High Sensitivity Two-Dimensional Electron Gas (2DEG) Quantum Well Hall Effect Sensors for Novel Pre-Failure Engineering Stress Analysis and Non-Destructive Testing Systems

Abstract

The research described in this thesis undertakes two major studies using highly sensitive Quantum Well Hall Effect (QWHE) sensors developed at the University of Manchester. The first one is the design of a handheld magnetic scanner using an array of QWHE sensors. A two-dimensional B-Field scanner was designed and built based on a 1 x 16 linear QWHE sensor array. The scanner laid the ground for non-destructive evaluation of flaws in ferromagnetic materials through Magnetic Flux Leakage (MFL) technique, and in nonferromagnetic metals through field leakages due to Eddy currents arising around defects, using a single device based on highly sensitive QWHE sensor. The second study is the correlation between magnetic and mechanical property of a ferromagnetic sample. To carry out this study a DC and an AC magnetic field illumination method have been considered. In the DC study, a tensile specimen is illuminated with a DC magnetic field after elongation and the leaking magnetic field is measured using a handheld magnetometer. An AC field study is also done to confirm the result obtained in the DC field study. The AC study is carried out using a desktop XY platform electromagnetic QWHE NDT system that scans stray magnetic fields at a resolution of 100µm 1mm above the surface of the tensile samples to reveal defects via a line scan and 2D colour maps. The result of the scan is then changed into colour pixel map and displayed in real-time on a host PC as the scanning progresses. Results of DC and AC scanning show that it is possible to detect surface-breaking defects as well as subsurface defects and flaws due to microstructural changes as a result of welding or mechanical stress. It is during this second study that the major contribution to the existing body of knowledge has been made. Using QWHE sensors and a grade 2205 duplex stainless steel sample, a direct relationship between the measured magnetic field, the engineering proof stress and plastic deformation is revealed. The study has contributed a novel method for determining the location of mechanical failure and associated engineering stress, revealing the plastic deformation site at proof stress, 2% of the total elongation. This has made it possible to predict which side of the specimen is likely to fail and as this is predicted at the proof stress, it was also possible to predict if the elastic to plastic transformation has happened. Moreover, the proof stress of the material can, therefore, be predicted with a reliable accuracy.

Date of Award	1 Aug 2020
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Mohamed Missous (Supervisor) & Max Migliorato (Supervisor)