Physical Optics Corporation

Torrance, CA

Victor Grubsky, Volodymyr Romanov, Keith Shoemaker, and Rodion Tikhoplav

7/15/2014

Recent Progress on

3D Backscatter X-Ray NDE

POC 2014-PR038 (VG) 2

Typical Aerospace Industry NDI

Requirements:

• NDI of large structures (need one-sided approach)

• NDI of nonuniform, multilayer, or composite structures

• Applicability to conductive and nonconductive materials

• 3D defect detection and visualization capability

• High resolution and contrast

• Noncontact operation

POC 2014-PR038 (VG) 3

One-Sided 3D NDI Using

Compton Imaging Tomography (CIT)

X-ray source

Slit collimator

X-ray camera

Defect (void)

Data to computer

Compton- scattered

X-rays

X-ray imaging optics

(e.g., aperture)

Sample

Planar X-ray beam

• Unlike other Compton backscatter methods, permits 3D imaging • Structure is acquired slice by slice, with subsequent stitching into 3D density map • 3D data can be visualized plane-by-plane or via volume rendering

Translation to next slice

POC 2014-PR038 (VG) 4

Main Features and Advantages of CIT

• Based on X-ray Compton scattering, rather than transmission (as in conventional radiography)

• Single-sided operation: suitable for large aerospace components

• Works well with multilayer and composite structures, conducting and insulating materials, no problems with air gaps

• 3D defect detection and localization with sub-mm accuracy

• High penetration in typical lightweight aerospace materials

• Easy-to-interpret output, with possibility for 3D data visualization

POC 2014-PR038 (VG) 5

CIT Applications and Results

POC 2014-PR038 (VG) 6

3D Inspection of Spacecraft

Thermal Protection System (TPS)

Porous ceramic matrix

Dense front surface

Fiberglass?

Carbon fiber layers

Ti honey-comb

z

x

y

Impact Site #1

Impact Site #2

Impact Site #3

x

z

y

NASA AETB-8 Tile Impact Site #1

3D Visualization

Orthogonal Projections

Porous ceramic

layer

Projectile fragments

Carbon fiber honeycomb

Cavity

Fiberglass layer

Cavity ends here

Preflight and postflight TPS inspection

In-space detection of critical micrometeoroid damage in TPS before re-entry

POC 2014-PR038 (VG) 7

NDI of Aluminum Honeycomb Structure:

Sample

Dimensions: 300 x 300 x 16 mm Cell size: ~4.4 mm Built-in defects: simulated delamination (Teflon inserts), ~200 µm thick

Defect sizes

POC 2014-PR038 (VG) 8

NDI of Al Honeycomb: Results

¼ in. dia. defect

½ in. dia. defect

Co

re/f

ace

inte

rfac

e

Mid

dle

cro

ss s

ecti

on

Side cross section (x-y)

Empty cells Filled cells

Internal pipes (empty and full)

POC 2014-PR038 (VG) 9

Detection of Defects and Disbonds in

Composite Honeycomb Structures Spacecraft payload

fairing sample

1

2

Area 2, Front Side

Area 2, Back Side -6

0-4

0-2

00

20

40

60

Y,

mm

-300 -250 -200 -150 -100 -50 0 50 100 150 200 250

Z, mm-6

0-4

0-2

00

20

40

60

Y,

mm

-300 -250 -200 -150 -100 -50 0 50 100 150 200 250

Z, mm

2 in. defect

1 in. defect

0.25 in. defect

Applicable to any honeycomb materials Scans both sides at the same time Detects disbonds as thin as 3 mil (75 µm) Current scan speed ~1 hr/ft2, potential speed ~1-4 min/ft2

2 in. defect 1 in. defect

0.25 in. defect

POC 2014-PR038 (VG) 10

NDI of Carbon Fiber Aircraft

Components Through Air Gaps

Hole Cut

-30

-20

-10

01

02

03

0

Y,

mm

-180 -160 -140 -120 -100 -80 -60 -40 -20 0

Z, mm

Back side of the sample

CIT image of the back side, taken from the front

side

CIT is currently the only technology capable of detecting defects in inner layers through air gaps

POC 2014-PR038 (VG) 11

Corrosion and Defect Detection in Multilayer

Aerospace Components

Reconstructed view with front side (scan side) on top

View from back

Corroded plate

Front

Back

Corrosion exposed by slicing through the attached plate

Corrosion

Aircraft part with corroded plate attached to its back

Corrosion can be nondestructively detected in hard-to-access locations of aerospace components by inspecting 3D images for abnormal density variations

POC 2014-PR038 (VG) 12

Corroded Diamond Plate Behind

Honeycomb Panels: Experimental Setup

Corroded Al Plate (Front)

