UNIVERSITI PUTRA MALAYSIA

STUDY ON OPTIMIZATION OF COMPOSITE TUBULAR ENERGY ABSORPTION SYSTEM

HAKIM S. SULTAN ALJIBORI.

FK 2004 55

STUDY ON OPTIMIZATION OF COMPOSITE TUBULAR ENERGY ABSORPTION SYSTEM

BY

HAKIM S. SULTAN ALJIBORI

Thesis Submitted to the School of Graduate Studies, University Putra Malaysia in fulfilment of the Requirements for the Degree of Master of Science

June 2004

DEDICATION

I am happy to dedicate this work to my country "Iraq". A country is great by the

character of its peopIe and not by its number. I adore my country because it is the

land of civilizations from the time immemorial.

I would like to express my gratitude to all the people who have been supportive of

my endeavor towards my M.Sc. study.

The support of my family has been encouraging me to pursue my M.Sc study.

Without their support I could not have achieved thus far. To my mother, brothers

and my wife I thank them for their supporting me for so many years. I wish to make

both of them proud. I thank my wife for her support, understanding and love. You

have been a constant source of strength throughout my M.Sc study whenever I need.

Abstract of thesis presented to the Senate of Universiti Putra Malaysia in fulfilment of the requirements for the degree of Master of Science

STUDY ON OPTIMIZATION OF COMPOSITE TUBULAR ENERGY ABSORPTION SYSTEM

BY

HAKIM S. SULTAN ALJIBORI

June 2004

Chairman: Elsadig Mahdi Ahmad, Ph.D.

Faculty : Engineering

A four-phase program to improve the specific energy absorbed by axially crushed

composite collapsible tubular energy absorber devices was undertaken. In the first

phase, the effects of trigged tube wall on the crushing behaviour were investigated.

At this stage, triggered tubes were fabricated and crushed. The second phase is

aimed at obtaining the best position for the triggered wall. The third phase focuses

on the effects of material sizing in order to understand the influence of triggered

wall Iength on the responses of composite circular tubes to the axial crushing load.

The results from these three phases lead to the fourth phase. The objective of the 4t"

phases was to optimise the shape geometry of the cross-section area to further

improve tube energy absorption capability. The tubes were manufactured from

woven roving glasslepoxy fabric and had the same lay-up providing a common

laminate for comparison. The failure modes were observed and the specific

sustained crushing loads were determined and compared against non-optimized

tubes of the same lay-up. The importance of differentiating between initiation

energy and propagation energy is shown, and a new parameter (energy capability

index (ECI)) is proposed, as a useful measure for comparing crush behaviour of

composite structures. The experimental results demonstrated strong potential

benefits of optimizing the material distribution. The sizing and shape optimization of

composite collapsible tubes exhibited a pronounced effect on their capability to

absorb high specific energy under axial compressive load.

For the effect of triggering it was that tubes (TN) observed to experience

catastrophic failure mode during the post crush stage also displayed very poor

energy absorption. Triggering a part of tube wall was very efficient in improving the

energy absorption capacity of circular composite tubes. Accordingly tubes with

triggered wall (T-tubes) exhibited highest energy absorption capacity compared with

non-triggered tubes. They also experience stable post-crush region of load-

displacement curves, which leads to high crashworthiness performance. It is also

evident from the experimental results that change in the triggered wall aspect ratio

significantly affected the energy absorption capability of tube with middle triggered

wall (TM-tubes). Distinct differences were observed between the different aspect

ratio, where TM tubes (i.e. tubes with triggered wall aspect ratio of 0.28) exhibited

the highest energy absorption capacity. Different failure modes were observed for

different triggered wall length ratios (Lt,/H). For the core tubes (TMC-), was

observed that core presence markedly improved the energy absorption capacity of

composite circular tubes. Among TMC- tubes, TMC3 tubes (i.e. tubes with core

thickness of 3.35mm) displayed highest energy absorption capacity.

Abstrak tesis yang dikemukakan kepada Senat Universiti Putra Malaysia sebagai memenuhi keperluan untuk ijazah Master Sains

KAJIAN MEGENAI PENGOPTIMUMAN SISTEM PENYERAPAN TENAGA TUBULAR KOMPOSIT

Oleh

HAKIM S. SULTAN ALJLBORI

Jun 2004

Pengerusi: Elsadig Mahdi Ahmad, Ph.D.

