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At least 253 records · Page 14

All sources NASA NTRS DOE OSTI

NASA NTRS2019

Manufacturing of Thermoset Polyimide Composites by Laser Sintering

Selective Laser Sintering (SLS) is an additive manufacturing technique that builds 3D models layer by layer using a laser to selectively melt cross sections in powdered polymeric materials, following sequential slices of the computer-aided design (CAD) model. SLS generally uses thermoplastic polymeric powders such as polyamides. The resultant 3D-printed objects are often weaker in their strength compared to traditionally processed materials, due to their higher porosity. This paper described the process development of using melt-processable imide oligomers terminated with reactive 4-phenylethynylphthalic anhydride (4-PEPA) to conduct laser sintering (LS). The first successful 3D-printing of high temperature RTM370 thermoset polyimide carbon fiber composites were further post-cured to promote additional crosslinking for achieving higher temperature (T g = 370°C) capability. Another novel imide oligomer, RTM385-SLS, formulated with a complex melt viscosity [ƞ*] of ~104-105 poise is also suitable for LS. RTM385-SLS resin powder was mixed with 20-25% of hexagonal boron nitride (h-BN) and subjected to LS to print out “Green” specimens which could be further post-cured to afford a thermally conductive but electrically insulating composites with high T g of 385 °C. The cured composite specimens were then subjected to mechanical testing, thermal conductivity and porosity measurements as well as SEM characterization.

additive Manufacturing↗

NASA NTRS1999

An Approach to Processable Polyimides

The use of polymer matrix composites (PMC's) in aircraft engines can lead to substantial weight savings over metals. This weight reduction correlates into better fuel economy, increased speed, and increased passenger load. Typically, high performance PMC's possess high thermal-oxidative stabilities (TOS) and high glass transition temperatures (Tg's) to withstand temperatures up to 316 C (600 F). One of the leading high temperature resins system available today is PMR-15 (Polymerization of Monomeric Reactants, MW=1500). This thermosetting polyimide utilizes addition curing through polymer endcaps which enables hand lay-up processing of carbon fiber composite parts with low void contents. However, the large amount of hand labor raises manufacturing costs and prohibits the use of PMR-15 in many aerospace applications. Resin Transfer Molding (RTM) provides an economical alternative, but it requires a melt Viscosity of less than 10(exp 3) centipoise (cP). This is much lower than the minimum melt viscosity of PMR-15 (about 10(exp 6) cP). To improve the processability of polyimides, the polymer backbone can be modified by incorporating flexible linkages, such as branching. bulky pendant groups, kinked structures, and twisted or non-coplanar moietes . The focus of this paper will be the introduction of non-coplanar biaryls into the PMR polyimide backbone to increase processability while maintaining high temperature performance.

Gariepy, Christopher A.↗

DOE OSTI2021

Corrosion Protection and Dissimilar Material Joining for Next Generation Lightweight Vehicles

The Arconic Technology Center working with Honda R&D Americas, LLC and the Ohio State University evaluated the corrosion performance of several multi-material conditions and demonstrated the production worthiness of the Resistance Spot Riveting (RSR™) process. RSR is a new technology being developed by Howmet Fastening Systems (formerly Arconic, Inc.) that employs a fastener that is installed using conventional resistance spot welding equipment to produce multi-material joints. The goal of the 3-year project was to demonstrate the use of RSR to join aluminum to steel and aluminum to carbon fiber composites on a prototype scale. Deployment of this technology would help the automotive industry achieve an additional 10 to 20% weight reduction over high strength steels. These weight-savings to the body in white generally translates to 2.5-5.0% of overall vehicle curb weight. The resulting total weight-savings could provide a 1.5% to 3.0% total improvement in fuel efficiency for vehicles that incorporate RSR for multi-material joining. The RSR technology addresses several production barriers to achieving DOE’s fuel efficiency targets including eliminating the need of additional capital for new joining technologies and the flexibility to process conventional steel and multi-material structures with the same equipment. Additionally, the trend towards ultra-high strength steels limits the availability of conventional joining technologies that can effectively process these multi-material combinations. In order to accomplish these goals, the following program milestones were completed by the team: 1) Developed RSR process parameters, producing multi-material joints for mechanical testing and corrosion assessments. 2) Conducted corrosion evaluation of RSR and baseline joints assembled between automotive type aluminum alloys, steels, and carbon fiber using several corrosion mitigation strategies. 3) Developed a production ready feed system and integrate into a robotic resistance spot welding station to simulate automotive production conditions. 4) Produced demonstration assemblies for testing and evaluation.

