Research On Electrohydraulic Vibration Exciter Controlled By 2D Valve And The Using In Fatigue Test System

Fatigue test is not only an essential test in the field of modern engineering technology, but also an important method in industrial product development, a variety of materials, parts, components in industrial production have to make fatigue testing in order to determine their mechanical properties and expected life cycle.Electro-hydraulic fatigue testing machine was the key equipment in fatigue test. With the development of modern industrial and aerospace technology, the higher test frequency is put forward to electro-hydraulic fatigue testing machine; but the vibration frequency is difficult to improve which is restricted by the frequency characteristics of electro-hydraulic servo valve. A novel scheme for an electro-hydraulic vibrator controlled by a two-dimensional valve (called 2D valve) is therefore proposed to achieve higher frequency. The spool of 2D valve has two degrees of freedom including circumferential rotation and axial sliding. When the spool of 2D valve rotates continuously, the special geometry layout between grooves in spools and windows in sleeves makes the oil pressure change alternately to drive the piston of hydraulic cylinder go back-and-forth reciprocating motion which is making fatigue testing to test object. Vibration frequency and amplitude of piston of cylinder is controlled by the rotary speed and axial sliding, and a parallel servo valve is also used to realize the offset control of the displacement of piston in cylinder. So the frequency, amplitude and offset of displacement of piston in cylinder can be contolled independently. The spool of 2D valve is small and slender with few inertial, and in oil environment with a good lubricating, it is easy to achieve higer frequency by increasing rotary speed of the spool of 2D valve. The main research of this paper as follows:1. The working frequency of the conventional electrohydraulic vibration exciters is limited to fairly narrow range by the frequency response capability of the servo valve. A scheme of electrohydraulic vibration exciter using a 2D valve is therefore proposed to carry out fatigue test in 5 ~ 200Hz, and maintain the the frequency, amplitude and offset of piston disaplacement be controlled independently in closed or open loop. 2. The mathematical model of the electro-hydraulic valve controlled by 2D valve is established based on the analysis of principle of the electro-hydraulic valve controlled by 2D valve, the displacement curve of piston and distortion curve deviated from sine wave are solved using the numerical simulation program based on the fourth-order Runge - Kutta method, the movement of the hydraulic power mechanism is discussed combined with 2D valve.3. The decoupling control method is proposed to contol the exciter frequency, amplitude and offset of displacement of electro-hydraulic exciter controlled by 2D valve which are controlled indenpendently and coupled each other. The curve between the amplitude and the axial sliding of 2D valve'spool, the curve between the offset and the axial sliding of bias valve's spool and the coupling laws between amplitude and offset in different frequency are drived using the numerical simulation program based on the introduce of decoupling control principle of electro-hydraulic exciter controlled by 2D valve, and the amplitude-frequency curves are also given to study the laws between amplitude and vibratin frequency.4. The phae-frequency characteristic of electro-hydraulic exciter controlled by 2D valve is studied according to the requirement of phase synchronization of load in multiaxial fatigure test system. The structural of electro-hydraulic four-axis high-frequency structural strength fatigue testing system is described. The synchronous control strategy and the initial phase synchronization control method of electro-hydraulic exciter controlled by 2D valve are proposed bason in the analysis of structure of 2D valve and the phase-frequency characteristic curve of electro-hydraulic exciter controlled by 2D valve is derived; Research shows that when the excitation frequency among 0.048 ~ 0.870 times of natural frequency, the impact to the phase from the excitation frequency and the 2D axial sliding spool valve is negligible, which can provide the theoretical basis for the electro-hydraulic exciter used in synchronous multi-axis fatigue test system under the open loop control.5. The single-axis fagitue test system and multi-axial structural strength fatigue test system based on the electro-hydraulic exciter controlled by 2D valve are established to carry out experimental study. The test displacement wavrform of pistion in 5~200Hz is measured by force and displacement sensors to verify the simuliation results.