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Research Papers

Experimental Investigations Into Nonlinear Vibro-Acoustics for Detection of Delaminations in a Composite Laminate

[+] Author and Article Information
Ashish Kumar Singh

Department of Mechanical Engineering,
National University of Singapore,
9 Engineering Drive 1,
Singapore 117575

Vincent B. C. Tan

Department of Mechanical Engineering,
National University of Singapore,
9 Engineering Drive 1,
Singapore 117575
e-mail: mpetanbc@nus.edu.sg

Tong Earn Tay, Heow Pueh Lee

Department of Mechanical Engineering,
National University of Singapore,
9 Engineering Drive 1,
Singapore 117575

1Corresponding author.

Manuscript received March 22, 2018; final manuscript received August 2, 2018; published online September 17, 2018. Assoc. Editor: Hoon Sohn.

ASME J Nondestructive Evaluation 2(1), 011002 (Sep 17, 2018) (11 pages) Paper No: NDE-18-1015; doi: 10.1115/1.4041122 History: Received March 22, 2018; Revised August 02, 2018

In recent years, nonlinear vibro-acoustic methods have shown potential to identify defects which are difficult to detect using linear ultrasonic methods. However, these methods come with their own challenges such as frequency dependence, requirement for a high excitation amplitude, and difficulties in distinguishing nonlinearity from defect with nonlinearity from other sources to name a few. This paper aims to study the dependence of nonlinear vibro-acoustic methods for detection of delaminations inside a composite laminate, on the excitation methods and excitation frequencies. It is shown that nonlinear vibro-acoustic methods are highly frequency dependent and commonly used excitation signals which utilize particular values of excitation frequencies might not always lead to a clear distinction between intact and delaminated regions of the specimen. To overcome the frequency dependence, signals based on frequency sweep are used. Interpretation of output response to sweep signals to identify damage is demonstrated using an earlier available approach, and a simpler approach is proposed. It is demonstrated that the damage detection with sweep signal excitations is relatively less dependent on excitation frequency than the conventional excitation methods. The proposed interpretation technique is then applied to specimens with delamination of varying sizes and with delaminations at different depths inside the laminate to demonstrate its effectiveness.

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Figures

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Fig. 1

Geometry of the specimen for the experiment: composite laminate (bigger square), input transducer (larger circle), output transducers (smaller circles), and delaminations (smaller squares)

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Fig. 2

Time of flight (ToF) images (C-scans) of the two delaminations. Left: top delamination; right: bottom delamination.

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Fig. 3

Schematic diagram of the experimental setup of the procedure (not to scale)

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Fig. 4

Amplitude (V) of the output transducers for a typical SFE test. Top: time domain; bottom: frequency domain.

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Fig. 5

Measured values from the frequency domain results for the four output transducers for SFE tests

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Fig. 6

Amplitude (V) of the output transducers for a typical VAM test. Top: time domain and bottom: frequency domain.

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Fig. 7

Measured values from the frequency domain results for the four output transducers for VAM tests with different pump frequencies

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Fig. 8

Measured values from the frequency domain results for the four output transducers for VAM tests with different probe frequencies

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Fig. 9

Amplitude (V) of the output transducers for a typical SSM test. Top: higher amplitude; middle: two times of the lower excitation and bottom: difference between the two.

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Fig. 10

Damage index for various frequency ranges for the SSM tests

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Fig. 11

Amplitude (V) of the four output transducers for a typical Sweeping harmonics method (SHM) test. Top: time domain and bottom: frequency domain.

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Fig. 12

Measured values from the frequency domain results for the four output transducers for SHM tests

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Fig. 13

Specimen with varying delamination sizes of 45 × 45 mm2 (below transducer 1), 40 × 40 mm2 (below transducer 2), and 35 × 35 mm2 (below transducer 3)

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Fig. 14

Measured values from the frequency domain results for the four output transducers for SHM tests for specimen with varying delamination sizes

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Fig. 15

Specimen with varying delamination depths of 4 (below transducer 2), 8 (below transducer 1), and 12 plies (below transducer 3) within the laminate

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Fig. 16

Measured values from the frequency domain results for the four output transducers for SHM tests for specimen with varying delamination depths

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