Modelling of the Energy-absorptive Process In Layered Bumpers

By Krzysztof Murawski

The book describes the theoretical model of an energy-absorptive bumper which protects vehicles from a crash. The first part describes the question of passive safety as well as the classification, criteria of quality and the state of researches.
In the next chapters the book presents the worked out method of projecting the layered bumper with the original construction (2 patents) and the method of analysis of the processes of absorption a crash energy by it in the four stage process.
The book describes: the study of conception of the bumper construction, execution the experimental researches with bumper elements and the model of the bumper, study of the algorithm of projecting as well as the execution the numeric 2D simulation of FEM of absorption by bumper the energy in the linear range with buckling and non-linear.
Is also presented the dynamic analysis of work of bumper, i.e. the differential equations for every stage of the energy consuming process and the calculation for the bumper.

• Language: English
• Publisher: Lulu.com
• Release date: Nov 13, 2017
• ISBN: 9781387337200

Book preview

Modelling of the Energy-absorptive Process In Layered Bumpers

Modelling of the Energy Absorptive Process In Layered Bumpers

Krzysztof Murawski

Reviewers:

Prof. dr hab. inż. Jerzy Osiński

Prof. dr hab. inż. Jerzy Zielnica

Copyright © 2017 by Krzysztof Murawski

All rights reserved. Any part of this publication as well as entirely may not be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of the copyright owner. This publication is dedicated only to individual buyers and cannot be borrowed individually or in      libraries, or at other institutions without the prior written permission with conditions from the copyright owner. No author’s formula cannot be used without the prior written permission with conditions. This book or any portion thereof may not be reproduced or used in any manner whatsoever without the express written permission of the publisher except for the use of brief quotations in a book review or scholarly journal

First Printing: 2012

ISBN 978-1-387-33720-0

Lulu Press, Inc.

3101 Hillsborough St, Raleigh, NC 27607

www.lulu.com

CONTENTS:

1. FUNCTIONS OF VEHICLES BUMPERS 

2. SURVEY OF THE LITERATURE

2.1.Criteria of quality and the classification of bumpers

2.2. Standards and tests of bumpers

3. AIMS AND THE RANGE OF THE DISSERTATION

4. CONCEPTION OF THE STRUCTURE AND WORK OF THE ENERGY-ABSORPTIVE BUMPER

5. EXPERIMENTAL WORKS ON THE LOSS OF STABILITY AND

ENERGY-ABSORPTION OF AXIALLY COMPRESSED TUBES IN INELASTIC STATES

5.1. Specimens and testing machines 

5.2. Description and the interpretation of the physical  phenomena observed during researches

5.3. Results of the research work

6. THEORY OF THE BUMPER ELEMENTS

6.1. Stability of the brackets

6.2. Energy-absorption of the brackets

6.3. Energy-absorption of the beam

6.4. Influence of deforming speed

6.5. Application of the Finite Element Method

7. PROJECTING OF THE BUMPER CONSTRUCTION

7.1. Calculation of the impact beam

7.2. Choice of the layered brackets

7.3. Strength of the impact beam

7.4. Projecting of the beam to work in the range of buckling

8. ANALYSIS OF THE ABSORBING ENERGY PROCESS IN THE BUMPER

8.1. Dynamic analysis of the crash

8.2. Numeric simulation of the bumper work

9. FINAL CONCLUSIONS

10. APPENDIX A: REVIEW OF BUMPER CONSTRUCTIONS

11. APPENDIX B: THE CHARACTERISTICS OF MATERIALS OF THE TEST SPECIMENS

12. APPENDIX C: THE TESTING MACHINES USED TO THE EXPERIMENTAL TESTS

13. REFERENCES

1. FUNCTIONS OF VEHICLES BUMPERS 

Vehicles contributed to the development of man's civilization in the significant way. The realization of the idea of a self-propelled vehicle began a new era in techniques and technology. Nevertheless, cars and trams as well as trains caused potential danger for people being inside and outside of vehicles from the dawn of their services to people. This problem is clearly visible in times of the mass production of vehicles, i.e. also in the present times, particularly in case of cars. This problem is the most visible in countries, in which the stage of motorizing of society has outdistanced the stage of development of the motorization infrastructure like roads, traffic rules and structural vehicles protections against crashes – determining the passive save of vehicles. The statistics of wounded and dead persons in the car accidents in Poland in the years: 1980-95 [1] and in Germany in the eightieth years [2] are compared in Fig.1.1 and Fig.1.2.  Results from them that the number of the wounded persons in Germany was in the narrow range between 320 and 370 thousand and the number of the dead persons decreased from 12 to 8 thousand. The number of the wounded persons in Poland was in the range from 42 to 65 thousand and the number of the dead people from 4.5 to 8 thousand; however, since the 1988 year it could be noticed the pronounced increase of these numbers. The decrement of these numbers in Poland in the 1995 year can be related to understating the statistical evidences, for what reproached the police and what was even passed to public news items. It should be considered here the fact that in the eightieth years the number of people of FRG was about 1.5 times bigger than in Poland. The seven times smaller number of the wounded persons in Poland existed in these statistics could suggest a positive phenomenon, but kept on the similar level the number of the dead persons suggest the different conclusions.

