Experimental study on shock isolation of metal rubber-disc spring composite shock absorber under different shock excitation

Due to the instability and aiming accuracy of the onboard laser emission system cannot meet the requirements of its work tasks, it is necessary to carry out vibration isolation optimization design for the laser emission system. This paper designs a metal rubber-disc spring composite shock absorber and conducts relevant experimental research on the shock isolation performance of the metal rubber-disc spring composite shock absorber. The shock isolation performance tests of the shock absorber under different shock excitation conditions with pendulum heights of 300 mm, 600 mm, 900 mm, and 1200 mm were carried out respectively. Through the experiments, it was found that when the pendulum height is 300 mm, the shock isolation effect of the metal rubber-disc spring composite shock absorber is the best, and the shock isolation rate is above 95%.


Introduction
In modern air defense missions, laser launch systems have advantages such as efficient cost ratio and graded killing, which can effectively enhance mission execution capabilities [1,2].In the face of the complex and changing terrain environment of the island reef, higher requirements are placed on the stability and aiming accuracy of the operation of the onboard laser launch system.Therefore, it is necessary to optimize the vibration isolation design of the laser launch system.The passive vibration isolation method is mainly used for system equipment vibration isolation.Chen et al. [3] studied the influence of subsystem parameters on the vibration isolation characteristics of a double-layer vibration isolation system.Wang et al. [4] designed a new vibration isolation system with inertial capacity and negative stiffness components based on vibration theory, and conducted dynamic and static experimental studies on it.Some scholars [5,6] have laid a physical foundation for shock isolation design by constructing physical structures with negative stiffness characteristics.Domestic scholars [7][8][9][10][11] have taken a different approach to achieve optimal design of the vibration isolation system through the manufacture of composite low yield points and multi-substructure of the power pack, effectively reducing the vibration response.Ikago et al. [12] proposed a type of Tuned Viscous Mass Damper (TVMD) isolator, and optimized its parameters using the traditional fixed point method [13] to apply the obtained optimal isolator to the vibration reduction research of buildings under seismic excitation.Whittaker et al. [14] and Tsai et al. [15] first proposed displacement bending energy dissipation dampers with X-shaped and triangular shapes; Tirca et al. [16] proposed a steel damper with in-plane force form and conducted performance analysis on mid to high-rise structures equipped with this damper, proving that this damper has good energy dissipation and seismic reduction capabilities.In addition, optimization algorithms have also been widely applied to the design of vibration isolation systems and achieved good application results.
The on-board ATP system plays an important role in detecting, locking, and targeting, so it is necessary to carry out vibration isolation design for the ATP system to reduce its vibration response and meet the optimization design requirements of the equipment.Therefore, this article designs a metal rubber disc spring composite isolator.In order to test the impact isolation performance of the metal rubber disc spring composite isolator, experimental studies were conducted on impact isolation under different impact excitations, and relevant experimental results were obtained.

Design of metal rubber disc spring composite shock absorber
In order to effectively reduce the shock response of the onboard laser launch system, a new metal rubber-disc spring composite shock absorber was designed in this paper.The shock absorber design mainly includes the selection of disc spring parameters and the determination of metal rubber density.
(1) In the selection of disc spring parameters, based on engineering experience and relevant calculations, the outer diameter D=30, inner diameter d=9.5, thickness t=0.55, and free height h=1.15 were selected.The parts were processed according to the determined geometric parameters of the disc spring.( 2) The selection of geometric parameters in the metal rubber mainly includes the determination of the density of metal rubber.(3) The external structure of the metal rubber-disc spring composite shock absorber.The structure of the shock absorber was processed according to the design parameters of the disc spring and the relative density of the metal rubber, so as to obtain the structure of the shock absorber.

Impact isolation performance test
This section uses a pendulum impact test to determine the impact isolation performance of a metal rubber-disc spring composite shock absorber and compares it with the impact resistance performance of a GSHG-050 steel wire rope vibration isolator to analyze the advantages and disadvantages of the impact performance of the metal rubber-disc spring composite shock absorber.

