Defense Technical Information Center Compilation Part Notice ADP 014084 TITLE : Recognition and Correction of Sonic Fatigue Damage in Fighter Aircraft DISTRIBUTION : Approved for public release , distribution unlimited
High performance aircraft that fly aggressive low altitude or high-angle of attack maneuvers will experience high acoustic loading, especially in the presence of external stores. These high acoustic loadscan lead to rapid sonic fatigue in thin gage metallic structure. As a means of prolonging fatigue life, while at the same time restoring structural load carrying capability in damaged structure, composite bonded repairs which incorporate damping layers have been developed. These damped composite bonded repairs are installed on F-15 flight test aircraft. This paper describes ways to recognize sonic fatigue damage, and the design and flight test results of represeintative damped patches.
Composite material repairs to metallic airframe components
The repair of metal structures by using composite materials is a technology that was pioneered in Australia, and excellent results have been obtained in over 500 repairs of corrosion and fatigue cracking. This paper will present details of the first in-service composite material repair applied to metal structure on USAF C-141B operational aircraft. This engineering study evaluated five locations representing both fatigue and corrosion cracking susceptible areas on the C-141B strategic airlift transport aircraft. Repairs using either boron/epoxy or graphite/epoxy are beneficial for crack retardation, end fastener effect relief, and field stress reduction. The most obvious time saving feature of these repairs is that no fastener removal or installation is involved. Extensive structural analysis utilizing finite element modeling was done to ensure that the repair design not only would have the requisite strength and durability but also would reduce the inspection burden after the aircraft was returned to service. A test program was also undertaken to substantiate the analytical investigation. Typical results from the finite element models as well as the specimen and component tests will be presented. Finally, the step-by-step procedure by which an actual boron/epoxy repair was applied to a fatigue crack on a C-141 center wing will be reported and "lessons learned" will summarize the benefits of applying the technology.
Numerical tools applied to power reactor noise analysis
In order to be able to calculate the space- and frequency-dependent neutron noise in real inhomogeneous systems in two-group theory, a code was developed for the calculation of the Green's function (dynamic transfer function) of such systems. This paper reports on the development as well as the test and application of the numerical tools employed. The code that was developed yields the space-dependence of the fluctuations of the neutron flux induced by fluctuating properties of the medium in the two-group diffusion approximation and in a two-dimensional representation of heterogeneous systems, for both critical systems and non-critical systems with an external source. Some applications of these tools to power reactor noise analysis are then described, including the unfolding of the parameters of the noise source from the induced neutron noise, measured at a few discrete locations throughout the core. Other concrete applications concern the study of the space-dependence of the Decay Ratio in Boiling Water Reactors, the noise-based estimation of the Moderator Temperature Coefficient of reactivity in Pressurized Water Reactors, the modeling of the beam- and shell-mode core-barrel vibrations in Pressurized Water Reactors, and the investigation of the validity of the point-kinetic approximation in subcritical systems driven by an external source. In most of these applications, calculations performed using the code are compared with at-power plant measurements. Power reactor noise analysis applications of the above type, i.e. core monitoring without disturbing plant operation, is of particular interest in the framework of the extensive program of power uprates worldwide.