Rocket Grain Research Articles

Regression Rate and Combustion Efficiency of Composite Hybrid Rocket Grains Based on Modular Fuel Units

This study investigated combustion characteristics of composite fuel grains designed based on a modular fuel unit strategy. The modular fuel unit comprised a periodical helical structure with nine acrylonitrile–butadiene–styrene helical blades. A paraffin-based fuel was embedded between adjacent blades. Two modifications of the helical structure framework were researched. One mirrored the helical blades, and the other periodically extended the helical blades by perforation. A laboratory-scale hybrid rocket engine was used to investigate combustion characteristics of the fuel grains at an oxygen mass flux of 2.1–6.0 g/(s·cm2). Compared with the composite fuel grain with periodically extended helical blades, the modified composite fuel grains exhibited higher regression rates and a faster rise of regression rates as the oxygen mass flux increased. At an oxygen mass flux of 6.0 g/(s·cm2), the regression rate of the composite fuel grains with perforation and mirrored helical blades increased by 8.0% and 14.1%, respectively. The oxygen-to-fuel distribution of the composite fuel grain with mirrored helical blades was more concentrated, and its combustion efficiency was stable. Flame structure characteristics in the combustion chamber were visualized using a radiation imaging technique. A rapid increase in flame thickness of the composite fuel grains based on the modular unit was observed, which was consistent with their high regression rates. A simplified numerical simulation was carried out to elucidate the mechanism of the modified modular units on performance enhancement of the composite hybrid rocket grains.

Uticaj cikličnih opterećenja na strukturna oštećenja pogonskih punjenja raketnih motora

Uticaj cikličnih opterećenja na strukturna oštećenja pogonskih punjenja raketnih motora

Analysis of viscoelastic behavior of a filled elastomer under action of different loads

Mechanical properties of viscoelastic filled polymers strongly depend on temperature and strain rate and vary for several orders of magnitude. During service life, a viscoelastic body, especially carboxy-terminated polybutadiene (CTPB) composite solid rocket propellant grain, is subjected to many stress-inducing loads. Its structural integrity analysis (hereafter: ?structural analysis?), unlike elastic bodies, is quite complex and sometimes impossible under the action of just a single load. An even greater problem occurs when multiple different types of loads act simultaneously. This study is based on a complete uniaxial mechanical characterization of a viscoelastic CTPB composite rocket propellant, made in MTI- -Belgrade, whose results were used for the analysis of the propellant grain reliability. Through an example, this paper shows a behavior of the viscoelastic propellant grain when it is subjected to extremely different environmental loads at the same time. Similar explicit examples are difficult to found in the literature, except in the form of recommended principles for analysis. It is shown that the tensile strength under the action of fast load due to the pressure may be almost 20 times greater than the tensile strength under the slow temperature load. A probabilistic approach is presented in evaluation the reliability and service life. An example is shown for a rocket propellant grain as a viscoelastic body. The presented principles of the analysis can be applied to any arbitrary viscoelastic body in other areas.

Reliability of solid rocket propellant grain under simultaneous action of multiple types of loads

A case-bonded solid propellant rocket grain is subjected to many stress-inducing loads during the service life, due to temperature, extended polymerization, transportation, vibration, acceleration, aerodynamic heating etc. and finally due to the operating pressure in the rocket motor. Composite propellant is a viscoelastic material whose mechanical properties highly depend on temperature and strain rate and sometimes may vary in the range of use of rocket motors for several orders of magnitude. Relationships between stresses and strains are much more complex than for the elastic material. Therefore, the stress and strain analysis and estimation of safety factor under the action of each individual load is quite complex and sometimes impossible. An even greater problem occurs when multiple different types of loads act simultaneously. An extreme case occurs in the moment of rocket motor ignition. Then, the very fast load acts due to the pressure, at which the propellant tensile strength is high. At the same time, the very slow thermal load acts on the grain, and in these conditions the propellant tensile strength is low. The vector addition of the stresses and strains due to different loads is not possible. It is also not possible to define the equivalent or resultant values of tensile strength and allowable strain. The principle of adding the current damage is applied here, similar to the model of cumulative damage. In addition, due to the large variations in mechanical properties of the rocket propellant, it is necessary to apply the methods of mathematical statistics for assessing the propellant grain reliability and service life.

Combustion of metal agglomerates in a solid rocket core flow

The need for access to space may require the use of solid propellants. High thrust and density are appealing features for different applications, spanning from boosting phase to other service applications (separation, de-orbiting, orbit insertion). Aluminum is widely used as a fuel in composite solid rocket motors because metal oxidation increases enthalpy release in combustion chamber and grants higher specific impulse. Combustion process of metal particles is complex and involves aggregation, agglomeration and evolution of reacting particulate inside the core flow of the rocket. It is always stated that residence time should be enough in order to grant complete metal oxidation but agglomerate initial size, rocket grain geometry, burning rate, and other factors have to be reconsidered. New space missions may not require large rocket systems and metal combustion efficiency becomes potentially a key issue to understand whether solid propulsion embodies a viable solution or liquid/hybrid systems are better. A simple model for metal combustion is set up in this paper. Metal particles are represented as single drops trailed by the core flow and reacted according to Beckstead's model. The fluid dynamics is inviscid, incompressible, 1D. The paper presents parametric computations on ideal single-size particles as well as on experimental agglomerate populations as a function of operating rocket conditions and geometries.

