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Research Papers

Creep Responses of Smart Sandwich Composites at Multiple Length Scales: Experiments and Modeling

[+] Author and Article Information
Anaïs Farrugia

Ecole Nationale Supérieure de Mécanique et d’Aérotechnique, 86961 Futuroscope Chasseneuil Cedex, France

Charles Winkelmann

Department of Mechanical and Aerospace Engineering, University of California, Davis, CA 95616

Valeria La Saponara1

Department of Mechanical and Aerospace Engineering, University of California, Davis, CA 95616vlasaponara@ucdavis.edu

Jeong Sik Kim

Texas A&M University, College Station, TX 77843

Anastasia H. Muliana1

Texas A&M University, College Station, TX 77843amuliana@neo.tamu.edu

1

Corresponding author.

J. Eng. Mater. Technol 133(1), 011008 (Dec 01, 2010) (6 pages) doi:10.1115/1.4002643 History: Received February 18, 2010; Revised July 13, 2010; Published December 01, 2010; Online December 01, 2010

Abstract

In service, composite structures present the unique challenge of damage detection and repair. Piezoelectric ceramic, such as lead zirconate titanate (PZT), is often used for detecting damage in composites. This paper investigates the effect of embedded PZT crystals on the overall creep behavior of sandwich beams comprising of glass fiber reinforced polymer laminated skins and polymer foam core, which could potentially be used as a damage-detecting smart structure. Uniaxial quasi-static and creep tests were performed on the glass/epoxy laminated composites having several fiber orientations, 0 deg, 45 deg, and 90 deg, to calibrate the elastic and viscoelastic properties of the fibers and matrix. Three-point bending creep tests at elevated temperature $(80°C)$ were then carried out for a number of control sandwich beams (no PZT crystal) and conditioned sandwich beams (with PZT crystals embedded in the center of one facesheet). Lateral deflection of the sandwich beams was monitored for more than 60 h. The model presented in this paper is composed by two parts: (a) a simplified micromechanical model of unidirectional fiber reinforced composites used to obtain effective properties and overall creep response of the laminated skins and (b) a finite element method to simulate the overall creep behavior of the sandwich beams with embedded PZT crystals. The simplified micromechanical model is implemented in the material integration points within the laminated skin elements. Fibers are modeled as linear elastic, while a linearized viscoelastic material model is used for the epoxy matrix and foam core. Numerical results on the creep deflection of the smart sandwich beams show good correlations with the experimental creep deflection at $80°C$, thus proving that this model, although currently based on material properties reported at room temperature, is promising to obtain a reasonable prediction for the creep of a smart sandwich structure at high temperatures.

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Figures

Figure 1

(a) Sandwich panel before resin infiltration with five pairs of visible PZTs under the red mesh. (b) Close-up of an embedded PZT after specimen’s cure. (c) Specimen with 0 deg orientation (shown from the arrow in the upper right corner). Note that the PZTs are slightly off-centered to avoid interference with boundaries and the tip of the dial indicator that would be applied at the center point of the average 177.8×50.8 mm2 beam. All dimensions in (c) are in mm.

Figure 2

Left: sketch of experimental set-up and right: actual fixture in the environmental chamber, allowing simultaneous testing of two specimens

Figure 3

Median creep displacements of control and treated specimens measured at the center of the bottom facesheet. Each box is the median of a group of specimens (five specimens each for 0_control, 90_control, 0_treated, and 90_treated, four specimens for 45_control, and three specimens for 45_treated).

Figure 4

Sandwich beam and its constituents

Figure 5

Creep responses of laminated skins with 0 deg, 90 deg, and 45 deg fiber orientations subject to axial loading at room temperature. No sensors were embedded in these laminates.

Figure 6

Creep responses of sandwich beams with 0 deg GFRP skins. Top: control specimens and bottom: specimens with embedded sensors. The multiscale FE model is based on room temperature data while the experimental data is obtained at 80°C.

Figure 7

Stress and displacement contours in the control sandwich specimens. Top: von Mises stress contour and bottom: lateral displacement contour.

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