Fakulti : Kejuruteraan

Suatu program empat fasa bagi meningkatkan tenaga tentu yang diserap oleh peranti

penyerap tenaga bagi komposit boleh-musnah tiub yang dihancurkan secara

menegak telah dijalankan. Dalarn fasa pertama, kesan dinding tiub berpicu ke atas

perlakuan hancur telah dikaji. Untuk ini, tiub berpicu dan tanpa-picu telah difabrikat

dan dihancurkan. Fasa yang kedua bertujuan untuk mendapatkan posisi terbaik bagi

dinding berpicu tersebut. Fasa ketiga memfokuskan kepada kesan pensaizan bahan,

untuk memahami pengaruh panjang dinding berpicu ke atas tindakbalas tiub-tiub

komposit membulat kepada beban paksi penghancuran. Keputusan yang dicapai oleh

ketiga-tiga fasa ini menyumbang kepada fasa yang keempat, yang inana objektifnya

adalah untuk mengoptimuinkan bentuk geometri bagi luas keratan rentas tiub untuk

lebih peningkatan dalam kebolehserapan tenaga oleh tiub. Tiub-tiub ini diperbuat

daripada jalinan pintal kacalfabrik epoksi dan mempunyai rekabentuk yang sama, ini

menyediakan pelapik biasa untuk perbandingan.Mod-mod kegagalan diperliatikan,

dan beban penghancuran berterusan tertentu telah ditentukan dan dibandingkan

dengan tiub-tiub tak-teroptimum yang sama rekabentuknya. Kepentingan untuk

membezakan di antara tenaga inisiasi dan tenaga propagasi ditunjukkan, dan satu

parameter baru (indeks kebolehan tenaga(EC1)) telah dicadangkan sebagai

pengukuran yang berguna untuk membandingkan perlakuan hancur struktur-struktur

komposit. Keputusan-keputusan eksperimen menunjukkan manfaat yang mungkin

diperoleh dalam mengoptimumkan taburan bahan. Pensaizan dan pengoptimuman

bentuk tiub komposit boleh-musnah menunjukkan kesan yang ketara dalam

kebolehannya untuk menyerap tenaga tentu yang tinggi di bawah beban mampatan

paksi .

Bagi kesan penamballan picu, adalah diperhatikan bahawa tiub-tiub dengan dinding

tanpa-picu (TN) mengalami mod kegagalan katastrofik semasa tahap pasca-hancur,

di samping menunjukkan kapasiti penyerapan tenaga yang amat rendah,

Penambahan picu ke atas sebahagian daripada dinding tiub didapati amat berkesan

dalam meningkatkan kapasiti penyerapan tenaga bagi tiub-tiub komposit membulat.

Dengan itu, tiub-tiub dengan dinding yang berpicu (T-tubes) menunjukkan kapasiti

penyerapan tenaga yang amat tinggi jika dibandingkan dengan tiub tanpa-picu. Ia

juga mengalami rantau pasca-hancur yang stabil dalam lengkuk beban-peralihan,

yang membawa kepada prestasi kebolehtahanan-musnah yang tinggi. Daripada

eksperimen juga dapat dibuktikan bahawa pertukaran dalarn nisbah aspek dinding

berpicu memberi kesan langsung kepada kebolehan penyerapan tenaga bagi TM-

tubes. Beberapa perbezaan ketara telah dikenalpasti di antara nisbah aspek yang

berlainan, di amna tiub TM (iaitu tiub dengan nisbah aspek dinding berpicu

sebanyak 0.28) menunjukkan kapasiti penyerapan tenaga yang tertinggi. Mod-mod

kegagalan yang berlainan telah diperhatikan untuk nisbah Lt,/H yang berlainan.

Bagi tiub-tiub teras (TMC-), adalah didapati bahawa kehadiran teras telah

meningkatkan kapasiti penyerapan tenaga untuk tiub-tiub komposit membulat. Di

antara tiub-tiub TMC-, tiub TMC3 (iaitu tiub yang mempunyai ketebalan teras

sebanyak 3.35mm) menunjukkan kapasiti penyerapan tenaga yang amat tinggi.

