This paper describes a new nonlinear ultrasonic (NLU) technique for creep damage characterization. Traditionally, nonlinear material response is evaluated at high amplitude levels. The present paper evaluates the nonlinear response of samples at much lower amplitude levels than used in any previous study of nonlinear material behavior. The newly observed nonlinear behavior occurs when dislocations are constrained between two quiescent lattice planes as defined by Cantrell. Three parameters are used to characterize the low amplitude nonlinear response during the progression of creep damage in 99.98% pure copper specimens studied here; these are parameters that characterize (a) the static displacement, (b) the second harmonic and (c) the third harmonic components of the ultrasonic through-transmitted signal. Various features of the received NLU amplitude vs. input amplitude to the ultrasonic transducer were observed to correlate well with micro-void concentrations caused by creep damage. © 2010 Elsevier Inc. All rights reserved.

Krishnan Balasubramaniam

Department of Mechanical Engineering

Raghu V. Prakash

Jitendra S. Valluri

CREEP DAMAGE

CREEP DAMAGES

HIGH AMPLITUDES

LATTICE PLANE

LOW AMPLITUDE

Non-linear response

Nonlinear behavior

NONLINEAR MATERIAL BEHAVIOR

NONLINEAR MATERIALS

NONLINEAR ULTRASONIC

PURE COPPER

Second harmonics

STATIC DISPLACEMENT

THIRD HARMONIC COMPONENTS

Three parameters

Transmitted signal

Copper

Ultrasonic testing

Ultrasonic transducers

Ultrasonics

Creep

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IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Materials Characterization

Higher harmonic generation using nonlinear ultrasonic is known to be very sensitive to microstructural degradation. This technique relies on nonlinear stress-strain relation i.e. nonlinear Hooke's law. The quantitative measurement to characterize the materials degradation is done by the nonlinear ultrasonic parameter, β. The objective of this work is to use nonlinear ultrasonic using Lamb wave to evaluate creep damage in modified 9Cr–1Mo steel. Relative change in β was seen to be dependent on the higher order elastic constants that evolve with microstructure as creep progresses as well as sub-structural changes. The extent of damage in the material due to creep exposure was evaluated by Kernel Average Misorientation (KAM) from EBSD and co-related with nonlinear acoustic parameter. © 2019 Elsevier Ltd

NDT and E International

Nonlinear Lamb wave for the evaluation of creep damage in modified 9Cr–1Mo steel

In this work grain growth associated with isochronous annealing in polycrystalline pure copper is studied using nonlinear ultrasonic method. In isochronous annealing, holding time is constant but annealing temperatures vary. It is observed that, grain growth due to isochronous annealing significantly influences the ultrasonic nonlinearity parameter, β. A decrease in nonlinearity parameter with increase in grain size is noticed. Further, micro-hardness measurements as well as metallographic results are presented to underscore the utility of the nonlinear ultrasonic method in gauging the progress of annealing. As the time and effort involved in this method is less, with suitable calibration, this method may be gainfully employed for determination of grain size on annealing. © 2015, Society for Experimental Mechanics.

Experimental Mechanics

An Experimental Investigation on the Influence of Annealed Microstructure on Wave Propagation

Sensitivity of nonlinear ultrasonic method towards isothermal annealing in pure copper is investigated in this study. It was reported that, recovery, recrystallization and grain growth associated with annealing has profound influence on nonlinearity parameter. Presence of precipitates and secondary phase particles, and its effect on nonlinearity parameter was considered by many authors. However, in this study, focus is on the influence of grain-growth on nonlinearity parameter. Variation of non-linearity parameter, β, with different holding durations were analyzed. All the samples were annealed at a temperature above its recrystallization temperature. Further, metallography studies as well as hardness measurements were performed to understand the relationship between microstructural changes and ultrasonic nonlinearity parameter. © 2014 AIP Publishing LLC.

AIP Conference Proceedings

Characterization of annealing in polycrystalline copper using harmonic generation technique

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. © The Chinese Society for Metals and Springer-Verlag Berlin Heidelberg.

