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REPORT No: NML/MST/IAF/1.13/66/2005.
September, 2005
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FAILURE INVESTIGATION OF ARK-19 SENSE ANTENNA OF
MIG-29 AIRCRAFTKS-905.
Sponsored by
223 SquadronAir Force
C/O 56 APO
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Materials Science & Technology Division
National Metallurgical Laboratory
(Council of Scientific and Industrial Research)
Jamshedpur - 831007
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NATIONAL METALLURGICAL LABORATORY, JAMSHEDPURFAILURE INVESTIGATION OF ARK-19 SENSE ANTENNA OFMIG-29 AIRCRAFT KS-905
Report No.: NML/MST/IAF/1.13/66/2005. September 2005. NATIONAL METALLURGICAL LABORATORY(Council of Scientific & Industrial Research)
JAMSHEDPUR
PROJECT COMPLETION REPORT
Project Title: FAILUREINVESTIGATIONOFARK-19 Project No.: TH p-"t ()D 9(,SENSEANTENNAOF MIG-29 AIRCRAFTKS-905.
Report No.: NML/MST/IAF/1.13/66/2005.
Date of Project Initiation: 02.09.2005
Date of Completion: 28.09.2005
Project Team Members: Class:Dr. G. Das (PL) Public document (Free/Priced)Dr. S.R.Singh (Co-PL) Restricted circulation (X)Mr. Swapan Das Only to client
Secret
Customer / Client's name and address: Classification:
Wg. Cdr. R. BhardwajIn-house
SEa Grant-in-aid
For CO Sponsored (X)
223 Sqn, AF ConsultancyC/O 56 APO Collaborative
Date of Report : 28.09.2005
Area: Material Characterisation. Specify Type:
Sub Area: Failure analysisOngoing Area: (X)New Area Initiated:
Key Words: Sense antenna, aluminium alloy, surface anodising, fatigue failure, beach marks, fatiguestriations, foreign particle impact.
Abstract: The Sense Antenna is made of heat resistant duralumin closely similar to alloy AA 2618. Themicrostructural investigation revealed that its strength is derived from distribution of fineprecipitates of CuMgAh and dispersed particles of Al9FeNi phase which resist coalescence athigher operating temperature up to 300°C. Moreover, the measured hardness of 129 HB isconsistent with the observed microstructure as well as the hardness of the alloy AA 2618. Thelongitudinal surface of the antenna is hardened/protected by anodizing process. The weathering ofthe anodic coating involves uniform erosion of coating by wind-bone solid particles. The erosionmanifested by longitudinal abrasion marks do not seem to breach the protective anodizing coating.However, the non-gliding impacts of larger particles have been observed on the surface. The crackinitiation, leading to fracture, is found to be due to one such impact. Embedded silicon containingforeign particles have been observed near the impact site. The transverse fracture surface is flatand decorated with concentric beach marks centered around a crack initiation site. Fractographicexamination revealed fatigue striations throughout the fatigue zone which extended up to 90% ofthe fracture surface while rest of the fracture surface is separated by overload induced ductiledimple rupture. The crack initiation site on the longitudinal surface is imprinted with a dentdeformation. All these observation indicated that the fracture is due to fatigue and the fatiguecrack is initiated by impact of air borne particle of size larger than 1 mIll, on its surface.
Details of IPRs (PI tick): NA If no IPR taken, reasons: NAPatentCopyrightTrade Marks
Report Issuance Authority: Dr. S. R. Singh Signature: r<<;'.R- .
NATIONAL METALLURGICAL LABORATORY, JAMSHEDPURFAILURE INVESTIGATION OF ARK-19 SENSE ANTENNA OF MIG-29 AIRCRAFT KS-905
Report No.: NML/MST/IAF/1.13/66/2005. September 2005
BACKGROUND
There was a flying incident of Mig-29 aircraft KS-905 of 223 squadron at 8 FBSU on
6th July 2005. The incident involved fracturing of ARK-19 Sense Antenna (hereafter, it will
be mentioned as antenna) which is made of metallic material. As the technical investigation
by IAF remains inconclusive, therefore, one of the retrieved fracture pieces of the antenna
was brought to NML on 02/09/05, for detailed investigation to find out the root cause of the
failure. The investigation is assigned to NML vide letter No. 223S/S 51l/lIEng, dated 2ih
August 2005, from 223 Sqn, AF.