36 MATERIALS SCIENCE↗

NASA NTRS2007

Characterization of Kevlar Using Raman Spectroscopy

This paper explores the characterization of Kevlar composite materials using Raman spectroscopy. The goal of the research is to develop and understand the Raman spectrum of Kevlar materials to provide a foundation for the development of nondestructive evaluation (NDE) technologies based on the interaction of laser light with the polymer Kevlar. The paper discusses the fundamental aspects of experimental characterization of the spectrum of Kevlar, including the effects of incident wavelength, polarization and laser power. The effects of environmental exposure of Kevlar materials on certain characteristics of its Raman spectrum are explored, as well as the effects of applied stress. This data may provide a foundation for the development of NDE technologies intended to detect the in-situ deterioration of Kevlar materials used for engineering applications that can later be extended to other materials such as carbon fiber composites.

Washer, Glenn↗

NASA NTRS2011

Continued Development of Meandering Winding Magnetometer (MWM (Register Trademark)) Eddy Current Sensors for the Health Monitoring, Modeling and Damage Detection of Composite Overwrapped Pressure Vessels

Composite Overwrapped Pressure Vessels (COPVs) are used in essentially all NASA spacecraft, launch. vehicles and payloads to contain high-pressure fluids for propulsion, life support systems and science experiments. Failure of any COPV either in flight or during ground processing would result in catastrophic damage to the spacecraft or payload, and could lead to loss of life. Therefore, NASA continues to investigate new methods to non-destructively inspect (NDE) COPVs for structural anomalies and to provide a means for in-situ structural health monitoring (SHM) during operational service. Partnering with JENTEK Sensors, engineers at NASA, Kennedy Space Center have successfully conducted a proof-of-concept study to develop Meandering Winding Magnetometer (MWM) eddy current sensors designed to make direct measurements of the stresses of the internal layers of a carbon fiber composite wrapped COPV. During this study three different MWM sensors were tested at three orientations to demonstrate the ability of the technology to measure stresses at various fiber orientations and depths. These results showed good correlation with actual surface strain gage measurements. MWM-Array technology for scanning COPVs can reliably be used to image and detect mechanical damage. To validate this conclusion, several COPVs were scanned to obtain a baseline, and then each COPV was impacted at varying energy levels and then rescanned. The baseline subtracted images were used to demonstrate damage detection. These scans were performed with two different MWM-Arrays. with different geometries for near-surface and deeper penetration imaging at multiple frequencies and in multiple orientations of the linear MWM drive. This presentation will include a review of micromechanical models that relate measured sensor responses to composite material constituent properties, validated by the proof of concept study, as the basis for SHM and NDE data analysis as well as potential improvements including design changes to miniaturize and make the sensors durable in the vacuum of space

Russell, Richard↗

NASA NTRS1993

Simulated space environmental effects on a polyetherimide and its carbon fiber-reinforced composites

The selection of materials for spacecraft construction requires identification of candidate materials which can perform reliably in the space environment. Understanding the effects of the space environment on the materials is an important step in the selection of candidate materials. This work examines the effects of energetic electrons, thermal cycling, electron radiation in conjunction with thermal cycling, and atomic oxygen on a thermoplastic polyetherimide and its carbon-fiber-reinforced composites. Composite materials made with non-sized fibers as well as materials made with fibers sized with an epoxy were evaluated. The mechanical and thermomechanical properties of the materials were studied and spectroscopic techniques were used to investigate the mechanisms for the observed effects. Considerations for future material development are suggested.