Fulltext

Acta Metallurgica Sinica (English Letters)

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

This paper describes the use of non-linear ultrasonic techniques for the characterization of material degradation in 99.98% pure copper due to high-temperature creep. Flat dog-bone-shaped specimens were subjected to constant load creep testing at different stress and temperature levels. Creep damage progression was monitored by conducting continuous and interrupted mode creep tests. In the case of continuous loading non-linear ultrasonic (NLU) measurements were conducted after fracture at different locations along the gage length of the sample. For interrupted tests the NLU measurements were conducted on different creep life fractions, through periodic interruption of the creep test. In all cases a through transmission NLU measurement technique was employed. Three different non-linear measurements, namely static displacement, second harmonic and third harmonic, were taken and their responses compared. The NLU measurements were found to be significantly sensitive to the extent of creep damage (∼200-2500% of base level), while the linear ultrasonic measurements, representing the change in longitudinal velocities, were only in the range 10-30% for a comparable creep damage level. NLU measurements carried out on fractured samples suggest that the NLU response was locally high at locations where the creep damage was concentrated, compared with other locations, even within the gage length of the specimen. This was confirmed using micrograph observations. Of the three non-linear measurements, the third harmonic data was most sensitive to creep damage. © 2009 Acta Materialia Inc.

Acta Materialia

Creep damage characterization using non-linear ultrasonic techniques

Recent experimental results showing the pulse width independence and the flat topped shape of static displacement generated during finite amplitude sinusoidal ultrasonic tone burst propagation in solids and the contradicting previous results reported in the literature are considered. The pulse width independence is analytically confirmed and the flat topped shape is explained by considering the progressive spatial and time domain shapes of the static strain and displacement pulses. A numerical simulation of the finite amplitude longitudinal ultrasonic wave propagation in solids has been performed to further verify the pulse width independence of the static displacement pulse. © 2009 American Institute of Physics.

Journal of Applied Physics

Issues on the pulse-width dependence and the shape of acoustic radiation induced static displacement pulses in solids

This paper deals with nonlinear domains (second harmonic amplitude) in order to evaluate creep damage in titanium alloy. Creep damage has been observed in the form of microvoids at primary α/transformed β interface and the volume fraction of voids increases progressively with creep deformation. A good agreement between the experimental results and metallographic studies indicate the usefulness of the method for in-service evaluation of creep damage. A nonlinear ultrasonic technique was found to be significantly more sensitive for the assessment of creep damage. © 2008 Acta Materialia Inc.

Scripta Materialia

Creep damage assessment in titanium alloy using a nonlinear ultrasonic technique

Nonlinear ultrasonic (NLU) harmonic generation system was used to characterize the fatigue damage in a flat hour-glass, high strength Al-Cu-Zn-Mg alloy, AA7175-T7351 specimens. Experiments were carried out to introduce controlled levels of fatigue damage under constant amplitude loading to determine the NLU response using surface acoustic wave (or Rayleigh mode) at regular intervals of fatigue life. The NLU parameter (A2 / 12) plotted as a function of percentage of fatigue life shows two peaks for all the samples tested, independent of the amplitude of fatigue loading. The first peak appeared between 40%-50% of fatigue life and the second peak between 80%-90% of fatigue life. Among the two flat surfaces of the specimen, a higher nonlinearity response was observed on the surface which had the first crack initiation. The appearance of two peaks in the nonlinear response during fatigue damage progression is explained based on the dislocation dynamics and dislocation-crack interaction present in the specimens during the fatigue process. © 2008 American Institute of Physics.

Fatigue damage characterization using surface acoustic wave nonlinearity in aluminum alloy AA7175-T7351

A simplified experimental technique to measure the acoustic radiation induced static strain during the longitudinal acoustic wave propagation in solids is proposed. Experiments have been carried out to extract the static displacement (dc) component without resorting to electronic filters, as in the case of previously reported experimental measurements. This prevents the influence of the filter time response characteristics on the measurement. The dependence of the static displacement amplitude on the square of the fundamental amplitude of the input wave, its being independent of the burst width of the tone burst, and its abnormal variation at low input amplitudes are reported. © 2007 American Institute of Physics.

Applied Physics Letters

Simplified experimental technique to extract the acoustic radiation induced static strain in solids

Creep damage characterization using a low amplitude nonlinear ultrasonic technique

Journal	Materials Characterization
ISSN	10445803
Open Access	No