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In this study, unidirectional carbon fiber prepregs that contain long carbon nanofiber (CNF) z threads as a through-thickness (z-directional) reinforcement were manufactured. The CNF z threads are long enough to thread through multiple carbon fiber (CF) arrays, which creates a multi-scale CNF/CF/resin-composite. The CNF z-threaded prepregs were manufactured using an electric-field aligned flow-transferring process. It was hypothesized that the CNF z-threads with the zig-zag threading pattern reinforces the interlaminar and intralaminar regions of the CFRP laminate thus improve the compressive strength by reducing the chance of carbon fiber buckling. Compressive testing was performed per modified version of ASTM D695 (i.e., SACMA SRM 1R 94) to evaluate the compressive strength of the CNF z-threaded CFRP (ZT-CFRP) laminates. The samples were manufactured using AS4 carbon fibers, EPON 862/Epikure-W resin and a 1wt% CNF content. ZT-CFRP testing results were compared with unaligned CNF-modified CFRP (UA-CFRP) and unmodified CFRP samples to investigate the impact of the CNF z-threads on the compressive strength. Results showed an increase of ~15% for the compressive strength of ZT CFRPs, whereas the UA-CFRPs experienced a decrease of ~8% when compared to unmodified CFRPs. It was concluded that CNF/carbon fiber interlocking stops and delays crack growth, and helps to stabilize carbon fibers from further buckling.
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Enhancement of Through-Thickness Thermal Transport in Unidirectional Carbon Fiber Reinforced Plastic Laminates due to the Synergetic Role of Carbon Nanofiber Z-Threads
This study experimentally and analytically examined the influence of carbon nanofiber (CNF) z-threads on the through-thickness (i.e., z-direction) thermal conductivity of unidirectional carbon fiber reinforced plastics (CFRPs). It was hypothesized that a network of CNF z-threads within CFRPs would provide a thermally conductive microstructure throughout the sample thickness that would increase the through-thickness thermal conductivity. The experiments showed that the through-thickness thermal conductivity of the CNF z-threaded CFRPs (9.85 W/m-K) was approximately 7.53 times greater than that of the control CFRPs (1.31 W/m-K) and 2.73 times greater than that of the unaligned CNF-modified CFRPs (3.61 W/m-K). Accordingly, the CNF z-threads were found to play a substantial role in increasing the through-thickness thermal conductivity of CFRPs. To better understand the role of the CNF z-threads in through-thickness thermal transport, simple logical models of the CFRPs were constructed and then compared with the experimental results. Through these analyses, it was determined that CNF z-threads substantially enhance the through-thickness thermal conductivity by creating carbon fiber-CNF linkages throughout the CFRP laminate; these linkages allow the heat flow to largely bypass the resistive resin that envelops the carbon fibers. In addition, thermal infrared tests illustrated that the increased through-thickness thermal conductivity of the CNF z-threaded CFRP enabled the location and visualization of defects within the laminate, which was not possible with the control CFRP.
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- Award ID(s):
- 1748369
- PAR ID:
- 10096110
- Date Published:
- Journal Name:
- Journal of Nanomaterials
- Volume:
- 2019
- ISSN:
- 1687-4110
- Page Range / eLocation ID:
- 1 to 13
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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This paper utilizes a periodic unit cell modeling technique combined with finite element analysis (FEA) to predict and understand the mechanical behaviors of a nanotechnology-enhanced carbon fiber reinforced polymers (CFRPs) composite. This research specifically focuses on the study of novel Z-threaded CFRPs (ZT-CFRPs) that are reinforced not only by unidirectional carbon fibers but also with numerous carbon nanofibers (CNFs) threading through the CFRP laminate in the z-direction (i.e., through-thickness direction). The complex multi-scaled orthogonally-structured carbon reinforced polymer composite is modeled starting from a periodic unit cell, which is the smallest periodic building-block representation of the material. The ZT-CFRP unit cell includes three major components, i.e., carbon fibers, polymer matrix, and carbon nanofiber Z-threads. To compare the mechanical behavior of ZT-CFRPs against unmodified, control CFRPs, an additional unit cell without CNF reinforcement was also created and analyzed. The unit cells were then meshed into finite element models and subjected to different loading conditions to predict the interaction among all their components. The elastic moduli of both unit-cells in the z-direction were calculated from the FEA data. By assuming the CNFs have the same mechanical properties of T-300 carbon fiber, the numerical modeling showed that the ZT-CFRPs exhibited a 14% improvement in z-directional elastic modulus due to the inclusion of 1 wt% CNF z-threads, indicating that ZT-CFRPs are stiffer compared to control CFRPs consisting of T-300 carbon fibers and epoxy.more » « less
