Ultrasonic Nonlinearity Parameter Research Articles

인공시효된 Al6061-T6의 초음파 비선형 특성 평가

Abstract Generally, the nonlinearity of ultrasonic waves is measured using a nonlinear parameter  , 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  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

Characterisation of microstructural damage evolution during tensile deformation of a near-α titanium alloy: Effects of microtexture

The evolution of microstructural damage during tensile deformation of a near-α titanium alloy has been characterised using nonlinear ultrasonic (NLU) parameters. Evolution of the damage state in the interrupted tensile specimens at different strain levels has been correlated with the second-order (NLU) parameter. It is shown that the second-order ultrasonic parameter does not change monotonically with increasing strain. The variation in (NLU) parameters is shown to be a function of both the density of dislocation substructure and the preferred crystallographic orientations that evolve during tensile deformation. The presence of microtexture predominantly affects the harmonics generation from the dislocation substructure. A physical basis for the above observation has been established using a dislocation string vibration model. Infrared thermal imaging has been used to map the evolution of damage along the gauge length of the specimens to take into account the in-homogeneities of deformation.

Non-linear ultrasonic response of plastically deformed aluminium alloy AA 7009

Using non-linear longitudinal wave and non-linear surface wave, the effect of plastic deformation on the non-linear ultrasonic parameter of aluminium alloy AA 7009 was studied. The results reveal that the second-order non-linear coefficient () increased with increasing the plastic strain for both types of non-linear waves. A simple power–law relation was developed between the ratio of and the plastic strain. The stress exponent index was found to be ∼2·35 and 1 for the non-linear longitudinal wave and the non-linear surface wave respectively. The difference of the non-linear ultrasonic responses was likely due to the microstructural difference between the near surface material and the material far away from the surface.

Nonlinear wave propagation in constrained solids subjected to thermal loads

Abstract The classical mathematical treatment governing nonlinear wave propagation in solids relies on finite strain theory. In this scenario, a system of nonlinear partial differential equations can be derived to mathematically describe nonlinear phenomena such as acoustoelasticity (wave speed dependency on quasi-static stress), wave interaction, wave distortion, and higher-harmonic generation. The present work expands the topic of nonlinear wave propagation to the case of a constrained solid subjected to thermal loads. The origin of nonlinear effects in this case is explained on the basis of the anharmonicity of interatomic potentials, and the absorption of the potential energy corresponding to the (prevented) thermal expansion. Such “residual” energy is, at least, cubic as a function of strain, hence leading to a nonlinear wave equation and higher-harmonic generation. Closed-form solutions are given for the longitudinal wave speed and the second-harmonic nonlinear parameter as a function of interatomic potential parameters and temperature increase. The model predicts a decrease in longitudinal wave speed and a corresponding increase in nonlinear parameter with increasing temperature, as a result of the thermal stresses caused by the prevented thermal expansion of the solid. Experimental measurements of the ultrasonic nonlinear parameter on a steel block under constrained thermal expansion confirm this trend. These results suggest the potential of a nonlinear ultrasonic measurement to quantify thermal stresses from prevented thermal expansion. This knowledge can be extremely useful to prevent thermal buckling of various structures, such as continuous-welded rails in hot weather.

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

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.

Comparative Study of Linear and Nonlinear Ultrasonic Techniques for Evaluation Thermal Damage of Tube-Like Structures

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.

