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Jose Luis Prego Borges

Jose Luis Prego Borges

LAMB: A simulation tool for air-coupled lamb wave based ultrasonic NDE systems.

Ph.D. Thesis title:

LAMB: A simulation tool for air-coupled lamb wave based ultrasonic NDE systems.

Author:

Jose Luis Prego Borges

Director:

Miguel García J. Hernandez

Reading Dates:

25/10/2010

Abstract:

 

Air-coupled ultrasonic Lamb waves represent an important advance in Non-Destructive Testing and Evaluation (NDT & NDE) techniques of plate materials and structures. Examples of these advances are the characterization and quality assessment of laminate materials in manufacturing processes, the location of damaged parts in aircrafts and structure monitoring in the aerospace industry. However the rich and complex nature of mechanical vibrations encountered in acoustics make the subject of analysis and study of these systems a very complex task. Therefore a simulation tool that permits the evaluation and testing of different configuration scenarios using the flexibility of a computer model is an invaluable aid and advantage.
The objective of this thesis is to provide the field of NDT with free open source software i.e. the LAMB Matlabrtoolbox. The toolbox is capable of simulating the behaviour of Lamb wave based NDE systems for single ideal isotropic laminates using air-coupled ultrasonic arrays. The programme usesa pitch-catch type of a C-scan NDE arrangement and is composed Air-coupled ultrasonic Lamb waves represent an important advance in Non-Destructive Testing and Evaluation (NDT & NDE) techniques of plate materials and structures. Examples of these advances are the characterization and quality assessment of laminate materials in manufacturing processes, the location of damaged parts in aircrafts and structure monitoring in the aerospace industry.

However the rich and complex nature of mechanical vibrations encountered in acoustics make the subject of analysis and study of these systems a very complex task. Therefore a simulation tool that permits the evaluation and testing of different configuration scenarios using the flexibility of a computer model is an invaluable aid and advantage.


The objective of this thesis is to provide the field of NDT with free open source software i.e. the LAMB Matlabrtoolbox. The toolbox is capable of simulating the behaviour of Lamb wave based NDE systems for single ideal isotropic laminates using air-coupled ultrasonic arrays. The programme usesa pitch-catch type of a C-scan NDE arrangement and is composed of three integrated sections each individually modelling a feature in the system:

          1. Excitation
          2. Propagation
          3. Reception.

For assessment of the individual modules of the toolbox the thesis presents comparisons between each section simulations and the data obtained from different acoustic experiments. The validation of the complete simulator was carried out by evaluation tests on the copper and aluminium plates by use of a real hardware prototype of a Lamb wave based NDE system with aircoupled concave arrays.
The negative impact on the performance of the real air-coupled NDE systembased on concave arrays was effectively confirmed by the programme. This was produced by the inherent directivity of the individual sensors as well as their concave arrangement. To emulate this behaviour the thesis introduces a simple two-dimensional geometric model for the inclusion of the spatial filtering effect of the sensors plus a group of simulations for a new proposed air-coupled plane array transducer.

The software also verified the spatial coherent nature of the Lamb wave fields emitted by a plate in air. This was demonstrated by the implementation of a delay and sum beamformer to constitute an initial signal processing stage in the reception section.
The main purpose of the present work was to contribute a working scenario for the simulation and testing of new air-coupled array designs and the development of enhanced signal processing techniques for the analysis of Lamb waves fields encountered in non-contact NDE of single isotropic systems.
Finally, although the issue related to the calibration of the programme was not attainable a reasonable degree of similarity with real NDE data was achieved.