diagnostics of degradative changes in paramagnetic alloys
TRANSCRIPT
Diagnostics of Degradative Changes
in Paramagnetic Alloys with the Use of
Low Frequency Impedance Spectroscopy
Zbigniew Hilary ZUREK1), Miroslaw WITOS2)
1) Silesian University of Technology 2) Air Force Institute of Technology
Poland
7th International Symposium on NDT in Aerospace 16 β 18 November 2015, Bremen, Germany
We5-A7
Outline: Introduction Motivation Low frequency impedance spectroscopy Drude model of metal LCR model of metal and its alloys Measurement equipment Some results Conclusion
Introduction
Safe aircraft operation requires the use of reliable non-destructive methods
(NDT) and structural health monitoring (SHM).
The NDT and SHM are specific in aeronautics due to complex load spectrum, influence of changing ambient conditions and variety of construction materials, among others : β’ ferromagnetic steels, β’ paramagnetic (austenitic) steels, β’ titanium alloys (ferro- and paramagnetic), β’ aluminum alloys, β’ magnesium alloys, β’ heat resistant alloys on the nickel and wolfram basis, β’ composites, β’ hybrid materials (metal - non-metallic filler - metal), β’ ceramics.
The materials of critical parts are different:
chemical composition,
microstructure,
mechanical and physical properties,
mechanisms of degradation.
For reliable diagnosis of the above mentioned materials the optimisation of
the NDT and SHM, so that the control actions do not disturb the main function of
the tested part of aeronautical engineering.
Motivation
During structural degradation D
of metals and their alloys the
following changes:
conductivity Ο,
magnetic permeability ΞΌ,
electrical permittivity Ξ΅.
Impedances:
- Elektromagnetic Zm
- Electric Ze
- Wave Zw
Vilysa J., Kvedarasb V., Dislocation Structure of Near Surface Layers of Deformed Low-carbon Steel. 15th Int. Metallurgical & Material Conference METAL 2006 .
The impedance of the surface layer is different from the impedance of the core.
The difference gives the state of microstructure, including dislocation density.
Motivation
For all metals and their alloys the observation frequency band
may be narrowed to:
0 - 100 kHz (ferromagnetic alloys)
0 - 10 MHz (paramagnetic and ferromagnetic alloys in the state of magnetic saturation).
Low frequency impedance spectroscopy Metals and their alloys
The parameters Ξ΅, ΞΌ, Ο and change in their values can be observed and analysed during
electromagnetic tests in radio frequency band from 3 Hz to 3 THz using various test
methods and techniques.
Metals and their alloys
Ferromagnetic π(π, Οππ) π0 β« 10 ,
but π(ππ ππ‘) π0 ~ 1.0
Metastable paramagnetic π π0 β (1.0, 2.0 > ,
but ΞΌ(Ξ΅ij, Οij)/ ΞΌ0 >> 2
Paramagnetic π π0 β (1.0, 2.0 >
Diamagnetic π π0 β (0, 1.0)
Diagnostic symptoms
Ο(0), Ξ΅(0), ΞΟ(t), ΞΞ΅(t)
Ο(0), Ξ΅(0), ΞΌ(0), ΞΟ(t), ΞΞ΅(t), ΞΞΌ(t)
Low frequency impedance spectroscopy State observer
The fatigue degradation process of metals is described by a nonlinear simple
problem
state of the microstructure β electric and magnetic parameters of the material
where: ππ = ππ π, π, π, π - material impedance, aim of the tests;
ππ = ππ π π , πΏ, πΆ, π - impedance of measurement probe,
state observer element;
π0 = π0 π - reference impedance;
ππ = ππ π, β, ππ,π - coupling coefficient of the probe
with the tested object,
ππ = π ππ, π0, ππ = π( π, β ππππ π’ππππππ‘πππππππ‘πππ
, π, π, ππππ‘πππππ πππππππ‘πππ
, π π , πΏ, π π, π, ππ πΉπππππ
πππππππ‘πππ
)
Reliable diagnosis of the material structure condition and
its degradation degree with coil requires correct solving of
a nonlinear inverse problem.