Fused Silica와 Al2024-T4의 비선형 파라미터 측정

금속 재료의 비선형 파라미터는 고유한 물성치로서 기본주파수의 음압의 크기(<TEX>$A_1$</TEX>)과 2차고조파의 음압의 크기(<TEX>$A_2$</TEX>)을 측정하면 산정할 수 있다. 하지만, 실험적으로 <TEX>$A_1$</TEX>과 <TEX>$A_2$</TEX>를 측정하는 것은 매우 복잡한 변환 과정이 필요하기 때문에 현재 많은 연구자들이 비선형 파라미터의 절대값을 측정하지 않고, 전압 변화를 관찰하는 비선형 파라미터의 상대값을 측정하고 있다. 하지만, 비선형 파라미터 상대값으로는 재료의 물성치를 대변할 수가 없기 때문에, 열화도에 따른 시편 측정에만 사용할 수 있는 제약이 있다. 따라서 본 연구에서는 정전용량 측정기법(capacitive detector)보다는 비용이 적게 소모되고 현장 적용이 가능한 압전형 수신기법(piezoelectric detection)을 이용하여 비선형 파라미터의 절대값을 측정하기 위한 시스템을 구축하였다. <TEX>$A_1^2vsA_2$</TEX> 그래프로 시스템의 선형성을 검증하고 시험편인 fused silica와 Al2024-T4에 대한 비선형 파라미터를 측정하였다. Nonlinearity parameter is an inherent property of materials measuring fundamental acoustic amplitude(<TEX>$A_1$</TEX>) and second harmonic amplitude(<TEX>$A_2$</TEX>). However, measurement of <TEX>$A_1$</TEX> and <TEX>$A_2$</TEX> has complex calibration procedure, many researchers prefer to measure relative nonlinearity parameter rather than absolute nonlinearity parameter. But, relative nonlinearity parameter is only detect materials degradation with various degradation samples, it is limited application in determining third order elastic constants of materials. Therefore, in this study, the piezoelectric detection method is adopted to measure absolute nonlinearity parameter due to experimental simplicity compare to capacitive detector. Linearity of measurement system is verified by <TEX>$A_1^2vsA_2$</TEX> plot, and we measured ultrasonic nonlinearity parameters of fused silica and Al2024-T4.

Research on Improvement the Second Harmonic Signal to Noise Ratio Using Pulse-Inversion Technique

Material degradation is usually preceded by nonlinear ultrasonic, and higher harmonics will be generated. The project studied the method to improve the second harmonic signal to noise ratio with pulse-inversion technique. A finite element method model of nonlinear was established by a special element which account for a nonlinear stress-strain relation. Calculation was performed for the influence of the pulse-inversion technique to ultrasonic nonlinearity parameters. The simulation results show that the second harmonic signal to noise ratio is obviously improved. Measurement method of nonlinearity parameters and signal processing algorithms with pulse-inversion technique were established, and a robust experimental procedure was developed. Using this method, ultrasonic nonlinearity parameters of a group of LY12 aluminum samples stretched were measured. The experimental results show that the pulse-inversion technique is very efficient in extracting this second-harmonic amplitude by canceling out the odd harmonics which are mainly due to the instrumentation. Introduction

Scatter in nonlinear ultrasonic measurements due to crystallographic orientation change induced anisotropy in harmonics generation

Present study endeavors to establish the physical basis of an unprecedented trend in scatter, observed in nonlinear ultrasonic (NLU) parameter, associated with varying degree of crystallographic orientation change across crystallites in a polycrystalline material. It is shown that this scatter arises due to anisotropy in harmonics generation as a result of orientation change of slip systems in polycrystals with respect to the wave propagation direction. A near α titanium alloy has been taken as a model alloy to demonstrate this effect of crystallographic orientation change vis-à-vis change in the orientation of slip systems. Scale of crystal orientation change is shown to have a strong correlation with the degree of scatter in NLU measurements. Further, the study establishes the dominating effect of the scale of crystalline orientation change on harmonics generation as compared to variation in other microstructural parameters such as dislocation density, interface structure etc. Frequency distribution analysis of the scatter indicates that the distribution depends on the colony size which exhibits a linear correlation with standard deviation value. The dislocation string vibration model has been extended for harmonics generation in polycrystalline aggregates to explain the trend in the scatter during measurement of NLU parameter in the material.

Creep Characterization in Advanced Heat-Resistant Steel Using Ultrasonic Nonlinearity Technique

The creep of heat-resistant steel (12Cr­3.45W alloy) is experimentally characterized to estimate damages using a nonlinear ultrasonic technique. The finite amplitude method has been used to measure the ultrasonic nonlinearity parameter in all creep damaged specimens by through transmitted longitudinal wave. The microstructure showed significant changes in precipitate size and dislocation density during creep. The normalized ultrasonic nonlinearity decreases significantly in stage I and decreases monotonously in stage II and stage III. However, the ultrasonic nonlinearity increase due to the formation of creep voids in the vicinity of the creep failure region. The correlation between the microstructural changes and ultrasonic nonlinearity is discussed. [doi:10.2320/matertrans.M2012146]

Nonlinear ultrasonic characterizing online fatigue damage and in situ microscopic observation

