c@ ~~ H~ 1"/ THf-'ft5()16IJ48LLrro~.. Restri ted Circulation I r REPORT No: NML/MST/IAF/1.13/66/2005. September, 2005 ~ FAILURE INVESTIGATION OF ARK-19 SENSE ANTENNA OF MIG-29 AIRCRAFTKS-905. Sponsored by 223 Squadron Air Force C/O 56 APO Ii ~ ~,,~ Materials Science & Technology Division National Metallurgical Laboratory (Council of Scientific and Industrial Research) Jamshedpur - 831007 rr-!'~'I "'\" -- . tit 'I~ '\. \ -. . i 1':0 ~ l!\)~ 1:Jf).[I V ' . L D~H; .~ cJ'?f.' ". I '- -.-
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c@~~H~ 1"/THf-'ft5()16IJ48LLrro~..Restri ted Circulation I r
REPORT No: NML/MST/IAF/1.13/66/2005.
September, 2005
~
FAILURE INVESTIGATION OF ARK-19 SENSE ANTENNA OF
MIG-29 AIRCRAFTKS-905.
Sponsored by
223 SquadronAir Force
C/O 56 APO
Ii
~~,,~
Materials Science & Technology Division
National Metallurgical Laboratory
(Council of Scientific and Industrial Research)
Jamshedpur - 831007
rr-!'~'I "'\" --. tit 'I~ '\. \ -. .
i 1':0~ l!\)~ 1:Jf).[I V' .
L D~H; .~ cJ'?f.' ". I'- -.-
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)
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