The frequency of the dead among wounded persons in the car accidents in Poland in the years 1980-95 as well as in Germany in the eightieth years established on the basis of two previous graphs is shown in Fig.1.3. From this graph results that in Poland, died on average every tenth wounded in an accident, whereas in Germany in eightieth years died on average every fortieth. It can be estimated that the coefficient of the passive safety of vehicles in Poland in relation to vehicles in Germany is in the order of 25%. The analysis of the number of the dead persons divided per ten thousand vehicles in use guides to the value of the relative coefficient of passive safety between evidences of the countries in the order of 40% (Tab.1.1 [1]). It suggests the need of improvement of the present situation in this range in Poland.

Fig.1.1. Numbers of wounded and dead persons in car accidents in Poland in the years: 1980 -95 [1].

Tab.1.1. Number of dead persons and the frequency of the dead persons among the wounded persons in car accidents divided per ten thousand vehicles used in Poland and in Germany in the year 1980 and 1993 [1].

Fig.1.2. Numbers of wounded and dead persons in car accidents in Germany in the eightieth years [2].

Fig.1.3. Frequency of dead persons among wounded persons in car accidents in Poland and in Germany in the years 1980÷1995.

Fig.1.4. Classification of car accidents based on the literature [3].

The analysis of qualitative statistics of accidents and their aftereffects is necessary to undertake the attempt of improvement of the vehicle passive safety.

A car accident was defined in the literature [3] as an incident of various vehicles came into being in traffic and causing victims in men or material losses.

Passive safety was defined as a set of undertakings with the aim of saving lives of participants of road traffic as well as a minimization of the aftereffects of collisions.

The classification of road incidents is shown in Fig.1.4 [3]. The average aftereffects of the accidents in the dependence on the kinds of the road incidents are presented in Tab.1.2.

From this table results that the most frequent and the most dangerous kind of the road accident in the aftereffects is the treading onto a pedestrian. Similarly dangerous is a crash of two vehicles. It should be noticed that the highest stage of destruction of vehicles causes a collision with an obstacle. The aftereffects of this type of an incident are generally heavier than in others cases. For example, the crash with a stationary obstacle at a speed of 60 km/h is equivalent to the aftereffects of a frontal crash of two cars also driving at speeds of 60 km/h.

The approximate results of the statistical analyses of crashes in the dependence on hits directions based on the data from the literature [3] are presented in Fig.1.5. The research team of the American Laboratory of Aeronautics in Cornell got the similar results [4]: the front crashes were in 56.5% cases of all road incidents and treading onto back - in 7.8%. The number of crashes in other directions of singular cars is equal to 35.7% of the number of the front crashes. They noticed that the 50% of the front crashes occurred at a speed, smaller than 65 km/h.

The research team of the University in Birmingham (England) worked out the analysis of the aftereffects of road accidents in the dependence on a direction of hits, i.e. the frequency of the occurrences of damages of different parts of cars - Tab.1.3. From it results that the damages of the front parts of vehicles (a front and both front corners) exceed 50% . It was also noticed that the aftereffects of a crash in the direction of the longitudinal vehicle axis are smaller in case of a front-side crash because of an increase of an angular speed what follows a sideways move.

From the analyses of the above presented statistical data, results unambiguously the need of projecting vehicles equipped with energy-consuming elements, particularly in the direction of the longitudinal axis of a vehicle. Such vehicles would be characterized with high passive safety.

The function of the passive safety can be divided on the preventative safety (prophylactic) as well as the safety resulting from a car construction. The function of the preventing safety relies on a limitation of dislocation possibilities of cargos and on correct placement of the elements being in a cabin. The function of a safe construction of a car relies on assuring suitable deformability and a suitable energy-absorption (ability to consume an energy) of front and rear parts of a car indispensable to save life space for passengers.

On the other side a safe structure should protect passengers against the results of a G-overload by extension of the time of crash duration, i.e. by minimization a value of acceleration acting on passengers.

The valuation of vehicle construction correctness is made in relation to the passive safety on the base of standards and regulations.

The American Standards MVSS (Motor