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ASM Block 7
Composites
| Question | Answer |
|---|---|
| What are two methods to apply pressure to a repair? | positive and negative |
| What is the best method of applying even pressure to a repair area? | negative |
| In a vacuum bag set up, Nylon is considered what type of release agent? | film |
| In a vacuum bag set up, what material is used to wick the excess adhesive from the repair site? | bleeder |
| What inert fillers can be used to make a potting compound? | chopped glass fibers, micro balloons, cab-o-sil |
| What substance causes a resin to cure? | catalyst/hardener |
| As little as how much of moisture can degrade the matrix material within a composite structure? | 1% |
| When is moisture removal performed? | Prior to performing any bonding (repair) |
| Which matrix system under goes a chemical change when it cures and cannot be reheated and reformed? | Thermoset resin |
| Which thermoset matrix is not to be used on structural components? | polyester resin |
| What transfers stresses between the load carrying facings (skin)? | core |
| Why is core density important? | maintains strength in the structure |
| What solvents work well on composite materials? | MEK, Trichloroethylene, and isopropyl alcohol |
| Which paint removal technique provides a quick removal rate? | abrasive blasting |
| During material removal you should always removed how much amount of sound material? | minimal |
| List some disadvantages of advanced composites? | Expensive raw material cost, labor intensive, moisture absorption, special training and skills are required, short shelf life. |
| The primary function of the core is to __________ from one laminate/face to the other. | Transfers the load |
| What is a laminate? | Two or more layers or plies of advanced composites bonded under heat and pressure |
| what part carries loads in a sandwich constructed panel? | Facing/laminate |
| How are advanced composite better than metals? | stiffness to weight ratio up to 10x higher than most metals, lighter, stronger |
| A composite is made of ____________ and a _____________ system. | fibers (filaments) and a matrix system |
| The fibers give the component ________ and __________ strength and the matrix system provides the component with its _____________ strength. | Tensile and shear, compression |
| What are the hardest and strongest advanced composite fibers? | boron |
| Define advanced Composite? | Embedding high stiffness fibers within a matrix. |
| What indicates the direction in which the strength lies and runs with the roll? | warp |
| What is the term used to ID the fibers running perpendicular to the roll? | fill |
| What is the stitching that runs up both sides of the fabric to keep the fibers from unraveling? | Selvage edge |
| What are the threads of a different color than the parent fibers running two inches apart indicating the warp and six inches apart indicating the fill? | tracer threads |
| What code is used to translate the engineer's angles to the repair site? | Standard Industrial Laminate orientation Code |
| What is a cross ply? | A cross ply lay-up in which the laminates are at right angles to one another |
| what are the two types of Quasi-isotropic lay ups? | symmetrical Laminate, balanced laminate |
| What inspection method is generally effective up to a surface thickness of .080? | Tap testing |
| What is a puncture? | 2. Hole punched through all plies of laminate |
| What are the three distinct steps in damage assessment? | Locate, evaluate, re-evaluate |
| Once advanced composite damage has been identified in should be classified as ? | 4. Negligible, repairable, and non-repairable |
| What is an adhesive failure at a bondline? It usually occurs between _________ and the _____________? | 5. Disbonds, honeycomb core and laminate/facings |
| What is considered one of the most critical steps of a repair? | Surface prep |
| What are the three methods of inspection? | 7. Visual testing, tap testing, and NDI |
| What is a scratch/gouge? | 8. One or more plies of broken fibers are damaged but the facing has not been fully penetrated |
| What is a dent? | 9. Hollow or low place usually caused by impacts Deformed but not broken fibers |
| What is the goal of damage removal? | 10. Eliminate the damage material and leave as much sound material as possible |
| What are used to define patch layouts and aid in construction and laying up repair patch plies? | 1. Templates |
| What are overly plies? | 2. Add additional plies that add strength |
| When performing a step-joint repair how are the damaged plies removed? | 3. Cut each ply is removed separately and the join has a stepped appearance when finished |
| What are three common repair joints? | 4. Step joint, scarf, overlap/scab |
