Remote Non-destructive Testing Research Articles

Development of an Autonomous Magnetic Permeability Sensor

In our days, there is an undeniable need for control over the quality of metals in machines, metal components, tools, and construction materials during production and maintenance. Nondestructive testing sensors have been proven to be the most effective way of determining the quality of the composition of materials since they can detect flaws, not only during their construction but also during maintenance, without interfering with, or obstructing, their use. This article focuses on the measurement of the magnetic permeability of ferromagnetic steels and alloys as a nondestructive method of correlating magnetic properties with residual stresses based on the use of a yoke-shaped sensor. Most importantly, an electromagnetic energy harvesting system has been designed and tested, based on the exploitation of mechanical vibrations. The combination of the sensor and the energy harvesting system can lead to an energy autonomous device, which can be placed in inaccessible locations for remote nondestructive testing where measurements can be taken and transmitted autonomously every 10 min. Said transmission is realized by a network of yoke sensors in multiplex configuration and sent to a central sensor, leading to an Internet of Things usable device.

Implementation and evaluation of an autonomous airborne ultrasound inspection system

ABSTRACT The mobility of an Unmanned Aerial Vehicle (UAV) offers significant benefits when deploying remote Non-Destructive Testing (NDT) inspections of large-scale assets. Ultrasonic inspection is primarily a contact-based NDT method, that grants the opportunity to remotely monitor the structural health of an industrial asset with enhanced internal integrity information. Presented in this paper is an implementation of an autonomous UAV system, equipped with an ultrasonic thickness measurement payload. This system is designed to conduct ultrasonic inspections of non-magnetic facilities and industrial infrastructure where surface adhesion cannot be achieved magnetically. Operating within a laboratory environment, this system autonomously positioned the transducer on a vertically mounted, unpainted, aluminium sample and completed an ultrasonic thickness measurement without manual intervention. An onboard laser scanner provided instantaneous UAV alignment and standoff error measurements versus the sample’s surface normal vector. While inspecting a region of the aluminium sample with 12.92 mm nominal thickness, the UAV system demonstrated a measurement error of 0.03 mm. During this process, the standard deviation of the craft’s positional error was recorded to be below 63.26 mm, accompanied by an angular alignment error versus the surface normal vector of below 2.71°. The accuracy of the UAV deployed inspection, including thickness measurement accuracy and positional accuracy, depends on many factors. As such, transducer alignment constraints, electrical noise and UAV stability are investigated and discussed. Findings from this paper may be taken to inform future research regarding autonomous airborne ultrasonic inspection of constructed infrastructure and industrial facilities.

Statistical analysis of favorable conditions for thermographic inspection of concrete slabs

Infrared thermography has been successfully applied as a remote non-destructive testing approach for access to the internal conditions of reinforced concrete bridge slabs. Due to the different thermal properties of concrete and air or water present in the subsurface defects, damaged areas can be detected by the thermal contrast recorded on the inspected concrete surface. Thus, inspections should be conducted at favorable conditions, where the highest thermal gradients facilitate damage detection. In this study, experimental models were created to simulate bridge slabs with different delamination patterns. A multivariate regression analysis was used to explain and predict the thermal behavior of the test samples using data collected at different weather conditions and different periods of the day and the year. Based on experimental and regression analysis, it was observed that environmental conditions have an important influence on the concrete surface temperature variation and, therefore, on thermal contrast. Within the scope of this study, time frames between 12:00 noon and 3:00 pm, with temperatures between 27.5 and 37.9 °C, a high level of direct solar radiation and low atmospheric pressure values set an ideal scenario for thermographic inspections in reinforced concrete bridge slabs under passive heating.

