Composite Structural Panels Research Articles

Bio-based composite roof structure: Manufacturing and processing issues

Bio-based composite materials were tested for suitability in roof structure. Structural beams were designed, manufactured and tested, yielding good results. Based on the beam results, large-scale composite structural panels were made. Soy oil-based resin and cellulose fibers, in the form of paper sheets made from recycled cardboard boxes, were successfully used to manufacture the composite structures. This recycled paper was previously tested in composite sheets and structural unit beams and gave the required stiffness and strength required for roof construction. The roof was designed and a 1/3 scale structure was manufactured. Following this 1/3 scale design, two composite panels of 2.59 m × 1.52 m × 0.089 m were manufactured to serve as the two sides of a pitched roof connected at the ridge. The depth of the panels and thickness of the composite skin were dictated by the design as a function if the two other dimensions to give the optimum strength and cost result. To test the manufacturing process for a full-depth roof structure, a 1.27 m × 0.53 m × 0.279 m panel was successfully manufactured. In the latter structure, a modified VARTM process was used to replace the solid mold surface with a bagging film. This enabled a visual inspection of the resin flow and provided a window for using additional vacuum and injection lines on the normally hidden bottom side. This bagging method was very successful without the need for mold modification or electronic sensors. Issues related to natural fibers composite processing such as moisture inhibition and drying are also discussed in this work.

Composite structural panels subjected to explosive loading

Details of an extensive large-scale test programme on a series of composite structural components subjected to explosive loading are presented in this paper. The test components include conventional reinforced concrete slabs, steel fibre reinforced concrete slabs, profiled steel sheeting reinforced concrete slabs, steel–air–steel sandwich panels and steel–concrete–steel sandwich panels. A total of seventy four specimens were tested using seventeen detonation phases; with charge weight ranging between 8 and 100 kg of bare high explosives and each at stand-off distance of 5 m. The main parameters observed in the tests were the generic construction form of the materials and slab thickness. Air-blast overpressure and accelerations of the specimens were captured. A modified plasticine displacement gauge was used to measure the maximum displacement. Failure modes of each type of specimens were recorded and are presented in the paper. Major conclusions relating to structural safety are summarised.

Distortion-free single point imaging of multi-layered composite sandwich panel structures

The results of a magnetic resonance imaging (MRI) investigation concerning the effects of an aluminum honeycomb sandwich panel on the B 1 and B 0 fields and on subsequent image quality are presented. Although the sandwich panel structure, representative of an aircraft composite material, distorts B 0 and attenuates B 1, distortion-free imaging is possible using single point (constant time) imaging techniques. A new expression is derived for the error caused by gradient field distortion due to the heterogeneous magnetic susceptibility within a sample and this error is shown not to cause geometric distortion in the image. The origin of the B 0 distortion in the sample under investigation was also examined. The graphite-epoxy `skin' of the panel is the principal source of the B 0 distortion. Successful imaging of these structures sets the stage for the development of methods for detecting moisture ingress and degradation within composite sandwich structures.

Genetic algorithm optimization and blending of composite laminates by locally reducing laminate thickness

Composite panel structure optimization is commonly decomposed into panel optimization subproblems, with specified local loads, resulting in manufacturing incompatibilities between adjacent panel designs. A new method proposed here for constructing globally blended panel designs uses a parallel decomposition antithetical to that of earlier work. Rather than performing concurrent panel genetic optimizations, a single genetic optimization is conducted for the entire structure with the parallelism solely within the fitness evaluations. A genetic algorithm approach, based on locally reducing a thick (guide) laminate, is introduced to exclusively generate and evaluate valid globally blended designs, utilizing a simple master–slave parallel implementation, implicitly reducing the size of the problem design space and increasing the quality of discovered local optima.

Optimization and Blending of Composite Laminates Using Genetic Algorithms with Migration

Optimization of aircraft-stiffened composite panel structures often results in manufacturing incompatibilities between adjacent panels. Using genetic algorithms to optimize local panel stacking sequences allows panel populations of stacking sequences to evolve in parallel and send migrants to adjacent panels so as to blend the local panel designs globally. The blending process is accomplished using the edit distance between individuals of a population and the set of migrants from adjacent panels. The objective function evaluating the fitness of designs is modified according the severity of mismatches detected between neighboring populations. This lays the groundwork for natural evolution to a blended global solution without leaving the paradigm of genetic algorithms.

