Composite and Non-Metallic Aircraft Materials PDF

COMPOSITE AND NON-METALLIC AIRCRAFT MATERIALS  COMPOSITES A COMPOSITE IS SOMETHING, WHICH IS MADE UP FROM 2 OR MORE CONSTITUENT PARTS, AND THIS TERM COULD BE APPLIED TO A WIDE RANGE OF ENGINEERING MATERIALS THESE WOULD INCLUDE NOT ONLY THE METALLIC...

COMPOSITE AND NON-METALLIC AIRCRAFT MATERIALS  COMPOSITES A COMPOSITE IS SOMETHING, WHICH IS MADE UP FROM 2 OR MORE CONSTITUENT PARTS, AND THIS TERM COULD BE APPLIED TO A WIDE RANGE OF ENGINEERING MATERIALS THESE WOULD INCLUDE NOT ONLY THE METALLIC ALLOYS, BUT ALSO BRICK, CONCRETE, AND GLASS IN THE AEROSPACE INDUSTRY, THE TERM ‘COMPOSITE’ IS USED WHEN REFERRING TO MATERIALS, WHICH, IN TURN, ARE A COMBINATION OF FIBROUS AND SYNTHETIC RESIN MATERIALS THE ADVANTAGE OF COMPOSITE MATERIALS IS THAT THEY GIVE AN EXCELLENT STRENGTH-TO-WEIGHT RATIOS  PLASTICS THE WORD PLASTIC COMES FROM THE GREEK PLASTIKOS – TO MOULD PLASTICITY IS THE ABILITY TO RETAIN A DEFORMATION AFTER THE LOAD HAS BEEN REMOVED PLASTICS ARE PARTICULARLY USEFUL FOR APPLICATIONS, WHICH INVOLVE RELATIVELY LOW-STRESS LEVELS, WHERE LIGHTNESS IS IMPORTANT, AND WHERE LOW ELECTRICAL OR THERMAL CONDUCTIVITY IS REQUIRED PLASTICS IS THE GENERIC NAME, USED TO IDENTIFY VARIOUS MATERIALS (NATURAL AND SYNTHETIC), BASED ON LONG-CHAIN MOLECULES (POLYMERS) OF CARBON  PLASTICS PLASTICS CAN BE CAST, EXTRUDED OR MOULDED INTO VARIOUS SHAPES OR DRAWN OUT INTO FILAMENTS TO BE USED AS FIBRES THERE ARE TWO MAJOR GROUPS OF PLASTICS: THERMOPLASTIC THERMOSETTING THE MANUFACTURE OF SYNTHETIC RUBBERS (CALLED ELASTOMERS) IS ALSO CONSIDERED TO BE PART OF THE PLASTICS INDUSTRY  THERMOPLASTICS THERMOPLASTIC MATERIALS, IN THEIR NORMAL STATE, ARE HARD BUT BECOME SOFT AND PLIABLE WHEN HEATED (THE GREEK WORD THERMO – HEAT) WHEN SOFTENED, THERMOPLASTIC MATERIALS CAN BE MOULDED AND SHAPED, AND THEY RETAIN THEIR NEW SHAPE WHEN COOLED UNLESS THEIR HEAT LIMIT IS EXCEEDED, THIS PROCESS CAN BE REPEATED MANY TIMES WITHOUT DAMAGING THE MATERIAL  THERMOPLASTICS TWO TYPES OF TRANSPARENT THERMOPLASTIC MATERIALS ARE USED FOR AIRCRAFT WINDSHIELDS AND SIDE WINDOWS, THESE ARE 1. CELLULOSE ACETATE 2. ACRYLIC OLDER AIRCRAFT USED CELLULOSE ACETATE PLASTIC BECAUSE OF ITS TRANSPARENCY AND LIGHT-WEIGHT ITS DISADVANTAGE IS THAT IT SHRINKS AND DISCOLOURS WITH TIME IT FADES TO A YELLOWISH TINT AND IT WILL GIVE OFF BLACK SMOKE WHEN IT BURNS  THERMOPLASTICS IT WILL ALSO REACT, AND SOFTEN, UPON CONTACT WITH SOME MATERIALS, SUCH AS ACETONE. ACRYLIC PLASTICS ARE IDENTIFIED BY SUCH TRADE NAMES AS PERSPEX (UK) AND PLEXIGLASS (USA) IT IS STIFFER THAN CELLULOSE ACETATE, MORE TRANSPARENT AND PRACTICALLY COLOURLESS ACRYLIC BURNS WITH A CLEAR FLAME AND GIVES OFF A FAIRLY PLEASANT ODOUR ACETONE, IF APPLIED TO ACRYLIC WILL CAUSE WHITE MARKS BUT WILL NOT AFFECT THE MATERIALS HARDNESS  USES OF THERMOPLASTICS THERMOPLASTICS ARE, NORMALLY, USED WHERE THERE ARE NO UNUSUAL TEMPERATURE CHANGES. THERMOPLASTIC PRODUCTION INCLUDES ACETATE - WIDELY USED FOR TOOL HANDLES, AND ELECTRICAL GOODS POLY-ETHYLENE - COMMONLY KNOWN AS POLYTHENE. ITS USES INCLUDE FLEXIBLE TUBING, CABLE INSULATION AND PACKAGING POLY-PROPYLENE - STRONGER, HARDER AND MORE RIGID THAN POLYTHENE. USED FOR SUCH ITEMS AS HIGH- PRESSURE AIR PIPING  USES OF THERMOPLASTICS POLY-VINYL-CHLORIDE - COMMONLY KNOWN AS PVC. VARYING DEGREES OF RIGIDITY/FLEXIBILITY ARE ACHIEVABLE BY VARYING THE AMOUNT OF PLASTICISER USED RIGID, MOULDED SECTIONS OR PIPING CAN BE PRODUCED AND ALSO FLEXIBLE ELECTRIC CABLE INSULATION POLYSTYRENE - CAN BE PRODUCED IN RIGID FORM, BUT IS MORE FAMILIAR IN THE EXPANDED FORM, WHEN IT IS USEFUL FOR THERMAL INSULATION, BUOYANCY OR SHOCK-RESISTANT PACKAGING  USES OF THERMOPLASTICS ACRYLICS - THESE ARE PARTICULARLY USEFUL WHERE LIGHT TRANSMISSION IS NECESSARY THEY HAVE EXCELLENT LIGHT TRANSMISSION PROPERTIES AND ARE ALSO RESISTANT TO SPLINTERING THERE IS A TENDENCY FOR SOME FINE CRAZE- CRACKING TO DEVELOP IF EXPOSED FOR LONG PERIODS TO ULTRA VIOLET LIGHT  USES OF THERMOPLASTICS ACRYLIC PLASTICS MAY BE SOLID OR LAMINATED WHEN LAMINATED TWO OR MORE LAYERS ARE BONDED TOGETHER WITH A CLEAR