Steel Non-Destructive Testing (NDT)

The Non-Destructive Testing (NDT) lab in the Advanced Steel Research Centre focuses on electromagnetic (EM) sensing for microstructure characterisation and contains a range of facilities to support the EM work:

1. Impedance analyser

Virtually every liquid and solid is able to pass a current when a voltage is applied to it. If a variable (ac) voltage is applied to the material, the ratio of voltage to current is known as the impedance. The measured impedance varies with the frequency of the applied voltage in a way that is related to the properties of the liquid or solid. This may be due to the physical structure of the material, to chemical processes within it or a combination of both.

The model 1260 Impedance/Gain-Phase Analyser is one of the most powerful, accurate and flexible Frequency Response Analysers available. Within the EM sensor NDT group we use the system with a range of in-house built EM sensors to obtain inductance verses frequency plots for different steel samples allowing us to develop relationships between the EM signal and steel microstructure.

Generator	Voltage	Current mode
ac Amplitude ≤10MHz >10MHz	0 to 3V rms 0 to 1V rms	0 to 60mA rms 0 to 20mA rms
Maximum ac resolution	5mV	100µA
dc bias range	±40.95V	±100mA
Frequency	range:10µHz to 32MHz, max resolution: 10µHz frequency (log or lin) ac/dc voltage, ac/dc current

^{Figure 1. Solartron Impedance Analyser 1260}

 

2. LR Mate 200iD Robotic arm - with the laser range sensor

The LR Mate 200iD is a compact six-axis mini robot with the approximate size and reach of a human arm

• reach: 717 mm
• load capacity at wrist: 7 kg
• Max speed: 450-1000 °/s
• Repeatability: ± 0.02 mm

Capabilities

• Advanced servo technology and highly rigid arm enable smooth motion without vibration in high-speed operations
• Working with the laser range sensor (measurement range 50±10 mm with 0.025 μm repeatability) to allow accurate inspection on components with complex geometry (for defects, microstructure, roughness, profile and positioning measurements and inspections, etc).
• Holding an EM sensor at an accurate lift-off to the testing sample and automatically doing grid scanning for signal mapping.

^{Figure 2. Fanuc LR Mate 200iD Robotic Arm with installed Keyence Laser range sensor}

 

3. Xstress 3000 G3 (X-ray stress analyser)

The Xstress 3000 system is an advanced X-ray stress analyser based on solid state linear sensor technique that converts the X-rays directly into electrical signals.

Capabilities:

X-ray diffraction is the conventional and time proven technique for measuring residual stresses. Using the interatomic spacing as the ultimate gauge length, the X-ray technique is ideal for, and applicable to, all crystalline materials, especially for metals, but also for ceramics. It measures the absolute stress without the need for an unstressed sample for calibration.

^{Figure 3. Xstress 3000 G3, X-ray stress analyser sensor}

4. Magnetic Hysteresis Analyser and In-situ Magnetic Domain Imager

The system consists of an in-house Magnetic Hysteresis Analyser, an Axioscope optical microscope featuring polarised light and extra z spacing enabling the setup of a magnetising rig to apply a magnetic field, a high-sensitivity high-speed camera for magnetic domain structure and domain wall movement imaging and a data syncing kit to sync high speed video with magnetic hysteresis data.

Capabilities

Magnetic Hysteresis Analyser
• Major and minor loop measurement
• Magnetic Barkhause Noise (MBN) analysis
• Independent field measurement

Magnetic Domain Imager
• Dynamic domain imaging by Bitter method
• In-situ magnetic hysteresis (BH loop) measurements
• Syncing high speed video with BH data
• Magneto-OpticKerr effect ready

BH Hysteresis Loop

A number of methods are available to measure the magnetic properties of steel, with permeability being of particular interest to our research group in relation to the use of low magnetic field electromagnetic sensors. One approach used in the our laboratory is measurement of major (and minor) B-H loops using a system developed by the University of Manchester for small samples, Figure 1. A current with low frequency time varying signal is applied to the excitation coils wrapped around the silicon steel core. The target sample is fitted into the slot in the core to maximise coupling between the core and the sample. The axial applied field (H) and the flux density of the induced field (B) are measured.

^{Figure 1. The BH measurement system, developed at the University of Manchester, to measure BH hysteresis loops and the permeability of small steel strip or rod samples}

The BH curves allow the magnetic properties of steel to be determined, including maximum and low field permeability, remanence, coercivity and saturation magnetisation, etc. The magnetic properties are affected by the microstructural parameters of the steel and Figure 2 shows the major loops and the initial magnetisation curves for the samples with different volume fractions of martensite.

^{Figure 2. The major loops and the initial magnetisation curves for samples with different volume fractions of martensite.}