Search NASA⌕ Search

Engineering topics

John W Connell

Publications and source records attributed to John W Connell.

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2022

In-Situ Consolidation Automated Fiber Placement of Thermoplastic Composites for High-Rate Aircraft Manufacturing

The National Aeronautics and Space Administration (NASA) initiated the Hi-Rate Composites Aircraft Manufacturing (HiCAM) project in 2021 with the goal of significantly increasing composite structures manufacturing rate in the commercial aircraft industry. The technologies currently under investigation include resin infusion and automated fiber placement (AFP) of novel thermoset materials and thermoplastic composites. Thermoplastic composites offer attractive solutions to rapid manufacturing due to their ability to be formed and consolidated quickly. NASA is particularly focused on assessing composite structure manufacturing utilizing an in-situ consolidation AFP of thermoplastics (ICAT) process employing a recently developed laser heating system. Two semi-crystalline polyaryletherketone thermoplastic tape materials were characterized to ascertain the ICAT process parameters at AFP placement speeds approaching 423 mm/s. The required laser power settings were determined at Electroimpact, measuring material temperatures utilizing a forward looking infrared (FLIR) thermal imaging camera and thermocouples. The material temperature, tool temperature, and placement speed were varied for resulting consolidation quality assessment. The resulting temperature data were also utilized to calibrate thermal analysis models under development at NASA. The experimental temperature data confirmed analytical results. An overview of the HiCAM project as well as initial data from ICAT process characterizations are described.

laser heating↗
NASA NTRS2021

Latent Cure Epoxy Resins for Reliable Joints in Secondary-Bonded Composite Structures

In high-performance polymer matrix composite assemblies, adhesive bonding is generally superior to mechanical fastening in structural performance and manufacturing efficiency. However, adhesive bonds are susceptible to minute levels of contamination accumulated during assembly that can lead to unpredictable, weak bonds. Current methods of measuring bond strength are all destructive mechanical tests. To overcome these challenges, redundant load paths (e.g., mechanical fasteners) are often implemented in secondary-bonded, primary-structures, which can greatly reduce structural performance. This study investigated reformulated aerospace epoxy matrix resins with stoichiometric offset to inhibit cure of the matrix resin prior to assembly. Inhibited resins can reflow and mix across the joint interface, which eliminates the material discontinuity and forms a homogenous joint with reliable fracture properties. The goal of this study was to develop and demonstrate secondary composite assemblies that are mechanically and microscopically indistinguishable from a co-cured composite joint. This article describes the development of latent epoxy resins, the fabrication of test articles, and the mechanical properties measured from experimental joints compared with conventional, co-cured laminates. Methods of in-line quality control using and infrared spectroscopy and post-assembly forensics are also described. The final mode-II fracture toughness measured from precracked AERoBOND specimens was similar to that measured from co-cured laminates indicating that later cure epoxy materials could be a suitable replacement for secondary bonding.

Polymer-matrix composites (PMCs)↗
NASA NTRS2020

Reduced Dependence on Redundant Fasteners in Secondary-Bonded Composite Structures Using Modified Epoxy Matrix Resins

This report describes a sub-set of over 20 experiments conducted to optimize materials and processes to maximize mechanical properties of the assembled joint. Infrared (IR) spectroscopy was used to measure the chemical state of the ER surface after primary cure. Laminates were fabricated with various HR and ER layer thicknesses, inspected using ultrasonic testing, and mechanically tested to measure fracture toughness.

