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Trends of Welding Engineering Activities in Japan TMT (Thirty Meter Telescope) Structure and its Manufacture
Mitsuyoshi Nakatani
Hitachi Zosen Corporation, Osaka, Japan Email [email protected], 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.