Aerospace Structures

Si sta preparando il Grande Spettacolo Spaziale Bis. Il capitalismo lo vuole. È in crisi da almeno un secolo, ma da un decennio a questa parte sembra morto: la produzione langue, enormi quantità di capitale fittizio attendono congelate che si muova qualcosa nell'economia per gettarsi sui mercati in nuove avventure speculative. Non esiste uno straccio di teoria economica che possa suggerire qualche rimedio. Così ci si rivolge ancora una volta al Cielo. I sintomi ci sono tutti, e stavolta la posta in gioco non è l'inutile e sterile Luna ma il pianeta meno dissimile dalla Terra, cioè Marte. Sondato, studiato, sorvolato da ricognitori satellitari, percorso da robot cingolati con annesso laboratorio di analisi, il Pianeta Rosso è preso di mira come possibile oggetto di colonizzazione. Per il vorace capitalismo giunto alla sua fase finale, una Terra non basta più, ne occorre un'altra, anche se il sistema solare offre, come possibile doppione, solo un freddo pianetino desertico, con un'atmosfera quasi inesistente e comunque fatta di gas tossici.

Citeremo un capitalista che si è fatto portavoce della necessità di "rendere multiplanetaria" la specie umana portandola su Marte. Ma la fuga dalla realtà capitalistica terrestre a un'altra (ipotetica) realtà capitalistica è impossibile.

This paper gives a brief overview of sandwih application history in general and present composite sandwich structures at Airbus. Current R&D developments for sandwich in primary structure s are being outlined followed by a discussion of potentials and challenges for composite sandwich structures.

Sandwich structures with face sheets made of carbon fiber reinforced plastics (CFRP) demonstrate a high potential to reduce both production costs and the weight of primary aircraft structures. This potential has however yet not been realized mainly due to the complex structural and material behavior of sandwich structures under different kinds of loading and adverse effects like moisture take up of honeycomb core material [1]. Using closed cell hard foams such as PMI foam, better known as Rohacell®, the issue of moisture take-up has been solved. One more critical issue however is the often criticized lack of damage tolerance of sandwich structures [2].
Impact damage resistance is part of the larger topic of damage tolerance. It can be treated separately as impacts may cause a damage that is used a starting point for a damage tolerance analysis while not vice versa. In consequence the resulting damage size of a predefined impact scenario is of great importance.

As a follow-up on the author's work on coupled BE/FE Method and modeling of structuralacoustic interaction, the present work utilizes BE formulation for both the acoustic and aerodynamic problem. For this purpose the unsteady aerodynamic problem which was earlier utilizes well-established lifting surface method is reformulated using BE approach. This scheme is presently outlined and worked out in the general framework of acousto-aeroelastic stability problem developed previously.

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Sandwich structures with  face sheets made of carbon fibre reinforced plastics  (CFRP) have a high potential in  reducing production costs and  weight of primary  aircraft structures. Their  advantage is based on their superior bending stiffness compared to solid laminates. This allows a less complex and highly integrated structural design which typically reduces the number of parts and joints significantly. The highlighted potential has however yet not been realized within primary aircraft structures mainly due to the complex structural behaviour. Another adverse effect often mentioned is moisture take up of the core material. Using closed cell hard foams such as PMI foam, better known as Rohacell®, for the core, the problem of moisture take-up has been solved. Damage tolerance however has been one of  the most critical  issues regarding the  use of sandwich structures [1]  [2]. Extensive research has been conducted on CFRP foam core sandwich structures with mostly PVC foam for application in marine vessels, which provides a large benefit for today’s level of understanding. Past and current research  concentrates on describing material behaviour with damage, damage growth under cyclic loading  and consequently  maximum  damage  sizes [3]-[5]. Less attention  has however  been given to damage initiation by localized impact events. Low Velocity impact may lead to face sheet
and/or core damages [6]-[8].

This study is focused on the structural optimization of an axial flow compressor rotating disk in a more simplistic way. Since optimization involves several runs, performing Finite Element Analysis (FEA) for a disk model in each run increases computational cost. Alternative response surface design models have been developed using the design of experiment (DOE) method to represent the FE disk model. These response equations are validated and used in optimization runs. A constraint nonlinear optimization procedure based on genetic algorithms has been used. FEA is completely avoided during the optimization runs with the help of response equations, resulting in less computational time and cost.

Structural Health Management (SHM) will be of critical importance to provide the safety, reliability and affordability necessary for the future long duration space missions described in America’s Vision for Space Exploration. Long duration missions to the Moon, Mars and beyond cannot be accomplished with the current paradigm of periodic, ground-based structural integrity inspections. As evidenced by the Columbia tragedy, this approach is also inadequate for the current Shuttle fleet, thus leading to its initial implementation of on-board SHM sensing for impact detection as part of the return to flight effort. However, future space systems, to include both vehicles as well as structures such as habitation modules, will require an integrated array of onboard in-situ sensing systems. In addition, advanced data systems architectures will be necessary to communicate, store and process massive amounts of SHM data from large numbers of diverse sensors. Further, improved structural analysis and design algorithms will be necessary to incorporate SHM sensing into the design and construction of aerospace structures, as well as to fully utilize these sensing systems to provide both diagnosis and prognosis of structural integrity. Ultimately, structural integrity information will feed into an Integrated Vehicle Health Management (IVHM) system that will provide real-time knowledge of structural, propulsion, thermal protection and other critical systems for optimal vehicle management and mission control. This paper will provide an overview of NASA research and development in the area of SHM as well as to highlight areas of technology improvement necessary to meet these future mission requirements.