Method of Multi-Angle Transmission Radiowave Tomography of Dielectric Objects

A method for solving the inverse problem for reconstructing the spatial distribution of dielectric permittivity from the results of multi-angle transmission broadband radiosounding is proposed. The method is based on inverse wave propagation. The average refractive index of the medium along the wave trajectory is calculated by comparing the results of the calculation of the time delay of the inverse signal in the entire sounding region and the forward propagation time in a homogeneous medium. This method takes into account diffraction effects in solving a direct problem, which allows one to obtain a resolution in the order of a wavelength. The combination of time delays obtained at different probing angles allows the restoration of the distribution of the refractive index in the medium. The paper presents the results of the numerical simulation of this method. The novelty of the proposed approach compared to the conventional back-projection algorithm is that ray approximation is not applied. Instead of the absorption coefficient (used in X-ray tomography), a time delay is considered, which is restored in the entire probed region. The developed method can be widely used in radiowave tomography or microwave tomography for remote non-destructive testing, diagnostics for the internal structures of inhomogeneous media and the restoration of the shapes of opaque objects based on multisensor sensing.

Design of a remote and integrated Sagnac interferometer that can generate narrowband guided wave through the use of laser and effective optics to detect defects occurred in plates

To inspect the integrity of specimens that are moving or no space available to mount sensors on their surfaces, laser generated guided wave (GW) becomes the only feasible option. However, conventional GW generated by laser-based emission is in broadband frequency range. Hence, unwanted GW modes, along with the emitted desired GW mode, also get produced simultaneously to the inspected specimen. The results generated from reflected GW become chaotic, making the identification of GW signals truly reflected by defects very difficult. Hence, substantial research efforts have been spent on reducing unwanted GW modes by spatially modulating the laser pattern to emit narrowband GW. Previous methods to generate narrowband GW include the use of slit mask, diffractive grating, lenticular array, and interference of laser beam. Among these techniques, each has certain shortcomings. A recent research achievement is the design of the integrated optical Mach-Zehnder system (IOMZ) (J. Chen et al, Opt. Lett., 42, 4255, 2017). It can emit desired narrowband Lamb wave into the aluminum plate by using pulsed laser and the designed optical system. Although the results showed IOMZ’s ability in emitting narrowband GW mode, significant unwanted noise was also generated, making the signal-to-noise ratio (SNR) of the received GW signals rather low. In this study a new optical system to overcome the shortcoming of the above reported devices is proposed. It is called integrated Sagnac interferometer-based optical system (SIOS) which can minimize generation of unwanted noise and substantially improve the SNR of reflected GW signals. A comparison study is also presented to illustrate the effectiveness of SIOS is superior to that of the IOMZ. Experimental results reveal that the proposed SIOS is promising for remote nondestructive testing and evaluation.

The Current State of Laser based Remote Non-destructive Testing and its Future Prospect

The Current State of Laser based Remote Non-destructive Testing and its Future Prospect

Remote Acoustic Emission Monitoring of Metal Ware and Welded Joints

An unusual phenomenon was revealed in the metal-ultrasound interaction. Microwave sensor generates surface electric conductivity oscillations from exposure to elastic ultrasonic vibrations on regions of defects embracing micro-defects termed as “crack mouth.” They are known as the region of “acoustic activity,” method of Acoustic Emission (AE) method. It was established that the high phase-modulation coefficient of reflected field generates intentional Doppler radar signal with the following parameters: amplitude-1–5 nm, 6–30 dB adjusted to 70- 180 mm. This phenomenon is termed as “Gorbunov effect,” which is applied as a remote non-destructive testing method replacing ultrasonic flaw detection and acoustic emission methods.

A photophone-based remote nondestructive testing approach to interfacial defect detection in fiber-reinforced polymer-bonded systems

Externally bonded fiber-reinforced polymer is an increasingly popular material to be used in strengthening and retrofitting aging structures. In such structures, debonding defects may occur at or near the interface between fiber-reinforced polymer and concrete. As such debonding in fiber-reinforced polymer-bonded systems is generally brittle in nature, there is a need of a reliable inspection technique that can provide early warning of interfacial defects such that premature failure of fiber-reinforced polymer-strengthened structures can be avoided. A remote nondestructive testing approach based on the working principle of a photophone is presented here as an economical alternative to laser Doppler vibrometry for detecting interfacial defects. Concrete specimens retrofitted with fiber-reinforced polymer are excited acoustically by white noise, while the surface of the structure is illuminated by a light source. If an interfacial defect exists beneath the surface, the surface will exhibit a frequency response different from an intact surface. The surface of the fiber-reinforced polymer portrays the role of flexible mirror in a photophone, which encodes information about surface vibration into amplitude-modulated light signal. A light detector then captures the irradiance of the reflected beam, and the amplitude modulation is converted into frequency domain in post-processing. With this technique, defect dimensions and thus damage extent can be inferred from the frequency spectrum obtained. The obtained results correspond well with the theoretical calculation, demonstrating the robustness and the applicability of the proposed technique in civil infrastructure.

