Godfrey Sauti’s research while affiliated with National Aeronautics and Space Administration and other places

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Publications (45)


Figure 6. Tensile test specimen post-failure on the hybrid MTS/Instron 250 kN test stand.
Figure 7. ENF test specimen under load in the MTS 25 kN Landmark 370.10 test frame.
Tg based on E', onset for 1078 and the candidate resins.
Rapid Curing Isothermal Resins for Aerospace Applications
  • Conference Paper
  • Full-text available

September 2024

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57 Reads

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Joseph G Smith

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Elizabeth H Moore

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Emilie J Siochi

Due to the aircraft market outlook, industry desires single-aisle composite aircraft production of 80 airplanes per month to meet projected demand by 2040. This will require production rates to be four to six times greater than currently possible. Resin infusion is a manufacturing method that has potential to enable fabrication and assembly of large primary structures at the desired rates. The resin influences the total time required to complete the infusion and curing process and contributes to the performance of the resulting composite. Currently approved resins for resin infusion processes do not cure rapidly enough to support the rates needed for 80 airplane deliveries per month. One approach is to design isothermal resins that reduce processing times. These are resins that can be infused and cured at the same temperature. This method enables shorter, energy efficient processing cycles by eliminating temperature ramps that would otherwise be required during or in between part fabrication. In this paper, data will be presented to demonstrate the potential of using isothermal rapid curing resins to produce composites with aerospace performance characteristics.

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Environment control in additive manufacturing of high-performance thermoplastics

April 2022

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339 Reads

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8 Citations

The International Journal of Advanced Manufacturing Technology

An expansion of the high-temperature/high-performance polymer 3D printing feedstock palette is critical for the adoption of the technology in more aerospace applications. Open-source printers are a potential platform for the insertion of new materials to the printing palette. However, as-purchased, they are not capable of printing high-temperature polymers. To address this, we developed an open-source-based 3D printer with increased environment controls. These include an enclosure and part heating using infrared energy focused on the printed part to keep it close to the desired temperature, while the printer components stay within their design operating ranges. This enables printing of high-temperature polymers while preventing damage to the machine. The effectiveness of this approach is demonstrated by printing polyetherimide parts (Tg = 217 °C). The temperature of the part as well as temperatures at various locations in the build chamber is monitored and assessed. We then evaluate the overall success of the approach by showing the relationship between part temperature and final properties such as surface flaws, tensile strength, and interfacial bonding.


Microstructural exploration of a carbon nanotube yarn reinforced composite using a peridynamic approach

January 2022

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39 Reads

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5 Citations

A framework using peridynamic theory is developed and demonstrated for deformation and failure analysis of carbon nanotube (CNT) yarn-based structural composites. Experimental work involved tension testing of a CNT yarn/polymer composite resulting in stress–strain response up to and including failure. The as-prepared specimen was characterized using x-ray micro computed tomography (CT), which was then converted into voxel-based data with CNT yarn, polymer, and void phases as well as surface undulation. A Density-Based Spatial Clustering of Applications with Noise algorithm was applied to detect and quantify the clusters of voids, of CNT-rich, and of resin-rich regions. The voxel data, with all microstructural details, were used in peridynamic simulations. These demonstrate the critical roles of resin and void clusters and surface undulation in fracture initiation and propagation. Additional analysis was performed to construct probability density functions (PDFs) of different phases (yarn, resin, and void) with the goal of constructing synthetic virtual composite specimens. The synthetically reconstructed peridynamic models correctly captured the experimental stress–strain response. The similarities and differences between the failure (initiation and propagation) behaviors predicted by x-ray CT-based and PDF-based peridynamic model simulations are presented in detail and discussed.


Temperature, Diffusion, and Stress Modeling in Filament Extrusion Additive Manufacturing of Polyetherimide: An Examination of the Influence of Processing Parameters and Importance of Modeling Assumptions

