Repair Efkctiveness Studies on Impact Damaged Sandwich Colnposite Corlstructions

&I. RAJU, C. RAJASEKHAR REDDY, M, R. NARASIMFIA SWAMY AND G. GIRIDHAR BIWS College of Engirzecrirzg, 3alzgnlo1-e

L. SRIKANTI~. M. RAJENDRA PRAKASH AND R. M. V. G. K. RAO* '-, ... .\ ,!

Fibr-e RL-'irfui'~ed Pla~tics Dil~isfot Ncrtio17cd A uospcrce Lobortrtur-ies ( N A L)

Bn,lgt~iol-~-'-560 11 17, Ijldin

ABS'I'RACT: Experirnentnl srudies were carried out using sandwich conlposite panel speci~nens, consisting of both polyureth~lne Foam core (PUF) and uramid honeycon~b cure. (Nomex) type cnnst ructions. These speci~nens were s11 bjecred to impact damage a t energy levels r;lngiilg be tween 7.56 and 15.6J. A ply-drop-patching \cchnitlue t v ; ~ el-nployed to rep;~ir the il-tlpact d : t~~~agcc l sandwich specimens. The undamaged (virgin), irllpact damaged, and I-epuired specimens were then subjected to flrsul-a1 ( four point bending) and edgewise conipression tests and st]-ength rccovcties were measured to determine the eiFic;tcy of [he repnir technique employed. Tn Jlesure. stl-engtll rccovcsies of L I pto 97'% in P UF core and 90% in Iloneycojnb core sa udwicl~ speei~nens were re:\lizcd after repair. whcl-eas in colnpression. the corsespo~iding v;ilucs were upto 9O'% in PUF core :lnd 88% in honeycomb core sandwich speci~nens. A repair ef'fectiveness f i~c to r ( R e f ) has been conceived nnJ introduced to quantify the: efficiency of the repair technique. Further, the repair quality WLIS : ) S S L ' S S ~ ~

using u siinple NDT method prior to subjecting the sandwich specilnens for destructive tests. , I .. I _

KEY WORDS: silndwich, impact damage, composite repair. repair efficiency.

I I E INCREASING USE of cumposi tes in boll1 1nilit;lry annd comrncrcial aircr;~ft rcquircs the development oS proven repair methods that rcstorc the integriry of the dainaged

slructure, with. minimum degradation in its functional capability and weight addition. urther, the implementation of online repairs crllls for simple brocednres and gildgets to

id excessive down time of the component. Thcreforc. continucd :uld expanded use of positcs critically dcpends on the devclopmcilt or both structurally adcquntc and omic:illy fcasi blc, rcpuir tcchniq ues. csently, one o f the main concerns of the composite aircraft industry is multiple

ination damage c:lused by ilccidental impacts such as bird bits. runway debris. damage, ctc. The cxtcnt of d;lmagc dictates thc choicc bctwccn repair oS thc

onent and its total replacement. Rcpairs involving adhesively bonded patches osites. because bonding produces no holes (for Fasteners), thus

~g regions of stress concentration. Ideally, the patch should be so designed and

cc S I I O L I J ~ l2e ;id Jrcsscil.

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b[. RAJU ET AL.

7'11~ ;LLLL]IOI.S LISC tll;lllkSlli to Dr 13. R. [':ti, Director, National Acrosp;tcc Litboratorics, Uangaiorc, for all tllc support dt~ritlg tllc invc'stigatiou.

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