Remote defect detection of FRP-bonded concrete system using acoustic-laser and imaging radar techniques

Two different remote nondestructive testing (NDT) techniques, the acoustic-laser and imaging radar techniques, are studied for near-surface defect detection in fiber-reinforced polymer (FRP) retrofitted systems. In the acoustic-laser technique, the targeted structure is excited by acoustic waves, while vibration data on a measurement point is remotely collected. In the imaging radar technique, radar signals (electromagnetic waves) are remotely emitted toward the target structure and measured when they are reflected from the structure. Three FRP-bonded concrete cylinders with various defect sizes were fabricated for laser and radar measurements. The pros and cons of these two techniques are described with the support of experimental result.

NDT for non-experts

Remote non-destructive testing of composites in aircraft is now possible. Jan Olav Endrerud of DolphiTech describes the development of such a system.

Thermal Non-destructive Testing and Evaluation: Coming of Age

As a specialized tool for Non-destructive Testing & Evaluation (NDT&E), Infrared Thermography (IRT) [1-10] involves as a remote mapping of temperature over test sample for finding out its surface and subsurface features with the emitted radiation from objects in the infrared band of the electromagnetic spectrum. It is a fast, remote, and safe non-destructive testing and evaluation (NDT&E) method for surface and sub-surface defect detection in various solid materials. Since most solids conduct heat, IRT largely owes its emergence and potentiality for defect detection in variety of materials such as metals [5], composites [6,7,11] and semiconductors [8,12]. IRNDT has numerous applications in the area of aeronautics, space, electrical, electronic, bio-medical and mechanical industries [5-27]. Of the various possibilities of thermal NDT implementations Infrared Thermography (IRT) or Infrared Non-destructive Testing (IRNDT) has, gained wide acceptance in NDT & E methods due to its merits. Various methods and techniques have further been developed by various research groups all over the world to improve and widen the use of IRT for non-destructive characterization [1,7,10,11,14,15,16,21,23,26]. This editorial is to present an overview on existing work and to describe the most relevant experiences devoted to the use of IRT methods for NDT&E.

A Study on Corrosion Defect Evaluation of Painted Metal by Using Nondestructive Tests

Importance on the detection of corrosion-related defect is undeniable from the fact that it can prevent significant economic loss and enhanced safety in mechanical equipments, pipes, ships, bridges, and other applications. Conventionally researched measurement methods for defect and thinning from corrosion are acoustic emission, EMAT using ultrasound, laser induced ultrasound, etc. However, these non-destructive testing methods have the shortcoming of accessibility to on-site. For instance, EMAT should be close to several millimeters to generate magnetic field in structure. For laser application, it can be applied to remote non-destructive testing, but some defect might not be possible to be detected by the surface condition of structure. In this study, infrared thermography camera is utilized to determine the degree of corrosion on paint-coated metal. In addition, fundamental researches to develop corrosion detection system for on-site metallic structure are conducted to provide the applicability of IR camera and possibility of thermal analysis method.

DEFECT DETECTION WITHIN A PIPE USING ULTRASOUND EXCITED THERMOGRAPHY

An UET (ultrasound excited thermography) has been used for several years for a remote non-destructive testing in the automotive and aircraft industry. It provides a thermo sonic image for a defect detection. A thermograhy is based On a propagation and a reflection of a thermal wave, which is launched from the surface into the inspected sample by an absorption of a modulated radiation. For an energy deposition to a sample, the UET uses an ultrasound excited vibration energy as an internal heat source. In this paper the applicability of the UET for a realtime defect detection is described. Measurements were performed on two kinds of pipes made from a copper and a CFRP material. In the interior of the CFRP pipe (70mm diameter), a groove (width - 6mm, depth - 2.7mm, and length - 70mm) was engraved by a milling. In the case of the copper pipe, a defect was made with a groove (width - 2mm, depth - 1mm, and length - 110 mm) by the same method. An ultrasonic vibration energy of a pulsed type is injected into the exterior side of the pipe. A hot spot, which is a small area around the defect was considerably heated up when compared to the other intact areas, was observed. A test On a damaged copper pipe produced a thermo sonic image, which was an excellent image contrast when compared to a CFRP pipe. Test on a CFRP pipe with a subsurface defect revealed a thermo sonic image at the groove position which was a relatively weak contrast.