Kern, Kristen T.↗

DOE OSTI2025

Scale-Up of Friction Self-piercing Riveting Process for Multi-material Joints

A single-class joining process known as “friction self-piercing riveting (F-SPR)” has been developed for joining various low-ductility lightweight materials on a laboratory scale. The frictional heat generated during the F-SPR process improved local ductility, resulting in crack-free joints and robust mechanical performance. This innovative joining technology was further advanced through the scale-up of the process using a new system with several key features (e.g., automatic rivet feeding and clamping system, vacuum system) toward industry readiness. The new integrated F-SPR systems were effectively demonstrated for joining different material combinations (e.g., carbon fiber composite to 7075 Al alloy, 7075 Al alloy to 7075 Al alloy, and 7075 Al alloy to casting Al Aural 5) with a unified technique. Crack-free joint with adequate mechanical interlocking resulted in good mechanical joint strength for each material combination. Then, the process was successfully scaled up by producing multiple joints without any cracks on larger CFC-Al and Al-Al components by the new integrated system, bringing it closer to industrial application.

Lim, Yong Chae [ORNL] (ORCID:0000000321773988)↗

DOE OSTI2026

Impact of DMP-30 catalyst concentration on the degradation and kinetics of bisphenol A epoxy thermosets cured with linear amine hardener

Epoxy thermosets are a crucial component in carbon-fiber composites, serving as the organic binding matrix. Catalysts are commonly used in prepolymer formulations to accelerate curing of the thermosets. However, the impact of catalysts on the thermal stability, degradation pathways, and kinetics of the final thermoset is poorly understood. Here, in this work, Product-Specific Kinetics (PSK) analysis was utilized with isoconversional kinetics to provide a first look into the degradation kinetics of major pyrolysis pathways in bisphenol A (BPA) epoxy resins and determine the impact of altering catalysis concentrations on these kinetic pathways. Results revealed new insights into previously identified degradation pathways, provided evidence of multiple degradation pathways for some products, and showed that use of excess catalyst results in polymer network alterations and reduced thermal stability of the thermosets.

Bisphenol A↗

DOE OSTI2023

Fluorescent aggregate structure revealed in bisphenol F epoxy thermoset

Bisphenol F (BPF) epoxy resin is a prepolymer component of thermosets used in construction of reinforced carbon fiber composites (RCFC). The fluorescence of this resin can provide information about chemical and structural alterations of the thermoset from thermal or mechanical damage. While some work has investigated the fluorescence spectra of bisphenol A epoxy resin, a structural analog of BPF, none have studied BPF. The purpose of this study is to investigate the baseline fluorescence spectra of the BPF epoxy resin for features that could be utilized for monitoring damage and structural alterations. Bisphenol F epoxy resin was found to have two emission peaks with a broad peak centered at 410 nm and a sharp peak centered at 550 nm. The broad emission peak was identified as the fluorescence from BPF epoxy monomer while the sharp emission peak was found to be from an aggregate structure present in the epoxy resin. It is hypothesized that this structure is an H-aggregate based on the emission features and structural stability of the aggregate compared to the alternative J-aggregate which was determined via density functional theory calculations. The H-aggregate was found to persist into one of the cured thermoset formulations evaluated but was lost when exposed to elevated temperatures below thermal degradation of the thermoset. This loss of aggregate structure was due to polymer network rearrangement. This new fluorescence signature can be used as an indicator of polymer network rearrangement from thermal exposure which may alter the expected material performance and precede thermal degradation.

