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All sourcesNASA NTRSDOE OSTI
NASA NTRSDate not supplied

Multiscale Prediction of Yarn Pullout Failure Mode in Unreinforced Textile Fabrics

Unreinforced woven fabrics have been implemented in a variety of high performance applications, including body armor, deployable structures, and as the reinforcement material in composites. Multiscale modeling techniques have significantly improved the capabilities of simulation-based tools to capture fabric mechanics efficiently and accurately, but often lack in their prediction of failure and require pairing with finite element analysis (FEA) software, limiting their application to the design of ‘fit-for-purpose’ materials. NASA’s Multiscale Analysis Tool (NASMAT) is a standalone multiscale program that has been traditionally used in the analysis of reinforced composites materials. More recently, it has been amended to simulate unreinforced fabric behavior by allowing the geometric state of the tows to change with applied loading due to the lack of a reinforcement material, such as the matrix seen in composites. Previous work has shown the ability of NASMAT to capture nonlinear macroscale behavior by predicting geometric changes in the state of each subcell as a function of the applied loading and allowing each subcell in the analysis to rotate according to these predicted changes, as well as predict nonlinear behavior due to the fiber breakage failure mode. In this work, the capability of predicting the onset and propagation of failure in plain woven fabrics in NASMAT is presented for the yarn pullout failure mode, which occurs when a fabric is loaded at an off-axis angle relative to the warp of weft tow direction. Yarn pullout behavior is initiated by determining the applied load in which the shear resistance of the contact area between yarn families is overcome. When failure is initiated, yarn pullout is determined to have occurred when the applied displacement, calculated from global strain, exceeds the deformed position of a given contact points between yarn families, determined from pin-joint kinematics. Contact points where pullout has occurred contribute to a global damage parameter used to modify the homogenized stiffness of the fabric, resulting in nonlinear behavior observed at the macroscale. The off-axis loading behavior and yarn pullout failure theory have been developed and implemented into NASMAT such that users can simulate off-axis tensile behavior of fabrics in a single, standalone multiscale tool. Simulations are compared to uniaxial tensile tests at various off-axis angles to demonstrate the capability of the tool in its prediction of both the onset of failure at each off-axis angles and the stress-strain behavior as failure progresses.

Materials↗
NASA NTRS1992

Fracture resistance development in ceramic composites with nonlinear fiber pullout relationship

This paper addresses the fracture resistance mechanism in fiber reinforced ceramics, and focuses attention on the specific effects associated with nonlinear nature of the fiber pullout mechanism. The model is based on a consideration of the representative boundary value problem typical for the bridging process. The theoretical solution includes an accurate account of the nonlinear fiber matrix friction. The developed approach allows consideration of several types of nonlinear fiber pullout-force dependence. The distinct features of the nonlinear process demonstrate that, contrary to the linear case, the universal fracture resistance curves cannot be developed in cases with significant nonlinear contribution in the fiber friction law. The resulting resistance curves depend strongly on the absolute values of the matrix fracture toughness. On the other hand, these distinct patterns may be used for identification of the particular friction law and determination of the friction parameters.

Rubinstein, Asher A.↗
NASA NTRS2018

Influence of Thin-Film Adhesives in Pullout Tests Between Nickel-Titanium Shape Memory Alloy and Carbon Fiber-Reinforced Polymer Matrix Composites

Strips of nickel-titanium (NiTi) shape memory alloy (SMA) and carbon fiber-reinforced polymer matrix composite (PMC) were bonded together using multiple thin film adhesives and their mechanical strengths were evaluated under pullout test configuration. Tensile and lap shear tests were conducted to confirm the deformation of SMAs at room temperature and to evaluate the adhesive strength between the NiTi strips and the PMC. Optical and scanning electron microscopy techniques were used to examine the interfacial bonding after failure. Simple equations on composite tensile elongation were used to fit the experimental data on tensile properties. ABAQUS models were generated to show the effects of enhanced bond strength and the distribution of stress in SMA and PMC. The results revealed that the addition of thin film adhesives increased the average adhesive strength between SMA and PMC while halting the room temperature shape memory effect within the pullout specimen.

