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At least 181 records · Page 10

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NASA NTRS1989

Orthotropic elastic-plastic behavior of AS4/APC-2 thermoplastic composite at elevated temperatures

Inelastic and strength properties of AS4/APC-2 composites were characterized with respect to temperature variation by using a one parameter orthotropic plasticity model and a one parameter failure criterion. Simple uniaxial off-axis tension tests were performed on coupon specimens of unidirectional AS4/APC-2 thermoplastic composite at various temperatures. To avoid the complication caused by the extension-shear coupling effect in off-axis testing, new tabs were designed and used on the test specimens. The experimental results showed that the nonlinear behavior of constitutive relations and the strength can be characterized quite well using the one parameter plasticity model and the failure criterion, respectively.

Sun, C. T.↗

NASA NTRS1992

Properties Of High-Performance Thermoplastics

Report presents review of principal thermoplastics (TP's) used to fabricate high-performance composites. Sixteen principal TP's considered as candidates for fabrication of high-performance composites presented along with names of suppliers, Tg, Tm (for semicrystalline polymers), and approximate maximum processing temperatures.

Johnston, Norman J.↗

NASA NTRS1992

Tough, high performance, addition-type thermoplastic polymers

A tough, high performance polyimide is provided by reacting a triple bond conjugated with an aromatic ring in a bisethynyl compound with the active double bond in a compound containing a double bond activated toward the formation of a Diels-Adler type adduct, especially a bismaleimide, a biscitraconimide, or a benzoquinone, or mixtures thereof. Addition curing of this product produces a high linear polymeric structure and heat treating the highly linear polymeric structure produces a thermally stable aromatic addition-type thermoplastic polyimide, which finds utility in the preparation of molding compounds, adhesive compositions, and polymer matrix composites.

Pater, Ruth H.↗

NASA NTRS1990

Development of thermoplastic components for structural validation

Recent activity directed toward advancing the development and validation of graphite reinforced thermoplastic primary and secondary structures is described. The efforts discussed include the design, manufacture and test of a highly-loaded multi-spar wing-box component, and the development of a flight-worthy article that is form, fit and functionally replaceable with the nose landing gear door of the V-22 Osprey.

Avery, John G.↗

NASA NTRS1992

Continuation of tailored composite structures of ordered staple thermoplastic material

The search for the cost effective composite structure has motivated the investigation of several approaches to develop composite structure from innovative material forms. Among the promising approaches is the conversion of a planar sheet to components of complex curvature through sheet forming or stretch forming. In both cases, the potential for material stretch in the fiber direction appears to offer a clear advantage in formability over continuous fiber systems. A framework was established which allows the simulation of the anisotropic mechanisms of deformation of long discontinuous fiber laminates wherein the matrix phase is a viscous fluid. Predictions for the effective viscosities of a hyper-anisotropic medium consisting of collimated, discontinuous fibers suspended in viscous matrix were extended to capture the characteristics of typical polymers including non-Newtonian behavior and temperature dependence. In addition, the influence of fiber misorientation was also modeled by compliance averaging to determine ensemble properties for a given orientation distribution. A design tool is presented for predicting the effect of material heterogeneity on the performance of curved composite beams such as those used in aircraft fuselage structures. Material heterogeneity can be induced during manufacturing processes such as sheet forming and stretch forming of thermoplastic composites. This heterogeneity can be introduced in the form of fiber realignment and spreading during the manufacturing process causing radial and tangential gradients in material properties. Two analysis procedures are used to solve the beam problems. The first method uses separate two-dimensional elasticity solutions for the stresses in the flange and web sections of the beam. The separate solutions are coupled by requiring that forces and displacements match section boundaries. The second method uses an approximate Rayleigh-Ritz technique to find the solutions for more complex beams. Analyses are performed for curved beams of various cross-sections loaded in pure bending and with a uniform distributed load. Preliminary results show that the geometry of the beam dictates the effect of heterogeneity on performance. The role of heterogeneity is larger in beams with a small average radius-to-depth ration, R/t, where R is the average radius of the beam and t is the difference between the inside and outside radii. Results of the anlysis are in the form of stresses and displacements and are compared to both mechanics of materials and numerical solutions obtained using finite element analysis.

Santare, Michael H.↗

NASA NTRS1991

Emerging polyheterocyclic films, coatings and resins - Thermoplastic polyquinolines

The processing and performance characteristics of a soluble, thermoplastic polyquinoline suggest its utility in a variety of high performance applications. The polymer is characterized by excellent thermal and oxidative stability, very low moisture absorption, good mechanical properties, very low dielectric constant, and an unusually low thermal expansion coefficient. This polymer, designated PQ-100 (TM), can be cast into strong, transparent, free standing films from common solvents. Coatings of variable thickness can be spin-coated on to silicon and other surfaces. After processing into films, PQ-100 (TM) can be rendered insoluble in a wide range of solvents using a proprietary process. The low CTE contributes to very low residual stress when the polymer is spin-coated onto silicon wafers. PQ-100 (TM) is currently under evaluation for use as an interlayer dielectric substrate in high-density interconnect applications, including multichip modules. Many of the characteristics of the polymer also suggest its utility as a high-performance film and as a matrix resin for specialty composite applications.

