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Research Papers: NDE

Improved Imaging of Fatigue Crack Profile in Thick Cruciform Samples Using Ultrasonic Phased Array Models

[+] Author and Article Information
S. Alavudeen, C. V. Krishnamurthy

Department of Mechanical Engineering, Centre for Non Destructive Evaluation, IIT Madras, Chennai 600 036, India

Krishnan Balasubramaniam1

Department of Mechanical Engineering, Centre for Non Destructive Evaluation, IIT Madras, Chennai 600 036, Indiabalas@iitm.ac.in

D. M. Pugazhendhi, G. Raghava, P. Gandhi

Fatigue Testing Laboratory, Structural Engineering Research Centre, Taramani, Chennai 600 113, India

1

Corresponding author.

J. Pressure Vessel Technol 132(1), 011501 (Dec 23, 2009) (8 pages) doi:10.1115/1.4000375 History: Received May 29, 2009; Revised September 10, 2009; Published December 23, 2009; Online December 23, 2009

The determination of depth profile of vertical fatigue cracks generated in thick cruciform samples using an ultrasonic phased array is investigated in this paper. The cracks were formed by conducting fatigue fracture test on two mild steel cruciform specimens of 135 mm thickness: one under room temperature and the other under subzero temperature (70°C). A semi-elliptical surface starter notch of 2 mm width and more than 400 mm length was initially created in the specimens. Alternating current potential drop technique and phased array ultrasonic technique were attempted in order to determine the depth profiles of the starter notch as well as that of the crack. Virtual experiments carried out with a finite-difference time domain based numerical model were found to be advantageous in reducing actual experimental trials, facilitate an understanding of the echo signatures, and help assess the crack depth. The profiles of the crack and the notch were verified through destructive assay of the samples and subsequent dye penetrant assisted physical measurements.

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Figures

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Figure 1

Schematic of the cruciform sample

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Figure 2

Cross section of the starter notch

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Figure 3

Schematic of the fracture test arrangement

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Figure 4

Schematic of the phased array system

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Figure 5

Schematic of the geometry and boundary conditions used in numerical simulation

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Figure 6

Screen shot of wave propagation inside the cruciform specimen

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Figure 7

Comparison of experimental and simulated B-scans

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Figure 8

The photos of the cruciform specimen

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Figure 9

Comparison of crack depth in subzero temperature sample determined from phased array UT readings and destructive assay

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Figure 10

Comparison of crack depth in room temperature sample determined from phased array UT readings and destructive assay

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Figure 11

Part of the finite-difference grid

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Figure 12

Time delay calculation for linear phased array

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