05-05-2012, 01:20 PM
Impact Experimental Analysis and Computer Simulation
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Abstract
In this paper, an automotive bumper system (a bumper connected to a frame through joints/connections) is
set up for small impact tests (nondestructive tests). During the tests, a steel bar is raised to certain highs
then released from there and hit onto the bumper system, the bumper system is fixed to the ground through
fully constraining the end of two shocks, the reaction forces at the end of shocks during the whole impact
process are measured and investigated in order to determine how they are transferred to the joints then to
the rest part of the frame. Also, other important experimental data are collected and studied to reflect the
actual impact process. A finite element model is created for the automotive bumper system and the impact
test is also simulated on the computer using ANSYS. The results from the experimental tests are compared
and correlated to the finite element simulation. From the comparison, it is found that the experiment results
and FEA results matches very well and the validity of the computer model is then verified. Additionally,
this paper also includes a hand calculation of the impact problem, where the bumper system is modeled as a
simple spring-damping system and solved using classical dynamic theory; the hand solutions are also
compared to the experimental results and the FEA results to verify the correctness and reliability of the
impact tests and computer simulation.
Introduction
This project is to compare and correlate the experimental results, the computer FEA results and the
theoretical results for a small impact case, then to show that for any small impact case a reasonable
computer model can be found to simulate it. In the project an automotive bumper system is used to perform
the impact tests, some important experimental data such as reaction forces and displacements at certain
locations are recorded, and a computer FEA model is created for the bumper system. A transient dynamic
analysis is performed to simulate the impact tests, and the corresponding computer results are obtained.
Finally, the bumper system is modeled as a simple spring-damping system and a hand calculation is done to
get the theoretical results, all the three results are compared and correlated, and the strengths and the
weaknesses of the project are discussed.
The objectives of the project are to verify the efficiency of the computer model and the computer
simulation, and to prove that there always existed a computer model that can be used to simulate any small
impact cases. At the same time, the behavior of the bumper system during the impact process is studied and
how the impact forces are transmitted to the joints and how they are transferred from the bumper to the
frame are explained through the project.
Literature Review
Before starting this project, some of published literatures and previous researches have been reviewed build
up a solid background in the area of experimental analysis and finite element analysis.
Toshiyuki Sawa, Yoshihito Suzuki, and Shoichi Kido used finite element method to analyze the stress wave
propagations in adhesive joints of similar hollow cylinders under static and impact tensile loadings in
elastic deformation range. They used DYNA3D to start the analysis and applied the impact loading to the
joint by dropping a weight. The effects of the Young’s modulus of the adhesive on the stress wave
propagation at the interfaces were examined and finally they found that the characteristics of the joints
subjected to impact loadings were opposite to those subjected to static loadings.[9]
Thomas J. Trella, Randa Radwan, Samaha (1995) described the development and validation of a computer
based model of the moving deformable barrier developed for side impact safety performance simulations
using LS-DYNA3D. They investigated the effects of important factors central to FEA modeling such as
material node merging, mesh density, and element type and then found that the material damping
coefficient and compacted Young’s modulus both had a strong influence on the simulated impact
responses.[