Francesco Danzi, Giacomo Frulla and Giulio Romeo
This paper aims to present a systematic performance-oriented procedure to predict structural responses of composite layered structures. The procedure has a direct application in…
Abstract
Purpose
This paper aims to present a systematic performance-oriented procedure to predict structural responses of composite layered structures. The procedure has a direct application in the preliminary design of aerospace composite structures evaluating the right and most effective material.
Design/methodology/approach
The aforementioned procedure is based upon the definition of stiffness invariants. In the paper, the authors briefly recall the definition and the physical explanation of the invariants, i.e. the trace; then they present the scaling procedure for the selection of the best material for a fixed geometrical shape.
Findings
The authors report the basic principles of the scaling procedure and several examples pertaining typical responses sought in the preliminary design of aeronautic structures
Research limitations/implications
Typically, during early stages, engineers had to perform the daunting task of balancing among functional requirements and constraints and give the optimum solution in terms of structural concept and material selection. Moreover, preliminary design activities require evaluating different responses as a function of as less as possible parameters, ensuring medium to high fidelity. The importance of incorporating as much physics and understanding of the problem as early as possible in the preliminary design stages is therefore fundamental. A robust and systematic procedure is necessary.
Practical implications
The time/effort reduction in the preliminary design of composite structures can increase the overall quality of the configuration chosen.
Social implications
Reduction in design costs and time.
Originality/value
In spite of the well-known invariant properties of composites, the application and extension to the preliminary design of composite structures by means of a scaling rule is new and original.
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Giacomo Frulla, Enrico Cestino, Federico Cumino, Alessio Piccolo, Nicola Giulietti, Eugenio Fossat and Ehsan Kharrazi
The purpose of this study is to investigate a new and innovative sandwich material evaluating its capability for use in space habitat structural components in deployable and…
Abstract
Purpose
The purpose of this study is to investigate a new and innovative sandwich material evaluating its capability for use in space habitat structural components in deployable and foldable configurations. The main habitat requirements were considered in the preliminary design of a typical space outpost, proposing a preliminary architecture.
Design/methodology/approach
The stiffness properties of the innovative sandwich (MAdFlex ®) were evaluated using numerical and experimental investigations. Four-point bending tests were performed for complete sandwich characterization. Numerical FE simulations were performed using typical material properties and performance. The application to a space habitat main structure as a basic material has also been discussed and presented.
Findings
MAdFlex basic stiffness performances have been determined considering its double behavior: sufficiently stiff if loaded in a specific direction, flexible if loaded in the opposite direction and enhanced folding performance. Successful application to a typical space habitat confirms the validity and convenience of such a material in designing alternative structures.
Research limitations/implications
The innovative material demonstrates wide potential for structural application and design in demanding space situations under operating conditions and in stored ones at launch.
Practical implications
Several simple deployable structural components can be designed and optimized both for the space environment and for the more traditional terrestrial applications.
Social implications
Simplification in structural design can be derived from deployable low-weight items.
Originality/value
Innovative customized material in sandwich configuration has been proposed and investigated with the aim to demonstrate its potentiality and validity in alternative design architecture.
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Claudia Bruni, Enrico Cestino and Giacomo Frulla
The purpose of the research activity is to identify the best configuration of piezoelectric (PZT) elements for a typical condition of wing aeroelastic instability. The attention…
Abstract
Purpose
The purpose of the research activity is to identify the best configuration of piezoelectric (PZT) elements for a typical condition of wing aeroelastic instability. The attention is mainly focused on the flutter behavior of the structure. However, the model can be extended with low-impact adjustments to other loading conditions.
Design/methodology/approach
The dynamic system consists of a thin-walled beam, whose longitudinal faces are perfectly bonded by two PZT layers and it is excited by the aerodynamic forces to assume a simple harmonic oscillation motion. The equations of motion are obtained using an energy approach by applying the extended Hamilton principle in conjunction with the Ritz method for modal approximation. The external forces acting on the system are modeled according to the Theodorsen derivation.
Findings
The flutter speed and the power generated from flutter oscillations can be increased by acting on the length of the PZT elements. The results show that the model with the beam substrate totally covered by the PZT in its longitudinal direction is more effective for low electrical resistance, whereas for high resistance values, the beam substrate that is partially covered provides the best results. Furthermore, both flutter postponement and energy harvesting functions can be maximized by properly choosing the beam stiffness ratio.
