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L08 Summary - Coggle Diagram
L08 Summary
Destructive testing
** will cause damage
- costly (materials need to be cut)
- time consuming (many sample)
- specimen are selected at random from a large piece to have good indication of result
must perform according to ISO / ASTM standard
Resin, Fiber and Void Content
- during manufacturing, high chance that voids will be produced (depends how many % of voids accepted)
- 2 methods to determine the Resin, Fiber and Void content
- Matrix Ignition Loss Method (fiberglass)
- Matrix Digestion Method
- Material inside acid solution > matrix will dissolve > residue is reinforcement > filtered > wash > dry > cool > weigh
- calculate fiber volume fraction assuming the void content is 0 by using the formula
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Microscopy
Determine microstructural parameters:
- voids
- fiber orientation
- spatial distribution of fiber
- ply count
- delamination
Sample preparation is very important before sample can be viewed under microscope:
- sectioning
- mounting
- grinding and polishing
Mechanical Testing
- Destructive -> require to test sample at a specific shape
- test develop for metals and plastic usually cannot be used for composites
- due to the anisotropic nature of composite, large no. of test are usually requires to fully characterized the material
- different fixtures are used to adapt the machine for different test
- Short beam shear test > used to bend the sample > allow to measure interlaminar shear strength
- similar to flexural test
- difference is that the material is shorter, the span length is also shorter > minimize flexural and maximise shear stress
- force will be in the middle with 2 support
- longitudinal waves
- V-notch beam testing method (in plane shear) -> iosipesco method
- force will be at both top and bottom (diagonally)
Compression after impact (residual strength) -> drop weight of known mass > impact energy is controlled by the height of the mass
ASTM / ISO guidelines:
- Specimen shape and size
- Precaution to be taken test set up and apparatus
- Specimen conditioning
- Acceptable failure mode
- Calculation and report
Testing Condition:
- Machining effects
- Alignment of specimen
- Conditioning and environmental test chamber
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Non Destructive testing
The main techniques used for composites parts are:
- Visual inspection
- Tap testing
- Ultrasonic
- Radiographic
- Thermography
Visual Inspection
- damage such as dent, penetration, crack can be observe
- visual aids: fiberscope, boroscope, magnifying glass, mirrors
- only surface defects can be detected
Tap Testing
- damage present when there is a change in sound
- indicative of an underlying defect
- automated tap testing cannot detect deep damages / small defects
Ultrasonic
- ultrasonic wave or energy will absorbed / reflected when there is damage
- travel through the material (no crack echo)
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- velocity = distance/time
- distance of defect = velocity x time
- air gap between transducer & specimen causes ultrasonic energy to reflect
- little energy pass through specimen
- couplant displace the air gap and facilitate the transmission of ultrasonic energy from the transducer into the test specimen
advantages
- detect deep defects
- determine size and shape
- safe method
disadvantages
- less suitable for large-area inspection
-> slow scanning and coupling needed
- not appropriate for thin component scanning
- required calibration standards
- thorough preparation needed for interpreting signals
Angle Beam Technique
- detect any flaws that is covered
- wedges are attached at various angles to cause refraction
- wedges are often used by straight beam probes to shield the surface of the transducer from scratches/abrasion.
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- transverse / shear waves
Thermography
- consists of all procedures used to calculate temperature differences for sections under examination by heat sensing instruments.
- commonly, heat source is present to heat up the component that is being tested
- once the part cools down, infrared camera monitor the part
- can detect debonding, delamination, inclusion and thickness and density variations
- defect-free areas conduct heat more successfully than areas with defects, showing the amount of heat reflected where any defects are present.
- can inspect large area quickly
- couplant are not needed
- suitable for thin laminates or when defects are near the surface
- difficult to detect deep defects
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Data representation
- A scan (plot of signal amplitude against time)
- B scan (transducer is move across the sample to generate cross-sectional view
- C scan (top view of scanned part)
-> transducer move systematically
Bond Testing
- Unlike conventional ultrasonic testing, bond testers uses a dual element probe that contains two elements
- One element transmits sound waves and the other element receives the waves.
- As audible sound energy is used, little loss of energy occurs and hence couplant is not needed.
- The presence of defects will cause changes in the amplitude and/or phase of the received sound waves.
Composite testing
**very important to quantify material properties and detects defects of material
- Design Data (can the material withstand the load)
- Quality control (does it meet criteria, check for defects)
- Failure analysis (find cause of failure)
- Repair and Maintainence (check for damage, where is the damage)
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Material property Data:
- Fiber volume ratio
-> load bearing properties
-> higher fiber > strength material properties
-> help to withstand high load
- Tensile properties
- Shear properties
- Flexural properties
- Compressive properties