The Key Technique Research Of Small Scale Time Delay Device Using Magneto-rheological Fluid

The delay device using magnetorheological fluid(MRF)is a kind of delay device which is designed according to magnetorheological effect and flow characteristic of MRF.It has the characteristic of long delay arming time,controllable and adjustable delay arming distance,strong anti-overload ability,econmy,practicality and good universality.Based on the engineering background of a delay arming device for small calibre projrctiles,this dissertation focuses on the deep investigations about the function realization of delay arming that it take the small scale delay device using MRF as research object.The theoretical modelling analysis,numerical simulation and experimental validation were employed,and the key technologies for storage of MRF for fuze,orifice discharge of MRF and adjustment of delay arming distance were studied.The main contributions are concluded as the followings:(1)The essential characteristics of MRF were studied from the micro-structure and the key parameters of discharge time mathematical model were determined.The yield stress model was established based on the chaining theory of MRF.The relationships between shear stress during orifice discharge and yield stress of MRF were determined under different rotational speed.The study indicated that MRF did not flow when the rotation speed was 35000r/min and below under the condition of magnetic field intensity was 150mT,that the safety of the device was ensured.The shear thinning mechanism of MRF was studied utilizing shear delamination theory based on characteristics of MRF.Then,the viscosity formula of MRF was derived at high shear rate.It laid the theoretical foundation for the calculation of the delay time.(2)In order to ensure the safety and reliability of the small scale delay device using MRF after long-term storage,an evaluation method of the storage time was proposed.The influences of temperature on the yield stress and viscosity of MRF and the device performance were analyzed by storage stability experiment.The accelerated life model was established based on experiment results that the ferromagnetic particles aggregated through high temperature after a long time.The evaluation method of the storage time of MRF was ensured,and the reliable storage life of the device under normal storage condition was calculated by this estimation method.The results indicated that the storage time of MRF at room temperature was 15.2 years which satisfied the requirements of fuze storage life form 10 to 20 years under the condition of confidence level ?=0.90 and the lower confidence limit of reliability RL=0.85.(3)The design scheme of small scale delay device using MRF was confirmed for the small-caliber projectile environment based on research results of yield characteristics and storage characteristics of MRF.The key dimension parameters were determined through analyzing structure and dynamic characteristics of main components,then the device was designed and processed.The strength and reliability of the deivce were examined through dynamic test,that satisfied the requirements under high overload and high rotation speed environment.The orifice discharge model and uniform force field mathematical model were established according to characteristics of MRF orifice discharge under high rotational speed,then the engineering algorithm of discharge time that MRF discharged under high rotational speed was presented.This engineering algorithm could predict the delay time of small scale delay device using MRF under high rotational speed.(4)To the problem that the device installed to the spinning centrifuge would exist eccentricity,pre-load time of the spinning centrifuge was too long,and the speed limit for the spinning centrifuge,the equivalent rotation experiment platform was designed based on operating principle of small scale delay device using MRF.Error analysis and correction coefficient were conducted for the platform,and the research results showed that the discharge status of MRF under high rotational speed could be equivalent by this platform successfully.The mathematical model of MRF discharge time was verified by this platform,and the local resistance coefficient was revised to improve the accuracy of the mathematical model through numerical simulation.The influences of the rotational speed,aperture and ratio of MRF on the delay time were further studied through the equivalent rotation experiment.The controlling method of delay time of small scale delay device using MRF under different rotational speed was put forward,that provided a reference for delay time control of small scale delay device using MRF.