RU2494504C1 - Antenna dome - Google Patents

Abstract

FIELD: radio engineering, communication.

SUBSTANCE: antenna dome consists of a ceramic cover and a metal attachment ring joined to each other by a heat-resistant adhesive. Bending stiffness of the inner flange of the ring is 85-95% of the bending stiffness of the cover in the cross-section passing through the front edge of the ring. The length of the adhesive joint is defined at maximum force action and the radial gap between the cover and the ring is equal to the maximum radial expansion of the ring due to thermal action on the dome. The end gap between the cover and the ring is taken as proportional to the radial gap, with the proportion factor equal to the ratio of the length of the adhesive joint to the outer diameter of the ring, taking into account Young's modulus of the adhesive.

EFFECT: enabling operation of the antenna dome for conditions of simultaneously satisfying the action of prevailing loads.

2 dwg

Description

The invention relates to the field of aeronautical-rocket technology, mainly to the designs of radiolucent fairings of aircraft, and can be used in the development of ceramic head fairings of high-speed missiles.

The main problem of creating a workable design for the rocket head fairing, consisting of a radiolucent ceramic shell and a metal butt frame and under the influence of aerodynamic load (external pressure), is due to the complexity of developing a reliable connection between the shell and the frame. Since ceramic materials of radiolucent shells mainly have a naturally low temperature coefficient of linear expansion (TEC), the choice of metallic materials for a frame with a TEC close to that of a ceramic is limited by a small number of precision alloys of the invar group.

In developing the design of the fairing, the aerodynamic load distributed over the surface of the shell is reduced to the distributed axial (longitudinal) and transverse components, the latter creating a bending moment relative to the shell base in connection with the frame. As a result of this, the bearing capacity of the ceramic shell in the joint zone is determined by tensile stresses caused by the combined action of both external force factors and internal thrust from the heated inner frame shelf, due to the thermal expansion coefficient of the materials of the connected structural elements. To exclude (or significantly reduce) the effect of thermal expansion of the frame on the shell when they are directly bonded, for example, with glue, the gaps between the shell and the frame, which determine the thickness of the adhesive layer, must simultaneously compensate for the difference in the mutual thermal movements of the shell and the frame (taking into account the deformability of the adhesive). The optimum thickness of the adhesive layer corresponds to the optimal distribution of forces from the aerodynamic load.

The task of developing the design of the fairing is to ensure that by choosing the parameters of the connection elements to ensure a level of the above tensile stresses that would be acceptable for the ceramic material of the shell. The parameters of the elements can be both the geometric characteristics of the joint and the thermomechanical properties of the materials used.

Recently, it has become urgent to create designs of rocket nose cones for such conditions when aerodynamic impacts on the cowl are highlighted in the spectrum of programmed flight paths of the rocket: with a maximum power component of the load with a slight heating of the structure (short trajectory) and with maximum heating of the joint at insignificant power load (longer trajectory in time). The aerodynamic effect on the remaining trajectories of the program spectrum is in the interval between the boundary trajectories. In most cases, the fairing should be resistant to aerodynamic effects in both extreme cases, excluding the simultaneous effect of maximum power and maximum thermal loads.

In the general case, it is permissible to ensure the operability of any fairing by simply increasing the wall thickness of the shell in the connection zone, but this is not technological, it increases the weight of the shell, and most often it is not possible due to insufficient construction height for the layout of the structure.

A number of technical solutions are known for the designs of antenna cowls, including a ceramic shell and a metal frame, in which operability can be provided either by some increase in the shell thickness in the connection zone, or by increasing the thickness of the frame in order to remove heat more inside the shell and reduce heating of the frame itself, or increase radial thermal gaps, as well as the installation of intermediate heat-insulating elements between the shell and the frame.

A known fairing design according to US patent No. 31114319, NKI 102.92.5, 1962, consisting of a ceramic shell and installed in its cavity with a gap of a metal ring (frame), connected through elastic rubber rings placed in the grooves of the outer surface of the metal ring.

The main disadvantage of this design is that to reduce the shell expansion during thermal expansion of the frame due to the elastic deformation of the rubber rings, it is necessary to increase the radial clearance as operating temperatures increase; at the same time, the strength of the adhesive joint decreases, the angular and meridional displacements of the shell and the frame increase, as a result of which the shell in the tension zone can be destroyed when it is supported on the front end of the frame.

The known design of the connecting one-piece node according to the patent of the Russian Federation No. 2145005, IPC 7 F16B 4/00, 11/20, 1998, consisting of a ceramic shell and a metal frame, which uses the effect of additional thermal resistance due to the execution of the frame of two parts interconnected by means of jumpers: the inner part is a solid ring, the outer part is not in contact with each other separate sections.

This design has the following disadvantages:

- uneven heating of the adhesive layer on the outer and inner parts of the metal frame makes it difficult to efficiently remove heat from the adhesive layer and the outer part of the frame with its inner part;

- high radial stiffness of the solid inner part of the frame with significant heating of the connection leads to the destruction of the shell from the expansion of its frame;

- low technological design.

The closest device in terms of features selected as a prototype is the fairing of RF patent No. 2168815, IPC 7 H01Q 1/42, 2000, consisting of a ceramic cap (shell) and a metal frame, interconnected by a layer of elastic heat-resistant adhesive. In this design, an elastic (adhesive) shell is inserted into the expanding cavity formed in the nose of the frame, and a heat accumulator is connected to or connected to the frame in one piece. In this design, the efficiency of heat removal from the heated shell and the adhesive layer in the case of using a frame made of a material with high thermal conductivity leads to rapid heating of the frame and the expansion of the ceramic shell, and when using a frame made of a material with low thermal conductivity, the most heat-loaded is the adhesive layer. As a result, the shell is destroyed either by spreading it with a frame, or due to the destruction of the elastic adhesive and loss of adhesive strength.