| Which common repair simply covers the damage area with a patch? | 5. Overlap/scab |
| Which type of repair method is used when curing two different resins at the same time? | 6. Co-cured |
| How can overlap repairs be fastened to the structure? | 7. Bonded or mechanically fastened |
| On what type of structures are Scarf repairs typically used? | 8. highly loaded structures |
| Scarf Ratios are determined according to the _________ that must be transferred? | 9. Loads |
| What grit sandpaper is used to rough sand by hand to scarf into the laminate? | 10. 80-150 |
| What is an advanced composite? | Embedding high stiffness fibers in a matrix (resin) |
| What type of strength do advanced composite fibers provide? | tensile and shear strength |
| What type of strength does a matrix provide? | compression |
| Compared to conventional composites what type of strength does Advanced composites provide? | Superior tensile and compression strength |
| What are some advantages of advanced composites? | High strength to weight ratio, Stiffness to weight ratio up to 10x higher than most metals, More resistant to fatigue than metals, Corrosion resistance, Aerodynamically smooth, LO characteristics, Low damage propagation, Increased design flexibililty |
| What are some disadvantages of advanced composites? | Expensive raw material cost, Manufacture and repair are labor intensive, Hidden damage is hard to detect, Short shelf life, Moisture absorption (aramid), Fabrication and repair require special training and skills, Require climate controls |
| What is the primary load carrying element in broadgoods? | fibers/filaments |
| What is meant by unidirectional? | all fibers run in the same direction woven fabric |
| What is the purpose of broadgoods? | carry loads applied to the laminate (tensile/shear strength) |
| What is warp? | indicates direction in which strength lies (longest) |
| what is meant by selvage edge? | seam stitching that runs up the edge of both sides of the fabric to keep the fibers from unraveling. |
| what are tracer threads? | different color threads that are used in directionally strong broadgoods to identify the warp and fill of the fabric. |
| What are some characteristics of fiberglass? | will not burn, fabric appears white, very flexible, can be woven/formed into almost any contour |
| What are some types of woven glass cloth? | E-Glass, S-Glass |
| What are the characteristics of E-Glass? | High electrical resistance, Most common all purpose glass fiber |
| What are the characteristics of S-Glass? | Higher tensile strength than E-glass, Used for special applications |
| What are some characteristics of carbon/graphite? | Most common advanced composite for acft structures, Dark gray or black in color, Moderately flexible, Stronger than fiberglass. |
| What type of broadgood can cause Galvanic corrosion on metal surfaces? | Carbon/graphite |
| Depending on the process of manufacturing for Carbon/graphite what can be modified? | Tensile strength and stiffness |
| What are the types of Carbon/graphite? | I, II, III |
| What type of Carbon/graphite is used most commonly in the aircraft industry? | II |
| What type of Carbon/graphite is used in the aerospace industry? | I |
| What type of Carbon/graphite is used in tooling and carbon brakes? | III |
| What are some characteristics for Aramid (Kevlar)? | Outstanding toughness (abrasive resistant), Stronger than fiberglass, Yellow color, Generally weak in compression, Tensile strength twice that of fiberglass, Difficult to cut due to abrasive resistance |
| What are the two types of Kevlar? | Kevlar 29 and 49 |
| Kevlar 29 is used for what applications and why? | ballistic applications because of lower stiffness and greater stretch |
| Kevlar 49 is used for what applications and why? | aircraft structures because of great stiffness and lower stretch |
| What is the stiffest and strongest fibers? | Boron |
| What are some characteristics of Boron? | High tensile and compressive strength, Low galvanic corrosion potential, Cannot be formed into complex shapes without snapping, Available only in unidirectional prepreg tape |
| What type of broadgood can be used for repairing cracked metallic structures? | Boron |
| What are some Non-structural conventional composites and their uses? | Chopped fiberglass, mat binder (fiberglass) and can be used for electrical junction boxes, battery boxes, and molded assemblies. |
| What is the purpose of matrix systems? | adhesives provide three dimensionally stabilizers/bonds fibers together in order to carry stress as needed |
| What are some properties of matrix systems? | Provides Compression, shear, inter-laminate shear strength and works within a range of service temps |
| What is the most common (standard) resin? | epoxy |