Practical Implications
Depending on the parameter we want to maximize, that is, the flutter speed or the energy harvested, it is possible to identify the best system configuration from the analysis presented in this paper.
Originality/value
The originality of the work appears in the sensitivity study performed on a three-dimensional piezo-aeroelastic fluttering wing, whose optimal behavior in terms of flutter postponement and power generation is analyzed using two distinct parameters, the beam stiffness ratio and the PZT length.
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Enrico Cestino and Giacomo Frulla
This study aims to analyse slender thin-walled anisotropic box-beams. Fiber-reinforced laminated composites could play an important role in the design of current and future…
Abstract
Purpose
This study aims to analyse slender thin-walled anisotropic box-beams. Fiber-reinforced laminated composites could play an important role in the design of current and future generations of innovative civil aircrafts and unconventional unmanned configurations. The tailoring characteristics of these composites not only improve the structural performance, and thus reduce the structural weight, but also allow possible material couplings to be made. Static and dynamic aeroelastic stability can be altered by these couplings. It is, therefore, necessary to use an accurate and computationally efficient beam model during the preliminary design phase.
Design/methodology/approach
A proper structural beam scheme, which is a modification of a previous first-level approximation scheme, has been adopted. The effect of local laminate stiffness has been investigated to check the possibility of extending the analytical approximation to different structural configurations. The equivalent stiffness has been evaluated for both the case of an isotropic configuration and for simple thin-walled laminated or stiffened sections by introducing classical thin-walled assumptions and the classical beam theory for an equivalent system. Coupling effects have also been included. The equivalent analytical and finite element beam behaviour has been determined and compared to validate the considered analytical stiffness relations that are useful in the preliminary design phase.
Findings
The work has analyzed different configurations and highlighted the effect of flexural/torsion couplings and a local stiffness effect on the global behaviour of the structure. Three types of configurations have been considered, namely, a composite wing box configuration, with and without coupling effects; a wing box configuration with sandwich and cellular constructions; and a wing box with stiffened panels in a coupled or an uncoupled configuration. An advanced aluminium experimental test sample has also been described in detail. Good agreement has been found between the theoretical and numerical analyses and the experimental tests, thus confirming the validity of the analytical relations.
Practical implications
The equivalent beam behaviour that has been determined and the stiffness calculation procedure that has been derived could be useful for future dynamic and aeroelastic analyses.
Originality/value
The article presents an original derivation of the sectional characteristics of a thin-walled composite beam and a numerical/experimental validation.
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Giacomo Frulla, Gianni Avalle and Vito Sapienza
The purpose of this paper is to investigate the effect of fatigue life reduction of 2024 Al alloy for aerospace components due to the corrosive (exfoliation) environment. Both…
Abstract
Purpose
The purpose of this paper is to investigate the effect of fatigue life reduction of 2024 Al alloy for aerospace components due to the corrosive (exfoliation) environment. Both standard fatigue tests on prior corroded samples and fatigue tests conducted with the samples in corrosive solution are developed to define some guidelines for the inclusion of such effect in design and to improve aircraft life management.
Design/methodology/approach
The effect of corrosion is taken into consideration, introducing specific concentration factors into the life estimation relationship. Differences between fatigue in corroded specimens and fatigue in presence of corrosive environment are emphasized. No crack propagation is considered. Two alternative procedures are considered in the analysis: “a-procedure” based on maximum stress calculated on un-corroded sample section; “b-procedure” based on stress calculated on final residual section, including corrosion.
Findings
Related concentration factors are derived and compared by the experimental results with the aid of an original proposed a “power law”. Typical power law (square kt) has been derived to cope with the coupling effect of fatigue and corrosive environment.
Research limitations/implications
The original approach developed in the paper is based on few samples. For this reason, the conclusions are addressed as tendency behaviour.
Practical implications
The combined effect of fatigue load acting in presence of corrosive environment reveals an important reduction in fatigue life that cannot be determined by means of classical fatigue tests performed on prior corroded samples.
Social implications
Specific design updating procedure can be determined to cope with ageing of structures during service improving structural integrity.
Originality/value
The derivation indicates a substantial equivalence of the considered two procedures both in the case of prior corroded samples and in combined situation. This tendency is consistent with the available data results. Original analytical relations are introduced to manage such kind of combined effect revealing consistency of data also if few samples were tested.