Frank L Palmieri↗
NASA NTRS2020

A Review of LIBS for Real-Time Detection of Trace Silicone Contaminants on CFRP Surfaces

Laser ablation is the removal of material by laser pulses through photochemical, photothermal, or photophysical mechanisms, which is useful to prepare an adherend surface for adhesive bonding. Laser surface treatment is a method that has been under research for the past decade at NASA Langley Research Center (LaRC) to prepare surfaces for adhesive joining of aerospace composite materials and metallic alloys. Laser ablation of composite materials increases surface area and removes the surface contaminants introduced during material handling and fabrication processes. By adjustment of laser parameters, it is possible to obtain repeatable surface conditions, and superficial contaminants can be selectively and efficiently removed without damaging the underlying carbon fibers or the carbon fiber reinforced polymer (CFRP) substrate. Laser induced breakdown spectroscopy (LIBS) is a surface characterization and inspection technique that can be seamlessly integrated into the laser surface treatment process. At NASA LaRC, a single laser system has been used for both laser surface treatment and LIBS, which enables in-situ monitoring of surface contaminants. This work focuses on the advancements at LaRC using LIBS to detect surface silicone contaminants on aerospace CFRP materials and to provide surface quality control in adhesive bonding.

Rodolfo I Ledesma↗
NASA NTRS2020

A Review of LIBS for Real-Time Detection of Trace Silicone Contaminants on CFRP Surfaces

Laser ablation is the removal of material by laser pulses through photochemical, photothermal, or photophysical mechanisms, which is useful to prepare an adherend surface for adhesive bonding. Laser surface treatment is a method that has been under research for the past decade at NASA Langley Research Center (LaRC) to prepare surfaces for adhesive joining of aerospace composite materials and metallic alloys. Laser ablation of composite materials increases surface area and removes the surface contaminants introduced during material handling and fabrication processes. By adjustment of laser parameters, it is possible to obtain repeatable surface conditions, and superficial contaminants can be selectively and efficiently removed without damaging the underlying carbon fibers or the carbon fiber reinforced polymer (CFRP) substrate. Laser induced breakdown spectroscopy (LIBS) is a surface characterization and inspection technique that can be seamlessly integrated into the laser surface treatment process. At NASA LaRC, a single laser system has been used for both laser surface treatment and LIBS, which enables in-situ monitoring of surface contaminants. This work focuses on the advancements at LaRC using LIBS to detect surface silicone contaminants on aerospace CFRP materials and to provide surface quality control in adhesive bonding.

Rodolfo I Ledesma↗
NASA NTRS2020

An Ultra-long Life, High-performance, Flexible Li-CO2Battery Based on Multifunctional Carbon Electrocatalysts

Integrating CO2 utilization and renewable energy delivery/storage, the rechargeable Li–CO2 battery has been considered as a promising candidate for next-generation secondary batteries. However, high-performance catalyst(s) for efficient formation and decomposition of the discharge product, Li2CO3, are an imperative part of a Li–CO2 battery. The development of flexible Li–CO2 batteries extends their applications into compliant and wearable devices/systems, but at the same time imposes a big challenge for battery fabrication and lifetime enhancement. In this study, a rechargeable quasi-solidus flexible Li–CO2 battery was designed and fabricated using highly active N,S-doped carbon nanotubes (N,S-doped CNTs) as the cathode catalyst, and a smart polymer gel as the flexible electrolyte. This newly-developed flexible Li–CO2 battery exhibited a capacity as high as 23560 mAh g−1 based on the catalyst mass and an ultra-long lifetime of up to 538 cycles with excellent mechanical flexibility. This work provides a platform for the design and development of high-performance flexible Li–CO2 batteries from low-cost, earth-abundant, carbon-based multifunctional cathode catalysts.

Superior stability↗
NASA NTRS2018

Nanomanufacturing of Graphene Nanosheets Through Hole Engineering

Facile and scalable fabrication of highly dense and high quality graphene films and articles is extremely attractive for a range of electronic and mechanical applications. Pristine, high quality graphene with its inherent impermeability poses challenges in fabricating dense films and thick parts with high electrical conductivity due to the difficulty in removing trapped air and/or solvents used in various fabrication methods. To overcome this deficiency, nano-holes were intentionally created in pristine graphene (“holey graphene”) with an average diameter of approximately 15 nm. The holes serve as pathways for the rapid removal of gases or liquids and enable the fabrication of dense holey graphene nanostructures. Subsequently, a high temperature process is applied to effectively repair the nano-holes and recover the high quality graphene conjugated network. Through the creation and repair of the nano-holes, dense graphene articles were created that exhibited an ultrahigh conductivity of 2209 S/cm and a high carrier mobility of 673 cm2V-1s-1. This unique processing methodology enables the facile and scalable fabrication of high quality graphene constructs for a variety of applications.

