NORITAKA YUSA1 AND SAKUO SAWADA2

1 DEPARTMENT OF QUANTUM SCIENCE AND ENERGY ENGINEERING,

TOHOKU UNIVERSITY

2 SAWADA TECHNICAL SERVICE CO., LTD.

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from Mainichi newspaper

Bolts are one of the most fundamental and common

elements in modern society.

Loosened bolts would cause serious situation.

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from Mainichi newspaper

http://gendai.ismedia.jp/articles/-/34525

About 270 concrete plates fixed at the ceiling of a tunnel suddenly dropped.

2012/12/02

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from http://kobayakawashunichi.blog.jp/archives/2875230.html

https://upload.wikimedia.org/wikipedia/commons/1/11/Sasago_Tunnel%28Ch%C5%AB%C5%8D_Expwy%29_collapsed_3D_model_2.png

Connected by bolts

-> loosened?

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Sometimes bolts are gradually loosened

while they are in use

even though they were sufficiently tightened

initially!!

Periodical inspections are

indispensable.

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Simple, but not so objective or quantitative

https://jp.images-monotaro.com/Monotaro3/pi/full/mono10784523-090203-02.jpg

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Ultrasonic (~MHz)

Vibration (~kHz)

Magnetic

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Ultrasonic (~MHz)

Vibration (~kHz)

Magnetic

A simpler, easier, and cheaper method is preferable.

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100 101 102 103 104 105 106 107 108

Audible range

Frequency [Hz]

Ultrasonic

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100 101 102 103 104 105 106 107 108

Audible range

Frequency [Hz]

Ultrasonic

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Accelerometer

(down to 0.5 Hz)

Test hammer Magnetic mounting base

A/D converter: NI9223USB

Sampling Frequency: 25 kHz

LP/HP Filter: none

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tighten

loose

loose

tighten

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Low frequency components are quite important.

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When a bolt is loosened,

the decay of vibration tends to become ‘gradual’.

The most plausible reason for ‘Not always’ is that

the impulse to vibrate the nut was imposed manually.

• Where to hit is unclear yet.

• Too weak impulse leads to no clear vibration signals; too strong

impulse causes too global vibration (probably). [difficulty in

experiments using a small specimen]

• Impulse to vibration the nut should not contain too much low

frequency components.

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input

output

Vibration signals when bolts were tightened to rated torque

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Probability that the decay of vibration became gradual.

rated torque

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1,800

510

450

200

M36 bolt on non-shrinkage mortar base

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Loose (tightened using a wrench)

middle (+30°by a hammer)

tight (+60°by a hammer)

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tight

middle#1

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tight

middle#2

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tight

middle#3

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tight

loose#1

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tight

loose#2

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tight

loose#3

•

•

•

•

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loose

tighten