Test protocol
3.1.1Test system.The impact test equipment for the metal rubber-disc spring composite shock absorber is shown in Figure 2. It mainly consists of a drop (pendulum) hammer light impact machine, two B&K4302 acceleration sensors, a Su Shi, and a Dong Ling vibration impact control system.During the test, the acceleration impact response values of the impact table and the simulated load are measured by the B&K4384 sensor.The Dong Ling vibration impact control system adjusts the height value of the drop hammer.When the height of the drop hammer reaches the set value, the operation switch is activated, causing the drop hammer to impact the impact table, thereby impacting the metal rubber-disc spring composite shock absorber.

Test conditions.
In order to conduct a more in-depth study on the impact isolation performance of the metal rubber-disc spring composite shock absorber, a vibration isolation manufacturer conducted a study on this type of shock absorber and the standard steel wire rope GSHG-050.According to the relevant test requirements of GJB150.18-86,we develop the following test conditions.This experiment adopts a vertical impact direction and a pendulum angle of 90 degrees.The impact isolation performance of the metal rubber disc spring composite isolator is studied using different impact excitations represented by the drop hammer heights of 0.3 m, 0.6 m, 0.9 m, and 1.2 m.See in table 1

Analysis of test results
Taking the impact test of the composite shock absorber under four working conditions as an example, the impact performance of the composite shock absorber was explored.The relative density of metal rubber was selected, and the composite shock absorber with a load mass of 10 kg and the GSHG-050 steel wire rope vibration isolator with the same load mass were used.Under different impact strengths, namely different drop heights, 300 mm, 600 mm, 900 mm, and 1200 mm, and under the same impact direction and pendulum angle, the impact response results of the metal rubber-disc spring composite shock absorber are shown in Figure 3.As can be seen from the figure: (1) For a certain pendulum height and a certain impact excitation, the load is much smaller than the base, the first waveform peak of the load acceleration response curve is greatly reduced, and the time response becomes longer, indicating that the metal rubber disc spring composite shock absorber can improve the impact resistance performance of the laser emission system by reducing the peak of the impact response and extending the time response.
(2) From Figures 3(a), (c), (e), and (g), it can be observed that under the four drop height conditions, there is a plateau period in the first peak of the absolute acceleration response curve of the load, which is due to the relatively small impact excitation response of the platform.From Figure 3(a), it can be seen that under the excitation of a drop height of 300 mm, there is a plateau period of approximately 2.85 m/s 2 before the first trough of the acceleration response of the load, which immediately decays to 1.84 m/s 2 .Under the excitation of drop heights of 300 mm and 600 mm, the first trough curve of the acceleration response curve of the load exhibits a continuous "V" shape.
(3) The load occurs at the first trough curve, which is caused by two factors.First, during the vertical drop hammer impact, the force of the metal rubber and the Belleville spring in the composite shock absorber during the elongation process is about twice as large as its own gravity during the compression process.Secondly, the composite shock absorber elongation process is in the trough stage when subjected to double sine shock action.During this process, the impact action is low-frequency and strong, and its pulse width is wider compared to the sine wave.The elongation deformation produced by the composite shock absorber is longer than the compression deformation.On the other hand, the greater the deformation of the metal rubber-Belleville spring composite shock absorber is, the stronger the load force of the composite shock absorber is.Therefore, the peak and trough values of the acceleration time-domain curve increase continuously for a certain period of time.When the deformation reaches the limit of material properties, the peak and trough values of the acceleration response curve no longer increase.
(4) From Figure 3(a), it can be found that there is a small plateau period when the acceleration response of the load reaches the first peak, and the acceleration immediately increases and climbs to form a spike during this small plateau period.The main reason for this phenomenon is that the composite shock absorber increases the deformation range during the compression process, and the axial force of the composite shock absorber immediately increases within a certain period of time.Similarly, under the impact excitation of the falling hammer at three distances, the first valley curve of the acceleration response curve of the load presents a continuous "V" shape.
(5) From Figures 3(c), (e), and (g), it can be found that when the height of the pendulum is 600 mm, 900 mm, and 1200 mm, the platform period slowly disappears when the acceleration response of the load reaches the first peak.Especially at 1200 mm, there is almost almost no platform period.The reason for this phenomenon is the excessive impact load, and the composite shock isolator exhibits a hard stiffness characteristic.However, the first trough in the acceleration response of the load still presents a "V" shape.The shock isolation rate is an important indicator to test the performance of the composite vibration isolator, and the larger the shock isolation rate value is, the better the shock resistance performance of the composite vibration isolator will be.Its definition is: Where load A represents the absolute acceleration response amplitude of the load, base A represents the absolute acceleration of the base, and  represents the response amplitude.
According to Formula (1), the impact isolation rate at different pendulum heights was calculated.It was found that when the pendulum height was 300 mm, the impact isolation effect of the metal rubber-disc spring composite shock absorber was the best, with an impact isolation rate of over 95%.
(6) From Figure 3 (b), (d), (f), and (h), it is found that the stable values of impact isolation device A under impact excitation with pendulum heights of 300 mm, 600 mm, 900 mm, and 1200 mm are 0.60 s, 0.67 s, and 0.72 s, respectively.Under impact excitation with pendulum heights of 300 mm, 600 mm, and 900 mm, the impact isolation device can quickly return to a stable state.However, the performance of larger impact excitation with pendulum heights of 1200 mm is poor, and further optimization can be carried out in subsequent device design.

