Pultruded Rod Research Articles

Preliminary Wing Study of General Aviation Aircraft with Stitched Composite Panels

A new approach in the design of aerospace vehicles was recently introduced by NASA and Boeing researchers to meet the new challenges in aviation. This innovative configuration is called pultruded rod stitched efficient unitized structure, a stitched carbon–epoxy material system that offers the opportunity for designing stiffer, lower weight, and more cost-efficient aircraft by eliminating fasteners and incorporating damage-tolerance concepts. Aside from superior structural performance and low-cost manufacturing methods, this configuration must also demonstrate advanced aeroelastic behavior to be fully implemented in commercial aircraft. A preliminary wing study of a general aviation aircraft that embodies pultruded rod stitched efficient unitized structure technology is presented in this paper, which will be compared with the structural, dynamic, and aeroelastic behavior of the original metallic wing model. The study showed that the presence of pultruded rod stitched efficient unitized structure panels leads to decreased deformations in static and aeroelastic analyses, higher natural frequencies and flutter speeds, and improved crashworthiness. Weight considerations are also presented to substantiate the comparison between pultruded rod stitched efficient unitized structure and metallic configuration.

Vibroacoustic Tailoring of a Rod-Stiffened Composite Fuselage Panel with Multidisciplinary Considerations

An efficient multi-objective design tailoring procedure seeking to improve the vibroacoustic performance of a fuselage panel while maintaining or reducing weight is presented. The structure considered is the pultruded rod stitched efficient unitized structure, a highly integrated composite structure concept designed for a noncylindrical, next-generation flight vehicle fuselage. Modifications to a baseline design are evaluated within a six-parameter design space including spacing, flange width, and web height for both frame and stringer substructure components. The change in sound power radiation attributed to a design change is predicted using finite-element models sized and meshed for analyses in the 500 Hz, 1 kHz, and 2 kHz octave bands. Three design studies are carried out in parallel while considering a diffuse acoustic field excitation and two types of turbulent boundary-layer excitation. Kriging surrogate models are used to reduce the computational costs of resolving the vibroacoustic and weight objective Pareto fronts. The resulting Pareto optimal designs are then evaluated under a static pressurization ultimate load to assess structural strength and stability. Results suggest that choosing alternative configurations within the considered design space can reduce weight and improve vibroacoustic performance without compromising strength and stability of the structure under the static load condition considered, but the tradeoffs are significantly influenced by the spatial characteristics of the assumed excitation field.

Nonlinear Analysis and Experimental Behavior of a Curved Unitized Stitched Panel

The pultruded rod stitched efficient unitized structure concept, developed by The Boeing Company, has been extensively studied as part of NASA’s environmentally responsible aviation project. The pultruded rod stitched efficient unitized structure concept provides a lightweight alternative to aluminum or traditional composite design concepts and is applicable to traditional-shaped fuselage barrels and wings, as well as advanced configurations such as a hybrid wing–body or truss-braced wings. Therefore, NASA, the Federal Aviation Administration, and The Boeing Company partnered in an effort to assess the performance and damage arrestments capabilities of the pultruded rod stitched efficient unitized structure concept by testing a full-scale curved panel in the Federal Aviation Administration full-scale aircraft structural test evaluation and research facility. Testing was conducted in this facility by subjecting the panel to axial tension loads applied to the ends of the panel, internal pressure, and combined axial tension and internal pressure loadings. Additionally, reactive hoop loads were applied to the skin and frames of the panel along its edges. The panel successfully supported the required design loads in the pristine condition and with a severed stiffener. The panel also demonstrated that the pultruded rod stitched efficient unitized structure concept could arrest the progression of damage, including crack arrestment and crack turning. This paper presents the nonlinear posttest analysis and correlation with test results for the curved pultruded rod stitched efficient unitized structure panel. It is shown that nonlinear analysis can accurately calculate the behavior of this panel under tension, pressure, and combined loading conditions.

Bonding Strength Properties of Adhesively-Timber Joint with Thixotropic and Room Temperature Cured Epoxy Based Adhesive Reinforced with Nano- and Micro-particles

This research work is concerned with in situ bonded-in timber connection using pultruded rod; where the manufacturing of such joint requires adhesive which can produce thick glue-lines and does not allow any use of pressure and heat. Four types of thixotropic (for ease application) and room temperature cured epoxy based were used namely CB10TSS (regarded as standards adhesive), Nanopox (modification of CB10TSS with addition of nanosilica), Albipox (modification of CB10TSS with addition of liquid rubber) and Timberset (an epoxy-based adhesive with addition of micro-size ceramic particles). The quality of the adhesive bonds was accessed using block shear test in accordance with ASTM D905. The bond strength depends on how good the adhesive wet the timber surface. Therefore the viscosity and contact angle was also measured. The nano- and microfiller additions increased the bond strength significantly. The viscosity correlates well with contact angle measurements where lower viscosities are associated with lower contact angles. However contact angle contradicts with measured strength and wettability.

