Ultrasonic Non-destructive Testing Methods Research Articles

Numerical simulation of ultrasonic time reversal on defects in carbon fibre reinforced polymer

An ultrasonic non-destructive testing method is under development for detecting small scale damage in carbon fibre reinforced polymer. This method relies on signal processing to detect the presence of nonclassical nonlinear signature of microcracking or delamination in the material. Using reciprocal time reversal with nonlinear spectroscopy, the ultrasound can be focused on defect which is in unknown location in test object and may be far from the sending or the receiving transducer. With spectral analysis of defect and delayed time reversal input, the defect can be excited to larger displacement amplitudes by using its resonance. The study is conducted using finite element simulations in two dimensions for carbon fibre composite plate.

Reinforcement Influence Accounting in Assessing the Strength of Reinforced Concrete Structures by Ultrasonic Nondestructive Testing Method

Reinforcement Influence Accounting in Assessing the Strength of Reinforced Concrete Structures by Ultrasonic Nondestructive Testing Method

Acoustic anisotropy and localization of plastic deformation in aluminum alloys

The process of uniaxial inelastic tension of 20 mm thickness corset specimens made of aluminum-manganese alloy was investigated by ultrasonic non-destructive testing method based on measuring of acoustic anisotropy. The value of acoustic anisotropy defines as the phase shift between velocities of propagation of shear waves with orthogonal polarization. Acoustic measurements were carried out at different stages of stepwise loading of specimens with ultrasonic device used for non-destructive testing of stress-strain state of structures in nuclear and oil and gas industries. Nonlinear dependence of acoustic anisotropy on total axial inelastic deformations of specimens was established. It was found that acoustic anisotropy is an indicator of autowaves of plastic flow localized in surface layer of metal. The obtained results can be used for non-destructive ultrasonic testing of plastic deformations in thick structures made of aluminum alloys.

Calibration of a Piezoelectric Transducer through Laser Measurements and Numerical Simulation

A piezoelectric transducer is an electromechanical sensor which converts electrical energy (voltage signal) to mechanical energy (displacement signal) and vice versa by taking advantage of the piezoelectric crystal. Depending on the physical combination of transducer parts, sensors may have a linear or non-linear response to the input signal. In seismic tests such as ultrasonic non-destructive testing (NDT) methods, analyzing stress wave propagation through the specimen gives an assessment of its condition. The signal attenuation is an important parameter to assess the condition of specimen which can be done by having the displacement signal as an output. However, instead of the displacement signal, the piezoelectric transducer provides the voltage signal as an output. Therefore, to get reliable and accurate results, it is essential to calibrate the transducers. An appropriate calibration results in a suitable Transfer Function (TF) which can be used to properly calculate the displacement signal. In this study, the output displacement of a 1 MHz piezoelectric transducer is measured using a laser vibrometer with a nanometer resolution. Measurements and calculated TF showed at frequencies of 0.1, 1, and 1.5 MHz, TF values are 0.8, 0.08, and 0.2 respectively which is a non-linear relation between displacement (absolute signal) and voltage (relative signal) as it was expected. Then, numerical simulation is implemented as part of this study to simulate all electrical and mechanical components of the piezoelectric transducer. The simulation was verified with the absolute displacement measurements result from the laser vibrometer.

NDT assessment of bonded assemblies - image optimization for weak bond characterization using ultrasonic array transducer

Compromised interface bonds in structural components can lead to premature loss of structural integrity. Such defects are very difficult to detect using traditional acoustic inspection techniques. We assess the ability of linear ultrasonic Non-Destructive Testing (NDT) methods to detect or differentiate between weak-kissing bonds from healthy ones, by using a set of contaminated and non-contaminated bonds. An Ultrasonic Array Transducer (UAT) enables increased informational content, hence they have been used to detect and differentiate compromised bonds. Considerable research has been made into detecting weak bonds, but a practical, cost effective and industrially applicable solution remains elusive. The key problem is the signal changes are small, therefore we have developed an iterative testing methodology, in which the experimental variation in each of the following steps is significantly reduced: Sample Preparation; Data Acquisition; Imaging[1, 2]; Feature Analysis[3, 4]; Characterization/Classification; Interpretation. Our research addresses the issues related to UAT measurement techniques, specifically Full Matrix Capture (FMC)[1, 2] and Total Focusing Method (TFM)[1, 2], Scattering Matrix(derived) [3, 4] extraction in time domain, and other related or derived methods. Here the optimization of bondline imaging, resulting in higher quality and coherence of the imaging, is presented and discussed.

