A comprehensive experimental investigation is performed to understand the damage sensing capabilities of thermoplastic intra-ply carbon/glass laminated composites embedded with Carbon Nanotubes (CNTs) under quasi-static interlaminar shear and mode-I fracture loading conditions. CNTs are dispersed in thermoplastic Elium® resin using a combination of ultrasonication and shear mixing processes. This resin mix is used in a vacuum infusion process to fabricate four different intra-ply laminated composites orientations; G-0-C-90 [Carbon fibers are in the longitudinal direction], G-90-C-0 [Glass fibers are in the longitudinal direction], G-45-C-45(R) [carbon and glass fibers are at +45°, and −45° from the longitudinal direction and form a repeating layup], and G-45-C-45(A) [carbon and glass fibers are at +45°, and −45°, but with alternating directions for each lamina in the layup]. Four-circumferential probes are utilized to obtain the piezo-resistance measurements associated with damage inside the composites under shear and mode-I loadings. In the shear experimentation, the G-45-C-45(A) orientation demonstrated the largest interlaminar shear strength, at 50% greater than the G-45-C-45(R) orientation. Both G-45-C-45(A) and G-45-C-45(R) had significantly larger shear strains compared to the G-90-C-0 and G-0-C-90 orientations. However, the best resolution in shear damage sensing was seen with the G-0-C-90 composites. In the mode-I fracture experiments, the greatest fracture initiation toughness is shown with the G-0-C-90 orientation, which is 80% greater than the G-90-C-0 orientation. Compared to all orientations, the G-0-C-90 orientation also provided the most sensitive electrical response.
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An experimental study was performed to investigate damage sensing and fracture toughness of multifunctional conductive glass fiber composites under dynamic mode-I fracture loading. Carbon nanotubes (CNTs) were dispersed within the epoxy matrix using a shear mixing and sonicating process. An electrostatic wet flocking process was used to reinforce milled short PAN-based carbon fibers onto each of the layers of glass fiber fabric along the thickness direction in the composites. These layers of flocked fabric were stacked, and a vacuum infusion process was employed to fabricate the composites. The parametric study consisted of two carbon fiber lengths (80 μm and 150 μm) and two fiber densities (1000 fibers/mm2and 2000 fibers/mm2) and was performed to investigate the damage sensing capabilities of a three-dimensional conductive network generated through CNTs and carbon fibers. A double cantilever beam (DCB) configuration was considered, and a modified Hopkinson pressure bar setup along with a high-speed camera was used to investigate dynamic fracture toughness of the composites. The piezo-resistance response of the composites during dynamic fracture was measured using a modified system of four probes. For comparison, composites were also characterized for fracture toughness and piezo-resistance under quasi-static fracture loading conditions. The addition of short, milled PAN-based carbon fibers significantly increased the fracture toughness of glass/epoxy composites. The piezo-resistance response of the composites was easily correlated with instances of sudden crack growth during static fracture loading.
more » « less- NSF-PAR ID:
- 10457428
- Publisher / Repository:
- SAGE Publications
- Date Published:
- Journal Name:
- Journal of Composite Materials
- Volume:
- 57
- Issue:
- 25
- ISSN:
- 0021-9983
- Page Range / eLocation ID:
- p. 4009-4023
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Novel conductive jute/epoxy laminated composites were fabricated by embedding carbon nanotubes (CNTs) in the matrix and flocking short carbon fibers between the laminates. A three‐dimensional electrical conductive network was generated inside the composites and the electrical resistivity values were measured using a four circumferential probe measurement system. A parametric study was performed to investigate the effect of three different weight percentages of CNTs (0%, 0.025% and 0.1%), two different carbon fiber lengths (150µm and 350µm), four different carbon fiber flock densities (500, 1000, 1500 and 2000 fibers/mm2) and two different laminates' orientations ((0‐0‐0‐0)Tand (0‐90‐0‐90)T) on the resistivity values of the composites. Composites with the lowest resistivity value of 0.019 Ohms‐m was achieved for 0.1 wt.% of CNTs and 350µm with flock density of 2000 fibers/mm2for ((0‐0‐0‐0)Tlaminate orientation. The increase in flock length from 150µm to 350µm significantly decreased the resistivity by several orders because 350µm generated better conductive network with neighbouring carbon fibers as well as with CNTs. The flock density of carbon fibers has a dominant effect on 150µm long fibers compared to 350µm when the flock density increased from 1000 fibers/mm2to 1500 fibers/mm2. Variation of both CNTs weight percentage and laminate orientation did not have significant effect on change in resistivity. The electrical measurement investigation of these novel conductive natural fiber composites will have applications in in‐situ damage sensing and structural health monitoring. POLYM. COMPOS., 40:E1189–E1198, 2019. © 2018 Society of Plastics Engineers
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