Polymer Matrix Composites↗
NASA NTRS1981

Ocular torsion on earth and in weightlessness

Otolith function is studied by means of measurements of ocular torsion under various acceleration environments on earth and in weightlessness. Photographic measurements of ocular torsion as indicated by the rotation of landmarks on the iris with respect to head-fixed fiducial marks were obtained in subjects undergoing horizontal linear acceleration in a ground-based version of the space sled, lateral acceleration from weightlessness during pullout from the free-fall portion of parabolic flight, and optokinetic stimulation about the roll axis in the supine position in the laboratory and during weightlessness. The responses of ocular torsion to horizontal acceleration are in agreement with a simple low-order linear system with a dominant time constant of 0.33 sec, with a transfer function fit by a model with a pure delay of 0 to 400 msec and a first-order lag. In the pullout experiment, torsion was not observed in response to the onset of acceleration in the right-ear-down position, although it was present in response to the lateral stimulus. Results of the roll vection experiments indicate the independence of ocular torsion and visually induced tilt. In addition, an automatic video system using a soft contact lens target is presented which has been developed for ocular torsion measurements.

Young, L. R.↗
NASA NTRS1985

Polymer matrix and graphite fiber interface study

Hercules AS4 graphite fiber, unsized, or with EPON 828, PVA, or polysulfone sizing, was combined with three different polymer matrices. These included Hercules 3501-6 epoxy, Hercules 4001 bismaleimide, and Hexcel F155 rubber toughened epoxy. Unidirectional composites in all twelve combinations were fabricated and tested in transverse tension and axial compression. Quasi-isotropic laminates were tested in axial tension and compression, flexure, interlaminar shear, and tensile impact. All tests were conducted at both room temperature, dry and elevated temperature, and wet conditions. Single fiber pullout testing was also performed. Extensive scanning electron microphotographs of fracture surfaces are included, along with photographs of single fiber pullout failures. Analytical/experimental correlations are presented, based on the results of a finite element micromechanics analysis. Correlations between matrix type, fiber sizing, hygrothermal environment, and loading mode are presented. Results indicate that the various composite properties were only moderately influenced by the fiber sizings utilized.

Adams, D. F.↗
NASA NTRS1992

Piloted simulation study of a balloon-assisted deployment of an aircraft at high altitude

A piloted simulation was used to study the feasibility of a balloon assisted deployment of a research aircraft at high altitude. In the simulation study, an unmanned, modified sailplane was carried to 110,000 ft with a high altitude balloon and released in a nose down attitude. A remote pilot controlled the aircraft through a pullout and then executed a zoom climb to a trimmed, 1 g flight condition. A small parachute was used to limit the Mach number during the pullout to avoid adverse transonic effects. The use of small rocket motor was studied for increasing the maximum attainable altitude. Aerodynamic modifications to the basic sailplane included applying supercritical airfoil gloves over the existing wing and tail surfaces. The aerodynamic model of the simulated aircraft was based on low Reynolds number wind tunnel tests and computational techniques, and included large Mach number and Reynolds number effects at high altitude. Parametric variations were performed to study the effects of launch altitude, gross weight, Mach number limit, and parachute size on the maximum attainable stabilized altitude. A test altitude of approx. 95,000 ft was attained, and altitudes in excess of 100,000 ft was attained.

Murray, James↗
NASA NTRS1993

High-altitude balloon-launched aircraft - A piloted simulation study

A real-time piloted simulation at the NASA Dryden Flight Research Facility was used to study the feasibility of launching a research aircraft from a high-altitude balloon. In the study, the simulated aircraft was launched in a nosedown attitude at zero airspeed from 110,000 ft. After launch, the pilot flew the aircraft through a near-maximum-lift pullout and then through a zoom climb to a trimmed, l-g flight condition at the test altitude. The study included parametric variations to measure the effects of launch altitude, gross weight, Mach number limit, and parachute size on the test altitude attained. The aerodynamic model of the simulated aircraft was based on flight test results, low Reynolds number windtunnel tests, and computational models; the model included significant Mach number and Reynolds number effects at high altitude. A small parachute was included in the simulation to limit Mach number during the pullout to avoid adverse transonic effects and their resultant energy losses. A small rocket motor was included in the simulation and was investigated for boosting the aircraft to a higher test altitude. In the study, a test altitude of approximately 95,000 ft was attained without rocket boost, and a test altitude in excess of 100,000 ft was attained using small rocket boost.

Murray, James E.↗
NASA NTRS1996

Development and testing of airfoils for high-altitude aircraft

Specific tasks included airfoil design; study of airfoil constraints on pullout maneuver; selection of tail airfoils; examination of wing twist; test section instrumentation and layout; and integrated airfoil/heat-exchanger tests. In the course of designing the airfoil, specifically for the APEX test vehicle, extensive studies were made over the Mach and Reynolds number ranges of interest. It is intended to be representative of airfoils required for lightweight aircraft operating at extreme altitudes, which is the primary research objective of the APEX program. Also considered were thickness, pitching moment, and off-design behavior. The maximum ceiling parameter M(exp 2)C(sub L) value achievable by the Apex-16 airfoil was found to be a strong constraint on the pullout maneuver. The NACA 1410 and 2410 airfoils (inverted) were identified as good candidates for the tail, with predictable behavior at low Reynolds numbers and good tolerance to flap deflections. With regards to wing twist, it was decided that a simple flat wing was a reasonable compromise. The test section instrumentation consisted of surface pressure taps, wake rakes, surface-mounted microphones, and skin-friction gauges. Also, a modest wind tunnel test was performed for an integrated airfoil/heat-exchanger configuration, which is currently on Aurora's 'Theseus' aircraft. Although not directly related to the APEX tests, the aerodynamics or heat exchangers has been identified as a crucial aspect of designing high-altitude aircraft and hence is relevant to the ERAST program.

