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Poly(urethane-urea) (PUU) has been infused into ultrahigh volume fraction carbon nanotube (CNT) forests using a heat-curable polymer formula. Polymer nanocomposites with carbon nanotube volume-fractions of 1%, 5%, 10%, 20%, and 30% were fabricated by overcoming densification and infusion obstacles. These polymer nanocomposites were nanoindented quasi-statically and dynamically to discern process-structure-(mechanical) property relations of polymerizing PUU in such densely-packed CNT forests. A 100× increase in indentation modulus has been observed, which is attributed not only to CNT reinforcement of the matrix, but also to molecular interactions in the matrix itself. Quasi-static elastic moduli ranging from 10 MPa–4.5 GPa have been recorded. Storage modulus for all materials is found to track well at loadings of 200 Hz, with little effect observed from increasing CNT volume fraction. Keywords: carbon nanotubes; polymer nanocomposites; polyurethane urea; self-assembly, United States. Army Research Office (Contract W911NF-13-D-0001)

A key concern in the design of micro autonomous vehicles is an onboard energy supply that is able to satisfy system power requirements while also limiting the mass/volume burden to the platform. The conventional solution is to increase the energy density of the power supply, typically a commercial battery. Another approach is to replace single-function structural components with multifunctional structural energy storage materials to supplement the main power supply. Here we report on the use of flexible carbon nanotube (CNT)-based composites for multifunctional structural energy storage applications. Supercapacitors were fabricated from aligned and non-aligned CNT-based polymer composites and were subject to electrical and mechanical characterization. In addition, an electromechanical characterization technique was used to explore the multifunctional behavior of the solid-state flexible supercapacitors. Initial tests showed that the specific capacitance of the composite materials increased by approximately 10% as the structure was subject to a 2% mechanical strain. These preliminary results indicate that these multifunctional solid-state composites could potentially replace micro vehicle flexible structural components, supplement system power requirements, and ultimately increase platform endurance., The original document contains color images.

This study describes the methodology for determining optimal gun tube centerline shape. It starts with describing system accuracy and then shows how different gun tube centerline shapes affect accuracy performance. The results show that the shape that imparts the smallest transverse disturbance has the best accuracy performance., Original contains color plates: All DTIC reproductions will be in black and white.

Gun barrel straightness is one of several manufacturing variables that must be held to a specified tolerance; therefore, barrel centerline measurement is a necessity. In the past, centerline measurement techniques have been developed specifically for this application, and machines to accomplish this have been produced on a small-quantity basis. This report describes the application of an off-the-shelf; three-dimensional laser tracker system, manufactured by Spatial Metrix Corporation (SMX), to measure the bore centerline of a 120-mm tank gun barrel. An introduction and tutorial about barrel straightness terminology, coordinate systems, and the level of precision required for such measurements are presented. A side-by-side comparison is then made between the SMX-based measurement and the standard or conventional measurement of several barrel centerlines, with the advantages and disadvantages of each system noted., Original contains color plates: All DTIC reproductions will be in black and white.

A slingatron is the name given to a propellantless mechanical means of launching a projectile. To date, slingatrons are only conceptual in nature, but their potential use as a ground-to-space launch mechanism for umnanned payloads is under investigation. Slingatrons can be configured in a variety of geometries; one form consists of a spiral track (or launch tube) that gyrates at a constant frequency about a set radius. Under proper conditions (design parameters), a projectile entering the spiral at its small radius end will undergo nearly constant tangential acceleration before exiting. The differential equations governing the motion of the projectile with the spiral are highly nonlinear, making the optimum design solution nonintuitive. This report describes how the slingatron works, from first principles, then uses the numerical integration procedures within the computer software environment of Simulink and MATLAB to search for and identify the optimum design solution parameters based on structural dynamics and mechanical design considerations., Original contains color plates: All DTIC reproductions will be in black and white.

