Wear and erosion. Research to explain, predict, 

 and prevent deterioration of materials undergoing 

 impingement by hot gases or particulates is urgent- 

 ly needed. The Army's gun tubes, and rocket, 

 missile, and aircraft turbine components are seri- 

 ously and adversely affected by hot gas erosion. 

 Dust erosion of helicopter rotors and rain erosion 

 of missile radomes, are also severe problems. 

 Mechanisms of erosion are neither well-defined 

 nor understood; solutions for erosion problems 

 have been largely based on empirical techniques, 

 and have addressed specific combinations of ma- 

 terials, geometries, and operating conditions (e.g., 

 in hot gas erosion, gun tube steel, chamber con- 

 figuration, projectile, propellant chemistry, pres- 

 sure, and temperature). The development of quan- 

 tifiable parameters is required for rational ap- 

 proaches to avoid or inhibit wear and erosion. 

 Analyses in the hot gas area are complex and 

 must be based on interdisciplinary approaches 

 embodying such diverse areas as thermometal- 

 lurgy, deformation and fracture criteria, inorganic 

 chemistry, fluid dynamics, and safe life predic- 

 tion. 



Mathematical analysis of nonlinear systems. The 

 principal thrust of the mathematics program is on 

 the analysis of nonlinear systems. A significant 

 component of this thrust is on the study of the 

 qualitative features of the basic equations of 

 classical applied mathematics which continually 

 arise in many Army problems such as heat transfer 

 in gun tubes, elastic-plastic analysis of structures, 

 penetration mechanics, and aerodynamics, among 

 others. Because these problems, in general, do 

 not lend themselves to closed-form solutions, 

 considerable effort is directed toward the develop- 

 ment of approximate, numerical, and statistical 

 methods for solving nonlinear systems including 

 nonlinear partial differential equations, nonlinear 

 optimization models, and nonlinear filtering and 

 estimation problems. 



Dynamic loading of structures and materials. 

 This major research program is concerned with 

 devising the principles for predicting the deforma- 

 tion and failure of structures and materials under 

 dynamic loads. Strong Army interest in this re- 

 search field arises due to weapon effects, armor 

 defeat, projectile impact, fragmentation, explosive 

 detonation, and aeroelasticity. Characteristic 

 times of these loadings vary from microseconds 

 to tens of milliseconds, illustrating the broad 

 range over which any phenomenological model 

 must be applicable. 



Improvement of helicopter performance. A ma- 

 jor research program concerned with the improve- 

 ment of rotorcraft performance is concentrated on 

 those pacing problem areas identified by field 

 experience and future air mobility objectives. 



Investigations are concerned with such areas of 

 interest as dynamic stall, strongly interacting 

 flows, aerodynamic drag, rotor downwash and its 

 effects, rotor-generated noise, aerodynamic stabil- 

 ity, and bluff body aerodynamics. Investigations 

 in these basic problem areas contribute to the 

 technology base required for making design stud- 

 ies for specific performance requirements of fu- 

 ture rotorcraft. 



Combustion processes in engines and propellants. 

 Research thrusts in the general field of combus- 

 tion are necessary to support Army requirements 

 for efficient propulsion of weapons and air or 

 ground vehicles. The understanding of combus- 

 tion processes requires investigations on propel- 

 lant ignition, flame propagation and stability, gas 

 dynamics, chemical kinetics, detonation and de- 

 flagration, thermodynamics, and materials. The 

 basic energy source, either propellant or fuel, 

 requires a fundamental examination as to such 

 characteristics as stability, ignition or flash point, 

 fire safety, thermal capacity, aging processes, and 

 the energy release mechanisms. 



Submillimeter technology. The Army's interest 

 in submillimeter technology is for imaging radar 

 and other applications. Emphasis is currently 

 being placed on obtaining information that would 

 make possible sensitive, compact detectors that 

 operate at room temperature (Schottky barrier). 

 The development of high-power coherent sources 

 is also a priority in this program. Current efforts 

 include the investigation of optically pumped 

 submillimeter lasers. A small effort is being devot- 

 ed to the characteristics of compact electron beam 

 pumped devices. It is expected that this thrust 

 area will be expanded, particularly with regard to 

 source and detector research. Several unusual 

 approaches are currently being considered for in- 

 clusion in the program. 



Fire safe fuels. This thrust area is concerned 

 with fuel mist flammability and the mechanism by 

 which certain additives can inhibit the ignition of 

 fuel sprayed or spewed into the atmosphere as the 

 result of the rupture of a fuel tank. Four work 

 units are currently underway, each examining the 

 basic questions from a different perspective. One 

 concerns mist flammability under initially nontur- 

 bulent conditions, and the effect of varying the 

 speed of flame propagation. The rest address 

 questions at a molecular level: the reaction with 

 oxygen of free radicals implicated in the initial 

 step, the intervention of halocarbon radicals or of 

 halogen atoms in inhibiting processes, the rates of 

 the various chemical reactions, and the identifica- 

 tion of intermediate species by mass spectroscopy 

 or matrix isolation infrared absorption spectrosco- 

 py- 

 Armor penetration. The interaction of kinetic 



DEFENSE 67 



