Trends of Welding Engineering Activities in Japan TMT (Thirty Meter Telescope) Structure and its Manufacture

Mitsuyoshi Nakatani

Hitachi Zosen Corporation, Osaka, Japan Email nakatani_m@hitachizosen.co.jp, phone +81-6-6551-9239, fax +81-6-6551-9086

Abstract The TMT (Thirty Meter Telescope) is a 30m diameter, optical infrared and next-generation Extremely Large

Telescope being planned for construction, and aiming to begin operation in 2024. The TMT will achieve a resolution and sensitivity that far surpasses those of the 8.2m diameter Subaru Telescope which has been successfully used for the world’s most advanced astronomical research over the past ten years. The TMT is therefore expected to open up new research fields in astronomy such as the exploration of extrasolar planets and figuring out the formation of astronomical objects in the early Universe.

The TMT has a structure with many pipes used due to its lightweight, high stiffness requirements. Also, to further

reduce weight, welding is used to join pipes. The substructure has a rotation mechanism for the azimuth, and the superstructure has one for elevation. The structure, in particular the superstructure, is subject to cyclic loading from the azimuthal and elevational rotation. The necessary amount of cycles is estimated at 40 rotations a day over 50 years of use, which adds up to 730,000 rotations (40 rotations x 365 days x 50 years), which requires a fatigue strength for high cycles.

The presentation has showed the TMT structure and its manufacture. Also, it showed the developed system for

manufacturing the TMT, and the high performance of the joints on fatigue strength and fracture toughness. The obtained results are listed below. 1. TMT consists of many pipes because of its high rigidity and light weight. 2. A weld joint design and cutting CAM system of multi-axial pipes was developed. 3. A pipe joint bead shape measuring system was developed. 4. Residual stress and deformation were measured on an actual-size multi-axial pipe structure. 5. Residual stress and deformation of a multi-axial pipe structure was calculated by an enhanced large-scale

analysis method. 6. A fatigue test was conducted for an actual-size multi-axial pipe joint. The fatigue strength satisfied the

required value. 7. A gusset plate joint with high fatigue strength was developed. 8. The fracture toughness of pipe welds was evaluated, and the toughness value satisfied the required value. The developed system and structure are planned to be used on the TMT.

Acknowledgments In Japan, National Astronomical Observatory of Japan (NAOJ) is leading telescope structure system including drive subsystem and control subsystem. Mitsubishi Electric Corporation is in charge of preliminary and detail design of these systems.

Structure of TMT（Thirty Meter Telescope）

2

水平回転

鉛直回転

Tube Head Support Structure

Top ring

Elevational Rotation Primary MirrorSegmented MirrorTertiary Mirror Support Tower

High Angle JournalHigh Angle Bearing

Workers' Access Lift

Azimuthal RotationNasmyth Platform

Azimuth Bearing

Pintle Bearing

Pier

Substructure

Superstructure

Required fatigue strengthNumber of cycle：730,000Stress amplitude：70MPa

3Weld pipe and pipe

Weld pipe and gusset plate

Node Structure of Multi Pipe Joint

Superstructure

Substructure

Weld Joint Design and Cutting CAM System of Multi-axial Pipes

3D Cutting

3D Auto Marking

Measurement of Bead Shape for Pipe Weld

pipe

pipe

Weld bead

Optical cutting method

Macroscopic section

25.3 mm

5.4 mm

10 mm Bead Shape Measurement System

Measured Data

Measurement of Residual Stress and Deformation in Multi-axial Pipe structure

GMAW

(Semi-automatic)

All Position Welding

Residual Stress : Compact X-ray Residual Stress Measurement Equipment3-D Shape Measurement : Total Station (Theodolite)

Actual Size Mock-up Test

Enhanced Large-scale Analysis Method and its Application to Multi-axial Pipe Weld

• 16 pipes (STK490)• 671,427 nodes, 563,412 elements• 90 welding passes

Axi

al s

hrin

kage

(m

m)

Pipe name

-2.50

-2.00

-1.50

-1.00

-0.50

0.00

pipe3 pipe7 pipe8 pipe11 pipe12

analysis

measurement

Fatigue Test of Actual-size Multi-axial Pipe Joint

Required fatigue strengthNumber of cycles：730,000Stress amplitude：55MPa

Gusset Plate Joint Structure

Tube-to-through gusset plate joint(Conventional)

②Rotate pipe to insert

Developed joint

Slit at pipe

Slit at gusset plate

①Cut head of pipe

Relationship between Stress Concentration andFatigue Strength

Pipe

Gusset plateGusset plate

Pipe

Required fatigue strengthNumber of cycles：730,000Stress amplitude：70MPa

Fracture Toughness Evaluation of Pipe Weld

(1)

(2)

(3)

(4)Maximum Stress

(7)

(10)

(14)(15)

(16) Pipe (2)

Pipe (3)Final layer toe

191.4MPa

Final layer toe

185.2MPa

First layer root

-9.6MPa

First layer root

115.7MPa

Weldedportion

Zone of maximum stress (enlarged)Block

Average temperature : 2℃Big earthquake once in a thousand years

Conclusions

The presentation showed the TMT structure and its manufacture. The obtained results are listed below.

1. TMT consists of many pipes because of its high rigidity and light weight.2. A weld joint design and cutting CAM system of multi-axial pipes was

developed.3. A pipe joint bead shape measuring system was developed.4. Residual stress and deformation were measured on an actual-size

multi-axial pipe structure.5. Residual stress and deformation of a multi-axial pipe structure was

calculated by an enhanced large-scale analysis method.6. A fatigue test was conducted for an actual-size multi-axial pipe joint.

The fatigue strength satisfied the required value.7. A gusset plate joint with high fatigue strength was developed.8. The fracture toughness of pipe welds was evaluated, and the

toughness value satisfied the required value.

The developed system and structure are planned to be used on the TMT.