The present invention is the creation of a workable design of the antenna fairing, resistant to diverse aerodynamic effects on the boundary paths, due to the rational choice of structural parameters of the elements of the connection node.

The problem is solved by the fact that the proposed:

An antenna cowl containing a ceramic shell and a metal frame connected to each other by heat-resistant adhesive, characterized in that the flexural rigidity of the inner shelf of the frame is 85-95% of the flexural rigidity of the shell in the cross section passing through the front edge of the frame, while the length of the adhesive joint ( the height of the frame) is determined at maximum force on the fairing, based on the value of the ultimate tensile strength on adhesive shear, the radial clearance between the shell and the frame (adhesive thickness th layer) become equal to the maximum radial expansion of the frame from the heat exposure, and tip clearance between the casing and frame attachment accept proportional radial clearance, with a proportionality coefficient which depends on the ratio between the length of the adhesive bond and the outer diameter of the frame, taking into account the value of the normal modulus of elasticity of the adhesive.

In figures 1 and 2 presents a General view of the antenna fairing with the connection node and its longitudinal section in the area of the connection node.

The antenna cowl includes a ceramic shell 1 and a metal frame 2, interconnected by heat-resistant adhesive 3. The length of the adhesive joint L (respectively, the height of the frame) is determined by the strength calculation of the maximum load, and the thickness of the adhesive layer by the maximum radial thermal gap S ₁ taking into account the deformation of the adhesive layer, depending on the modulus of normal elasticity of the adhesive.

When the heat force load caused by aerodynamic impact on the fairing is perceived, a bending moment M _arr emerges at the junction of the shell with the frame (Fig. 1), which moves the shell in the tension zone to the front end of the frame, choosing the thermal gap S ₁ , and in the compression zone - to the end face of the frame, choosing the gap S ₂ (figure 2). Depending on the strength of the adhesive joint, determined by the length L of the adhesive layer 3, and the ratio of the gaps S ₁ and S ₂ , the support of the shell in the tension zone on the front edge of the frame (conditionally - T.A in figure 1) may occur earlier or later bearing the end face of the frame in the compression zone (conditionally - B in figure 1), choosing a gap S ₂ filled with damping material 4, for example, heat-resistant sealant or fiberglass impregnated with sealant, to prevent direct contact of ceramics and metal. When the shell rests on the front edge of the frame before supporting it on the end in the compression zone, the cross section of the shell in the stretched zone becomes the most stressed, because the strength of the ceramic material in bending and stretching is an order of magnitude lower than the compressive strength. Therefore, when parts made of ceramic material are used in devices, they are forced to "work" under compression conditions.

In order to avoid destruction of the shell when resting on the front edge of the frame, the following conditions must be met:

- the support of the shell on the frame in TB must occur earlier than the support in TA, and the load from the bending moment should be perceived by the compressed end of the shell, and in the ideal case, simultaneously;

- the bending stiffness of the frame should be less than the bending stiffness of the shell, which leads to faster deformation of the frame and the absence of local pressure from inside the shell; however, in the latter there are no additional zones of contact stresses.

It is known that the bending stiffness of the cross section of a cylindrical shell is determined by the product E · I, where:

E is the modulus of normal elasticity of the shell material;

I is the moment of inertia of the section.

Thus, the condition for the forward deformation of the frame in the tensile zone (T.A) is the ratio:

$$E_{wP}\cdot I_{wP}<E_{\mathrm{about}b}\cdot I_{\mathrm{about}b}\left(\mathrm{one}\right)$$

Theoretical calculations and experimentally established that to satisfy condition (1), the bending stiffness of the frame should be no more than 85-95% of the bending stiffness of the shell.

Since the magnitude of the gap S ₁ due to the maximum thermal expansion of the frame by the maximum thermal load in the area coupling the node, then the condition of advancing the shell bearing on the frame in the compression zone (t.B) size of the gap S ₂ must be proportional to the clearance S ₁ with a proportionality factor, determined from the relation:

$$\begin{array}{l}{S}_{\mathrm{one}}=\mathrm{to}\cdot S_2,\mathrm{to}=f\left(D/2L,E_{wP},E_{\mathrm{but}dg}\right)\\ \mathrm{to}=S_{\mathrm{one}}/S_2=D/2L\left(2\right)\end{array}$$

The proportionality coefficient should always be greater than one:

$$\mathrm{to}>\mathrm{one}\left(3\right)$$

If the gap S ₂ is selected constructively (taking into account the deformation of the gasket), then the gap S _{1 is} also determined from relation (2), but should not be less than the calculated thermal gap (taking into account the deformation of the adhesive).

The achieved result of the application of the invention was the creation of workable designs of antenna fairings under conditions of increased aerodynamic heat-force impact for cases of operation along one or several programmed paths with prevailing either power or heat loads.

Claims (1)

Antenna fairing containing a ceramic shell and a metal frame, interconnected by heat-resistant adhesive, characterized in that the bending stiffness of the inner shelf of the frame is 85-95% of the bending stiffness of the shell in the cross section passing through the front edge of the frame, while the length of the adhesive joint is determined at maximum force on the fairing, the radial clearance between the shell and the frame is taken equal to the maximum radial expansion of the frame from the heat and the end gap between the shell and the frame is taken proportionally to the radial clearance, with a proportionality coefficient depending on the ratio between the length of the adhesive joint and the outer diameter of the frame, taking into account the value of the normal elastic modulus of the adhesive.

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