Ultrasonic Nonlinearity Research Articles

Demodulation technique to identify nonlinear characteristics of vibro-acoustic NDT measurements

A novel approach for nonlinear ultrasonics is presented which uses the demodulated response of a nonlinear vibro-acoustic signal. The demodulation process is similar to the quadrature demodulation process used in telecommunications. It is shown that the demodulation method provides an alternative approach for the analysis of nonlinear behavior compared to the analysis of frequency spectra or other techniques. The proposed method suggests that a representative reconstruction of the time-domain nonlinearity behavior of the system can be obtained. The paper provides a theoretical background to the technique as well as experimental validation. The proposed method is demonstrated for the analysis of four different types of contact acoustic nonlinear interfaces. It is shown that the demodulated waveforms are consistent with the expected mechanical behavior of the different interfaces. The results suggest that this method can provide more insight into the nonlinear behavior of a system compared to conventional spectral amplitude analysis techniques.

A Novel Multi-frequency Nonlinear Ultrasonic Approach for the Characterization of Annealed Polycrystalline Microstructure

A multi-frequency nonlinear ultrasonic measurement is used to characterize grain size variations and distributions unambiguously. The ultrasonic nonlinearity parameter varies linearly with grain size in the Rayleigh scattering regime but deviates from linear behavior at the Rayleigh-to-stochastic transition zone. Frequency dependence of this parameter is found to be a reliable tool for rapid screening of materials where grain size varies widely.

Applicability of nonlinear ultrasonic technique to evaluation of thermally aged CF8M cast stainless steel

Abstract Cast austenitic stainless steel (CASS) is used for fabricating different components of the primary reactor coolant system of pressurized water reactors. However, the thermal embrittlement of CASS resulting from long-term operation causes structural safety problems. Ultrasonic testing for flaw detection has been used to assess the thermal embrittlement of CASS; however, the high scattering and attenuation of the ultrasonic wave propagating through CASS make it difficult to accurately quantify the flaw size. In this paper, we present a different approach for evaluating the thermal embrittlement of CASS by assessing changes in the material properties of CASS using a nonlinear ultrasonic technique, which is a potential nondestructive method. For the evaluation, we prepared CF8M specimens that were thermally aged under four different heating conditions. Nonlinear ultrasonic measurements were performed using a contact piezoelectric method to obtain the relative ultrasonic nonlinearity parameter, and a mini-sized tensile test was performed to investigate the correlation of the parameter with material properties. Experimental results showed that the ultrasonic nonlinearity parameter had a correlation with tensile properties such as the tensile strength and elongation. Consequently, we could confirm the applicability of the nonlinear ultrasonic technique to the evaluation of the thermal embrittlement of CASS.

A Study on Fatigue State Evaluation of Rail by the Use of Ultrasonic Nonlinearity.

Nonlinear ultrasonic testing has been accepted as a promising manner for evaluating material integrity in an early stage. Stress fatigue is the main threats to train safety, railways examinations for stress fatigue are more significant and necessary. A series of ultrasonic nonlinear wave experiments are conducted for rail specimens extracted from railhead with different degree of fatigue produced by three-point bent loading condition. The nonlinear parameter is the indicator of nonlinear waves for expressing the degree the fatigue. The experimental results show that the sensitivity of a third harmonic longitudinal wave is higher than second harmonic longitudinal wave testing. As the same time, collinear wave mixing shows strong relative with fatigue damages than a second longitudinal wave nondestructive testing (NDT) method and provides more reliable results than third harmonic longitudinal waves nonlinear testing method.

