Effect of Cyclic Buckling Under Combined Loading on Pre-Damaged Composite Stiffened Box

The results obtained on two pre-damaged closed boxes composed by four graphite-epoxy curved stiffened panels, and manufactured by Agusta/Westland, are presented. The closed box configuration allows to apply shear load on each panel by subjecting the box to torque. The pre-damages are obtained using Teflon inserts between three stringers and the skin, so to reproduce skin-stringer disbonding. The boxes are tested under axial compression and torque, applied individually and in combination, both statically and cyclically. The static tests allow to compare different procedures of loading application and to investigate the effect of post-buckling combined loads on the damage propagation. The cyclic tests allow to investigate the influence of cyclic post-buckling combined loads in terms of global behaviors, of collapse modalities and of damage propagation. The results show the reliability of these structures, even if pre-damaged, to safely operate in the post-buckling field, also when the buckling load is reached thousands of times during the operative life

Efficient Discrete Element Modeling of Particle Dampers

Particle dampers’ dissipative characteristics can be difficult to predict because of their highly non-linear behavior. The application of such devices in deformable vibrating systems can require extensive experimental and numerical analyses; therefore, improving the efficiency when simulating particle dampers would help in this regard. Two techniques often proposed to speed up the simulation, namely the adoption of a simplified frictional moment and the reduction of the contact stiffness, are considered; their effect on the simulation run-time, on the ability of the particle bed to sustain shear deformation, and on the prediction of the dissipation performance is investigated for different numerical case studies. The reduction in contact stiffness is studied in relation to the maximum overlap between particles, as well as the contacts’ duration. These numerical simulations are carried out over a wide range of motion regimes, frequencies, and amplitude levels. Experimental results are considered as well. All the simulations are performed using a GPU-based discrete element simulation tool coupled with the multi-body code MBDyn; the results and execution time are compared with those of other solvers

Metamodels for Optimum Design of Composite Stiffened Structures under Torsion Loading

A numerical study has been carried out to approximate the post-buckling responses of stiffened box structures as shown in Figure 1. The structure is made of carbon fibers reinforced plastics and subjected to torsion loading. In a previous study [1], metamodeling methodology has been applied on axially loaded stiffened composite panels were significant post-buckling deformations have been observed before the final collapse of the structure. The proposed approach is based on the combined use of probabilistic structural analysis by sampling of computer experiments and approximating of the load shortening structural responses

Metamodels for the Optimization of Damagetolerant Composite Structures

The research here presented regards the development of an optimization technique for the design of damage-tolerant stiffened composite structures subjected to combined compression and shear loading. Some techniques are already presented in literature regarding the optimization of composite stiffened panels [1-3]. The proposed methodology wants to satisfy a number of different performance requirements, such as buckling load and post-buckling stiffness for various states of damage. In particular, the design must be tolerant of predetermined degradation, due to disbonding between the skin and the stiffeners

Metamodels for Optimum Design of Composite Stiffened Structures under Torsion Loading

A numerical study has been carried out to approximate the post-buckling responses of stiffened box structures as shown in Figure 1. The structure is made of carbon fibers reinforced plastics and subjected to torsion loading. In a previous study [1], metamodeling methodology has been applied on axially loaded stiffened composite panels were significant post-buckling deformations have been observed before the final collapse of the structure. The proposed approach is based on the combined use of probabilistic structural analysis by sampling of computer experiments and approximating of the load shortening structural responses

In-Flight Demonstration of a Novel Contactless Sensor for Helicopter Blade Motion Measurement

This paper focuses on the path which led to the final flight demonstration of an innovative helicopter main rotor blade attitude measurement system, based on stereoscopic cameras. The system has been designed, developed and implemented within the project MANOEUVRES, carried on in the framework of the Clean Sky Green Rotorcraft 5 research programme and aimed at developing an integrated system capable of informing the pilot of the real-time noise generation and of suggesting possible corrective actions for low-noise maneuvering. The integrated systems relies on an innovative blade attitude sensor, being the main rotor state one of the factors which mostly impact on noise generation, not retrievable by means of conventional systems. In this paper, the full sensor development process is briefly described, with emphasis laid on its flight demonstration, performed on board an AgustaWestland AW139 prototype helicopter, and on the analysis of the flight test results

Laser and vision-based measurements of helicopter blade angles

In this paper, three novel non-contact measurement systems for helicopter rotor blades, based on the 2D laser triangulation, the single camera and the stereo camera respectively, are designed and developed. The three measurement systems are applied to reconstruct the spatial position of the blade, and consequently its attitude angles. The measuring qualities of the three systems are assessed by means of experiments, including vibration tests, coupled rotation and vibration tests, and accuracy tests with complex motion configurations. These tests demonstrate that the three solutions can perform continuous operation correctly in a relevant dynamic environment. The results of accuracy tests show that, while all the systems can be successfully applied for the measurement of the angles of a helicopter blade, the stereo camera system provides a better accuracy than the other two systems. In particular, for the stereo camera system, the discrepancies of the three angles are comprised between 0.1 and 0.3 degrees in case of realistic blade motion conditions