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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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Using Z-Axis Milled Fibers to Toughen Carbon Fiber Composites
Carbon fiber fabrics are surface-coated with Z-axis oriented milled carbon fibers and processed into 3-D reinforced prepregs. These milled carbon fibers provide Z-axis interlaminar reinforcement that increases compressive toughness by over 300% and compressive strength by 35% without any detriment to stiffness. These improvements are important for the construction of light yet durable bicycles that prioritize the safety of cyclists.
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- Award ID(s):
- 1820051
- PAR ID:
- 10098258
- Date Published:
- Journal Name:
- SAMPE 2019 - Charlotte, NC
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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As a next generation composite material, carbon fiber reinforced polymer (CFRP) has great potential to be widely used in manufacturing industries due to its outstanding mechanical properties. The high strength to weight ratio, and high stiffness inherent to CFRPs make them a desired material in various kinds of applications. CFRPs frequently experience bending loads while in use for such things as aircraft, automobiles, bridges, etc. Anisotropic behavior and limited in through thickness properties are major concerns which affect the performance of CFRPs. Moreover, in the interlaminar region, traditional CFRPs are often vulnerable to matrix sensitive damage such as compressive failure, delamination, and shear failure due to the absence of enough strength in through thickness direction. The tensile and compressive stress generated by the bending loads can weaken the interlaminar shear properties due to the absence of fibers in through thickness and ultimately can lead to catastrophic failure. This study introduces a novel approach with z-threaded CFRP (ZT-CFRP), which incorporates electrically aligned z-threaded carbon nanofibers (CNFs) as reinforcement. Flexural test using 3-point bending was performed on both control CFRP and ZT-CFRP samples reinforced with 1.0 wt.% carbon nanofiber z-threads. The results showed a 15% improvement in the flexural strength and about 36% linear elastic range increase for the ZT-CFRP laminates compared to the unmodified CFRP laminates, and validated the effectiveness of nanofiber Z-threading strategy in strengthening composite materials against flexural loading.more » « less
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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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Methods to sequester and store atmospheric CO2 are critical to combat climate change. Alkaline-rich bioashes are potential carbon fixing materials. This work investigates potential co-benefits from mineralizing carbon in biomass ashes and partially replacing high embodied greenhouse gas (GHG) Portland cement (PC) in cement-based materials with these ashes. Specifically, rice hull ash (RHA), wheat straw ash (WSA), and sugarcane bagasse ash (SBA) were treated to mineralize carbon, and their experimental carbon content was compared to modeled potential carbonation. To understand changes in the cement-based storage materials, mortars made with CO2-treated WSA and RHA were experimentally compared to PC-only mortars and mortars made with ashes without prior CO2 treatment. Life cycle assessment methodology was applied to understand potential reductions in GHG emissions. The modeled carbonation was ∼18 g-CO2/kg-RHA and ∼180 g-CO2/kg-WSA. Ashes oxidized at 500 °C had the largest measured carbon content (5.4 g-carbon/kg-RHA and 35.3 g-carbon/kg-WSA). This carbon appeared to be predominantly residual from the biomass. Isothermal calorimetry showed RHA-PC pastes had similar heat of hydration to PC-pastes, while WSA-PC pastes exhibited an early (at ∼1.5 min) endothermic dip. Mortars with 5 % and 15 % RHA replacement had 1–12 % higher compressive strength at 28 days than PC-only mortars, and milled WSA mortars with 5 % replacement had 3 % higher strength. A loss in strength was noted for the milled 15 % WSA, the CO2-treated 5 %, and the 15 % WSA mortars. Modeled reductions in GHG emissions from CO2-treated ashes were, however, marginal (<1 %) relative to the untreated ashes.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.33599/nasampe/s.19.1372
