Geopolymers, as a potentially environmentally friendly alternative to Portland cement, are increasingly attracting attention in the construction industry. Various methods have been applied for customizing the properties of geopolymers and improving their commercial viability. One of the promising methods for refining the properties of geopolymers such as their toughness is the use of short fibers. The effectiveness of a high‐strength short fiber in the geopolymer matrix is largely dependent on the interfacial bonding between the fiber and its surrounding matrix. While the importance of this interfacial chemistry is highlighted in the literature, the characteristics of this bonding structure have not been fully understood. In this paper, we aim to investigate the bonding mechanism between the carbon fiber and metakaolin‐based geopolymer matrix. For the first time, the existence and nature of the chemical bonding at the interfacial region (interphase) between carbon fiber and geopolymer matrix has been revealed. X‐ray pair distribution function computed tomography (PDF‐CT), field emission‐scanning electron microscopy imaging, and nanoindentation techniques are employed to discern the chemo‐mechanical properties of the interphase. PDF‐CT results show the emergence of a new atom–atom correlation at the interfacial region (around 1.82 Å). This correlation is a characteristic of interfacial bonding between the fiber and its surrounding matrix, where the existence of chemical linkages (potentiallyVAl‐O‐C) between fibers and the matrix contributes to the adhesion between the two constituents making up the composite. Due to such chemical bonding, the nanomechanical properties of the interfacial region fall between that of the carbon fiber and geopolymer. The combination of advanced techniques is proved useful for enhancing our understanding of the interfacial chemistry between fibers and the binding matrix. This level of knowledge facilitates the engineering of composite systems through the manipulation of their nanostructure.
- NSF-PAR ID:
- 10129102
- Date Published:
- Journal Name:
- Journal of Applied Mechanics
- Volume:
- 86
- Issue:
- 10
- ISSN:
- 0021-8936
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract -
more » « less
Abstract Natural fibers are lightweight, cost‐effective, readily available, and eco‐friendly materials. However, natural fiber‐reinforced composites are constrained by biological inconsistency and inferior fiber‐matrix interfacial properties, which restrict effective processing using advanced additive manufacturing methods. In this study, we develop a novel concept for natural fiber composite interfaces by growing hydroxyapatite (HAP) nanocrystals on jute fibers. The resulting hybrid composite is characterized using mechanical testing, nanoindentation, and modulus mapping. The interfacial region suggests a 31.4% increase in stiffness and possesses a storage modulus of up to 7.5 GPa. The tensile modulus and strength of the hybrid composite improves by 30% and 33%, respectively. Furthermore, we develop a novel process for the additive manufacturing of jute fiber thermoset composites through a direct writing (DW) process. The HAP modification increases thermal conductivity, consequently improving the curing process during DW and enhancing composite manufacturability. We demonstrate that the DW process enables the printing of intricate multilayer geometries with varying fiber content.
Highlights Hydroxyapatite is used for natural fiber composite interfacial modification.
Nanoindentation shows the interfacial region exhibits 31.4% higher stiffness.
Modified composites possess superior mechanical performance.
Jute fibers are thermally functionalized for composite additive manufacturing.
A direct writing method is developed for continuous functionalized jute fiber.
-
Additively manufactured (AM) composites based on short carbon fibers possess strength and stiffness far less than their continuous fiber counterparts due to the fiber’s small aspect ratio and inadequate interfaces with the epoxy matrix. This investigation presents a route for preparing hybrid reinforcements for AM that comprise short carbon fibers and nickel-based metal-organic frameworks (Ni-MOFs). The porous MOFs furnish the fibers with tremendous surface area. Additionally, the MOFs growth process is non-destructive to the fibers and easily scalable. This investigation also demonstrates the viability of using Ni-based MOFs as a catalyst for growing multi-walled carbon nanotubes (MWCNTs) on carbon fibers. The changes to the fiber were examined via electron microscopy, X-ray scattering techniques, and Fourier-transform infrared spectroscopy (FTIR). The thermal stabilities were probed by thermogravimetric analysis (TGA). Tensile and dynamic mechanical analysis (DMA) tests were utilized to explore the effect of MOFs on the mechanical properties of 3D-printed composites. Composites with MOFs exhibited improvements in stiffness and strength by 30.2% and 19.0%, respectively. The MOFs enhanced the damping parameter by 700%.more » « less
-
Debonding at the core–skin interphase region is one of the primary failure modes in core sandwich composites under shear loads. As a result, the ability to characterize the mechanical properties at the interphase region between the composite skin and core is critical for design analysis. This work intends to use nanoindentation to characterize the viscoelastic properties at the interphase region, which can potentially have mechanical properties changing from the composite skin to the core. A sandwich composite using a polyvinyl chloride foam core covered with glass fiber/resin composite skins was prepared by vacuum-assisted resin transfer molding. Nanoindentation at an array of sites was made by a Berkovich nanoindenter tip. The recorded nanoindentation load and depth as a function of time were analyzed using viscoelastic analysis. Results are reported for the shear creep compliance and Young’s relaxation modulus at various locations of the interphase region. The change of viscoelastic properties from higher values close to the fiber composite skin region to the smaller values close to the foam core was captured. The Young’s modulus at a given strain rate, which is also equal to the time-averaged Young’s modulus across the interphase region was obtained. The interphase Young’s modulus at a loading rate of 1 mN/s was determined to change from 1.4 GPa close to composite skin to 0.8 GPa close to the core. This work demonstrated the feasibility and effectiveness of nanoindentation-based interphase characterizations to be used as an input for the interphase stress distribution calculations, which can eventually enrich the design process of such sandwich composites.more » « less
-
more » « less
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.
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1115/1.4044086
