems are not able to provide required protection for the occupant to attain optimal kinematics, but active and pre-acting restraint systems can achieve that if optimally designed.