tailieunhanh - Vehicle Crash Dynamics P3

To supplement full scale dynamic testing of vehicle crashworthiness, mathematical models and laboratory tests (such as those using a Hyge sled or a vehicle crash simulator) are frequently employed. The objective of these tests is the prediction of changes in overall safety performance as vehicle structural and occupant restraint parameters are varied. To achieve this objective, it is frequently desirable to characterize vehicle crash pulses such that parametric optimization of the crash performance can be defined. Crash pulse characterization greatly simplifies the representation of crash pulse time histories and yet maintains as many response parameters as possible | CHAPTER 2 CRASH PULSE CHARACTERIZATION INTRODUCTION To supplement full scale dynamic testing of vehicle crashworthiness mathematical models and laboratory tests such as those using a Hyge sled or a vehicle crash simulator are frequently employed. The objective of these tests is the prediction of changes in overall safety performance as vehicle structural and occupant restraint parameters are varied. To achieve this objective it is frequently desirable to characterize vehicle crash pulses such that parametric optimization of the crash performance can be defined. Crash pulse characterization greatly simplifies the representation of crash pulse time histories and yet maintains as many response parameters as possible. The response parameters used to characterize the crash pulse are those describing the physical events occurring during the crash such as maximum dynamic crush velocity change time of dynamic crush centroid time static crush and separation rebound velocity. In addition the kinematic responses of the test such as transient acceleration velocity displacement in time domain and energy absorption in the displacement domain are compared. Frequency contents and spectrum magnitudes of harmonic pulses in a Fourier series pulse characterization can be utilized for frequency domain analysis. A number of crash pulse approximations and techniques have been developed for the characterization. These are divided into two major categories according to whether or not the initial deceleration is zero. Pulse approximations with non-zero initial deceleration Average Square Wave ASW Equivalent Square Wave ESW Tipped Equivalent Square Wave TESW Pulse approximations with zero initial deceleration Fourier Equivalent Wave FEW and Sensitivity Analysis Trapezoidal Wave Approximation TWA Bi-Slope Approximation BSA Basic Harmonic Pulses Each one of the approximation techniques is solved analytically for a closed-form formula which satisfies certain boundary conditions based on the