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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 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Interfacial adhesion of carbon fibers

Relative adhesion strengths between AS4, AS1, and XAS carbon fibers and thermoplastic polymers were determined using the embedded single filament test. Polymers studied included polycarbonate, polyphenylene oxide, polyetherimide, polysulfone, polyphenylene oxide blends with polystyrene, and polycarbonate blends with a polycarbonate polysiloxane block copolymer. Fiber surface treatments and sizings improved adhesion somewhat, but adhesion remained well below levels obtained with epoxy matrices. An explanation for the differences between the Hercules and Grafil fibers was sought using X ray photon spectroscopy, wetting, scanning electron microscopy and thermal desorption analysis.

Bascom, Willard D.↗
NASA NTRS1985

The effects of molecular weight on the single lap shear creep and constant strain rate behavior of thermoplastic polyimidesulfone adhesive

The bonded shear creep and constant strain rate behaviors of zero, one, and three percent endcapped thermoplastic polyimidesulfone adhesive were examined at room and elevated temperatures. Endcapping was accomplished by the addition of phthalic anhydrides. The primary objective was to determine the effects of molecular weight on the mechanical properties of the adhesive. Viscoelastic and nonlinear elastic constitutive equations were utilized to model the adhesive. Ludwik's and Crochet's relations were used to describe the experimental failure data. The effects of molecular weight changes on the above mentioned mechanical behavior were assessed. The viscoelastic Chase-Goldsmith and elastic nonlinear relations gave a good fit to the experimental stress strain behavior. Crochet's relations based on Maxwell and Chase-Goldsmith models were fit to delayed failure data. Ludwik's equations revealed negligible rate dependence. Ultimate stress levels and the safe levels for creep stresses were found to decrease as molecular weight was reduced.

Dembosky, Stanley K.↗
NASA NTRS1987

Surface characterization in composite and titanium bonding: Carbon fiber surface treatments for improved adhesion to thermoplastic polymers

The effect of anodization in NaOH, H2SO4, and amine salts on the surface chemistry of carbon fibers was examined by X-ray photoelectron spectroscopy (XPS). The surfaces of carbon fibers after anodization in NaOH and H2SO4 were examined by scanning transmission electron microscopy (STEM), angular dependent XPS, UV absorption spectroscopy of the anodization bath, secondary ion mass spectrometry, and polar/dispersive surface energy analysis. Hercules AS-4, Dexter Hysol XAS, and Union Carbide T-300 fibers were examined by STEM, angular dependent XPS, and breaking strength measurement before and after commercial surface treatment. Oxygen and nitrogen were added to the fiber surfaces by anodization in amine salts. Analysis of the plasmon peak in the carbon 1s signal indicated that H2SO4 anodization affected the morphological structure of the carbon fiber surface. The work of adhesion of carbon fibers to thermoplastic resins was calculated using the geometric mean relationship. A correlation was observed between the dispersive component of the work of adhesion and the interfacial adhesion.

Devilbiss, T. A.↗
NASA NTRS1986

Nondestructive evaluation of adhesive bond strength using the stress wave factor technique

Acousto-ultrasonic nondestructive evaluation has been conducted to evaluate the adhesive bond strength between rubber and steel plates using the stress wave factor (SWF) measurement technique. Specimens with different bond strength were manufactured and tested using the SWF technique. Two approaches were used to define the SWF. One approach defines the SWF as the signal energy and the other approach defines the SWF as the square root of the zero moment of the frequency spectrum of the received signal. The strength of the rubber-steel adhesive joint was then evaluated using the destructive peel strength test method. It was observed that in both approaches higher values of the SWF measurements correspond to higher values of the peel strength test data. Therefore, these results show that the stress wave factor technique has the potential of being used in quality assurance of the adhesive bond strength between rubber and steel substrates.