Drela, Mark↗
NASA NTRS2011

Modifying Matrix Materials to Increase Wetting and Adhesion

In an alternative approach to increasing the degrees of wetting and adhesion between the fiber and matrix components of organic-fiber/polymer matrix composite materials, the matrix resins are modified. Heretofore, it has been common practice to modify the fibers rather than the matrices: The fibers are modified by chemical and/or physical surface treatments prior to combining the fibers with matrix resins - an approach that entails considerable expense and usually results in degradation (typically, weakening) of fibers. The alternative approach of modifying the matrix resins does not entail degradation of fibers, and affords opportunities for improving the mechanical properties of the fiber composites. The alternative approach is more cost-effective, not only because it eliminates expensive fiber-surface treatments but also because it does not entail changes in procedures for manufacturing conventional composite-material structures. The alternative approach is best described by citing an example of its application to a composite of ultra-high-molecular- weight polyethylene (UHMWPE) fibers in an epoxy matrix. The epoxy matrix was modified to a chemically reactive, polarized epoxy nano-matrix to increase the degrees of wetting and adhesion between the fibers and the matrix. The modification was effected by incorporating a small proportion (0.3 weight percent) of reactive graphitic nanofibers produced from functionalized nanofibers into the epoxy matrix resin prior to combining the resin with the UHMWPE fibers. The resulting increase in fiber/matrix adhesion manifested itself in several test results, notably including an increase of 25 percent in the maximum fiber pullout force and an increase of 60-65 percent in fiber pullout energy. In addition, it was conjectured that the functionalized nanofibers became involved in the cross linking reaction of the epoxy resin, with resultant enhancement of the mechanical properties and lower viscosity of the matrix.

Zhong, Katie↗
NASA NTRS2011

Fiber-Reinforced Reactive Nano-Epoxy Composites

An ultra-high-molecular-weight polyethylene/ matrix interface based on the fabrication of a reactive nano-epoxy matrix with lower surface energy has been improved. Enhanced mechanical properties versus pure epoxy on a three-point bend test include: strength (25 percent), modulus (20 percent), and toughness (30 percent). Increased thermal properties include higher Tg (glass transition temperature) and stable CTE (coefficient of thermal expansion). Improved processability for manufacturing composites includes faster wetting rates on macro-fiber surfaces, lower viscosity, better resin infusion rates, and improved rheological properties. Improved interfacial adhesion properties with Spectra fibers by pullout tests include initial debonding force of 35 percent, a maximum pullout force of 25 percent, and energy to debond at 65 percent. Improved mechanical properties of Spectra fiber composites (tensile) aging resistance properties include hygrothermal effects. With this innovation, high-performance composites have been created, including carbon fibers/nano-epoxy, glass fibers/nano-epoxy, aramid fibers/ nano-epoxy, and ultra-high-molecularweight polyethylene fiber (UHMWPE).

Zhong, Wei-Hong↗
NASA NTRS2016

Z-2 Threaded Insert Design and Testing Abstract

The Z-2 Prototype Planetary Extravehicular Space Suit Assembly is a continuation of NASA's Z series of spacesuits. The Z-2 is another step in the NASA's technology development roadmap leading to human exploration of the Martian surface. To meet a more challenging set of requirements than previous suit systems standard design features, such as threaded inserts, have been re-analyzed and improved. NASA's Z-2 prototype space suit contains several components fabricated from an advanced hybrid composite laminate consisting of IM10 carbon fiber and fiber glass. One requirement NASA levied on the suit composites was the ability to have removable, replaceable helicoil inserts to which other suit components would be fastened. An approach utilizing bonded in inserts with helicoils inside of them was implemented. The design of the interface flanges of the composites allowed some of the inserts to be a "T" style insert that was installed through the entire thickness of the laminate. The flange portion of the insert provides a mechanical lock as a redundancy to the adhesive aiding in the pullout load that the insert can withstand. In some locations it was not possible to utilize at "T" style insert and a blind insert was used instead. These inserts rely completely on the bond strength of the adhesive to resist pullout. It was determined during the design of the suit that the inserts did not need to withstand loads induced from pressure cycling but instead tension induced from torqueing the screws to bolt on hardware which creates a much higher stress on them. Bolt tension is determined by dividing the torque on the screw by a k value multiplied by the thread diameter of the bolt. The k value is a factor that accounts for friction in the system. A common value used for k for a non-lubricated screw is 0.2. The k value can go down by as much as 0.1 if the screw is lubricated which means for the same torque, a much larger tension could be placed on the bolt and insert. This paper summarizes testing that was performed to determine a k value for helicoil inserts in the Z2 suit and how the insert design was modified to resist a higher pull out tension.

