Seminar on

ByAUGUSTINE DSOUZA

(1MJ15MAE02)

Under the guidance ofP.DINESH KUMAR

Asst. Professor MVJCE

COMPOSITE MATERIALREPAIR METHODOLOGIES

What is Composite MATERIAL ?

• A composite material is  a  material  made  from  two  or  more constituent  materials  with  significantly different physical or chemical  properties that,  when  combined, produce  a  material  with  characteristics  different  from  the individual  components.  The  individual  components  remain separate and distinct within the finished structure. 

APPLICATIONS OF COMPOSITE MATERIAL IN AEROPLANE

INTRODUCTION

• Repair  methods  need  to  be simple  but  effective  in  order  to maintain  the  structural  integrity and  future  operational effectiveness.• Common operational damages of composites  are  Because  of Impact  of    Bird,  Debris  or  Tool drop  during  servicing  and Atmospheric  Erosion  due  to Dust/Rain,  Moisture  Absorption Etc.,

TYPES OF DAMAGES

All repair types are “zone dependent “requiring aerodynamic/aero elastic considerations

EROSION DAMAGE(without major fiber damage) - abrade, clean, fill and fair with suitable epoxy or polyurethane filler.

MINOR SCRATHES OR DINGS AFFECTING SURFACE PLY - Abrade, to remove paint around damage down to the laminate surface, fill scratches or ding with filler paste and apply 1-layer of fine glass fabric with epoxy.

DAMAGE INTO OR BEYOND OUTER PLY OF LAMINATE

-Remove and replace damaged plies or apply a bonded doubler repair

DAMAGE INTO SANDWICH CORE STRUCTURE

-Remove and replace damaged core and structural plies in damaged skin or apply doubler

DAMAGE THROUGH STRUCTURE

-Remove damage through structure and repair from both sides (if accessible) using repair plies or doublers .Option : repair from one side using “no backside access” techniques

Damage Evaluation

• Location of Damage

• Assesment of Damaged Area

• Calculation of Damage Tolerance

• Residual Strength Estimation

REPARING CRACK

PATCH REPAIR – A STARTING POINT FOR THE RESEARCH

REPAIR TECHNIQUES

NON PATCHING TECHNIQUES

If the defects in composite structures is very small in size and magnitude i.e. a scratch or a crack within the structure then it can be resolved by Resin Infusion method of simple injecting resin over the cracked region within the structure.

PATCHING TECHNIQUES

If the extent of damage is severe this has to be repaired using specific techniques to retain the original strength of the structure.

TYPES OF NON PATCH TECHNIQUE

• FILLER OR PLOTTING REPAIR• FUSION REPAIR

Filler repair It is used for minor indentations in laminates provided that there is no internal damage. Here, the defective region is filled with resin. Fusion repair It takes the advantage that thermoplastics are fusible and is consist of applying heat and pressure to the damaged region.

TYPES OF PATCHING TECHNIQUE• BONDED EXTERNAL PATCH • BONDED SCARF PATCH• BOLTED EXTERNAL PATCH  

BONDED EXTERNAL PATCH :• Suitable for repairs to laminates up to 16 plies thick.• Excellent restoration of mechanical properties.• Easy to implement, well suited for field application.• Minimum further damage to structure.

BONDED SCARF PATCH:• Suitable only to thick laminates.• Excellent restoration of mechanical properties.• Obtrusive; requires significant material removal.• Difficult to repair, suited to depot level repair.

BOLTED EXTERNAL PATCH:• Suitable only to thick laminates.• Limited restoration of mechanical properties.• Require large number of extra fasteners holes.• Easy to implement, well suited for field application

EQUIPMENT AND ANCILLARIES FOR REPAIRS

Detail of vacuum bag lay-up

SEALING FLEXIBLE BAG OVER LAY-UP

APPLYING VACCUM TO THE SYSTEM

In this case the thickness of the original laminate is made up with filler plies and the repair materials are bonded to the surface of the laminate.

1. Patch repair

2. Taper sanded or scarf repair

In this case an area around the hole is sanded to expose a section of each ply in the laminate. Sometimes one filler ply is added to produce a flatter surface.

3. Step sanded repair

The laminate is sanded down so that a flat band of each layer is exposed, producing a stepped finish

1. Patch repair Extra ply 

Repair plies 

Film adhesive 

Filler plies Backup ply 

2. Taper sanded repair( Scarf repair  ) 

Extra ply 

Repair plies 

Film adhesive 

Filler ply  Backup ply 

3. Step sanded repair Extra ply 

Repair plies 

Film adhesive 

Filler ply  Backup ply 

Advantages

 Quick and simple to do, requires minimum preparation

Patch repair

Taper sanded or scarf repairRepair is only marginally thicker than the original

 Each repair ply overlaps the ply that it is repairing giving a straighter, stronger load path

 Good bonds can be achieved on the freshly exposed surfaces 

Step sanded repairSame as taper sanded repair 

DisadvantagesPatch repair                                                                                                                               

             A repaired laminate is thicker and heavier than the original

 Very careful surface preparation is needed for good adhesion

Time 

consuming

Taper sanded or scarf repair

 High skill needed and difficult to achieve

Step sanded repairExtremely difficult to do

CONCLUSIONThe  repair  of  composite  materials  are  done  using  all  the explained Techniques. 

With  the  increasing  usage  of  fiber-reinforced  composites  in aircraft structures, it has become necessary to establish reliable repair  methods  that  will  restore  the  structure’s  integrity.    The purpose  of  this  document  was  to  investigate  the  effective composite repair technique. 

REFERECNCE

T. Mitrevski, I.H. Marchall, R. Thomson, R. Jones, B. Whittingham, The effect of impactor shape on the impact response of composite laminates, Composite Structures 67 (2005) 139–148.

AC20-107B, Composite Aircraft Structures, FAA, 1984.

Keith B. Armstron, et al., Care and Repair of Advanced Composite, SAE International, 2005 .

Shin-etsu Fujimoto, Hideki Sekine, Identification of crack and disband fronts in repaired aircraft structural panels with bonded FRP composite patches, Composite Structures 77 (2007) 533–545

Standard test method for compressive residual strength properties of damaged polymer matrix composite plates, 2005.Baker A, Dutton S, Donald K. Composite materials for aircraft structures. American Institute of Aeronautics and Astronautics; 2004.

Giangiacomo Minak, Daniele Ghelli, Influence of diameter and boundary conditions on low velocity impact response of CFRP circular laminated plates, Composites Part B: Engineering 39 (2008) 962–972.

THANK YOU