Dos Reis, Henrique L. M.↗
NASA NTRS1987

Adhesion, friction and deformation of ion-beam-deposited boron nitride films

The tribological properties and mechanical strength of boron nitride films were investigated. The BN films were predominantly amorphous and nonstoichiometric and contained small amounts of oxides and carbides. It was found that the yield pressure at full plasticity, the critical load to fracture, and the shear strength of interfacial adhesive bonds (considered as adhesion) depended on the type of metallic substrate on which the BN was deposited. The harder the substrate, the greater the critical load and the adhesion. The yield pressures of the BN film were 12 GPa for the 440C stainless steel substrate, 4.1 GPa for the 304 stainless steel substrate, and 3.3 GPa for the titanium substrate.

Miyoshi, K.↗
NASA NTRS1988

Interfacial adhesion: Theory and experiment

Adhesion, the binding of different materials at an interface, is of general interest to many branches of technology, e.g., microelectronics, tribology, manufacturing, construction, etc. However, there is a lack of fundamental understanding of such diverse interfaces. In addition, experimental techniques generally have practical objectives, such as the achievement of sufficient strength to sustain mechanical or thermal effects and/or have the proper electronic properties. In addition, the theoretical description of binding at interfaces is quite limited, and a proper data base for such theoretical analysis does not exist. This presentation will review both experimental and theoretical aspects of adhesion in nonpolymer materials. The objective will be to delineate the critical parameters needed, governing adhesion testing along with an outline of testing objectives. A distinction will be made between practical and fundamental objectives. Examples are given where interfacial bonding may govern experimental consideration. The present status of theory is presented along wiith recommendations for future progress and needs.

Ferrante, John↗
NASA NTRS1988

Initial adhesive screening of novel polyamide-imides and their copolymers

Continued interest by the research community in thermally stable, tough, high temperature adhesives has resulted in the investigation by Langley Research Center of two linear aromatic polyamide-imide (PAI) homopolymers and two linear aromatic PAI copolymers. The homopolymers were made with either 3,3'=DABA or 4,4'-DABA and BTDA. The two polymers were prepared with a monomer ratio of 0.75 DABP:0.25 DABA:1.00 BTDA. These aromatic PAIs possess high thermal stability because of intermolecular hydrogen bonding and chain stiffness. Lap shear strength (LSS) was the main criteria used to evaluate the polymers as adhesives. LSS of bonded Ti-6Al-4V was determined at room temperature (RT), 177, 204 and 232 C. The glass transition temperature and the type of bond failure were also determined. The best LSS values of the four adhesive systems investigated were obtained with the PAI copolymer identified in the report as LARC-TPI (25 percent 3,3'-DABA); however, it did not produce LSSs nearly as high as LARC-TPI. The poor flow properties observed appear to be due to a combination of high molecular weight and the increased interchain electronic interactions associated with the amide group.

Donald J Progar↗
NASA NTRS1988

Reducing adhesion and agglomeration within a cloud of combustible particles

The study of combustible particle clouds inside flame tubes is of fundamental scientific interest as well as a practical concern. Only the suspended concentration is important to the combustion process, so that assurances must be provided that a minimum of particles adheres to the tube wall. This paper demonstrates experimentally the ability to minimize adhesion and agglomeration of acoustically-mixed lycopodium particles within a 5-cm diameter lexan flame tube. The area density of particles (ADP) adhering to the wall of bare lexan tubes was measured at greater than 100 particles/sq mm. The nature of adhesion was found to be clearly electrostatic, with the ADP level aggravated by increased mixing time, vigor, and the concentration of particles. Increases in the conductivity of the air and the tube wall did not affect ADP levels substantially. However, the observed adhesion was reduced to less than 10 p/sq mm when the air was ionized by use of an alpha emitter mounted on the inner walls of the flame tube.

