Showing papers on "Sandwich-structured composite published in 1975"

Optimal Acoustic Design of Sandwich Panels

Abstract: An optimization study to investigate the feasibility of an optimal acoustic design process for sandwich panels is presented here Using a pattern search procedure it is shown that the average transmission loss of a panel may be improved through optimization over a range of frequency, and that the optimization procedure results in a shift of the panel symmetric coincidence frequency beyond the range of interestSubject Classification: 5575

Sandwich panel construction

Abstract: A typical embodiment of the resinous foam sandwich construction that characterizes the invention has face sheets of fiber reinforced thermoplastic resin laminates. The foam core is a mixture of hollow glass spheres and resin, in which the resin in the core is the same as the resin used to form the face sheets.

Impact Damage Tolerance of Graphite/Epoxy Sandwich Panels.

Abstract: The resistance of graphite/epoxy sandwich panels to low energy, foreign object impact damage was studied. Falling weight impact tests were performed on 104 rectangular sandwich panel specimens. The effect of several material, geometry, and loading parameters on damage susceptibility was explored. Damage observed visually was related to residual strength of specimens taken from the impact region, and in some cases, to static indentation tests carried out on companion specimens. Sandwich test specimens were fabricated with face sheets of graphite or S-glass/epoxy with a 1-in. depth nomex honeycomb core. Fiber type, core density, and laminate orientation were fabrication variables. Drop weight tests were accomplished using a 2-in.-diameter steel ball. Initial and residual static shear strength were measured on notched, four-point bend specimens. Impact tests showed that graphite sandwich panels are much more susceptible to foreign object damage than S-glass panels. The impact energy required to sustain the same relative damage level was an order of magnitude greater for the S-glass than for the graphite panels. The failure characteristics observed suggest that this is due primarily to the low strain to failure of graphite composites. Local core crushing occurred in all tests, and all but the S-glass panels suffered fiber fracture and permanent indentation at low energy levels. Core stiffness had an observable effect on impact resistance, but other parameters studied did not appear to significantly affect damage tolerance. An analysis was carried out in which the sandwich panel was represented as an orthotropic sheet on an elastic foundation, and a classical, double Fourier series approach was taken. The load condition was approximated by an influence function technique to effect a constant radius of bending curvature, simulating the region around the drop weight ball. The capability exists to vary the material constants of the face sheet and core to investigate the nature of indentation failure, and to identify factors contributing to impact resistance. Numerical results were obtained for some of the material parameters employed in the impact tests.

Sandwich panel fabrication

Abstract: In the manufacture of sandwich panels, a filler assembly is made up of rib elements and core elements that are roll bonded into a unitary structure, and slices are then cut from the unitary structure forming filler assemblies to be positioned between surface sheets. The surface sheets and the filler assemblies are then bonded together to form the panel.

Composite lattice structure

Abstract: A lattice type structural panel concept which exploits the unidirectional character of filamentary advanced composite materials was described. This lattice has potential for applications where stiff lightweight structures are needed such as large area panels for space satellites. Formulae are presented to calculate the panel weight and plate bending stiffness. This analysis indicates that structures with significantly lighter weight than conventional minimum gauge sandwich construction can be fabricated. A suggested fabrication procedure is also presented along with photographs of some typical panels.

Fatigue, creep, and impact resistance of aramid fiber reinforced composites

Abstract: Kevlar® 49 a high-strength, high-modulus, low-density organic fiber has gained significant acceptance as a weight-reducing replacement for E-glass in aircraft applications and for S-glass in filament-wound missile components. New end-use applications require a better understanding of the static and dynamic fatigue and impact resistance of these composites. The tension-tension fatigue life of both unidirectional fiber and fabric-reinforced laminates was greater than that of comparable glass-reinforced composites. The creep rate under continuous tensile stress was comparable to that of glass composites. The ball-drop impact resistance of Kevlar 49 fabric laminate-faced sandwich panels was dependent on 'fabric weave construction and number of face sheet plies. This relationship was significantly different for sandwich beams having glass-reinforced facings.

Optimally Reinforced Axisymmetric Plates

Abstract: A sandwich plate is considered in which the reinforcement fibers are located entirely within the outer faces of the plate. The layout of the fibers is determined within the faces of the plate to minimize the total fiber consumption. The variation of fiber material within the optimal plate to resist the internal stress resultants due to a given loading may be obtained once the fiber layout has been determined. Only one loading case is considered for a simply supported plate, clamped plate, and simply supported annular plate.

Application of PATCHES-III to the Three-Dimensional Response of Laminated Composite Structures,

Abstract: : A recently developed program for the stress analysis of general solids of composite material is applied in this study to a sandwich panel impact problem and a partially cracked laminate problem Objectives of the study are: (1) to determine the load distribution, the stresses and the deformations in individual plies of these composite laminates and (2) to demonstrate the modeling capabilities and limitations of the PATCHES-III program Preparatory to the analyses, the program was updated to automate the superposition of symmetry - asymmetry subcases for more efficient modeling The present application of the PATCHES-III system to laminated composites was successful in predicting the three-dimensional response of individual plies at very reasonable modeling and computational costs Engineering checks of the overall response with hand calculations using beam and plate models were in good agreement for both the sandwich panel and the partially cracked laminate A modeling error in the boundary conditions for the latter problem introduced fictitious normal forces for the asymmetry subcase These forces were evaluated when the error was discovered and found to be small, on the order of 0015 lbs maximum, and judged not to have a significant effect on the redistribution of load around the crack The constraint force calculations were made possible by a postprocessor data file system developed as one of the objectives of the effort The Experience gained from the present study also indicates the need for improvement in certain areas

Stressed-Skin Panel - Deflections and Stresses.

Abstract: : The paper presents a mathematical analysis based on 'shear flow' and 'shear lag' theories to determine deflections and stresses for stressed-skin panels wherein skins are rigidly bonded to stringers. Experimental examination of several panel constructions showed that the analysis can provide a rational basis for the design of stressed-skin panels. Designs based on the analysis will result in more efficient use of materials.