In order to solve the problem that the photoelectric instrument may fail when the vibration response of the truss composite structure is too large, the method of applying the viscoelastic-constrained damping layer on the truss wall and the box panel is used to reduce the vibration of the whole structure. In this article, a broken long tube with viscoelasticconstrained damping layer is introduced. The long tube of the original structure is broken into two identical short tubes, and a tube with free damping layer is added to the junction of the two short pipes, which is connected by adhesive and broken long pipe. By analyzing the frequency response of the traditional space truss and spaceflight load structure, and a broken long tube structure, the acceleration response cloud diagram and the acceleration response curve of the fixed measuring node are obtained. Experiments were carried out to verify the feasibility of the structure. The test results show that the method of broken long pipe with viscoelastic-constrained damping layer can achieve better damping effect than the traditional truss structure, and it can effectively reduce the vibration level of the space load at the end of the truss, and has important reference significant for the vibration reduction design of other space structures.
With the development of spacecraft toward the direction of large scale and complexity, the space truss has been applied more and more widely because of its easy disassembly, good technology, light weight, and the ability to adjust the structure according to the specific needs. It is also an important part of the International Space Station as shown in Figure 1. The space truss is mainly used in two aspects. One is to connect the related optoelectronic equipment at the top of the space truss to separate the electronic equipment so as to reduce the interference between each other. The other is as a supporting structure to support large deployable antennas in space and solar panels on satellites.
The space truss and its load are launched through the launch vehicle. The vibration environment experienced by the launch vehicle is mainly divided into random vibration environment and low-frequency sinusoidal vibration environment.1 Random vibration is mainly caused by engine exhaust noise during take-- off, aerodynamic noise in transonic flight section, and pressure pulsation in the combustion chamber of the engine. The low-frequency sinusoidal vibration is mainly caused by the pogo vibration, engine start, flameout, and interstage separation of the projectile structure; the low-order modal free oscillation is caused by the gust and the shock wave oscillation in the transonic flight segment; and low-order longitudinal oscillation is caused by incomplete combustion of the engine. This kind of low-frequency vibration environment will cause the space truss structure to be damaged, the connection will be loose, the structural parts will be deformed, and the performance will be decreased. At the same time, this vibration will cause the precision of the photoelectric instruments to be reduced, mechanical fatigue, short circuit, and open circuit instantly, as well as functional failure.2 Therefore, it is necessary to study the vibration characteristics and vibration suppression of space truss and its load.3 There are many literatures on the vibration reduction of space truss structures, which are mainly divided into two categories: damper and damping layer. In previous works,4–6 dampers were designed according to the structure of the space truss, and the relationship between the placement position of the damper and the damping control effect was studied. YM Park et al.7 proposed a semi-active control method using dry friction dampers to reduce the transient vibration of the space truss structure. J Yang et al. studied the vibration and damping properties of a hybrid carbon fiber composite pyramidal truss sandwich panel embedded in a viscoelastic layer in a panel. The damping effect of the damping layer is analyzed by simulation and experiment.8 Based on the modal strain energy (MSE) method, C Liu analyzed the vibration fundamental frequency, loss factor, and resonance response peak of the composite truss structure with different damping layers. The influence of structural parameters and material parameters of damping layer on the damping effect of composite truss was studied.9 In the traditional space truss, the damping layer is directly applied to the long pipe,10 and the damping effect is not good due to the long pipe and the large stiffness. In this article, the traditional truss structure is improved, with a free damping layer on the connection of multisection short pipe, and the growth tube is connected by adhesive and short pipe. The viscoelastic damping layer is applied to the space truss and space load structure for vibration reduction according to actual needs. Through simulation and experimental comparison, the new composite structure is lighter in weight, less rigid, and better in damping effect. Such a complete system of mutual verification of simulation tests has a positive guiding significance for the application of viscoelastic damping layer in aerospace field.
Basic theory of viscoelastic damping materials
When elastic material is subjected to external force,11 the stress and strain increase or decrease at the same time, the phase of the two is basically the same, and the stress–strain relationship is a straight line. The viscoelastic damping material is different from the elastic material,12 after the external force is applied. The strain lags behind the stress, and the hysteresis phase angle is a, as shown in Figure 2(a). The stress–strain relation shows a curve,13 as shown in Figure 2(b).
Design of truss and load structure
For space truss structure modeling and space load, as shown in Figures 3 and 4, the whole structure is made up of long tube, before and after the short tube, cover up and down, left and right sides cover plate, plate, connecting block many parts, fixtures and fittings, standard screw, weighs 15.848 kg, and the material for AL7075.
The structure of the space load box is made of a plate-like structure, with a hollow structure inside, and a screw is used to connect the various surfaces. In addition to the eight faces of the structure of the box structure, the center of the other surfaces has a circular groove with a diameter of 18 mm and a depth of 2 mm. It is used for connecting pieces, connecting the long pipe, short pipe, and connecting block through the connecting piece.
The establishment of finite element model
The finite element model adopts the right-hand coordinate system: the origin o is located at the center line of the lower cover plate along the space load length direction, the left cover plate points to the right cover plate and the y axis along the space load width direction, and the front cover plate points to the back cover plate in the positive direction of z axis.
By choosing the international system of units, the mesh is divided by the whole automatic part manually, the mesh elements are triangular and quadrilateral elements, and the connecting blocks and connectors are partitioned by volume mesh, as shown in Figure 5.
The other parts are divided into shell meshes, and the finite element model is shown in Figure 6. The number of units is 338,564, the number of nodes is 162,717, and the weight of the model is 15.23 kg.
A broken long tube structure is introduced. As shown in Figure 7, the long tube of the original structure is broken into two identical short tubes, and a AL7075 tube with a length of 50 mm, an outer diameter of 12 mm, and a wall thickness of 2 mm is added at the junction of the two short tubes. A free damping layer with thickness of 2.5 mm is applied to it, which is connected by adhesive and broken long pipe.