Dynamic impact experiment and response characteristics analysis for 1:2 reduced-scale model of hydraulic support

It is significant to research the impact resistance properties of hydraulic support due to its key support role in the fully mechanized mining face.However,it is difficult for the entire hydraulic support to implement the impact experiment underground and analyze the response characteristic.Therefore,a dynamic impact experiment for the entire hydraulic support was proposed in this paper,where a 1:2 reducedscale model of hydraulic support was designed and its response characteristics under dynamic impact load were analyzed.Firstly,a comprehensive monitoring scheme was proposed to achieve an effective monitoring for dynamic response of hydraulic support.Secondly,a multi-scale impact experiment was carried out for the entire hydraulic support and dynamic behaviors of hydraulic support under the multi-scale impact load were revealed by experimental data.Then a dynamic impact experiment of the entire hydraulic support was simulated in ADAMS with the same experiment conditions,and the experimental and simulation data were verified mutually.Finally,the characteristics of energy conversion and dissipation of the entire experiment system after impact were analyzed.The experiment results showed that the impact resistance properties of hydraulic support largely depended on the initial support conditions and different vertical rigidities affected energy distribution proportion of the entire support system.

Numerical and experimental studies on impact dynamics of a planar flexible multibody system

In this paper a computational methodology on impact dynamics of the flexible multibody system is presented. First, the floating frame of reference approach and nodal coordinates on the basis of finite element formulation are used to describe the kinematics of planar deformable bodies. According to the kinematic description of contact conditions, the contact constraint equations of planar flexible bodies are derived. Based on the varying topology technique the impact dynamic equations for a planar multibody system are established. Then the initial conditions of the equations in each contact stage are determined according to the discontinuity theory in continuum mechanics. The experiments between the aluminum rods are performed to check the correctness of the proposed method. Through the comparison between the numerical and experimental results the proposed method is validated. Experimental results also show that the impulse momentum method cannot accurately predict the complex impact dynamic phenomena and the continuous model may lead to a serious error when used to simulate the impact problems with significant wave propagation effects.

航空发动机风扇转子叶片外物损伤I.鸟撞击试验研究(英文)

The conditions of experiment for bird impact to blades have been improved. The experiment of bird impact to the fan rotor blades of an aeroengine is carried out. Through analyzing the transient state response of blades impacted by bird and the change of blade profile before and after the impact, the anti-bird impact performance of blades in the first fan rotor is verified. The basis of anti-foreign object damage design for the fan rotor blades of an aeroengine is provided.

Shock-induced reaction behaviors of functionally graded reactive material

In this paper,the ballistic impact experiments,including impact test chamber and impact double-spaced plates,were conducted to study the reaction behaviors of a novel functionally graded reactive material(FGRM),which was composed of polytetrafluoroethylene/aluminum(PTFE/Al)and PTFE/Al/bismuth trioxide(Bi_(2)O_(3)).The experiments showed that the impact direction of the FGRM had a significant effect on the reaction.With the same impact velocity,when the first impact material was PTFE/Al/Bi_(2)O_(3),compared with first impact material PTFE/Al,the FGRM induced higher overpressure in the test chamber and larger damaged area of double-spaced plates.The theoretical model,which considered the shock wave generation and propagation,the effect of the shock wave on reaction efficiency,and penetration behaviors,was developed to analyze the reaction behaviors of the FGRM.The model predicted first impact material of the FGRM with a higher shock impedance was conducive to the reaction of reactive materials.The conclusion of this study provides significant information about the design and application of reactive materials.

Impact of GNSS radio occultation bending angle data assimilation in YH4DVAR system

Global Navigation Satellite System （GNSS） radio occultation measurements have been assimilated into the four- dimensional variational data assimilation system （YH4DVAR） using a one-dimensional bending angle operator （GBAO） as a new type of observation. For the sake of verifying the impact of GNSS radio occultation （RO） measurements to the data assimilation system, three experiments have been conducted. The statistical results of the analysis error experiment and forecast skill experiment show that the GNSS RO measurements have an impact on the analysis system. The typhoon forecast experiment shows the impact on the important weather process. They all have a positive impact on the weather forecast. Lastly, we look forward to future work on the observation system simulation experiment （OSSE） to investigate the impact of GNSS RO measurements as a function of observation number, which is an effective method to estimate the saturation of the observation number.

PROGRESSIVE FRAGMENT MODELING OF FAILURE WAVE IN CERAMICS UNDER PLANAR IMPACT LOADING

Polycrystalline ceramics have heterogeneous meso-structures which result in high singularity in stress distribution. Based on this, a progressive fragment model was proposed which describes the failure wave formation and propagation in shocked ceramics. The governing equation of the failure wave was characterized by inelastic bulk strain with material damage and fracture. And the inelastic bulk strain consists of dilatant strain from nucleation and expansion of microcracks and condensed strain from collapse of original pores. Numerical simulation of the free surface velocity was performed in good agreement with planar impact experiments on 92.93% aluminas at China Academy of Engineering Physics. And the longitudinal, lateral and shear stress histories upon the arrival of the failure wave were predicted, which present the diminished shear strength and lost spall strength in the failed layer.