36 MATERIALS SCIENCE↗

DOE OSTI2025

Tailored glycolysis of Nylon 6 to enable upcycling into high-strength adhesives

Nylon is a high-strength polyamide widely used in automotive, textiles, packaging, etc. However, its durability makes nylon waste difficult to manage, with recycling limited to mechanical grinding to make fillers. Here, we report a catalytic glycolysis approach to deconstruct Nylon 6 into controlled-length oligomers, enabling upcycling into value-added materials. A low-molecular-weight oligomer (M n = 1.8 kg/mol) was repolymerized with diepoxy-terminated poly(bisphenol A-co-epichlorohydrin) via mechanochemistry to create a high-performance adhesive. This copolymer achieves lap shear strengths over 22 MPa on steel and bonds steel to carbon fiber composites, nearly tripling the performance of commercial adhesives even at 90°C. Thermomechanical analyses show that the adhesive retains thermal stability similar to nylon 6 but melts at lower temperatures, allowing easier processing. The material can be reprocessed and reused without significant performance loss. This study demonstrates a strategy to convert nylon 6 waste into valuable materials, offering a sustainable path for difficult-to-recycle plastics.

Nylon waste↗

DOE OSTI2023

Continuous Processing of Carbon Foam Products Made from Coal at Atmospheric Pressure

The main goal of the project was to create a continuous manufacturing process for carbon foam that operates at atmospheric pressure and can generate well-formed carbon foam panels and lightweight aggregates. This objective was accomplished and has enabled a platform where carbon foam products can be manufactured at significantly reduced cost and cycle time relative to the conventional high-pressure batch process, which in turn can enable the manufacture of much larger volumes of carbon foam. All these features should enable carbon foam to enter much larger markets and create meaningful demand for U.S. coal. Carbon foam panels and aggregate both consisted of at least 70 weight percent carbon per program requirements (typical was over 90-wt%), and at least 51 weight percent of the carbon was to be coal derived (typical was over 90-wt% carbon was from coal). Analyses regarding life cycle, technoeconomics, and final technological gaps have been documented in separate reports. This final report documents the methods used to attain the main goal and describes the technical results.

01 COAL, LIGNITE, AND PEAT↗

DOE OSTI2024

Abrasive Waterjet Machining

The abrasive waterjet machining process was introduced in the 1980s as a new cutting tool; the process has the ability to cut almost any material. Currently, the AWJ process is used in many world-class factories, producing parts for use in daily life. A description of this process and its influencing parameters are first presented in this paper, along with process models for the AWJ tool itself and also for the jet–material interaction. The AWJ material removal process occurs through the high-velocity impact of abrasive particles, whose tips micromachine the material at the microscopic scale, with no thermal or mechanical adverse effects. The macro-characteristics of the cut surface, such as its taper, trailback, and waviness, are discussed, along with methods of improving the geometrical accuracy of the cut parts using these attributes. For example, dynamic angular compensation is used to correct for the taper and undercut in shape cutting. The surface finish is controlled by the cutting speed, hydraulic, and abrasive parameters using software and process models built into the controllers of CNC machines. In addition to shape cutting, edge trimming is presented, with a focus on the carbon fiber composites used in aircraft and automotive structures, where special AWJ tools and manipulators are used. Examples of the precision cutting of microelectronic and solar cell parts are discussed to describe the special techniques that are used, such as machine vision and vacuum-assist, which have been found to be essential to the integrity and accuracy of cut parts. The use of the AWJ machining process was extended to other applications, such as drilling, boring, milling, turning, and surface modification, which are presented in this paper as actual industrial applications. To demonstrate the versatility of the AWJ machining process, the data in this paper were selected to cover a wide range of materials, such as metal, glass, composites, and ceramics, and also a wide range of thicknesses, from 1 mm to 600 mm. The trends of Industry 4.0 and 5.0, AI, and IoT are also presented.