ＣＡＭＵＩハイブリッドロケット内部の熱・流動特性の数値解析

The authors have proposed an advanced fuel configuration to overcome the defect of conventional hybrid rockets, i.e., the low thrust level. The key feature of this new type of hybrid rocket, named Cascaded Multi-staged Impinging jet (CAMUI), is that the cylindrical fuel blocks with two ports parallel to the axis are arranged in a row in the combustion chamber. This fuel configuration allows mixing and combustion to occur in and around the impinging jet regions. In the present paper, a CFD simulation clarifies the fundamental features of the flow field and the heat transfer distributions in the CAMUI hybrid rocket grain. Following results are obtained: Higher heat transfer occurs near the edge of the impinging jet region. A fountain flow caused by the collision of the wall jets enhances the heat transfer on the backward end of the upstream fuel block. A semi-cylindrical swirling flow appearing near the inlet of the fuel port increases the convective heat transfer in this region.

Use of Mueller matrices in the photoelastic determination of the stress distribution in a model for a solid propellant rocket grain

We introduce some basic optical rules dealing with Mueller matrices as phenomenological descriptors of optical devices. Specific simple examples illustrate how all the Stokes parameters of a beam passing through a system of several devices can be determined by the multiplication of the individual Mueller matrices of the respective system components and the Stokes vector of the incident beam. Two resulting families of interference fringes in the (visible) emerging field of the de- vices considered are separated from each other by the introduction of suitable additional system components. The ''isochromatic'' family of fringes can thus be isolated from the ''isoclinic'' family, and a natural application to photoelastic problems becomes evident. Thus, a second purpose is to use this technique and these fringes to photoelastically determine the stress distribution in a disk with a square perforation, when the disk is subjected to a uniformly distributed pressure, acting at its outside or at its inside periphery. This enables the visualization and quantification of the stresses developed during the burning of the grain. The size of the square hole and the radii of the fillets at the corners of the square are variables of the study. Results are given as stress concen- tration factors, in dimensionless form, and are of use to the designer of solid propellant rocket grains. An analogy is given to suggest another application at longer wavelengths to calibrate or discriminate between some radar signals in the microwave region. © 2003 Society of Photo-Optical

Void damage model and service life prediction for solid high polymer

Based on the analysis of three void damage variety models, this note presents (i) a method that regards the void content as a damage variation of the grain and (ii) a geometric model for micro-unit of void damage. Equations of the void damage variety containing void content are analyzed. This work is focused on the measurement of internal damage level and the damage variety estimation is directly related to the life predication in the practical engineering applications. Nowadays, the critical service life of the solid grain/polymers is usually presumed at domestic and international level. The strength or strain reduction of 20% or the stabilizer consumption of 50% is generally regarded as a critical storage life of the solid grain/polymers, and the service life is predicted by the extrapolation method on Anhenius formula. The applications, however, show that the above method is unreliable and has significant errors. With the aid of the discontiguous automatic measuring device of real time volume deformation and void content, the master curve of void damage variety, the storage service life and the surplus life of a solid rocket grain are obtained. Since the critical storage life has been measured, and the accuracy of the service life prediction has been greatly increased. It is a novel ideal and a break-through technique.

Numerical experiments on the solution of the Helmholtz equation in the case of domains of complicated boundary shape

Domains of complicated boundary shape are of great practical importance in several fields of technology and applied science; e.g. solid propellant rocket grains, electromagnetic and acoustic waveguides, and certain elements used in nuclear engineering. The technical literature contains very few comparative studies of analytical and numerical solutions when dealing with such rather complex geometries. The present study constitutes an effort in that direction.

Fracture of Rocket Grain Models Subjected to Cooldown: A Study of Temperature-Initiated Fractures of Two-Dimensional Rocket Grain Models

Abstract A method is presented for evaluating two-dimensional crack behavior resulting from thermal cooldown loading of rocket motor configurations in which the grain is bonded to a stiff case. The associated analytical solution used to quantitatively interpret the data is also presented. For three different grain geometries of a brittle epoxy tested, comparison was quite good between analytical predictions (using elastic fracture mechanics methods) and experimental observations. The results of this study can be applied to fracture analyses of solid propellant rocket grains and other structures containing cracks extending partially through the thicknesses of the structures.

Viscoelastic rocket grain fracture analysis

A viscoelastic fracture analysis has been developed for rocket grain fracture predictions. The fracture analysis uses a stress intensity factor technique to predict crack velocity histories under thermal and pressurization loading conditions. The theory is compared with two-dimensional pressurized tests of two typical rocket motor geometries using the viscoelastic material, Solithane 113.

