Number Of Aerospace Applications Research Articles

Analytical and Experimental Studies of Composite Isogrid Structures with Integral Passive Damping

Composite isogrid structure are currently in use in a number of aerospace applications where the control of structural vibration response is an important design consideration. In this paper, a recent investigation of the modal vibration characteristics of composite isogrid structures with embedded viscoelastic damping layers will be summarized. Analysis was done by means of the finite-element-based modal strain energy method, while experiments were done by using an impulse-frequency response technique. Composite isogrid test panels were fabricated by a fast and inexpensive thermoplastic stamping process using co-mingled glass/polypropylene. The viscoelastic layer damping materials were embedded at the interface between the ribs and the skin, where the shear deformations are greatest in order to significantly improve the damping properties of the structures. Good agreement between measured and predicted modal frequencies and damping factors was found in the cases where degradation of the damping layer during the thermoplastic stamping process was avoided by using a secondary bonding process. It was also found that the required amount of damping material could be reduced significantly if it is optimally placed.

Analytical/experimental studies of integral passive damping in composite isogrid structures

Composite isogrid structures are currently in use in a number of aerospace applications where the control of structural vibration response is an important design consideration. In this presentation, a recent investigation of the modal vibration characteristics of composite isogrid structures with embedded viscoelastic damping layers will be summarized. Analysis was done by means of a finite element method implementation of the modal strain energy method, while experiments were done by using an impulse-frequency response technique. Composite isogrid test panels were fabricated by a fast and inexpensive thermoplastic stamping process using two different co-mingled materials: glass/polypropylene and carbon/nylon. The damping materials were embedded at the interface between the ribs and the skin where the shear deformations are greatest in order to significantly improve the damping properties of the structures. It is found that the required amount of damping material can be reduced significantly if it is optimally placed. The modal vibration characteristics of composite isogrid structures are also compared with those of other composite structures such as laminates and sandwich panels. The authors gratefully acknowledge the support of the WSU Institute for Manufacturing Research, as well as donations of materials by Vetrotex America, Cytec Fiberite, and 3M Company.

Analysis of a Hybrid Dual-Combustion-Chamber Solid-Propellant Gas Generator

Solid-propellantgas generators (SPGGs) have a number of aerospace applications, includingmunitionsdispersion, pilot emergency escape systems, submarinemissile launching,powering actuators and valves, and short-term power supply. Recently, the increased demand for so-called smart automotive airbags has increased the need for SPGG designs capable of real-time, tailorable output. Dual-combustion-chamber gas generators provide several distinct advantagesover single-combustor units in systems where optimumperformance is needed at several operating conditions. The objective of this work is to evaluate the attainable performance characteristics of a proposed dual-combustion-chambergas generator. The work includes a simulation of the transient, thermochemical events associated with the Ž ring of an SPGG. The simulations also include the dynamics of coupled events such as ignition, heterogeneous combustion, and mass discharge. The baseline gas generator being simulated in this work is a hybrid SPGG in ator with two combustion chambers. Studies are made of the distribution of propellant between combustion chambers and the times at which the propellant within each combustion chamber is Ž red.

Characterization of beryllium foil produced by hot rolling

Beryllium foil is important for a number of aerospace applications including honeycomb structures and metal-matrix composites. In this study, a method of producjng beryllium foil directly from powder or flake is demonstrated. A variety of foils were produced in the thickness range 90–300 μm, free from defects such as pinholes and excessive surface roughness, and exhibiting sufficient formability for honeycomb manufacture. Foil produced directly from powder or flake exhibits crystallographic texture, microstructure, and formability equivalent to foil produced from more massive precursors.