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Technical Discussions
Rolf Diederichs
Director,
NDT.net, Germany, Joined Nov 1998, 608

Rolf Diederichs

Director,
NDT.net,
Germany,
Joined Nov 1998
608
07:30 Sep-01-1998
September 1998 Forum Introduction 'NDT of aircraft structures'


As usual, this month's issue will focus on our discussion theme. If you are interested in other nondestructive testing topics, don't hesitate to discuss them in this forum as well.

The NDT.net Forum of this month is focusing on aircraft structures.
For references we are including a list of 7th ECNDT articles that are related to this topic. While we intend to deal with all the important issues related to the determination of the integrity of aircraft structures we would like to concentrate on NDE of composites.

One such article is 'Characterization of Defects in Composite Materials Using Rapidly Acquired Leaky Lamb Wave Dispersion Data,' co-authored by Y. Bar-Cohen, Zensheu Chang - Jet Propulsion Lab and A.K. Mal, - UCLA, USA. In conjunction with this article, we are pleased to introduce Dr. Yoseph Bar-Cohen, who will serve as the coordinator for the questions and comments on NDE of Aircraft Structures for the September 1998 Forum of NDT.net. He is now our Virtual Session Chairman. Dr. Bar-Cohenis an NDE expert with over 27 years experience in aerospace related issues. He discovered the leaky Lamb wave and the polar backscattering phenomena in composites and co-pioneered their application to NDE of these materials. Dr. Bar-Cohen is the Group Leader for the NDE and Advanced Actuators (NDEAA) technologies at the Jet Propulsion Laboratory, Pasadena, California as well as an Adjunct Professor at the Mechanics and Aerospace Engineering Dept., University of California, Los
Angeles (UCLA). Also, he is the Chair of the ASNT Ultrasonic Committee. Dr. Bar-Cohen was an author on over 140
publications, made numerous presentations at national and international conferences, and has 10 patents.

Publications on NDTnet:
> Characterization of Defects in Composite Materials
Using Rapidly Acquired Leaky Lamb Wave Dispersion Data
> Autonomous rapid inspection of aerospace structures
> Polymer piezoelectric transducers for ultrasonic nde
> International ndt technical collaboration using the internet

Composite materials are used to construct flaw critical structures and they are taking a growing percentage of the makeup of aircraft and spacecraft structures. The cost of composite structures is significantly higher than the equivalent metallic made structures, reaching levels of orders of magnitude higher cost. Evaluation of the cost elements showed that about one third is spent on both mechanical and nondestructive testing. The key to the assurance of inspection efficiency is the ability to apply effective tests for the determination of the integrity, stiffness and durability (residual life) and thus allowing the use of less material, i.e. smaller safety factors, while assuring the performance of the structures. Also, it is necessary to minimize the amount of costly mechanical tests. NDE methods are developed to detect and characterize flaws and to determine the material properties (e.g., stiffness) of test specimens. The strength and durability are parameters that cannot be determined byNDE methods since they are associated with physical processes that are statistical in nature and cannot be measured nondestructively.

The standard NDE methods that are used to inspect metallic structures were adapted by the industry for inspection of composite materials, partially accounting for the multi-layered anisotropic nature of these materials. The standard NDE methods provide limited and mostly qualitative information about the material properties and defects. The discovery of the LLW and the Polar Backscattering phenomena in composites enabled new capabilities that address the anisotropy and offered the potential of quantitative testing. Methodologies were developed that allow inversion of the elastic stiffness coefficients and the quantitative characterization of defects as well as the evaluation of the quality of adhesively bonded joints. In recent years, other NDT methods have also emerged including the laser induced ultrasound, reverse geometry radiography and shearography. While there is significantly more work needed towards making these methods standard NDE tools, efforts are also needed to enable rapid inspection of composite structures in the field. To address this important issue, robotic tools are being are incorporated with NDE sensors and intelligent NDE methodologies.

To start the discussion let me turn to you the participants and I would like to welcome any questions or comments that you may have.
- Enjoy -

Rolf Diederichs



 
 Reply 
 
david.b
david.b
09:03 Mar-16-2000
lamb waves



 
 Reply 
 
david.b
david.b
08:28 Mar-17-2000
lamb waves



 
 Reply 
 
shridhar garge
shridhar garge
08:57 Feb-18-2001
i want info about leaky lamb waves and polar back scattering
: respected sir
I want some explanation about leaky lamb waves and polar
back scattering. please let me know as early as possible.
yours
shridhar

: As usual, this month's issue will focus on our discussion theme. If you are interested in other nondestructive testing topics, don't hesitate to discuss them in this forum as well.

: The NDT.net Forum of this month is focusing on aircraft structures.
: For references we are including a list of 7th ECNDT articles that are related to this topic. While we intend to deal with all the important issues related to the determination of the integrity of aircraft structures we would like to concentrate on NDE of composites.