ACKNOWLEDGEMENTS

IN THE NAME OF ALLAH, GRACIOUS, MERCIFUL

I wish to acknowledge the following individuals whose enormous contributions led

to the successful completion of this thesis:

Dr. El-Sadig Mahdi, thanks for your immense contribution to my academic

advancement and your tremendous patience during many challenging moments.

A man of limitless patience, I am glad to have been associated with you. Thanks

for your friendship and concern. You made the work easier with your caring

words and advices.

Dr. A. M. S. Hammouda, thanks for his ennobling association. Thanks for

giving me another dimension to life. Thanks for taking time off your busy

schedule to serve on my committee.

Dr. Ashraf Ali, thanks for the tremendous help you offered for this thesis. Your

guidance and assistance were priceless. Thanks for your support and vision and

for your ennobling association

I certify that an Examination Committee met on 18th June 2004 to conduct the final examination of Hakim Samawi Sultan Aljibori on his Master of Science thesis entitled "Optimization of Composite Tubular Energy Absorption System" in accordance with Universiti Pertanian Malaysia (Higher Degree) Act 1980 and Universiti Pertanian Malaysia (Higher Degree) Regulations 198 1. The Committee recommends that the candidate be awarded the relevant degree. Members of the Examination Committee are as follows:

MOHD SAPUAN SALIT, Ph.D. Associate Professor Faculty of Engineering Universiti Putra Malaysia (Chairman)

ABDUL AZIZ JAAFAR, Ph.D. Faculty of Engineering Universiti Putra Malaysia (Member)

ABD RAHIM ABU TALIB, Ph.D. Faculty of Engineering Universiti Putra Malaysia (Member)

CHE HASSAN CHE HARON, Ph.D. Associate Professor Faculty of Engineering Universiti Kebangsaan Malaysia (Independent Examiner)

ProfessoriDeputy ~ g n School of Graduate Studies Universiti Putra Malaysia

Date: 2 6 AUG 2004

This thesis Submitted to the Senate of Universiti Putra Malaysia and has been accepted as fulfilment of the requirements for the degree of Master of Science. The members of the Supervisory Committee are as follow:

ELSADIG MAHDI AIIMED, Ph.D. Faculty of Engineering Universiti Putra Malaysia (Chairman)

ABDEL MAGID S. HAMOUDA, Ph.D. Associate Professor Faculty of Engineering Universiti Putra Malaysia (Member)

ASHRAF ALI, Ph.D. Faculty of Engineering International Islamic Universiti Malaysia (Member)

AlNI IDENS, Ph.D. Professor1 Dean School of graduate Studies University Putra Malaysia

Date: 1 0 SEP 2004

DECLARATION

I herby declare that the thesis is based on my original work except for quotation and citations which have been duly acknowledged. I also declare that it has not been previously or concurrently submitted for any other degree at UPM or other institutions.

HAKIM S. SULTAN ALJIBORI

Date: 3- 7 10 8 /20ei/

TABLE OF CONTENTS

DEDICATION ABSTRACT ABSTRAK ACKNOWLEDGEMENT DECLARATION LIST OF TABLES LIST OF FIGURES NOMENCLATURE

CHAPTER

INTRODUCTION 1 . 1 Problem Statement 1.1 Research Objectives 1.2 Significance of the Study 1.3 Thesis Layout

LITERATURE REVIEW

Crashworthiness Parameters of Collapsible Energy Absorption Devices 2.1.1 Load-Displacement of Axially Crushed

Composite Shells 2.1.2 Load-Carrying Capacity 2.1.3 Crush Force Efficiency and Crushed Strain 2.1.4 Energy Absorption Capability Crushing Behaviour of Metallic and Composite Circular tubes 2.2.1 Metallic Tubes 2.2.2 Composite Tubes Compressive Failure Mechanisms of FRP Tubes 2.3.1 Euler Buckling 2.3.2 Progressive Folding 2.3.3 Brittle Fracture Factors Affecting the Energy Absorption Capability of Composite Tubes 2.4.1 Effect of Fibre Reinforcement types 2.4.2 Effect of Matrix Types 2.4.3 Fibre Architecture 2.4.4 Geometry of Specimen 2.4.5 Effect of Processing Conditions 2.4.6 Effect of Fibre Volume Fraction 2.4.7 Effect of Crushing Speed