Hendricks, Neil H.↗

NASA NTRS1991

High performance addition-type thermoplastics (ATTs) - Evidence for the formation of a Diels-Alder adduct in the reaction of an acetylene-terminated material and a bismaleimide

Recently, the concept and demonstration of a new versatile synthetic reaction for making a large number of high-performance addition-type thermoplastics (ATTs) were reported. The synthesis shows promise for providing polymers having an attractive combination of easy processability, good toughness, respectable high temperature mechanical performance, and excellent thermo-oxidative stability. The new chemistry involves the reaction of an acetylene-terminated material with a bismaleimide or benzoquinone. In order to clarify the reaction mechanism, model compound studies were undertaken in solutions as well as in the solid state. The reaction products were purified by flash chromatography and characterized by conventional analytical techniques including NMR, FT-IR, UV-visible, mass spectroscopy, and high pressure liquid chromatography. The results are presented of the model compound studies which strongly support the formation of a Diels-Alder adduct in the reaction of an acetylene-terminated compound and a bismaleimide or benzoquinone.

Pater, R. H.↗

NASA NTRS1991

Characterization of elastic-plastic behavior of AS4/PEEK thermoplastic composite for temperature variation

Inelastic and strength properties of AS4/PEEK composites were characterized with respect to temperature variation by using a one-parameter orthotropic plasticity model and a one-parameter failure criterion. Simple uniaxial off-axis tension tests were performed on coupon specimens of unidirectional AS4/PEEK thermoplastic composite at various temperatures. To avoid the complication caused by the extension-shear coupling effect in off-axis testing, new tabs were designed and used on the test specimens. Experimental results showed that the nonlinear behavior of constitutive relations and the strength can be characterized quite well using the one-parameter plasticity model and the failure criterion, respectively.

Sun, C. T.↗

NASA NTRS1990

Nonlinear analysis of AS4/PEEK thermoplastic composite laminate using a one parameter plasticity model

A one-parameter plasticity model was shown to adequately describe the orthotropic plastic deformation of AS4/PEEK (APC-2) unidirectional thermoplastic composite. This model was verified further for unidirectional and laminated composite panels with and without a hole. The nonlinear stress-strain relations were measured and compared with those predicted by the finite element analysis using the one-parameter elastic-plastic constitutive model. The results show that the one-parameter orthotropic plasticity model is suitable for the analysis of elastic-plastic deformation of AS4/PEEK composite laminates.

Sun, C. T.↗

NASA NTRS1992

The development of an alternative thermoplastic powder prepregging technique

An alternative powder prepregging technique is discussed that is based on the deposition of powder onto carbon fibers that have been moistened using an ultrasonic humidifier. The dry fiber tow is initially spread to allow a greater amount of the fiber surface to be exposed to the powder, thus ensuring a significant amount of intimate contact between the fiber and the matrix. Moisture in the form of ultrafine water droplets is then deposited onto the spread fiber tow. The moisture promotes adhesion to the fiber until the powder can be tacked to the fibers by melting. Powdered resin is then sieved onto the fibers and then tacked onto the fibers by quick heating in a convective oven. This study focuses on the production of prepregs and laminates made with LaRC-TPI (thermoplastic polyimide) using this process. Although the process appears to be successful, early evaluation was hampered by poor interfacial adhesion. The adhesion problem, however, seems to be the result of a material system incompatibility, rather than being influenced by the process.

Ogden, A. L.↗

NASA NTRS1993

Portable Device Slices Thermoplastic Prepregs

Prepreg slitter designed to slit various widths rapidly by use of slicing bar holding several blades, each capable of slicing strip of preset width in single pass. Produces material evenly sliced and does not contain jagged edges. Used for various applications in such batch processes involving composite materials as press molding and autoclaving, and in such continuous processes as pultrusion. Useful to all manufacturers of thermoplastic composites, and in slicing B-staged thermoset composites.

Taylor, Beverly A.↗

NASA NTRS1993

Program For Two-Dimensional Thermoplastic Deformation

SOLAS contains number of utility programs for use with finite-element simulations. Designed to handle two-dimensional problems of quasi-static thermoplastic deformation. Includes optional postprocessing software, independent of solution codes, generating unified element-by-element list of quantitative results of computation, plus file containing signed equivalent stresses, equivalent strains, and multiaxiality factor parameter. Signs of equivalent quantities expressed either with respect to maximum principal quantities or with respect to directions defined by user. Written in UNIX shell script and FORTRAN 77.

