# Performance of a New Fine Particle Impact Damper

Authors: Yanchen Du; Shulin Wang; Yan Zhu; Laiqiang Li; Guangqiang Han
Journal: Advances in Acoustics and Vibration
 (2008)

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## Abstract

The energy dissipation mechanisms of conventional impact damper (CID) are mainly momentum exchange and friction. During the impact process, a lot of vibration energy cannot be exhausted but reverberated among the vibration partners. Besides, the CID may produce the additional vibration to the system or even amplify the response in the low-frequency vibration. To overcome these shortcomings, this paper proposes a new fine particle impact damper (FPID) which for the first time introduces the fine particle plastic deformation as an irreversible energy sink. Then, the experiments of the cantilevered beam with the CID and that with the FPID are, respectively, carried out to investigate the behavior of FPID. The experimental results indicate that the FPID has a better performance in vibration damping than in the CID and the FPID works well in control of the vibration with frequency lower than 50 Hz, which is absent to the non-obstructive particle damper. Thus, the FPID has a bright and significant application future because most of the mechanical vibration falls in the range of
low freqency.


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## Body

## 1. Introduction

Impact damping technology has been developed and widely
used for decades in manufacture of machine tool, robot, turbo machine,
airplane, rocket launcher, and so forth. At present, representative conventional impact damper (CID) includes single unit impact damper
[1–5], multiunit
impact damper [6–8], bean bag
impact damper [9, 10], and non-obstructive particle damper [11, 12]. Any one of CID features momentum exchange or friction, where momentum exchange cannot exhaust vibration energy
but reverberates it among impact partners [1–5], and friction is only
good at the high-frequency vibration but bad or even magnifying at the low-frequency
vibration [12].It is well known that plastic deformation can exhaust
energy as an irreversible energy sink. Many efforts have been made to use
plastic deformation to absorb shock and vibration energy such as civil
engineers utilize plastic deformation of minor structures to absorb earthquake
energy, so that the damage could be limited, and the major structure may be kept
safe [13]; ship engineers utilize plastic deformation of ship bow to absorb
collision energy between ship and pier, so that both the ship and the pier
could be prevented from damage [14]; automobile technicians utilize plastic
deformation of bumpers to absorb energy from collisions, so that the losses in
the accidents could be alleviated [15].Wang [16] found that plastic deformation as an irreversible energy sink is prone to occur in the plastic or fine particles, especially under the circumstance of violent vibration. Based on
these findings, in this paper, we propose a new fine particle impact damper (FPID)
which for the first time introduces the plastic deformation in fine particles to vibration system as perpetual energy dissipation.


## 2. Structure and Mechanism of FPID

Fine particles are enrolled as damping
agents among the impact partners (larger balls as usual) in FPID, as shown in
Figure1. Because the surface attraction of fine particles is greater than its gravity
[17], the whole surface of impact partners is surrounded and affixed by the fine
particles. The FPID, in which the plastic deformation
of fine particles due to collisions of impact partners exhausts most of the vibration
energy, for the first time introduces
the plastic deformation of fine particles
as perpetual energy dissipation and overcomes the shortcomings of momentum
exchange and friction. Thus, it is necessary to investigate the performance
of FPID by experiments.Figure 1
Structure of FPID.