Discussion

Page ii iii v

viii xi xv xvi xix

xii

METHODOLOGY

Introduction Mandrel Preparation Composite Constituents Fabrication Process of Specimens Crushing Process Discussion

RESULTS AND DISCUSSION

Design Parameters Crashworthiness Parameters 4.2.1 Crush Force Efficiency-Crush Strain Relation 4.2.2 Initial Failure Indicator 4.2.3 Energy Absorption Capability Results 4.3.1 Tubes with Non-Triggered and Triggered Wall

Placed at Different Positions (T-tubes) 4.3.1.1 Load-Displacement Relationship 4.3.1.2 Load Carrying Capacity 4.3.1.3 Energy Absorption Capabilities 4.3.1.4 Failure Modes 4.3.1.5 Effect of Triggered Wall Position on

Crashworthiness Parameters 4.3.1.6 Conclusion

4.3.2 Tubes with Different Triggered Wall Aspect Ratio LtdH (TM-Tubes) 4.3.2.1 Load -Displacement and Crushing

History 4.3.2.2 Load Carrying Capacity 4.3.2.3 Energy Absorption Capabilities 4.3.2.4 Failure Modes 4.3.2.5 Effect of LtdH Ratio on the

Crashworthiness Parameters 4.3.2.6 Conclusion

4.3.3 Core-Tubes (TMC) 4.3.3.1 Load-Displacement and Crushing

History 4.3.3.2 Load Carrying Capacity 4.3.3.3 Energy Absorption Capabilities 4.3.3.4 Failure Mode 4.3.3.5 Effect of Core on Crashworthiness

Parameters 4.3.3.6 Conclusion

... X l l l

Energy Dissipation Mechanisms

4.4.1 Pre-Initial Crush Failure Stage 4.4.2 Post-CrushFailure Stage Energy Capability Index Conclusion

CONCLUSION AND RECOMMENDATIONS

General Conclusion Triggering of Tube Wall (TN tubes) Triggered Wall Position (T-tubes) Triggered Wall Aspect Ratio (TM-tubes) Core-Tubes (TMC) Suggestion for Further Work

REFERENCES APPENDICES BIODATA OF THE AUTHOR

LIST OF TABLES

Table

Constituent materials

characteristics of the Dimensions Composite Tubes

Summarized Results of the Energy Absorption Capabilities for (T-) Tubes

Measured Crashworthiness Parameters of (T-) tubes

Results of the Energy Absorption Capabilities for TM- Tubes

Measured Crashworthiness Parameters of TM- Tubes

Summarized Results of Energy Absorption Capabilities of Tubes with TM and TMC

Measured Crashworthiness Parameters of TM and TMC Tubes

Page

Energy Absorption Analysis of Axially crushed composite 1 1 1 tubes

LIST OF FIGURES

Figure

2.1 Schematic Presentation of The Load-Displacement Curve of Composite Tube Subjected to Axial Crushing

2.2 Axial collapse of metallic tube

Page

7

2.3 General Failure Mechanisms And Load-Displacement Characteristic 17 of a Progressive Folding, FRP Tube

Schematic Representation of Load-Displacement Characteristic for an FRP Tube Failing by Stable Brittle

Schematic Representation of the Formation of the Splaying / Lamina 19 Bending Mode

Schematic Representation of the Formation of Fragmentation / Transverse Shearing Mode

Flow Chart Describes the Experimental Work

Schematic diagrams of mandrel with T- Tubes

Schematic Diagrams of Mandrel for TM- Tubes

Schematic Diagrams of Developed Woven Roving Glass Fibres

Schematic Diagrams of Woven roving Winding Process

Triggered Wall Distribution of T- ,TM and TMC Tubes

Typical Sketch of TM Tubes with Lt,/H

Typical Sketch of Core-Tubes

Typical Photographic of T-Tubes

Typical Photographic of TM Tubes with L,/H

Typical Photographic of TMC Tubes

Composite Tube under Axial Crushing

Typical Load-Displacement Curve and Deformation Histories of TN Tube

xvi

4.2 Load-Displacement Curve and Deformation Histories of TI Tube 5 7

4.3 Load-Displacement Curve and Deformation Histories of TO Tube

4.4 Load-Displacement Curve and Deformation Histories of TM Tube

4.5 Typical Load-Displacement Relations of Composite Circular Tubes with Non-Triggered (TN) Inner (TI), Outer (TO) and Middle (TM)