Orient, George E.↗

NASA NTRS1992

Study of compression-loaded and impact-damaged structurally efficient graphite-thermoplastic trapezoidal-corrugation sandwich and semisandwich panels

The structural efficiency of compression-loaded trapezoidal-corrugation sandwich and semisandwich composite panels is studied to determine their weight savings potential. Sandwich panels with two identical face sheets and a trapezoidal corrugated core between them and semisandwich panels with a corrugation attached to a single skin are considered. An optimization code is used to find the minimum weight designs for critical compressive load levels ranging from 3000 to 24,000 lb/in. Graphite-thermoplastic panels based on the optimal minimum weight designs were fabricated and tested. A finite element analysis of several test specimens was also conducted. The results of the optimization study, the finite element analysis, and the experiments are presented. The results of testing impact damage panels are also discussed.

Jegley, Dawn C.↗

NASA NTRS1991

Consolidation of graphite thermoplastic textile preforms for primary aircraft structure

The use of innovative cost effective material forms and processes is being considered for fabrication of future primary aircraft structures. Processes that have been identified as meeting these goals are textile preforms that use resin transfer molding (RTM) and consolidation forming. The Novel Composites for Wing and Fuselage Applications (NCWFA) program has as its objective the integration of innovative design concepts with cost effective fabrication processes to develop damage-tolerant structures that can perform at a design ultimate strain level of 6000 micro-inch/inch. In this on-going effort, design trade studies were conducted to arrive at advanced wing designs that integrate new material forms with innovative structural concepts and cost effective fabrication methods. The focus has been on minimizing part count (mechanical fasteners, clips, number of stiffeners, etc.), by using cost effective textile reinforcement concepts that provide improved damage tolerance and out-of-plane load capability, low-cost resin transfer molding processing, and thermoplastic forming concepts. The fabrication of representative Y spars by consolidation methods will be described. The Y spars were fabricated using AS4 (6K)/PEEK 150g commingled angle interlock 0/90-degree woven preforms with +45-degree commingled plies stitched using high strength Toray carbon thread and processed by autoclave consolidation.

Suarez, J.↗

NASA NTRS1991

Structural response of bead-stiffened thermoplastic shear webs

The results of an experimental and analytical study of the structural response and failure characteristics of selected bead-stiffened thermoplastic shear-webs are presented. Results are given for specimens with one stiffeneer, with two stiffeners, and different stiffener geometries. Selected analytical results that were obtained with the Computational Structural Mechanics (CSM) Testbed computer code are presented. Analytical results that describe normal and transverse shear stress are also presented.

Rouse, Marshall↗

NASA NTRS1992

Characterization of damage modes in impacted thermoset and thermoplastic composites

Composite materials remain extremely vulnerable to out-of-plane impact loads, which may lead to severe losses in strength and stiffness. Impact induced damage is often a complex mixture of transverse cracks, delaminations and fiber failures. An experimental investigation was undertaken to quantify damage tolerance and resistance in composite materials impacted using the drop-weight method. Tests were conducted on laminates of several different carbon-fiber composite systems such as epoxies, modified epoxies, and amorphous and semicrystalline thermoplastics. In this paper, impacted composite specimens have been examined using destructive and nondestructive techniques to establish the characteristic damage states. Specifically, optical microscopy, ultrasonic and scanning electron microscopy techniques have been used to identify impact induced damage mechanisms. Damage propagation during post impact compression was also studied.

Srinivasan, K.↗

NASA NTRS1993

Impact-damaged graphite-thermoplastic trapezoidal-corrugation sandwich and semi-sandwich panels

The results of a study of the effects of impact damage on compression-loaded trapezoidal-corrugation sandwich and semi-sandwich graphite-thermoplastic panels are presented. Sandwich panels with two identical face sheets and a trapezoidal corrugated core between them, and semi-sandwich panels with a corrugation attached to a single skin are considered in this study. Panels were designed, fabricated and tested. The panels were made using the manufacturing process of thermoforming, a less-commonly used technique for fabricating composite parts. Experimental results for unimpacted control panels and panels subjected to impact damage prior to loading are presented. Little work can be found in the literature about these configurations of thermoformed panels.

Jegley, D.↗

NASA NTRS1985

A thermoplastic copolyimide

A copolyimide, STPI/LARC, was prepared from the reaction of 3,3'4,4'-benzophenonetetracarboxylic dianhydride (BTDA), equimolar quantities of m-phenylenediamine and 4,4'-oxydianiline, and a small amount of phthalic anhydride to control the molecular weight. The processability and adhesive properties of STPI/LARC were compared to those of a commercially available form of LARC-TPI. LARC-TPI, a thermoplastic polyimide, from the reaction of BTDA and 3,3'-diaminobenzophenone, had previously shown promise as a high temperature structural adhesive. Lap shear specimens were fabricated using adhesive tape prepared from each of the two polymers. Lap shear tests were performed at room temperature, 177 C, and 204 C before and after exposure to a 72-hour water-boil and to aging at 204 C.

Progar, D. J.↗