ADHESIVE IN THIS FORM, THEY ARE MORE SHATTER-RESISTANT AND ARE IDEALLY SUITED TO PRESSURISED AIRCRAFT WINDOWS AN EVEN STRONGER AND MORE SHATTERPROOF TRANSPARENT PLASTIC CAN BE ACHIEVED BY STRETCHING THE ACRYLIC IN BOTH DIRECTIONS BEFORE FINAL SHAPING  USES OF THERMOPLASTICS THESE IMPROVED PROPERTIES, RESULT FROM THE STRETCHING OPERATION CAUSING A PREFERENTIAL ALIGNMENT OF THE LONG-CHAIN MOLECULES EXTREME CARE SHOULD BE TAKEN WHEN HANDLING ACRYLICS, AS THEY ARE THEY ARE EASILY SCRATCHED THE ACRYLICS ARE SUPPLIED WITH A PAPER OR RUBBERISED FILM, WHICH SHOULD NOT BE REMOVED, UNTIL REQUIRED FOR USE  USES OF THERMOPLASTICS IF DIRTY, THEY SHOULD BE CLEANED WITH COLD WATER OR SOAPY WATER CARE SHOULD ALSO BE TAKEN WHEN USING SOLVENTS IN THE VICINITY OF ACRYLICS SOME SOLVENTS, OR THEIR VAPOURS, MAY CAUSE CRAZING OF THE MATERIAL REFERENCE TO THE APPROPRIATE MANUALS OR MANUFACTURERS’ SPECIFICATION SHEETS ARE ESSENTIAL  USES OF THERMOPLASTICS POLY-CARBONATES - THESE HAVE SIMILAR USES TO THE ACRYLICS (PERSPEX ETC) BUT ARE MORE TEMPERATURE- RESISTANT AND ALSO HAVE SUPERIOR IMPACT STRENGTH. THEY ARE ALSO MORE EXPENSIVE NYLON - BELONGS TO THE POLYAMIDE FAMILY AND IS AN EXTREMELY USEFUL AND VERSATILE MATERIAL. IT IS STRONG, TOUGH AND ALSO HAS LOW FRICTION PROPERTIES IT CAN BE USED AS A FIBRE OR PRODUCED AS A MOULDING. POPULAR USES INCLUDE TEXTILES, FURNISHINGS, ROPES, TYRE REINFORCEMENT, BUSHES, PULLEYS, GEARS, AND LIGHTWEIGHT MOULDINGS SUCH AS BRACKETS, HANDLES ETC  USES OF THERMOPLASTICS POLY-TETRA-FLUORO-ETHYLENE - COMMONLY KNOWN AS ‘PTFE’, IT IS SIMILAR TO NYLON IN APPEARANCE BUT IS DENSER, WHITER AND MUCH MORE EXPENSIVE IT HAS A WAX-LIKE SURFACE AND THIS CHARACTERISTIC RESULTS IN VERY LOW FRICTION PROPERTIES, WHICH MAKE IT SUITABLE FOR BUSHES AND GEARS IT ALSO HAS A HIGH TEMPERATURE CAPABILITY (OVER 300ºC) AND IS EXTENSIVELY USED AS A NON-STICK COATING E.G. TEFLON PTFE TAPE IS OFTEN USED AS A THREAD SEALANT FOR OXYGEN PIPE THREADS, AND AS BACKING RINGS FOR HYDRAULIC SEALS  THERMOSETTING MATERIALS THERMOSETTING MATERIALS (ALSO CALLED THERMOSETS) WILL, INITIALLY, SOFTEN WHEN HEATED, BUT WILL REMAIN SOFT FOR ONLY A SHORT TIME AND WILL SET (HARDEN) IF THE HEAT CONTINUES TO BE APPLIED THE HARDENING PROCESS IS CALLED ‘CURING’ AND CURING CAN ALSO BE ACHIEVED BY CHEMICAL REACTIONS (EXOTHERMIC) DURING THE CURING PROCESS, THE LONG-CHAIN MOLECULES OF THE MATERIAL, “CROSS-LINK” AND, ONCE THE CROSS-LINKS ARE FORMED, THE PLASTIC BECOMES HARD AND CANNOT BE RE-SOFTENED BY HEATING  THERMOSETTING MATERIALS THERMOSETS ARE, CHOSEN WHERE A PLASTIC COMPONENT WILL BE EXPOSED TO RELATIVELY HIGH TEMPERATURES, AS SOME OF THEM CAN TOLERATE TEMPERATURES IN EXCESS OF 250°C BEFORE BEGINNING TO CHAR THERMOSETTING MATERIALS ARE GENERALLY STRONGER, HAVE A LOWER DUCTILITY AND LOWER IMPACT PROPERTIES THAN THE THERMOPLASTICS  RESINS NATURAL RESINS ARE OBTAINED FROM CERTAIN TREES AND OTHER PLANTS THEY CAN BE CLEAR, TRANSLUCENT, YELLOW (AMBER), BROWN, SOLID, OR SEMISOLID AND ARE USED IN INKS, LACQUERS, LINOLEUM, VARNISHES AND, PLASTICS RESINS MAY BE USED ALONE TO FORM PLASTICS BUT, USUALLY, ADDITIVES ARE MIXED WITH THEM, TO ASSIST IN THE MOULDING CHARACTERISTICS, OR TO ENHANCE THE PROPERTIES OF THE FINISHED PRODUCT PLASTICS REFERS TO THE MATERIAL IN THE FINISHED ITEMS WHILE RESINS ARE THE RAW MATERIALS WHICH MAY BE FOUND IN THE FORM OF FLAKES, PELLETS, POWDER, OR A SYRUP  RESINS THE RESIN MAY BE THICKENED AND GIVEN MORE ‘BODY’ BY THE ADDITION OF INERT FILLERS, WHICH MAY BE USED TO FILL GAPS AND VOIDS IN THE STRUCTURE TYPICAL FILLERS ARE MICRO-BALLOONS, COTTON AND GLASS FLOCK AND AEROSIL (FUMED SILICA) REINFORCING AGENTS, PLASTICIZERS, STABILISERS, COLORANTS, FLAME-RETARDANTS, SMOKE SUPPRESSANTS AND PROCESSING AIDS, SUCH AS LUBRICANTS AND COUPLING AGENTS, ARE AMONG THE OTHER ADDITIVES USED WITH RESINS  RESINS RESINS HAVE LITTLE STRENGTH IN THEMSELVES AND ARE GENERALLY USED TO IMPREGNATE LINEN, PAPER, AND ‘CLOTHS’ MADE UP FROM VARIOUS SYNTHETIC FIBRES AIRCRAFT CONTROL CABLE PULLEYS ARE MADE FROM THERMOSETTING RESINS, REINFORCED WITH LAYERS OF LINEN CLOTH THESE PULLEYS ARE CURED IN A MOULD, AT