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A test system designed specifically to acquire the complex moduli of viscoelastic materials in shear is described. Unique and innovative approaches in the mechanical design, temperature control system, and data acquisition methods provide a standard of accuracy that is rarely seen in dynamic mechanical properties of viscoelastic materials. The system operates on the principle of direct complex stiffness measurements. Unique sensors, hardware layout, and data acquisition and reduction methods maximize the frequency bandwidth and the dynamic range of stiffness, data acquisition speed, and temperature uniformity. Forced liquid convection temperature control also provides unparalleled speed and uniformity in specimen temperatures. Results are demonstrated and scrutinized using characterization software. Characterized data are stored in a database that provides the designer with the capability of searching based on the mechanical parameters commonly needed for damping designs. The end product is an end-to-end system capable of superior data accuracy and acquisition rates, and software that enables the most critical evaluation of results and ready storage in a manner that is efficient for damping design applications.

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This paper describes the development ofdamped structure for the Supportable Technology for Affordable Fighter Structures (STAFS) Program. The study started with analytical design trade studies and progressed through a series of tests to characterize adhesive behavior, performance testing of a component level integrally damped panel concept, and full scale design integration. Analyses were performed on finite element panel models with viscoelastic elements in the bond areas to determine the sensitivities of configuration and adhesive type to overall damping achieved. The concepts studied showed that as much as 10 percent structural damping could be obtained in the structural modes of interest. Test panels with and without damping treatments were fabricated using super plastically formed-adhesive bonded 2095 aluminum, and tested to measure the comparative response improvementin the dampedpanels. A substantial weight savings was realizedin comparison tothemonolithic metalpanels which would be required to withstand the acoustic environment. BACKGROUNDAdvanced aircraft structure when subjected to the extreme dynamic environments associated with air to ground maneuvers of attack aircraft are characteristically prone to sonic fatigue. For the USAF sponsored STAFS program, it was determined that structural dynamics considerations were significant for such structure as internal weapons bay enclosures, engine bay doors, fuel tank enclosures, and access doors. The STAFS article is shown in Fig. 1. The objective of the STAFS program is to develop supportable and affordable advanced metallic technologies with the goal of developing structural concepts to improve system performance through reducing system life cycle cost by 30 percent and weight by 10 percent. Due to the high acoustic loading requirements of the internal weapons bay, SPF/AB construction using damping and structural adhesives are being employed for sonic fatigue resistance. In order to choose an adhesive with the best combination of stiffness and damping properties for the SPF/AB walls ofthe weapons bay, a survey was performed to determine the best candidate adhesives and SPF/AB configurations which would exhibit significant damping and structural performance. Two and four sheet concepts were studied using finite element panel models with viscoelastic elements in the bond areas to determine the sensitivities of configuration and adhesive type to overall damping achieved. Material stiffness, strength, and damping data were assembled for three chosen adhesives; FM 300, AF 32, Y-9469. Test panels were fabricated using SPF/AB 2095 aluminum, and tested to measure the response in comparison to undamped two sheet SPF/AB panels. A weight savings of 60% was realized in comparison to the monolithic metal panels which would be required to withstand the acoustic environment. 54 ISPIE Vol. 244S O-8194-1794-7/95/$6.OO Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/23/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx

Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. ABSTRACTResearch to create advanced vibration isolator designs and practical design techniques for Launch Vehicle (LV) manufacturers is discussed. Avionics of launch vehicles have unique requirements for isolation since many generate heat and cannot use convection cooling for dissipation. Nearly all isolation systems are ineffective thermal conductors unless expensive custom modifications are performed. The cost of a custom isolation design can rarely be justified, particularly with expendable vehicles. While viscoelastic isolators offer simplicity and affordability, such materials with high loss factors (greater than 0.25) also exhibit aggressive changes in stiffness with both temperature and frequency. Materials having new and unique formulations are introduced which have an order of magnitude higher thermal conductivity than today's materials of similar stiffness. This enables appreciable heat conduction with nominal temperature increases to isolated packages. The formulation of nearly all elastomeric vibration isolators creates heavy coupling between their loss factors and the rate of change in their storage moduli. High loss factors result in an aggressive temperature-dependent shift in the resonant frequencies of an isolated element. New compounds introduced in this paper address this limitation. A software utility has also been developed that greatly simplifies isolation design. The utility solves the equations of motion for a rigid body on flexible mounts and allows performance predictions using base vibration inputs. New progress in material technology and design techniques enables LV manufacturers to implement affordable designed vibration isolation systems on avionics and similar systems.