4.6 Energy-Displacement Relations of T- Tubes

4.7 Energy Absorption as a Function of Triggered Wall Aspect ratio r/t

4.8 Crushing Loads as a Function of Aspect Ratio r/t

4.9 Typical Load-Displacement Curve and Deformation Histories of Triggered Wall Aspect Ratio (Ltr/H) of 0.42 (TMl)

4.10 Load-Displacement Curve and Deformation Histories of Triggered 72 Wall with Triggered Wall Aspect Ratio (Ltr/H) of 0.57

4.11 Load-Displacen~ent Curve and Deformation Histories of Triggered Wall Aspect Ration (LtJH) of 0.71 (TM3)

4.12 Typical Load-Displacement Relations of TM- Tubes

4.13 Energy-Displacement Relations of TM- Tubes

4.14 Energy Absorption Capabilities as a Function of Triggered Wall Aspect Ratio (Ltr/H)

4.15 Crushing Loads as a Function of Triggered Wall Aspect Ratio (LtdH)

4.16 Load-Displacement Curve and Deformation Histories of TMC 1 Tube

4.17 Typical Load-Displacement Curve and Deformation Histories of TMC2 Tube

4.18 Load-Displacement Curve and Deformation Histories of TMC3 Tube

4.19 Load-Displacement Relations for TMC- and TM Tubes

4.20 Energy-Displacement Relations for TMC- and TM Tubes

4.21 Energy Absorption capabilities as a Function of Core Thickness (t,) for TMC- and TM Tubes

xvii

4.22 Crushing Loads as a Function of Core Thickness (t,) for TMC- and 95 TM Tubes

4.23 Optical Micrographs (1 00p) of TI-Tubes

4.24 Optical Micrographs ( 1 0 0 ~ ) of TO and TM Triggered Wall Tubes

4.25 Optical Micrographs ( 1 0 0 ~ ) of TM Tubes with Triggered Wall Aspect Ratio (LtdH)

4.26 Optical Micrograph ( 1 0 0 ~ ) of TMC1 Tubes

4.27 Optical Micrograph ( 1 0 0 ~ ) of TMC3 Tubes

NOMENCLATURE

FRP

H

TMC

TMC 1

Fibre Reinforced Plastic

Total Height of Tube (mm)

Triggered Wall Length (mm)

Triggered Wall Aspect Ratio

Non-Triggered Tube

Tube with Triggered Wall Placed at Inner Position

Tube With Triggered Wall Placed at Outer Position

Tube with Triggered Wall at Middle Position and (Ltr/ H) of 0.28

Tube with TM and (LtJ H) of 0.42

Tube with TM and (Ltrl H) of 0.57

Tube with TM and (Ltd H) of 0.71

Tube with TM and Core

Tube with TM and Core Thickness of 2. lmm

Tube with TM and Core Thickness of 2.75mm

Tube with TM and Core Thickness of 3.35mm

Crushed Distance (mni)

Thickness of the Triggered Wall (mm)

Thickness of the Core (mm)

CFE

Mean Top Diameter of Tube (mm)

Mass of the Tube ( kg)

Cross-Sectional Area (m2)

Volume of Material (m3)

Mass Density of Structure (kg/m3)

Volume of Structure (m3)

Cross-Sectional Area of Material (m2)

Cross-Sectional Area of Structure (m2)

Specific Energy Absorption (kJ/kg)

Energy Absorption per Unit Volume ( k ~ l m ~ )

Instant Crush Failure Load (kN)

The Total Work Done (kJ)

Instantaneous Displacement (mm)

Mean Crush Failure Load (kN)

Critical Crush Failure Loads (kN)

First Peak Crush Failure Load (kN)

Initial Failure Indicator

Crush Force Efficiency

Crushed Strain

CHAPTER 1

INTRODUCTION

In recent years there is an increasing demand in the use of composite materials for

the automotive, aerospace and rail industry. The automotive and aerospace

applications over the past quarter-century have been primarily in special areas such

as energy absorber devices. As the automotive manufacturers have to take

environmental issues into consideration, the composite space-frame concept has

become more and more attractive in the design of vehicles. When using composite

in the body structure of a vehicle, considerable weight reductions can be achieved

compared to conventional isotropic structures, which leads to reduced fuel

consumption and consequently lower carbon dioxide emissions.

