* ISO 9001 Dr. S. R. Singh Deputy Director MST Division ct.&o r National Metallurgical Laboratory (Council of Scientific & Industrial Research) Jamshedpur 831 007, India BY COURIER Ref.: NML/MST/EML/l82 15thApril, 2005 To: Sqll. Ldr. s. nnhunuru~nll DClmty Chief of Quality Assunance For Commanding Officcr 4BRD Air Forcc Stntion, Chakcri Kallpur-208008. Subiect: Failure Mode Analvsis/Metallure.ical Examination of Viper Aeroene.ine Jet . Pipe Bellow Assemblv Ex Aircraft U-719. . Report No.: NML/MST/IAF/1.13/58/2005. April 2005. Dear Sqn. Ldr. Balamurugan, Plense refer lo yom letter No.4 BlH)14552/1/DI/Tech.dilled Jill .IIIIIIIIII'Y 2005, regarding the above-referred investigation.The investigation is completed and linal report is enclosed herewith fo~your informationand necessaryaction at your end. The invoice of this investigation will be sent to AOC, Air Force Station, Tambram, Chennai, under intimation to you, shortly by our office. If you need any clarification, please do not hesitateto contact me. ------ Yours sincerely -::::.Q.<; <~ <=~ ~ J (S. R. Singh) /\ Enc!.: ReportNo. NML/MST/IAF/I.13/58/2005,April 2005. \~v Fax: (0657)2270527; Telephone: (0657)2270027 (0), (0657)2431556 (R). E-mail: srsingh(cl).nmlindia.org N"ML tyrc-k.t'~ -:2-dO S- ( (;) ~:>
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*ISO 9001
Dr. S. R. SinghDeputy DirectorMST Division
ct.&or
National Metallurgical Laboratory(Council of Scientific & Industrial Research)
Jamshedpur 831 007, India
BY COURIERRef.: NML/MST/EML/l82
15thApril, 2005
To:
Sqll. Ldr. s. nnhunuru~nllDClmty Chief of Quality AssunanceFor Commanding Officcr4BRDAir Forcc Stntion, ChakcriKallpur-208008.
Subiect: Failure Mode Analvsis/Metallure.ical Examination of Viper Aeroene.ine Jet. Pipe BellowAssemblv Ex Aircraft U-719. .
Report No.: NML/MST/IAF/1.13/58/2005. April 2005.
Dear Sqn. Ldr. Balamurugan,Plense refer lo yom letter No.4 BlH)14552/1/DI/Tech.dilled Jill .IIIIIIIIII'Y2005,
regarding the above-referred investigation.The investigation is completed and linal report isenclosedherewithfo~your informationand necessaryaction at your end.
The invoice of this investigationwill be sent to AOC, Air Force Station, Tambram,Chennai, under intimation to you, shortly by our office. If you need any clarification, pleasedo not hesitateto contact me.
Abstract: The viper aeroengine jet pipe bellow assembly ex aircrull U-719, failed owing to bellow burst.The objective of root cause failure analysis is to find out whether it is caused by either material itself or byexcessive stresses. Circumferential cracking is observed at number of locations on the component. Samplinghos bccn done lI'om the two such crackcd locations i. c onc Ihull corrugoted (austcnitic stainless stccl, type8309(0) and othcr from non-corrugalcd (austcnitic stainlcss stcel. typc S329(0) rcgion. The hardness value,optical and scanning electron microscopy exuminations rcvcal, that the crack initiation occurs byintergranular decohesion owing to overheating induced intergranular precipitation of brittle phases. Usuallyfatigue crack moves from the location of tensile to compressive type of stressed location i.e from outer toinner surface. In the present situation, crack initiates from inner surface and propagates toward outer surfaceand circumferential direction i.e from compression to tensile side by fatigue mechanism. During serviceexposure, perhaps due to sudden rise in temperature, at thl' inner surface compressive stress changes totensile stress. Absence of dimple rapture indicates fililure took place in the brittle mode, which is caused byoverheating during service exposure.
Details of IPRs (PI tick): NA If no IPR taken, reasons: N/\
Patent
CopyrightTrade Marks
Report Issuance Authority: Dr. S. R. Singh Signature: S.R. :--, . ',-
NATIONAL MET ALLU ItG ICAL LADOItA TO It\' ,JAMSII EDI'UItFAILUREMODEANALYSIS/METALLlJRGICALEXAMINATIONOF VIPER AEROENGINEJET PIPE BELLOW
vibration loading may promote Hltigue failure. Sudden rise in the stress value (over load) may
also result in failure, which takes place by micro-void coalescence (dimple rapture).
- EXPEIUMRNTAL RESULTS & DISCUSSIONS
From the failed component, two locations are chosen (marked by arrow in Fig.l) and
characterised. The location of failure is observed visually to find out its appearance and to
measure its dimension. The fracture surfaces are examined in secondary electron mode in
JEOL JSM 840A scanni'ng electron microscope equipped with Kevex energy dispersive
spectrometer to reveal the fracture mode. Metallography samples are prepared from the
thicknesssection as well as the surface section of the component.These samples are etched in
glycergia to reveal the microstructure and subsequently examined in optical microscope and
SEM for determining the phase dislrihillion and grain si:t.l'. Ilnnlm'ss of Ihl' IIInll'rinl is nisI!
lI1easureu in Vickers scale lIsing J0 Kgf load. The details of the investigation arc prcscnted in
the following subsections.
