Bassam A. Abu-Nabah

Eddy current residual stress profiling in surface-treated engine alloys

Recent research results indicate that eddy current conductivity measurements can be exploited for nondestructive evaluation of subsurface residual stresses in surface-treated nickel-base superalloy components. According to this approach, the depth-dependent electric conductivity profile is calculated from the measured frequency-dependent apparent eddy current conductivity spectrum. Then, the residual stress depth profile is calculated from the conductivity profile based on the piezoresistivity coefficient of the material, which is determined separately from calibration measurements using the known external applied stresses. This paper reviews the basic principles, measurement procedures, advantages, and limitations of eddy current residual stress profiling.

RECENT IMPROVEMENTS IN HIGH‐FREQUENCY EDDY CURRENT CONDUCTIVITY SPECTROSCOPY

Due to its frequency‐dependent penetration depth, eddy current measurements are capable of mapping near‐surface residual stress profiles based on the so‐called piezoresistivity effect, i.e., the stress‐dependence of electric conductivity. To capture the peak compressive residual stress in moderately shot‐peened (Almen 4–8A) nickel‐base superalloys, the eddy current inspection frequency has to go as high as 50–80 MHz. Recently, we have reported the development of a new high‐frequency eddy current conductivity measuring system that offers an extended inspection frequency range up to 80 MHz. Unfortunately, spurious self‐ and stray‐capacitance effects render the complex coil impedance variation with lift‐off more nonlinear as the frequency increases, which makes it difficult to achieve accurate apparent eddy current conductivity (AECC) measurements with the standard four‐point linear interpolation method beyond 25 MHz. In this paper, we will demonstrate that reducing the coil size reduces its sensitivity to c...

High‐Frequency Eddy Current Conductivity Spectroscopy for Near‐Surface Residual Stress Profiling in Surface‐Treated Nickel‐Base Superalloys

Recent research indicated that eddy current conductivity measurements can be exploited for nondestructive evaluation of subsurface residual stress in surface‐treated components. This technique is based on the so‐called piezoresistive effect, i.e., the stress‐dependence of electric conductivity. Previous experimental studies were conducted on excessively peened (Almen 10–16A peening intensity levels) nickel‐base superalloy specimens that exhibited harmful cold work in excess of 30% plastic strain. The main reason for choosing peening intensities above recommended normal levels was that the eddy current penetration depth could not be decreased below 0.2 mm without conducting accurate measurements above 10 MHz, which is beyond the operational range of most commercially available eddy current instruments. In this paper we report the development of a new high‐frequency eddy current conductivity measuring system that offers an extended inspection frequency range up to 80 MHz with a single probe coil. In additio...

Virtual environment assessment for laser-based vision surface profiling

Oil and gas businesses have been raising the demand from original equipment manufacturers (OEMs) to implement a reliable metrology method in assessing surface profiles of welds before and after grinding. This certainly mandates the deviation from the commonly used surface measurement gauges, which are not only operator dependent, but also limited to discrete measurements along the weld. Due to its potential accuracy and speed, the use of laser-based vision surface profiling systems have been progressively rising as part of manufacturing quality control. This effort presents a virtual environment that lends itself for developing and evaluating existing laser vision sensor (LVS) calibration and measurement techniques. A combination of two known calibration techniques is implemented to deliver a calibrated LVS system. System calibration is implemented virtually and experimentally to scan simulated and 3D printed features of known profiles, respectively. Scanned data is inverted and compared with the input pr...

LIMITATIONS OF EDDY CURRENT RESIDUAL STRESS PROFILING IN SURFACE‐TREATED ENGINE ALLOYS OF VARIOUS HARDNESS LEVELS

Recent research results indicated that eddy current conductivity measurements might be exploited for nondestructive evaluation of subsurface residual stresses in surface‐treated nickel‐base superalloy components. This paper presents new results that indicate that in some popular nickel‐base superalloys the relationship between the electric conductivity profile and the sought residual stress profile is more tenuous than previously thought. It is shown that in IN718 the relationship is very sensitive to the state of precipitation hardening and, if left uncorrected, could render the eddy current technique unsuitable for residual stress profiling in components of 36 HRC or harder, i.e., in most critical engine applications. The presented experimental results show that the observed dramatic change in the eddy current response of hardened IN718 to surface treatment is caused by very fine nanometer‐scale features of the microstructure, such as γ’ and γ” precipitates, rather than micrometer‐scale features, such a...