Low frequency impedance spectroscopy Methodology (5 steps)
1. Measurement of the measuring probe's impedance response ππ π and
coupling coefficient ππ π of the probe with a tested material in selected
frequency band π β ππππ, ππππ₯ β same as ET NDT and PMFT NDT.
2. Estimation of the frequency response of the material impedance ππ π
3. Quantitative and qualitative analysis of the impedance response ππ π ,
with the reference impedance response π0 π
Ξπ π =ππ π β π0 π
π0 π
4. Analysis of the material nonlinearity degree on the basis of the material
impedance distortion response
ππ»π·π π = π π β π 2ππ=2
π π 2 or Ξπ π, ΞπΌ =
π π, πΌ β π0 π, πΌ0π0 π, πΌ0
5. Diagnostic reasoning:
Active experiment β building diagnostic criteria,
NDT & SHM: diagnosis on the basis of revised criteria.
Drude model of metal Assist in the development of diagnostic criteria
In general, complex conductivity is rank-2 tensors (9 of complex numbers)
π = π1 + ππ2 = ππ·πΆ +ππ2 π + πππ1 π
Note: The Drude conductivity considers only the conduction electrons in a metal (omits the
polarisation of the ion cores, which may occur at the final stage of material degradation).
The frequency response of conductivity of metals and its alloys is well
described by the Drude model (1900) β it is a simplistic model for conduction.
π = π1 + ππ2 = ππ·πΆ 1 + π2π2 + π ππππ·πΆ 1 + π
2π2
In the 10 MHz frequency band
ππ β ππ«πͺ and ππ β ππππ«πͺ The value of the conductivity at the maximum is
π1 0 = ππ·πΆ = ππ2π 4π
where: ππ β the plasma frequency (a few THz),
π β the relaxation time (typically 10-14 second).
π1
π2 Silver
Low frequency impedance
spectroscopy
DobrzaΕski J.: SposΓ³b szacowanie czasu dalszej bezpiecznej pracy materiaΕΓ³w pracujΔ cych w warunkach peΕzania na przykΕadzie charakterystyk materiaΕowych stali 10CrMo9-10 po dΕugotrwaΕej eksploatacji. XIV Konferencja Naukowo-Techniczna Projektowanie, Innowacje Remontowe i Modernizacje w Energetyce PIRE 2012,
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0,1 0,8 1,0 0,6 0,4 0,2
Electric model of metals and their alloys
When the electromagnetic radiation wave is many times longer than the size of microstructure
elements and plasma frequency ππ in the Drude model, the local and global parameters of
a metal may be modelled as a real inductor.
ππ = ππ + ππΏ + ππΆ =1
π π+1
π π + πππΏ+1
π πΆ + π1ππΆ
The admittance of LCR circuit (Ym = 1/Zm)
Measurement Contactless method (coil), near field
Wave impedance Zw is described by: source type of wave reflection losses , RE, RM absorption loss, A
The Hioki IM 3532-50 LCR HiTester offers:
wide testing frequency: 42 Hz to 5 MHz
testing frequency while delivering 0.08%
accuracy;
high-speed measurement of 5 ms,
measurement data transmission to a
computer via USB 2.0,
control of the testing programme from
an external computer.
Measurement instruments
1. Laboratory digital LCR bridge
2. Cheap handheld digital LCR bridges (< 350 $)
The UT 612 model is a typical representative of cheap RLC meters
which enable automatic measurement and transmission of
measurement data to a computer via USB 2.0.
It is primarily designed to measure capacitance, inductance, resistance,
DC resistance and their associated quality factor, dissipation and phase
angle using a serial or parallel measurement mode.
Measurement frequency: 100 Hz, 120 Hz, 1 kHz, 10 kHz and 100 kHz.
Best accuracy: 0.5%.
