Investigation of Aerodynamic and Icing Characteristics of Water-Inertia-Separation Inlets for Turbojet Engines

The results of an investigation of several internal water-inertia-separation inlets consisting of a main duct and an alternate duct designed to prevent automatically the entrance of large quantities of water into a turbojet engine in icing conditions are presented. Total-pressure losses and icing characteristics for a direct-ram inlet and the inertia-separation inlets are compared at similar aerodynamic and simulated icing conditions. Complete ice protection for inlet guide vanes could not be achieved with the inertia-separation inlets investigated. Approximately 8 percent of the volume of water entering the nacelles remained. In the air passing into the compressor inlet. Heavy alternate-duct-elbow ice formations caused by secondary inertia separation resulted in rapid total-pressure losses and decreases in mass flow. The duration in an icing condition for an inertia-separation- inlet, without local surface heating, was increased approximately four times above that for a direct-ram inlet with a compressor-inlet screen. For normal nonicing operation, the inertia-separation- inlet total-pressure losses were comparable to a direct-ram installation. The pressure losses and the circumferential uniformity of the mass flow in all the inlets were relatively independent of angle of attack. Use of an inertia-separation inlet would in most cases require a larger diameter nacelle than a direct-ram inlet in order to obtain an alternate duct sufficiently large to pass the required engine air flow at duct Mach numbers below 1.0 at the minimum area

Fundamental Studies Relating to the Mechanical Behavior of Solid Propellants, Rocket Grains and Rocket Motors

The former reports provided considerable information about foam and continuum rubbers under three types of tensile loading (i.e. uniaxial, strip-biaxial and homogeneous-biaxial tension). Since continuum rubbers are almost incompressible it is extremely difficult to determine the strain energy function beyond the linear term. On the other hand the highly dilatable foam rubber enables one to determine the functional form of the strain energy valid up to higher order terms. Special attention is being paid to foam rubber, since it represents .the limiting case of completely dewetted propellant. The present report will (i) furnish the method of determination of strain energy function and the associated constitutive stress-strain law for large deformations out to fracture and (ii) present the triaxial tensile test data needed to double check item (i)

Fundamental Studies Relating to Systems Analysis of Solid Propellants

As in the previous progress reports, the contents in this report have been categorized so as to present a clear picture of their role in contributing to the problem of mechanical failure analysis. The subject of material representation by mechanical failure analysis. The subject of material representation by mechanical models is discussed in Section I, while Section II contains additions to the subject of Elastic Solutions for cylinders. The Engineering Analysis section includes an example of the strain response of an internal star grain to pressure. A damped sinusoid has been assumed for the pressure rise, and the use of stress concentration factors for a star grain is demonstrated. Section V on failure includes some preliminary test results which indicate the feasibility of the cumulative damage concept for composite (polyurethane) propellants, at least in the limited range tested. Recommendations are given which would expand this testing to show how damage accumulates under other conditions such as low temperatures, high strain-rates and with other types of propellant

Quality of CAD-CAM inlays placed on aged resin-based composite restorations used as deep margin elevation: a laboratory study

OBJECTIVES To assess the impact of the age of resin-based composite (RBC) restorations used for deep margin elevation (DME) on the marginal quality and fracture resistance of inlays. MATERIALS AND METHODS Permanent human molars with direct RBC restorations, involving the mesial, occlusal, and distal surface (MOD), were allocated to four groups (each n = 12). Half of the teeth underwent thermomechanical loading including 240,000 occlusal load cycles and 534 thermal cycles (TML, 5 °C/55 °C; 49 N, 1.7 Hz). With RBC left in one proximal box as DME, all teeth received MOD inlays, made from lithium disilicate (LDS) or a polymer-infiltrated ceramic network material (PICN). The restored teeth underwent TML including 1.2 million occlusal cyclic loadings and 2673 thermal cycles. The marginal quality was assessed at baseline and after both runs of TML. Load-to-fracture tests were performed. The statistical analysis comprised multiple linear regressions (α = 0.05). RESULTS Simulated aging of RBC restorations had no significant effect on the marginal quality at the interface between the RBC and the tooth and the RBC and the inlay (p ≥ 0.247). Across time points, higher percentages of non-continuous margin were observed between the inlay and the tooth than between the tooth and the RBC (p ≤ 0.039). The age of the DME did not significantly affect the fracture resistance (p ≥ 0.052). CONCLUSIONS Artificial aging of RBC restorations used for DME had no detrimental effect on the marginal quality and fracture resistance of LDS and PICN inlays. CLINICAL RELEVANCE This laboratory study suggests that-in select cases-intact, direct RBC restorations not placed immediately before the delivery of an indirect restoration may be used for DME

