1、Nuclear Instruments and Methods in Physics Research A 542(2005)4551Classification of defects in honeycomb composite structure ofhelicopter rotor bladesM.Balasko a,?,E.Sva bb,Gy.Molna rc,I.VerescaKFKI Atomic Energy Research Institute,H-1525 Budapest,POB 49,HungarybResearch Institute for Solid State P
2、hysics and Optics,H-1525 Budapest,POB 49,HungarycAircraft Maintenance Branch of Hungarian Defence Forces,H-1885 Budapest,POB 25,HungaryAvailable online 2 February 2005AbstractThe use of non-destructive testing methods to qualify the state of rotor blades with respect to their expected flight hours,w
3、ith the aim to extend their lifetime without any risk of breakdown,is an important financial demand.In order to detectthe possible defects in the composite structure of Mi-8 and Mi-24 type helicopter rotor blades used by the HungarianArmy,we have performed combined neutron-and X-ray radiography meas
4、urements at the Budapest Research Reactor.Several types of defects were detected,analysed and typified.Among the most frequent and important defects observedwere cavities,holes and/or cracks in the sealing elements on the interface of the honeycomb structure and the sectionboarders.Inhomogeneities o
5、f the resin materials(resin-rich or starved areas)at the core-honeycomb surfaces proved to bean other important point.Defects were detected at the adhesive filling,and water percolation was visualized at the sealinginterfaces of the honeycomb sections.Corrosion effects,and metal inclusions have also
6、 been detected.r 2005 Elsevier B.V.All rights reserved.PACS:81.05.?t;81.40.NpKeywords:Neutron radiography;X-ray radiography;Rotor blade;Non-destructive testing;Honeycomb structure1.IntroductionThe lifetime extension of helicopter rotor bladeshas an essential importance because of their highvalue.In
7、the Hungarian Army,majority of thehelicopters are Russian-made Mi-8 and Mi-24types.Although their age is over several decades,the flight hours are below the allowed limit.Therefore,theuseofnon-destructivetestingmethods to qualify the state of rotor blades withrespect to their expected flight hours,w
8、ith the aimto extend their lifetime without any risk ofbreakdown,is an important financial demand.In the last 3 years we have undertaken acomplex non-destructive testing investigation todetectthepossibledefectsinthecompositeARTICLE IN PRESS front matter r 2005 Elsevier B.V.All rights reserved.doi:10
9、.1016/j.nima.2005.01.010?Corresponding author.Tel.:+3613922634;fax:+3613922589.E-mail address:balaskosunserv.kfki.hu(M.Balasko ).structure of helicopter rotor blades using com-bined neutron-and X-ray radiography(XR),andvibration diagnostics measurements at the Buda-pest Research Reactor 1.Here,we gi
10、ve a short description of our radio-graphy experimental work and some of the latestresults obtained on several Mi-24 type helicopterrotor blades.Terms used in Ref.2 for descriptionof defects in helicopter composite structures werefollowed.2.Experimental2.1.Investigated objectsThe investigated rotor
11、blades of Mi-24 typehelicopter are made of composite structures.Eachone contains 18 sections of honeycomb construc-tion and several bonded surfaces.The mostimportant parts of a rotor blade,from our pointof view,are marked in the schematic drawing inFig.1.The key part of the rotor blade comprisesthe
12、aluminum alloy metal main holder(spar)bonded to the honeycomb structure.The bladesare about 10m long,0.7m broad and their width isbetween 3 and 60mm.The weight is 110kg.For the radiography imaging each rotor bladewas divided into four bands horizontally(AD)and 53 columns vertically,as it is indicate
13、d inFig.1.A band gives information mainly on thestate of trailing edge and the backside stringer.Bband shows the state of the honeycomb structure.The quality of the bonded area at the aluminum-alloy spar is represented by C band.The D bandshows the state of the anti-ice heater and leading(front)edge
14、 of the rotor blade.These identifierswere used as markers for segmenting the rotorblades.The radiography image of the whole rotorbladewas reconstructedfrom 216 individualradiography images(146mm?140mm)using aspecial software package 3.2.2.Experimental facilityMeasurements were performed at the radio
15、-graphy station at the 10MW Research Reactor inBudapest using thermal neutrons 4,5.At thesample position the diameter of the beam was180mm,the neutron flux was 108ncm?2s?1.ForXR a portable X-ray generator was used,adjustedto 150kV and 3mA.Scintillation screens wereused for converting the beam into l
16、ight,and thelight images were detected by CCD camera.Three types of radiography measurements wereperformed for each blade.?In the first step neutron radiography(NR)wasapplied in the original state of the blades,calleddry NR.?In a next step the blade was watered on its entiresurface,with the aim to simulate the effect ofnatural moistening(rain),and was radiographedby neutrons once again(called wet NR).?In the third step XR measurement was per-formed in the wet state of the blade.?Fig.2 shows reco