## 3. Experimental Descriptions

We use a damped cantilevered beam as depicted in Figure2 in these experiments. The cantilevered beam
made of steel is 315 mm in length, 45 mm in width, and 2.1 mm in thickness. The damper container is
fixed near the tip of cantilevered beam, where the largest displacement is
obtained at the first flexural mode of 12.9 Hz. The damper container is in the
shape of column with 12 mm in diameter and 20 mm in height, also made of steel.
In the damper container, a 10 mm  in diameter steel ball with 4.1 g mass and a small quantity of copper
particles with 100μm in diameter are filled. The accelerometer placed on the
back of the damper measures the tip displacement of the beam which is excited near the root through a
stinger attached to an electromagnetic exciter.Figure 2
Schematic diagram of experimental setup.To investigate the performance of FPID,
experiments are, respectively, carried out on the undamped beam, on the beam damped
by particle impact damper, on the beam damped by single unit impact damper, and
on the beam damped by FPID. The contents of damper cavity in above four cases
are listed in Table1. In these four cases, the tip displacement of cantilevered
beam at free vibration and that for the first flexible mode at harmonic excitation are measured to study
the performance of FPID.Table 1
Contents in damper cavity.
CaseDamper typeSteel ball in damper cavityCopper particles in damper cavity(1)No damperNoneNone(2)Particle impact damperNone100μm in diameter, 4.6 g mass(3)Single unit impact damperSingle, 10 mm in diameter,
4.1 g massNone(4)FPIDSingle, 10 mm in diameter,
4.1 g mass100μm in diameter,
0.5 g massIn the FPID, the damper cavity is filled
with the fine particles and a steel ball with 10 mm in diameter.
As shown in Figure1, assume
that the damper cavity has a total volume of Vc, the steel ball has a volume of Vb, and the filled fine particles have a
volume of Vp. Thus, we
define the fine particles volumetric packing ratio rp in the FPID as (1)rp=VpVc−Vb. To test the effect of quantity of filled
fine particles on the performance of FPID, the tip displacements of cantilevered
beam, damped by the FPID with different
volumetric packing ratio rp of 100μm in diameter copper particles, are measured at harmonic excitation.
For the filled 100μm in diameter copper particles in the FPID designed in this paper, the
relation between volumetric packing
ratio rp and mass m is listed in Table 2.Table 2
Relation between volumetric packing ratiorp and mass m for the filled copper particles in the
FPID.
Volumetric packing ratiorp10%20%40%60%80%100%Massm (g)0.25 g0.5 g1.0 g1.5 g2.0 g2.5 gThe experiments
of cantilevered beam, damped by the FPID withrp  =  20% of 100μm in diameter copper particles and that with rp  =  20% of 400μm in diameter zinc particles, are
performed at harmonic excitation to indicate the effect of different mental particles.


## 4. Mode Analysis on Cantilevered Beam

The mode analysis on the undamped cantilevered
beam adopts the signal analysis system manufactured by the China Orient
Institute of Noise and Vibration. The cantilevered beam tested is equally
divided into ten parts, and an accelerometer
is placed on the fifth point to measure the response. A force hammer knocks each point five times and
for each knocking, the force signal from the force hammer and the acceleration
signal measured on the fifth
point are collected by the data acquisition system. The mode analysis based on these signals is performed
with the signal analysis software. The experimental scheme for the mode
analysis is shown in Figure3.Figure 3
Schematic diagram of
experimental scheme for mode analysis.The obtained top five flexural modes of cantilevered beam are shown in Figure4.Schematic diagram of the top
five flexural modes of cantilevered beam (a) the first flexural mode (13.183 Hz), (b) the second flexural mode (89.889 Hz), (c) the third flexural mode
(262.667 Hz), (d) the fourth flexural mode (448.979 Hz), (e) the fifth flexural
mode (524.518 Hz).
(a)(b)(c)(d)(e)