Pressurized Crack Behavior in Two-Dimensional Rocket Motor Geometries

A method is presented for evaluating two-dimensional crack behavior in rocket motor geometries for pressure loadings in which the pressure is applied directly to the crack surfaces. The experimental requirements associated with pressurizing the crack necessitated the application of pressure over the two-dimensional plane surface of the specimen. Analytical solutions are developed which include the side pressure and relate the stress intensity factors to the classical unpressurized situation. Stress intensity factors for the complex cracked rocket motor geometries were evaluated using finite element computer techniques based on strain energy methods. Comparison between analytical predictions using elastic fracture mechanics and experimental observations of a brittle epoxy was quite good for the three different geometries tested. The work has application in fracture analysis of solid propellant rocket grains and in pressure vessels containing partial-thickness cracks which emanate from the inside.

A pseudo two-dimensional photoelastic method of testing axisymmetric geometries

Problems involving three-dimensional bodies which possess axial symmetry reduce to two-dimensional analytical problems. If a wedge-shaped portion of an axisymmetric body is tested subjected to the proper boundary condition, then a pseudo two-dimensional photoelastic method of testing may be used. This results in tremendous simplification in testing procedures, particularly when slight changes in model geometry are to be made during the course of testing. This method has been applied to axisymmetric solidpropellant rocket grains to conduct a parametric study of various conicyl geometries. Both pressure and thermal loads were considered for a case-bonded grain. Six parameters were required to define the geometry. The effects of these parameters and of the material properties of the grain were investigated, and parametric curves showing the variation of the maximum stress with those parameters are presented. The experimental results are compared with results obtained from a finite-element computer solution. Good agreement is obtained.

Some Pressure-Temperature Equivalences in Elasticity, With Applications to Case-Bonded Solid Propellant Rocket Grains

Some Pressure-Temperature Equivalences in Elasticity, With Applications to Case-Bonded Solid Propellant Rocket Grains

Stresses in hollow cylinders with conical ends bonded to shell and shrunk

This paper deals with, the three-dimensional photoelastic analysis of stresses and strains in two long, hollow circular cylinders with conical ends of 45° and 60°. The cylinders were bonded to a steel casing on the outer surface. The stresses and strains due to restrained shrinkage have been determined at the interface. The maximum stress for both geometries was found to occur at the end of the bond, and to be about 40% higher in the 60° cylinder than in the 45° cylinder. A study was also made at the opposite end of the two cylinders, where a natural meniscus was formed. The results should be of interest in the design of solidpropellant rocket grains.

Constant-acceleration stresses in a composite body

This paper is a contribution to the experimental stress analysis of composite structures subjected to gravitational forces. It is proved, generally, that the immersion analogy can be used to analyze these stresses in composite bodies provided all the materials of such bodies have the same weight per unit volume. Applications are described in two-dimensional problems immersing urethane-rubber models bonded to epoxy shells in a thallium-formate solution. Photoelasticity is used to determine stresses. The method increases the response obtained and will have application in the solution of problems where constant-acceleration stresses are important, as in dams and solid-propellant rocket grains.

STRESS CONCENTRATIONS IN A RECTANGULAR PLATE WITH CIRCULAR PERFORATIONS ALONG ITS TWO BONDED EDGES AND SUBJECTED TO RESTRAINED SHRINKAGE

Two‐dimensional photoelasticity is used for minimising stress concentration associated with a fillet present at the end of a solid propellant rocket grain subjected to restrained shrinkage. For this purpose, successive holes were added along the bonded interface of case and propellant, but no decrease was obtained. The photoelastic method used illustrates two uncommon techniques of interest to experimental stress analysts: (1) restrained shrinkage loading and (2) a parametric stress‐analysis solution obtained with a single model.

Maximum stress at the angular corners of long strips bonded on one side and shrunk

The value of the maximum stress, and its position, at the corner of long strips bonded on one side and shrunk, has been determined using photoelasticity. The angle of the strip end varies from zero (crack) to 180 deg (no corner). The radius at the corner varies from less than 0.0001 to 0.125 in. The solution obtained is an approximation to a plane-stress solution and will have application in composite-materials problems (coatings, solid-propellant rocket grains, etc.).

Gravitational Stresses Determined Using Immersion Techniques

This paper deals with a generalization of an immersion analogy suggested by Biot. A simple general proof of the analogy is given. Applications are described to two-dimensional problems (using urethane rubber specimens immersed in thallium formate) and to three-dimensional problems (using epoxy models immersed in mercury). Two and three-dimensional photoelasticity is used to determine stresses. The increase in response obtained by using the immersion technique permits the solution of a number of new problems where gravitational stresses play an important role; for example, in dams and in solid propellant rocket grains.

Some studies of gravitational loads on United Kingdom solid-propellant rocket grains.

Covers advancements in spacecraft and tactical and strategic missile systems, including subsystem design and application, mission design and analysis, materials and structures, developments in space sciences, space processing and manufacturing, space operations, and applications of space technologies to other fields.