Showing papers on "Ultrasonic testing published in 2013"

Complete noncontact laser ultrasonic imaging for automated crack visualization in a plate

Abstract: This paper presents an automated crack visualization technique using ultrasonic wavefield images obtained by a complete noncontact laser scanning system. First, the complete noncontact laser scanning system is built by integrating and synchronizing a Q-switched Nd:YAG laser for ultrasonic generation, a laser Doppler vibrometer for ultrasonic measurement and galvanometers for scanning. Then, four different laser scanning schemes are compared to find the most effective and practical ultrasonic scanning strategy for the presented application. Second, a novel image processing technique is developed to isolate and visualize crack-induced standing wave energy from the constructed ultrasonic propagation images. Finally, the effectiveness of the proposed laser ultrasonic scanning system and imaging processing technique is experimentally verified using ultrasonic scanning images obtained from an aluminum plate. The test results confirmed that a hidden notch invisible from the scanned surface was successfully detected and visualized, while no false positive alarm was triggered for an intact specimen.

Experimental Study on Ultrasonic Monitoring of Splitting Failure in Reinforced Concrete

Abstract: This paper investigates inspection of reinforced concrete elements sensitive to the splitting failure. The behaviour of a reinforced concrete specimen subjected to a tensile stress is considered. The damage detection procedure is based on the ultrasonic wave propagation technique. The piezoelectric transducers are located on both ends of the specimen and the measurements are taken periodically during the incrementally increased loading. The features of measured signals in time and frequency domains as well as wavelet transforms before and after the splitting failure are studied. The experimental results show that proposed method can be used for monitoring of damage evolution in concrete elements. The method makes possible detection of the moment just before the splitting failure occurs.

Nondestructive Evaluation of Corrosion in Varying Environments Using Guided Waves

Abstract: This work reports nondestructive evaluation of reinforcing bars that are corroding in the presence and absence of chlorides utilizing ultrasonic guided waves. The effect of rates of corrosion and its progression in the two environments on the ultrasonic signals is discussed. Surface and core seeking guided wave modes were used to monitor beams undergoing accelerated impressed current corrosion. Effective combination of guided wave modes could relate to the differences in corrosion mechanisms and rates in the two environments. Calibration of the ultrasonic data with the physical condition of the bar in the two environments has been attempted. It is done by conducting destructive tests of mass loss, tensile strength, and pull out strength at different stages of corrosion.

Evaluation of Concrete Distributed Cracks by Ultrasonic Travel Time Shift Under an External Mechanical Perturbation: Study of Indirect and Semi-direct Transmission Configurations

Abstract: Techniques based on non-linear acoustics have been proven sensitive to micro-defects in heterogeneous materials, such as concrete, but their implementation on-site is very restrictive. Ultrasonic travel time shift, a technique where a high frequency ultrasonic wave probes the medium while a low frequency elastic wave disturbs it to create a “time delay”, is a new promising technique that may be used efficiently on-site. This technique is based on nonlinear behaviour of concrete. Moreover, this technique offers the possibility of evaluating linear parameter, such as ultrasonic pulse velocity of direct waves. The scope of this paper is to study the applicability of the technique at different level of concrete damage and define its advantages, limitations in order to optimize its use. Because of the large dimensions, the geometry and limited access to various faces of existing structures, the transducers often have to be set on the same side. Two types of configurations, the indirect transmission (with incident waves at 90∘) and the semi-direct transmission (with incident waves at 45∘), were studied with cement base samples at different levels of damage (generated by freeze-thaw cycles). Up to now, test results have shown that time-shift is more sensitive when used in an indirect configuration of transmission rather than in a semi-direct configuration. Overall, the non-linear time-shift technique is much more sensitive to the initiation of cracking than linear indicators and its versatility (different indicators for different levels of damage) is of interest for rapid testing of structures.