1. VISUAL EXAMINATION
The as received failed jet pipe bellow assembly is shown in Fig.l. Circumferential
cracking has been observed at number of locations. Besides the crack-I and 2, crack-3 is
found to be located 160mm and 180mm away from crack-2 and crack-I with the length of
140mm. On the opposite face of the component, one failed region has been found out (not
shown in figure) having the length of 160mm. Dent marks (length of dented region 300mm)
near crack (25mm length) are also observed. Out of the different cracked regions, considering
the symmetry of locations, two zones have been investigated(marked 1 and 2). Visually, the
fracture surfaces are darkened due to affect of heat. The cracked regions IA and IB of crack-I
have dull grainy appearance. The length of the crack-I is 210mm. At the middle of the
sample-I, the wall thickness is -0.48111111.which rcduccd to -0.24mll1 ncar fracturcd cnd. This
indicates a 50% reduction in thickness which may be caused by localiscJ nccking. For the---------
cracked regions 2A and 2B of crack-2, the fracture surfaces are folded with shinning
appearance. At the same crack-2 another crack formation takes place with the length of
28mm. Apparently, shinning appearance of these regions infer, that alter initial crack
formation owing to rubbing contact the features of failed region is lost. The crack length of
crack 2 is 41mm. The thicknessof this area remains uniform (-1.18mm) over the entire crack
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NATIONAL METALLtIIU;ICAL I,AUOI{ATOIW. .IAMSIIEIH'IJI{FAILUREMOUEANALYSIS/METALLURGICALEXAMINATIONOFVIPER AEROENGINEJET I'II'E BELLOW
ASSEMBLYEx AmCRAFT U-719REPORTNo. NMLlMST/IAF/1. I3/58/2005. April 2005
is formed near the opposite surface of crack-I and 2 having the length oflength. Crack-4
35mm.
'" "",..; ".. ,.,
Figs. I(a-f): Photographs of as-received component with different types of fractureLocation (FL) and sampling locations (SL): a) failed component, b) crack-I(sample -I), c) crack-3, d) crack-4, e) crack-2 and f) dent mark. Crack-I and 3 areon corrugated part while crack-2 and 4 arc on non-corrugated part or the component.
observed. No overload ZUlU; (Iilst li'Helurc 01' dililple rupturc) Oil thc liuellllc slllliH:e Is
observed because cracked ends are still connected.
Microvoid coalescence i.e dimple rapture is also found having shallow depth
indicating low ductility. This feature is perhaps not the outcome of service exposure rather
mechanicaltearing during handling i.e overload generatingan artefact. The fracture surface in
this region is not darkened becausc it is not cxposctlhcat source.
The cracking in non-corrugatcd region is also examinetl. The fracture surfaces of
samples 2A and 2B reveal the abrasion marks on its surface. This abrasion mark may be
formed allcr initial cracking Hndsubscqucnt rubbing contact. Thereforc, the original fracture
morphology is lost and nothing can be conc\udetl. Ilowever; in some localisctl region
intergranularcracking is also observed.The wide variation in hardness is observed at the two
locations i.e. 2A and 2B. At one end the low hardness indicates that the material is ductile
enough and on the other end high hardness value indicates low ductility. Inhomogeneity of
material is also responsible fix the failure. The rubbing marks rUIl more or less parallel to. ------
open edges of the sample along its longitudinal direction.
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NATIONAL METALLlmGICAL LAUOI{ATOIW,JAMSIIEUI'UI{FAILURE MOl>!<: ANAL.YSIS/METALLURGICAL EXAMINATION OF VII'EI~ AEltOEN(tlN.: JKI' I'IPE Ih:LLOW
ASS.:MnLYEx AmcRAFT U-719REPORTNo. NML/MST/IAF/I.13/58/2005. Avril 2005
"- -~"'
Figs. 7(a, b, c & d): SEM fractographs of sample 1A show~ng (a) intergranularfracture at the crack initiation site, (b) transgranular fracture imprinted with
fatigue striations (FS), (Q)fatigue crack initiation location and secondary crack(SC) and (d) beach marks (13M).
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NATIONAL METALLURG ICAL LABORATORY, JA MSIIIWI'U RFAILURE MODE ANALYSiS/METALLURGICAL EXAMINATION OF VIPER AEROENGINE JET PIPE BELLOW
ASSEMBLY Ex AIRCRAFT U-719REPORT No. NMLlMST/IAF/I.13/5H/2005. April 2005
~
----. ..
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Figs. 8(a & b): SEM fraclographs of sampic IB showing (a) fatiguc striations (FS) andsecondary cracks (SC), and (b) ductile dimple rupture.
Figs. 9: SEM fractographof fracture surfaceof sample 2A showing abrasion marks (AM).
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NATIONAL METAI.UJlWICAI, I.AIJOI{ATOnV, JAMSIIEIWlJl{FAILUREMODEANALYSIS/METALLllltGICALEXAMINATIONOFVIPElt AEROENGINEJET PIPE BELLOW