THE FEASIBILITY OF EDDY CURRENT CONDUCTIVITY SPECTROSCOPY FOR NEAR‐SURFACE COLD WORK PROFILING IN TITANIUM ALLOYS

The NDE community has been investigating the feasibility of numerous nondestructive inspection methods for residual stress profiling in surface‐treated nickel‐base superalloys for a couple of years. Because of direct exposure to erosion and foreign body impact damage, nondestructive characterization of low temperature inlet fan and compressor blades, which are usually made of titanium alloys, is even more important than that of high temperature turbine components downstream, which are usually made of nickel‐base superalloys. One of the main reasons why titanium alloys were originally thought to be less promising candidates for eddy current inspection is that they dominantly crystallize in hexagonal symmetry, therefore exhibit significant texture induced electric anisotropy on the order of 3‐4% relative conductivity variation. On the other hand, although crystallographic anisotropy does not affect the electric conductivity of cubic materials, such as nickel‐base superalloys, as‐forged Waspaloy and IN718 co...

Sonic IR crack size estimation using 2D heat diffusion model with arbitrary heat source function along the crack

Abstract Over the past decade, sonic infrared (IR) has been gaining rapid popularity in fatigue crack detection. Accuracy and robustness of crack size estimation using existing temperature-based image processing techniques are rather limited due to the absence of analytical solutions describing the heat diffusion around the crack. In this study, a 2D heat diffusion model with an arbitrary heat source function along a crack line is developed to make the technique more practical and capture the random nature of heat generation along the crack. The validity of the forward 2D heat diffusion model is established in close comparison with 2D finite element (FE) results. The validated analytical solution is used as a basis for best-fit analysis to retrieve the arbitrary heat source functions along the crack, which are used to estimate crack sizes. Using the 2D FE simulations with and without random temperature uncertainties, the proposed method delivers high accuracy in estimating crack sizes. Moreover, the accuracy in estimating crack sizes is validated using experimental sonic IR data. This makes it a practical approach to unlock the potential capabilities and limitations of sonic IR inspection technology.

Solar air-conditioning: Case study of solar absorption versus photovoltaic vapor compression systems

Due to recent research and development activities in solar-based air-conditioning systems, the GCC engineering community has been investigating alternative solutions to assess the feasibility towards adopting solar absorption refrigeration as a sustainable air-conditioning approach in hot environments. This study investigates the feasibility of two solar air-conditioning technologies, namely solar thermal absorption refrigeration and photovoltaic vapor compression technologies. Based on commercially available efficiencies of solar collectors and photovoltaic panels, this case study indicates that photovoltaic vapor compression air-conditioning systems have higher coefficient of performance and require smaller surface area when compared to solar thermal absorption refrigeration systems.

Iterative Inversion Method for Eddy Current Evaluation of Near‐Surface Residual Stress Profile in Surface‐Treated Metals

Because of their frequency‐dependent penetration depth, eddy current measurements are capable of mapping the near‐surface depth profile of the electric conductivity. This technique can be used to nondestructively characterize the subsurface residual stress distribution in certain types of shot‐peened metals, e.g., in nickel‐base superalloys. To predict the depth‐dependent, but frequency‐independent, intrinsic electric conductivity from the frequency‐dependent apparent eddy current conductivity (AECC), a highly convergent iterative inversion procedure is presented. The proposed technique exploits three specific features of the subsurface electric conductivity variation caused by near‐surface residual stresses in shot‐peened metals. First, compressive residual stresses are limited to a shallow surface region of depth much less than typical probe coil diameters. Second, the change in electric conductivity due to residual stresses is always very small, typically less than 1%. Third, the electric conductivity ...

Noncontacting Thermoelectric Detection of Material Imperfections in Metals

This project was aimed at developing a new noncontacting thermoelectric method for nondestructive detection of material imperfections in metals. The method is based on magnetic sensing of local thermoelectric currents around imperfections when a temperature gradient is established throughout a conducting specimen by external heating and cooling. The surrounding intact material serves as the reference electrode therefore the detection sensitivity could be very high if a sufficiently sensitive magnetometer is used in the measurements. This self-referencing, noncontacting, nondestructive inspection technique offers the following distinct advantages over conventional methods: high sensitivity to subtle variations in material properties, unique insensitivity to the size, shape, and other geometrical features of the specimen, noncontacting nature with a substantial stand-off distance, and the ability to probe relatively deep into the material. The potential applications of this method cover a very wide range from detection metallic inclusions and segregations, inhomogeneities, and tight cracks to characterization of hardening, embrittlement, fatigue, texture, and residual stresses.