## 5. Experimental Results

Figure5 shows the experimental
results under free vibration with the same initial displacement from the four
cases listed in Table 1. The particle impact damper including 4.6 g copper
particles in the cavity has only a little effect on the reduction of the tip
displacement of cantilevered beam; the single unit impact damper even magnifies
the tip displacement for the violet collision between steel and cavity; the FPID
of rp  =  20% of copper particles has a good performance in the rapid attenuation of the tip
displacement.Tip displacement histories of the cantilevered beam with (a) no damper, (b)
particle impact damper, (c) single unit impact damper and (d) FPID withrp  =  20% of copper particles,
at free vibration of the same initial displacement.
(a)(b)(c)(d)Figure6 shows the experimental
results under the same harmonic excitation from the four cases listed in Table 1. The
particle impact damper only including 4.6 g copper particles in the cavity
makes the tip displacement of cantilevered beam reduce approximately 20% for
the first flexural mode; the single unit impact damper has the similar
performance as the particle impact damper; the FPID of rp  =  20% of copper particles is good at damping, which makes the tip displacement of cantilevered
beam reduce over 65% for the first flexural mode.Figure 6
Tip
displacement of the cantilevered beam with no damper (□), particle impact damper
(△), single unit impact
damper (◊) and FPID with rp  =  20% of copper particles (▪), at the same harmonic excitation.These results show that the FPID
has significant ability to absorb vibration energy and works well in low frequency
(lower than 50 Hz). Because the auxiliary masses are kept same in the last
three cases (particle impact damper, single unit impact damper, and FPID withrp  =  20% of copper particles), the excellent performance of FPID can be only attributed
to the plastic deformation occured in the fine particles.Figure7 is the experimental
results from the FPID with different volumetric packing ratio rp of 100μm in diameter
copper particles at the same harmonic excitation. The FPID of
rp  =  20% and that of
rp  =  40% work better than
others, that is,  too little or too much volumetric packing ratio  rp has bad effect on the performance of FPID. No matter how much copper particles are, the FPID has
better damping ability than the single unit impact damper.Figure 7
Tip displacement of the cantilevered
beam with single
unit impact damper (▴), FPID with
rp  =  10% of copper particles
(◊), FPID with
rp  =  20% of copper particles (▪), FPID with rp  =  40% of copper particles (◆), FPID with rp  =  60% of copper particles (◊) and FPID with rp  =  80% of copper particles (△), at the same harmonic excitation.The results show that there exists an optimal packing ratio of
particles in FPID, which is similar to the
particle impact damping. When the packing ratio is too large, the impact
partner does not have enough space to be excited, which limits the plastic
deformation occurred in fine particles. While when the packing ratio is too
little, the impact partner is not coated sufficiently, and thus the FPID
behaves more like a single unit impact damper.The FPID ofrp  =  20% of 100μm in diameter copper particles and that
of rp  =  20% of 400μm in diameter
zinc particles are compared at the same harmonic excitation, as shown in Figure 8. The FPID of
rp  =  20% of 100μm in diameter copper particles is only a little better than that
of rp  =  20% of 400μm in diameter
zinc particles, especially at the the first resonant point. It seems that both
the material and the geometrical sizes of the fine particles (especially metal
particles) do not alter the performance of FPID. While the samples used in this
paper are still very limited, thus the effect of different material and size
scale of fine particles on the performance of FPID deserves further research.Figure 8
Tip displacement of the cantilevered
beam with FPID
withrp  =  20% of copper particles (▪) and FPID with rp  =  20% of zinc particles (◊), at the same harmonic excitation.


## 6. Conclusions

This paper proposes the FPID which
introduces the fine particles plastic deformation as an irreversible energy sink.
From the experiments of the cantilevered beam damped by the FPID and that by the
CID, we draw the conclusions as follows.(1)
The FPID has a better performance than the CID in the rapid
attenuation of the tip displacement of cantilevered beam at the free vibration.(2)
The FPID can make the tip displacement of cantilevered beam reduces over
65% for the first flexural mode at the harmonic
excitation, which is much more excellent than that of the CID.(3)
There exists an optimal volumetric packing ratio to achieve the
better performance of FPID; no matter how much particles are, the FPID has
better damping ability than the single unit impact damper.(4)
The mental particles of the same volumetric packing ratio
have only a little influence on the performance of FPID at the harmonic
excitation, and the effect of different material and size scale of fine
particles on the performance of FPID deserves further research.(5)
The FPID works well in the frequency lower than 50 Hz, which is
absent in the non-obstructive particle damper.In spite of so many conclusions are
drawn from this paper, the study has not compared the performance of proposed
version to an equivalent conventional impact damper having a lower coefficient
of restitution to see if the plastic deformations of the fine particles cause a
significantly different response than a single particle with equivalent plastic
deformations because the lower coefficient of restitution usually would not
happen in the conventional impact damper.



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*Source: 140894-2008-09-30.xml*