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Traditional Carbon Fiber Reinforced Plastics (CFRPs), carry high in-plane strength and electrical conductivity but exhibit intrinsic weaknesses in strength, toughness and conductivity in the through-thickness direction (i.e. z-direction). This paper presents a novel approach to align and thread Carbon Nanofibers (CNFs) through the porous medium (Carbon fiber fabric) using an interesting radial-flow alignment method and manufacture a novel CNFs z-threaded CFRP prepreg. This new radial-flow alignment approach is unique and has been found highly effective to z-thread the array of carbon fibers (diameter ~ 7 microns) with numerous long CNFs (length ~ 50-200 microns) under a Scanning Electronic Microscope (SEM) analysis. Experimental tests performed on a cured laminate sample prepared by this novel technique with 1 wt% aligned CNF concentration showed a significant improvement on the z-directional electrical conductivity for direct current (DC). The 1 wt% CNFs z-threaded CFRP was found about 100 times as conductive as the control CFRP; whereas the unaligned 1 wt% CNFs modified CFRP was only about 16 times as conductive as the control sample.more » « less
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Previous studies have shown that carbon nanofiber (CNF) z-threaded carbon fiber-reinforced polymer (ZT-CFRP) laminates exhibit improved mechanical performance in comparison to traditional carbon fiber-reinforced polymer (CFRP) laminates when exposed to extreme elevated temperatures. Z-threaded reinforcement is a technique for strengthening the through-thickness of a laminate by introducing perpendicularly aligned carbon nanomaterial to be threading into the continuous fiber array. Improved performance has already been observed in properties such as interlaminar shear strength (ILSS) without extreme heat exposure, but there has also been evidence that z-thread inclusion may mitigate strength loss due to thermal degradation of the matrix. This study examined how ILSS was diminished in both CFRP and ZT-CFRP samples with matrix degradation caused by extreme temperature exposure. Test samples were heated to 350 ˚C for 10 minutes and then allowed to return to room temperature. SBS testing in accordance with ASTM D2344 was conducted on both untreated and heat-treated samples for comparison. All samples were at room temperature during testing. It was found that ZT-CFRP samples (with 0.5wt% CNF concentration the matrix) exhibited higher ILSS with and without heat treatment over the traditional CFRP samples with and without heat treatment by +33.96% and +25.12%, respectively. ZT-CFRP ILSS was found to decrease by 10.584 MPa (-14.56%) after the extreme heat treatment, while CFRP ILSS decreased by only 4.627 MPa (-8.53%). Microscopic image analysis was also performed to provide insight into how the CNF z-threads may have provided a mechanism for retaining ILSS performance even with matrix thermal degradation.more » « less
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A rapid fatigue characterization method using full-field temporal surface temperature measurements has been used to study the effect of microstructural modification in unidirectional carbon fiber reinforced plastics (UD- CFRP) via electrically aligned Z-threaded carbon nanofibers (CNF). 1 wt% CNF were aligned in the Z-direction via electric means using a patented roll-to-roll process, enabling ZT-CNF-CFRP prepreg production. Three conf igurations were tested under fatigue: ZT-CNF-UD-CFRP (ZTE), UD-CFRPs with Unaligned CNF, and UD-CFRPs without CNF (Control). Mean surface temperatures measured via passive infrared thermography (IRT) was used to estimate the fatigue limit for these materials using a staircase loading method. Further, harmonic analysis of the obtained temporal full-field temperature data was used to monitor the damage evolution. Finally, the fatigue limit was also determined using the residual threshold method based on the second harmonic signal. Fatigue limits obtained for the three configurations via the bi-linear method were 62.36 ± 0.42 % σ 64.7 ± 1.83 % σ uts for Unaligned and 49.29 ± 2.47 % σ uts uts for ZTE, for Control. While the presence of 1 wt% CNF improves the fatigue limit; the effect of Z-threading could not be accurately quantified since the Z-threading manufacturing process was found to increase the matrix content of the composite. CNF Z-threads increased thermal conductivity, enabling better in situ damage monitoring. Different failure modes were found and discussed to understand the roles of CNF in the fatigue behavior of UD-CFRP laminates.more » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1155/2019/8928917