A robust experimental procedure was developed, by which the evolution of fatigue damage in AZ31 magnesium alloy was tracked online with the ultrasonic nonlinearity parameter β. β values of three sets of samples under different stress levels were measured. Microstructures of specimens at different fatigue stages were observed in situ by optical microscopy. The experimental results show that there is a significant increase in β linked to the accumulation of persistent slip bands (PSBs) and micro-cracks at the early stages of fatigue life and reaches the maximum, about 55% of fatigue life. Ultrasonic attenuation coefficient increases with the expanding of micro-cracks and leads to β decrease slightly after 55% of fatigue life. The variation of β with fatigue cycles is in good agreement with the growth of PSBs and micro-cracks. In addition, it has no significant effect on the experimental results for the changes of low- and high-cycle fatigue and the fatigue mode with tension-tension and tension-compression.

Fatigue Damage Characterization of Magnesium Thick Plate Using Nonlinear Rayleigh Wave

In order to extend engineering application of nonlinear ultrasonic nondestructive testing technique in wave structure, an experimental technique for excitation and reception directly of Rayleigh wave by fixing piezoelectric sensor on the edge of the specimen is presented. Using the experimental system and procedure, the surface fatigue damage of AZ31 magnesium thick plate is detected by nonlinear Rayleigh waves. Although the experimental results have some dispersion, the ultrasonic nonlinearity parameters overall increase apparently with the fatigue cycles increasing, which demonstrates the Rayleigh wave nonlinearity parameters are sensitive for the changes of microscopic defects in the materials internal, and the experimental system and procedure are reliable. The Rayleigh wave nonlinearity parameters for the thick plate structure fatigue life prediction have potential engineering applications.

Simulation and Experiment of Fatigue Damage Detection in Magnesium Thick Plate Using Nonlinear Rayleigh Wave

In order to extend engineering application of nonlinear ultrasonic nondestructive testing technique in wave structure,an experimental technique for excitation and reception directly of Rayleigh wave by fixing piezoelectric sensor on the edge of the specimen is presented,this method is verified by simulation of the finite element method(FEM).By using the experimental system and procedure,cumulative effect of nonlinear Rayleigh waves is proved,nonlinearity parameters nearly linear increase with Rayleigh wave propagation distance increasing,which demonstrates the Rayleigh wave nonlinearity parameters are sensitive for the changes of microscopic defects in the materials internal,and the experimental system and procedure are reliable.Finally,the surface fatigue damage of AZ31 magnesium thick plate is detected by nonlinear Rayleigh waves.Although the experimental results have some dispersion,the ultrasonic nonlinearity parameters overall increase apparently with the fatigue cycles increasing,which shows the Rayleigh wave nonlinearity parameters for the thick plate structure fatigue life prediction have potential engineering applications.

Effect of microstructure on non-linear behavior of ultrasound during low cycle fatigue of pearlitic steels

Influence of microstructural changes on the second harmonics of sinusoidal ultrasonic wave during low cycle fatigue (LCF) deformation in pearlitic steel was studied. Fatigue tests were interrupted and at every interruption, non-linear ultrasonic (NLU) parameter (β) was determined. Microstructures of cyclically deformed specimens at various cycles were examined by transmission electron microscopy (TEM). The variation of β with fatigue cycles was correlated with the microstructural changes and the results were explained through the variation in dislocation morphology and carbon content of the steel.

A study on precipitation characteristics induced strength variation by nonlinear ultrasonic parameter

Nonlinear ultrasonic study has been carried out to characterize the variation in strength induced by precipitation characteristics. An age hardenable aluminum alloy has been taken as a model alloy for the present investigation. It is shown that the second order nonlinear ultrasonic (NLU) parameter scales with strength property that in turn depends on coherent to incoherent precipitation phase transition. The observed variations in NLU parameter has been explained by modifying an existing dislocation-coherent precipitate interaction model for harmonics generation in order to account for a weaker dislocation-semicoherent precipitate interaction. The model proposed can in general be applicable to all precipitation hardenable alloy systems undergoing coherent to incoherent precipitate phase transition.