October 2021

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79 Reads

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36 Citations

Additive Manufacturing

Fused filament fabrication (FFF), a form of filament-based material extrusion additive manufacturing (AM), is an extremely useful technique for the rapid production of highly customized products; however, empirical evidence is heavily relied upon for understanding of the process. Initial modeling attempts have traditionally focused on predicting heat transfer and either interlayer diffusion and adhesion or stress development but have not taken a combined approach to analyze all three components simultaneously in a multiphysics model. In this study, we implement finite difference models to examine the combined heat transfer, polymer diffusion represented as degree of healing (Dh), and residual stress development in FFF of poly(ether imide) (PEI). Printing with PEI is of great interest because of its desirable mechanical properties and high use temperatures, but it also creates a more challenging modeling problem with higher thermal gradients and greater potential thermal processing window compared to traditionally modeled AM materials, such as acrylonitrile-butadiene-styrene (ABS) and polylactic acid (PLA). The larger processing window can potentially allow for more processing options but can also significantly complicate the optimization process. In this study, experimental analyses including trouser tear tests and part warpage measurements provide correlation to predicted Dh and stress levels. The models suggest that the temperature of a layer is influenced by the subsequent printing of up to at least three layers in the geometry studied. The results of this study further demonstrate the sensitivity of the molecular mobility and degree of healing to the reptation time (τrep), such that a small change in the τrep on the order of 2-3x can result in an order of magnitude difference in the time before interfacial healing can begin, culminating in significantly less healing occurring. Furthermore, the reptation time and subsequent healing predictions are highly reliant on the extrapolation method used to extend the reptation time to temperatures below those at which it was measured resulting in significantly different predictive results, even if the same experimental data is used.


Contact Thermal Resistance between Silver Nanowires with Poly(vinylpyrrolidone) Interlayers

May 2021

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51 Reads

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12 Citations

Nano Letters

Various nanofillers have been adopted to enhance the thermal conductivity of polymer nanocomposites. While it is widely believed that the contact thermal resistance between adjacent nanofillers can play an important role in limiting thermal conductivity enhancement of composite materials, lack of direct experimental data poses a significant challenge to perceiving the effects of these contacts. This study reports on direct measurements of thermal transport through contacts between silver nanowires (AgNWs) with a poly(vinylpyrrolidone) (PVP) interlayer. The results indicate that a PVP layer as thin as 4 nm can increase the total thermal resistance of the contact by up to an order of magnitude, when compared to bare AgNWs, even with a larger contact area. On the other hand, the thermal boundary resistance for PVP/silver interfaces could be significantly lower than that between polymer-carbon nanotubes (CNTs). Analyses based on these understandings further show why AgNWs could be more effective nanofillers than CNTs.


Modifying carbon nanotube fibers: A study relating apparent interfacial shear strength and failure mode

March 2021

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64 Reads

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35 Citations

Carbon

Achieving high strength in fiber reinforced structural composites requires effective load transfer between the high-performance fiber reinforcement, e.g., carbon nanotube (CNT) yarn, and the matrix. Various processing approaches to enhance the interaction between CNT fiber and the matrix were investigated. The apparent interfacial shear strengths (IFSS) of pristine CNT yarns, post-treated CNT yarns (cross-linked, functionalized, and polymer incorporation by resistive heating), and pre-infiltrated polymer/CNT composite fibers measured using single fiber pull-out tests were used to screen the efficacy of the processing methods. Pristine CNT yarns had a low apparent IFSS (<5 MPa) due to shear failure within their dry cores. In post-treated CNT yarns which did not exhibit good IFSS, the failure surface consisted of a resin-infiltrated sheath near the surface of the yarn and a dry section within the yarn core; failure occurred in the dry core. This failure mode is unlike those observed in traditional carbon fiber reinforced composites which fail at the fiber/matrix interface. In contrast to the sword-in-sheath failure modes of post-treated CNT yarns, pre-infiltrated polymer/CNT composite fibers displayed high apparent IFSS (>20 MPa). Improved wet-out of the fiber eliminated the dry-core shear failure mode.


Citations (34)


... It has been found that carbon fillers such as carbon nanotubes [12], graphene/graphene oxide [13], and expanded graphite [14] may increase the mechanical, thermal, and electrical properties of native polymers. Although underestimated in the literature, graphite, a three-dimensional pure form of carbon with a layered hexagonal crystalline form, can be an attractive filler in comparison with carbon nanotubes and graphene because of its low cost and high availability. ...

Reference:

Effect of Mechanically Exfoliated Graphite Flakes on Morphological, Mechanical, and Thermal Properties of Epoxy
Fabrication of carbon nanotube epoxy prepreg towards lightweight structural composites
  • Citing Article
  • February 2024

Composites Part B Engineering

... The focus of most of the published research studies on composite material developed for use in MEX production is the mechanical characterization of printed fibre-reinforced polymers by comparison with pure polymer material. Various research studies have been carried out in which short fibres [11][12][13][14][15][16][17] [18][19][20], nanofibres [20][21][22][23] and continuous fibres [24][25][26][27][28][29][30][31][32][33][34][35][36][37] are used in MEX production. The fibres have been combined with thermoplastic matrix materials such as Polyamide (PA), PLA, ABS, Polyphenylene Sulfide (PPS), and polyethyleneimine (PEI) for most of the references cited [38]. ...