Yanan Chen↗
NASA NTRS2016

Synthesis, Characterization and Evaluation of Urethane Co-Oligomers Containing Pendant Fluoroalkyl Ether Groups

Coatings with the ability to minimize adhesion of insect residue and other debris are of great interest for future aircraft. These aircraft will exhibit increased fuel efficiency by maintaining natural laminar flow over greater wing chord distances. Successful coatings will mitigate the adhesion of debris on laminar flow surfaces that could cause a premature transition to turbulent flow. The use of surface modifying agents (SMA) that thermodynamically orient towards the air side of a coating can provide specific surface chemistry that may lead to a reduction of contaminate adhesion. Aluminum surfaces coated with urethane co-oligomers containing various amounts of pendant fluoroalkyl ether groups were prepared, characterized and tested for their abhesive properties. The coated surfaces were subjected to controlled impacts with wingless fruit flies (drosophila melanogaster) using both a benchtop wind tunnel and a larger-scale wind tunnel test facility. Insect impacts were recorded and analyzed using high-speed digital photography and the remaining residues characterized using optical surface profilometry and compared to that of an aluminum control. It was determined that using fluorinated oligomers to chemically modify coating surfaces altered the adhesion properties relative to the adhesion of insect residues to the surface.

Jereme R Doss↗
NASA NTRS2005

Space Environmentally Durable Polyimides and Copolyimides

Polyimides displaying low color in thin films, atomic oxygen resistance, vacuum ultraviolet radiation resistance, solubility in organic solvents in the imide form, high glass transition (T(sub g)) temperatures, and high thermal stability are provided. The poly(amide acid)s, copoly(amide acid)s, polyimides and copolyimides are prepared by the reaction of stoichiometric ratios of an aromatic dianhydride with diamines which contain phenylphosphine oxide groups in polar aprotic solvents. Controlled molecular weight oligomeric (amide acid)s and imides can be prepared by offsetting the stoichiometry according to the Carothers equation using excess diamine and endcapping with aromatic anhydrides The polyimide materials can be processed into various material forms such as thin films, fibers, foams, threads, adhesive film, coatings, dry powders, and fiber coated prepreg, and uses include thin film membranes on antennas, second-surface mirrors, thermal optical coatings, and multilayer thermal insulation (MLI) blanket materials.

John W Connell↗
NASA NTRS2002

Composition of and Method for Making High Performance Resins for Infusion and Transfer Molding Processes

A composition of and method for making high performance imide resins that are processable by resin transfer molding (RTM) and resin infusion (RI) techniques were developed. Materials with a combination of properties, making them particularly useful for the fabrication of composite parts via RTM and/or RI processes, were prepared, characterized and fabricated into moldings and carbon fiber reinforced composites and their mechanical properties were determined. These materials are particularly useful for the fabrication of structural composite components for aerospace applications. The method for making high performance resins for RTM and RI processes is a multi-faceted approach. It involves the preparation of a mixture of products from a combination of aromatic diamines and aromatic dianhydrides at relatively low calculated molecular weights (i.e. high stoichiometric offsets) and endcapping with latent reactive groups. The combination of these monomers results in a mixture of products, in the imide form, that exhibits a stable melt viscosity of less than approximately 60 poise below approximately 300 C.

