Investigating FOD Damage Part 3 Denver FOD Conference

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Investigating FOD DamagePart 3 Denver FOD
Conference
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Example 1 DC-10 2

• Vibrations in 2 engine during take-off
• Take-off aborted
• Engine pulled for fan blade damage

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Example 1 DC-10 2
Good place to sample
Circular symmetry
Apparent thread marks
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Example 1 DC-10 2
LE fan blade damage
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Example 1 DC-10 2 Analysis

• Power setting was high (takeoff)
• Impacts resulted in blade tearing and loss of
  blade material
• Most impacts occurred to the LE concave surface
  (Indicates the impacting object entered through
  the intake)

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Example 1 DC-10 2 Analysis

• There is circular damage symmetry
• There is rectangular damage symmetry
• There are apparent thread marks
• Blades are made of titanium

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Example 1 Analysis
FAST samples reveal nickel - chrome plated steel
tool material
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Example 1 DC-10 2 Conclusion
Source of thread marks
A nickel - chrome plated crescent wrench accounts
for the damage
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Example 2 Blade fracture in HPC

• Engine removed for compressor blade damage.
• One HPC-1 blade suffered loss of material
• Numerous other blades suffered impact damage
• Borescope inspection revealed no damage to fan or
  fan booster.
• Compressor had been completely restored during
  375 hours prior to this event.

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Example 2 Blade fracture in HPC

• Many blades revealed TE section scratches/dents
  on concave surface
• Typical when an object becomes stuck on a vane
  aft of blade
• As blade rotates, it makes contact with the
  object
• FAST samples revealed that stuck object was
  liberated blade material

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Example 2 Blade fracture in HPC

• Several IGVs show TE impacts
• FAST samples confirmed impacts due to missing
  section from broken HPC-1 blade

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Example 2 Blade fracture in HPC

• HPC-2 blade shows a LE impact to the concave
  surface
• Not expected shape from liberated airfoil section
  of broken HPC-1 blade

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Example 2 Blade fracture in HPC

• Macro photo of blade shows
• LE impact to concave surface
• Fatigue zone
• Fast fracture zone

Fatigue zone
LE concave surface impact
Fast fracture
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Example 2 Blade fracture in HPC
20X SEM photo showing LE impact deformation to
concave surface
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Example 2 Blade fracture in HPC
1000X SEM photo showing fatigue striations in
fatigue crack growth zone aft of impact
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Example 2 Blade fracture in HPC
500X SEM photo showing ductile dimples at tip
fast fracture zone
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Example 2 Blade fracture in HPC
300 stainless steel found in fractured blade LE
impact.
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Example 2 Blade fracture in HPC
300 stainless steel was also found in HPC-2 LE
impact.
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Example 2 CONCLUSIONS

• Engine suffered impact from aircraft 300 series
  stainless steel fastener hardware
• Impact occurred many engine cycles prior to blade
  breakage
• Impact created a stress concentration from which
  a fatigue crack began to grow
• Blade broke when remaining blade material holding
  blade together could no longer sustain normal
  engine load

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Example 3 Blade Failure on Takeoff
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Example 3 Blade Failure On Takeoff

• Flight crew heard loud bang and noticed vibration
  on 2 engine during takeoff roll
• Takeoff was aborted
• While taxing off the runway and back to gate,
  another aircraft reported seeing smoke and flames
  coming from the 2 engine (aft fuselage mounted)
• Engine was shut down

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Example 3 Investigation
There was no LE impact damage to the inlet struts
One inlet strut showed TE damage
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Example 3 Investigation
A number of blades show circular shaped impacts,
which are not the shape of the blade edges
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Example 3 Investigation
Blade fracture convex surface
Blade fracture concave surface
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Example 3 Investigation
Macro fracture features indicate instantaneous
overload
500X SEM photo confirms
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Example 3 Investigation
Fractured blade shows a LE concave surface impact
deformation
FAST sample from LE reveals aluminum as foreign
debris
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Example 3 Conclusions

• Engine ingested an aluminum object, the size and
  shape suggests a flash light
• Power setting was high (takeoff)
• Blades broke instantaneously
• Taxiing with engine running resulted in more
  damage

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Example 4 HPC-10 Blade Failure
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Example 4 HPC-10 Blade Failure
LE impact to concave surface of HPC-1 blade
HPC-1 through HPC-9 damage included small
cylindrical and circular dents and nicks
Damage aft of HPC-10 was heavy
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Example 4 Investigation
TE fast fracture
Fatigue
LE impact
Beach marks
HPC-10 blade fracture with appropriate areas
labeled
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Example 4 Investigation
300 series stainless steel found as foreign
debris on HPC-10 LE impact
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Example 4 Investigation
300 series stainless steel found as foreign
debris on HPC-1 HPC-2 impacts
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Example 4 Investigation
300 series stainless steel safety wire accounts
for the physical damage
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Example 4 Conclusion

• Engine suffered impact by aircraft safety wire
• LE impact to HPC-10 blade created a stress
  concentration from which a fatigue crack began to
  grow
• Blade broke when crack grew to approximately 70
  across the chord width
• Impact by safety wire occurred many engine cycles
  prior to blade breakage