Phased Array inspection system applied to complex geometry Carbon Fibre Reinforced Polymer ...

106 Pages·2015·5.3 MB·English

by  André Cereja

Phased Array inspection system applied to
complex geometry Carbon Fibre Reinforced Polymer parts

André Filipe da Conceição Cereja

Thesis to obtain the Master of Science Degree in
Mechanical Engineering

Supervisor: Prof. Maria Luísa Coutinho Gomes de Almeida

Examination Committee
Chairperson: Prof. Rui Manuel dos Santos Oliveira Baptista
Supervisor: Prof. Maria Luísa Coutinho Gomes de Almeida
Members of the Committee: Dr. Nuno Miguel Carvalho Pedrosa
Prof. Telmo Jorge Gomes dos Santos

May 2015
“Success consists of going from failure to failure without loss of enthusiasm.”
Winston Churchill
Acknowledgments
First and foremost, a word of gratitude goes to Professor Luísa Coutinho, my scientific advisor, who has
challenged me from the very first class I had with her, to become a better engineer, and a better person.
The opportunity that I was given to develop this work must be mentioned, as well as the motivation,
counselling and revision efforts she placed into this MSc thesis.
Secondly, an acknowledgment to Dr. Nuno Pedrosa, who welcomed me with open arms in ISQ.
Dr. Nuno Pedrosa gave me the tools that enabled me to develop this work: from him I learned about
various sorts of subjects I had no previous contact with, during the months I spent in ISQ. Whenever I
had a doubt, or when I was unsure on how to proceed when facing a challenging situation, he always
had a guiding word to give.
To the rest of the staff in ISQ, namely the engineers Daniel Leitão, Liliana Santos and José Pedro
Sousa, a sincere word of appreciation for all the guidance and support they gave when I was developing
this work. Their technical knowledge, which they were so kind to share during my stay in ISQ proved
vital when I was faced with difficulties along the way.
To the company EXTENDE, namely Caroline Quintanilha, for being so kind as to supply me with a CIVA
license, so that I could develop my work.
To all the friends I met during my stay in ISQ, specifically João Amorim, João Borges, João Nabais,
Gonçalo Silva and Paulo Meyrelles, for all the help and cheerful moments.
To all the friends I was fortunate enough to make during my years in IST, both those I made during my
Mechanical Engineering studies and during my enrolment in Projecto FST Novabase, namely the
FST 04e team, thank you for sharing the most important moments in my life so far, that contributed to
making me the man I am today.
Last but definitely not least: there are not enough words to thank my parents, José Manuel and Maria
Valentina and my brother, João, for all the unconditional love they always gave me, together with the
confidence they always had in me. Only we and God know how hard they worked so that I could be
where I am today. Finally, my last word goes to my special someone, my girlfriend Joana Prata, for
reading this document and for always being there when I needed the most.

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Abstract
Following the growing use of composite materials in the aerospace industry, particularly carbon fibre
reinforced polymer (CFRP), arises the need to develop procedures to guarantee the monitoring and
evaluation of CFRP components. Moreover, the cost associated with destructive testing should be
eliminated, using methods that do not harm the parts’ service life.
Ultrasonic testing methods, namely the advanced phased array technique, can be a useful tool for
dealing with the challenges engineers face, when having to perform evaluation procedures for
components subject to fatigue and/or impacts.
A simulation software, CIVA, is used before the physical inspection of both planar and complex geometry
parts is performed. With CIVA, the phased array probes are selected, together with the inspection
parameters, e.g. probe aperture and focal laws. A study is performed on the methods CIVA employs to
calculate the acoustic field in the parts, as well as the homogenization algorithms behind the handling
of the anisotropy of CFRP. The difficulties expected when performing the physical inspection, namely
attenuation, are predicted. For the complex geometries, an evaluation is done on the potential to inspect
these components.
Afterwards, physical inspections are performed. Three components are analysed: a testing specimen
with embedded defects, a component subjected to fatigue loading, and a reinforcing omega-stringer.
The defects (delaminations) in the test specimen are identified and characterized, in size and depth.
Lacks of resin and debondings are discovered in the fatigue specimen. The stringer, impacted with
known energies, is analysed and the resulting flaws identified and measured.