Most conventional sub-caliber long rod penetrators maintain flight stability by using near-full-caliber hardcoated aluminum fins that extend from the base end of the projectile. Prior to launch, these fins are buried within the propellant bed of the ammunition cartridge case. During launch, the fins are subjected to high propellant gas temperature and pressure, as well as propellant grain impacts. This thermally abrasive in-bore environment can remove pieces of the fin's hardcoat, thus exposing the aluminum substrate to temperatures far beyond its melting point. Thermal erosion of the fin degrades projectile stability and accuracy. Thus, the U.S. Army is exploring more effective thermal coatings and/or substitute fin materials to replace hardcoated aluminum. The use of plastics is one alternative. This report will document some of the successes and failures of plastic fin assemblies on kinetic energy (KE) penetrators. For example, it was found that fins made from some plastics incur less in-bore thermal damage than hardcoated aluminum. On the other hand, it appears that plastic fins, at least relatively thin plastic fins, are susceptible to mechanical failure out of bore if they traverse the reverse muzzle gas flow at all but small yaw angles. Nonetheless, there appears to be design latitude for a plastic fin assembly that would be lighter in weight and more erosion resistant than the current hardcoated aluminum fin.

During firing, the gun barrel centerline profile and muzzle pointing angle change due to thermal distortion. There are several causes of thermal distortion; we will discuss two: uneven cooling, and non-uniform wall thickness. We will briefly explain the mechanisms by which these two effects produce gun barrel bending and describe how these effects are modeled. We will demonstrate our model by predicting the muzzle pointing angle change for a particular gun tube firing five rounds, one every two minutes. The predictions are compared with experimental results; some agreement is noted., This article is from 'Proceedings of the U.S. Army Symposium on Gun Dynamics (7th) Held in Newport, Rhode Island on 11-13 May 1993', AD-A278 075, p272-281.

Advances in manufacturing techniques have reduced, but not eliminated, cross-barrel wall thickness variation in the production of gun barrels. Structurally, these small variations will not appreciably diminish the strength of the barrel, and are, therefore, riot a firing safety concern. However, even small variations will produce cross-barrel temperature differences that can increase with the number of rounds fired, and thereby produce thermal distortion of the barrel, which degrades gun accuracy. This investigation presents a theoretical (finite difference) analysis of the cross-barrel temperature difference expected to occur as a result of typical and atypical wall thickness variation in production-line guns. The results indicate that typical barrels will riot incur an appreciable thermal bend due to wall thickness variation. However, current manufacturing tolerances would allow an atypical barrel to be fielded that could undergo significant thermal distortion due to a cross-barrel temperature difference created by asymmetric wall thickness.... Gun barrel heating, Finite difference theory, Wall thickness variation, Cross-barrel, Temperature difference, M256 120-mm gun barrel, Repeated firing, Gun barrels.

Heating of a gun barrel by repeated firing is modeled in a computer program that solves the one-dimensional (radial) unsteady heat condition equation by a second-order finite-difference procedure. Coupling with interior ballistics is accomplished by employing as input data the bore temperature and heat transfer histories computed by interior ballistics codes. Limited comparisons of outputs with experimental results show favorable agreement (20% differences or less). The code is exercised to study a number of aspects of the heat transfer process qualitatively (e.g., time history of heat transfer before and after shot exit) and to relate the current model to a more simplified analytical-empirical model.

Evaluating the thermal performance of tank cannon components, such as thermal shrouds, muzzle reference system collimators, barrel paint, or thermal signature, by means of firing live ammunition has distinct drawbacks. Not only is range time uncertain, labor and ammunition expensive, but firing must be done outdoors, where uncontrollable environmental factors (such as sunlight, precipitation, and wind) may complicate the analysis and make experimental repeatability difficult. This report will discuss non-firing test alternatives, using various laboratory heating devices, to input heat to the barrel and its accessories in a controllable and repeatable fashion. (jhd)

An analytical technique is outlined for predicting the blast wave from a rapid but asymptotic expansion of an inner piston-like surface. The method more accurately describes real blasts compared to conventional point source models and agrees favorably with the exact method of characteristic solution for wave Mach numbers exceeding approximately 1.1. The method makes two a priori assumptions: (1) that the blast wave density can be described by a power law, and (2) that an equation exists for the motion of the driving piston. The present treatment extends the work of Bach and Lee, who assume a zero radius piston (i.e., a point source).