Aluminum foam integral armor: a new dimension in armor design

Closed-cell aluminum foam offers a unique combination of properties such as low density, high stiffness, strength and energy absorption that can be tailored through design of the microstructure. During ballistic impact, the foam exhibits significant non-linear deformation and stress wave attenuation. Composite structural armor panels containing closed-cell aluminum foam are impacted with 20-mm fragment-simulating projectiles (FSP). One-dimensional plane strain finite element analysis (FEA) of stress wave propagation is performed to understand the dynamic response and deformation mechanisms. The FEA results correlate well with the experimental observation that aluminum foam can delay and attenuate stress waves. It is identified that the aluminum foam transmits an insignificant amount of stress pulse before complete densification. The ballistic performance of aluminum foam-based composite integral armor (CIA) is compared with the baseline integral armor of equivalent areal-density by impacting panels with 20-mm FSP. A comparative damage study reveals that the aluminum foam armor has finer ceramic fracture and less volumetric delamination of the composite backing plate as compared to the baseline. The aluminum foam armors also showed less dynamic deflection of the backing plate than the baseline. These attributes of the aluminum foam in integral armor system add a new dimension in the design of lightweight armor for the future armored vehicles.

ＦＲＰ複合材パッチで接着補修されたき裂を有する矩形構造パネルにおける補修効率の評価

Repair with bonded fiber-reinforced polymer composite patches has been recognized as an efficient and cost-effective method to extend the service life of aging aircraft. In this paper, a two-dimensional three-layered finite element model consisting of layers of composite patch, adhesive and cracked structural panel is made to analyze the stresses in cracked rectangular structural panels repaired with a bonded circular composite patch. The composite patch and structural panel are modeled as separate layers which are covered with Mindlin plate elements, whereas the adhesive is modeled as a thin elastic layer. The modified crack closure method is used to obtain stress intensity factors at the crack tip. First, by calculating the stress intensity factors, the effects of the diameter and thickness of the circular composite patch on the patching efficiency are examined. The stress intensity factors are also calculated at various hygrothermal conditions and the effect of the environment on the patching efficiency is clarified. Finally, the diagram of patching efficiency is presented to evaluate easily the patching efficiency at hygrothermal conditions.

Enhancing the post-buckling response of a composite panel structure utilising shape memory alloy actuators – a smart structural concept

Restoration forces, associated with embedded activated pre-strained shape memory alloy wires, have successfully been employed to enhance the post-buckling behaviour of a laminated panel structure. An extensive experimental and numerical programme has been conducted, of which, results will be presented. The manufacturing methodology of the hybrid SMA/carbon/epoxy panel is outlined. The panel specimen features 0.3 mm diameter shape memory alloy wires embedded and partially consolidated to the host matrix at desired locations. Numerical thermal analysis has been employed to predict the non-uniform temperature profile, attributed to shape memory alloy activation through resistive heating, within the laminate. Structural finite element (FE) analysis has been employed to determine the hybrid panel's adaptive response while under the influence of the uniaxial compressive load in excess of its pseudo-critical buckling value. It is shown that, utilising the control authority generated from the small SMA actuator volume fraction employed, the out-of-plane displacement of the post-buckled laminated panel can be reduced. With the increase in use of composite materials within aerospace platforms, it is envisaged that the hybrid adaptive SMA/laminate configuration will extend the operational performance over conventional materials and structures, particularly when the structure is exposed to an elevated temperature.

Design optimisation of composite panel structures with stiffening ribs under multiple loading cases

An optimisation procedure for composite panel structures with stiffening ribs is presented in this paper. The procedure employs standard FE structural analysis, structural system profile analysis, and multi-factor optimisation techniques to predict an optimum structural design. A composite antenna reflector structure in space environment is optimised. Laminate, sandwich configuration and rib shape in the structure are optimised in this application. The optimisation improves antenna performance under multiple loading cases and minimises structural mass simultaneously.

A Flat Composite Panel Design Advisory System Using Knowledge Based and Case Based Reasoning

A method of cooperatively using Knowledge Based and Case Based Reasoning is proposed to assist designers in the design of flat composite panel structures. A Prototype Design Advisory system is constructed of heuristic and experiential rules which are acquired from composites design experts, and published text which is implemented in the CLIPS Knowledge Based System shell. The system includes design cases of previous composites design scenarios implemented in a Case Based Reasoning System using DesignMUSE. The cases all depict design of composites applied to commercial and military aircraft. The application of heuristic rules and prior similar design cases is focused upon the early stages of the design process. It is believed that such a design advisory system can aid in preventing unforeseen mistakes during the design and manufacture of composite structures, can assist in predicting the results of candidate designs, and can ultimately reduce the design cycle time.