Ross, Howard D.↗
NASA NTRS1987

Evaluation of polyimide films as adhesives

A commercially available LARC-TPI film and an experimentally prepared film of LARC-TPI with 5 mol pct of 4,4-prime-oxydianiline (ODA), designated as LARC-TPI/ODA, were evaluated as thermoplastic adhesive films for bonding Ti-6Al-4V. Lap shear strength was used to evaluate the materials as adhesives. They were characterized after fracture by determining the glass transition temperature, T(g). The mode of failure is also reported. Thermal exposure at 240 C for 500 and 1000 h and a 72-h water-boil were conducted on lap shear specimens prepared with the two adhesive films. Lap shear tests were conducted at room temperature, 177 C, 204 C, and 232 C before and after exposures.

Progar, Donald J.↗
NASA NTRS1989

Effect of adhesive interleaving and discontinuous plies on failure of composite laminates subject to transverse normal loads

Results of a series of tests to determine the effects of adhesive interleaving and discontinuous plies (plies with end-to-end gaps) on the displacements, failure loads and failure modes of graphite-epoxy laminates subjected to transverse normal loads are presented. Adhesive interleaving can be used to contain local damage within a group of plies, i.e., to arrest crack propagation on the interlaminate level, and it can increase the amount of normal displacement the laminate can withstand before failure. However, the addition of adhesive interleaving to a laminate does not significantly increase its load carrying capability. A few discontinuous plies in a laminate can reduce the normal displacement and load at failure by 10 to 40 percent compared to a laminate with no discontinuous plies, but the presence of the ply discontinuities does not generally change the failure location or the failure mode of the laminate.

Jegley, Dawn C.↗
NASA NTRS1989

Simplified procedures for designing adhesively bonded composite joints

Procedures for the preliminary design of composite adhesive joints are described. Typical joints, their respective free body diagrams, and approximate equations for estimating the stresses in each of these typical joints are summarized. Equations are also presented to check the critical conditions of the joint such as minimum length, maximum adhesive shear stress, and peel-off stress. To illustrate the procedure, sample designs are described in step-by-step fashion for a butt joint with single doubler subjected to static loads, cyclic loads, and environmental effects. The results show that unsymmetric adhesive joints are inefficient and should be avoided, and hygrothermal environments and cyclic loads dramatically reduce the structural integrity of the joint and require several joint lengths compared with those for static load with no environmental effects.

Chamis, C. C.↗
NASA NTRS1988

A comparison of pure mode I and mixed mode I-III cracking of an adhesive containing an open knit cloth carrier

Static and fatigue tests were carried out on two commercial modified epoxy film adhesives with a wide open knit polyester carrier in order to compare crack resistance in mode I and mixed mode I-III loading. The carrier cloth is found to have a significant influence on the cracking behavior of the adhesives. The open air net carrier used in this study separates from the adhesive in mode I cracking but shreds during mixed-mode crack extension. This decreases the opening mode toughness but increases the mixed-mode toughness as compared with results obtained earlier using a heavier knit carrier. The results suggest that the type of carrier may have a far larger influence on crack resistance than is generally recognized.

Ripling, E. J.↗
NASA NTRS1988

Interfacial adhesion - Theory and experiment

Adhesion, the binding of different materials at an interface, is of general interest to many branches of technology, e.g., microelectronics, tribology, manufacturing, construction, etc. However, there is a lack of fundamental understanding of such diverse interfaces. In addition, experimental techniques generally have practical objectives, such as the achievement of sufficient strength to sustain mechanical or thermal effects and/or have the proper electronic properties. In addition, the theoretical description of binding at interfaces is quite limited, and a proper data base for such theoretical analysis does not exist. This presentation will review both experimental and theoretical aspects of adhesion in nonpolymer materials. The objective will be to delineate the critical parameters needed, governing adhesion testing along with an outline of testing objectives. A distinction will be made between practical and fundamental objectives. Examples are given where interfacial bonding may govern experimental consideration. The present status of theory is presented along with recommendations for future progress and needs.