SCOPE OF WORK
Based on the information on incident scenario, it was decided to do the following.
1.
2.
3.
Visual examination, photography, macrophotography and dimensional measurements.
Fractographic analysis of fracture surfaces to find out the fracture mode/mechanism.
4.
5.
Microstructural and hardness analysis to find out unusual features, if any.
EDS microanalysis of material.
SEM surface studies of the longitudinal surface of the antenna to find out mechanism
6.
of surface degradation/damage.
To find out the root cause of failure.
EXPERIMENTAL RESULTS
1. Visual examination, photography, macro photography and dimensional
measurements:
The photograph of fractured piece consisting of assembled cut pieces of sense antenna
is shown in Fig. 1a. It has failed at a height of 36.79 mm at thicker edge and 54 mm at thinner
edge from the root (Fig.la). It is aerodynamically designed with leading (thin) and trailing
(thick) edges. The fracture surface has maximum width of 14 mm and the length between
leading & trailing edges is 45 mm (Fig. lc). The fracture occurred in transverse section of the
antenna and the fracture surface is flat. The longitudinal surface has smooth shiny finish. Few
dark grooves on the longitudinal surface of the antenna (marked on the surface of the Figs.
Ia,b) have been observed, that may be formed due to gliding impact of wind-borne particles.
One of the grooves near to the fracture initiation point (marked in the Fig. 1d) is very
prominent. Probably the fracture initiated from the mechanically damaged surface region and
further crack propagation on fracture plane occurred due to fatigue. The macroscopic view of
2
NATIONAL METALLURGICAL LABORATORY, JAMSHEDPURFAILURE INVESTIGATION OF ARK-19 SENSE ANTENNA OFMIG-29 AIRCRAFT KS-905
Report No.: NML/MST/IAF/1.13/66/2005. September 2005
fracture surface (Figs. l(c & d) clearly reveals the .signature of the fatigue failure, i.e.,
radiating marks at crack initiation site, concentric beach marks covering most of the fracture
surface and dull fast fracture zone at the opposite end of the crack initiation site. These
manifestations of fatigue failure have to be further substantiated by SEM fractographic
analysis. The beach marked fatigue zone covers nearly 90% of fracture surface. While rest of
the dull region is overload induced fast fracture zone. Therefore, material seems to have
sufficient strength and toughness.
2. Fractographic analysis of fracture surfaces to find out the fracture
mode/mechanism.
SEM fractographs of the fracture surface are shown in the Figs. 2(a & b). Low
magnification SEM fractograph (Fig. 2a) shows beach marks superimposed on transgranular
fracture surface whereas fatigue striations are observed in between beach marks at higher
magnification, shown in the Fig. 2b. It has been noticed that the spacing of fatigue striations
are not uniform throughout the fracture surface, indicating that the cyclic stress imposed on
the antenna is of irregular nature. The irregular cyclic stress may be arised due to random
nature of atmospheric wind presslire. The fatigue fracture initiation site (marked by arrow) is
shown in the Fig. 3a. This is more clearly visible in macrophotographs, shown in Figs. ~(c &
d). These observations clearly indicate that the fracture took place due to fatigue mechanism.
No traces of corrosive agents are found. Therefore, the possibilities of stress corrosion
cracking and corrosion fatigue are ruled out.
