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56 Cards in this Set

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