• Journal of the Korean Society for Nondestructive Testing
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• v.37 no.2
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• pp.115-121
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• 2017

The nonlinear ultrasonic technique is a potential nondestructive method to evaluate material degradation, in which the ultrasonic nonlinearity parameter is usually measured. The ultrasonic nonlinearity parameter is defined by the elastic nonlinearity coefficients of the nonlinear Hooke's equation. Therefore, even though the ultrasonic nonlinearity parameter is not equal to the elastic nonlinearity parameter, they have a close relationship. However, there has been no experimental verification of the relationship between the ultrasonic and elastic nonlinearity parameters. In this study, the relationship is experimentally verified for a heat-treated aluminum alloy. Specimens of the aluminum alloy were heat-treated at $300^{\circ}C$ for different periods of time (0, 1, 2, 5, 10, 20, and 50 h). The relative ultrasonic nonlinearity parameter of each specimen was then measured, and the elastic nonlinearity parameter was determined by fitting the stress-strain curve obtained from a tensile test to the 5th-order-polynomial nonlinear Hooke's equation. The results showed that the variations in these parameters were in good agreement with each other.

• Journal of the Korean Society for Nondestructive Testing
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• v.36 no.2
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• pp.121-129
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• 2016

As the lifespan of concrete structures increases, their load carrying capacity decreases owing to cyclic loads and long-term effects such as creep and shrinkage. For these reasons, there is a necessity for stress state monitoring of concrete members. Particularly, it is necessary to evaluate the concrete structures for behavioral changes by using a technique that can overcome the measuring limitations of usual ultrasonic nondestructive evaluation methods. This paper proposes the use of a nonlinear ultrasonic method, namely, nonlinear resonant ultrasonic spectroscopy (NRUS) for the measurement of nonlinearity parameters for stress monitoring. An experiment compared the use of NRUS method and a linear ultrasonic method, namely, ultrasonic pulse velocity (UPV) to study the effects of continuously increasing loads and cyclic loads on the nonlinearity parameter. Both NRUS and UPV methods found a similar direct relationship between load level and that parameter. The NRUS method showed a higher sensitivity to micro-structural changes of concrete than UPV method. Thus, the experiment confirms the possibility of using the nonlinear ultrasonic method for stress state monitoring of concrete members.

• Journal of the Korean Society for Nondestructive Testing
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• v.27 no.6
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• pp.576-581
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• 2007

Ultrasonic nonlinearity has been considered as a promising method to evaluate the micro damage of material; however, its magnitude is so small that its measurement is not easy. Especially, when we use contact PZT transducer, if the contacting pressure is not kept in constant during the measurement then there exists extraneous fluctuation in the measured nonlinearity caused by the unstable contact condition, In this paper, we developed a pneumatic control system to keep the contacting pressure of transducer in constant during the measurement and analyzed the effect of contacting pressure to the ultrasonic nonlinearity measurement As a result, we found that the pressure of transducer in our measurement system should be greater than 170 kPa to measure the ultrasonic nonlinear parameter in stable with no dependency on the contacting pressure.

• Journal of the Korean Society for Nondestructive Testing
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• v.33 no.1
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• pp.1-6
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• 2013

Ultrasonic guided wave techniques have been widely used for long range nondestructive detection in tube-like structures. The present paper investigates the ultrasonic linear and nonlinear parameters for evaluating the thermal damage in aluminum pipe. Specimens were subjected to thermal loading. Flexible polyvinylidene fluoride (PVDF) comb transducers were used to generate and receive the ultrasonic waves. The second harmonic wave generation technique was used to check the material nonlinearity change after different heat loadings. The conventional linear ultrasonic approach based on attenuation was also used to evaluate the thermal damages in specimens. The results show that the proposed experimental setup is viable to assess the thermal damage in an aluminum pipe. The ultrasonic nonlinear parameter is a promising candidate for the prediction of micro-damages in a tube-like structure.