Distributed fiber-optic laser-ultrasound generation based on ghost-mode of tilted fiber Bragg gratings

Abstract: Active ultrasonic testing is widely used for medical diagnosis, material characterization and structural health monitoring. Ultrasonic transducer is a key component in active ultrasonic testing. Due to their many advantages such as small size, light weight, and immunity to electromagnetic interference, fiber-optic ultrasonic transducers are particularly attractive for permanent, embedded applications in active ultrasonic testing for structural health monitoring. However, current fiber-optic transducers only allow effective ultrasound generation at a single location of the fiber end. Here we demonstrate a fiber-optic device that can effectively generate ultrasound at multiple, selected locations along a fiber in a controllable manner based on a smart light tapping scheme that only taps out the light of a particular wavelength for laser-ultrasound generation and allow light of longer wavelengths pass by without loss. Such a scheme may also find applications in remote fiber-optic device tuning and quasi-distributed biochemical fiber-optic sensing.

Comparison of the very high cycle fatigue behaviors of INCONEL 718 with different loading frequencies

Abstract: In order to clarify the differences of very high cycle fatigue (VHCF) behavior of nickel based superalloy IN718 with different loading frequencies, stress-controlled fatigue tests were carried out by using ultrasonic testing method (20 KHz) and rotary bending testing method (52.5 Hz), both at room temperatures, to establish stress versus cycles to failure (S-N) relationships. Results disclosed that cycles to failure at a given stress level increased with an increase of the applied frequency, i.e., the higher frequency produced an upper shift of the S-N curves. Fractographic analysis suggested that crack initiation and propagation behaviors had large differences: cracks in low-frequency tests preferentially initiated from multiple sources on the specimen surface, while in high-frequency tests, cracks mostly originated from a unique source of subsurface inclusions. Subsequently, frequency-involved modeling was proposed, based on the damage accumulation theory, which could well illustrate qualitatively those comparisons due to different loading frequencies.

Influence of small temperature variations on the ultrasonic velocity in concrete

Abstract: Ultrasonic methods are valuable tools for quality assessment and structural imaging of concrete. In such applications, accurate and reliable determination of ultrasonic wave velocities is essential, as they are affected by various experimental and environmental factors. In this research coda wave interferometry (CWI) was used to determine the influence of temperature (0 to 50 °C) on ultrasonic wave velocity in concrete samples. A resolution of better than 10−4 was achieved in the measurement of relative velocity changes. Reversibility and repeatability as well as the influence of moisture were taken into account. In addition the influence of sensor (transmitter and receiver) positioning errors on the results of the interferometric algorithm was evaluated as well as the benefit of newly developed, permanently embedded sensors. The presented results can be used to evaluate and refine data from ultrasonic monitoring systems.

Resonance ultrasonic thermography: Highly efficient contact and air-coupled remote modes

Abstract: A frequency match between the driving ultrasonic wave and characteristic frequency of a defect provides an efficient energy pumping from the wave directly into the defect. The application of the concept of local defect resonance is shown to enhance substantially the efficiency of vibro-thermal conversion in ultrasonic thermography (ULT). Therefore, the resonance modes of ultrasonic thermography require much lower acoustic power to activate defects that makes it possible to avoid high-power ultrasonic instrumentation and proceed to a remote ultrasonic thermography version by using air-coupled ultrasonic excitation.

Sub-surface defect detection in a steel sheet

Abstract: In recent years, the focus on quality control in the steel industry has shifted from offline to inline non-destructive testing in order to detect defects at the earliest possible stage in the production process. The detection and elimination of such defects is vital for sustaining product quality and reducing costs. Various measurement principles (e.g. ultrasonic testing, electromagnetic acoustic transducer, x-ray inspection) were analyzed and their advantages and disadvantages are discussed regarding their usability in a steel plant. Based on these findings a magnetic method combined with a new sensor concept was chosen. By using highly sensitive sensors based on the giant magnetoresistive effect, it is possible to detect magnetic flux leakage variations on the surface of a magnetized steel strip caused by defects or inhomogeneities inside the material. Based on promising measurement results of preliminary tests and simulation results obtained by finite element method-models, a prototype is now being built for offline measurements and the optimization of the measurement method. In the event that the development of this second prototype is successful, an inline configuration will be implemented.