| What is a laminate construction on advanced composites? | 2 or more plies bonded under heat and pressure |
| What translates the engineer's angles to the repair site? | Standard Industrial Laminate Orientation Code |
| What type of ply is oriented at only right angles with respect to the principal fiber direction? | Cross ply 0°, 90° or -45°, +45° |
| What is an angle ply? | Containing plies alternately oriented to any angle to reference axis not including 0 and 90. 60°, -60°, -45°, +45° |
| What ply has equal strength in virtually all directions? | Quasi-Isotrpic |
| How are plies oriented on Quasi-Isotropic? | Symmetrical with an equal number of plies at 0°, +/_ 45°, 90° |
| What type of ply is mirrored about the laminate mid-plane but not necessarily Quasi-Isotropic? | Symmetrical |
| What has each positively angled ply is balanced by negatively angled ply and the location of the opposing angled ply can be located anywhere in the laminate ? | Balanced |
| What type of construction has a core bonded to laminate/face plies? | Sandwich construction |
| What carries the load that is applied to the structure? | facings |
| What transfers load from one laminate/facing to another? | core |
| What is a filament wound? | Single strand of filament wound over a specially designed form, mold or die |
| What type of aircraft part is made using a filament wound? | fighter radomes |
| What are the three ways for inspecting composites? | visual, coin tap, NDI |
| What are the three steps in damage assessment? | Locate, Evaluate, Re-evaluate |
| what is performed during the locate step of damage assessment? | Locate center of damage, establish Coordinate system (orientation code), perform a visual insp, tap test and/or NDI inspection. |
| What TO would you use for the general reference during Evaluation step of damage assessment? | TO 1-1-690 |
| What do you determine during the evaluation step? | Type, depth and size of damage. |
| What TO do you always refer to during the Evaluation step? | Weapon system specific structrual TO |
| What two steps are used in damage removal in the Evaluation step? | 1. remove minimal amount of sound material. 2. use simple geometric shapes |
| What are reasons for re-evaluating the repair? | Damage may have been enlarged during removal, Defects can be hidden under other defects that are closer to the surface. |
| What are some damage causes? | Vibration, ground handling, rain erosion, electrical discharge (static), Water |
| What does water damage do? | Destroys electrical effectiveness and range of radar, causes delaminations and disbonds. |
| What are some signs of static discharge or electrical damage? | pin holes, burn spots |
| What can have an high speed impact and lead to rapid deterioration of composite surfaces? | rain erosion |
| What type of damage can be caused by careless mx practices and items be pushed or blown against the acft? | Ground handling |
| What causes worn holes, delamination and cracks? | vibration |
| What are the three classifications of damage? | Negligible, repairable, non-repairable |
| What classification has no fiber damage? | negligible |
| What classification has fiber damage but can be fixed on base? | repairable |
| What classification cannot be fixed on base? | Non-repairable |
| What is a surface scratch? | does not damage the parent laminate fibers or the internal structure |
| What is a dent? | A hollow or low place usually caused by impact, It will usually have deformed fibers, but no broke fibers |
| What is delamination? | Separation of the plies in the laminate |
| What is a disbond? | Separation (adhesive failure) at the bondline between the core and facing/laminate |
| What is a scratch and gouge? | One or more plies are broken Structure/skin has not been fully penetrated |
| What is a puncture/perforation? | any penetration of a structure |
| What is heat/burn damage? | Exposure in excess of the part cure temperature |
| What are some common repair joints? | scarf joint, step-joint, overlap |
| What type of joint repair is typically used to repair laminates on highly loaded structures? | Scarf Joint |
| During a scarf joint repair how are plies removed? | by sanding forming a smooth, shallow depression |
| Is is meant by Scarf Ratio and how is it determined? | Depth of damage removed to width of damage removed of repair and is determined by the load the panel must transfer/carry. |
| During scarf sanding what grits are used and what is the purpose of the grits? | 80-150 for rough sanding, 150-240 finish sanding |
| How is a Step-joint repair accomplished? | Plies removed separately forming a terraced or “stepped” shape, Achieved by physically cutting and peeling the plies or by machining with a router and template (on Boron composites) |