Conclusion
Faced with the reality that the vibration isolation performance of steel wire rope vibration isolators cannot meet the high stability requirements and strict aiming accuracy requirements of laser launch systems, this article mainly conducted experimental research on the shock isolation performance of metal rubber-disc spring composite shock isolators.The following conclusions were drawn: Based on the transient strong shock working environment of laser launch systems, the drop hammer test was ICAMIM-2023 Journal of Physics: Conference Series 2720 (2024) 012042 IOP Publishing doi:10.1088/1742-6596/2720/1/0120426 selected to test the shock isolation performance of this type of composite shock isolator.Through comparative tests of different shock excitation parameters, it was concluded that when the pendulum height is 300 mm, the shock isolation effect of the metal rubber-disc spring composite shock isolator is the best, with a shock isolation rate of over 95%.
Figure 1 shows the prototype of the designed metal rubber-disc spring composite shock absorber.Number 1 in the figure represents metal rubber; Number 2 represents the disc spring.

Figure 1 .
Figure 1.The principle profile of the metal rubber-disc spring composite isolator.

Figure 2 .
Figure 2. Flow chart of impact test equipment.

Figure 3 .
Figure 3. Acceleration response of the load and the acceleration response of the shock absorber, where (a), (c), (e), and (g) are the acceleration responses of the load with a pendulum height of 300 mm, 600 mm, 900 mm, and 1200 mm, respectively; (b), (d), (f) and (h) are the acceleration responses of the shock absorber with a pendulum height of 300 mm, 600 mm, 900 mm, and 1200 mm, respectively.As can be seen from the figure:(1) For a certain pendulum height and a certain impact excitation, the load is much smaller than the base, the first waveform peak of the load acceleration response curve is greatly reduced, and the time response becomes longer, indicating that the metal rubber disc spring composite shock absorber can improve the impact resistance performance of the laser emission system by reducing the peak of the impact response and extending the time response.(2)From Figures3(a), (c), (e), and (g), it can be observed that under the four drop height conditions, there is a plateau period in the first peak of the absolute acceleration response curve of the load, which is due to the relatively small impact excitation response of the platform.From Figure3(a), it can be seen that under the excitation of a drop height of 300 mm, there is a plateau period of approximately 2.85 m/s 2 before the first trough of the acceleration response of the load, which immediately decays to