Research On Dissipating Mechanism And Design Of The Elastomer Absorber

With the development of missiles and underwater weapons, their explosion equivalent and shock duration increase apparently. Consequently blasts imperil naval vessels and shipborne equipments more severely. On the other hand, accuracy of the electronic countermeasure, equipped weapon control and communication navigation is higher, and cause more requirements of their working environments. Therefore, it is an urgent task for safe operation of the shipborne equipments to increase their ability of shock resistance. However,elastomer dampers can protect these equipments, which are sensitive to shock velocity and can absorb the shock energy effectively, so as to reduce the dynamic response of the structures and the localized stress of the node. Therefore, it is a raring problem to design an elastomer damper, which is suitable to work on the ship to increase the anti-shock ability of the shipborne equipments. Aimed to solve above problems, the dissipating mechanism of the elastomer damper is investigated and a new damper product is designed using both theoretical and experimental research. The main research contents and results are described as follows:The constitutive equation of the elastomer modeled by the fractional derivative Maxwell model has been investigated. Based on the thermodynamics constraints analysis of the physical parameters of the fractional derivative Maxwell model, the relaxation modulus and the creeping modulus of the model are analyzed. The analysis results show clearly that the fractional derivative Maxwell model can embody both the creeping and the relaxing of the viscoelastic materials. Moreover, the stress attenuates to zero quickly for the given strain. Therefore, conclusions can be drawn that the fractional derivative Maxwell model is a better model to model that viscoelastic fluid. And the reliability of the fractional derivative Maxwell model to model the elastomer is validated by the shear rheological test.The pipe flow of the fractional derivative Maxwell fluid has been investigated, which supplies a theory base for the model of the elastomer damper. The velocities of the starting-up flow and the oscillating flow of the fractional derivative Maxwell fluid are solved. It is found from the analysis of the starting-up flow that the boundary effect happens and the hard core of the flow speeds up equably. However, the flow near the pipe wall is lagged out till cease because of the friction. It is found from the analysis of the oscillating pipe flow that the flow behaves like Newton fluids flow when the excited frequency is lower, and the flow reversal occurs when the excited frequency is higher. Moreover, two velocity series approximations are calculated. The result shows that the velocity is parabolic and not in phase with the imposed pressure gradient when the coefficient of the pipe radius is smaller. When the coefficient of the pipe radius is bigger, the phase angle of the velocity far from the wall of the pipe is shifted by 90°and the velocity at the centerline is smaller than that of steady Poiseuille flow. Furthermore, the Richardson annular effect of the velocity near the wall of the pipe is found. This conclusion generalizes the Richardson annular effect in the pipe flow from the Newton fluid to the viscoelastic Non-Newton fluid. And then the wall friction in the pipe induced by the oscillating flow is investigated profoundly. It is found from the investigation that the wall friction if effected by both the rheological parameters and pipe radius. Moreover, the smallest pipe radius for the elastomer damper, in which the resonance can't happen, is calculated numerically.Based on the above-mentioned theoretical research, the models of the viscoelastic damper working for anti-vibration and anti-shock are analyzed respectively. In order to simplify analysis of the mechanical characteristics of the damper for vibration, which is modeled by the fractional derivative Maxwell model, a sinusoidal algorithm is derived. The credibility and the advantage of this algorithm are validated by comparing the calculating results of this sinusoidal algorithm with the existing theoretical and experimental results. Furthermore, a calculating method of the dissipated energy of the viscoelastic damper modeled by the fractional derivative Maxwell model is supplied. In order to facilitate the structural design of the damper, the work principle of the double-acting elastomer fluid damper working for anti-shock, the damping of which is caused by the shearing flow of the fluid flowing through a ring gap, is analyzed. Based on the Maxwell viscoelastic fluid model, the velocity and the shear stress of the fluid flowing through the gap between the piston and the cylinder of the damper is solved using the separation of variables method. And then the velocity-related power mechanical model of the damper is derived. Simulating the work circumstance of the elastomer damper, the drop test is selected to amend the derived model and to bring the base design equation into being. At last, the first elastomer damper specimen is designed using this base design equation. The drop tests of this specimen validate that this base design equation is useful for the structural design of the damper.In order to meet the requirement of the shipborne equipments to protect impacts, a new elastomer is designed. In the process of design, the structural design of the piston rod, piston, cylinder, guide sleeve, ends, fillings and limit device is determined using strength calculation, and the corresponding safety verifications are performed. According to the base design equation of the elastomer damper, the curve of the damper cavity generatrix is obtained by numerically simulating the equation of a system consisting of a drop machine and the damper. This cavity forms the buffer zone. Based on the piston size, the brake zone is designed in the ends of the damper. Therefore, the new elastomer damper combines the isolator and limiter together and has cramped construction. The dynamic characteristics of the new elastomer damper are researched by drop tests. The results validate the calculation method of the curve of the damper cavity generatrix. Moreover, the dynamic characteristics of the new elastomer damper and a hydraulic oil Pro225MF damper are compared by tests. The experimental results show clearly that the new elastomer damper has many advantages over the hydraulic oil Pro225MF damper. It presents smaller damping force peaks. It has bigger capacity. It expresses better work performance. And it works more smoothly. Moreover, prototype testing confirms that the new elastomer damper represents good shock-resisting characteristics.