Thermoplastic material inspection/types of defects Flashcards
List some manufacturing defects found in thermoplastic materials
- delamination
- resin starved area
- resin rich areas
- blisters, air bubbles
- wrinkles
- voids
- thermal decomposition
List some of the sources of manufacturing defects found in thermoplastic materials
- improper cure or processing
- improper machining
- mishandling
- improper drilling
- tool drops
- contamination
- improper sanding
- substandard material
- inadequate tooling
- mislocation of holes or details
Describe fiber breakage
- can be critical as structures are typically designed to be fiber dominant
- typically limited to a zone near the point of impact / contained by the impact object size and energy
Describe Matrix Imperfections
- usually occur on the matrix-fiber interface or int he matrix
parallel to the fibers - can slightly reduce material properties, but seldom critical to
the structure - may develop into delaminations, which are more critical
Describe Delamination and Debonds
- Delaminations form on the interface between the layers in the
laminate - Delaminations may form from matrix cracks that grow into
the interlaminar layer - Debonds can also form from production nonadhesion along
the bondline between two elements and initiate delamination
in adjacent layers
List the criteria for determining how critical delamination or debonds are
- dimensions
- number of delaminations at a given location
- location - in the thickness of laminate, in the structure,
proximity to free edges,
stress concentration region, geometrical discontinues, etc - load - behavior of delaminations and debonds depond on
loading type
List some in service defects on thermoplastic materials
- environmental degradation
- impact damage
- fatigue
- cracks from local overload
- debonding
- delamination
- fiber fracturing
- erosion
How do you inspect composites?
Nondestructive Inspection of Composites (NDI)
using flashlights, magnifying glasses, mirrors, and borescopes
What types of composite damage can be seen visually?
resin starvation
resin richness
wrinkles
ply bridging
discoloration
impact damage
foreign matter
blisters
debonding
What are some damages that can be seen visually when inspecting composite materials?
delamination
disbonds
matrix crazing
List some of the NDI inspection techniques used to inspect composite material
- Audible Sonic Testing (Coin Tapping)
- Automated Tap Test
- Ultrasonic Inspection
- Through Transmission Ultrasonic Inspection
- Pulse Echo Ultrasonic Inspection
- Ultrasonic Bondtester Inspection
- Phased Array Inspection
- Radiography
- Thermography
- Neutron Radiography
- Moisture Detector
Describe Audible Sonic Testing (Coin Tapping)
- most common technique used for the detection of
delamination and/or disbond - a clear, sharp ringing sound indicates a well bonded structure/
a dull thud indicates a discrepant area - not reliable on structures with more than 4 plies
Describe Automated Tap Test
- similar to the manual tap test, but uses a solenoid instead of a hammer
Describe Ultrasonic Testing
- useful for the detection of internal delaminations, voids, or inconsistencies in composite components not found with visual or tap methods
- there are many different types of ultrasonic techniques for testing
- all techniques use sound wave energy
What are the 4 most common ultrasonic techniques?
- Through Transmission Ultrasonic Inspection
- Pulse Echo Ultrasonic Inspection
- Ultrasonic Bondtester Inspection
- Phased Array Inspection
Describe Through Transmission Ultrasonic Inspection
- uses 2 transducers, one on each side of the area to be inspected
- ultrasonic signal transmitted from one transducer to the other
- loss of signal strength is measure by the instrument
- instrument shows loss as a percent of the original strength / loss in decibels
- Areas with a greater loss than the reference standard indicates a defective area
Describe Pulse Echo Ultrasonic Inspection
- a single search unit is working as a transmitting and a
receiving transducer - electrical pulses activate the transducer element
- the element converts electrical energy into mechanical energy
- a waveform is generated in the test part and picked up by the
transducer - any change in amplitude or time required for echo to return to
transmitter indicates a defect
Describe Ultrasonic Bondtester Inspection
- low frequency and high frequency bondtesters are used
- high frequency bondtester is used to detect delamination and
voids - low frequency bondtester is used to detect delamination,
voids, and skin to honeycomb core disbands - this method cannot detect defects smaller than 1.0 inch
What types of defects in composite material can be seen using Radiography?
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
Is high or low energy rays used when x-raying composite materials? Why?
Low energy rays must be used since most composites are nearly transparent to xrays
Describe Thermography
- comprises all methods in which heat-sensing devices are used to measure
temperature variations for parts under inspection - 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 - most effective for thin laminates or for defects near the surface
Describe Neutron Radiography
- capable of visualizing the internal characteristics of a sample
- it is a complementary technique to X-ray radiography
- the advantage of neutron radiography is its ability to reveal light elements
such as hydrogen found in corrosion products and water
Describe a Moisture Detector
- used to detect water in sandwich honeycomb structures
- measures radio frequency power loss caused by the presence of water
- often used to detect moisture in nose radomes