Keywords
Carbon fibre reinforced polymer
Non-destructive testing
Phased array ultrasonic testing
Self adaptive algorithm
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Resumo
Acompanhando o uso crescente de materiais compósitos na indústria aeroespacial, particularmente
fibra de carbono (CFRP), surge a necessidade de desenvolver procedimentos que assegurem a
correcta monitorização e avaliação destes componentes. Ainda, o custo associado a ensaios
destrutivos deve ser eliminado, recorrendo a métodos que não prejudiquem a vida útil das peças.
Ensaios com ultrassons, nomeadamente a técnica avançada phased array, podem ser uma ferramenta
útil para lidar com os desafios que os engenheiros enfrentam, para avaliar componentes sujeitos a
fadiga e/ou impactos.
O programa de simulação CIVA é empregue antes da realização dos ensaios de peças de geometria
plana e complexa. Com o CIVA, seleccionam-se das sondas phased array, junto com a definição dos
parâmetros de inspecção, e.g. abertura da sonda e leis focais. Estudam-se os métodos empregues
pelo CIVA no cálculo do campo acústico, como o algoritmo de homogeneização responsável pelo
tratamento das características anisotrópicas do CFRP. As dificuldades esperadas aquando dos testes
físicos, nomeadamente a atenuação, são previstas. Para as peças complexas, é feita uma avaliação
do potencial de inspeccionar estes componentes.
Posteriormente são realizados os ensaios, a três componentes diferentes: um componente de teste
com defeitos inseridos no material, uma peça sujeita a fadiga, e uma longarina de reforço em ómega.
Os defeitos (delaminações) no componente de teste são identificados e caracterizados, em dimensão
e localização. No componente sujeito a fadiga são descobertas faltas de resina e descolagens. A
longarina, após sofrer impactos com energias conhecidas é analisada, identificando e medindo os seus
defeitos.
(Este resumo está escrito de acordo com o antigo acordo ortográfico.)

Palavras-chave
Fibra de carbono
Ensaios não destrutivos
Ensaios de ultrassons phased array
Algoritmo adaptativo