Measurement instruments
3. Low cost evaluation module (< 50 $)
The LDC1000 Inductance-to-Digital Converter TI company measures the parallel impedance of an LC resonator. It accomplishes this task by regulating the oscillation amplitude in a closed-loop configuration to a constant level, while monitoring the energy dissipated by the resonator. By monitoring the amount of power injected into the resonator, the LDC1000 can determine the value of: impedance Rp with 16-bit resolution inductance L with 24-bit resolution. LC frequency range (carrier frequency of LCRs tank): 5 kHz β 5 MHz.
The LDC1101 converter is similar in its functionality to the LDC1000. The LDC1101 features dual inductive measurement cores, allowing for > 150 ksps 16-bit Rp and L measurements simultaneous, with a high-resolution L measurement with can sample at > 180 ksps with a resolution of up 24-bit. LC frequency range (carrier frequency): 500 kHz β 10 MHz.
Measurement instruments Low cost evaluation module (<50$)
The AD5933/34 Analog Device is a high precision impedance converter system solution that combines an on-board: frequency generator with a 12-bit, and < 0.1 Hz resolution (27-bits) allows an external
complex impedance to be excited with a known frequency to a max. frequency of 100 kHz. analog-to-digital converter (ADC): 1 MSPS for AD5933, 250 kSPS for AD5934, DSP engine with DFFT. Impedance measurement range from 1 kΞ© to 10 MΞ© with 0.5% accuracy. The response signal from the impedance is sampled by the on-board ADC and a discrete Fourier transform (DFT) is processed by an on-board DSP engine. The DFT algorithm returns a real (R) and imaginary (I) data-word at each output frequency.
Rs
Rp
SRF
ΟL
Q-factor
Results HCF of the ASTM 289 class C austenitic steel
Very small in impedance changes outside the scope resonance probe
Results Quality control of the aluminum alloy (AlSi13Mg1CuNi)
Very small in impedance changes outside the scope resonance probe
Diagnostic symptoms are available in the data of handheld LCR bridge!
Results Low frequency estimators Parj = f(Zs, Zs,0, Ξ, Ο)
HCF of the ASTM 289 class C austenitic steel Quality control of AlSi13Mg1CuNi)
Results Resonance method, which is used by LDC1000 and LDC1101
Very high sensitivity and orthogonality impact of change in ΞΌ and (Ο, Ξ΅).
Artificial 2 defects
Artificial 2 defects
Results Resonance method β reference impedance Z0
Note: While precise data analysis should take into account the frequency
characteristics of the coil (Rs, Ls, Q-factor).
Rs value changes under the skin effect.
SRF of coil >> SRF of LCR circuit. LDC Reference Coils Userβs Guide. Userβs Guide TI. http://www.ti.com
Example:
PCB circular coil, Ξ¦13 mm, 4 layers, 25turns/layer
SRF = 9.3 MHz
Conclusion
1. Taking above present results into account, the low frequency
impedance spectroscopy provides possibilities to diagnose the
degradation degree of structure of paramagnetic alloys,
including:
detecting early stages of material degradation (work
hardening, cyclic weakness)
verify the quality of the microstructure (the quality of
material production and supply of spare parts)
2. Low frequency impedance spectroscopy can be implemented
(as NDT and SHM applications) for metals and their alloys with
the use of cheap microprocessor devices (the unit cost of
electronics is below 50 $).
Diagnostics of Degradative Changes
in Paramagnetic Alloys with the Use of
Low Frequency Impedance Spectroscopy
Zbigniew Hilary ZUREK1), Miroslaw WITOS2)
1) Silesian University of Technology 2) Air Force Institute of Technology
Poland
7th International Symposium on NDT in Aerospace 16 β 18 November 2015, Bremen, Germany
We5-A7
Thank you for your attention
Any questions?
More info: http://www.researchgate.net/profile/Zbigniew_Zurek3 http://www.researchgate.net/profile/Miroslaw_Witos