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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

PBI nanofiber mat-reinforced anion exchange membranes with covalently linked interfaces for use in water electrolysers

Anion exchange membranes (AEM) are key components in anion exchange membrane water electrolysers. Recently developed materials are less susceptible to the alkaline degradation of the polymer backbone and quaternary ammonium groups. A remaining challenge is the mechanical stability in contact with hot water and dimensional stability when the temperature of the feed solution changes. One solution is to reinforce membranes with a porous support. Since support materials like PEEK or PTFE have a different swelling behavior than the matrix and no strong interactions with the matrix, voids can form, and gas crossover increases. In this work, we approach this issue by pore filling polybenzimidazole nanofiber mats with the bromomethylated precursor of mTPN, an ultra-stable AEM material. During drying, a covalent interaction between support (PBI amine groups) and matrix (-CH 2 Br) is established. After quaternization, the optimized PBI/mTPN-50.120 composite membrane still shows a high conductivity of 62 mS cm –1 , but 37% reduced length swelling in comparison to the non-reinforced membrane. Tensile strength and Young's modulus increase 17% and 56% to 49 MPa and 680 MPa, respectively. In an electrolyser, a stable voltage of 1.98V at 0.25 A cm –2 was achieved, and no change in membrane resistance was observed over the test time of 200 h (50°C, 1 M KOH, catalysts based on Ni/Fe and Mo).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1996

Mullite fiber reinforced reaction bonded Si3N4 composites

Fracture toughnesses of brittle ceramic materials have been improved by introducing reinforcements and carefully tailored interface layers. Silicon carbide and Si3N4 have been emphasized as matrices of structural composites intended for high temperature service because they combine excellent mechanical, chemical, thermal and physical properties. Both matrices have been successfully toughened with SiC fibers, whiskers and particles for ceramic matrix composite (CMC) parts made by sintering, hot pressing or reaction forming processes. These SiC reinforced CMCs have exhibited significantly improved toughnesses at low and intermediate temperature levels, as well as retention of properties at high temperatures for selected exposures; however, they are vulnerable to attack from elevated temperature dry and wet oxidizing atmospheres after the matrix has cracked. Property degradation results from oxidation of interface layers and/or reinforcements. The problem is particularly acute for small diameter (-20 tim) polymer derived SiC fibers used for weavable toes. This research explored opportunities for reinforcing Si3N4 matrices with fibers having improved environmental stability; the findings should also be applicable to SiC matrix CMCs.

Saleh, T.↗
NASA NTRS1997

Effects of Interface Modification on Mechanical Behavior of Hi-Nicalon Fiber-Reinforced Celsian Matrix Composites

Unidirectional celsian matrix composites having approx. 42 volume percent of uncoated or BN/SiC-coated Hi-Nicalon fibers were tested in three-point bend at room temperature. The uncoated fiber-reinforced composites showed catastrophic failure with strength of 210 +/- 35 MPa and a flat fracture surface. In contrast, composites reinforced with BN/SiC-coated fibers exhibited graceful failure with extensive fiber pullout. Values of first matrix cracking stress and strain were 435 +/- 35 MPa and 0.27 +/- 0.01 %, respectively, with ultimate strength as high as 960 MPa. The elastic Young's modulus of the uncoated and BN/SiC-coated fiber-reinforced composites were measured as 184 q 4 GPa and 165 +/- 5 GPa, respectively. Fiber push-through tests and microscopic examination indicated no chemical reaction at the uncoated or coated fiber-matrix interface. The low strength of the uncoated fiber-reinforced composite is probably due to degradation of the fibers from mechanical surface damage during processing. Because both the coated and uncoated fiber reinforced composites exhibited weak interfaces, the beneficial effect of the BN-SiC dual layer is primarily the protection of fibers from mechanical damage during processing.

Bansal, Narottam P.↗
NASA NTRS1988

Interfaces in polymer, ceramic, and metal matrix composites; Proceedings of the Second International Conference on Composite Interfaces (ICCI-II), Cleveland, OH, June 13-17, 1988

The present conference on interfacial factors in advanced composite materials discusses such topics in their development status and properties as silane coupling, the electrochemical and plasma-surface treatment of carbon fibers, fiber surface-analytical techniques, polymer molecular scale characterization by atom-probe field-ion microscopy, the study of carbon fiber-epoxy resin interface interactions by means of labeling techniques, and the surface tailoring of SiC by ion implantation. Also discussed are developments in laser light-scattered photoelasticity, microstructural evolutions under heat treatment and radiation damage, TEM for composites, the interfaces of carbon fiber-reinforced Al composites, the influence of the interface on macroscopic composite properties, and the status of the theoretical understanding of composite interfaces.

