RU2727211C1 - Device for testing strength of reinforcing plates of elastic nozzle hinge of solid-propellant rocket engine - Google Patents

Abstract

FIELD: test equipment.

SUBSTANCE: invention relates to experimental testing of strength of elastic hinges (EH) of rotary control nozzles of solid-propellant rocket engines (SPRE) and can be used in optimization of design of EH. Disclosed is a device for testing the strength of the plates by loading them separately, outside the design of the elastic hinge assembly, with an axial compressive force, which enables to simulate their operation as part of an elastic hinge of the SPRE nozzle.

EFFECT: this device is especially useful in development of design of elastic hinge with plates from plastic, when there is a problem of selecting the most suitable plastic brand from among the offered by industry; in this case, costs are significantly reduced, and development process is accelerated by excluding manufacture and testing of structure of elastic hinge assembly.

1 cl, 3 dwg

Description

A device for testing the strength of the reinforcing plates of the elastic hinge of the solid propellant rocket engine nozzle

The invention relates to the field of experimental testing of the strength of elastic hinges (ESH) of rotary control nozzles of solid propellant rocket engines (SRMT) and can be used to optimize the ESH design.

In order to determine the safety factors of the ES, it is loaded with loads that lead to the destruction of reinforcing plates, which are its weakest element.

Reinforcing plates ESh are thin-walled shells in the form of annular spherical belts, whose thickness is 30-60 times less than the size along the meridian (generatrix), the length of which, in turn, is 20-40 times less than the circumference of the plate. This makes it possible to consider the reinforcing plate as a ring with a thin-walled profile during testing. A description of the ESh design is given, for example, in the monograph: "Designs of solid fuel rocket engines", under total. ed. Corresponding Member RAS, prof. L.N. Lavrova - M: Mechanical Engineering, 1993, p. 154, fig. 3.29.

Known design of a device for testing the compression of samples of various materials used in mechanical engineering (GOST 25.503-97, Appendix B, Figure B.1).

The disadvantage of this design is the impossibility of providing loading conditions for a separate ESh plate, corresponding to the conditions of its loading when operating as part of a nozzle. To ensure these conditions, the plate must be loaded with linear torque distributed along the circular center line of the plate.

The technical problem of this invention is the development of a device for testing the strength of reinforcing plates ESH, which makes it possible to experimentally test the strength of one single ESH plate by loading it with a running torque distributed along the circular center line of the plate.

The technical result consists in the fact that in the proposed device the plate is tested outside the structure of the elastic hinge by an axial compressive force, which provides loading of it with a linear torque distributed along the circular center line of the plate, as a result of which the costs of developing the ESH strength are significantly reduced, and the mining process is accelerated.

The technical result is achieved by the fact that in the device for testing the strength of the reinforcing plates of the elastic hinge of the nozzle of a solid fuel rocket engine, containing an annular base and a load ring, between which the test plate is placed, the outer surface of the annular base is made equidistantly to the inner surface of the plate from the side of the larger end with the possibility of applying pressure along a part of the inner surface of the plate from the side of its larger end, and the inner surface of the load ring is made equidistantly to the outer surface of the plate from the side of the smaller end with the possibility of applying pressure along a part of the outer surface of the plate from the side of its smaller end, while rubber is placed between the equidistant surfaces gaskets.

Distinctive features of the proposed technical solution are essential.

The outer surface of the annular base, together with the rubber gasket glued to it, equidistant along the narrow annular area of the inner surface of the plate from the side of its larger end, provides a reaction to the plate in the form of pressure along the aforementioned narrow annular area during axial compression.

Similarly, the inner surface of the load ring, together with the rubber gasket glued to it, equidistant along the narrow annular area of the outer surface of the plate from the side of its smaller end, provides, during axial compression, the reaction to the plate in the form of pressure along the corresponding narrow annular area.

With a tight, under the action of axial compression, contact, thanks to the rubber gaskets, the reaction pressure will be distributed quite evenly in the annular direction along the contact areas, practically along the normal to them. Acting on the inner surface of the plate at its larger end and on the outer surface of the plate at its smaller end, the reaction pressures form a linear torque relative to the circular center line of the plate. The amount of axial compression required to create a linear torque equal to the linear torque acting on the plate during its operation as part of the ES is determined by the method described below.

FIG. 1 shows a diagram of a device for testing a separate ESH plate with a linear torque.

FIG. 2 shows a diagram of the pressure distribution along the gas path of the nozzle for calculating the axial force acting on a separate plate in standard ES conditions during the operation of solid propellants.

FIG. 3 shows a diagram of geometric parameters for determining the load on the ESH plate under test conditions (Fig. 1).