Additive Manufacturing of Multifunctional Components Using High Density Carbon Nanotube Yarn Filaments

... These surface functional groups act as reactive sites and play a crucial role in enhancing the interfacial adhesions between the CF and the polymer matrix [31][32][33][34][35][36][37][38][39]. In addition, a multiscale hierarchy with nano-or micro-scale fillers is an innovative and efficient approach for considerably enhancing the interfacial properties of the CFRP by increasing the interfacial interactions and adhesion between the CFs and the polymer matrix [40][41][42][43]. In most cases, interfacial interaction and adhesion enhance the interfacial properties of the CFRPs [44][45][46]. ...

Multi-scale hierarchical carbon nanotube fiber reinforced composites towards enhancement of axial/transverse strength and fracture toughness
  • Citing Article
  • April 2023

Composites Part A Applied Science and Manufacturing

... This expression in combination with Equations (1) and/or (2) may yield a closed form expression for the signum function. In [28], a simple non-equilibrium chaotic system with only one signum function for generating multidirectional variable hidden attractors and its hardware implementation was introduced, whilst in [29,30], analytical expressions of Heaviside step function, ramp function, and signum function were presented. ...

Step, Ramp, Delta, and Differentiable Activation Functions Obtained Using Percolation Equations

Mathematics and Statistics

... Open-source printers have limitations when controlling the temperature of high-performance materials, but post-processing by after heating printed objects can substantially increase surface quality [22,23], leading to researches in auxiliary heating plates near the printing head to increase mechanical properties [16], ambient temperature control for increase in bonding between layers [22], and bed temperature control for better surface characteristics. Achieving an optimal bed temperature is essential for maximizing adhesion during the printing process and minimizing downtime between prints, thereby facilitating easy part removal and potentially reducing overall cycle times in additive manufacturing operations [24]. ...

Environment control in additive manufacturing of high-performance thermoplastics

The International Journal of Advanced Manufacturing Technology

... They presented that the tensile strength of CNT composites is 69% of that of CNT yarn itself. Also, Barber et al. [26] analyzed the deformation as well as the failure strength of composites made with CNT yarns and polymer. They utilized X-ray to characterize the specimens and showed that sharp gradients and the accumulation of the resin are two major reasons for failure. ...

Microstructural exploration of a carbon nanotube yarn reinforced composite using a peridynamic approach
  • Citing Article
  • January 2022

... Coogan and Kazmer [27] additionally combined the diffusion model with a pressuredriven contact model to take neck growth into account in addition to diffusion and thus improve the accuracy of the prediction. Gilmer [42] has compared the different approaches to τ w using the example of PEI (Polyetherimide) and shown that the various descriptions predict consistent trends for healing. ...

Temperature, Diffusion, and Stress Modeling in Filament Extrusion Additive Manufacturing of Polyetherimide: An Examination of the Influence of Processing Parameters and Importance of Modeling Assumptions
  • Citing Article
  • October 2021

Additive Manufacturing

... To explore the unique thermal transport properties in nanomaterials, several experimental techniques have been developed in recent years [103,104]. These intensive efforts are primarily adopted for nanotubes, nanowires, and nanoribbons. ...

Contact Thermal Resistance between Silver Nanowires with Poly(vinylpyrrolidone) Interlayers
  • Citing Article
  • May 2021

Nano Letters

... Carbon nanotubes (CNTs) have become an attractive reinforcement in polymer composites due to their outstanding thermal, electrical, and mechanical properties [1][2][3][4][5][6]. New structural forms of CNTs, such as yarns, tapes, and sheets [1], have permitted the development of lightweight macroscale components used in many multifunctional structures [1,3,6,7]. ...

Modifying carbon nanotube fibers: A study relating apparent interfacial shear strength and failure mode
  • Citing Article
  • March 2021

Carbon

... To explore the unique thermal transport properties in nanomaterials, several experimental techniques have been developed in recent years [103,104]. These intensive efforts are primarily adopted for nanotubes, nanowires, and nanoribbons. ...

Electrical and Thermal Transport through Silver Nanowires and Their Contacts – Effects of Elastic Stiffening
  • Citing Article
  • August 2020

Nano Letters