Ishida, Hatsuo↗
DOE OSTI2021

Recycled Cardboard Containers as a Low Energy Source for Cellulose Nanofibrils and Their Use in Poly(l-lactide) Nanocomposites

Cellulose nanomaterials have attracted a great deal of interest as sustainable alternatives to nonrenewable or fossil fuel-derived materials, particularly in composite applications. Cellulose nanofibrils (CNF) are most often derived from wood sources through energy-intensive and costly mechanical fibrillation processes. Here, recycled cardboard, referred to as old corrugated cardboard (OCC), was investigated as an alternate CNF source. OCC is a recycled material that can be obtained at one-tenth the cost of the commonly used bleached softwood Kraft pulp and can be refined to similar levels with nearly one-half of the energy consumption. Additionally, the distinct composition and morphology of OCC-derived CNF provides a more favorable fiber–matrix interface and better reinforcement capabilities of the cellulose nanofibrils in polymer matrices, displaying an over 70% increase in tensile modulus at a loading of 40 wt % with no decrease in tensile strength. When paired with biobased poly(l-lactide) (PLLA), OCC-derived CNF is proven to be an attractive low-cost and low-energy reinforcing agent for sustainable, high performance nanocomposites.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1972

Moisture effects on the high-temperature strength of fiber-reinforced resin composites.

Under NAS 8-27435, the Convair Aerospace Division of General Dynamics and their subcontractor, Hercules Incorporated, have conducted studies on the effects of moisture on the properties of fiber-reinforced resin composites and on the epoxy resins presently used in advanced composites. Data are presented on the resins and composites subjected to varying time/temperature/humidity or time/temperature/water-boil exposures. The effects of moisture on matrix, reinforcement, and fiber/resin interface are discussed and supported by experimental test data.

Hertz, J.↗
NASA NTRS1993

Thermodynamic analysis of chemical compatibility of several compounds with Fe-Cr-Al alloys

Chemical compatibility between Fe-19.8Cr-4.8Al (weight percent), which is the base composition for the commercial superalloy MA956, and several carbides, borides, nitrides, oxides, and silicides was analyzed from thermodynamic considerations. The effect of addition of minor alloying elements, such as Ti, Y, and Y2O3, to the Fe-Cr-Al alloy on chemical compatibility between the alloy and various compounds was also analyzed. Several chemically compatible compounds that can be potential reinforcement materials and/or interface coating materials for Fe-Cr-Al based composites were identified.

Misra, Ajay K.↗
NASA NTRS1992

Role of interfacial thermal barrier in the transverse thermal conductivity of uniaxial SiC fiber-reinforced reaction bonded silicon nitride

The transverse thermal conductivity of reaction-bonded Si3N4 is significantly affected by an interfacial barrier at the interface formed with SiC reinforcing fibers. A comparative study of composites with and without reinforcing-fiber carbon coatings found the coating to reduce effective thermal conductivity by a factor of about 2; this, however, is partially due to a thermal expansion-mismatch gap between fiber and matrix. HIPing of composites with coated fibers led to an enhancement of thermal conductivity via improved interfacial thermal contact and greater grain size and crystallinity of the fibers.

Bhatt, H.↗
NASA NTRS1991

Transverse ductility of metal matrix composites

The role of the fiber matrix interface bond on the transverse ductility of continuous fiber reinforced composites has been investigated. Two specific systems have been considered: an Aluminum alloy matrix reinforced by Alumina fibers, characterized by a strong interface and a Titanium alloy reinforced by coated Silicon Carbide fibers, characterized by a weak interface. A micro-mechanical study indicates that the bond condition has a significant effect on the state of stress in the matrix which in turn dictates the available matrix ductility. The micro-mechanical predictions are in good agreement with the experimental results for the two systems.

Gunawardena, S. R.↗
NASA NTRS1990

Characterization of interfacial failure in SiC reinforced Si3N4 matrix composite material by both fiber push-out testing and Auger electron spectroscopy

AES depth profiling and a fiber push-out test for interfacial shear-strength determination have been used to ascertain the mechanical/chemical properties of the fiber/matrix interface in SiC-reinforced reaction-bonded Si3N4, with attention to the weak point where interfacial failure occurs. In the cases of both composite fracture and fiber push-outs, the interfacial failure occurred either between the two C-rich coatings that are present on the double-coated SiC fibers, or between the inner C-rich coating and the SiC fiber. Interface failure occurs at points of very abrupt concentration changes.