FIG. 1-3 the following position numbers are accepted for the device parts and ES:

1 - test plate;

2 - load ring;

3 - annular base;

4, 5 - rubber gaskets for uniform load application (1Н-I-ТМКЩ-С-4 GOST 7338 plate, 4 mm thick is used);

6 - rubber layers in the ES, providing a change in the ES shape when the rotary part of the solid propellant rocket nozzle is deflected.

Also accepted: axis "x" - axis of the nozzle; point "O" on the axis "x" - the center of rotation of the rotary part of the nozzle.

Rubber gaskets 4, 5 are glued, respectively, to the inner surface of the annular shoulder of the load ring 2 and to the outer surface of the annular shoulder of the annular base 3 (Fig. 1). The contacting surfaces of the gaskets 4, 5 and the test plate 1 must be dry and free of dust and dirt.

To carry out the tests, it is necessary to determine the compressive force Q (Fig. 1), which simulates the nature and magnitude of the loads acting on the considered plate as part of the ES when the engine is running. This is done as follows.

For the considered plate, the ES contains an axial force T, which is the resultant of the intra-chamber pressure forces acting on the surface of the gas path from a point with a radius r _H to the nozzle exit (radius r _A , Fig. 2)

where T ₀ is the integral of variable pressure forces acting on the surface of the gas path from the nozzle exit (radius r _A ) to the section along the frontal point (radius r ₀ ), after which (radius r≥r ₀ ) the pressure on the surface of the gas path remains constant, equal to the pressure in the engine housing P;

r _H is the outer cylindrical radius of the plate under consideration (Fig. 2, 3).

The force T for the plate under consideration determines the value of the average contact pressure q of rubber acting on the spherical surfaces of the plate (due to the small thickness of the plate, it is assumed that the pressure q is the same on both of its surfaces)

where r _B is the inner cylindrical radius of the plate under consideration (Figs. 2, 3).

The stress state of the plate in the ES is determined by the linear torque distributed along the circular center line of the plate and depending on the nozzle deflection angle δ and the initial geometric shape of the ES.

The component of the linear torque on the considered plate, depending on the angle δ, is determined by the formula

where q is the average contact pressure on the plate according to the formula (2);

L is the length of the plate section along the meridian (Fig. 3);

γ is the relative shift along the meridian in the plane of deflection of the ES in the rubber layers adjacent to the plate under consideration (the difference in the shifts of these layers is neglected, the formulas for determining γ depending on the nozzle deflection angle δ are given below);

h _p is the thickness of the rubber layers (Fig. 3);

α is the polar angle measured from the plane of ESh deflection around the nozzle axis "x".

The component of the linear torque on the plate under consideration, due to the initial bevels of the side surfaces of the rubber-metal package ESh (angles ϕ ₃ , ϕ ₄ in Fig. 3), is determined by the formula

where h _T is the thickness of the plates (Fig. 3);

ϕ ₃ , ϕ ₄ - the angles between the lateral surfaces and the spherical radii from the center of rotation of the ES, defining the considered plate (Fig. 3).

Consequently, the considered plate in the section along the plane of deflection of the ES (α = 0) is loaded with a linear torque

Since the moment m ₀ is axisymmetric (4), am ₁ changes smoothly proportionally to cos α in the directions from the plane of deviation (formula (3)), it is assumed that from the point of view of the beginning of destruction of the plate, the load depending on the angle α according to the formula (5) is equivalent to an axisymmetric load according to formula (5) at α = 0. This assumption is in good agreement with the experimental data. The destruction of the plates takes place in the plane of ESh deflection (α = 0).

When the plate under consideration is twisted (angle θ in Fig. 3) under the action of the moment (5), at the points of its cross section, passing to a larger cylindrical radius, there is annular tension. Annular compression takes place at the points of the section passing to a smaller cylindrical radius. In this case, the magnitude of the annular deformations of the material is found by the formula

where θ is the angle of rotation of the plate section under the action of the moment m (5) (Fig. 3 shows the positive direction of the angle);

z is the coordinate of the section point (Fig. 3);

R is the spherical radius of the plate (Fig. 3).

As a result of such a deformed state, a bending moment M is formed in the plate section, calculated from the condition of static equilibrium by the formula

where m is the running torque according to the formula (5);

R is the spherical radius of the plate (Fig. 3).

The value of M can be used to determine the hoop stresses in the sections of the considered plate. For a perfectly elastic material, the maximum stresses are determined by the formula

- момент сопротивления сечения рассматриваемой тарели.Where

- moment of resistance of the section of the considered plate.

With nonlinear relationships between stresses and strains, stresses are determined by the value of M from the condition that the shape of the plate section does not change during deformation, and ring strains are distributed over the section according to formula (6).