Corroded Al Plate (Back)

X-ray tube

New large-area X-ray detector

Al plate

Al honeycomb panels (1 in.

total thickness)

Scanning direction

POC 2014-PR038 (VG) 13

Reconstructed CIT Cross Sections

of the Corroded Diamond Plate

-60

-50

-40

-30

-20

-10

01

02

03

04

05

06

0

Y,

mm

-160 -140 -120 -100 -80 -60 -40 -20 0 20 40 60 80 100 120

Z, mm

-60

-50

-40

-30

-20

-10

01

02

03

04

05

06

0

Y,

mm

-160 -140 -120 -100 -80 -60 -40 -20 0 20 40 60 80 100 120

Z, mm

Depth = -7.5 mm

Depth = -6.4 mm

-60

-50

-40

-30

-20

-10

01

02

03

04

05

06

0

Y, m

m

-160 -140 -120 -100 -80 -60 -40 -20 0 20 40 60 80 100 120

Z, mm

Depth = -8.6 mm

-60

-50

-40

-30

-20

-10

01

02

03

04

05

06

0

Y,

mm

-160 -140 -120 -100 -80 -60 -40 -20 0 20 40 60 80 100 120

Z, mm

Depth = -9.7 mm

-60

-50

-40

-30

-20

-10

01

02

03

04

05

06

0

Y,

mm

-160 -140 -120 -100 -80 -60 -40 -20 0 20 40 60 80 100 120

Z, mm

Depth = -10.8 mm

-35

-30

-25

-20

-15

-10

-50

51

01

52

02

53

03

5

X, m

m

-60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60

Y, mm

Side view

Honeycomb #1

Honeycomb #2

Corroded Al plate

1

2

3

4

5

Scanning direction

POC 2014-PR038 (VG) 14

Corroded Aircraft Fuselage Section

Electrochemical corrosion (front side of skin)

Corrosion underneath

longeron

Scanning from front side

Corroded portion

POC 2014-PR038 (VG) 15

Reconstructed CIT

Cross Sections of

Corroded Fuselage

-60

-50

-40

-30

-20

-10

01

02

03

04

05

06

0

Y,

mm

-140 -120 -100 -80 -60 -40 -20 0 20 40 60

Z, mm-3

5-3

0-2

5-2

0-1

5-1

0-5

05

10

15

20

25

30

35

X,

mm

-60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60

Y, mm

-60

-50

-40

-30

-20

-10

01

02

03

04

05

06

0

Y,

mm

-140 -120 -100 -80 -60 -40 -20 0 20 40 60

Z, mm

-60

-50

-40

-30

-20

-10

01

02

03

04

05

06

0

Y,

mm

-140 -120 -100 -80 -60 -40 -20 0 20 40 60

Z, mm

Side view

Skin layer

Skin to longeron attachment layer

Longeron layer

Skin corrosion

Al corroded away

Build-up of corrosion products

POC 2014-PR038 (VG) 16

3D Imaging for FOD Detection and

Reverse Engineering

Front view Back view

Bottom view Side views: whole structure (left) and

exposed door edge (right)

Rivet

Holes

Artifacts

Repair

Rubber gasket

Door edge

Front

Back

3D Visualization of an Aircraft Door Section

One-sided scanning achieves tomographic 3D imaging of large components in situ, without their disassembly or removal

Convenient GUI provides easy 3D manipulation and virtual dissection

POC 2014-PR038 (VG) 17

Underwater NDI

3D Reconstruction at Various Depths

Facilitates underwater structural analysis through non-contact, one-sided 3D imaging of internal structure

3D rendering of internal electronics structure is possible

-140 -120 -100 -80 -60 -40 -20 0 20 40 60 80 100 120 140

Y, mm

-120

-100

-80

-60

-40

-20

0

Z, mm

Sealed electronic circuit attached to a surface underwater

1. 2.

3. 4.

POC 2014-PR038 (VG) 18

In-Process, Real-Time Weld Quality Control

Welded steel sheet Reconstructed (from 3D data) weld cross sections at various depths

Measured weld cross sections (can be used for real-time quality monitoring)

CIT imaging through the whole weld thickness is possible in real time (while the weld is still hot) and can be used for adjusting welding parameters on the fly

After weld completion, 3D images can be used for final inspection and QC

POC 2014-PR038 (VG) 19

CIT Hardware Development

POC 2014-PR038 (VG) 20

Benchtop CIT Prototype

(Early 2012)

February 29, 2012

Mounted test sample

X-ray camera

Vertical lead slit

Sample translation

Translation stage

225-kV X-ray source

POC 2014-PR038 (VG) 21

Gen-I Mobile CIT Scanner for Aircraft NDI

(9/2012)