The buckling performance of composite stiffened panel structures subjected to combined in-plane compression and shear loading

In this paper a study is made of the buckling behaviour of some composite stiffened panel structures subjected to in-plane compression and shear load combinations. The finite strip method, a computer aided engineering analysis procedure, is employed to determine the buckling solutions. Since the prediction of structural performance is quickly and accurately determined through computer simulation, the analysis capabilities of the finite strip method promotes the examination of many design alternatives. The designer is encouraged and indeed readily aided to make the most efficient use of materials and thus the development of highly reliable structural components, which are able to operate at optimised performance levels, can be achieved. A basic strip formulation for composite material construction is presented which is able to predict the complex buckling modes associated with in-plane load combinations. The buckling displacement fields are represented by algebraic polynomials across the strip and trigonometric functions along the strip length. The inclusion of sufficient harmonics in the appropriate displacement representations provides the required flexibility of the strip formulation to accommodate the more elaborate buckling modes associated with the presence of in-plane shear loading. The results presented in the paper are those pertaining to the buckling capabilities of stiffened panels manufactured from high strength carbon-epoxy composite material. The results illustrate, graphically, the effect on buckling performance of changes in stiffener geometry. Interaction curves are presented in the paper which detail the limiting boundaries for critical load combinations of specific structural configurations.

Measurement of elastic moduli of composite panels at elevated temperatures by vibration excitation

Damage by fire of materials used in the structure of buildings, ships, aircraft and in many other applications is often a major design consideration. The authors present an evaluation method to measure the loss of rigidity and other mechanical properties in composite structural panels when subject to intense flame heating. Polymeric composite materials are lightweight, corrosion resistant and have many other attractive qualities. Also, the fire resistant properties of these materials have been much improved, one feature being the advances in fire resistant coatings that effectively char, have ablative properties and in other ways insulate and protect the underlying composite material. This is so that it can retain much of its stiffness and form during and after flame exposure at peak temperatures well above the glass transition temperature of the matrix material. The experimental method developed was to excite panels into vibrational modes that both bent and twisted a specimen so that both flexural and shear moduli could be measured as the centre of the panel was flame heated. These results were compared with those obtained from panel specimens heated in ovens. The measurements of the flexural and shear moduli were recorded during the heating and cooling of the specimens in both the flame and oven experiments.

Composite panel structure : Green, P.H. (Willowdale, Ontario, Canada) US Pat 4 879 152 (7 November 1989)

Composite panel structure : Green, P.H. (Willowdale, Ontario, Canada) US Pat 4 879 152 (7 November 1989)

Sound related floor system and method of constructing same

A sound rated flooring is provided comprising a sound attenuation layer having a composite panel structure having a core and at least one acoustically semi-transparent facing of fibrous material bonded to the core and a rigid layer positioned on the sound attenuation layer. A moisture inhibiting barrier may be positioned between the composite panel structure and the rigid layer. A method for constructing a sound rated floor is also provided, comprising the steps of positioning the composite panel structure described herein over a substantially horizontal base surface and then positioning the rigid layer over the composite panel structure. The finished covering is then placed over the rigid layer.

General Panel Sizing Computer Code and Its Application to Composite Structural Panels

A computer code for obtaining the dimensions of optimum (least mass) stiffened composite structural panels is described. The procedure, which is based on nonlinear mathematical programming and a rigorous buckling analysis, is applicable to general cross sections under general loading conditions causing buckling. A simplified method of accounting for bow-type imperfections is also included. Design studies in the form of structural efficiency charts for axial compression loading are made with the code for blade and hat stiffened panels. The effects on panel mass of imperfections, material strength limitations, and panel stiffness requirements are also examined. Comparisons with previously published experimental data show that accounting for imperfections improves correlation between theory and experiment.

Five New Machines and Six Products Can Triple Commodity Recovery from Southern Forests

Abstract Mixed southern pine-hardwood stands now yield 20 to 22 percent of their biomass in wood products. A new energy self-sufficient system using tree pullers, wet-fuel burners, mobile chippers, shaping-lathe headrigs, and continuous kilns can convert 67 percent of the biomass (above- and below-ground parts of trees of all species) into products worth about $150 per dry ton. Products of the system are pallets; dowel-laminated crossties (no adhesive); structural exterior flakeboard; structural lumber glue-laminated from veneer: studs; and hogged fuel for plant energy. Composite structural panels or fiberboards could be made also. Application of the system could provide high returns to private landholders while halting incursion of low-grade hardwoods into the southern pinery.

Mastic composition and composite structural panels formed therefrom : Geschwender, R.C. (Lancaster Research and Development Corporation) US Pat 3 990 936 (9 November 1976)

Mastic composition and composite structural panels formed therefrom : Geschwender, R.C. (Lancaster Research and Development Corporation) US Pat 3 990 936 (9 November 1976)