Morphology analysis of tracks in the aerogels impacted by hypervelocity irregular particles

As an attractive collector medium for hypervelocity particles,combined with outstanding physical properties and suitable compositional characteristics,SiO2 aerogel has been deployed on outer space missions and laser shock-loaded collection experiments.In this paper,impact experiments were conducted to understand the penetration process of irregular grains,irregular Al_(2)O_(3) grains with two different sizes and speeds(~110μm@7 km/s,~251μm@2.3 km/s)at various density silica aerogels.By classifying the shapes of projectile residues and tracks,the morphology of tracks was analyzed.It was observed that there were several kinds of typical tracks in the penetration of irregular grains,accompanied by residues with the shapes of near-sphere,polyhedron,streamlined body wedge,and rotator.The rotational behavior was demonstrated by the final status of one flake projectile as direct evidence.In addition,there was no obvious relationship between the track length and experimental parameters,which may be caused by the uncertain interaction between aerogels and irregular particles.In addition,it confirmed the existence of fragmentation,melting situation by observing the shape of the impact entrance hole.At the same time,optical coherence tomography was used to observe the detail of tracks clearly,which provided a method to characterize the tracks nondestructively.

Coefficient of restitution for particles impacting on wet surfaces： An improved experimental approach

The coefficient of restitution is widely used to characterize the energy dissipation rate in numerical simulations involving particle collisions. The challenge in measuring the coefficient of restitution is the strong scatter seen in experimental data that results from varying particle properties, i.e. shape and surface roughness, and from imperfections in the experimental technique. To minimize this scattering, a novel experimental setup was developed based on two synchronized high-speed cameras capturing the collision behaviour of a particle in three dimensions. To measure the wet restitution coefficient, which describes particle impact in the presence of a liquid layer in the contact region, additional accuracy can be achieved by measuring the liquid layer thickness by a high-precision optical confocal sensor. The coefficient of restitution was measured for glass particles with two different diameters, at different relative velocities and liquid layer thicknesses, with a focus on small collision velocities and thin liquid layers, using both the improved （three dimensional） and the conventional （two dimensional） approaches to quantify the improvement of the new method＇s accuracy.

Biological analysis of woodpecker’s brain after impact experiments

Woodpeckers can withstand a fierce impact during pecking.Previous studies have focused on the biomechanical analysis of the pecking process,the properties of the beak and hyoid bone of woodpecker;however,the biological characteristics of the woodpecker brain are also important in resisting impact injuries.We employed impact experiments and biological analysis in normal and injured brains to reveal the impact-resistant biological characteristics of woodpecker brains,as well as the impact energy’s biological effects on the woodpecker brain.The hoopoe,which has a similar size but only a slight pecking behavior,was selected as the control group to compare brain morphology and neuronal cells differences in normal brains between woodpecker and hoopoe by sectioning and staining.A loading device was designed to conduct a quantifiable impact energy to the woodpeckers’head.Four groups of woodpeckers were impacted with the same energy on the forehead,beak,tempus and occiput,respectively.Biological changes in the injured brains were evaluated by Nissl staining and enzyme-linked immunosorbent assay.The results showed that:(1)woodpeckers had a larger cerebellum and a higher density of Nissl bodies than hoopoe;(2)Nissl apoptosis appeared in the brain samples after the forehead and the occiput impact experiments,but no obvious Nissl body apoptosis was observed after impact on the tempus and the beak;(3)β-amyloid protein accumulated in the normal status woodpecker brain.This study reveals that:woodpecker brain morphology is well-adapted to impact,woodpecker heads display location-dependent protective performance,with beak and tempus regions having a better protective performance than the forehead and occiput,Nissl apoptosis appears in injured woodpecker brains,and that the accumulation ofβ-amyloid protein does not show a direct relationship with the injury state of woodpecker’s brain tissue in our study.

Initial Conditions of Impact Dynamics

The effects of the initial conditions of impact dynamics equations are investigated numerically and experimentally.The inadequacies of previous studies on initial conditions are pointed out.Then a coefficient of velocity jump at the moment of impact is introduced,and the experiments for the mental rods are implemented to validate the appending constraints modeling methods for impact process.The comparisons between the experimental and simulated results at different coefficients are used to study the effects of the velocity jump conditions to the numerical simulation.The results indicate that the physical velocity response of bodies during impact is smooth;the different values of velocity jump only have small effects on numerical oscillation of velocity response,and they have no effects on the time history of impact force.