| What type of Joint repair is used primarily on Boron and Aramid? | Step-Joint |
| How is an Overlap repair secured to the panel? | Bonded and/or bolted |
| Where is an Overlap repair normally used? | used on thicker laminate structures where scarf or step repairs would not be feasible |
| What repair materials are used to repair core damage using a potted repair method? | Epon 815, curing agent, Cab-O-Sil, fiberglass woven cloth |
| What repair material is different on the potted repair method than the core replacement method? | Core replacement method has a replacement core |
| What are three ways to remove paint? | Hand sanding, power sanding, plastic media blasting |
| What tool is used specifically to remove damage in composite materials? | Diamond coated cutters or carbide/cobolt cutters |
| What is used to remove damage from a metal facing? | Router bit |
| How much material should be removed from the repair? | minimal amount |
| What is required prior to bonding composite repairs? | moisture removal |
| What is used for accurate cutting of repair plies? | template |
| What type of repair method is most commonly used in the field? | wet lay-up (A-Stage Resin) |
| During the Wet lay-up what does vacuum assisted impregnation used for and why is it preferred? | to saturate the fabric with more control and is preferred for tight-knit weaves and when near optimum resin to fiber ratio is required. |
| What is meant by co-cure? | Curing repairs plies and simultaneously bonding them to the prepared structure during the same cure cycle |
| What is meant by pre-cured? | Patch is pre-manufactured (cured) then bonded to structure during another cure cycle |
| What is meant by Resin injection? | Resin injected to fill a delaminated region |
| What is the purpose of the cure process? | to achieve the max strength of the repair |
| Describe a "J" wire Thermocouple. | connectors/ plugs are black in color, round pins, pos lead (white), neg lead (red) |
| Describe a "K" wire Thermocouple. | connectors/ plugs are yellow in color, flat pins, pos lead (yellow), neg lead (red) |
| What type of care should be taken for Thermocouples? | No sharp bends, no kinks, test before use |
| What is a Thermocouple? | A two-wire probe that when connected to a reading device indicates the temperature in the repair area |
| What are you measuring when the thermocouples are attached to the panel? | Temp of Adhesive |
| How should thermocouples be placed on the repair site of the panel? | Strategically located around the repair area to ensure good sampling of heat measurement, 1/2"inch from adhesive line, Control TC must be 90° from the power cord, Distance from ac power cords approx. 1â, no TC wires under vac ports & no wires crossed |
| When testing thermocouples describe the procedures ensure no issues will occur. | Check for correct wiring and positive/negative terminals for tightness, Unwind TC wire check for kinks, Inspect junction (weld), Place wire between fingers –temperature should rise and fall when released, measure room temp |
| When welding the thermocouple together what temp should be obtained to ensure a good thermocouple? | 800° F |
| How much insulation should be stripped off Thermocouple prior to welding? | 1/2" |
| What does a hot bonder monitor and control? | cure temps and vac levels |
| What alarm code would describe under temp and what would be cause? | "U", TC is too far from repair site |
| What alarm code would describe Low Vacuum? | V |
| What alarm code would describe over-temp? | O |
| What alarm code would describe the TC open and not sensing? | T |
| What alarm code would describe high/low limit? | H/L |
| What alarm code would describe no heat and what would be the cause? | P, Heat blanket failed or not plugged in |
| When temps are falling what is the alarm code and what may be the cause? | F, TC may be wired backwards |
| What is the best way to detect moisture? | using radiography (x-ray) |
| Describe the weight method for moisture removal? | weight method- weigh before then heat to 150° until dry, then weigh again until weight is the same consistently. |
| When is "Reading" the laminate required? | when data showing ply orientation is not available |
| What is meant by "Reading" the laminate ? | a process where the ply orientation is identified |
| When creating a template what is important in achieving max strength in a repair? | Patch Drawing (visual aid) “blueprint”, Stacking sequence |
| What does a sanding template do? | Protects undamaged material, Aids in making repair the desired shape and size |
| What is a cutting template used for? | cutting patch plies |
| What is a Stacking template used for? | stacking patch plies |
| When handling B-Stage Resins what is required before using them? | Remove materials from freezer, Allow repair material to come up to room temp before opening, No visible moisture on the outside of the bag |