Rhodes, RIchard↗
NASA NTRS1972

Required critical aspect ratio of fibers intended for stress rupture applications.

The observed critical aspect ratio for pullout specimens of tungsten wire in a copper matrix tested in stress rupture at 649 and 816 C was slightly greater than for tension tests at the same temperature. Time for failure of the stress rupture specimens was controlled by the properties of the fiber (tungsten) at aspect ratios greater than the critical aspect ratio and by the properties of the matrix (copper) at aspect ratios less than the critical ratio.

Jech, R. W.↗
NASA NTRS1972

Responses of blind fish to gravitational changes as achieved in parabolic flight

Blind fish, during parabolic flight, display a measurable and consistent behavior. The most spectacular new behavioral response is the forward looping of blind fish in or near weightlessness. This response shows no measurable adaptation during the entire period of weightlessness of about 30 sec. During the entrance and exit of weightless parabolas (pushover and pullout) respectively, the fish assumes a forward tilted diving position. Parabolic flight with negative g in the range between 0g and -1g causes similar diving responses of the fish with the only difference being that the dive is directed toward the top of the fish tank. When the response to a g value less than 1g is compared to the response to increased g load on the ground (escape of darting response) an essential difference is seen: higher horizontal acceleration or jerk on the ground causes fish to swim, or even dart, against the direction of inertial force; fish during weightless parabolas move into the direction of the inertial or gravitational force. Since the vestibular system of fish is homologous to that of man, the observed behavior of fish in weightless flight could help to better understand human performance and sensations in comparable situations.

Vonbaumgarten, R. J.↗
NASA NTRS1978

A pilot evaluation of two G-seat cueing schemes

A comparison was made of two contrasting G-seat cueing schemes. The G-seat, an aircraft simulation subsystem, creates aircraft acceleration cues via seat contour changes. Of the two cueing schemes tested, one was designed to create skin pressure cues and the other was designed to create body position cues. Each cueing scheme was tested and evaluated subjectively by five pilots regarding its ability to cue the appropriate accelerations in each of four simple maneuvers: a pullout, a pushover, an S-turn maneuver, and a thrusting maneuver. A divergence of pilot opinion occurred, revealing that the perception and acceptance of G-seat stimuli is a highly individualistic phenomena. The creation of one acceptable G-seat cueing scheme was, therefore, deemed to be quite difficult.

Showalter, T. W.↗
NASA NTRS1981

Pull-out fibers from composite materials at high rate of loading

Numerical and experimental results are presented on the pullout phenomenon in composite materials at a high rate of loading. The finite element method was used, taking into account the existence of a virtual shear deformation layer as the interface between fiber and matrix. Experimental results agree well with those obtained by the finite element method. Numerical results show that the interlaminar shear stress is time dependent, in addition, it is shown to depend on the applied load time history. Under step pulse loading, the interlaminar shear stress fluctuates, finally decaying to its value under static loading.

Amijima, S.↗
NASA NTRS1982

Crash tests of four low-wing twin-engine airplanes with truss-reinforced fuselage structure

Four six-place, low-wing, twin-engine, general aviation airplane test specimens were crash tested under controlled free flight conditions. All airplanes were impacted on a concrete test surface at a nomial flight path velocity of 27 m/sec. Two tests were conducted at a -15 deg flight path angle (0 deg pitch angle and 15 deg pitch angle), and two were conducted at a -30 deg flight path angle (-30 deg pitch angle). The average acceleration time histories (crash pulses) in the cabin area for each principal direction were calculated for each crash test. In addition, the peak floor accelerations were calculated for each test as a function of aircraft fuselage longitudinal station number. Anthropomorphic dummy accelerations were analyzed using the dynamic response index and severity index (SI) models. Parameters affecting the dummy restraint system were studied; these parameters included the effect of no upper torso restraint, measurement of the amount of inertia-reel strap pullout before locking, measurement of dummy chest forward motion, and loads in the restraints. With the SI model, the dummies with no shoulder harness received head impacts above the concussive threshold.

Williams, M. S.↗