Feasibility of using Earth-Bounded NDT Techniques for the Space Environment

MIT

V. Nikou, P.F. Mendez, K. Masubuchi & T.W. EagarMassachusetts Institute of Technology, Cambridge, USA

Explain the presentation is about NDT of welds done in space

MIT

February 1st, 2003

Inspecting things in space is difficult

Space Shuttle Columbia

The Need for Non Destructive Testing in Space

General NDT in space: NASA 1980?

NDT of welding in space: this work

Welding in space is at an advanced stage:Russians did it in spaceJapanese and Americans did it on planesNASA has a prototype design

Weld requirements: especially strict in spaceSpace structures: sufficient life to make economic

senseNDT in space only considered for monitoring

Summary MIT

1) Space Environment

2) Review of available NDT methods

3) Evaluation of NDT methods

4) Recommendations

What is this?

MIT

The Space Environment

1. Zero Gravity:• Low Gravity condition (g/g0=10-5 to 10-7)• Physics change (density, convection, surface tension)

2. Space Vacuum:• Mean pressure @ 250-500Km in the order of 10-9 Atm• Thickness of residual atmosphere is very small• Local pressure gradients instantaneously equalized

3. Space Radiation:• Vacuum Ultraviolet radiation (VUV)• Wide temperature variations on structures (–1100C to 1500C)

4. Composition of space environment:• Atomic Oxygen (very corrosive)• Atomic Hydrogen• Space Debris• Meteoroids

What is this?

NDT Methods ReviewedMIT

1. Visual (easy, less accurate)

2. Radiographic (very sensitive, portable, radiation hazard)

3. Ultrasonic (space-graded compounds needed as couplants)

4. Magnetic (surface defects, dry method OK)

5. Penetrant (can operate only up to 10-5 Atm)

6. Electrical-Eddy Current (surface and shallow crack detection)

7. Acoustic Emission (has to be detected in real time, better for

monitoring)

NDT Methods ReviewedMIT

1. Visual

2. Radiographic

3. Ultrasonic

4. Magnetic

5. Penetrant

6. Electrical (Eddy Current)

7. Acoustic Emission

1. Radiographic

2. Magnetic

3. Ultrasonic

4. Eddy Current

Use a consistent order for sorting them.

MIT

NDT (Welding - Monitoring)

Flaw detection

WeldgeometryMaterials

Safety Versatility

NDT Techniques Performance Factors

Flaw Detection: Minimum detectable flaw size Maximum detectable flaw depth

Materials: Al Ti Metal Matrix Composites (MMC) Austenitic Stainless Steel Martensitic Stainless Steel

Geometry of welds:

Brazing (B) Electron Beam Welding (EBW) Laser Beam Welding (LBW) Arc Welding (AW) Resistance Welding (RW)

Methods Radiographic Ultrasonic Magnetic Eddy current

Size 2% of thickness > 1-5 mm depending on

frequency

> 0.5 mm > 0.1 mm

Fla

w

Det

ecti

on

Depth 25mm SS

80mm Al

<500 mm Surface or near surface cracks

<13 mm SS

<3.5 mm Al

Al Y Y N Y

Ti Y Y N Y

MMC Y Y N N

SS1 Y N N Y M

ater

ials

SS2 Y Y Y Y

B Y N N N

EBW Y Y N Y

LW Y Y N Y

AW Y Y N Y

Geo

met

ry o

f w

eld

s

RW N N N Y

Ease of operation

Good Good Good Good

User’s Safety Radiation None None None

NDT Methods Evaluation

• Eddy Current: most suitable

•Why?

• Ultrasonic: maybe for MMC

•Why?

• Radiographic:

•heavy

• Magnetic: less suitable

•Why?

MIT

Explain why in little bullets

Conclusions

No welding in space without NDT of welds

Review of NDT methods for welds made in space

Earth-bounded NDT processes could be used in space

Eddy-Current most all-around suitable technique

Ultrasonic suitable for MMC

Future work involves examining the defect generation of specific

welding methods