The high efficiency of any energy absorber device may be defined as its ability to

decelerate smoothly the occupant compartment to the rest within the allowable

limit [I]. It is well-known that responses of axially crushed non-trigger tubes (i.e.

tube with constant thickness and squared ends) are characterized by recording very

high resistances till reach their full load carrying capacity after which definite

different degrees of unstable behaviours take place [2]. Therefore, it is strongly

believed that for core-less tubular energy absorber devices stable load-deformation

curve could only be obtained by steering the failure initiation to occur in a designed

region along the shell meridional direction. In that manner, two approaches based

on material and geometry properties have been suggested to avoid the Euler-

buckling failure mechanism or any mechanism leads to catastrophic failure. These

approaches can be classified in two categories. The first Category based on material

properties employs core thin-walled structures filled with crushable medium (i.e.

synthesised or natural cellular materials filler). It has been extensively shown that

tubes with filled cores achieved high and stable load carrying capacity along the

gross deformation with very high total energy absorbed and very specific energy

absorption compared with the core-less tubes [3]. This Category is being criticised

because of apparent weight increasing, despite the specific filler density. More over

researchers in composite structures introduces hybrid structures using different

fibres types 141. The hybridisation relatively improved the load-carrying capacity

without a profound enhancement in the specific energy absorbed. A designed

beneficial imperfection in the structure introduced by Hui [5] was introduced to

enhance the energy absorption. This method resulted in a combination of instable

and stable failure mode. The second Category based on geometry properties are

also categorized in many groups. According to Farley [6] and Farley & Jones [7]

reported that energy absorption capability is a non-linear function of inside

diameter to wall thickness ratio (Dlt) for tubular specimens. They stated that

specific energy absorption was found to fall as Dlt increased. Mamalis, et a1 [8] and

Mahdi, et al. [9] reported that the crushing behaviour is dominated by increasing

the cone vertex angle.

1.1 Problem Statement

The main objective to manufacturers and materials community is to produce

vehicles with lightweight; therefore, using composite material for automotive and

aerospace industry it is very attractive to be the main materials for many car

components. One of these components is crash energy devices. Energy absorbs

devices should be designed to meet the requirements and standards for the

protections of the occupants or passengers in vehicles accident. However,

behaviour of the composite energy absorber devices is often unstable in absorbing

crash event and most probably leads to catastrophic failure mechanism. This

instability is one of the more critical problems in using fibre composites for crash

energy management. This is the main factor behind this present project.

Accordingly this project introduces many aspects to improve the energy absorption

capability of composite circular tubes under quasi-static axial compressive load.

1.2 Objectives

The purpose of this study is to optirnise the structure of composite tubular energy

absorber device in order to maximize its specific energy absorption capability. The

only known quantities in this problem are the loading, support conditions and the

structure domain. The detail objectives of this study can be summarised as follows:

1. To study the effect of triggering on the crushing behaviour of composite

circular tubes.

2. To examine the effect of the triggered wall position on the energy

absorption of composite circular tubes.

3. To determine the effect of the triggered wall aspect ratio on the energy

absorption of composite circular tubes.

4. To examine the effect of material distribution and shape optimisation on

the energy absorption of composite circular tubes.

1.2 Significance of the Study

This work is important because of the following:

1. Any generic technology or structural system in the various engineering

fields offers safety and provide enhanced levels of protection ought to be

of considerable interest, that composite materials based structures is one

such technology is not in doubt.

2. The efficient use of composite tubes as energy absorber depends on the

understanding of their crushing behaviour.

3. The results of this study and the produced data can be helpful in the design

stage of energy absorber elements made from composite material.