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Table of Contents
Acknowledgments .....................................................................................................................................i
Abstract.................................................................................................................................................... iii
Keywords ................................................................................................................................................. iii
Resumo ....................................................................................................................................................v
Palavras-chave .........................................................................................................................................v
Table of Contents .................................................................................................................................... vi
List of Figures ...........................................................................................................................................x
List of Tables .......................................................................................................................................... xii
List of Symbols and Acronyms .............................................................................................................. xiv
1 Introduction ...................................................................................................................................... 1
1.1 Scope ....................................................................................................................................... 1
1.2 Work contribution ..................................................................................................................... 2
1.3 Objectives ................................................................................................................................ 2
1.4 Document Structure ................................................................................................................. 2
2 State of The Art ............................................................................................................................... 4
2.1 Historical background .............................................................................................................. 4
2.1.1 Composite Materials in the Aerospace Industry .............................................................. 4
2.1.1.1 Manufacturing of CFRP ............................................................................................... 4
2.1.1.2 Applications of CFRP on the Aerospace Industry ....................................................... 5
2.1.2 History of non-destructive evaluation .............................................................................. 5
2.1.2.1 NDE: the beginning ..................................................................................................... 5
2.1.2.2 Importance of NDE ...................................................................................................... 6
2.2 Composite Fundamentals ........................................................................................................ 7
2.2.1 Materials used in PMCs ................................................................................................... 7
2.2.1.1 Matrix ........................................................................................................................... 7
2.2.1.2 Reinforcement ............................................................................................................. 8
2.2.2 Composite manufacturing processes ............................................................................ 10
2.2.3 Mechanical Properties of CFRP .................................................................................... 11
2.2.3.1 Anisotropic Constitutive Model .................................................................................. 11
2.2.3.2 Orthotropic Constitutive Model .................................................................................. 12
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2.2.3.3 Transversely Isotropic Constitutive Model ................................................................. 13
2.2.3.4 Rule of Mixtures ......................................................................................................... 14
2.2.4 Damage Mechanisms in Composite Materials .............................................................. 16
2.2.4.1 Fatigue damage ......................................................................................................... 16
2.2.4.2 Impact Damage ......................................................................................................... 16
2.2.4.3 Manufacturing defects ............................................................................................... 16
2.3 Ultrasonic non-destructive testing ......................................................................................... 17
2.3.1 Fundamentals of sound propagation ............................................................................. 17
2.3.1.1 Wave types ................................................................................................................ 17
2.3.1.2 Wave velocity ............................................................................................................. 20
2.3.1.3 Acoustic intensity and attenuation ............................................................................. 21
2.3.1.4 Frequency and defect detection ................................................................................ 23
2.3.1.5 Interface influence on sound propagation ................................................................. 23
2.3.2 Ultrasonic Inspection ..................................................................................................... 24
2.3.2.1 Transducer ................................................................................................................. 24
2.3.2.2 Beam characteristics ................................................................................................. 25
2.3.2.3 Inspection technique .................................................................................................. 25
2.3.2.4 UT data representation .............................................................................................. 26
2.3.3 Phased array advanced technique ................................................................................ 26
2.3.3.1 Probes ....................................................................................................................... 26
2.3.3.2 Beam control .............................................................................................................. 27
2.3.3.3 Adaptive Algorithm..................................................................................................... 28
2.3.3.4 Advantages and limitations of PAUT compared to other methods ............................ 29
2.4 Chapter summary .................................................................................................................. 31
3 Acoustic Model .............................................................................................................................. 32
3.1 CIVA software overview ........................................................................................................ 32
3.2 CFRP test specimens ............................................................................................................ 33
3.2.1 Calibration specimen ..................................................................................................... 33
3.2.2 Fatigue test panel .......................................................................................................... 35
3.3 Material properties ................................................................................................................. 37
3.4 PAUT probes ......................................................................................................................... 40
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3.4.1 Probe selection criteria .................................................................................................. 41
3.4.2 Characteristics of the selected probes .......................................................................... 41
3.5 Parameter case studies ......................................................................................................... 42
3.5.1 Signal characterization .................................................................................................. 42
3.5.2 Attenuation influence on the acoustic field .................................................................... 44
3.5.2.1 Attenuation case study 1: 5 MHz probe .................................................................... 45
3.5.2.2 Attenuation case study 2: 3,5 MHz probe ................................................................. 47
3.5.3 Aperture influence on the acoustic field ........................................................................ 48
3.5.4 Multi-point focusing technique ....................................................................................... 51
3.6 Amplitude differences between interface and backwall echo ................................................ 53
3.7 Defect characterization .......................................................................................................... 54
3.8 Complex geometry part inspection ........................................................................................ 56
3.9 Chapter summary .................................................................................................................. 57
4 Physical Inspection ........................................................................................................................ 58
4.1 Overview of the system ......................................................................................................... 58
4.1.1 Hardware ....................................................................................................................... 58
4.1.2 Software ......................................................................................................................... 60
4.2 General physical studies ....................................................................................................... 61
4.2.1 Gain ............................................................................................................................... 62
4.2.2 Maximum inspection velocity ......................................................................................... 62
4.2.3 Inspection step............................................................................................................... 63
4.2.4 Total inspection time ...................................................................................................... 64
4.3 Acoustic Impedance studies .................................................................................................. 65
4.4 Attenuation coefficient measurements .................................................................................. 66
4.5 SAUL algorithm testing .......................................................................................................... 67
4.6 Calibration specimen testing results ...................................................................................... 67
4.7 Fatigue panel and omega stringer testing results ................................................................. 71
4.7.1 Flat panel ....................................................................................................................... 71
4.7.2 Omega stringers ............................................................................................................ 74
4.8 Chapter summary .................................................................................................................. 76
5 Conclusions ................................................................................................................................... 77
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