Nondestructive assessment of tensile properties of cold worked AISI type 304 stainless steel using nonlinear ultrasonic technique

A new approach based on nonlinear ultrasonic (NLU) technique is presented for nondestructive evaluation of yield strength and tensile strength of cold worked AISI type 304 stainless steel (SS). In this approach, the ultrasonic harmonics generated in cold worked stainless steel, as a result of interaction of ultrasonic wave with dislocations and substructural changes, are measured precisely and the nonlinear ultrasonic parameter, β is determined. A quadratic relationship, with a correlation coefficient better than 0.99, is found between the yield strength and the β parameter as well as between the tensile strength and β parameter of the cold worked specimens. The observed behavior is explained based on microscopy, variations in martensite volume fraction and dislocation density determined from X-ray diffraction profile analysis. The proposed approach can be effectively used for nondestructively ensuring the uniformity of tensile properties of steel components on shop-floor during various stages of manufacturing and also as feedback module in intelligent processing of materials concept.

Microstructural characterization of M250 grade maraging steel using nonlinear ultrasonic technique

Nonlinear ultrasonic (NLU) technique is used for characterization of microstructures in M250 grade maraging steel subjected to solution annealing at 1093 K for 1 h followed by ageing at 755 K for various ageing durations in the range from 0.25 to 100 h. Using pulse inversion technique, feeble second harmonic is extracted to determine nonlinear ultrasonic parameter, β, and the relative β parameter (RBP) which is the ratio of β parameter of the precipitation hardened specimen to that of the solution annealed specimen. Normalized mean square strain, volume fraction of reverted austenite and hardness have been measured and transmission electron microscopy (TEM) has been carried out to understand the microstructural changes that occur during ageing and to study the correlation between these measured parameters. Hardness and normalized mean square strain are found to increase during initial stages of ageing due to precipitation of intermetallics and decrease at longer durations due to formation of reverted austenite and coarsening of precipitates. This study establishes that NLU technique can be used for non-destructive characterization of ageing behaviour of M250 grade maraging steel.

Electric field dependence of nonlinearity parameters and third order elastic constants of 0.70Pb(Mg1/3Nb2/3)O3–0.30PbTiO3 single crystal

Through second harmonic measurements, the ultrasonic nonlinearity parameters of [001](c) and [111](c) polarized 0.70Pb(Mg(13)Nb(23))O(3)-0.30PbTiO(3)(PMN-0.3PT) single crystals have been measured as a function of bias electric field. It was found that the nonlinearity parameter increases almost linearly with field at low field but shows a drastic increase near the coercive field. The [111](c) polarized single domain crystal has much smaller nonlinearity parameter than that of the [001](c) polarized multidomain crystal. Based on effective symmetries of these crystals, we were able to derive the field dependence of several third order elastic constants, which are important parameters for high field applications.

Nonlinear ultrasonics for in situ damage detection during high frequency fatigue

In this paper, we report the use of the feedback signal of an ultrasonic fatigue system to dynamically deduce fatigue damage accumulation via changes in the nonlinear ultrasonic parameter. The applicability of this parameter in comparison to the resonant frequency for assessment of fatigue damage accumulation in a wrought aluminum alloy has been demonstrated, without the need for coupling fluids or independent generation of incident ultrasonic waves. The ultrasonic nonlinearity increased and the resonant frequency of the system decreased with initiation and propagation of the major crack. The nonlinear ultrasonic parameter shows greater sensitivity to damage accumulation than the resonant frequency. The number of cycles for crack propagation, estimated based on the changes in the nonlinear ultrasonic parameter, is in very good agreement with calculated crack growth rates based on the fractography studies.

Observation of two stage dislocation dynamics from nonlinear ultrasonic response during the plastic deformation of AA7175-T7351 aluminum alloy

Systematic nonlinear ultrasonic (NLU) studies using longitudinal and guided surface acoustic waves (SAW) were conducted on AA7175-T735 aluminum alloy specimens that were plastically deformed to varying levels of residual strain. The variation of nonlinear ultrasonic (NLU) parameter ( A 2 / A 1 2 ) as a function of residual plastic deformation, suggests an increase in NLU parameter at a slow rate up to a certain level of deformation and thereafter there is a significant increase in NLU parameter with further increase in the strain level. X-ray diffraction methods to characterize line broadening and etch pit dislocation distribution studies suggest that the smaller rate of increase in NLU parameter could be due to the increase in the dislocation density and higher rate of increase could be caused by formation of cellular dislocation pattern. Thus, our study shows that it is possible to study the two stage dislocation dynamics observed during residual plastic deformation of Al alloy 7175-T7351 using nonlinear ultrasonic technique.