Remote nondestructive testing of concrete structures

Remote nondestructive testing of concrete structures

Lockin-ESPI interferometric imaging for remote non-destructive testing

Electronic-speckle-pattern-interferometry (ESPI) is a sensitive interferometric imaging technique that responds to changes of surface topography caused, e.g., by pressure changes or by thermal expansion. Hidden defects are revealed by the inhomogeneity of such deformation fields. Unfortunately, field distortion may also be caused by, e.g., inhomogeneous excitation. Therefore the lockin technique has been transfered to ESPI in order to enhance its sensitivity by this kind of phase-sensitive narrow-band filtering where finally a self-normalised phase-angle image is obtained. Such an image displays features which are usually deeply hidden in noise, as will be shown on various examples.

Development of a Self-reference Lock-in Thermography for Remote Nondestructive Testing of Fatigue Crack (1st Report, Fundamental Study Using Welded Steel Samples)

In the thermoelastic stress analysis, stress distribution is measured by lock-in infrared thermography, which correlates temperature change due to the thermoelastic effect with reference loading signal. Loading signal from external source, such as load-cell, strain gage or displacement gage, is usually employed as a reference signal in the conventional lock-in technique. In this study, a self-reference lock-in infrared thermography was newly developed, in which a reference signal was constructed by using the same sequential data on thermoelastic temperature change. Temperature change in a region of interest was correlated with that in a remote area for reference signal construction. The lock-in algorithm based on the least squares method was employed for signal processing under random loading. It enabled us to measure the distribution of relative intensity of applied stress under random loading without using any external loading signal. Proposed self-reference lock-in thermography was applied for crack identification based on the detection of significant thermoelastic temperature change due to the singular stress field in the vicinity of crack tips. It was found that significant temperature change was observed at the crack tip in the self-reference lock-in thermal image, demonstrating the feasibility of the proposed technique

On Possibilities of Acoustic Remote Nondestructive Testing of Long Objects

The maximum sounding depth is estimated on the basis of an analysis of acoustic channel equations for the echo pulse testing method when the classical method of ultrasonic flaw detection by means of longitudinal waves is used and the testing technology is realized by means of Pohgammer waves.

Ultrasonic system for remote non-destructive testing using mobile telephony

In distributed non-destructive testing (NDT), the acquisition of ultrasonic measurements occasionally has to be performed at different locations distant from the central station, where the ultrasonic data must be analysed and displayed. In this paper, the design details of an ultrasonic system with such objective are described. The system aims to perform remote acquisitions and transmit them to a central station using mobile telephony. Ultrasonic and telecommunication sub-systems involved in this system are described. The practical implementation here depicted combines own-designed modules with some low-cost commercial devices. Some design consideration and the block schemes of each subsystem are detailed. Finally, a laboratory prototype, developed for design viability purposes, is presented. This development includes stages for: transducer driving by means of a high-voltage pulse generator, broad-band amplification, acquisition, multiplexing and A/D conversion of signals, ultrasonic data transmission by mobile telephony, and the control of telemetering aspects by remote and local software.

Three-dimensional finite element analysis of nondestructive testing of metallic tubular product

This paper presents the analysis of the remote field eddy current phenomenon for the nondestructive testing of metallic tubular products. A finite element code using linear tetrahedral edge elements is used for the analysis. The calculated results for different frequencies of exciting coil are evaluated. In the model without a hole in the pipe, the absolute value of the phase of the remote field depends on the frequency of the exciting coil. The phase varies around the hole and the phase difference compared with the case without hole also depends on the frequency. The calculated results and the developed code can be used for the design of the remote field nondestructive testing probe.