Longitudinal surface of the fractured end is also examined in SEM to reveal the
origin/nature of fatigue crack initiation site. A low magnification SEM surface micrograph
(Fig. 3b) shows impact induced cracked and deformed zone at the crack initiation site. The
length of the cracked zone is about 1 mm. This might have been induced by impact of air-
borne foreign particles of size larger than 1 mm. Moreover, abrasive wear tracks oriented
along longitudinal direction (along length of the antenna) have also been observed to form
because of abrasion by finer air-borne particles. The abrasion do not breached the surface
protective anodized layer of the antenna. A higher magnification surface micrograph (Fig. 3c)
shows impact induced flattened region at the intersection edge of longitudinal surface and
fracture surface. Few Si containing embedded particles (bright contrast) have also been
observed in the deformed zone. All the observations clearly indicated that the fatigue crack is
3
NATIONAL METALLURGICAL LABORATORY, JAMSHEDPURFAILURE INVESTIGATION OF ARK-19 SENSE ANTENNA OFMIG-29 AIRCRAFT KS-905
Report No.: NML/MST/IAF/1.13/66/2005. September 2005
initiated by the impact of air-borne foreign partic1e~. The impact site appeared as dark
patches/spots in the micrographs (Fig. 1).
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Figure 1: (a) Assembled cut pieces of the broken sense antenna, (b) side view of the fractured
portion, (c) macrograph of the fracture surface showing concentric beach marks,
and (d) crack initiation site (marked by arrow).
4
NATIONAL METALLURGICAL LABORATORY, JAMSHEDPURFAILURE INVESTIGATIONOF ARK-19 SENSEANTENNAOFMIG-29 AIRCRAFTKS-905
Report No.: NML/MST/IAF/1.13/66/2005. September 2005
Figure 2: SEM fractographs of the fractured piece showing the (a) lower magnification view
of beach marks, and (b) fatigue striations confirming the fatigue failure of the sense
antenna.
5
NATIONAL METALLURGICAL LABORATORY, JAMSHEDPURFAILURE INVESTIGATION OF ARK-19 SENSE ANTENNA OF MIG-29 AIRCRAFT KS-905
Report No.: NML/MST/IAF/1.13/6612005. September 2005
Figure 3: (a) Low magnification SEM fractograph showing the fatigue crack initiation site
marked by arrow, (b) dent marks near the fracture initiation point and (c) bright
embedded particles near impact site.
6
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NATIONAL METALLURGICAL LABORATORY, JAMSHEDPURFAILURE INVESTIGATIONOF ARK-19 SENSEANTENNAOF MIG-29 AIRCRAFTKS-905
Report No.: NML/MST/IAF/1.13/66/2005. September 2005
Figure 4(a & b): SEM micrographs showing the coarse elongated particles and fineprecipitates.
3. Microstructural Studies, EDS Microanalysis & Hardness Evaluation:
The transverse metallography section is prepared and etched in 0.5% HF solution to
reveal the microstructural constituents in the alloy. The lower and higher magnification SEM
micrographs are shown in Figs. 4a & b respectively. It shows dispersion of coarse elongated
particles and fine precipitates. EDS microanalysis of these phases indicated that they are
A19FeNi(Fig. 5a) and CuMgAh (Fig. 5b) respectively. The EDS microanalysis from the bulk
alloy is shown in Fig. 6. The quantified chemical analyses of all the three EDS spectra are
presented in Table 1-3. The bulk composition is closely similar to heat resistant dura1umin
(aluminium alloy) AA 2618. No unusual microstructural features have been detected. The
measured Brinne1 hardness (BHN) of the material is 129 HB which is above the required
minimum of 115 HB for the alloy AA 2168 in T61 temper condition. Therefore, the material
has desired microstructure and mechanical properties.
7
NATIONAL METALLURGICAL LABORATORY, JAMSHEDPURFAILUREINVESTIGATIONOFARK-19 SENSEANfENNAOF MIG-29 AIRCRAFTKS-905
Report No.: NMLIMSTIIAF/l.13/66/2005. September 2005
Fe~ NIK..Fe~ NIK~ _keY
10
Figure 5a: EDS spectrum of elongated particles of Al9FeNi.
Table 1: Elemental composition of the phase AI9FeNi.
Cu~NIKa.
K ~!I.1q! keV10
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5000
4000
IK"
3000
2000
1000NILNIL..