Mechanical Behavior of Cross-Laminated Timber Panels Made of Low-Added-Value Timber

Abstract The cross-laminated timber (CLT) construction system has recently emerged as an excellent alternative for civil construction. The objective of this work is to analyze the structural performance of CLT panels using plantation lumber, especially eucalyptus (Eucalyptus grandis) heartwood and pine (Pinus taeda). After visual grading, all boards were mechanically graded through the ultrasonic nondestructive testing method. Boards were organized to compose four types of three-layered CLT panels: 1) exclusively eucalyptus heartwood (EEE), 2) eucalyptus in the outer layers and pine in the central layer (EPE), 3) exclusively pine (PPP), and 4) pine in the outer layers and eucalyptus in the central layer (PEP). Three panels with graded timber were manufactured for each type, and one more panel was made out of ungraded timber, so each group had four panels altogether. Panels containing eucalyptus in the outer layers (EEE and EPE) were stiffer than the ones with pine in outer layers (PPP and PEP). However, the first two groups presented lower bending strength than the second ones. Modulus of elasticity and modulus of rupture results were compared to values observed in the literature and to the international standard that regulates CLT (American National Standards Institute/American Plywood Association PRG 320). From the four types studied, only panels containing mostly eucalyptus (EEE and EPE) could meet the PRG 320 E2 class. Panels containing mostly pine (PPP and PEP) did not reach the thresholds of any class in terms of stiffness although their resistance was much higher than that specified in the standard.

APPROBATION AND ANALYSIS OF EXPERIMENTAL RESEARCHES'S RESULTS OF THE EXTENDED METHOD OF PHYSICAL-MECHANICAL CHARACTERISTICS STEELS'S CONTROL

Most of the oil and gas equipment complex is subjected to cyclic-variable, mechanical, thermal loads and corrosive-active environment. These effects causing a change in the structural statr of the metal contribute to the accelerated development of defects, especially in places with stress concentrators, which ultimately lead to the constructions destruction. Available ultrasonic, electromagnetic, and eddy-current non-destructive testing methods are currently aimed at solving defect detection problems. However, it is more important to timely identify the initial stage of the process of damage accumulation in a metal by determining changes in the structural state of the metal. The article proposes a methodology for studies of steel structural changes arising in the process of exploitation and their impact on mechanical characteristics. A reasonable choice of the optimal indicator characterizing the image of the acoustic structural noise of the material obtained by applying ultrasonic flaw detector in a complete set with piezoelectric converters with a phased array is substantiated. The complex of physical and mechanical parameters of the investigated samples are measured and the results obtained were analyzed. The modern methods of determination of mechanical characteristics of steels are considered, their deficiencies are determined and the methods of their optimization are proposed. The regression-correlation analysis of the experimental studies results was carried out, which resulted in the equation of dependence between a set of non-destructive control parameters and mechanical characteristics of steels was obtained. In order to verify the adequacy of the proposed model and to establish the possibility of controlling the casing and tubing on the samples made, series of experimental studies were carried out, which confirmed the reliability of the resulting calculation model for determining the mechanical characteristics of the steels by using two informative parameters, namely hardness and integral density of images of acoustic structural noise.

High-frequency ultrasonic methods for determining corrosion layer thickness of hollow metallic components

Corrosion in internal cavity is one of the most common problems occurs in many hollow metallic components, such as pipes containing corrosive fluids and high temperature turbines in aircraft. It is highly demanded to non-destructively detect the corrosion inside hollow components and determine the corrosion extent from the external side. In this work, we present two high-frequency ultrasonic non-destructive testing (NDT) technologies, including piezoelectric pulse-echo and laser-ultrasonic methods, for detecting corrosion of Ni superalloy from the opposite side. The determination of corrosion layer thickness below ∼100 µm has been demonstrated by both methods, in comparison with X-CT and SEM. With electron microscopic examination, it is found that with multilayer corrosion structure formed over a prolonged corrosion time, the ultrasonic NDT methods can only reliably reveal outer corrosion layer thickness because of the resulting acoustic contrast among the multiple layers due to their respective different mechanical parameters. A time-frequency signal analysis algorithm is employed to effectively enhance the high frequency ultrasonic signal contrast for the piezoelectric pulse-echo method. Finally, a blind test on a Ni superalloy turbine blade with internal corrosion is conducted with the high frequency piezoelectric pulser-receiver method.

