dingcapacityimprovementofmachinestructuresbyclosepackingwithballs-外文文獻(xiàn)-文庫(kù)吧資料
2025-05-22 19:00本頁面
【正文】 n damping ratio (F=150 N).The response acceleration wave of the square pipewith F=150 N and L=500 mm is shown in Fig. 4(a). Fig.4(b) gives the frequency response of Fig. 4(a). The natural frequency of the fundamental mode was approx. 650Hz, and the damping ratio obtained by the halfpowermethod was approx. .. Effect of ball size and excitation direction ondamping characteristicsThe effect of the ball size d on the maximum acceleration amaxboth in vertical and horizontal excitation isFig. 4. Damping characteristics of square pipe without glass ballpacking (F=150 N, L=500 mm). (a) Response acceleration, (b) frequency response.Fig. 5. Effect of ball size on maximum acceleration.shown in Fig. 5. The horizontal broken line shows themaximum acceleration in square pipe without ball packing. In the vertical excitation, amaxfor ball diameterssmaller than d=10 mm is nearly equal to 60% of thevalue for the square pipe without ball packing, and isnot affected by the ball diameter. However, in the caseof dH1135012 mm, amaxis larger than that for dH1134910 mm. Asa result, the dynamic rigidity of model structures packedwith glass balls of dH1135012 mm is not improved due to thelarge acceleration response. On the other hand, in thehorizontal excitation, the value of amaxwithin the regiondH1134917 mm is evidently smaller than the value for thesquare pipe without ball packing.The effect of the ball size d on the natural frequencyf of the fundamental mode both in vertical and horizontalexcitation is shown in Fig. 6. The horizontal broken lineshows the natural frequency of the square pipe withoutball packing. In the figure, the effect of the excitationdirection is not clear. The natural frequency within theFig. 6. Effect of ball size on natural frequency.470 Y. Wakasawa et al. / International Journal of Machine Tools amp。 Machine structure1. IntroductionAn outstanding design criterion for machine toolstructure with an effective damping capacity is requiredto achieve high accuracy and highefficiency cuttingoperations, since even a small vibration generated in amachine tool seriously affects machining accuracy.Some papers have reported damping capacityimprovement, including those dealing with steel–resinconcrete posite structure [1], overlaid with fiberreinforced plastics [2] which are a laminated positeof steel and high damping capacity material, and sandwich beam [3] in which a viscoelastic core is insertedbetween two steel plates. Moreover, various techniqueswere devised. In the nonobstructive particle damping(NOPD) technique [4], smalldiameter holes are drilledat appropriate locations inside the vibrating structuresand filled to the optimum level with a layer of particles,and the maximum damping capacity is attained for thedesired mode (or modes). An impact damper with granular materials [5] packed and movable in a container fixed* Corresponding author. Fax: +81565365924.Email address: (Y. Wakasawa).08906955/02/$ see front matter ? 2020 Elsevier Science Ltd. All rights reserved.PII: S08906955(01)001432to the primary vibrating system and a powder positedamper [6] packed with powder in a steel container witha high packing ratio, have also been reported. However,when packed materials were inserted in the structurecavity, the effects of impulsive excitation magnitude, thekinds of packed material, cavity shape etc. on the damping capacity were not made sufficiently clear in suchreports.In a precision machine tool, measures must be considered against the impulsive force from surroundingmachines in the light of many uncertain and unknownfactors. Many practical vibration isolation systems [7]for machinery and tools and for floor and building havebeen developed. However, when these plicated isolation systems are applied to machine tools, machiningcosts may be increased. If the damping capacity of themachine structure can be improved without anyadditional apparatus, it is more practical for machinetool operation.In the present study, the damping characteristics ofmachine structures packed with glass balls were investigated experimentally. Experiments were carried out forvarious impulsive
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