Damage Tolerance Methodology - ESAC - Ref. X029PR0608046 - Issue 1 Damage Tolerance Methodology Chicago, IL Prepared by Emilie MORTEAU, Chantal FUALDES Presented by Chantal FUALDES Airbus Head of Composite stress analysis Composite Senior Expert FAA Workshop for Composite Damage Tolerance and Maintenance July 19-21, 2006 Composites @ Airbus
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FAA Workshop for Composite Damage Tolerance and ... Composites... · Airbus Head of Composite ... FAA Workshop for Composite Damage Tolerance and Maintenance July 19-21, 2006 ...
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4For Airbus composite parts (CWB, Keel Beam, aileron, spoiler, HTP, VTP, LGD, etc)
relevant impacts for DT analysis are from maintenance i.e. tool drop, removable panel drop, and in a smaller extent from operation by runway debris (LGD), 4Shape of damage can be simulated by low impactor diameter (diameter
generally used for composite test and DT substantiation is from 6 to 25mm), and 4Resulting damages have similar diameter, mainly the dent depth (and crack length for edges), and depend on the impact energy
For transverse impact, the damage metric used for detectability is the
dent depth
For edge impact, the damage metric used for detectability is the dent
depth and/or cracks length
Has to be revisited for composite fuselage application for consistency
with impact sources (ground handling)Damage metric
The minimum impact damage surely detectable by scheduled inspection
4Dent depth criterion as a damage metric is widely used for composites. (It is acceptable to use additional criteria (not just dent depth) when establishing the limit of detectability, if this is justified by appropriate testing)4It corresponds to a probability of detection of 90% with an interval of confidence of 95%.4It provides a reasonable level of robustness for the structure design
–the aim is to sustain UL with BVID
Two values for the BVID criterion are established dependent on the visual inspection type : DET and GVI
DET Inspection§Detection of damages on different composite panels (size: from 100*100mm to 0.8m², painted or not, glossy or mat,white, grey, blue or green paint, primer) §Duration of inspection : not limited§Distance of inspection : 50 cm§Lighting condition : available lighting+grazing light (if required)§Several impactor diameter : 6mm and 16mm§A total of 902 inspections
GVI Inspection§Inspection on large panel (8m*1.2 m)§Two configurations : horizontal or vertical panels§Distance of inspection : 1m§Duration of inspection : 30sec/panel§Artificial lighting representative of Natural daylight§Several impacts on painted panel: from 0.3mm deep to perforation§Several impactor diameter : from 6 to 120mm§A total of 240 inspections
FOR BVID TRANSVERSE IMPACT
Supporting tests and analysis and in-service survey
85% of collected impact damages (dent) (around 1000 damage records) detected through GVI inspection (A, C check, daily, weekly, etc) are below Airbus established detectability threshold
Airbus BVID(GVI) is consistent with Airline survey findings
Survey in European airlineCumulative curve of dent depth
The relaxation is the phenomenon that leads to damages that become less detectable over time: a damage being detectable at time of impact, can become undetectable after an interval of inspection due to mechanical, thermal cycling, wet and ambient ageing and temperature.
Material A
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After impact After 20 mn After 48H After WA Beforefatigue
After110cycles
0,6Fr
After fatigue
Event
Den
t dep
th e
volu
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(mm
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18J impact+WA70/95%HR1500h and fatigue (r=10c/c) at 20°
18J impact+WA70/95%HR1500h and fatigue (r=10c/c) at -40°
18J impact+WA70/95%HR1500h and fatigue (r=-1 t/c)at 20°
20J impact+WA70/95%HR1500h and fatigue (r=10c/c) at 20°
20J impact+WA70/95%HR1500h and fatigue (r=10c/c) at -40°20J impact+WA70/95%HR1500h and fatigue (r=-1 t/c)at 20°
23J impact+WA70/95%HR1500h and fatigue (r=10c/c) at 20°
23J impact+WA70/95%HR1500h and fatigue (r=10c/c) at -40°23J impact+WA70/95%HR1500h and fatigue (r=-1 t/c)at 20°
Influent parameters were studied, the wet ageing until saturation covers all environmental and mechanical effects during the aircraft life.For tests, impact inflicted to the structure takes into account the relaxation of the dent under environmental conditions.
The impact threat is the mathematical description of impact severities associated to their probability of occurrence. It is supported by extensive survey of in-service incidents.
4A survey on wing impact damage, covering the whole Airbus types, totalling 18,740,000 flight hours and 9,800,000 flight cycles4A similar survey extended the data to the fuselage, covering A320 family, totalling 1,140,000 flight hours 4A similar survey covering the whole aircraft covering A320 family, totalling 500,000 flight hours4And another source of data was a survey, totalling 10,330,000 flight hours
Extensive survey available from which the current impact threat is derived.
Impact threat parameters have a solid foundation, new in-service data, additional applications (A380 for example) and associated in-service history should lead to future updates with a more complete understanding of damage threats.
• Large Damage Capability, LDC: not realistic damage
Design precautions to protect against the unknown.
• Design precautions
4 Fail Safe demonstration on main joint areas: hinged structures, high load introduction (disconnection of one load path) …
4 In addition, for each typical technology / design, arbitrary typical damages are assumed for LDC assessment, such as: – Stringer disbond analysis for co-bonded technology – Missing fasteners at load introduction area– Large hole in typical area
• Hailstorms data is based on meteorological survey defining:
4 Size of hailstones :– Standard hailstorm, (Dia 10mm) for a P of 50% of hailstorms– Rare hailstorm, (Dia 25mm) for a P of 5% of hailstorms– Extremely rare hailstorm, (Dia 50mm) for a P of 0.1% of hailstorms.
4 Concentration per unit area: number of hailstones impacting a surface based on the size of the storm.
4 Velocities for the energy of hails impact on ground and flight conditions.
• Structure Damage tolerance approach, 2 points are considered:
4 Unloaded Structure, hail on ground for commercial aspect– Showers of Dia 10 and 50 mm ( 33m/s; 32 Joules)
4 Loaded structure, hail in flight considered in damage tolerance analysis (Energy, loading, risk analysis)– Tests determine the structure behaviour
Means of compliance AMC25-6034 § 6.2.1 Structural details, elements, and subcomponents of critical structural
areas should be tested under repeated loads to define the sensitivity of the structure to damage growth. This testing can form the basis for validating a no-growth approach to the damage tolerance requirements.[…]
4 § 6.2.3 …The evaluation should demonstrate that the residual strength of the structure is equal to or greater than the strength required for the specified design loads… For the no-growth concept, residual strength testing should be performed after repeated load cycling.
Tests performed for compliance4 No initiation of damages checked defining good design practices4 Critical Non detectable damage/defects under repeated loads
during one DSG4 Critical detectable damage under repeated loads during at least one
interval of inspection4 A residual test after cycling to validate required design loads
The damage tolerance method4 Dent depth versus impact energy4 Damage size versus impact energy4 Residual strength versus damage size4 Failure criterion
Relies on coupons&detail tests of the test pyramidAnd is enhanced at higher level of the test pyramid
Parameters accounted for4 Material differences4 Laminate thickness4 Lay-up and stacking sequence4 Hot/wet4 Support condition for impact4 Net section for residual4 Scatter (B-value)4 etc
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