HIGH TEMPERATURE, AND HAVE HIGH STRENGTH WITHOUT CAUSING WEAR TO THE CONTROL CABLES  RESINS WHEN LAYERS OF PAPER ARE IMPREGNATED WITH A THERMOSETTING RESIN SUCH AS PHENOL- FORMALDEHYDE OR UREA-FORMALDEHYDE, THEY CAN BE MOULDED INTO FLAT SHEETS OR OTHER SHAPES ONCE HARDENED, THE MATERIAL MAKES AN EXCEPTIONAL ELECTRICAL INSULATOR AND CAN BE FOUND IN USE AS TERMINAL STRIPS AND PRINTED CIRCUIT BOARDS  POLYESTER RESINS POLYESTER RESIN CAN BE EXTRUDED INTO FINE FILAMENTS AND WOVEN INTO FABRIC (LIKE NYLON) IT CAN BE CAST INTO SHAPE AND IT IS ALSO USEFUL AS A HEAT-RESISTANT LACQUER GLASS FIBRES AND GLASS FIBRE MAT, HAVE GREAT STRENGTH FOR THEIR WEIGHT, BUT LACK RIGIDITY SO, TO CONVERT GLASS FIBRE INTO A USEFUL STRUCTURAL MATERIAL, IT IS IMPREGNATED WITH POLYESTER RESIN AND MOULDED INTO A DESIRED FORM  POLYESTER RESINS POLYESTERS CURE BY CHEMICAL ACTION, AND, SO, DIFFER FROM MATERIALS, WHICH CURE BY THE EVAPORATION OF AN OIL OR SOLVENT AS POLYESTER IS THICK AND UNMANAGEABLE, MONOSTYRENE IS ADDED TO MAKE IT THINNER AND EASIER TO WORK IF LEFT ALONE, THE MIXTURE OF POLYESTER AND STYRENE WILL, EVENTUALLY, CURE INTO A SOLID MASS, SO INHIBITORS ARE ADDED TO DELAY THIS CURING PROCESS AND TO IMPROVE SHELF LIFE  POLYESTER RESINS A CATALYST HAS TO BE USED TO START THE CURING PROCESS, AND BY ADDING AN ACCELERATOR THE CURING TIME OF THE RESIN WILL REDUCE, DEPENDING ON THE TEMPERATURE AND MASS OF THE RESIN THE ACTUAL CURE OF POLYESTER RESIN OCCURS WHEN A CHEMICAL REACTION BETWEEN THE CATALYST AND ACCELERATOR GENERATES HEAT WITHIN THE RESIN THIS (EXOTHERMIC) REACTION CAN BE SEEN WHEN A THICK LAYER CURES MORE RAPIDLY THAN A THIN LAYER  THIXOTROPIC AGENTS THE HEAT, GENERATED BY THE CHEMICAL REACTION, CAN REDUCE ITS VISCOSITY AND CAUSE IT TO ‘RUN’, PARTICULARLY IF IT IS ON A VERTICAL SURFACE TO OVERCOME THIS PROBLEM, A THIXOTROPIC AGENT IS ADDED TO THE RESIN AFTER MIXING, TO INCREASE ITS VISCOSITY. THE INCREASED VISCOSITY ALLOWS THE RESIN TO REMAIN IN PLACE NO MATTER WHERE IT MAY BE USED  EPOXY RESIN ANOTHER TYPE OF RESIN THAT CAN BE USED IN PLACE OF POLYESTER IN LAMINATED STRUCTURES IS EPOXY RESIN EPOXY RESIN HAS A LOW PERCENTAGE OF SHRINKAGE, HIGH STRENGTH FOR ITS WEIGHT AND THE ABILITY TO ADHERE TO A WIDE RANGE OF MATERIALS EPOXY RESINS REQUIRE A HARDENER OR CURING AGENT WITHOUT THE NEED TO APPLY HEAT THE MIXING RATIOS BETWEEN POLYESTER AND EPOXY RESINS DIFFER. FOR POLYESTER RESIN, THE RATIO IS 64:1, RESIN TO CATALYST WHILST, FOR EPOXY RESIN, THE RATIO IS 4:1, RESIN TO HARDENER  ELASTOMERS FROM THE GREEK WORD ELASTOS – ELASTIC, ELASTOMERS MAY BE NATURAL OR, SYNTHETIC MATERIALS (POLYMERS) WHICH HAVE CONSIDERABLE ELASTIC PROPERTIES BECAUSE THEY MAY ALSO BE MOULDED INTO SHAPES, WHICH THEY RETAIN, THEY QUALIFY TO BE INCLUDED IN THE CATEGORY OF PLASTICS ELASTOMERS WILL TOLERATE REPEATED ELONGATION AND RETURN TO THEIR ORIGINAL SIZE AND SHAPE, IN A SIMILAR WAY TO NATURAL RUBBER  ELASTOMERS SOME OF THE MORE COMMON ELASTOMERS, TO BE FOUND IN THE AEROSPACE INDUSTRY INCLUDE BUNA ‘N’ - ALSO KNOWN AS NITRILE IS A SYNTHETIC RUBBER, MADE BY THE POLYMERISATION OF BUTADEINE (Bu) AND SODIUM (Na) IT HAS EXCELLENT RESISTANCE TO FUELS AND OILS, AND IS USED FOR OIL AND FUEL HOSES, GASKETS, AND SEALS THIS MATERIAL ALSO HAS LOW ‘STATIC FRICTION’ PROPERTIES, WHEN IN CONTACT WITH METAL, AND IS, THEREFORE, PARTICULARLY SUITED TO ‘MOVING-SEAL’ APPLICATIONS  ELASTOMERS BUNA - ‘S’ RELATIVELY CHEAP MATERIAL, ALSO WITH A PERFORMANCE SIMILAR TO NATURAL RUBBER IT IS OFTEN USED FOR TYRES AND TUBES, BUT ITS POOR RESISTANCE TO FUELS/OILS/CLEANING FLUIDS MAKES IT UNSUITABLE FOR SEALS FLUORO-ELASTOMERS - THESE HAVE EXCEPTIONAL HIGH-TEMPERATURE PROPERTIES AND CAN BE USED AT 250ºC THEY ARE ALSO SOLVENT-RESISTANT AND ARE MAINLY USED FOR HIGH-TEMPERATURE SEALS. A COMMON NAME FOR THESE MATERIALS IS VITON  ELASTOMERS NEOPRENE - HAS VERY GOOD TENSILE PROPERTIES AND EXCELLENT ELASTIC RECOVERY QUALITIES IT IS ALSO SOLVENT-RESISTANT AND, THEREFORE, HAS A WIDE RANGE OF APPLICATIONS AS FUEL AND HYDRAULIC SEALS AND GASKETS BECAUSE OF ITS SPECIAL ELASTIC RECOVERY PROPERTIES, IT IS ALSO IDEALLY SUITED TO