Nonlinear Ultrasonic Testing Research Articles

Nondestructive Evaluation of Early Stage Plasticity and Fatigue Damage of Aluminum Alloy Using Nonlinear Ultrasonic Method

Early stage of plasticity and fatigue damage are difficult to detect by using conventional ultrasonic techniques.Nonlinear ultrasonic technique based on harmonic generation has been shown to have the ability to solve the question.A nonlinear ultrasonic high power transmission testing system is developed to detect early-stage plasticity and fatigue damage of Aluminum 2024-T4 alloy.During the test,the nonlinear parameter of the material based on the amplitude of second harmonic is monotonically correlated with the plasticity and fatigue damage of the samples.The experimental nonlinearities are successfully reduced by using the natural filter effect of piezo-electric discs,which makes the experimental method more robust.The experimental results show that the nonlinear ultrasonic technique based on harmonic generation can be used to detect early-stage plasticity and fatigue damage of aluminum alloy.

Evaluating Damage of Concrete with Nonlinear Ultrasonic and Acoustic Emission Techniques

In this research, the non-linear ultrasonic and acoustic emission techniques were used to evaluating damages induced in concrete under compression loading. Cubic concrete specimens were produced with three different w/c. The nonlinear ultrasonic evaluation was based upon measuring the change in fundamental amplitude with increasing damage and output power level. In acoustic emission testing technique 4 sensors were used to record the AE events under various loading and unloading cycles. An increase in AE hits was observed with increasing damage. Since concrete contains microcracks even under initial loading stages, none of the test specimens exhibited clear signs of the occurrence of Kaiser Effect. Normalized values of Felicity Ratio were plotted and compared with the nonlinear ultrasonic test data. A correlation between acoustic emission and nonlinear ultrasonic techniques in assessing damage growth in concrete was investigated.

Nonlinear Ultrasonic Investigation of Concrete Damaged under Uniaxial Compression Step Loading

This research explains an experimental investigation of the concrete applying nonlinear ultrasonic testing technique. Eighteen cubic specimens, 150 150 150 mm, were prepared from three concrete batches with w/c of 40, 50, and 60%, respectively. The hardened concrete specimens after 28-day of curing were simultaneously subjected to uniaxial compression and nonlinear ultrasonic testing. The specimens were damaged by gradually loading them in compression in several steps representing 0, 20, 40, 60, and 80%, respectively, of the specimen's ultimate strength. At the end of each loading step ultrasonic evaluation was performed and the time domain waveforms were recorded at different power levels. Fast Fourier transformation FFT of the time domain waveforms was conducted to produce the frequency spectra. The data obtained from frequency spectra was used to study the change in signal amplitude or signal attenuation. It was found that attenuation is quite sensitive to different damage and power levels. The Fourier amplitudes obtained from FFT of the time domain data were normalized at fundamental frequency. Normalized spectra were used to examine the generation of second harmonic wave components. It was also found that the formation of second harmonic components are highly sensitive to increase in damage and change in power levels.

Non-linear ultrasonic evaluation of damaged concrete based on higher order harmonic generation

Non-linear ultrasonic testing, based on higher order harmonic generation, is a true mean for nondestructive evaluation of concrete allowing damage detection at early stages of damage. Using conventional non-destructive testing methods like pulse echo, velocity and impact echo for evaluation of such damages is difficult because poor sensitivity of these methods to early damage occurrence. In this paper an experimental investigation of 18 cubic concrete specimens, caste with three different water–cement ratios, using non-linear ultrasonic technique is presented. The specimens were ultrasonically evaluated both in damaged and undamaged conditions. The specimens were damaged progressively by loading them under compression in several steps up to their ultimate load bearing capacity. At the end of each loading step ultrasonic evaluation was performed and time domain waveforms were recorded at different power levels. Frequency spectra were prepared by performing Fast Fourier Transformation of the recorded time domain waveforms. The frequency spectra were used to obtain the first three harmonic amplitudes. The captured harmonic amplitudes were used to calculate the second and third harmonic ratios. Comparison of the harmonic ratios has shown the extraordinary sensitivity of the non-linear ultrasonic method, used in this study, to early damage detection. It was also observed that this sensitivity further increases as water cement ratio increases.