: One such article is 'Characterization of Defects in Composite Materials Using Rapidly Acquired Leaky Lamb Wave Dispersion Data,' co-authored by Y. Bar-Cohen, Zensheu Chang - Jet Propulsion Lab and A.K. Mal, - UCLA, USA. In conjunction with this article, we are pleased to introduce Dr. Yoseph Bar-Cohen, who will serve as the coordinator for the questions and comments on NDE of Aircraft Structures for the September 1998 Forum of NDT.net. He is now our Virtual Session Chairman. Dr. Bar-Cohen is an NDE expert with over 27 years experience in aerospace related issues. He discovered the leaky Lamb wave and the polar backscattering phenomena in composites and co-pioneered their application to NDE of these materials. Dr. Bar-Cohen is the Group Leader for the NDE and Advanced Actuators (NDEAA) technologies at the Jet Propulsion Laboratory, Pasadena, California as well as an Adjunct Professor at the Mechanics and Aerospace Engineering Dept., University of California, Los
: Angeles (UCLA). Also, he is the Chair of the ASNT Ultrasonic Committee. Dr. Bar-Cohen was an author on over 140
: publications, made numerous presentations at national and international conferences, and has 10 patents.

: Publications on NDTnet:
: > Characterization of Defects in Composite Materials
: Using Rapidly Acquired Leaky Lamb Wave Dispersion Data
: > Autonomous rapid inspection of aerospace structures
: > Polymer piezoelectric transducers for ultrasonic nde
: > International ndt technical collaboration using the internet

: Composite materials are used to construct flaw critical structures and they are taking a growing percentage of the makeup of aircraft and spacecraft structures. The cost of composite structures is significantly higher than the equivalent metallic made structures, reaching levels of orders of magnitude higher cost. Evaluation of the cost elements showed that about one third is spent on both mechanical and nondestructive testing. The key to the assurance of inspection efficiency is the ability to apply effective tests for the determination of the integrity, stiffness and durability (residual life) and thus allowing the use of less material, i.e. smaller safety factors, while assuring the performance of the structures. Also, it is necessary to minimize the amount of costly mechanical tests. NDE methods are developed to detect and characterize flaws and to determine the material properties (e.g., stiffness) of test specimens. The strength and durability are parameters that cannot be determined by NDE methods since they are associated with physical processes that are statistical in nature and cannot be measured nondestructively.

: The standard NDE methods that are used to inspect metallic structures were adapted by the industry for inspection of composite materials, partially accounting for the multi-layered anisotropic nature of these materials. The standard NDE methods provide limited and mostly qualitative information about the material properties and defects. The discovery of the LLW and the Polar Backscattering phenomena in composites enabled new capabilities that address the anisotropy and offered the potential of quantitative testing. Methodologies were developed that allow inversion of the elastic stiffness coefficients and the quantitative characterization of defects as well as the evaluation of the quality of adhesively bonded joints. In recent years, other NDT methods have also emerged including the laser induced ultrasound, reverse geometry radiography and shearography. While there is significantly more work needed towards making these methods standard NDE tools, efforts are also needed to enable rapid inspection of composite structures in the field. To address this important issue, robotic tools are being are incorporated with NDE sensors and intelligent NDE methodologies.

: To start the discussion let me turn to you the participants and I would like to welcome any questions or comments that you may have.
: - Enjoy -

: Rolf Diederichs




 
 Reply 
 
Yoseph Bar-Cohen
R & D,
Jet Propulsion Lab (JPL), USA, Joined Nov 1998, 26

Yoseph Bar-Cohen

R & D,
Jet Propulsion Lab (JPL),
USA,
Joined Nov 1998
26
09:29 Feb-18-2001
Re: i want info about leaky lamb waves and polar back scattering

shridhar,

I have a website in which I have been archieving all
my publications since 1997. You can find there articles
about the subjects of LLW and PBS. The address is
http://ndeaa.jpl.nasa.gov/nasa-nde/nde/nde-hp.htm