DIAPHRAGMS AND HYDRAULIC SEALS  ELASTOMERS POLY-SULPHIDE RUBBER - ALTHOUGH IT POSSESSES RELATIVELY POOR PHYSICAL PROPERTIES, IT HAS EXCEPTIONALLY HIGH RESISTANCE TO FUELS AND OILS AND IS WIDELY USED FOR LINING OR SEALING FUEL TANKS IT IS ALSO USED FOR LIGHTLY STRESSED SEALS AND HOSES, WHICH COME INTO CONTACT WITH FUELS OR OILS THIS COMPOUND IS COMMONLY KNOWN UNDER THE TRADE NAMES OF PRC OR THIOKOL  ELASTOMERS SILICONE RUBBER - HAS VERY GOOD HIGH AND LOW TEMPERATURE PROPERTIES SO IT HAS MANY APPLICATIONS OVER A WIDE TEMPERATURE RANGE (+ 200ºC TO ‑80ºC) IT IS OFTEN USED FOR SEALS IT IS ALSO USED FOR THE POTTING OF ELECTRICAL CIRCUITS, BECAUSE OF ITS ABILITY TO RETAIN ITS RUBBERY STATE, EVEN AT LOW TEMPERATURES  ADVANTAGES OF PLASTICS LIGHTNESS - MOST PLASTICS HAVE SPECIFIC GRAVITIES OF 1.1 TO 1.6 WHEREAS THE MORE COMMON ENGINEERING MATERIALS, SUCH AS ALUMINIUM AND STEEL, HAVE VALUES OF 2.7 AND 7.8 RESPECTIVELY CORROSION RESISTANCE - PLASTICS WILL TOLERATE HOSTILE CORROSION ENVIRONMENTS AND MANY OF THEM RESIST ACID ATTACK LOW THERMAL CONDUCTIVITY - THIS PROPERTY MAKES MANY PLASTICS IDEAL FOR THERMAL INSULATORS  ADVANTAGES OF PLASTICS ELECTRICAL RESISTANCE - PLASTICS ARE USED IN ENORMOUS QUANTITIES FOR ELECTRICAL INSULATION APPLICATIONS FORMABILITY - MANY PLASTICS ARE EASILY FORMED INTO THE FINISHED PRODUCT, BY CASTING MOULDING OR EXTRUSION, OFTEN IN A SINGLE OPERATION SURFACE FINISH - EXCELLENT SURFACE FINISHES CAN BE ACHIEVED IN THE BASIC FORMING OPERATION, SO FINISHING OPERATIONS ARE NOT NECESSARY  ADVANTAGES OF PLASTICS RELATIVELY LOW COST – THE LACK OF MACHINING NECESSARY AND THE HIGH PRODUCTION RATES POSSIBLE, KEEPS THE COSTS DOWN LIGHT TRANSMISSION - SOME PLASTICS ARE NATURALLY CLEAR, WHILST OTHER ARE OPAQUE. THESE CHARACTERISTICS, PROVIDE THE POSSIBILITY FOR A RANGE OF LIGHT-TRANSMISSION AND OPTICAL PROPERTIES VIBRATION DAMPING - MANY PLASTICS ARE NATURALLY RESISTANT TO FATIGUE AND, BECAUSE OF THE HIGH VALUE OF INTERNAL DAMPING PRESENT, RESONANCES WILL TEND TO BE OF RELATIVELY LOW AMPLITUDE  DISADVANTAGES OF PLASTICS LACK OF STRENGTH - MOST PLASTICS ARE WEAKER THAN METALS AND MILD STEEL HAS APPROXIMATELY SIX TIMES THE STRENGTH OF NYLON. MILD STEEL, HOWEVER, IS SIX TIMES THE WEIGHT OF NYLON SO, ON A STRENGTH/WEIGHT RATIO, THEY ARE COMPARABLE LOW STIFFNESS - PLASTICS HAVE A VERY INFERIOR VALUE OF YOUNG’S MODULUS OF ELASTICITY COMPARED WITH THE COMMON METALS LOW IMPACT STRENGTH - MANY PLASTICS HAVE POOR IMPACT STRENGTH, BUT THERE ARE A FEW EXCEPTIONS, SUCH AS WITH CERTAIN POLYCARBONATES  DISADVANTAGES OF PLASTICS POOR DIMENSIONAL STABILITY - MAINLY DUE TO HIGH VALUES OF THERMAL COEFFICIENT OF EXPANSION POOR HIGH-TEMPERATURE CAPABILITY - THE MAXIMUM OPERATING TEMPERATURE FOR PLASTICS, IS NOT NORMALLY ABOVE 250ºC. MOISTURE ABSORPTION - MANY TYPES OF PLASTIC ABSORB MOISTURE, WHICH CAN RESULT IN A SIGNIFICANT LOSS OF STRENGTH ULTRA VIOLET LIGHT - SOME PLASTICS DETERIORATE WHEN EXPOSED TO UV LIGHT FOR LONG PERIODS. INCREASED BRITTLENESS AND LOSS OF STRENGTH CAN OCCUR  PLASTIC MANUFACTURING PROCESSES CASTING - THE MOLTEN MATERIAL IS SIMPLY POURED INTO A MOULD AND ALLOWED TO SET MOULDING - POWDER, LIQUID OR PASTE IS FORCED INTO A SET OF SHAPED DIES EXTRUSION - PLASTIC IS FORCED THROUGH A SHAPED DIE TO PRODUCE ROD, SHEET, TUBE, OR ANGLE SECTIONS ETC LAY-UP - LOAD-CARRYING PLASTIC FIBRES AND AN ADHESIVE ARE LAYERED IN A MOULD OR AROUND A FORMER  PLASTIC MANUFACTURING PROCESSES SANDWICH-CONSTRUCTION - PLASTIC FACINGS HAVE, SANDWICHED BETWEEN THEM, A HONEYCOMB OR FOAM CORE. VERY STIFF, BUT LIGHT, STRUCTURES ARE ACHIEVED BY THIS METHOD COMPRESSION MOULDING – THE MATERIAL IS PUT INTO A HEATED, HARDENED, POLISHED STEEL CONTAINER (THE DIE) AND FORCED INTO SHAPE, BY A PLUNGER VACUUM FORMING - THE PLASTIC IS SUCKED INTO CONTACT WITH THE SHAPED DIE (A METHOD OFTEN USED TO MANUFACTURE AIRCRAFT INTERIOR TRIM) COMPOSITE MATERIALS GLASS FIBRE REINFORCED PLASTIC (GFRP) GLASS CAN BE SPUN INTO CLOTH AND USED FOR FIRE- PROOF CURTAINS OR (WHEN EXTREMELY PURE GLASS IS USED), MADE INTO FIBRES WHICH ARE ABLE TO TRANSMIT LIGHT OVER LONG DISTANCES THE ULTIMATE TENSILE