30 Questions
What is the most frequently used inspection method in aviation?
Visual inspection
Why is it important to thoroughly inspect a damaged composite structure?
To determine if it is worth repairing
What helps in determining whether damage on a composite structure is repairable?
The classification of damage
Which document outlines inspection procedures, damage classification factors, and recommended repair methods?
Manufacturer's structural repair manual
What do composite structures require besides ongoing inspection intervals?
Non-scheduled damage inspection and testing
Why do many metal inspection and NDT methods transfer to composite applications?
Similar inspection principles and techniques
What is a useful tool for visual inspection to detect surface irregularities in composite materials?
Strong light and magnifying glass
Which type of defects can ultrasonic inspection detect in composite materials?
Internal damage like delaminations
What is the purpose of tap testing inspection in composites?
To check for good bond line and air pockets
In ultrasonic testing, which method involves generating ultrasonic pulses and receiving the return echo displayed on an oscilloscope?
Pulse echo method
What are some defects that visual inspection with a magnifying glass can help detect in composites?
Fibre break-out and blistering
Why is a tap testing tool used in composites inspection?
To identify the presence of air pockets or poor bond lines
What is impact damage?
Damage caused by improper handling or transportation
Why are sandwich panel face sheets very susceptible to impact damage?
Because they are made of thin material
What is delamination?
Separation of fabric layers in a laminate
What can accompany delamination, particularly when it occurs?
Impact damage
How does disbonding differ from delamination?
Disbonding is composite material separation from an adhesive bond
What are the causes of delamination?
Impact, moisture ingress, and lightning strikes
What can cause damage to the resin matrix of composite materials?
UV rays
Why is water intrusion a common problem with high-temperature repairs?
The heat causes trapped water to turn to steam and disbond face sheets
What issue can arise from holes drilled in the wrong location, size, or number in composite materials?
Hole damage
How does water intrusion impact honeycomb cores in aircraft structures?
It can lead to corrosion in aluminium honeycomb
Which factor contributes to the progression of converting a small area of damage into a larger one during repairs?
Trapped water turning to steam due to heat
What can lead to hole damage in composite materials?
Over-torqued fasteners or drilling holes in the wrong location
What is the most desirable type of permanent repair to a composite structure?
Laminating new repair plies in the damaged area
What is the purpose of potted repairs in composite structures?
To provide an alternative to core material plugs
In the damage assessment and repair process for composites, what is done after laying up and installing the repair?
Cleaning up the repair site
What is a disadvantage of filling a hole with a resin-and-filler mixture in composite repairs?
Decreases flexibility of the part
Why is it important to inspect the repair site for structural integrity after the repair procedure?
To verify that the repair has restored structural integrity
What technique is used to assess the extent of damage in composites during the repair process?
Using visual and NDI techniques
Study Notes
Impact Damage
- Occurs when a foreign object strikes a part, with degree of damage ranging from slight to severe
- Most common cause is careless handling during transportation or storage
- Thin face sheets on sandwich panels are susceptible to impact damage
- Impacted area should be inspected for delamination
Delamination
- Separation of fabric layers in a laminate
- Can occur with no visible indications from the outer skin
- Often accompanies other types of damage, particularly impact damage
- Causes include impact, moisture ingress, and lightning strikes
Disbonds
- Separation of composite material from another material to which it has been adhesively bonded
- Different from delamination, which refers to separation between plies or layers of the composite
Composite Inspection
- Requires ongoing inspection intervals and non-scheduled damage inspection and testing
- Methods include visual inspection, tap testing, and ultrasonic inspection
Visual Inspection
- Most frequently used inspection method in aviation
- Used to detect surface irregularities, resin-rich areas, and edge delamination
- Tools used include strong light and magnifying glass, and sometimes a small microscope
Tap Testing
- Effective way to discover if a finished job/repair has a good bond line or air pockets
- Uses a small tap testing tool
Ultrasonic Inspection
- Most common instrumental NDT method used on composites
- Detects internal damage such as delaminations, core crush, and subsurface defects
- Methods include pulse echo and through-transmission methods
Cracking and Resin Matrix Damage
- Caused by fire, excessive heat, UV rays, paint stripper, impacts, etc.
- Damage to resin matrix can lead to further damage and repair issues
Water and Aircraft Fluid Intrusion
- Especially problematic with honeycomb cores, causing weight gain, contamination, corrosion, and disbonds
- Water intrusion can occur during high-temperature repairs, leading to disbonds and damage expansion
Hole Damage
- Caused by impact damage, over-torqued fasteners, or fastener pullthrough
- Holes can be difficult to repair, and may require lamination of new repair plies in the damaged area
Composites Damage Assessment and Repair Process
- Basic steps include:
- Find the damage and clean the area
- Assess the extent of the damage using visual and NDI techniques
- Define the repair procedure
- Fabricate and install the repair
- Clean up and inspect the repair site for structural integrity
Potted Repairs
- Use a filler to complete the composite repair process
- Provide an alternative to installing a core material plug, but do not provide as much strength
- Filling a hole with a resin-and-filler mixture adds weight and decreases flexibility
Test your knowledge on composite inspection techniques and non-destructive testing (NDT) methods used for determining the airworthiness of structures, with a focus on composite applications and ongoing inspection intervals.
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