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Research Papers

On Mechanical Properties of Composite Sandwich Structures With Embedded Piezoelectric Fiber Composite Sensors

[+] Author and Article Information
Hari P. Konka1

Department of Mechanical Engineering,  Louisiana State University, Baton Rouge, LA 70803hkonka1@tigers.lsu.edu

M. A. Wahab

Department of Mechanical Engineering,  Louisiana State University, Baton Rouge, LA 70803

K. Lian

Center for Energy and Environmental Studies,  Southern University, Baton Rouge, LA 70813

1

Corresponding author.

J. Eng. Mater. Technol 134(1), 011010 (Dec 08, 2011) (12 pages) doi:10.1115/1.4005349 History: Received July 06, 2011; Revised October 10, 2011; Published December 08, 2011; Online December 08, 2011

The smart sandwich structures have been widely used in the aerospace, automobile, marine, and civil engineering applications. A typical smart sandwich structure is usually comprised of two stiff face skins separated by a thick core with variety of embedded sensors to monitor the performance of the structures. In this study, the smart composite sandwich structure (CSS) samples are fabricated with glass microballoons syntactic foam core and resin infused glass-fiber face skins (with piezoelectric fiber composite sensors (PFCS) embedded inside the resin infused glass-fiber face skins). One of the main concerns associated with embedding sensors inside composite structures is the structural continuity, compatibility, and interface stress concentrations caused by the significant differences in material property between sensor and host structures. PFCS are highly flexible, easily embeddable, highly compatible with composite structures and their manufacturing processes, which makes them ideal for composite health monitoring applications. In this study, in-plane tensile, tension–tension fatigue, short beam shear, and flexural tests are performed to evaluate the effect on strengths/behavior of the CSS samples due to embedded PFCS. Then carefully planned experiments are conducted to investigate the ability of the embedded PFCS to monitor the stress/strain levels and detect damages in CSS using modal analysis technique. The tensile tests show that both the average ultimate strength and the modulus of elasticity of the tested laminate with or without embedded PFCS are within 7% of each other. The stress–life (S-N) curves obtained from fatigue tests indicates that the fatigue lives and strengths with and without the PFCS are close to each other as well. From short beam and flexural test results, it is observed that embedded PFCS leads to a reduction of 5.4% in the short beam strength and 3.6% in flexural strength. Embedded PFCS’s voltage output response under tension–tension fatigue loading conditions has been recorded simultaneously to study their ability to detect the changes in input loading conditions. A linear relationship has been observed between the changes in the output voltage response of the sensor and changes in the input stress amplitude. This means that by constantly monitoring the output response of the embedded PFCS, one could effectively monitor the magnitude of stress/strain acting on the structure. Experiments are also performed to explore the ability of the embedded PFCS to detect the damages in the structures using modal analysis technique. Results from these experiments show that the PFCS are effective in detecting the initiations of damages like delamination inside these composite sandwich structures through changes in natural frequency modes. Hence embedded PFCS could be an effective method to monitor the health of the composite sandwich structures’ in-service conditions.

Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Sandwich structure

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Figure 2

Defects and imperfections in sandwich structures [4]

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Figure 3

Schematics of (a) PFC and (b) macro fiber composite (MFC)

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Figure 4

(a) Final cured syntactic foam core; (b) scanning electron micrograph of syntactic foam

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Figure 5

Vacuum-assisted resin infusion bagging process used to laminate skins directly on the syntactic foam slabs

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Figure 6

Details of the test specimen for tensile test

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Figure 7

Sample mounted on 810-MTS universal testing machine

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Figure 8

Load versus displacement response for the specimens

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Figure 9

Microscopic images of final failure regions of the specimens at the end of tensile test

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Figure 10

Ultimate strength, failure strain, and Young’s modulus of the composite sandwich structures specimens with and without embedded sensor

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Figure 11

Fatigue life for the different specimens

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Figure 12

The horizontal shear load diagram for short beam strength test as per ASTM standard D 2344/D 2344 M

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Figure 13

Short beam test experimental setup

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Figure 14

Details of the test specimen for short beam strength test

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Figure 15

Load versus displacement response for the specimens

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Figure 16

Short beam strength and failure strain of the composite specimens with and without embedded sensor

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Figure 17

Microscopic images of failure regions of the different specimens after short-beam strength test

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Figure 18

The three-point bend test setup

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Figure 19

Load versus displacement curves obtained from the flexural testing

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Figure 20

Bending strength and failure strain of the composite specimens with and without embedded sensor

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Figure 21

Failure of the different specimens after the short-beam strength test

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Figure 22

Experimental setup

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Figure 23

Voltage output response from embedded PFCS (MFC), when the specimen is loaded at different stress ratios

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Figure 24

Voltage output response from embedded PFCS (MFC and PFC), when the specimen is loaded at different σmax and maintaining σmin  = 1 MPa (constant)

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Figure 25

Experimental setup for the modal analysis

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Figure 26

The typical output response of the PFCS (MFC) when the tip of the cantilever is displaced to about 0.5 in

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Figure 27

Changes in the mode-1 and mode-2 natural frequencies of composite sandwich structure beam with various levels of delamination (between the top face skin and core) assessed by the PFCS output response

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