STRENGTH OF UNDAMAGED, VERY SMALL DIAMETER GLASS FIBRES IS EXTREMELY HIGH, ALTHOUGH THE STRENGTH IS REDUCED SIGNIFICANTLY IF THE FIBRES ARE SLIGHTLY DAMAGED IN ITS STRUCTURAL USE IT IS OFTEN MERELY REFERRED TO AS GLASS FIBRE OR FIBREGLASS, WHEN GLASS FIBRES (IN VARIOUS FORMS) ARE BONDED TOGETHER BY APPROPRIATE RESINS GLASS FIBRE REINFORCED PLASTIC (GFRP) WHEN MOULDED WITH RESIN, THE RESULTING COMPOSITE IS, ALSO, OF COMPARATIVELY LOWS TRENGTH GOOD GFRP STRUCTURES ARE STRONGER THAN MILD STEEL AND, ON A SIMPLE STRENGTH-FOR-WEIGHT BASIS, CAN BE COMPARABLE TO HIGH TENSILE STEEL IF THE FIBRE FORM AND LAY-UP IS NEAR OPTIMUM IT IS CONSIDERABLY LESS STIFF THAN STEEL OR EVEN ALUMINIUM NON-STRUCTURAL ITEMS MAY BE MADE FROM A PERCENTAGE OF CHOPPED STRAND MAT, (I.E. GLASS FIBRES IN A RANDOM, NON- WOVEN STATE) GLASS FIBRE REINFORCED PLASTIC (GFRP) WHERE CONSIDERABLE STRENGTH IS REQUIRED, UNI- DIRECTIONAL GLASS CLOTH IS USED TO PROVIDE ALL ROUND STRENGTH, SHEETS OF UNI- DIRECTIONAL CLOTH CAN BE LAYED UP AT 90º TO EACH OTHER, IN A SIMILAR MANNER TO THE GRAIN IN PLYWOOD SOMETIMES SUCH SHEETS ARE USED AS FACINGS FOR AN INTERNAL HONEYCOMB OF PLASTIC-IMPREGNATED PAPER, TO GIVE A VERY EFFICIENT STRUCTURE IN TERMS OF STRENGTH, STIFFNESS AND WEIGHT GLASS FIBRE REINFORCED PLASTIC (GFRP) THE GLASS FIBRE SHEET MATERIAL CAN BE SUPPLIED WITH CLOTH ALREADY IMPREGNATED WITH RESIN AND PARTIALLY CURED (‘PRE-PREG’), IN WHICH CASE IT IS KEPT IN A REFRIGERATED STORAGE RESIN CURING IS USUALLY DONE AT HIGHER TEMPERATURES (120°C - 170ºC), WITH THE GRP COMPONENT IN ITS MOULD AND, OFTEN, UNDER PRESSURE, IN AN AUTOCLAVE OVEN GFRP ARE USED: WHERE METAL CANNOT BE USED (E.G. FOR RADAR DOMES OR OTHER NON-ELECTRICAL CONDUCTING APPLICATIONS GLASS FIBRE REINFORCED PLASTIC (GFRP) THE EASE AND LOW COST OF PRODUCING VERY COMPLEX SHAPES TO PROVIDE GOOD STRENGTH/WEIGHT RATIO ITS ABILITY TO PRODUCE SELECTED DIRECTIONAL STRENGTH THE MAIN DISADVANTAGE OF GLASS FIBRE IS THAT IT LACKS STIFFNESS AND, AS SUCH, IS NOT SUITABLE FOR APPLICATIONS SUBJECT TO HIGH STRUCTURAL LOADINGS  CERAMIC FIBRE MADE BY FIRING CLAY OR OTHER NON-METALLIC MATERIALS, CERAMIC FIBRES ARE A FORM OF GLASS FIBRE, USED IN HIGH-TEMPERATURE APPLICATIONS THEY CAN BE USED AT TEMPERATURES UP TO 1650°C AND ARE SUITED FOR USE AROUND ENGINE AND EXHAUST SYSTEMS CERAMIC FIBRES ARE HEAVY (AND EXPENSIVE) AND ARE ONLY USED WHERE NO OTHER MATERIALS ARE SUITABLE  CARBON FIBRE REINFORCED PLASTIC CFRP (ALSO REFERRED TO AS ‘GRAPHITE’) IS A COMPOSITE MATERIAL, WHICH WAS PRIMARILY DEVELOPED TO RETAIN (OR IMPROVE UPON) THE HIGH STRENGTH-TO-WEIGHT RATIO CHARACTERISTICS EXHIBITED BY GFRP, BUT WITH VERY MUCH GREATER STIFFNESS VALUES CARBON FIBRES ARE VERY STIFF AND, WHEN FORMED INTO A COMPOSITE, THE YOUNG'S MODULUS (‘E’) VALUE CAN BE HIGHER THAN STEEL CFRP IS NOT ONLY SIX TIMES STIFFER THAN GFRP BUT IS ALSO OVER 50% STRONGER. IT ALSO HAS TWICE THE STRENGTH OF HIGH-STRENGTH ALUMINIUM ALLOY AND THREE TIMES THE STIFFNESS  CARBON FIBRE REINFORCED PLASTIC CARBON FIBRES ARE TYPICALLY LESS THAN 0.01 MM (0.0004 IN) IN DIAMETER THEY ARE PRODUCED BY SUBJECTING A FINE THREAD OF A SUITABLE NYLON-TYPE PLASTIC TO A VERY HIGH TEMPERATURE (TO DECOMPOSE THE POLYMER), AND BURNING OFF ALL OF THE ELEMENTS WITH THE EXCEPTION OF CARBON THE CARBON THREAD IS THEN STRETCHED, AT WHITE HEAT (2000°C-3000ºC), TO DEVELOP STRENGTH. THE PROCESS IS COMPLEX AND VERY COSTLY  CARBON FIBRE REINFORCED PLASTIC CFRP CAN OFFER CONSIDERABLE WEIGHT SAVINGS OVER CONVENTIONAL MATERIALS. CFRP COMPONENTS ARE GENERALLY MADE FROM ‘PRE-PREG’ SHEET SOME SPECIALIST ITEMS ARE MADE BY A LABORIOUS PROCESS CALLED ‘FILAMENT WINDING’, IN WHICH A CARBON FIBRE STRING IS WOUND OVER A FORMER IN THE SHAPE OF THE WORKPIECE WHILST BONDED WITH RESIN. BECAUSE OF CFRP'S HIGH YOUNGS MODULUS OF ELASTICITY, IT IS ALSO USED EXTENSIVELY TO STIFFEN GFRP OR ALUMINIUM ALLOY STRUCTURES  CARBON FIBRE REINFORCED PLASTIC A MATERIAL KNOWN AS CARBON-CARBON (WHERE THE RESIN IS ALSO GRAPHITISED), IS USED FOR THE ROTORS AND STATORS ON BRAKE UNITS IT OFFERS A SIGNIFICANT WEIGHT SAVING, AS WELL AS HIGH EFFICIENCY, DUE TO THE FACT THAT IT DISSIPATES THE HEAT GENERATED VERY QUICKLY REPLACING 40% OF AN ALUMINIUM ALLOY STRUCTURE BY CFRP WOULD RESULT IN A 40% SAVING IN TOTAL STRUCTURAL WEIGHT AND CFRP IS USED ON SUCH ITEMS AS THE WINGS, HORIZONTAL AND VERTICAL STABILISERS, FORWARD FUSELAGES AND SPOILERS OF MANY AIRCRAFT.  