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.
Engineering bio-inks for 3D bioprinting cell mechanical microenvironment
Three-dimensional (3D) bioprinting has become a promising approach to construct­ing functional biomimetic tissues for tissue engineering and regenerative medicine. In 3D bioprinting, bio-inks are essential for the construction of cell microenviron­ment, thus affecting the biomimetic design and regenerative efficiency. Mechanical properties are one of the essential aspects of microenvironment, which can be char­acterized by matrix stiffness, viscoelasticity, topography, and dynamic mechanical stimulation. With the recent advances in functional biomaterials, various engineered bio-inks have realized the possibility of engineering cell mechanical microenviron­ment in vivo. In this review, we summarize the critical mechanical cues of cell micro­environments, review the engineered bio-inks while focusing on the selection princi­ples for constructing cell mechanical microenvironments, and discuss the challenges facing this field and the possible solutions for them.