Comparing the Efficiency of Ultrasonic Infrared Thermography under High-Power and Resonant Stimulation of Impact Damage in a CFRP Composite

The quality control of composite materials remains an important topic of research in nondestructive testing (NDT) of modern materials, in particular, the ones intended for aerospace industry. Over the last decade, there has been a noticeable increase in interest to the ultrasonic stimulation of tested materials and analysis of dynamic temperature distributions. This method is commonly implemented with two techniques, viz. high-power stimulation at a fixed acoustic-signal frequency and low-power resonant ultrasonic stimulation. Results are provided on comparing the above ultrasonic NDT methods using the example of an impact damage in a graphite epoxy-filled composite. The comparison is made based on the criteria of temperature signals, revealed flawed zone, and productivity of testing.

Local damage evaluation of a laminate composite plate using ultrasonic birefringence of shear wave

Abstract This paper presents an ultrasonic non-destructive testing method to locally characterize composite material damage through the analysis of the anisotropy behavior variation induced by damage. The approach is based on shear wave contact measurements and analyses shear wave birefringence to estimate variation of the attenuation coefficient and shear moduli ratio between warp and weft directions. The method only requires a single piezo-electric contact sensor and thus, is easy to implement for practical applications. Moreover, unlike other methods, it does not require any reference measurement in a calibrated medium such as water to evaluate attenuation coefficient variation and shear moduli ratio. It is shown that the proposed method allows to locally qualify damage with good repeatability and robustness.

Измерение коэффициента затухания ультразвуковых волн в неоднородных материалах при одностороннем доступе

The article considers an improved method for measuring the ultrasonic wave attenuation coefficient in objects made of materials with a heterogeneous structure under the conditions of unilateral access to objects. The method is primarily aimed at assessing the structural condition of critical bulky objects made of concrete, cast iron, and other intricately structured materials with a view to prevent possible accidents and disasters. The ultrasonic wave attenuation coefficient is determined by processing the realizations of structural noise resulting from the reflection of a probing signal from numerous heterogeneities in the object. The article suggests an improved algorithm for processing the realizations of structural noise, the use of which makes it possible to obtain better accuracy of measurements, to expand the applicability limits of the method, and to simplify the received signals processing procedure. Matters concerned with optimizing the probing signal parameters and the transducer characteristics are studied. A number of experiments were carried out for checking the efficiency of the proposed method and of the new algorithm for processing structural noise realizations. Measurements of the longitudinal ultrasonic wave attenuation coefficient in a specially fabricated concrete block were carried out. The measurements were carried out using two methods: the classic shadow method and the proposed method based on processing the structural noise realizations. The experiments showed good results: the measurement accuracy has been improved by almost 10 times compared with the previous version of the proposed method. The most appropriate application field of the proposed method is monitoring the structural state of critical bulky objects made of materials with a heterogeneous structure like dams and bridge supports under the conditions in which it is impossible to apply other ultrasonic non-destructive testing methods, e.g., those based on ultrasonic wave velocity measurements.

Signal processing methods to improve the Signal-to-noise ratio (SNR) in ultrasonic non-destructive testing of wind turbine blade

Ultrasonic non-destructive testing (NDT) methods are being used quite effectively nowadays, but the multilayered structure of composite materials results in the serious problem in the detection of defects/flaws. The resulting ultrasonic signal is often noisy and denoising of this signal is necessary in order to extract useful information so that faults can be detected, located and sized. Currently, there is a high demand for automatic ultrasonic signal processing techniques to not only remove the need for manual flaw detection and assessment, but also increase the accuracy, reliability and repeatability of the non-destructive evaluation. There are various signal processing techniques which can be used in ultrasonic measurements and selection of appropriate method is one of the major key factors in the field of ultrasonic testing of composite materials. In the presented work, the sample of wind turbine blade (WTB) manufactured using glass fiber reinforced plastic (GFRP) was investigated using ultrasonic NDT in order to estimate the artificially made disbond type defects of 15 mm and 25 mm diameter on the trailing edge. The transmitting and receiving transducers were fixed on movable panel at distance of 50 mm and guided waves (GW) were received at each one millimeter step along the scanning distance of 500 mm. The measurement is performed using low-frequency (LF) ultrasonic system which was developed by Ultrasound Institute of Kaunas University of Technology. Various signal processing techniques were applied to overcome the structural noise and/or extract the information about the defects. The three most promising signal processing techniques: cross-correlation methods, wavelet transform (WT) and Hilbert-Huang (HHT) transform were discussed and compared in the process of defects estimation.