Using piezoelectric sensors for ultrasonic pulse velocity measurements in concrete

Abstract: The ultrasonic pulse velocity (UPV) test has been a widely used non-destructive testing method for concrete structures However, the conventional UPV test has limitations in consistency of results and applicability in hard-to-access regions of structures The authors explore the feasibility of embedded piezoelectric (PZT) sensors for ultrasonic measurements in concrete structures Two PZT sensors were embedded in a reinforced concrete specimen One sensor worked as an actuator driven by an ultrasonic pulse-receiver, and another sensor worked as a receiver A series of ultrasonic tests were conducted to investigate the performance of the embedded sensors in crack-free concrete and concrete specimens having a?surface-breaking crack under various external loadings Signals measured by the embedded sensors show a broad bandwidth with a centre frequency around 80 kHz, and very good coherence in the frequency range from 30 to 180 kHz Furthermore, experimental variability in ultrasonic pulse velocity and attenuation is substantially reduced compared to previously reported values from conventional UPV equipment Findings from this study demonstrate that the embedded sensors have great potential as a low-cost solution for ultrasonic transducers for health monitoring of concrete in structures

Nondestructive Porosity Assessment of CFRP Composites with Spectral Analysis of Backscattered Laser-Induced Ultrasonic Pulses

Abstract: The laser-ultrasonic method for nondestructive quantitative local porosity assessment for CFRP composites is proposed and realized experimentally for only one available flat surface of a specimen or a product. This method combines the laser thermoelastic generation and the high-sensitivity piezoelectric detection of broadband pulses of longitudinal ultrasonic waves and does not require the detection of the backwall echo ultrasonic signal. The generation and the detection of ultrasonic pulses is carried out with the specially designed laser-ultrasonic transducer, which allows one to obtain both the temporal profile and the frequency spectrum of a part of the ultrasonic signal backscattered by gas voids in a composite specimen. The frequency spectrum of backscattered ultrasonic pulses is analyzed for three sets of CFRP specimens with different epoxy matrix fractions and porosity. The empirical relation between porosity of CFRP specimens and the spectral power (structural noise power) of ultrasonic signals backscattered by voids is obtained for porosity values up to 0.15. This relation allows one to evaluate the local porosity from measured structural noise power both for CFRP specimens and products fabricated from the same composite material. The proposed laser-ultrasonic setup demonstrates a basis for a system of CFRP porosity assessment in field conditions. It can be very useful especially for nondestructive detection of structural changes of composite materials that will allow evaluation of products during their life time.

An Ultrasonic Through-Wall Communication (UTWC) System Model

Abstract: Ultrasonic waves at 1 MHz are used to send information across solid walls without the needs for through wall penetrations. A communication channel is established by attaching a set of three ultrasonic transducers to the wall. The first transducer transmits a continuous ultrasonic wave into the wall. The second transducer is mounted on the opposite side of the wall (inside) and operates as a receiver and signal modulator. The third transducer, the outside receiving transducer, is installed on the same side as the first transducer where it is exposed to the signal reflected from the blended interface of the inside wall and inside transducer. Inside sensor data is digitized and the bit state is used to vary in time the electrical load connected to the inside transducer, changing its acoustic impedance in accordance with each data bit. These impedance changes modulate the amplitude of the reflected ultrasonic signal. The modulated signal is detected at the outside receiving transducer, where it is then demodulated to recover the data. Additionally, some of the ultrasonic power received at the inside transducer is harvested to provide energy for the communication and sensor system on the inside. The entire system (ultrasonic, solid wall, and electronic) is modeled in the electrical domain by means of electro-mechanical analogies. This approach enables the concurrent simulation of the ultrasonic and electronic components. A model of the communication system is implemented in an electronic circuit simulation package, which assisted in the analysis and optimization of the communication channel. Good agreement was found between the modeled and experimental results.