Metamaterial improved nonlinear ultrasonics for fatigue damage detection

This article presents an improved nonlinear ultrasonic technique for fatigue damage detection utilizing a kind of carefully designed aluminum-lead composite metamaterial. It focuses on developing a bandgap metamaterial to improve the accuracy and identifiability of the superharmonic features from fatigue cracks by eliminating the inherent nonlinear components in the nonlinear ultrasonic technique. The study starts with the unit cell design through modal analysis by applying the Bloch–Floquet boundary condition to obtain the band structure. Based on the local resonance mechanism, by adjusting the height ratio between the aluminum and lead cylinders, the bandgaps covering the required frequency ranges can be opened up. Then, a chain of regularly arranged unit cells is modeled to analyze the spectral response and verify the bandgap effect through harmonic analysis. The targeted ultrasonic frequency component of guided waves within the bandgap can be mechanically filtered out. Subsequently, a finite element model of the pitch-catch active sensing procedure for fatigue crack detection is constructed via the coupled-field transient dynamic analysis. Nonlinear ultrasonic experiments with the designed metamaterial are carried out to verify the theoretical and numerical investigations. This paper demonstrates that the metamaterial, with its outstanding wave manipulation capability, shows great potential on structural health monitoring and nondestructive evaluation applications. The paper finishes with summary, concluding remarks, and suggestions for future work.

Nonlinear Acoustic Spectroscopy and Frequency Sweep Ultrasonics: Case on Thermal Damage Assessment in Mortar

An exhaustive study on thermal damage of Portland cement-based materials is addressed. Damage carried out at different temperatures on concrete between 40 and $$525\,^{\circ }\hbox {C}$$ were assessed by means of microstructural, physical and nondestructive tests. Microstructural analysis (thermogravimetry and scanning electron microscopy) showed the principal changes of the Portland cement hydrated products for the different analysed temperatures. Compressive and flexural strengths remained constant or even increased at a low heating temperature range, while the mass loss increases. Dilatometry analysis revealed important information about deformation incompatibilities between the paste and the aggregate. These results have been correlated with nondestructive tests: nonlinear impact resonance acoustic spectroscopy (NIRAS) and ultrasonic measures. The dynamic modulus and ultrasonic pulse velocity have closely predicted the linear stiffness decay of the specimens. However, hysteretic parameter from NIRAS analysis exhibited a different trend from stiffness-related parameters, keeping constant until $$250\,^{\circ }\hbox {C}$$ and suffering a huge increasing for 400 and $$525\,^{\circ }\hbox {C}$$ . Ultrasonic attenuation computed with a broadband ultrasonic signal (chirp) revealed interesting information about scattering components inside the material, and is sensitive to interfacial transition zone between aggregate and paste in a large range of frequencies. The correlation between microstructural, mechanical and nondestructive techniques were carried out successfully. Nonlinear vibration and ultrasonic attenuation are non-conventional parameters that gave specific information about a complex damage process, such as a thermal attack in highly heterogeneous materials (e.g. Portland cement composites).

The measurement of weld morphology and inclusions using ultrasonics

The morphology of welding pool (fusion zone and heat affected zone) includes a variety of microstructural constitutions (the formation of new boundaries, pores, and textures) that can affect the integrity of welded joint. Currently, microscopic observations are the common method to characterize the welding pool, which is a destructive post-welding procedure, and requires a complex preparation process. In this paper, linear and non-linear ultrasonic methods are investigated to measure the weld morphology and the presence of porosity nondestructively in welds manufactured with gas tungsten arc welding (GTAW). The weld morphology and the presence of porosity are quantified using microscopic investigations. The measurements show that the ultrasonic energy obtained by linear ultrasonics and the acoustic nonlinearity parameter obtained by nonlinear ultrasonics have good correlation with the weld morphology. The relationship between the ultrasonic energy and the weld morphology is validated further with numerical models. The linear UT at 1 MHz is not sensitive to the presence of porosity as the resolution is limited by ultrasonic wavelength. However, nonlinear ultrasonics has better sensitivity to the inclusions due to sub-wavelength resolution.