CARBON FIBRE REINFORCED PLASTIC THE USE OF COMPOSITES, IN THE MANUFACTURE OF HELICOPTER ROTOR BLADES, HAS LED TO SIGNIFICANT INCREASES IN THEIR LIFE AND, IN SOME CASES, THEY MAY HAVE AN UNLIMITED LIFE SPAN (ON DEFECT) THE MODERN BLADE IS HIGHLY COMPLEX AND MAY BE COMPRISED OF CFRP, GFRP, STAINLESS STEEL, A HONEYCOMB CORE AND A FOAM FILLING  ARAMID FIBRE REINFORCED PLASTIC ARAMID FIBRES ARE RELATED TO THE NYLON-TYPE OF SYNTHETIC FIBRES BUT HAVE BETTER TOUGHNESS, STRENGTH-TO-WEIGHT CHARACTERISTICS AND HEAT- RESISTANCE TYRES, REINFORCED WITH ARAMID FIBRES ARE COMPARABLE TO THOSE REINFORCED WITH STEEL CORDS BETTER KNOWN UNDER ITS TRADE NAME – KEVLAR –IN CLOTH FORM, IT IS A SOFT, YELLOW, ORGANIC FIBRE THAT IS EXTREMELY LIGHT, STRONG AND TOUGH DUE TO ITS IMPACT-RESISTANCE IT IS USED IN AREAS, WHICH ARE LIABLE TO BE STRUCK BY DEBRIS, SUCH AS AREAS AROUND ENGINE REVERSE-THRUST BUCKETS  GENERAL A SHEET OF FIBRE REINFORCED MATERIAL IS ‘ANISOTROPIC’, - WHICH MEANS ITS PROPERTIES DEPEND ON THE DIRECTION OF THE FIBRES RANDOM DIRECTION FIBRES WOULD RESULT IN A MUCH LOWER STRENGTH THAN UNI-DIRECTIONAL FIBRES, LAYING PARALLEL TO THE APPLIED LOAD THE STRENGTH (AND STIFFNESS) OF A UNI- DIRECTIONAL LAY-UP WOULD BE VERY LOW, WITH THE APPLIED LOAD AT 90º TO THE FIBRES, HENCE THE USUAL PRACTICE OF PLACING LAMINATIONS AT 90º TO EACH OTHER)  GENERAL DUE TO VARIATIONS IN THE SIZE OF FIBRES, THE FINAL QUALITY OF THE FINISHED COMPONENT (WHICH CAN BE AFFECTED BY CARELESS HANDLING, CLEANLINESS OR LAY-UP, VOIDS, PRESSURES, TEMPERATURES, ETC), STRESS RESERVE FACTORS ARE ALLOWED FOR COMPOSITES HAVE VERY LOW ELONGATION PROPERTIES AND TOUGHNESS. ALUMINIUM ALLOY HAS A TYPICAL ELONGATION-TO-FRACTURE VALUE OF 11%, WHEREAS COMPOSITES RANGE FROM 3% FOR GFRP TO 0.5% FOR CFRP THE MAXIMUM OPERATING TEMPERATURES, FOR GFRP, CFRP AND KEVLAR COMPOSITES ARE, GENERALLY, IN THE RANGE 220°C-250ºC  GENERAL SOME COMPOSITES, SUCH AS CARBON FIBRE IN A CARBON MATRIX, HAVE VERY HIGH PERMISSIBLE OPERATING TEMPERATURES (AROUND 3000ºC) THEY ARE USED FOR HIGH-ENERGY BRAKING APPLICATIONS AND AS THERMAL BARRIERS FOR SPACE VEHICLES BORON, TUNGSTEN, SILICON CARBIDE AND QUARTZ MAY ALSO BE USED TO PROVIDE FIBRES FOR HIGH-TEMPERATURE COMPOSITES  LAMINATED PLASTICS LAMINATED PLASTICS CONSIST OF LAYERS OF SYNTHETIC RESIN-IMPREGNATED FIBRES (OR OTHER, COATED, FILLERS), WHICH ARE BONDED TOGETHER (USUALLY HEATED AND UNDER PRESSURE), TO FORM A SINGLE LAMINATE OR SHEET OF COMPOSITE MATERIAL PLASTIC LAMINATES ARE USED TO ‘FACE’ OTHER STRUCTURAL MATERIALS, IN ORDER TO PROVIDE A MORE DURABLE SURFACE TO A SOFTER (LESS EXPENSIVE) MATERIAL  LAMINATED PLASTICS ENHANCE THE SURFACE APPEARANCE (COLOUR, POROSITY, SMOOTHNESS ETC.) INCREASE THE STRENGTH AND RIGIDITY OF MANY NON-METALLIC STRUCTURES PRODUCE OTHER DESIRABLE SURFACE CHARACTERISTICS SUCH AS WHEN ACID- OR CORROSION- RESISTANCE, NON-CONDUCTIVITY, NON- MAGNETISABILITY OR THE EASE OF KEEPING A SURFACE CLEAN IS REQUIRED  SANDWICH STRUCTURES TO PROVIDE A LIGHT-WEIGHT STRUCTURE, WHICH POSSESSES STRENGTH AND RIGIDITY, ONE OF SEVERAL STRUCTURAL MATERIALS, IS SANDWICHED BETWEEN TWO LAMINATED COMPOSITES THE SANDWICHED MATERIAL (THE CORE) MAY BE MADE OF A SOLID MATERIAL, SUCH AS WOOD, OR A SERIES OF THIN CORRUGATIONS OF A MATERIAL, WHICH ARE JOINED AND PLACED END-ON (IN THE FORM OF THE CELLS OF A HONEYCOMB), WITHIN THE LAMINATES WHERE WOOD IS USED, AS THE CORE MATERIAL, IT USUALLY CONSISTS OF LOW-DENSITY BALSA WOOD, CUT ACROSS THE GRAIN AND SANDWICHED BETWEEN TWO LAYERS OF REINFORCED RESIN (OR A METAL)  LAMINATED PLASTICS THIS CONSTRUCTION IS EXTREMELY LIGHT, YET STRONG WHICH CAN BE USED AS FLOOR PANELS, WALL PANELS AND, OCCASIONALLY, AIRCRAFT SKINS THE CELLULAR CORE, USED FOR LAMINATED HONEYCOMB MATERIAL, MAY BE MADE FROM RESIN-IMPREGNATED PAPER, OR FROM ONE OF THE MANY FIBRE CLOTHS