Residual life and degradation assessment of wood elements used in soil bioengineering structures for slope protection

Soil bioengineering techniques to repair slope failures and increase slope stability are often used, when possible, as alternatives to traditional structures in order to mitigate environmental impact without compromising effectiveness. However, such techniques use live plants and entrust most of their structural resistance to wood members whose mechanical characteristics diminish with time. To date, the decay of mechanical characteristics of wood elements employed in soil bioengineering techniques and lifetime predictions has been little explored. Such information is also important for durability forecasting. In this paper we present the results of experimental analyses carried out to evaluate the degradation of mechanical properties of untreated timber elements which were collected from single and double live cribwalls or check-dams built about ten years ago in the Vesuvius National Park (Naples, Southern Italy). To help interpret the behavior of a complex material such as wood, a novelty of this study lies not only in combining ultrasonic and sclerometric nondestructive testing (NDT) methods so as to reduce measurement errors, but also in framing the outcomes from mechanical tests within the biological analysis of fungi detected on the timbers. Exploratory statistical analyses reveal that there exist hardly any correlations between moisture contents in the timber elements and both transversal and longitudinal ultrasonic velocities, although some clustering provides insights into the results obtained. Comparisons between results using data measured on “old” and “new” timber elements enable some evaluations of residual safety factor assessment to be carried out.

Effect of sulfate attack on the stress–strain relationship of FRP-confined concrete

Concrete structures in marine areas frequently suffer from sulfate attack, which causes structural performance deterioration. External bonding of fiber reinforced polymer (FRP) is an effective method to improve the mechanical performance of these concrete structures. Thus, this paper presents a study of mechanical performance of FRP-confined sulfate-attacked concrete columns. An accelerated corrosion test by sulfate solution in a high-temperature dry–wet cycle was introduced to simulate the external sulfate corrosion environment. Thirty circular columns with a diameter of 150mm and a height of 300mm were subjected to sulfate exposure for a range of time periods and then confined with FRP jackets. All the columns were axially loaded to failure. Both the strength deterioration of the unconfined concrete after sulfate corrosion and the stress–strain relationship of the FRP-confined sulfate corroded concrete were recorded. Two damage indexes, i.e., the concrete strength deterioration rate and the rate of change in ultrasonic velocity of concrete, were carefully defined to quantitatively characterize the mechanical damage to the concrete due to sulfate attack. High correlation between these two damage indexes is detected and modeled. The effect of sulfate-induced damage on the ultimate strength, strain capacity, initial elastic modulus, and strain-hardening modulus of FRP confined concrete columns is quantified in terms of the two above damage indexes. On this base, a stress–strain relationship model is finally developed. A comparative analysis of the test results indicates that the model can provide reasonably accurate predictions. As the rate of change in ultrasonic velocity of concrete by sulfate attack can be measured easily using an ultrasonic non-destructive testing method, the proposed stress–strain relation model is of great significance to the design and life-cycle assessment of FRP strengthened sulfate-corroded concrete columns.

Influence of Water Content on Fundamental Frequency of Mortar Sample

Ultrasonic non-destructive testing methods such as Impact-echo are often conducted under different conditions. Such results might be distorted by ambient temperature or by water content of the tested sample. Tested mortar sample displayed shift of the fundamental frequency by 3.7 %. This article confirms necessity of standardized conditions during ultrasonic testing for both laboratory and in-situ testing.