0 l:t I
0
2500Mg
2000
IK"1500
1000
500CullCuLoNILNI!-
0 u0
Figure 5b: EDS spectrum of finer precipitates of CuMgAl2 phase.
Table 2: Elemental composition of the phase CuMgAh.
Ka 35.5 1.2999 0.0102 0.0078 1.44 2.14 1.8602 0.00 0.00Ka 1506.7 8.4705 0.4432 0.3377 52.77 70.55 1.5626 0.00 0.00Ka 11.2 0.7305 0.0035 0.0027 0.49 0.63 1.8390 0.00 0.00Ka 102.8 2.2126 0.2544 0.1938 20.53 12.61 1.0593 0.00 0.00Ka 89.8 2.0684 0.2888 0.2200 24.77 14.06 1.1257 0.00 0.00
1.0000 0.7620 100.00 100.00 0.00 0.00
NATIONAL METALLURGICAL LABORATORY, JAMSHEDPURFAILURE INVESTIGATIONOF ARK-19 SENSEANTENNAOF MIG-29 AIRCRAFTKS-905
Report No.: NML/MST/IAF/1.13/66J2005. September 2005
1000
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AIKa
Mg
iKa
Cul~CulaNil ~Nil a
Fel~Fela
Til ~Til a keY
CONCLUSIONS
The Sense Antenna is made of heat resistant dura1umin closely similar to alloy AA
2618. The microstructural investigation revealed that its strength is derived from
distribution of fine precipitates of CuMgAlz and dispersed particles of A19FeNi
phase which resist coalescence at higher operating temperature up to 300°C.
Moreover, the measured hardness of 129 HB is consistent with the observed
microstructure as well as the hardness of the alloy AA 2618.
1.
9
Figure 6: EDS spectrum of the bulk material.
Table 3: Elemental composition of the bulk alloy.u -- .
29.8 0.5463 0.0211 0.0189 2.08 2.40 1.1004 0.00 0.001246.6 3.5308 0.9029 0.8085 89.79 93.63 1.1110 0.00 0.002.7 0.1629 0.0020 0.0018 0.36 0.36 1.9819 0.00 0.000.7 0.0808 0.0013 0.0012 0.14 0.08 1.1665 0.00 0.003.2 0.1792 0.0125 0.0112 1.27 0.64 1.1324 0.00 0.003.1 0.1761 0.0189 0.0169 1.92 0.92 1.1362 0.00 0.005.2 0.2285 0.0413 0.0370 4.44 1.97 1.2006 0.00 0.00
1.0000 .0.8955 100.00 100.00 0.00 0.00
NATIONAL METALLURGICAL LABORATORY, JAMSHEDPURFAILURE INVESTIGATIONOF ARK-19 SENSEANTENNAOFMIG-29 AIRCRAFTKS-905
Report No.: NML/MST/IAF/1.13/66/2005. September 2005
2. The longitudinal surface of the antenna is hardened/protected by anodizing process.
The weathering of the anodic coating involves uniform erosion of coating by wind-
bone solid particles. The erosion manifested by longitudinal abrasion marks do not
seem to breach the protective anodizing coating. However, the non-gliding impacts~-
of larger particles have been observed on the surface. The crack initiation, leading
to fracture, is found to be due to one such impact. Embedded silicon containing
foreign particles have been observed near the impact site.
3. The transverse ftacture surface is flat and decorated with concentric beach marks
centered around a crack initiation site. Fractographic examination revealed fatigue
striations throughout the fatigue zone which extended up to 90% of the fracture
surface while rest of the ftacture surface is separated by overload induced ductile
dimple rupture. The crack initiation site on the longitudinal surface is imprinted
with a dent deformation. All these observation indicated that the ftacture is due to
fatigue and the fatigue crack is initiated by impact of air borne particle of size
larger than 1 mm, on its surface.
RECOMMENDATIONS
A ftequent inspection of sense antenna for the presence of dark spots/patches is required.
If it is observed, the surface has to be refurbished to avoid recurrence of such type of
failure.
10
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