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Wing attachment frames
Center Fuselage:
I/F with wing and MLG
Wing attachment frames
Matthijs Plokker / Derk Daverschot - ICAF 2009 20/05/2009 Page 9
© AIRBUS DEUTSCHLAND GMBH. All rights reserved. Confidential and proprietary document.
Problem description
• Problem description:
• Investigation showed that main frame under rear wing attachment is SLP
structure instead of MLP.
• Hence, frame had to be inspected on small cracks, instead of failed part.
Design criterium had to be stricter, resulting in low allowable DT-stresses
to ensure slow crack growth
• Design had to be improved => severe weight impact when concept of
integral frame would have been kept.
Rear wing attachment
Severe Wing Spectrum introduced in this
frame and surrounding structure.
Matthijs Plokker / Derk Daverschot - ICAF 2009 20/05/2009 Page 10
© AIRBUS DEUTSCHLAND GMBH. All rights reserved. Confidential and proprietary document.
Problem description
• Wing spectrum caused in frame inner flange below rear wing
attachment:
1. High Fatigue Stresses in inner flange
2. High tensional static loads
• Resulting in:
1. To meet inspection interval detecable crack length 1-2 mm
– Risk due to low probability of detection
2. Critical crack length is extremely small (enhanced by brittle alloy)
• Risk on Multiple Element Damage (MED) due to similar high stress level
in neighbouring frames
Matthijs Plokker / Derk Daverschot - ICAF 2009 20/05/2009 Page 11
© AIRBUS DEUTSCHLAND GMBH. All rights reserved. Confidential and proprietary document.
Concept study
• Study was carried out on improvement of the main frame looking at:
Safety (Inspectibility, DT-behaviour)
Weight
Cost
• 3 options were investigated:
1. Thickening of the aluminium inner flange to reach an acceptable stress
level.
2. Riveted Titanium strap attached to the inner flange.
3. FML strap adhesively bonded to the inner flange.
Matthijs Plokker / Derk Daverschot - ICAF 2009 20/05/2009 Page 12
© AIRBUS DEUTSCHLAND GMBH. All rights reserved. Confidential and proprietary document.
Concept study
• Coupon test program performed to investigate crack growth behaviour
of FML reinforced inner flange.
• The test results showed a constant crack growth rate for a wide range
of crack lengths. This is due to the „crack bridging“ effect.
With metal isotropic material an increasing crack growth rate will be
found for longer cracks.
At same stress level only FML
strap can meet the inspection
requirement.
Matthijs Plokker / Derk Daverschot - ICAF 2009 20/05/2009 Page 13
© AIRBUS DEUTSCHLAND GMBH. All rights reserved. Confidential and proprietary document.
Concept study - FML strap
Concept of FML Reinforcement:
The aim of the bonded FML-strap is to control both the fatigue
crack growth behaviour of the frame and the residual strength
capability of the hybrid design.
The FML strap will retard or stop any potential fatigue crack in the
frame.
Frame Inner Flange
FML Strap
„Crack Bridging“ effect analogue to GLARE
Cross-section
Matthijs Plokker / Derk Daverschot - ICAF 2009 20/05/2009 Page 14
© AIRBUS DEUTSCHLAND GMBH. All rights reserved. Confidential and proprietary document.
Concept study - Conclusions
Results of concept study:
• FML reinforcement was favourised:
Lowest weight
Meeting best all DT requirements. Static requirements were fulfilled as
well.
Relatively low costs per lost kg per A/C.
• Titanium reinforcement:
Heavier compared to FML strap solution
Could not satisfy with meeting all DT-requirements
• Integral frame:
Could not meet DT requirements with acceptable weight.
Matthijs Plokker / Derk Daverschot - ICAF 2009 20/05/2009 Page 15
© AIRBUS DEUTSCHLAND GMBH. All rights reserved. Confidential and proprietary document.
Concept study - Conclusions
Integral - -
Aluminium
FML Strap ++ ++
Titanium Strap + --
Effort to detect
cracks
Weight
opportunity
Option
Matthijs Plokker / Derk Daverschot - ICAF 2009 20/05/2009 Page 16
© AIRBUS DEUTSCHLAND GMBH. All rights reserved. Confidential and proprietary document.
Concept study - Conclusions
• In general the FML reinforcement bonded application is a solution for
structural parts that are highly loaded under tension.
Without FML-reinforcement this structural part would be a SLP or a
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