Bond performance of FRP rebars with various surface deformations in reinforced concrete

AbstractOne of the methods used to overcome the corrosion problem associated with steel rebars in reinforced concrete is the application of reinforced polymer (FRP) rebars. Bonding between the rebar and concrete is one of the major factors affecting the mechanical behavior of the structures. In this study, FRP rebars with four different surface configurations and geometries were constructed and their bonding to concrete was examined. These include a pultruded rod with a smooth surface (RO), externally wound FRP rib on the pultruded rod (RT), pultruded rod with sand sprayed on the surface (RS), and a combination of the last two configurations (RTS). Bonding strength of the rebars to concrete was assessed using pull‐out test at the embedment lengths of 12 and 18 cm. Results showed that the increase in surface roughness of the rebars and hence a greater inter‐mechanical locking, plays a major role in their bonding strength to concrete. RO rebar showed the lowest bonding strength to the concrete followed by the RT rebar. Bonding strength to concrete in the latter type was entirely controlled by the adhesion strength of the externally wound FRP rib to the pultruded core. RTS rebars with embedment length of 12 cm showed greater adhesion to the concrete, where as, in samples with embedment length of 18 cm, RTS and RS rebars showed close results. In all the tests conducted, delaminating of the surface texture was the major failure mode. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers

Analysis of stress concentration during tension of round pultruded composite rods

The stress state in a solid round transversely isotropic rod loaded with balanced shear stresses on a part of its lateral surface is considered. The change in gripping conditions is simulated by varying the distribution of statically equivalent shear stresses. The solution for the stress state was obtained using exact equations of linear theory of elasticity of anisotropic body. An analysis of the distribution of longitudinal and hoop stresses showed that at the grip edges a very high stress concentration is possible, which depends on the radius of the tensioned rod and the distribution of shear stresses on the gripped surface. At the grip edges, the longitudinal and hoop stresses tend to infinity. It is suggested to estimate the stresses at the singular point by averaging the stresses across the thickness of a subsurface layer; this thickness depends upon the susceptibility of the composite to the stress concentration. As a numerical example, the stress state of an intermediate-modulus carbon-fiber reinforced polymer pultruded rod is considered. The results obtained show that the decrease of tensile strength with increasing diameter of the rod is related to the nonuniformity of stress distribution near the grips, independent of any type of size dependent variation in material strength. By changing the distribution of the applied shear stresses it is possible to mitigate this effect and to increase the tensile load-carrying capacity of round pultruded rods.

Diametral compression of pultruded composite rods as a quality control test

A diametral compression test involving the loading of a rod perpendicular to its longitudinal axis was used to determine the transverse tensile strength of pultruded, circular, small diameter, unidirectional composite rods. The test method is convenient because it involves a simple compression test and specimen preparation is easy because it only requires cutting the rod into short length segments. Data reduction is also simple since a closed-form solution is used to relate the applied load to the transverse tensile stress. Material systems studied include graphite and Kevlar fibres with several combinations of matrix. The test method may have merit as a quality control test to evaluate the relative performance of pultruded rod material. Rod length affected transverse tensile strength with shorter rods yielding higher strengths in most of the systems; this effect was verified using Weibull statistical theory.

Strength and Failure Modes in Notched Pultruded Rod Tension Specimens

Failure mode in a notched pultruded rod containing unidirectional E-glass fibers depends on the ratio of gage length L to specimen diameter d at the notch. For a tensile failure, a large L/d ratio is required. At smaller L/d ratios, long pull-out or crushing at the grips occurs. Based on the failure mode observation and tensile strength evaluation, development of a V-notched tension test with large L/d ratio is suggested as a possible replacement for the current ASTM tension test (ASTM Test Method for Tensile Properties of Pultruded Glass Fiber-Reinforced Plastic Rod [D 3916]).

Syntatic foam pultrusion

AbstractA simple circular pultruded rod was used to evaluate the mechanical and economic performance of four commercially available hollow spherical fillers (microbubbes). The incorporation of such glass or silicate microbubbes in a pultruded rod produced a decrease in density, strength and modulus. However, the loss of strength and modulus was more than compensated for by the decrease in density so that a 50 percent material cost saving was possible without any sacrifice in flexural or torsional properties. Thus for simple profile (rods, bars. Panels) the use of hollow spherical fillers can be economically advantageous in reducing material costs. The syntactic pultrusions posses many of the desirable properties of wood such as toughess, low density, high strength and stiffness plus the ability to accommodate nails and screws. The operating conditions of the pultruder wee normal with the exception that half as much force was needed on the puller and the pultruder would only operate satisfactorily when the resin/glass fiber/microbubble concertrations were within specified boundaries. Pyrex type glass bubbles were found to be less prone to damage during processing and performed better than silicate type microbubbles.