Non-destructive evaluation of concrete in damaged and undamaged states

This paper presents findings on nonlinear ultrasonic testing of concrete. The study was focused on testing cubic concrete specimens. It consisted of the non-destructive evaluation of concrete cubes using nonlinear ultrasonic technique with different frequency transducers. Concrete cubes of 150 mm × 150 mm × 150 mm in size and three distinct w/c 40%, 50%, and 60% were examined in damaged and undamaged states. Prior to inducing damages, the concrete cubes were ultrasonically evaluated in undamaged conditions. The damages were induced into the concrete cubes under compression testing. The transducer used at the wave-transmitting end had a broadband frequency of 100 kHz. However, at the receiving end, transducers of 200 and 300 kHz broadband frequency were used. The test results obtained for each concrete cube, in both damaged and undamaged conditions, were plotted and compared. The ratios of harmonic generations, nonlinear material parameters, and attenuation or loss in fundamental amplitude were calculated. The performance obtained by using transducers with different frequency as receivers in measuring the higher harmonics was also examined. The nonlinear ultrasonic test method using low frequency transducer as receiver exhibited greater sensitivity over high frequency transducer. Similarly, the third harmonic ratio was found more sensitive to concrete cracking than the second harmonic ratio. As concrete is a high attenuation material, the change in fundamental amplitude or attenuation was also found sensitive to using transducers with different frequency. The test results were also analyzed to find correlation between w/c, wave attenuation and higher harmonic generation based nonlinear parameters. These findings are very helpful for understanding the behavior of damaged concrete sections under nonlinear ultrasound testing.

Nonlinear Ultrasonic Nondestructive Testing Using Opening and Closure of Defects by Pumping Wave

Nonlinear Ultrasonic Nondestructive Testing Using Opening and Closure of Defects by Pumping Wave

Nonlinear Ultrasonic Testing with Resonant and Pulse Velocity Parameters for Early Damage in Concrete

Many types of damage or deterioration in concrete cause microcracking. Damage usually progressed from evenly distributed microcracks, to major cracks, to eventual failure of the concrete. This article reports on a study undertaken to compare the effectiveness of a nonlinear ultrasonic testing method with established ASTM testing methods in detecting early damage in concrete. In this study, geometrically identical concrete specimens were evaluated with nonlinear ultrasonic techniques. When the fundamental ultrasonic frequency interacts with a material, harmonics are generated. As damage increases, the magnitude of the nonlinear interaction increases, causing a greater portion of the fundamental frequency to be converted to higher harmonics. The authors included specimens of three distinct water-cement ratios which were compressed at regular load increments to induce damage. At each load increment, no cracking was visually observed. However, with increases in damage to the specimens, increases in harmonic ratios were measured. These increases were markedly larger as compared with changes noted with other nondestructive ASTM tests performed. The authors conclude that the nonlinear ultrasonic method shows considerable promise as a sound, nondestructive evaluation technique for detecting early damage in concrete. Sensitivity of this method generally increased with increasing water to cement (w/c) ratio.

414 非線形超音波を用いた疲労き裂開閉口挙動の解析

Nonlinear ultrasound in the solid is expected as the promising tool for evaluating a crack which is difficult to evaluate with the linear ultrasound. We developed a procedure to introduce closed fatigue crack and controlled a crack closure accurately using tensile load during nonlinear ultrasonic testing. Transmitted echoes through the crack were analyzed with FFT varying the applied tensile load and the amplitude of incident ultrasound. As the results, especially in the case of oblique incidence, the strong subharmonic wave found to be appeared in addition to the superharmonics. Details of the subharmonic wave behaviors due to a crack closure were investigated and the mechanism of the subharmonic wave also discussed. Amplitude of the peak frequency of the subharmonic wave found to be a tool for monitoring the crack closure.

Characterization of bonding quality of composites with the nonlinear modulation method

The nonlinear ultrasonic nondestructive testing technique is emerging as a valuable tool for material characterization and diagnostics. The most widely used nonlinear method is based on measurements of harmonic distortion of the probing ultrasonic wave. Another approach, developed by the authors, utilizes effect of modulation of ultrasound by low-frequency vibration. This method is more sensitive to various material and structural flaws, such as cracks, debonding, delamination, etc. It is also much easier to implement in practice. The present work focuses on characterization of bonding quality of composite plates used in the aerospace industry. The test was performed on 14 samples with various (known) degrees of bonding. The ultrasonic frequencies in the range of 50 kHz to 1.5 MHz were examined to determine the most sensitive frequencies. The modulating vibrations were in much lower frequency range up to 1 kHz. It was found that the average (across the frequency range) normalized modulation level is proportional to the bonding quality and can be used for its quantitative assessment.

Ultrasonic absorption in gaseous methane: Acustica, Vol 19, No 6 (1967/68) pp 344–349

Nonlinear ultrasonic testing method is one of few techniques that are effective for evaluating early material degradation and micro-crack initiation by analysing the nonlinear effects of ultrasonic waves. This study presents a noncontact nonlinear ultrasonic testing method based on lasers for closed surface crack inspection. A pulsed laser grating source by grating mask is applied to generate narrowband surface acoustic wave of a chosen frequency. A nonlinear numerical simulation based on Finite Element Method (FEM) is developed to simulate the generation of higher harmonics by closed surface crack. The simulation results show that the acoustic nonlinearity parameter increases with the micro closed crack length, while decreases with the micro closed crack buried depth. Moreover, the detection capability of this method is verified by an experiment. The experimental results show that the proposed laser-based nonlinear ultrasonic testing method can provide a fully noncontact and coupling-free measurement method for closed surface crack inspection.