THE CORE IS FORMED OR SHAPED AND THEN BONDED BETWEEN TWO FACE SHEETS OF RESIN-IMPREGNATED CLOTH  LAMINATED PLASTICS THE FINISHED SANDWICH STRUCTURE IS VERY RIGID, HAS A HIGH STRENGTH-TO-WEIGHT RATIO, AND IS TRANSPARENT TO ELECTROMAGNETIC (RADAR/RADIO) WAVES, MAKING IT IDEAL FOR RADOMES OF ALL KINDS METAL HONEYCOMB CORES (MADE FROM LIGHT ALLOY OR STAINLESS STEEL), ARE ALSO SANDWICHED BETWEEN TWO FACE SHEETS OF FIBRE- REINFORCED RESINS ON OTHER OCCASIONS THE METAL HONEYCOMBS MAY BE FOUND SANDWICHED BETWEEN SHEETS OF LIGHT ALLOY, STAINLESS STEEL OR TITANIUM  LAMINATED PLASTICS THIS TYPE OF CORE IS REFERRED TO AS ‘METAL- FACED HONEYCOMB’ AND IS USED WHERE ABRASION- AND HEAT-RESISTANCE IS IMPORTANT OR WHEN SOUND-ABSORPTION QUALITIES ARE DESIRED IN LARGE STRUCTURES, ANGLE SECTIONS FRAMES RIBS AND STRINGERS ARE MADE FROM SIMILAR MATERIALS AS THE OUTER LAYERS OF THE SANDWICH STRUCTURE, THEN COVERED WITH THE SURFACE ‘SKIN’, BEFORE THE STRONGER, METALLIC SPARS AND HINGES ARE ATTACHED SUCH A STRUCTURE CAN SAVE MANY KILOGRAMS (OR POUNDS) IN THE WEIGHT OF THE FLYING CONTROL SURFACES (OR THE FIN STRUCTURE) OF A LARGE AIRCRAFT. NON METALLIC COMPONENTS  SEALS SEALS OR PACKING RINGS RETAIN FLUIDS AND GASES, WITHIN THEIR RESPECTIVE SYSTEMS, AS WELL AS TO EXCLUDE AIR, MOISTURE AND CONTAMINANTS THEY ALSO HAVE TO WITHSTAND A WIDE RANGE OF TEMPERATURES AND PRESSURES AND, BECAUSE OF THIS, THEY HAVE TO BE MANUFACTURED IN A VARIETY OF SHAPES AND MATERIALS THE MOST COMMON MATERIALS, FROM WHICH SEALS ARE MANUFACTURED, ARE NATURAL RUBBER, SYNTHETIC RUBBER AND PTFE  SEALS O-RING SEALS EFFECTIVELY SEAL IN BOTH DIRECTIONS OF MOVEMENT. THEY ARE USED TO PREVENT BOTH INTERNAL AND EXTERNAL LEAKAGE, AND ARE THE MOST COMMONLY USED SEALS IN AVIATION WHERE INSTALLATIONS OPERATE AT PRESSURES ABOVE 1500 PSI, ADDITIONAL BACK-UP RINGS CAN BE USED TO PREVENT THE O-RING FROM BEING FORCED OUT OR EXTRUDED THESE BACK-UP RINGS ARE USUALLY MADE FROM TEFLON, WHICH DOES NOT DETERIORATE WITH AGE, THJEY ARE UNAFFECTED BY SYSTEM FLUIDS AND VAPOURS AND TOLERATES TEMPERATURES WELL IN EXCESS OF THOSE FOUND IN HIGH-PRESSURE HYDRAULIC SYSTEMS  SEALS O-RINGS ARE AVAILABLE IN MANY DIFFERENT MATERIALS AND SIZES (BOTH DIAMETER AND THICKNESS) THEY ARE SUPPLIED IN INDIVIDUAL, HERMETICALLY- SEALED, ENVELOPES WITH ALL THE NECESSARY INFORMATION MARKED ON THE PACKAGING FOR APPLICATIONS (SUCH AS IN ACTUATORS) THAT SUBJECT A SEAL TO PRESSURE FROM TWO SIDES, TWO BACK-UP RINGS CAN BE USED BUT, WHEN THE PRESSURE IS FROM ONE SIDE ONLY, A SINGLE BACK-UP RING IS ADEQUATE  SEALS OTHER SEALS, COMMONLY FOUND ARE V-RING AND U- RING SEALS THE V-RING HAS AN OPEN ‘V’ FACING THE PRESSURE AND IS LOCATED BY THE USE OF A MALE AND FEMALE ADAPTER THE U-RING SEALS WILL, USUALLY, BE FOUND IN BRAKE UNIT ASSEMBLIES AND MASTER CYLINDERS, WHERE PRESSURES BELOW 1000 PSI ARE ENCOUNTERED AS THEY ONLY SEAL IN ONE DIRECTION, THE CONCAVE SURFACE MUST FACE TOWARDS THE PRESSURE  COMPOSITE DEFECTS DETECTION WHILE COMPOSITES DO NOT SUFFER THE CORROSION AND CRACKING PROBLEMS, ASSOCIATED WITH METALS AND ALSO HAVE GOOD FATIGUE CHARACTERISTICS, THEY DO, HOWEVER, REQUIRE REGULAR INSPECTION FOR THE DEFECTS TO WHICH THEY ARE PARTICULARLY PRONE THE AREAS TO BE INSPECTED ARE, USUALLY WELL KNOWN AND THEY WILL BE DETAILED IN THE RELEVANT CHAPTER (51-57 FOR AIRFRAME TOPICS, 61-61 FOR PROPELLERS) OF THE AIRCRAFT MAINTENANCE MANUAL (AMM)  COMPOSITE DEFECTS DETECTION THE INSPECTION METHODS TO BE USED WILL BE FOUND IN THE NON-DESTRUCTIVE TESTING MANUAL (NTM) AND THE APPROVED REPAIR PROCEDURES WILL BE OUTLINED IN THE STRUCTURAL REPAIR MANUAL (SRM) REPAIRS IN UNEXPECTED AREAS, OR DAMAGE, WHICH IS NOT COVERED IN THE SRM, WILL NECESSITATE THE REQUEST OF SPECIFIC REPAIR DRAWINGS FROM THE AIRCRAFT MANUFACTURER  CAUSES OF DAMAGE IF A SHARP OBJECT STRIKES A THERMOSETTING PLASTIC, THE PLASTIC IS LIABLE TO CRACK AND SHATTER, LIKE GLASS, WITH STRAIGHT SHARP EDGES THE REASON FOR THIS IS THAT, ONCE A CRACK STARTS IN THE PLASTIC, IT TRAVELS VERY EASILY AND QUICKLY IN A STRAIGHT LINE DAMAGE OF THIS KIND WOULD BE DISASTROUS IN A LOAD-BEARING COMPONENT THE DAMAGE APPEARS