Thermoplastic material inspection/types of defects

Question 1

List some manufacturing defects found in thermoplastic materials

Answer 1

1. delamination
2. resin starved area
3. resin rich areas
4. blisters, air bubbles
5. wrinkles
6. voids
7. thermal decomposition

Question 2

List some of the sources of manufacturing defects found in thermoplastic materials

Answer 2

1. improper cure or processing
2. improper machining
3. mishandling
4. improper drilling
5. tool drops
6. contamination
7. improper sanding
8. substandard material
9. inadequate tooling
10. mislocation of holes or details

Question 3

Describe fiber breakage

Answer 3

1. can be critical as structures are typically designed to be fiber dominant
2. typically limited to a zone near the point of impact / contained by the impact object size and energy

Question 4

Describe Matrix Imperfections

Answer 4

1. usually occur on the matrix-fiber interface or int he matrix
   parallel to the fibers
2. can slightly reduce material properties, but seldom critical to
   the structure
3. may develop into delaminations, which are more critical

Question 5

Describe Delamination and Debonds

Answer 5

1. Delaminations form on the interface between the layers in the
   laminate
2. Delaminations may form from matrix cracks that grow into
   the interlaminar layer
3. Debonds can also form from production nonadhesion along
   the bondline between two elements and initiate delamination
   in adjacent layers

Question 6

List the criteria for determining how critical delamination or debonds are

Answer 6

1. dimensions
2. number of delaminations at a given location
3. location - in the thickness of laminate, in the structure,
   proximity to free edges,
   stress concentration region, geometrical discontinues, etc
4. load - behavior of delaminations and debonds depond on
   loading type

Question 7

List some in service defects on thermoplastic materials

Answer 7

1. environmental degradation
2. impact damage
3. fatigue
4. cracks from local overload
5. debonding
6. delamination
7. fiber fracturing
8. erosion

Question 8

How do you inspect composites?

Answer 8

Nondestructive Inspection of Composites (NDI)
using flashlights, magnifying glasses, mirrors, and borescopes

Question 9

What types of composite damage can be seen visually?

Answer 9

resin starvation
resin richness
wrinkles
ply bridging
discoloration
impact damage
foreign matter
blisters
debonding

Question 10

What are some damages that can be seen visually when inspecting composite materials?

Answer 10

delamination
disbonds
matrix crazing

Question 11

List some of the NDI inspection techniques used to inspect composite material

Answer 11

1. Audible Sonic Testing (Coin Tapping)
2. Automated Tap Test
3. Ultrasonic Inspection
4. Through Transmission Ultrasonic Inspection
5. Pulse Echo Ultrasonic Inspection
6. Ultrasonic Bondtester Inspection
7. Phased Array Inspection
8. Radiography
9. Thermography
10. Neutron Radiography
11. Moisture Detector

Question 12

Describe Audible Sonic Testing (Coin Tapping)

Answer 12

1. most common technique used for the detection of
   delamination and/or disbond
2. a clear, sharp ringing sound indicates a well bonded structure/
   a dull thud indicates a discrepant area
3. not reliable on structures with more than 4 plies

Question 13

Describe Automated Tap Test

Answer 13

1. similar to the manual tap test, but uses a solenoid instead of a hammer

Question 14

Describe Ultrasonic Testing

Answer 14

1. useful for the detection of internal delaminations, voids, or inconsistencies in composite components not found with visual or tap methods
2. there are many different types of ultrasonic techniques for testing
3. all techniques use sound wave energy

Question 15

What are the 4 most common ultrasonic techniques?

Answer 15

1. Through Transmission Ultrasonic Inspection
2. Pulse Echo Ultrasonic Inspection
3. Ultrasonic Bondtester Inspection
4. Phased Array Inspection

Question 16

Describe Through Transmission Ultrasonic Inspection

Answer 16

1. uses 2 transducers, one on each side of the area to be inspected
2. ultrasonic signal transmitted from one transducer to the other
3. loss of signal strength is measure by the instrument
4. instrument shows loss as a percent of the original strength / loss in decibels
5. Areas with a greater loss than the reference standard indicates a defective area

Question 17

Describe Pulse Echo Ultrasonic Inspection

Answer 17

1. a single search unit is working as a transmitting and a
   receiving transducer
2. electrical pulses activate the transducer element
3. the element converts electrical energy into mechanical energy
4. a waveform is generated in the test part and picked up by the
   transducer
5. any change in amplitude or time required for echo to return to
   transmitter indicates a defect

Question 18

Describe Ultrasonic Bondtester Inspection

Answer 18

1. low frequency and high frequency bondtesters are used
2. high frequency bondtester is used to detect delamination and
   voids
3. low frequency bondtester is used to detect delamination,
   voids, and skin to honeycomb core disbands
4. this method cannot detect defects smaller than 1.0 inch

Question 19

What types of defects in composite material can be seen using Radiography?

Answer 19

Internal anomalies, such as:
delaminations in the corners
crushed core
blown core
water in core cells
voids in foam adhesive joints
relative position of internal details

Question 20

Is high or low energy rays used when x-raying composite materials? Why?

Answer 20

Low energy rays must be used since most composites are nearly transparent to xrays

Question 21

Describe Thermography

Answer 21

1. comprises all methods in which heat-sensing devices are used to measure
   temperature variations for parts under inspection
2. the types of defects that affect the thermal properties include:
   debonds, cracks, impact damage, panel thinning, and water ingress into composite
   materials or honeycomb core
3. most effective for thin laminates or for defects near the surface

Question 22

Describe Neutron Radiography

Answer 22

1. capable of visualizing the internal characteristics of a sample
2. it is a complementary technique to X-ray radiography
3. the advantage of neutron radiography is its ability to reveal light elements
   such as hydrogen found in corrosion products and water

Question 23

Describe a Moisture Detector

Answer 23

1. used to detect water in sandwich honeycomb structures
2. measures radio frequency power loss caused by the presence of water
3. often used to detect moisture in nose radomes