Monday, December 31, 2018

Model Based Defect Reconstruction in Ultrasonic Non-Destructive Testing

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Although the history of iron converting can be traced back long before Christ [1], steel had over the centuries only a minor role as material. It was in most cases only used in war techniques. This changed around the 19th century with the beginning of the industrial revolution, inventions like the steam engine (1712 by Thomas Newcomen) and the railway, the market for steel grew rapidly. In the middle of the 19th century faster production methods were developed by Henry Bessemer (1855) and Sidney Gilchrist Thomas (1855) to cover the demand. But with this new market also new requirements were made on the produced components. They had to stand high pressure or enormous
forces. As a consequence, there were too many accidents like boiler explosions, derailing or even bridge collapses, often caused by only little defects in some components. Reliable methods for material testing had to be developed.
Until the end of the 19th century there were no e↵ective methods for testing steel components. Although one was able to evaluate several material properties, it was hardly possible to find defects inside the material. This changed with the discovery of x-rays by Wilhelm Conrad R¨ontgen in 1895. But while x-rays came to immediate use in medical science the use in non-destructive material testing was problematic. The equipment was big and expensive, the testing process was time-consuming and dangerous, and only thin material could be tested. Due to these facts the x-ray non-destructive testing did not become important until 1930. With the discovery of the piezoelectric e↵ect (page 9) by Pierre Curie in 1883 the foundation for ultrasonic testing was laid. Ultrasonic testing did not possess the disadvantages of x-rays but it still took 60 years until the first feasible equipment was produced.

1. Introduction
2. Ultrasonic Non-Destructive Testing (NDT)
3. Defect Reconstruction: State of the Art
4. Model
5. Inversion - an Overview
6. Inversion 1 - Deconvolution
7. Inversion 2 - Clustering
8. Inversion 3 - Defect Reconstruction
9. Numerical Results
10. Conclusions
Curriculum Vitae

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