Yosi


: : respected sir
: I want some explanation about leaky lamb waves and polar
: back scattering. please let me know as early as possible.
: yours
: shridhar
.
.
.
.
: : As usual, this month's issue will focus on our discussion theme. If you are interested in other nondestructive testing topics, don't hesitate to discuss them in this forum as well.
.
: : The NDT.net Forum of this month is focusing on aircraft structures.
: : For references we are including a list of 7th ECNDT articles that are related to this topic. While we intend to deal with all the important issues related to the determination of the integrity of aircraft structures we would like to concentrate on NDE of composites.
.
: : One such article is 'Characterization of Defects in Composite Materials Using Rapidly Acquired Leaky Lamb Wave Dispersion Data,' co-authored by Y. Bar-Cohen, Zensheu Chang - Jet Propulsion Lab and A.K. Mal, - UCLA, USA. In conjunction with this article, we are pleased to introduce Dr. Yoseph Bar-Cohen, who will serve as the coordinator for the questions and comments on NDE of Aircraft Structures for the September 1998 Forum of NDT.net. He is now our Virtual Session Chairman. Dr. Bar-Cohen is an NDE expert with over 27 years experience in aerospace related issues. He discovered the leaky Lamb wave and the polar backscattering phenomena in composites and co-pioneered their application to NDE of these materials. Dr. Bar-Cohen is the Group Leader for the NDE and Advanced Actuators (NDEAA) technologies at the Jet Propulsion Laboratory, Pasadena, California as well as an Adjunct Professor at the Mechanics and Aerospace Engineering Dept., University of California, Los
: : Angeles (UCLA). Also, he is the Chair of the ASNT Ultrasonic Committee. Dr. Bar-Cohen was an author on over 140
: : publications, made numerous presentations at national and international conferences, and has 10 patents.
.
: : Publications on NDTnet:
: : > Characterization of Defects in Composite Materials
: : Using Rapidly Acquired Leaky Lamb Wave Dispersion Data
: : > Autonomous rapid inspection of aerospace structures
: : > Polymer piezoelectric transducers for ultrasonic nde
: : > International ndt technical collaboration using the internet
.
: : Composite materials are used to construct flaw critical structures and they are taking a growing percentage of the makeup of aircraft and spacecraft structures. The cost of composite structures is significantly higher than the equivalent metallic made structures, reaching levels of orders of magnitude higher cost. Evaluation of the cost elements showed that about one third is spent on both mechanical and nondestructive testing. The key to the assurance of inspection efficiency is the abilityto apply effective tests for the determination of the integrity, stiffness and durability (residual life) and thus allowing the use of less material, i.e. smaller safety factors, while assuring the performance of the structures. Also, it is necessary to minimize the amount of costly mechanical tests. NDE methods are developed to detect and characterize flaws and to determine the material properties (e.g., stiffness) of test specimens. The strength and durability are parameters that cannot be determined by NDE methods since they are associated with physical processes that are statistical in nature and cannot be measured nondestructively.
.
: : The standard NDE methods that are used to inspect metallic structures were adapted by the industry for inspection of composite materials, partially accounting for the multi-layered anisotropic nature of these materials. The standard NDE methods provide limited and mostly qualitative information about the material properties and defects. The discovery of the LLW and the Polar Backscattering phenomena in composites enabled new capabilities that address the anisotropy and offered the potential of quantitative testing. Methodologies were developed that allow inversion of the elastic stiffness coefficients and the quantitative characterization of defects as well as the evaluation of the quality of adhesively bonded joints. In recent years, other NDT methods have also emerged including the laser induced ultrasound, reverse geometry radiography and shearography. While there is significantly more work needed towards making these methods standard NDE tools, efforts are also needed to enable rapid inspection of composite structures in the field. To address this important issue, robotic tools are being are incorporated with NDE sensors and intelligent NDE methodologies.
.
: : To start the discussion let me turn to you the participants and I would like to welcome any questions or comments that you may have.
: : - Enjoy -
.
: : Rolf Diederichs
.



 
 Reply 
 
Rolf Diederichs
Director,
NDT.net, Germany, Joined Nov 1998, 608

Rolf Diederichs

Director,
NDT.net,
Germany,
Joined Nov 1998
608
00:15 Feb-18-2001
Re: i want info about leaky lamb waves and polar back scattering
shridhar,

some of Yosi's articles on NDT.net dealing with LLW.

http://www.ndt.net/article/v06n02/barcohen/barcohen.htm
NDE of Composites Using Leaky Lamb Waves (LLW)
NDT.net - February 2001, Vol. 6 No. 2

http://www.ndt.net/article/v05n06/barcohen/barcohen.htm
Experimental Enhancements of LLW Dispersion Data Acquisition and Implementation Challenges to NDE of Composites
NDT.net - June 2000, Vol. 5 No. 6

http://www.ndt.net/article/v04n01/jpl_obus/jpl_obus.htm
NDE of hidden flaws in aging Aircraft Structures using Obliquely Backscattered Ultrasonic Signals (OBUS)
NDT.net - January 1999, Vol.4 No.1

http://www.ndt.net/article/ecndt98/aero/013/013.htm
Characterization of Defects in Composite Material Using Rapidly Acquired Leaky Lamb Wave Dispersion Data
NDT.net - September 1998, Vol.3 No.9

: shridhar,
.
: I have a website in which I have been archieving all
: my publications since 1997. You can find there articles
: about the subjects of LLW andPBS. The address is
: http://ndeaa.jpl.nasa.gov/nasa-nde/nde/nde-hp.htm
.
: Yosi
.
:
: : : respected sir
: : I want some explanation about leaky lamb waves and polar
: : back scattering. please let me know as early as possible.
: : yours
: : shridhar
: .



 
 Reply 
 

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