Ferrante, John↗
NASA NTRS1989

Initial evaluation of novel polyamide-imides and their copolymers as adhesives

Continued interest by the research community in thermally stable, tough, high temperature adhesives has resulted in the investigation by Langley Research Center of two linear aromatic polyamide-imide (PAI) homopolymers and two linear aromatic PAI copolymers. The homopolymers were made with either 3,3'=DABA or 4,4'-DABA and BTDA. The two polymers were prepared with a monomer ratio of 0.75 DABP:0.25 DABA:1.00 BTDA. These aromatic PAIs possess high thermal stability because of intermolecular hydrogen bonding and chain stiffness. Lap shear strength (LSS) was the main criteria used to evaluate the polymers as adhesives. LSS of bonded Ti-6Al-4V was determined at room temperature (RT), 177, 204 and 232 C. The glass transition temperature and the type of bond failure were also determined. The best LSS values of the four adhesive systems investigated were obtained with the PAI copolymer identified in the report as LARC-TPI (25 percent 3,3'-DABA); however, it did not produce LSSs nearly as high as LARC-TPI. The poor flow properties observed appear to be due to a combination of high molecular weight and the increased interchain electronic interactions associated with the amide group.

Progar, Donald J.↗
NASA NTRS1989

Instrumented adhesion tests on plasma sprayed thermal barrier coatings

The failure mechanisms of plasma-sprayed two-layer coatings consisting of an NiCrAlY or NiCrAlZr bond coat with an yttria-stabilized zirconia overlay are presently examined by tensile adhesion tests. It has been found that adhesive failure within the bond coat exhibits greater failure strain than the cohesive failure of the ceramic overlay, supporting the view of the intermediate coatings being highly compliant. The absolute extension exhibited by failures occurring only through the ceramic coating is greater than that of adhesive failure, since the ceramic coating is much thicker than the bond coat.

Berndt, Christopher C.↗
NASA NTRS1991

Fast-Acting Rubber-To-Coated-Aluminum Adhesive

Cyanoacrylate adhesive used to join rubber to coated aluminum easier to apply and more effective. One-part material applied in single coat to aluminum treated previously with epoxy primer and top coat. Parts mated as soon as adhesive applied; no drying necessary. Sets in 5 minutes. Optionally, accelerator brushed onto aluminum to reduce setting time to 30 seconds. Clamping parts together unnecessary. Adhesive comes in four formulations, all based on ethyl cyanoacrylate with various amounts of ethylene copolymer rubber, poly(methyl methacrylate), silicon dioxide, hydroquinone, and phthalic anhydride.

Comer, Dawn A.↗
NASA NTRS1990

The looped adhesive strip: An example of coplanar delamination interaction

The phenomenon of peeling and debonding of thin layers is a subject of interest to those concerned with adhesives, thin films, and layered materials. In recent years much attention has been focused on such problems as a result of increased interest and application of advanced composites and thin film coatings. A related problem which is of interest for its own sake but also represents a simple example of a tangled adhesive strip and of coplanar delamination interaction, is the problem of a looped adhesive strip. This is the subject of the present study. Researchers consider here the problem of an elastic strip which possesses an adherend on (at least) one of its surfaces. If the strip is deformed so that two portions of such a surface are brought into contact, a position of the strip becomes bonded and a loop is formed. Researchers are interested in determining the equilibrium configuration of such a strip and investigating the behavior of the strip when its edges are pulled apart. The problem is approached as a moving interior boundary problem in the calculus of variations with the strip modeled as an inextensible elastica and the bond strength characterized by its surface energy. A Griffith type energy criterion is employed for debonding, and solutions corresponding to the problem of interest obtained. The solution obtained will be seen to predict the interesting phenomenon of bond point propagation, as well as the more standard peeling type behavior. Numerical results demonstrating the phenomena of interest are presented as well and will be seen to reveal both stable and unstable propagation of the boundaries of the bonded portion of the strip, depending upon the loading conditions.

Bottega, W. J.↗