Eldridge, J. I.↗
DOE OSTI2024

Equivalent Properties of Interfacial Void Defects at the CFRTP-adhesive Interface and Their Detrimental Effects on the Bonding Performance of Metal-CFRTP Dissimilar Joints

This paper revealed the detrimental effects of micro-scale air interfacial voids on the debonding at the interface of carbon-fiber-reinforced polyphthalamide (CFRPPA) and thermoset adhesive, representing a weak adherend-adhesive interface, within a dissimilar joint made of an aluminum alloy and a CFRPPA. The reduced lap shear strength of the joint, due to different void area fractions at the CFRPPA-adhesive interface, can be computationally described by using equivalent interfacial properties in the modeling to avoid the explicit modeling of the micro-scale interfacial voids. Such equivalent interfacial properties (e.g., interfacial normal strength, etc.) was found to have a non-linear relationship with respect to interfacial void area fraction as well as lap shear strength. This work has practical applications by utilizing equivalent interfacial properties for the analytical and/or computational design(s) of adhesively bonded joints.

Qiao, Yao↗
NASA NTRS2004

Multilayer Fiber Interfaces for Improved Environmental Resistance and Slip in Carbon Fiber Reinforced Composites

Ultraviolet-enhanced chemical vapor deposition (UVCVD) has been developed to lower the required substrate temperature thereby allowing for the application of metal oxide-based coatings to carbon and ceramic fibers without causing significant fiber damage. An effort to expand this capability to other ceramic phases chosen to maximize oxidation protection in the likely event of matrix cracking and minimize possible reaction between the coating and fiber during long-term high temperature use will be presented along with studies aimed at the demonstration of these and other benefits for the next-generation interface coating systems being developed herein.

Babcock, Jason R.↗
NASA NTRS2013

A Test for Characterizing Delamination Migration in Carbon/Epoxy Tape Laminates

A new test method is presented for the purpose of investigating migration of a delamination between neighboring ply interfaces in fiber-reinforced, polymer matrix tape laminates. The test is a single cantilever beam configuration consisting of a cross-ply laminate with a polytetrafluoroethylene insert implanted at the mid-plane and spanning part way along the length of the specimen. The insert is located between a 0- degree ply (specimen length direction) and a stack of four 90-degree plies (specimen width direction). The specimen is clamped at both ends onto a rigid baseplate and is loaded on its upper surface via a piano hinge. Tests were conducted with the load-application point located on the intact portion of the specimen in order to initiate delamination growth onset followed by migration of the delamination to a neighboring 90/0 ply interface by kinking through the 90-degree ply stack. Varying this position was found to affect the distance relative to the load-application point at which migration initiated. In each specimen, migration initiated by a gradual transition of the delamination at the 0/90 interface into the 90-degree ply stack. In contrast, transition of the kinked crack into the 90/0 interface was sudden. Fractography of the specimens indicated that delamination prior to migration was generally mixed mode-I/II. Inspection of the kink surface revealed mode-I fracture. In general, use of this test allows for the observation of the growth of a delamination followed by migration of the delamination to another ply interface, and should thus provide a means for validating analyses aimed at simulating migration.

Ratcliffe, James G.↗
NASA NTRS2012

Characterizing Delamination Migration in Carbon/Epoxy Tape Laminates

A new test method is presented for the purpose of investigating migration of a delamination between neighboring ply interfaces in fiber-reinforced, polymer matrix tape laminates. The test is a single cantilever beam configuration consisting of a cross-ply laminate with a polytetrafluoroethylene (PTFE) insert implanted at the mid-plane and spanning part way along the length of the specimen. The insert is located between a 0-degree ply (specimen length direction) and a stack of four 90-degree plies (specimen width direction). The specimen is clamped at both ends onto a rigid baseplate and is loaded on its upper surface via a piano hinge. Tests were conducted with the load-application point located on the intact portion of the specimen in order to initiate delamination growth onset followed by migration of the delamination to a neighboring 90/0 ply interface by kinking through the 90- degree ply stack. Varying this position was found to affect the distance relative to the load-application point at which migration initiated. In each specimen, migration initiated by a gradual transition of the delamination at the 0/90 interface into the 90- degree ply stack. In contrast, transition of the kinked crack into the 90/0 interface was sudden. Fractography of the specimens indicated that delamination prior to migration was generally mixed mode-I/II. Inspection of the kink surface revealed mode-I fracture. In general, use of this test allows for the observation of the growth of a delamination followed by migration of the delamination to another ply interface, and should thus provide a means for validating analyses aimed at simulating migration.

