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L09 Summary - Coggle Diagram

- - - - poor design -> product cannot withstand exposure to typical condition -> poor structural or material selection
    - - products used do not have the properties needed / have to many defects
    - - Conditions of operation which are beyond the specification specifications
        
        E.g misuse or irregular conditions of operation
  - - - fibers are broken
        
        90deg to fiber
    - - layers have separated
        
        delamination
    - - only matrix OR fiber/matrix interface are broken
        
        crack
        
        white area/line
  - - - wear disposable clothing and respirators to prevent contamination so that it will not come in contact with skin and prevent it from entering our lungs
        
        failed composite parts may contain splinter, loose fibers and dust
        
        disintergrated fibers are small (micro size) can enter to our lungs and cause skin irritation
    - - preserve original fracture surface
        
        so that fracture morphology is not obscured
      - mechanical or chemical
      - makes it harder to detect surface fracture
      - if never handle properly, it can create more damage unnecessary
  - - - 2. Visual Inspection
        
        provide information on fracture modes
        
        Suggest sub-surface damage (ultrasonic is possible but have risk, tap testing, etc)
        
        Damage below surface (interlaminar) can be hidden
        
        Use non destructive testing to identify the hidden damage
        
        3. Non-Destructive testing
        
        The extent of sub-surface damage should be determined to prevent the destruction of important information during dissection
        
        use ultrasonic testing -> delamination can be identified
        
        if there is contaminants -> use couplant
        
        4. PHOTOGRAPHY
        
        to keep record of failed parts before dissection
        
        parts must be labelled and measured (length)
        
        take wide shots THEN close up
        
        5. Dissection
        
        water cooled cutting (not recommended)
        
        dry diamond rotary saw (recommended)
        
        chisels, wedges and lever can cause more fracture surface but can exposed delamination
        
        fracture surface need to be cleaned
        
        use light fiber or compressed air gun if the dust is obscuring the surface
        ->if both method does not work use, use ultrasonic bath then dry with vacuum oven
        -> this method will remove chemical residue that cause the failure
        -> hence this process should be done with caution
        
        6. Verification of material and construction
        
        common mistake: incorrect stacking
        -> used materialography to confirm the stacking sequence
        
        fiber perpendicular -> cutting direction is circular
        
        fiber parallel -> cutting direction is lines
        
        cutting at angle can help to identify the angle of plies (+45°, -45°)
        
        FTIR: identify chemical species
        -> matrix type may be characterized
        
        DSC: measure glass transition temperature and residual heat of reaction
        ->determined degree of curing of matrix
        
        Matrix digestion and matrix ignition: remove matrix material in composition
        -> determined fiber volume content
        
        7. Optical and Electron microscope
        
        optical (light)
        
        electron (SEM)
        
        SEM used when high magnification(nanometer) and greater depth of field is needed
        
        SEM can only allow limited size of fracture
        -> large fracture is harder
        
        SEM must be examined in high vacuum
        
        if material is wet / contaminated, it is harder to examine the material
        -> evaporation will cause it harder to obatin high vacuum levels
        
        if damage is due to contaminant, do not use SEM
        
        non-conductive need to be coated with conductive film before examination
- - - - compression
        
        microbuckling
        
        fiber that undergo microbuckling will be bent
        
        fiber surface will reveal chop mark
        
        flexural failure
        
        presence of both tensile and compressive failures
      - tension
        
        radial lines
        
        crack grows from initiation site, fracture will be rougher forming the radial lines
        
        can tracked crack growth direction
        
        can indicate fiber/matrix strength
        
        fiber/matrix strength is weak > degree of debonding is high > broom like structure
        
        fiber/matrix strength is high > degree of debonding is low > smooth fracture surface
  - - - direction of delamination can be deduced from the textured microflow and scarps
        
        delamination may be formed by multiple fractures occurring and converging
        
        when separate crack fronts meet -> scarp formed
        
        scarp usually parallel with the overall crack growth direction
      - riverlines can help us to conclude the direction of crack growth
        
        convergence of pairs of cracks form the “tributaries” of the rivers and ultimately converging into one crack.
        
        therefore , the direction of the crack is the same as the direction in which the riverlines converge