AS A ‘STAR’ IN THE COMPOSITE, PROVIDING IT HAS NO SURFACE FINISH APPLIED TO IT  CAUSES OF DAMAGE AN IMPORTANT POINT ABOUT THIS TYPE OF DAMAGE IS THAT THERE IS LITTLE LOSS OF STRENGTH IN THE OVERALL MATERIAL, IN ADDITION TO THE ABSENCE OF THE SHATTERING THAT OCCURS WITHOUT FIBRE REINFORCEMENT THE MAJORITY OF DAMAGE TO COMPOSITE STRUCTURES OCCURS DURING GROUND HANDLING (SUCH AS FROM DROPPED TOOLS), AND DAMAGE FROM GROUND EQUIPMENT BIRD-STRIKE DAMAGE CAN ALSO REQUIRE EXTENSIVE REPAIRS  CAUSES OF DAMAGE DAMAGE TO COMPOSITE STRUCTURES MAY RESULT FROM A NUMBER OF OTHER CAUSES SUCH AS: EROSION CAUSED BY RAIN, HAIL, DUST ETC FIRE OVERLOAD CAUSED BY HEAVY LANDINGS, FLIGHT THROUGH TURBULENT AIR AND EXCESSIVE ‘G’ LOADING LIGHTNING STRIKES AND STATIC DISCHARGE CHAFING AGAINST INTERNAL FITTINGS SUCH AS PIPES AND CABLES  TYPES OF DAMAGE THE TYPES OF DAMAGE, WHICH MAY AFFECT FIBRE- REINFORCED STRUCTURES ARE: CRACKS - WHICH MAY SIMPLY AFFECT THE OUTER LAMINATION OR MAY PENETRATE THROUGH THE SKIN DELAMINATION - WHICH INVOLVES SEPARATION OF THE FIBREGLASS LAYERS AND MAY AFFECT SINGLE OR MULTIPLE LAYERS DEBONDING - THE SANDWICH STRUCTURES ARE DAMAGED, THE HONEYCOMB SEPERATES FROM THE SKIN.  TYPES OF DAMAGE ONCE THERE IS DEBONDING, THE STRENGTH OF THE WHOLE STRUCTURE IS REDUCED BY A SIGNIFICANT AMOUNT GREATER DAMAGE CAN BE DONE DUE TO THE CRUSHING OF THE HONEYCOMB CORE ITSELF BLISTERS - WHICH INDICATE A BREAKDOWN IN THE BOND WITHIN THE OUTER LAMINATIONS  TYPES OF DAMAGE BLISTERSMAY BE CAUSED BY MOISTURE PENETRATION THROUGH A SMALL HOLE, OR BY POOR INITIAL BONDING HOLES - THESE MAY RANGE FROM SMALL PITS, AFFECTING ONE OR TWO OUTER LAYERS, TO HOLES, WHICH COMPLETELY PENETRATE THE COMPONENT HOLES MAY BE CAUSED BY LIGHTNING STRIKES , BY STATIC DISCHARGE, IMPACT DAMAGE INSPECTION METHODS  VISUAL INSPECTION VISUAL INSPECTION IS USED TO DETECT CRACKS, SURFACE IRREGULARITIES (FROM AN INTERNAL FLAW) AND SURFACE DEFECTS SUCH AS DELAMINATION AND BLISTERING A LAMP AND A MAGNIFYING GLASS ARE USEFUL IN DETECTING CRACKED OR BROKEN FIBRES A SMALL MICROSCOPE OR A X20 MAGNIFIER MAY BE HELPFUL IN DETERMINING WHETHER THE FIBRES IN A CRACKED SURFACE ARE BROKEN, OR IF THE CRACKS AFFECT ONLY THE RESIN  VISUAL INSPECTION DELAMINATION MAY SOMETIMES BE FOUND BY VISUAL INSPECTION. IF THE AREA IS EXAMINED AT AN ANGLE, WITH A BRIGHT LIGHT ILLUMINATING THE SURFACE, THE DELAMINATED AREA MAY APPEAR TO BE A BUBBLE, OR AN INDENTATION IN THE SURFACE WHEN VIEWED FROM THE INSIDE, A CHANGE OF COLOUR COULD INDICATE DELAMINATION BECAUSE OF A CHANGE IN LIGHT REFLECTION A VISUAL INSPECTION CAN ALSO FIND SEVERAL MANUFACTURING DEFECTS SUCH AS RESIN-RICH OR RESIN-STARVED AREAS, PINHOLES, BLISTERS AND AIR BUBBLES  RING OR PERCUSSION TEST TO DETECT INTERNAL FLAWS, OR AREAS SUSPECTED OF DELAMINATIONS, A RING OR PERCUSSION, TEST CAN BE USED IN SOME INSTANCES A PROPERLY DESIGNED MINIATURE HAMMER IS USED FOR THE TEST IN OTHER PROCEDURES, A LENGTH OF AN APPROPRIATE HARDWOOD, OR A PARTICULAR SIZE OF COIN IS EMPLOYED TO TAP AGAINST THE SURFACE OF THE SUSPECT AREA. VARIATIONS IN THE TAPPING SOUND PRODUCED WILL PROVIDE CLUES AS TO ANY SUSPECTED DAMAGE  RING OR PERCUSSION TEST A SHARP SOLID SOUND INDICATES A GOOD BOND, WHILST A DULL THUD INDICATES BOND SEPARATION CARE MUST BE TAKEN TO MAKE ALLOWANCES FOR CHANGES IN MATERIAL THICKNESS, FASTENERS AND EARLIER REPAIRS, ALL OF WHICH CAN GIVE FALSE INDICATIONS WHENEVER DAMAGE IS FOUND VISUALLY, THEN A PERCUSSION TEST SHOULD BE DONE AROUND THE AREA IF THERE IS A HOLE, CRACK OR OTHER DAMAGE, THERE IS LIKELY TO BE DELAMINATION AS WELL  ULTRASONIC INSPECTION TO DETECT INTERNAL DAMAGE, AN ULTRASONIC TEST MAY BE DONE BY AUTHORISED, SPECIALIST, PERSONNEL THIS PROCEDURE INVOLVES THE DIRECTING OF A LOW-FREQUENCY ULTRASONIC BEAM THROUGH THE STRUCTURE AND VIEWING THE PATTERN OF THE RESULTING SOUND ECHO ON AN OSCILLOSCOPE  RADIOGRAPHY RADIOGRAPHY CAN, SOMETIMES, BE USED TO DETECT CRACKS IN THE SURFACE IN ADDITION TO BEING ABLE LOCATE INTERNAL FAULTS THAT CANNOT BE VISUALLY DETECTED RADIOGRAPHIC PROCEDURES MAY ALSO BE EMPLOYED TO DETECT WATER INGRESS WITHIN HONEYCOMB CORE CELLS