Design procedure of ultrasonic tomography system with steel pipe conveyor

Abstract: Non-invasive ultrasonic tomography has a dominant role in extracting cross-sectional images of objects. The front-end structure of the proposed ultrasonic tomography system with a steel pipe conveyor is explained in this paper. In the novel ultrasonic tomography system presented, a non-invasive sensing technique is applied for detecting gas bubbles inside the steel pipe. A method of visualising the structure of the steel pipe with finite element software (COMSOL Multiphysics 4.2) is also presented in this paper. An appropriate sensor with 40 kHz resonance frequency, based on simulation results, is selected and experimentally mounted on the periphery of the vessel. Several reviews regarding the common tomography technique proposed and hardware preparation are also discussed. Twelve dual-function (transmitter/receiver) ultrasonic sensors with a fan-shaped beam projection capability are used as the sensory part of the system. Details of the circuitry of the system are also presented, which consists of various parts such as a signal generator, signal conditioning and signal acquisition strategy. Finally, the experimental results of the proposed system, which are useful for further investigation for the application of ultrasonic tomography in industry, are illustrated.

Non-destructive evaluation (NDE) of aerospace composites: ultrasonic techniques

Abstract: This chapter discusses the defects in aerospace composite structures and the ultrasonic techniques used for their non-destructive detection and characterization. The defects discussed include manufacturing defects such as porosity, errors in ply layup or stacking sequence, ply waviness, and service-induced delamination, disbond, crushed core, and microcracks. Ultrasonic inspection of both solid laminates and honeycomb sandwiches is discussed. The techniques addressed include novel processing of C-scan images in water-coupled ultrasonic testing, application of air-coupled ultrasound, and electromagnetically generated shear waves to exploit their strong interaction with fiber direction. In terms of instrumentation, this chapter discusses laboratory systems, stationary systems used in manufacturing environment, and portable inspection systems for field applications.

SAFT and TOFD—A Comparative Study of Two Defect Sizing Techniques on a Reactor Pressure Vessel Mock-up

Abstract: Defect sizing is required for a quantitative assessment of the quality and reliability of safety relevant components and materials using ultrasonic non-destructive testing. The SAFT (Synthetic Aperture Focussing Technique) and the TOFD technique (Time Of Flight Diffraction) are such promising sizing candidates, extracting more information from the raw ultrasound echo data and the corresponding crack tip response. In this work the phased array technique is used to inspect a clad mock-up model of a pressure vessel section. The full scale model contains artificial test reflectors which are located in the weld and in the cladding region as well. The defects—representing typical flaws at a very early stage—are analysed with different frequencies, beam angles and directions of incidence. For the reconstruction of reflector indications a SAFT algorithm is applied to the phased array measurement results. Additionally the reflectors are analysed by means of the TOFD technique, using different beam angles at the same time. Both analysis methods are performed using different directions of incidence considering the complex cladding structure underneath the inner surface of the mock-up model. A direct comparison of the SAFT and TOFD techniques shows that, besides the clarity of the results, the detection and sizing capabilities of SAFT are far better.

A low-cost ultrasonic wind speed and direction measurement system

Abstract: The paper deals with a low-cost transducer that implements an improved technique for wind speed measurement in open air. The instrument is a 2-axis ultrasonic anemometer, capable of monitoring both wind speed and direction. Its main advantage is that using the ultrasonic technique it has no moving parts, allowing for the utilization in a variety of applications requiring low maintenance and fast response to rapid wind gusts. Wind speed measurement for power turbine control can be considered as a reference application of it. The proposed instrument presents a simple design and is constructed using commercially available components, to reduce development costs. In the paper the proposed architecture is presented, discussing the algorithm applied to process the transduced ultrasonic signals. Some results obtained during the first tests are also presented and discussed, suggesting for successive improvements.

Probabilistic Fatigue Life Prediction and Structural Reliability Evaluation of Turbine Rotors Integrating an Automated Ultrasonic Inspection System

Abstract: The paper presents a general method and procedure for fatigue reliability assessment integrating automated ultrasonic non-destructive inspections. The basic structure of an automated ultrasonic inspection system is presented. Fatigue reliability assessment methodology is developed using uncertainty quantification models for detection, sizing, and fatigue model parameters. The probability of detection model is based on a classical log-linear model coupling the actual flaw size with the ultrasonic inspection reported size. Using probabilistic modeling, the distribution of the actual flaw size is derived. Reliability assessment procedure using ultrasonic inspection data is suggested. A steam turbine rotor example with realistic ultrasonic inspection data is presented to demonstrate the overall method. Calculations and interpretations of assessment results based on risk recommendations for industrial applications are given.