From the formula (5) for the linear torque m it follows that the internal bending moment M in the formula (7) is variable in the annular direction, proportional to the cosine of the polar angle a. It follows from this that, in addition to bending stresses (8), shear stresses will act in the plate sections, determined by the Zhuravsky formula, which in this case takes the form

where for the maximum value of τ, which takes place in the middle of the plate section z = 0 (Fig. 3) in the plane perpendicular to the ES deflection plane (α = π / 2), the parameters included in the formula are:

- цилиндрический радиус середины сечения тарели (фиг. 3);

- the cylindrical radius of the middle of the plate section (Fig. 3);

- статический момент инерции половины сечения тарели относительно центра тяжести (сечения тарели);

- static moment of inertia of half of the plate section relative to the center of gravity (plate section);

- момент инерции сечения тарели;

- moment of inertia of the plate section;

q is the average contact pressure on the plate according to the formula (2);

α = π / 2 is the value of the polar angle at which the maximum value

γ - relative shear of rubber in the plane of deflection of ES;

ϕ _1i , ϕ _2i are the angles defining the layer of the package related to the plate under consideration (Fig. 3).

Practice has shown that accounting for τ is relevant only for plastic containers. Therefore, the shear strength of the plastic in the plane tangent to the spherical surface of the plate should be checked using formula (9) with a safety factor of about 2.0.

The value of the relative shift γ in the rubber layers adjacent to the plate under consideration depends on the distribution of the total deflection angle of the ESh δ over the angles of deflection of individual rubber layers inversely proportional to their angular stiffness. Thus, the maximum shear deformation in the i-th layer of rubber, which occurs in the plane of deflection of the ES (at α = 0), is determined by the formula

where δ is the total deflection angle of the ES;

R _i - inner spherical radius of the rubber layer (Fig. 3);

h _p is the thickness of the rubber layer (Fig. 3);

С _Σ is the total angular stiffness of the ES (formula (11));

C _{i is the} angular stiffness of the i-th rubber layer (formula (12)).

From the fact that when the ES is deflected, all rubber layers are loaded with the same moment of the steering units, it follows that the total angular stiffness of the ES C _Σ is determined by the formula

where the summation is performed over all rubber layers.

The angular stiffness of an individual rubber layer is determined by the formula

where G is the shear modulus of the rubber;

ϕ _1i - inner corner defining the rubber layer (Fig. 3);

ϕ _2i is the outer corner defining the rubber layer (Fig. 3).

Reduced to the central annular line of the plate under consideration, the value of the linear torque m of the _ICP during autonomous tests by its force Q according to the diagram in Fig. 1 is determined by the formula

- диаметр центральной кольцевой линии тарели (фиг. 1);Where

- the diameter of the central ring line of the plate (Fig. 1);

s - shoulder of a pair of linear reactions n ₁ n ₂ , creating a linear torque m _ICP on the considered plate under the action of the force Q (Fig. 1);

β ₁ , β ₂ - the angles of inclination of the contact zones of the considered plate in the test equipment (Fig. 1).

It is assumed that due to the weak compressibility of rubber, reactions n ₁ , n ₂ (Fig. 1) are perpendicular to the plate surface in the contact zones.

From the equality of the linear torque in the test tooling m _ICP (13) to the linear torque m (5) at α = 0, acting on the considered plate in the deflection plane during the ESH operation under standard conditions, the value of the force Q is determined, when tested as part of the tooling the strength of the plate in question should not be compromised.

With an increase in the force Q until the destruction of the plate, its strength is determined. It should be noted that the force Q should be determined with a safety factor ƒ in accordance with the strength standards used in the development of ES (usually ƒ = 1.3).

Thus, the proposed technical solution makes it possible to experimentally test for strength one single ESh plate by loading it with a linear torque distributed along the circular center line of the plate, thereby replacing the tests of the ESH assembly

This device is especially useful in the development of the design of ESH with plastic plates, when the problem arises of choosing the most suitable brand of plastic from among those offered by the industry. In this case, the costs are significantly reduced, and the development process is accelerated by eliminating the manufacture and testing of the ESH assembly.

Claims (1)

A device for testing the strength of the reinforcing plates of the elastic hinge of the nozzle of a solid propellant rocket engine, containing an annular base and a load ring, between which the test plate is placed, characterized in that the outer surface of the annular base is made equidistantly to the inner surface of the plate from the side of the larger end with the possibility of applying pressure on a part of the plate's inner surface from the side of its larger end, and the inner surface of the load ring is made equidistantly to the plate outer surface from the smaller end with the possibility of applying pressure on a part of the plate outer surface from its smaller end, while rubber gaskets are placed between the equidistant surfaces.

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