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

Krishnan Balasubramaniam

Department of Mechanical Engineering

Avijit Kr Metya

acoustics

elastic constants

Stress-strain curves

Surface waves

Ultrasonic applications

Ultrasonic waves

CREEP DAMAGES

KERNEL AVERAGE MISORIENTATION (KAM)

NON-LINEAR ULTRASONIC

Nonlinear Lamb waves

THIRD ORDER ELASTIC CONSTANTS

Creep

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IIT Madras

NDT and E International

Abstract Nonlinear Lamb wave was used to analyse the effect of tempering temperature on modified 9Cr-1Mo (P91) steel. As-received material was normalized at 1080°C and then tempered in temperature range of 600-850°C with a step size of 50°C for 1.5 h and followed by furnace cooling. Nonlinear ultrasonic parameter β was determined at each temperature using Lamb wave and correlated with microstructural characteristics like size of precipitate and density of dislocation. It was seen that acoustic nonlinearity parameter (β) was sensitive towards precipitate-matrix coherency strain, generated during tempering. © 2015 Elsevier Inc.

Materials Characterization

Effect of tempering temperatures on nonlinear Lamb wave signal of modified 9Cr-1Mo steel

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.

Creep damage characterization using a low amplitude nonlinear ultrasonic technique

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

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

Journal of Applied Physics

Creep damage characterization using nonlinear ultrasonic guided wave method: A mesoscale model

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

Journal	Data powered by TypesetNDT and E International
Publisher	Data powered by TypesetElsevier Ltd
ISSN	09638695
Open Access	No