vibro-acoustic of table tennis rackets: influence of the ... · vibro-acoustic of table tennis...

Vibro-acoustic of table tennis rackets:

Influence of the blade plywood design

Experimental & Sensory analyses

Lionel. Manin1, Marc Poggi2 ,Cyril Bertrand1,, Nicolas Havard3

1 Université de Lyon, CNRS, INSA-Lyon, LaMCoS , Villeurbanne, France2 Feeltest, France, www.feeltest.com

3 Cornilleau, France, www.cornilleau.fr

ISEA 2014 – Sheffield - Vibro-acoustic of table tennis rackets …. 2/18

Tables Rackets Accessories

�� research investigations for competition rackets

Tables Indoor et Outdoor…


pli 1 & 5

pli 2 & 4

pli 3

Table tennis racket composition

� Blade (plywood)

•Composed of several wood layers

(plies) & several wood type

• The plies are oriented at 0 or 90 °

from the handle

� Covering

•Max thickness : 4 mm

• Rubber + Sponge


Context of the research

performances of a table tennis racket can be subjectively qualified with

several adjectives like: fast, slow, stiff, adhesive, controllable, etc.

The acoustic signature at ball impact is the first appreciation element of the

racket performances

A “good” sound may give a positive a priori to the player

Usually, players associate a short and sharp sound to a fast racket, is it true?

What is the correlation between the rackets vibrations at ball impact and he

sound emitted?

Has the plywood composition an influence?

What role does the covering plays on the vibro-acoustic?

Are the lab measurement consistent with the sensory analysis performed by

the players?


Test definition, Vibro-acoustic experimental set up

Guiding tube

Manometer

Pneumatic hand

racket

90 cm

accelerometer

Microphone

20 cm

racket

Pneumatic hand

Manometer


Test definition, experimental set up

Handle pneumatic tightening

Manometer

Microphone

Teardrop accelerometers

Data acquisition and postprocessing

Accelerometers and microphone recordings

Accelerometers and microphone average spectrum


Acoustic spectrogram

tim

e (s

)

(Hz)

Acoustic and vibration spectra

(dB

)

(Hz)

(m/s

²)

Acoustic levelAcceleration

Experimental results: sound and vibrations analysis

Superposed plots of the average spectra- vibration/acoustic peaks- identification of 2 main frequencies

Acoustic spectrogram- acoustic spectrum evolution vs time- useful tool to observe the sound /time


Experimental modal analysis using a vibrometer

� The advantage of the vibrometer is that it does not modify the tested structure

� The racket blade surface is meshed to define the measurement points

� A shock hammer is used to hit the racket at the ball impact point on the back of the scanned surface.

� the vibrometer software rebuilds the vibration behavior of the racket blade for any given frequency

Laser vibrometer

Chipsmode

MembranemodeScanned points


Main vibro-acoustic frequencies and modal shapes

� Modal analysis + the vibro-acoustic tests �identification of the modes corresponding to the dominant frequencies of the vibro-acoustic spectra:

the chips and the membrane modes

� Following the ball impact, the racket blade vibrates and its vibration behavior

results in a combination of its two main vibration modes.

Chips vibration mode Membrane vibration mode


Modal analysis / vibro-acoustic test

Vibrations Acoustic Laser vibrometer

1055 Hz 1058 Hz 1058 Hz

1543 Hz 1533 Hz 1540 Hz

1748 Hz 1790 Hz

Racket blade

Microphone

Accelerometer

1

2

1 2

Acoustic spectrogram

tim

e (s

)

Acoustic and vibration spectra

(dB

)

(Hz)

Acoustic levelAcceleration

(m/s

²)


Influence of the coverings (rubber)

• Essais Vibro-acoustiques� Raquette J

Acoustic and vibration spectra Acoustic and vibration spectra

Acoustic spectrogram Acoustic spectrogram

(dB

)

(dB

)

tim

e (s

)

tim

e (s

)

(Hz) (Hz)

(Hz) (Hz)

(m/s

²)

(m/s

²)

Acoustic level

AccelerationAcoustic level

Acceleration

Racket Blade Racket Blade+ Rubbers

�Effect of the rubbers�Same mode shape�30 % decrease of the resonance frequencies� higher damping on the membrane mode


Effect of the plywood composition on the racket vibro-acoustic

Plywood : symmetric sandwich of several layers (wood essence , thickness)

Use of prototype rackets for the influence analysis

NameWood

essenceThickness

Wood essence

E (MPa)

Set 1 : Essence of ply 3Kiri

AyousBalsa

3,6 mm

Akazie 16900

Ayous 7260

Set 2 : Thickness of ply 3 Kiri3 mm

3,4 mm3,8 mm

Balsa 5140

Hinoki 10145

Set 3 :Thickness of plies 2 & 4 Ayous0,4 mm

0,6 mm0,8 mm

Kiri 4500

Koto 13140

Set 4 : Essence of plies 2 & 4Limba

AkaziePine

0,6 mm

Limba 11750

pin 11000


Vibro-acoustic analysis: Influence of ply 3ply 1 & 5

ply 2 & 4

ply 3

Kiri,

3,6 mm

essence E (MPa)ρ ρ ρ ρ

((((kg/m3)

E/ρρρρ(m²/s²)

Kiri 4500 250 18e3

Ayous 7260 380 19.1e3

Balsa 5140 140 36.7e3


ply 1 & 5

ply 2 & 4

ply 3

Ayous,

0,6 mm

Wood essence

E (MPa)

ρ ρ ρ ρ ((((kg/m3)

E/ρρρρ(m²/s²)

Akazie 16900 720 23.5e3Limba 11750 540 21.7e3

pin 11000 450 14.7e3

Vibro-acoustic analysis: Influence of ply 2&4


Sensory analysis vs. vibro-acoustic analysis (laboratory)

4 players (national competition level)

Sound following a ball drop

Sound when playing (2 min)

10 rackets tested, same covering, identical appearance

Racket description Chips mode (Hz) Membrane mode (Hz)

A Ply 3 – KIRI 3.6 mm 973 1447

B Ply 3 – BALSA 3.6 mm 885 1394

C Ply 3 – KIRI 3 mm 739 1172

D Ply 3 – KIRI 3.8 mm 851 1367

E Ply 2/4 – AYOUS- 0.4 mm 747 1269

F Ply 2 /4– AYOUS - 0.8 mm 910 1360

G Ply 2/4 – LIMBA – 0.6 mm 939 1336

H Ply 1 /5– 1 mm – AYOUS 848 1377

I Ply 1 /5– HINOKI – 0.6mm 782 1433

J Ply 1/5 – KOTO 0.6 mm 884 1483


Sensory analysis vs. vibro-acoustic analysis (laboratory)

Classification of the racket with two criteria for the sound

Low/Sharp

Plain/Hollow

Comparison of the mappings


Conclusions

An experimental approach has been defined to determine the vibro-acoustic

signature of table tennis rackets

Clear correlation between the vibratory and the acoustic behaviors after ball

impact

Two vibrations modes are mainly responsible of the racket acoustic, there

are the chips and membrane modes.

The rubbers translate the frequencies peaks toward low values but the mode

shapes are the same.

The composition of the plywood has a great influence on the vibro-acoustic

spectrum

The ply thickness is the most influent parameter

No significant influence of the wood essence

Sensory analysis

The racket classification made by the players show some consistancy with the

vibro-acoustic lab observations.


Questions?


Impact simulation with abaqus explicit

2.25 ms after ball impact 4 ms after ball impact

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