Ultrasonic nonlinearity parameter in uniaxial stress condition

The ultrasonic nonlinearity parameter derived for one-dimensional propagation of a longitudinal wave in an isotropic material has been considered useful in the evaluation of material degradation. To demonstrate this, many researchers have reported on the correlation with the yield strength obtained from a tensile test. However, there is an essential issue with this procedure – which is that the ultrasonic nonlinearity parameter is derived in a state where the lateral strain is restrained, whereas the tensile test to measure the yield strength is carried out under uniaxial stress conditions, where lateral deformation is free. In this study, to address this issue, the authors have defined the ultrasonic nonlinearity parameter under uniaxial stress conditions which were the same as the tensile test, and showed that the correlation with the yield strength was higher than the currently used ultrasonic nonlinearity parameter. To verify the validity of the proposed ultrasonic nonlinearity parameter, experiments were carried out for Al6061-T6 alloy specimens heat-treated with different aging times. Results showed that the proposed ultrasonic nonlinearity parameter exhibited a much higher correlation with yield strength than the currently used nonlinearity parameter.

Nondestructive evaluation of adhesive joints by using nonlinear ultrasonics

Adhesive bonding technology has now gained much attention in many industries as a very versatile assembling technique. However, to be used for structural joining and critical application, high reliability is needed. Thus, efficient non-destructive control strategy should be proposed to evaluate the nominal bonding quality but also possible progressive in-service degradations. Promising results have been presented in the literature using ultrasound-based methods. While linear ultrasound is efficient to detect decohesion or voids in a structure, it is barely sensitive to bond strength. In this work, we present a method to generate high amplitude plane wave, which may produce nonlinear phenomenon that are able to reveal kissing bonds or other types of adhesion defects. In this purpose a method based on a chaotic cavity transducer has been developed to generate high energy plane wave. Then the method is evaluated on metallic bonds with bonding defects. Combined with the pulse inversion technique, nonlinear phenomenon can be measured in the form of harmonic generation in the defect zone. We use this method to image a defect created by spraying PTFE on one adherent prior to bonding.

Characterization of Microstructural Evolution by Ultrasonic Nonlinear Parameters Adjusted by Attenuation Factor

The use of an acoustic nonlinear response has been accepted as a promising alternative for the assessment of micro-structural damage in metallic solids. However, the full mechanism of the acoustic nonlinear response caused by the material micro-damages is quite complex and not yet well understood. In this paper, the effect of material microstructural evolution on acoustic nonlinear response of ultrasonic waves is investigated in rolled copper and brass. Microstructural evolution in the specimens is artificially controlled by cold rolling and annealing treatments. The correlations of acoustic nonlinear responses of ultrasonic waves in the specimens corresponding to the microstructural changes are obtained experimentally. To eliminate the influence of attenuation, which was induced by microstructural changes in specimens, experimentally-measured nonlinear parameters are corrected by an attenuation correction term. An obvious decrease of nonlinearity with the increase of grain size is found in the study. In addition, the influences of material micro-damages introduced by cold rolling on the acoustic nonlinear response in specimens are compared with the ones of grain boundaries controlled by heat treatment in specimens. The experimental results show that the degradation of material mechanical properties is not always accompanied by the increase of acoustic nonlinearity generated. It suggested that the nonlinear ultrasonic technique can be used to effectively characterize the material degradations, under the condition that the variations of grain sizes in the specimens under different damage states are negligible.

Nonlinear ultrasonic damage evaluation system research and development and its application on S355J2W steel for high speed train

The nonlinear ultrasonic (NLU) technique has been proposed to monitor structure health. It is well known that damage of materials is generally accompanied by increase of the materials’ nonlinearity. However, after processing such as welding, the microstructure of the material will change, which might affect the behavior of materials’ nonlinearity after degradation, further, inducing inaccuracy in evaluation of the structure life. An NLU system is developed to characterize the damage due to plastic deformation in S355J2W weathering resistant steel specimens which underwent different heat treatment processes. The experimental results show that the NLU system is effective and accurate for the measurement of higher harmonic components, and acoustic nonlinear parameters (ANP) increase with the increase of tensile stress. The results also show that ANP response relates to the grain size.