| Where is the film adhesive placed? | Placed on bottom of patch |
| How is the patch replacement placed on the structure? | using ply orientation code |
| What is the min vac level for a Vacuum application in hot bonding? | 20 Hg (20 inches of mercury) |
| When placing the vac ports how should the vac be pulled and where should the measuring vac port be placed in hot bonding application? | Pull vac from one side of repair and Measure vac from opposite side of repair |
| What should you not do when placing vac ports in hot bonding application? | place Vacuum ports on top of Heat blanket or any wires |
| When are you able to de-bag the repair? | When cure is complete |
| What is the first step when de-bagging the repair? | Disconnect from the hot bonder |
| What items should be disconnected from the hot bonder before debagging? | TC, Heat blanket, and vac hoses |
| The time between soaks at which the temp is either rising or falling is called? | ramp rate |
| The ramp rate should fall within how many degrees a min? | 3-10° book or 4-8° AirForce |
| What items that have been used with any type of resin systems must be cleaned immediately after use? | any tools that |
| Which is the most commonly used plug? | J |
| Why should you test thermocouples? | to get an accurate temp reading |
| What min temp should you attain when welding TCs? | 800° |
| On a "J" type plug connector what color is the pos lead? | white |
| When doing a laminate and overlap repair place the TC how far from the adhesive edge? | 1/2" |
| Where should the control TCs be positioned? | 90° from the power cord |
| How far do the TCs have to be from AC (alternating current) power cords? | 1" |
| Why should TCs wires never be crossed when inside a vac bag? | can cause damage to the TCs and cause false readings |
| What is the portable, self-contained hot bonding system designed to do? | Control temps and monitor curing temps and vac levels |
| On an HB-2 Hot Bonder, how many thermocouples can be assigned per zone? | 8 per zone |
| What is the max number of soaks that can be programmed? | 6 soaks |
| Once an alarm has sounded, what key do you press to acknowledge that a problem exists? | E |
| If an alarm is sounded and a visual flashing "T" is displayed, what are you going to troubleshoot on the HB-2? | TC |
| If an alarm is sounded and a visual flashing "V" is displayed, what are you going to troubleshoot on the HB-2? | Vacuum |
| HB-2 Hot Bonder, an alarms is sounded and a visual flashing "P" is displayed, what is the reason for the alarm? | No heat, heat blanket may not be working or unplugged |
| How is moisture detected in the core? | Radiography (x-ray) (preferred) or weight method |
| What should be included in a patch drawing? | coordinate system, stacking sequence, and ply orientation |
| The first step in generating a patch drawing is? | transfer coordinate system |
| After the patch drawing has been completed on a scarf repair what should be constructed next? | Sanding template |
| What material should be used when constructing a stacking template? | mylar or other wax free material |
| What material is used for a cutting template? | mylar or nylon |
| What info is found on a cutting template? | orientation code, ply orientation, stacking sequence |
| Sanding templates can be constructed from what? | mylar, flash tape, or masking tape |
| Ply orientation and stacking sequence are both very important in achieving what in a repair? | Max strength |
| When handling film adhesives, prepreg fabrics or parts with prepared surfaces, what type of gloves must be worn? | powder free latex, clean white cotton lint free, nitrile gloves |
| A common rule of thumb for drying a composite is to heat the part to how hot and hold it at the temp until dry? | 150° |
| What is required when using a flat fluted drill bit to drill composites? | Drill guide |
| What type of bits shall not be used for drilling composites? | Standard twist drill bits. |
| What type of damage will a standard twist drill bit cause? | ply delamination, fiber damage, and unacceptable hole quality. |
| What type of drill bit would you use on graphite and fiberglass? | Straight-fluted carbide drill reamer |
| What type of drill bits are used for Boron? | diamond coated |
| What do you use when drilling into composites? | sacrificial back up material |
| How do you minimize dust when drilling? | use a vacuum while drilling |
| During hole inspection what are you checking for? | Splintering, delamination, fraying, and elongation |
| When countersinking what is the max depth allowed? | 2/3 of skin thickness |
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comso9o
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