Borderline Aggregation Kinetics in ``Dry'' and ``Wet'' Environments

We investigate the kinetics of constant-kernel aggregation which is augmented by either: (a) evaporation of monomers from finite-mass clusters, or (b) continuous cluster growth -- \ie, condensation. The rate equations for these two processes are analyzed using both exact and asymptotic methods. In aggregation-evaporation, if the evaporation is mass conserving, \ie, the monomers which evaporate remain in the system and continue to be reactive, the competition between evaporation and aggregation leads to several asymptotic outcomes. For weak evaporation, the kinetics is similar to that of aggregation with no evaporation, while equilibrium is quickly reached in the opposite case. At a critical evaporation rate, the cluster mass distribution decays as $k^{-5/2}$, where $k$ is the mass, while the typical cluster mass grows with time as $t^{2/3}$. In aggregation-condensation, we consider the process with a growth rate for clusters of mass $k$, $L_k$, which is: (i) independent of $k$, (ii) proportional to $k$, and (iii) proportional to $k^\mu$, with $0<\mu<1$. In the first case, the mass distribution attains a conventional scaling form, but with the typical cluster mass growing as $t\ln t$. When $L_k\propto k$, the typical mass grows exponentially in time, while the mass distribution again scales. In the intermediate case of $L_k\propto k^\mu$, scaling generally applies, with the typical mass growing as $t^{1/(1-\mu)}$. We also give an exact solution for the linear growth model, $L_k\propto k$, in one dimension.Comment: plain TeX, 17 pages, no figures, macro file prepende

Fundamental Studies Relating to Systems Analysis of Solid Propellants : Progress Report No. 6 - GALCIT 101, Subcontract No. R 69752, January 1, 1960-May 31, 1960

Previous reports of this series have attempted to define some of the important parameters affecting structural integrity of solid propellant rocket grains. Three general areas have been discussed, namely material properties, analytical procedures, and criteria for mechanical failure. This particular report is devoted to failure criteria, including both limiting deformation and fracture. First of all, the characteristic material properties of filled and unfilled elastomers are described, followed by a brief description of current and proposed tests which can be conducted to obtain experimental information relating to these characteristics in such a form that they can be incorporated in structural integrity analyses. In particular, the necessity for multi-axial tests is stressed in conjunction with minor requirements for new experimental equipment. The selection of appropriate fracture criteria is discussed. Most progress, however, can be reported only in criteria for unfilled elastomers for small and large strains where it appears a distortion strain energy density may be used. It is necessary to delay any really definitive remarks upon filled elastomers or actual grain composites, and subsequent use with cumulative damage analyses, until additional experimental data for propellants is forthcoming

Geochemical considerations for Hot, Dry Rock Systems

Circulating systems intended to model the P-T conditions found in the natural HDR (Hot Dry Rock) geothermal system at Los Alamos have been built. Experiments with these systems have determined the following parameters for the ''down hole'' reservoir: sample weight loss, circulating solution composition, textural changes in the rock, mineral loss from the rock and effects of chemical additives on rock erosion. The analyses of solutions generated from rock-water interactions in the experimental systems show the extremely dilute nature of the working fluid. These solutions are not brines. Silica scaling in the surface heat exchanger was found to account for the difference between loss of sample rate and analyzed silica in the solution. The weight loss data indicate that there was continuous transport of silica from the ''down hole'' rock to the heat exchanger. Experiments contrasting felsic and mafic rocks in the HDR concept indicate that a reservoir consisting of glass bearing basaltic rock would tend to produce greater scaling problems than systems emplaced in granite. Experimental results suggest that Na{sub 2}CO{sub 3} solutions may provide a means of increasing permeability and thereby increasing the effective heat transfer area of the reservoir. A brief description is given of a small test loop for simulating the flow of a geothermal solution through a heat exchanger. This loop, which is being built, will be used to study the coagulation and precipitation of silica under conditions similar to those expected in the field

Mechanical Properties of Dual-Cured Resin Luting Agents for Ceramic Restoration

Purpose: The aim of the present study was to evaluate the mechanical properties including surface hardness, flexural strength, and flexural modulus of two dual-cured resin luting agents (New Resin Cement [NRC] and Variolink II [VLII]) irradiated through four different thickness of leucite ceramics (0, 1, 2, and 3 mm) and their shear bond strength to zirconia ceramic (Cercon) using each ceramic primer. Materials and Methods: Knoop hardness was measured on a thin layer of resin luting agent on the ceramic surface. Three-point bending tests were performed after 24 h storage at 37°C. Two different-shaped zirconia ceramic specimens with or without sandblasting with alumina were treated with each primer. The specimens were then cemented together with each resin luting agent. Half of the specimens were stored in water at 37°C for 24 h and the other half were thermocycled 5,000 times. Results: VLII revealed statistically higher Knoop hardness and flexural modulus than NRC for each thickness of ceramic. No significant differences in flexural strength were observed between VLII and NRC for each ceramic spacer. Reduction of the mechanical properties with increase of ceramic thickness varied for each property. However, these properties were similar between the two materials. Blasting with alumina was significantly effective for increasing shear bond strength of both resin luting agents before and after thermal cycling. The use of New Ceramic Primer showed the highest shear bond strength and maintained bond durability after 5,000 thermocycles. Conclusion: Mechanical properties of NRC dual-cured resin luting agent appear adequate for ceramic restorations.This is an electronic version of an Article published in Journal of Prosthodontics 16(5): 370-376, 2007