Design and Evaluation of a Reinforced Advanced-Grid Stiffened Composite Structure
Abstract : A composite grid-stiffened structure concept was selected for the payload fairing of the Minotaur launch vehicle. Compared to previous designs, this concept is lighter weight and requires reduced manufacturing costs. Various failure mechanisms were examined for the composite grid-stiffened structure. The controlling criterion for this design was determined to be joint peel-off failure. The identification of this failure mechanism and the assessment of bounding strains to control it, required extensive test and analysis effort. The final fairing design incorporated an undesirably thick skin to reduce the strain between the skin and ribs. This project investigated a means of controlling joint failure of the un-reinforced grid-stiffened structure in an effort to reduce the skin thickness. Implementing lightweight foam inserts between the stiffeners on the interior of the fairing delayed failure to higher loads. A foam reinforced test panel, designed with equal mass to the current structure, withstood a substantially greater compressive force. The alternative concept also demonstrated an improved response, failing in global buckling instead of experiencing early failure due to joint strain.
Stability design of honeycomb sandwich radome with asymmetric shape
Abstract The die radome, which is made of honeycomb sandwich structure, should be entirely refitted, for a big electronic observation facility is being fixed at the head section of an aircraft. In this work, the stability design of honeycomb sandwich radome is investigated. Initially, a local buckling failure is observed in the refitted radome during the preliminary calculation. Then design improvements are made to the existing radome, like some L-shaped stiffeners are added on the inner surface of metal faring in order to improve the stability of radome. In this way, the critical buckling load of radome increases more than 10 times. Different layout schemes for the stiffeners are studied during this work, and the best structure layout is obtained by discrete optimization method and also the relationship between stability and bar spacing is examined. Finally, the stability of radome under 45 load cases is calculated to validate the design. The result shows that the optimized design greatly improves the stability of radome. This method can be applied to structure design in preliminary assessment.
Effective Widths of Compression-Loaded Plates With a Cutout
A study of the effects of cutouts and laminate construction on the prebuckling and initial postbuckling stiffnesses, and the effective widths of compression-loaded, laminated-composite and aluminum square plates is presented. The effective-width concept is extended to plates with cutouts, and experimental and nonlinear finite-element analysis results are presented. Behavioral trends are compared for seven plate families and for cutout-diameter-to-plate-width ratios up to 0.66. A general compact design curve that can be used to present and compare the effective widths for a wide range of laminate constructions is also presented. A discussion of how the results can be used and extended to include certain types of damage, cracks, and other structural discontinuities or details is given. Several behavioral trends are described that initially appear to be nonintuitive. The results demonstrate a complex interaction between cutout size and plate orthotropy that affects the axial stiffness and effective width of a plate subjected to compression loads.