• Journal of the Korean Society for Nondestructive Testing
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• v.34 no.3
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• pp.220-225
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• 2014

Generally, the nonlinearity of ultrasonic waves is measured using a nonlinear parameter ${\beta}$, which is defined as the ratio of the second harmonic's magnitude to the power of the fundamental frequency component after the ultrasonic wave propagates through a material. Nonlinear parameter ${\beta}$ is recognized as an effective parameter for evaluating material degradation. In this paper, we evaluated the nonlinear parameter of Al6061-T6 which had been subjected to an artificial aging heat treatment. The measurement was using the transmitted signal obtained from contact-type transducers. After the ultrasonic test, a micro Vickers hardness test was conducted. From the result of the ultrasonic nonlinear parameter, the microstructural changes resulting from the heat treatment were estimated and the hardness test proved that these estimates were reasonable. Experimental results showed a correlation between the ultrasonic nonlinear parameter and microstructural changes produced by precipitation behavior in the material. These results suggest that the evaluation of mechanical properties using ultrasonic nonlinear parameter ${\beta}$ can be used to monitor variations in the mechanical hardness of aluminum alloys in response to an artificial aging heat-treatment.

• Journal of the Korean Society for Nondestructive Testing
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• v.30 no.4
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• pp.345-351
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• 2010

The oblique incidence technique for ultrasonic nonlinear characterization was studied in stainless steel 316L alloy subjected to high cycle fatigue. A dog-bone plate specimen was prepared to make different faitgue-driven deformation at each position where the stress concentration could occur in the middle of specimen. In addition to the normal transmission technique, the oblique incidence technique which is newly suggested in this study, was used to measure ultrasonic nonlinear parameter. The fatigued specimen shows higher ultrasonic nonlinear parameter than the virgin specimen for both techniques. Ultrasonic nonlinear parameter highly increases in the middle of test specimen where the stress concentration existes. Relative nonlinear parameter has strong correlation with fatigue damage. Consequently, the oblique incidence technique with longitudinal wave can be potential to characterize high cycle fatigue damage.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.10
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• pp.1133-1137
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• 2014

The ultrasonic nonlinear parameter ${\beta}$ is generally known as an effective parameter for evaluating material degradation. Thus far, most research has been conducted using a contact method. However, since measurement by this contact method is affected by the contact conditions between the transducer and the specimen, additional devices are required to maintain the contact conditions stable during the measurement. To avoid this inconvenience, this paper proposes a noncontact method. In this study, only the receiver was replaced with a noncontact receiver, and then, the ultrasonic nonlinear parameters measured by the newly developed noncontact receiver were compared with those measured by the contact receiver. Results obtained using both these receivers for heat-treated aluminum alloy specimens showed good agreement. From this result, we can confirm that the ultrasonic nonlinear parameter ${\beta}$ can be measured using the proposed noncontact ultrasonic method.

• Nuclear Engineering and Technology
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• v.52 no.3
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• pp.621-625
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• 2020

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.

• Journal of the Korean Society for Nondestructive Testing
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• v.28 no.4
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• pp.358-363
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• 2008

Ultrasonic nonlinearity has been considered as a promising method to evaluate the micro damage of material; however, its magnitude is so small that its measurement is not easy. Thus, in this study, we investigate the effects of such experimental system dependent factors in the measurement of ultrasonic nonlinear parameter by using contact PZT transducer. Experimental results showed that the effect of system dependent nonlinearity is reduced when the contact pressure and transducer input voltage are sufficiently large. These results will be very useful to find out the proper experiment condition to measure rather accurate nonlinear parameter.

• Proceedings of the KSME Conference
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• 2001.11a
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• pp.222-227
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• 2001

Nonlinear acoustic effect has been considered as an effective tool for the evaluation of material degradation. In this paper, the applicability of nonlinear acoustic effect to the evaluation of degradation of 2.25Cr-1Mo steel is investigated. Firstly, a number of 2.25Cr-1Mo steel samples were heat-treated, and their damage mechanism was examined. Secondly, Ultrasonic nonlinear parameter was measured. Nonlinear acoustic parameter was found to be clearly sensitive to the material degradation.