Structure-property relationship of HTPB-based propellants. I. Effect of hydroxyl value of HTPB resin

Composite propellants based on hydroxyl-terminated polybutadience (HTPB) resin are the most common contemporary solid propellants for launch vehicle and missile applications. A series of HTPB resins, manufactured by free-radical polymerisation using a peroxide initiator, with varying molecular weights and hydroxyl values, was used in propellant formulation experiments with a view to studying the resin production variables and their influence on the resultant propellant properties. It is seen that HTPB resins with a wide range of hydroxyl values could be effectively utilized in propellant formulations. Also, propellants with higher strain capability and chain flexibility could be produced from lower hydroxyl value resins. © 1993 John Wiley & Sons, Inc.     

Electroplating of Nickel Using a Modified Barrel Design

Nickel is a metal electroplated on a wide variety of articles both ferrous and nonferrous. Small articles which are difficult to jig are frequently plated by barrel plating technique.

In conventional barrel plating the parts to be plated are contacted by either a rod, dangler or metallic wall as they rotate inside the barrel. A modified barrel design has been effected by changing the dangler contact with uniformly distributed contact tips at varying points on the periphery of the barrel. A modification in anode positioning is also made. Improvement in thickness uniformity brought about by use of this modified design are reported in this paper.     

Validating numerical semidefinite programming solvers for polynomial invariants

Semidefinite programming (SDP) solvers are increasingly used as primitives in many program verification tasks to synthesize and verify polynomial invariants for a variety of systems including programs, hybrid systems and stochastic models. On one hand, they provide a tractable alternative to reasoning about semi-algebraic constraints. However, the results are often unreliable due to “numerical issues” that include a large number of reasons such as floating-point errors, ill-conditioned problems, failure of strict feasibility, and more generally, the specifics of the algorithms used to solve SDPs. These issues influence whether the final numerical results are trustworthy or not. In this paper, we briefly survey the emerging use of SDP solvers in the static analysis community. We report on the perils of using SDP solvers for common invariant synthesis tasks, characterizing the common failures that can lead to unreliable answers. Next, we demonstrate existing tools for guaranteed semidefinite programming that often prove inadequate to our needs. Finally, we present a solution for verified semidefinite programming that can be used to check the reliability of the solution output by the solver and a padding procedure that can check the presence of a feasible nearby solution to the one output by the solver. We report on some successful preliminary experiments involving our padding procedure.     

AB‐type crosslinked polymer networks from vinyl terminated polyurethane and poly(methyl methacrylate)

Vinyl terminated polyurethanes (VTPUs) were prepared by endcapping isocyanate terminated prepolymers with vinylbenzyl alcohol (VBA). AB‐type crosslinked polymer (ABCP) networks were generated by crosslinking the telechelic polyurethane with methyl methacrylate (MMA) in the presence of 2,2′‐azobisisobutyronitrile (AIBN) as free radical initiator. The spectral, thermal and mechanical properties of ABCPs were studied using Fourier Transform IR, thermogravimetry, dynamic mechanical analysis and stress‐strain analysis. The FTIR results confirm the formation of VBA, TP and ABCPs. Thermal behaviour of crosslinked polymers showed no significant weight loss up to 300 °C, indicating improved thermal stability. Dynamic mechanical tests revealed confinement of phase separation and good damping behaviour for the crosslinked networks. Stress‐strain analysis showed that tensile strength increases with increasing amounts of methyl methacrylate. © 2001 Society of Chemical Industry     

Film cooling at hypersonic Mach numbers using forward facing array of micro-jets

Experimental investigations are carried out in the IISc hypersonic shock tunnel on film cooling effectiveness of a single jet (diameter 2 mm and 0.9 mm), and an array forward facing of micro-jets (diameter 300 μm each) of same effective area (corresponding to the respective single jet). The single jet and the corresponding micro-jets are injected from the stagnation zone of a blunt cone model (58° apex angle and nose radius of 35 mm). Nitrogen and Helium are injected as coolant gases. Experiments are performed at freestream Mach number 5.9, at 0° angle of attack, with a stagnation enthalpy of 1.84 MJ/kg, with and without injections. The ratios of the jet stagnation pressure to the freestream pitot pressure used in the present study are 1.2 and 1.45. Up to 50% reduction in surface heat transfer rate was observed with the array of micro-jets, compared to that of the respective single jet with nitrogen as the coolant, while the corresponding reduction was up to 37% for helium injection, with the schlieren flow visualizations showing no major change in the shock standoff distance, and thus no major changes in other aerodynamic aspects such as drag.     

A multiscale model for polymer crystallization. II: Solidification of a macroscopic part

In part I of this paper, we presented two efficient front-tracking methods to simulate the growth of a spherulite within an imposed temperature field. In this second part we present a method that predicts the final microstructure in a macroscopic part by coupling these front-tracking techniques with (a) a stochastic model for the nucleation of individual spherulites, (b) a cellular model for spherulite impingement and solid fraction evolution and (c) a Finite Difference Method (FDM) for latent heat release and heat diffusion. The method tracks the physical phenomena on several length scales: a course grid for the heat diffusion, a fine grid for solid fraction evolution and a very fine grid for the shape of the individual spherulites and the lamellae within them. To our knowledge this is the first time that fully coupled multiscale model has been applied to the solidification of polymers which gives realistic microstructure evolution, orientation of the different lamellae within spherulites and maps of the solid fraction and temperature fields during solidification. The model provides us with a quantitative predictive tool that can be used to optimize industrial processes.