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56 Cards in this Set
- Front
- Back
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4 General Considerations of Test Specimens
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Quantifiable Measurement
Specimen Configurations Repeatability Preperation of Specimen |
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How to Avoid Defects in Testing
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Anisotropy (Load and test in direction of use)
Loading Rate Samling Statistics |
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How to test to see if resin is good?
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Viscosity test
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Pot Life
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How long lasting after mixing
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Shelf Life
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Hoow Long Resin can be Used
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Single fiber pull out test
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One single fiber embedded in resin. Fiber breaks first because of lower elongation.
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Gel Time
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How long the resin takes to cure.
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How to test for Gel Time
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Mix resin and poke with a stick, look for no liquid on the stick.
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Peak Exotherm
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Max temperature reached during cure.
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How to test fibers
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TMA (mechanical)
Laminate testing Density |
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Pre-Preg Testing looks for
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Resin content of pre-preg
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Seven pre-preg testing methods
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Burn Out
Solvent Extraction Acid Digestion Tack and Drape Microscope slide with coverslip (Degree of cure) Flow Testing Volatile Content |
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Flow Testing Procedure
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Make test coupon
Weigh it Laminate it Curin press under pressure Measure % Flow |
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Volatile Content Procedure
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Suspend sample in oven
Measure % Volatile |
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What are you looking for with the volatile content test?
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Solvents
Moisture Aerospace specifications |
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Three approaches to laminate testing
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Assemblies
Subassemblies prior to full ass. Test specimens |
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How do you do destructive testing, but not harm the sample
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Make a test coupon on the layup.
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How do you modify tensile testing for composites?
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Pot core on the tabs
Make tabs thicker |
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Bow-Tie Specimen vs. Dog Bone
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Much more gradual transision from midpart to clamping region
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How do you test for laminate shear properties
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Short beam shear test.
Staggered duel notch Torsion Tube (best for +- 45 orientations) Picture frame Rail shear |
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Compression modes of failures
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Brooming
Induced transverse matrix failure Fiber microbuckling Large scale buckling Delamination failures |
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Most desirable form of shear failure
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Fiber microbuckling
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What is brooming caused by?
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Compression loading head on (directly on the end)
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How do you aviod brooming?
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Load differently or add aluminum sleeve to turn load into a shear load.
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Induced Transverse Matrix Failure
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Tensile failure of matrix/fiber interface
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Fiber Microbuckling
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Fibers buckling and putting an extensional load.
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Three modes of adhesive failure
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Substrate
Adhesive Cohesive |
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What kind of adhesive failure is most desirable?
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Substrate failure
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Cohesive Failure
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Failure of the adhesive itself. Adhesive itself was not strong enough.
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Adhesive Failure
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Comes off the substrate
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Dillman recommended method of surface prep. (8 steps)
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1. Remove peel ply immediately before bonding
2. Rinse surface 3. Dry 4. Abrade surface 5. Clean 6. Clean with solvent 7. Rinse 8. Dry |
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How do you avoid punch through at loading points?
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Doublers
Add potting compound to loading area. |
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What's the first step to identifiying the cause of failure?
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Collect background info
- Circumstances under which it failed - Service history Was this expected? - Were services performed? |
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What if the fracture is not adequatetly explained by the background info?
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Continue with stress analysis
Develope special tests if needed. |
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What if the fracture is adequatetly explained by the background info?
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Non-destructive examination
Material configuration verification. - Correct materials were used - Correct sequences were used |
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How do you define a fracture?
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Origin
Mode Environment Contaminants Defects Damage before failure |
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Why use quantifiable measurements for test methods?
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Less judgement the better
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Why are dogbone testing samples poor?
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Slippage and failure at the neck.
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Three modes of failure in a sample.
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1. Intralaminar
2. Interlaminar 3. Translaminar |
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Intralminar Failure
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Matrix failure
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What are the contributing causes to intralaminar failure?
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Poor fiber-matrix bonding
Too resin rich |
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Interlaminar Failure
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Failure at the interface between the plies
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Causes of interlaminar failure
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Large angles between plies
Expired pre-preg Poor handling |
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Translaminar
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Broken fibers
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How do you tell a peel failure?
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Cracks point towards origin
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How do you tell a shear failure?
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Hackles. Matrix raised above the surface.
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Ultrasonic tests
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Non destructive, can do 100% test.
Lighter the color bad. |
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What can you tell from an ultrasonic test?
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Foam density
Honeycomb Potting Location of reinforcement |
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Problems with mechanical fasteners: (6)
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- Holes
- Corrosion in carbon - Fastener can damage composite - Must add insert to screw - Compressive loads - Stress concentrations |
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Advantages to mechanical failures: (6)
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- Disassembly/repair
- Inspection - Existing technology - Non-toxic - Small joints - faster - Good for peel loads |
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Advantages of adhesive bonding: (11)
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- Avoids holes
- Complex shapes/contoures - Disperses load - Faster for large parts - Fewer total parts - Lighterweight - Smoother surfaces - Large joints less expensive - No corrosion issues - Perform better in most cases - Better fatigue props. |
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Disadvantages to adhesive bonding: (6)
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- Poor peel performance
- Disassembly/inspection - Poor high temp performance - Creep @ high temps and shear - Testing is mandatory (variables) - Accuracy is critical |
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Two most important things for bonding:
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1. Surface area of bond.
2. Thickness of bond (want thing as possible as long as you have a continuous bond) |
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What makes for a good adhesive: (4)
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- Must be compatible with the substrate
- Mechanical properties - Properties below/above the Tg - Don't want adhesive to be super stiff. (Flex reduces stresses at joint) |
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Why when the area of a bond significantly increases does the strength improve very little?
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Nothing has been done to reduce the stress concentrations on the end of the joint.
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How do you increase the sterength of a bond?
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Bevel the edges. Square edges - no good.
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