Modulated high frequency excitation approach to nonlinear ultrasonic NDT

A novel approach for nonlinear ultrasonics is presented which relies on an amplitude modulated high-frequency excitation, as distinct from the conventional vibro-acoustic approach based on a low-frequency pumping wave in combination with a high-frequency probing wave. This amplitude modulated excitation contains three frequencies that interact in the presence of nonlinearity and transfers energy to frequencies not part of the original input. This effect can be exploited to detect and quantify damage-induced nonlinearity. This novel method is demonstrated experimentally for three distinct contact conditions, utilising different types of transducer and excitation signals of various amplitudes and frequencies. The performance is compared with the conventional vibro-acoustic technique. It is shown that the new technique has comparable performance to existing methods. Specialized measurement system design with superb sensitivity is also demonstrated. Unlike conventional cross-modulation based nonlinear ultrasonic techniques, this new method does not require two separate excitation sources. This represents a significant practical advantage which will greatly facilitate the implementation of nonlinear ultrasonic methods for a wide range of applications.

Assessment of Creep damage in Welded Joint for ASME Grade 91 Heat Resisting Steel with Nonlinear Ultrasonics

Assessment of Creep damage in Welded Joint for ASME Grade 91 Heat Resisting Steel with Nonlinear Ultrasonics

Evaluation of Creep damage in Welded Joint for High Cr Ferritic Heat Resisting Steels with Nonlinear Ultrasonics

Evaluation of Creep damage in Welded Joint for High Cr Ferritic Heat Resisting Steels with Nonlinear Ultrasonics

Combined Damage Index to Detect Plastic Deformation in Metals Using Acoustic Emission and Nonlinear Ultrasonics.

Understanding the amount of degradation using nondestructive evaluation (NDE) methods provides an effective way of determining the fitness to service and the residual life of structural components. Due to uncertainties introduced by the single NDE method, a combined damage index using multi-sensor data increases the reliability of damage assessment. In this paper, the outputs of three NDE methods including acoustic emission (AE), linear ultrasonics (LUT), and nonlinear ultrasonics (NLUT) are merged to identify the amount of plastic deformation in aluminum 1100. The sensitivities of individual and combined methods to microstructural changes are evaluated. The coupon samples are loaded up to different strain levels and then unloaded. AE data is recorded in real time and ultrasonic data is recorded from the unloaded samples. The major features combined in the damage index are cumulative AE absolute energy and nonlinear coefficient. The microstructural state is verified with microscopic analysis and hardness testing. The developed damage index can nondestructively assess the amount of plastic deformation with higher reliability.

Higher harmonic generation of Rayleigh wave at debondings in FRP-retrofitted concrete structures

The use of ultrasonic nonlinearity for damage detection and monitoring of structures has attracted growing attention. Interaction of guided waves with contact-type damage, such as debonding, is one of the major sources of ultrasonic nonlinearity. This paper investigates higher harmonic generation of Rayleigh waves in FRP-retrofitted concrete structures due to debonding between FRP and concrete. In this study, propagation and scattering of Rayleigh wave are simulated using a three-dimensional finite element model. The numerical simulations of both linear and nonlinear Rayleigh wave are validated with experimentally measured data. There is very good agreement between numerical and experimental results. This paper also investigates the scattering directivity patterns of second and third harmonics of Rayleigh wave. The results provide physical insights into nonlinear Rayleigh wave generated by debonding between FRP and concrete. Overall, the findings of this study can further advance the damage detection methods using the nonlinear Rayleigh wave.

Nonlinear ultrasonic detection for evaluating fatigue crack in metal plate

In engineering structures, metal materials always endure fatigue cracks under long-term service. There has been a demand for developing a structural health monitoring method to evaluate micro-sized fatigue cracks, as cracking is considered as a precursor to structural failure. However, conventional linear-ultrasound-based technology is not sensitive to crack when it is barely visible in a metal medium. In this article, we present a nonlinear ultrasonic technology based on crack–wave interaction to investigate the growth of a fatigue crack. A breathing-crack model with a plastic zone around it was precisely established to reveal the change in the Lamb wave. The relative nonlinear parameter calculated from the fundamental and harmonic components of the Lamb wave showed linearly increasing with the growth of the fatigue crack. The relative nonlinearity was related to ultrasonic parameters, such as the cycle number and the excited frequency of the tone-burst signal. In addition, it was also related to the angle between the sensor and the crack rather than their distance. A set of experiments were conducted, demonstrating that the increasing trend of ultrasonic nonlinearity fits very well to the finite element analysis results. In conclusion, the nonlinear ultrasonic method that can be applied to the detection of micro fatigue cracks in metal plates is an effective structural health monitoring technique.