Assessment of sensitization in AISI 304 stainless steel by nonlinear ultrasonic method

Abstract: A nonlinear ultrasonic technique has been developed to evaluate sensitization in Type 304 stainless steel. In order to achieve different degree of sensitization (DOS), specimens have been subjected to heat treatment at 675 °C at varying soaking time (0.5, 1.0, 2.0, 3.0 and 4.0 h). Heat treated specimens were subjected to intergranular corrosion tests as per ASTM standards A262 and G108. Sensitization in longer soaked material has been confirmed through ditch microstructures, cracks on the bend tested specimens and higher degree of sensitization. Nonlinear ultrasonic studies showed variation in the nonlinearity parameter with soaking time which also confirms sensitization. A good correlation was observed between the degree of sensitization measured by the electrochemical potentiokinetic reactivation test and the ultrasonic nonlinearity parameter. This study clearly demonstrated that nonlinear ultrasonic technique can be used as a potential technique for non-destructive characterization of sensitization in austenitic stainless steel.

Ultrasonic characterization of delamination in aeronautical composites using noncontact laser generation and detection

Abstract: The characterization of delamination in composite plates with ultrasonic waves generated and detected by lasers is presented. Composite materials have become one of the most important structural materials in the aviation industry because of their excellent mechanical properties, such as high specific stiffness and antifatigue. This paper reports a new application of the laser ultrasonic technique to perform nondestructive detection of carbon-fiber-reinforced plastic (CFRP) and continuous-fiber-reinforced ceramic matrix composites (CFCCs) containing artificial internal defects, based on propagation characteristic of ultrasonic waves generated by pulse laser with a wavelength of 1064 nm and pulse duration of 10 ns. A laser interferometer based on two-wave mixing is used to measure ultrasonic wave signals. The main advantage of this technique over conventional ultrasonic testing techniques is the ability to carry out detection without using coupling agents. The research results prove that the laser ultrasonic technique is effective for the detection of internal defects in both CFRP and CFCC composite components, which should promote and expand the application of the technique in the aviation industry.

Main Features of a Complete Ultrasonic Measurement Model: Formal Aspects of Modeling of Both Transducers Radiation and Ultrasonic Flaws Responses

Abstract: This paper aims at describing the theoretical fundamentals of a reciprocity-based ultrasonic measurement model. This complete inspection simulation can be decomposed in two modeling steps, one dedicated to transducer radiation and one to flaw scattering and echo synthesis. The physical meaning of the input/output signals used in these two modeling tools is defined and the theoretical principles of both field calculation and echo computation models are then detailed. The influence on the modeling results of some changes in the simulated configuration (as the incident angle) or some input signal parameters (like the frequency) are studied: it is thus theoretically established that the simulated results can be compared between each other in terms of amplitude for numerous applications when changing some inspection parameters in the simulation but that a calibration for echo calculation is generally required.

Defect Inspection of Flip Chip Solder Bumps Using an Ultrasonic Transducer

Abstract: Surface mount technology has spurred a rapid decrease in the size of electronic packages, where solder bump inspection of surface mount packages is crucial in the electronics manufacturing industry. In this study we demonstrate the feasibility of using a 230 MHz ultrasonic transducer for nondestructive flip chip testing. The reflected time domain signal was captured when the transducer scanning the flip chip, and the image of the flip chip was generated by scanning acoustic microscopy. Normalized cross-correlation was used to locate the center of solder bumps for segmenting the flip chip image. Then five features were extracted from the signals and images. The support vector machine was adopted to process the five features for classification and recognition. The results show the feasibility of this approach with high recognition rate, proving that defect inspection of flip chip solder bumps using the ultrasonic transducer has high potential in microelectronics packaging.

Ultrasonic phased array testing apparatus

Abstract: A plurality of subsets of ultrasonic transducers in an array of ultrasonic transducers are configured to transmit ultrasonic waves at various angles simultaneously toward a test object so that an anomaly of any orientation in the test object can be detected efficiently.