Ultrasonic Attenuation Based Inspection Method for Scale-up Production of A206–Al2O3 Metal Matrix Nanocomposites

A206–Al2O3 metal matrix nanocomposite (MMNC) is a promising high performance material with potential applications in various industries, such as automotive, aerospace, and defense. Al2O3 nanoparticles dispersed into molten Al using ultrasonic cavitation technique can enhance the nucleation of primary Al phase to reduce its grain size and modify the secondary intermetallic phases. To enable a scale-up production, an effective yet easy-to-implement quality inspection technique is needed to effectively evaluate the resultant microstructure of the MMNCs. At present the standard inspection technique is based on the microscopic images, which are costly and time-consuming to obtain. This paper investigates the relationship between the ultrasonic attenuation and the microstructures of pure A206 and Al2O3 reinforced MMNCs with/without ultrasonic dispersion. A hypothesis test based on an estimated attenuation variance was developed and it could accurately differentiate poor samples from good ones. This study provides useful guidelines to establish a new quality inspection technique for A206–Al2O3 nanocomposites using ultrasonic nondestructive testing method.

FEM Analyses of the TOFD Technique in Unequal Thickness Component

The time-of-flight diffraction (TOFD) technique is a new ultrasonic nondestructive testing method. It utilize the longitudinal diffraction signal that generated from the defects, we can confirm whether there is a discontinuity in butt weld by the analysis of diffracted waves. This detection method has wide application prospects and detect flaws with high precision of localization and quantification. In this paper, two-dimensional numerical simulation of ultrasonic TOFD technique is carried out on unequal thickness butt weld of Drum Cylinder and Spherical Head, the propagation characteristics and laws of ultrasonic wave in unequal thickness component are analyzed by using finite element software ABAQUS. The simulation results show that the ABAQUS software can effectively simulate ultrasonic TOFD technique in such pressure vessel component, so the application range of ultrasonic TOFD technique will be extended.

Signal quality enhancement using higher order wavelets for ultrasonic TOFD signals from austenitic stainless steel welds

Time of flight diffraction (TOFD) technique is a well-developed ultrasonic non-destructive testing (NDT) method and has been applied successfully for accurate sizing of defects in metallic materials. This technique was developed in early 1970s as a means for accurate sizing and positioning of cracks in nuclear components became very popular in the late 1990s and is today being widely used in various industries for weld inspection. One of the main advantages of TOFD is that, apart from fast technique, it provides higher probability of detection for linear defects. Since TOFD is based on diffraction of sound waves from the extremities of the defect compared to reflection from planar faces as in pulse echo and phased array, the resultant signal would be quite weak and signal to noise ratio (SNR) low. In many cases the defect signal is submerged in this noise making it difficult for detection, positioning and sizing. Several signal processing methods such as digital filtering, Split Spectrum Processing (SSP), Hilbert Transform and Correlation techniques have been developed in order to suppress unwanted noise and enhance the quality of the defect signal which can thus be used for characterization of defects and the material. Wavelet Transform based thresholding techniques have been applied largely for de-noising of ultrasonic signals. However in this paper, higher order wavelets are used for analyzing the de-noising performance for TOFD signals obtained from Austenitic Stainless Steel welds. It is observed that higher order wavelets give greater SNR improvement compared to the lower order wavelets.

Measurement of the thickness of U-30MES-5NT and VGM-L sealing compound layers in aircraft products using the ultrasonic nondestructive testing method

A method for measuring the thickness of sealant layers between glass-fiber reinforced plastic and metallic parts of airframes accessible only from one side is proposed. The method is based on use of general-purpose ultrasonic flaw detectors and special-purpose laser-acoustic equipment. It is shown that the developed method allows for measurement of sealant layers with thicknesses less than the ultrasonic wave length.

Ultrasonic nondestructive testing and evaluating system for the brazing quality of a guide ring

The important status of guide ring in large power plants and its manufacturing methods were introduced. The advantages of manufacturing methods including welding and electrolysis were discussed. In order to ensure the brazing quality of the guide ring, ultrasonic nondestructive testing (UNDT) method was used in this study. According to the features of the defects that may show up during brazing, the feasibility and reliability of UNDT were proved in theory. Based on the theory, an ultrasonic C-scan imaging test method was developed using a water immersion focusing probe. According to the features of the inspected images, the defects were segmented using a morphology image processing based method. The defects can be localized and sized by employing the algorithm of area reconstruction. At last, the combination ratio of brazing interface can be calculated and the brazing quality of the guide ring can be evaluated.