36 MATERIALS SCIENCE↗

NASA NTRS1980

Assessment of the risk due to release of carbon fiber in civil aircraft accidents, phase 2

The risk associated with the potential use of carbon fiber composite material in commercial jet aircraft is investigated. A simulation model developed to generate risk profiles for several airports is described. The risk profiles show the probability that the cost due to accidents in any year exceeds a given amount. The computer model simulates aircraft accidents with fire, release of fibers, their downwind transport and infiltration of buildings, equipment failures, and resulting ecomomic impact. The individual airport results were combined to yield the national risk profile.

Pocinki, L.↗

NASA NTRS1980

High-voltage spark carbon-fiber sticky-tape data analyzer

An efficient method for detecting carbon fibers collected on a stick tape monitor was developed. The fibers were released from a simulated crash fire situation containing carbon fiber composite material. The method utilized the ability of the fiber to initiate a spark across a set of alternately biased high voltage electrodes to electronically count the number of fiber fragments collected on the tape. It was found that the spark, which contains high energy and is of very short duration, is capable of partially damaging or consuming the fiber fragments. It also creates a mechanical disturbance which ejects the fiber from the grid. Both characteristics were helpful in establishing a single discharge pulse for each fiber segment.

Yang, L. C.↗

NASA NTRS1982

Polymer materials research at NASA Ames Research Center

Polymers that provide significant improvements in both efficiency and safety for civilian transport aircraft and military combat aircraft were developed. High strength to weight structures such as carbon fiber composites with long term durability are requirements common to both classes of aircraft. Aircraft safety improvements in fire resistance and crashworthiness of primary and secondary structures are long term objectives for transport aircraft. Void filler ballistic foams, intumescent coatings, and radiation-resistant transparent plastics contribute to vulnerability reduction in combat military aircraft. Low and high velocity impact tolerance, fire resistance, thermal stability, and long term durability of polymers and components are emphasized.

J. A. Parker↗

NASA NTRS1983

An investigation of adhesive/adherend and fiber/matrix interactions. Part B: SEM/ESCA analysis of fracture surfaces

Adhesion was studied with emphasis on the characterization of surface oxide layers, the analysis of fracture surfaces, and the interaction of matrices and fibers. A number of surface features of the fractured lap shear samples were noted in the SEM photomicrographs including the beta phase alloy of the Ti 6-4 adherend, the imprint of the adherend on the adhesive failure surface, increased void density for high temperature samples, and the alumina filler particles. Interfacial failure of some of the fractured lap shear samples is invariably characterized by the appearance of an ESCA oxygen photopeak at 530.3 eV assigned to the surface oxide layer of Ti 6-4 adherend. The effect of grit blasting on carbon fiber composites is evident in the SEM analysis. A high surface fluorine concentration on the composite surface is reduced some ten fold by grit blasting.

Beck, B.↗

NASA NTRS1987

A cure-rate model for the Shuttle filament-wound case

An epoxy and carbon fiber composite has been used to produce a light-weight rocket case for the Space Shuttle. A kinetic model is developed which can predict the extent of epoxy conversion during the winding and curing of the case. The model accounts for both chemical and physical kinetics. In the model, chemical kinetics occur exclusively up to the time the transition temperature equals the reaction temperature. At this point the resin begins to solidify and the rate of this process limits the rate of epoxy conversion. A comparison of predicted and actual epoxy conversion is presented for isothermal and temperature programmed cure schedules.

Cagliostro, D. E.↗

NASA NTRS1991

Polymer Infiltration Studies

Progress was made on the preparation of carbon fiber composites using advanced polymer resins. Processes reported include powder towpreg process, weaving towpreg made from dry powder prepreg, composite from powder coated towpreg, and toughening of polyimide resin (PMR) composites by semi-interpenetrating networks. Several important areas of polymer infiltration into fiber bundles will be researched. Preparation to towpreg for textile preform weaving and braiding and for automated tow placement is a major goal, as are the continued development of prepregging technology and the various aspects of composite part fabrication.

Marchello, Joseph M.↗