In situ nonlinear ultrasonic technique for monitoring microcracking in concrete subjected to creep and cyclic loading

This research conducts in situ nonlinear ultrasonic (NLU) measurements for real time monitoring of load-induced damage in concrete. For the in situ measurements on a cylindrical specimen under sustained load, a previously developed second harmonic generation (SHG) technique with non-contact detection is adapted to a cylindrical specimen geometry. This new setup is validated by demonstrating that the measured nonlinear Rayleigh wave signals are equivalent to those in a flat half space, and thus the acoustic nonlinearity parameter, β can be defined and interpreted in the same way. Both the acoustic nonlinearity parameter and strain are measured to quantitatively assess the early-age damage in a set of concrete specimens subjected to either 25 days of creep, or 11 cycles of cyclic loading at room temperature. The experimental results show that the acoustic nonlinearity parameter is sensitive to early-stage microcrack formation under both loading conditions – the measured β can be directly linked to the accumulated microscale damage. This paper demonstrates the potential of NLU for the in situ monitoring of mechanical load-induced microscale damage in concrete components.

Numerical study on static component generation from the primary Lamb waves propagating in a plate with nonlinearity

Under the discipline of nonlinear ultrasonics, in addition to second harmonic generation, static component generation is another frequently used nonlinear ultrasonic behavior in non-destructive testing (NDT) and structural health monitoring (SHM) communities. However, most previous studies on static component generation are mainly based on using longitudinal waves. It is desirable to extend static component generation from primary longitudinal waves to primary Lamb waves. In this paper, static component generation from the primary Lamb waves is studied. Two major issues are numerically investigated. First, the mode of static displacement component generated from different primary Lamb wave modes is identified. Second, cumulative effect of static displacement component from different primary Lamb wave modes is also discussed. Our study results show that the static component wave packets generated from the primary S0, A0 and S1 modes share the almost same group velocity equal to the phase velocity of S0 mode tending to zero frequency cplate. The finding indicates that whether the primary mode is S0, A0 or S1, the static components generated from these primary modes always share the nature of S0 mode. This conclusion is also verified by the displacement filed of these static components that the horizontal displacement field is almost uniform and the vertical displacement filed is antisymmetric across the thickness of the plate. The uniform distribution of horizontal displacement filed enables the static component, regardless of the primary Lamb modes, to be a promising technique for evaluating microstructural damages buried in the interior of a structure. Our study also illustrates that the static components are cumulative regardless of whether the phase velocity of the primary and secondary waves is matched or not. This observation indicates that the static component overcomes the limitations of the traditional nonlinear Lamb waves satisfying phase velocity matching condition to achieve cumulative second harmonic generation. This nature also enables the primary Lamb waves excited at a low center frequency to generate static component used for inspecting large-scale structures with micro-scale damages.

Creep Damage Evaluation In P92 Steel Using Second Harmonic Of High Power Ultrasonic Signal

In the present investigation, studies were done to measure the acoustic nonlinearity by second harmonic generation of ultrasonic wave, known as non-linear ultrasonic (NLU), due to materials damage during creep in P92 steel. Creep rupture behaviour of this steel was carried out at a temperature of 600°C and stress level of 160MPa. Non linearity parameter (β) which is defined as the ratio of the amplitude of second harmonic to the square of the amplitude of the transmitted signal frequency of ultrasonic wave was evaluated. About two order change in non linearity parameter was observed between as tempered and creep ruptured samples. The influence of microstructure on the nonlinear wave propagation was analyzed. Based on metallographic studies, it was revealed that value of β in the material increases due to a rising of the precipitation area fraction, disappearance of prior austenite grain boundary, coarsening of precipitates, as well as formation of new precipitates like Laves phase. The nonlinear ultrasonic wave exhibits the potential for the creep damage monitoring of in-service components.