Scanning head (includes a 225-kV

X-ray source, camera, and imaging optics)

Translation frame (for scanning and 2D

positioning)

Power, signal, and control cables

Motorized cart with a lift table

Demonstrated at Warner-Robins AFB in 2012

POC 2014-PR038 (VG) 22

Gen-II Portable CIT Scanner for General NDI

(9/2013)

Developed in NASA Phase II SBIR as an intermediate prototype Includes integrated translation stage for scanning Robust, can be mounted on a robotic arm to handle a variety of surfaces Dimensions: ~70x45x35 cm; weight ~75 kg

X-ray source (200 kV)

X-ray imager

Integrated translation

stage (for scanning)

Support frame

POC 2014-PR038 (VG) 23

Gen-II Portable CIT Scanner for

Underwater NDI (3/2014)

Prototype developed for ONR (Navy Phase II SBIR) Capable of operating at depths up to ~10-30 m Includes translation stage for scanning Attached to a surface with suction cups Dimensions: ~70x60x50 cm; weight ~100 kg

Underwater housing with X-ray source (200 kV) and

detector

Translation stage

(for scanning)

Suction cups

POC 2014-PR038 (VG) 24

Gen-III Lightweight Portable CIT Scanner

(~9/2014)

Currently under development for NASA R&D (Phase II SBIR) Field of view: 20 cm (w) x 12 cm (h) x 10 cm (d) Dimensions: 76x72x33 cm; weight ~48 kg Fully enclosed system: no external moving parts

Lightweight X-ray source

(200 kV)

X-ray imager

Integrated translation

stage

Scanning area

POC 2014-PR038 (VG) 25

Key Specifications

Parameter Value

Resolution (x/y/z) 1.5-2.5 mm

Field of view (width) ~10-15 cm

Field of view (length) ~15-30 cm (depends on translation range)

Field of view (depth) ~5-10 cm

Density resolution ~2-3%

POC 2014-PR038 (VG) 26

Resolution Characterization

Al test sample and its CIT image

50

40

30

20

10

0-1

0-2

0-3

0-4

0-5

0

Y,

mm

-80 -60 -40 -20 0 20 40 60

Z, mm

MTF and resolution analysis

0.01

2

3

4

5

67

0.1

2

3

4

5

67

1

MT

F

0.50.40.30.2

Frequency, lines/mm

10% of MTFmax

fmax = 0.43 l/mm Res. = 1/fmax = 2.3 mm

POC 2014-PR038 (VG) 27

February 29, 2012

Typical CIT Penetration Depth

with a 200 – 250 kV Source

Experimental penetration depth estimate:

σ(E) = scattering cross section for photon energy E ~80-100 keV ρ = material density

E

ELEL attCIT2

2~

POC 2014-PR038 (VG) 28

Scanning Speed

Current scanning speed: 80 min/ft2 (8-s exposure per 1-mm slice, 15 cm (5 in.) wide)

Potential straightforward enhancements in speed:

System Modification Speed Improvement

Higher-power X-ray source (3 kW vs. current 1.2 kW)

2.5x

Multiple cameras (four vs. one) or large flat-panel detector

2x – 4x

Optimization of the scanning geometry, imaging optics, and sample irradiation uniformity

2x – 3x

Total: 10x – 30x

Therefore, potential scanning speed is: 3-8 min/ft2

POC 2014-PR038 (VG) 29

Safety

Any NDE system utilizing X-rays is a potential safety hazard. However, a CIT-based NDE system is inherently much safer than comparable X-ray radiography systems, because:

Most of the generated X-ray flux is blocked immediately in front of the source with the slit aperture; only 1-2% of the flux is used for sample irradiation.

Backscattered X-rays not used for imaging can be effectively blocked by appropriate shielding.

Any unabsorbed portion of the X-ray beam transmitted through the sample can be minimized by choosing appropriate X-ray source voltage (lower voltage higher absorption fewer residual X-rays).

The exclusion zone for the current CIT prototype:

~4-5 m: in open air (can be reduced to 2-3 ft with further optimization)

<1 m: in underwater environment.

POC 2014-PR038 (VG) 30

Future CIT Development

Two new NASA SBIR Phase I’s recently started:

Multifunctional Compton Inspection Tool (MCIT) Improved system design, with fewer moving parts, smaller weight and size, and increased functionality

Thermal Protection Systems Nondestructive Evaluation Tool (THRON) System optimization primarily targeted at more effective 3D NDE of the TPS - collaboration with SpaceX

POC thanks NASA for its continued support!