John W Connell↗
NASA NTRS2002

Phenylethynyl Containing Reactive Additives

Phenylethynyl containing reactive additives were prepared from aromatic diamines containing phenylethynyl groups and various ratios of phthalic anhydride and 4-phenylethynylphthalic anhydride in glacial acetic acid to form the imide in one step or in N-methyl-2-pyrrolidinone to form the amide acid intermediate. The reactive additives were mixed in various amounts (10% to 90%) with oligomers containing either terminal or pendent phenylethynyl groups (or both) to reduce the melt viscosity and thereby enhance processability. Upon thermal cure, the additives react and become chemically incorporated into the matrix and effect an increase in crosslink density relative to that of the host resin. This resultant increase in crosslink density has advantageous consequences on the cured resin properties such as higher glass transition temperature and higher modulus as compared to that of the host resin.

John W Connell↗
NASA NTRS1988

Polyenamines from aromatic diacetylenic diketones and diamines

The synthesis and characterization of several ployenamine ketones are discussed wherein conjugated diacetylenic diketones and aromatic diamines are used as a route to the formation of high molecular weight polyenamine ketones which exhibit good mechanical properties and can be cast into creasible films. Typical polymerization conditions involved the reaction of stoichiometric amounts of 1,4- or 1,3-PPPO and a diamine at 60°-130° C. in m-cresol at (w/w) solids content of 8-26% for a specified period of time under a nitrogen atmosphere. Novel polyenamine ketones were prepared with inherent viscosities as high as 1.99 dl/g and tough, clear amber films with tensile strengths of 12,400 psi and tensile moduli of 397,000 psi were cast from solutions of the polymers in chloroform. The polymers exhibited T g s as high as 235° C. and weight losses of 14% after aging at 232° C. in circulating air for sixty hours. The specific conditions for the preparation of the various polyenamine ketones are presented in Table I. In most cases, the elemental analyses for the polyenamine ketones, shown in Table II, agree within ±0.3% of the theoretical values.

Paul M Hergenrother↗
NASA NTRSDate not supplied

Solvent-Free Preparation of High Energy, Binder-Free Electrodes Enabled by Dry Compressible Holey Graphene

Graphene is an atomically thick sheet consisting of a graphitic carbon network with excellent mechanical strength, electrical and thermal conductivity, and chemical stability. Holey graphene, a structural derivative of graphene, has an array of through-the-thickness holes across the lateral surface of the nanosheet. The presence of these holes has minimal detrimental effect on the graphene properties and leads to enhanced performance in applications such as electronics, sensors, and energy storage. For example, these holes allow more facile cross-plane ion and gas transport than intact graphene, making holey graphene an ideal electrode material for electrochemical energy storage. This presentation will focus on the ability of holey graphene to be compression molded into robust articles or architectures under solvent-free conditions without the need for potentially parasitic binders. The unique dry compressibility of holey graphene has enabled facile fabrication of high mass loading electrodes with both high density and high porosity, which have found use in supercapacitors and various high-energy battery systems such as lithium-oxygen, lithium-sulfur, and lithium-selenium batteries.

Yi Lin↗
NASA NTRSDate not supplied

TPSAS-NF1676L-34357-DND

Explore the source record for details and available documents.

Frank Louis Palmieri↗
NASA NTRSDate not supplied

Dry Pressed, High Areal Loading Electrode Architectures Enabled by Holey Graphene

For future electric aviation, advanced battery cell chemistry beyond lithium ion batteries are required to meet mission requirements. High energy density battery concepts such as lithium-sulfur (Li-S) and lithiumoxygen (Li-O2) chemistries are being intensively investigated to realize their extraordinary theoretical promise in terms of energy density. Most fabrication methods of cathodes for these novel battery chemistries followed a conventional approach. In this approach, the active material is mixed with a polymer binder and a conductive carbon in a high-boiling organic solvent to form a slurry, followed by casting onto a current collector and solvent evaporation. The process is usually lengthy and poses environmental hazards due to the use of organic solvents.

Lin Yi↗