Ratcliffe, James G.↗
NASA NTRS2006

Mode I Toughness Measurements of Core/Facesheet Bonds in Honeycomb Sandwich Structures

Composite sandwich structures will be used in many future applications in aerospace, marine and offshore industries due to the fact that the strength and stiffness to mass ratios surpass any other structural type. Sandwich structure also offers advantages over traditional stiffened panels such as ease of manufacturing and repair. During the last three decades, sandwich structure has been used extensively for secondary structure in aircraft (fuselage floors, rudders and radome structure). Sandwich structure is also used as primary structure in rotorcraft, the most common example being the trailing edge of rotor blades. As with other types of composite construction, sandwich structure exhibits several types of failure mode such as facesheet wrinkling, core crushing and sandwich buckling. Facesheet/core debonding has also been observed in the marine and aerospace industry. During this failure mode, peel stresses applied to an existing facesheet/core debond or an interface low in toughness, results in the facesheet being peeled from the core material, possibly leading to a significant loss in structural integrity of the sandwich panel. In an incident during a test on a liquid hydrogen fuel tank of the X-33 prototype vehicle, the outer graphite/epoxy facesheet and honeycomb core became debonded from the inner facesheet along significant areas, leading to failure of the tank. As a consequence of the accident; significant efforts were made to characterize the toughness of the facesheet/core bond. Currently, the only standardized method available for assessing the quality of the facesheet/core interface is the climbing drum peel test (ASTM D1781). During this test a sandwich beam is removed from a panel and the lip of one of the facesheets is attached to a drum, as shown in Fig. 1. The drum is then rotated along the sandwich beam, causing the facesheet to peel from the core. This method has two major drawbacks. First, it is not possible to obtain quantitative fracture data from the test and so the results can only be used in a qualitative manner. Second, only sandwich structure with thin facesheets can be tested (to facilitate wrapping of the facesheet around the climbing drum). In recognition of the need for a more quantitative facesheet/core fracture test, several workers have devised experimental techniques for characterizing the toughness of the facesheet/core interface. In all of these cases, the tests are designed to yield a mode I-dominated fracture toughness of the facesheet/core interface in a manner similar to that used to determine mode I fracture toughness of composite laminates. In the current work, a modified double cantilever beam is used to measure the mode I-dominated fracture toughness of the interface in a sandwich consisting of glass/phenolic honeycomb core reinforced with graphite epoxy facesheets. Two specimen configurations were tested as shown in Fig 2. The first configuration consisted of reinforcing the facesheets with aluminum blocks (Fig. 2a). In the second configuration unreinforced specimens were tested (Fig. 2b). Climbing drum peel tests were also conducted to compare the fracture behavior observed between this test and the modified double cantilever beam. This paper outlines the test procedures and data reduction strategies used to compute fracture toughness values from the tests. The effect of specimen reinforcement on fracture toughness of the facesheet/core interface is discussed.

Nettles, Alan T.↗
NASA NTRS1986

High-resolution Surface Analysis by Microarea Auger Spectroscopy: Computerization and Characterization

A custom scanning Auger electron microscope (SAM) capable of introducing a 3-5 keV electron beam of several nA into a 30 nm diameter sample area was fitted with a sample introduction system and was fully computerized to be used for materials science research. The method of multispectral Auger imaging was devised and implemented. The instrument was applied to various problems in materials science, including the study of the fiber/matrix interface in a SiC reinforced titanium alloy, the study of SiC whiskers in Al alloy 2124 (in cooperation with NASA-Langley), the study of NiCrAl superalloys (in collaboration with NASA-Lewis), the study of zircalloy specimens (in collaboration with Stanford University), and the microstructure of sintered SiC specimens (in collaboration with NASA-Lewis). The report contains a number of manuscripts submitted for publication on these subjects.

Browning, R.↗
NASA NTRS2000

Effects of Interface Coating and Nitride Enhancing Additive on Properties of Hi-Nicalon SiC Fiber Reinforced Reaction-Bonded Silicon Nitride Composites

Strong and tough Hi-Nicalon SiC fiber reinforced reaction-bonded silicon nitride matrix composites (SiC/ RBSN) have been fabricated by the fiber lay-up approach. Commercially available uncoated and PBN, PBN/Si-rich PBN, and BN/SiC coated SiC Hi-Nicalon fiber tows were used as reinforcement. The composites contained approximately 24 vol % of aligned 14 micron diameter SiC fibers in a porous RBSN matrix. Both one- and two-dimensional composites were characterized. The effects of interface coating composition, and the nitridation enhancing additive, NiO, on the room temperature physical, tensile, and interfacial shear strength properties of SiC/RBSN matrix composites were evaluated. Results indicate that for all three coated fibers, the thickness of the coatings decreased from the outer periphery to the interior of the tows, and that from 10 to 30 percent of the fibers were not covered with the interface coating. In the uncoated regions, chemical reaction between the NiO additive and the SiC fiber occurs causing degradation of tensile properties of the composites. Among the three interface coating combinations investigated, the BN/SiC coated Hi-Nicalon SiC fiber reinforced RBSN matrix composite showed the least amount of uncoated regions and reasonably uniform interface coating thickness. The matrix cracking stress in SiC/RBSN composites was predicted using a fracture mechanics based crack bridging model.

Bhatt, Ramakrishana T.↗