Resonant Enhancement of Standing Magnetoelastic Waves By Laser-generated Thermoelastic Waves In Ribbons of Metallic-glass

Experimental evidence of magneto-elastic wave amplitude enhancement by thermo-elastic waves is reported. This enhancement is shown to be optimized under resonance conditions. The thermo-elastic waves have been excited in a metal alloy ribbon sample by a high repetition rate CO2 laser. The results are explained in terms of a simple theoretical treatment of the thermo-magnetic elastic waves under the conditions investigated

Stochastic Approach to Damage Resistance Analysis of Stiffened Composite Panels

Composite materials exhibit complex phenomena associated with damage onset, and are characterized by significant uncertainties in their material properties. The development of damage resistance design methodology, especially for damage induced by low velocity impacts in aircraft structures, have allowed a more efficient management of the damage in composites. In this paper a probabilistic approach has been adopted in order to evaluate the impact of the material properties scattering on the damage resistance of a composite panel. Furthermore two different composite panels have been investigated and compared in order to detect, based on a probabilistic approach, the one exhibiting the best performances in terms of damage resistance

A fast procedure for optimizing thermal protection systems of re-entry vehicles

The aim of the present work is to introduce a fast procedure to optimize thermal protection systems for re-entry vehicles subjected to high thermal loads. A simplified one-dimensional optimization process, performed in order to find the optimum design variables (lengths, sections etc.), is the first step of the proposed design procedure. Simultaneously, the most suitable materials able to sustain high temperatures and meeting the weight requirements are selected and positioned within the design layout. In this stage of the design procedure, simplified (generalized plane strain) FEM models are used when boundary and geometrical conditions allow the reduction of the degrees of freedom. Those simplified local FEM models can be useful because they are time-saving and very simple to build; they are essentially one dimensional and can be used for optimization processes in order to determine the optimum configuration with regard to weight, temperature and stresses. A triple-layer and a double-layer body, subjected to the same aero-thermal loads, have been optimized to minimize the overall weight. Full two and three-dimensional analyses are performed in order to validate those simplified models. Thermal-structural analyses and optimizations are executed by adopting the Ansys FEM code

New materials and related fabrication processes for hot structures on RLV'S

The next generation of Reusable Launch Vehicles (RLV's) will implement the substitution of traditional blunt bodies with new aerodynamic configurations characterized by slender profiles with sharp leading edges. The main advantage of this redesign of hypersonic space vehicle is represented by enhanced maneuverability and improved cross range capability and consequently increased mission safety, In addition the reduction of wave drag in the ascent phase will reduce the costs of the payload deployment. The real possibility to adopt sharp profiles is strictly related to the selection and availability of materials with suitable performance. In fact at hypersonic speeds, sharp edges of slender configurations reach values of the surface temperatures much higher than any temperature allowable by traditional thermal protection system (TPS) and more the geometrical radius of curvature decreases, more the heat flux at leading edge increases. Recent research and developments of a new class of materials named Ultra High Temperature Ceramics (UHTC) seems to offer the right chance to fabricate hot structures for RLV's applications which can withstand temperatures above 2000°C. This paper deals with a new process technology based on the employment of zirconium diborides ceramic matrix composites that appropriately modified and reinforced can be considered, as our previous numerical investigation showed, very promising candidate materials for the fabrication of hot structures of slender bodies such as nose cap, wing leading edges, etc. The materials developed in the frame of a consistent scientific collaboration coordinated by CIRA, and involving Centre Sviluppo Materiali SpA (CSM) and University of Rome "La Sapienza", have been thermally and mechanically characterized in order to assess their applicability to a specific space mission requirements. Copyright © 2003 by the International Astronautical Federation. All rights reserved

Numerical/Experimental Correlation of a Plasma Wind Tunnel Test on a UHTC-Made Nose Cap of a Reentry Vehicle

The nose cap demonstrator named Nose-2 has been tested for the second time in the plasma wind tunnel (PWT) facility which is part of the sharp hot structure (SHS) technology project, focused on the assessment of the applicability of ultrahigh temperature ceramics (UHTC) to the fabrication of high performance vehicles and SHS for reusable launch vehicles. In this paper the FEM based thermal analyses, carried out for the rebuilding of this PWT test, are presented. Experimental data measured in the PWT have been compared with numerical ones in order to validate the FEM model and to help in interpreting the experimental test itself. The knowledge on the physical phenomenon under investigation has been greatly improved, thanks to the synergy between numerical and experimental activities. In particular, a qualitative study of the modeling of the tip-dome interface has been performed in order to estimate the thermal contact resistance that heat flux encounters in passing through the demonstrator. The correlation between numerical and experimental temperature curves has been found to be satisfactory for both internal and surface temperature distribution, and the FEM model was found reliable in reproducing the thermal behavior of the nose cap

THE VIBRATIONAL-TRANSLATIONAL RELAXATION OF CF2HCL IN ARGON

We report in this paper results concerning the vibrational-translational (VT) rates of CF2HCl diluted in Ar as a neutral buffer. The dependence on the buffer concentration and on the initial vibrational energy distribution are obtained by using the 9R(48) and the 9R(34) CO, laser lines for the excitation process. The differences observed between the results corresponding to the two lines bear valuable information about the dependence of the VT relaxation process on the specific initial conditions of vibrational excitation