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A395 P09 Summary Note - Coggle Diagram

- - - - Flow direction of the structure is in the growth direction of the fracture
    - - For easier identification of the overall crack growth direction, think of the scarp and textured microflow creating an arrow to show the direction
- - - - Typical conditions: temperature, pressure, humidity
      - Due to poor structural design or material selection
  - - - Misuse, unusual serive condition such as operating in extremely high temperature, under excessive pressure, etc
- - - - 90 Degree or perpendicular to the fiber direction
  - - - Matrix / Resin / Fiber matrix starts to split
  - - - Layers have been separated
        
        90 Degree or perpendicular to the fiber direction
- - - - Skin puncture, skin irritation and contaminants entering the lungs can occur
  - - - Must be prevented so the fracture morphology is not obscured
      - Destroy clues that enable the determination of the root cause of failure
      - Makes interpretation of fracture surface difficult
        
        Unable to differentiate damage caused during failure or post failure
- - - - Background infomation
        
        Material used, lamiante design (stacking sequence), Manufacturing method, Service history, Repair history (if applicable)
      - Visual inspection
        
        Provide information about fracture mode by inspectinfg fracture surfaces
        
        Deformation of surfaces may suggest sub-surface damages
      - Non-destructive testing (NDT)
        
        Determine the sub-surface damage
        
        Prevent the destruction of vital information during dissection
        
        Ultrasonic testing can allow for the detection of sub-surfaces damages such as delamination
        
        Not usable when contaminants are suspected to be the cause of failure
        
        Couplants used in ultrasonic testing can remove or change the contaminants
      - Photography
        
        Record the failed component before dissection
        
        Sample shoiuld be labelled and with a scale provided
        
        Wide angle shots are taken before closer shots
        
        Provide context for people analysing the photo
      - Dissection
        
        Water-cooled dissecting equipment should not be used
        
        Carbon dust and oils or liquid from cooling system may contaminate fracture surface
        
        Dry diamond rotary saw is mostly used
        
        Chiels, wedges and levers are used for exposing delamination and leveraging fracture surface apart
        
        Care should be taken during dissection to prevent damage to fracture surface
        
        Fracture surface need ti be cleaned before and after dissection
        
        Cleaning is difficult and there is a probability that artefacts may be introduced, confusing the interpretation of fracture surface
        
        Presence of dust on surface
        
        Brushing with light fiber brush or use dry compressed air
        
        Ultrasonic bath and drying in vacuum oven can be used if previous method does not work
        
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      - Verification of material and construction
        
        Wrong stacking sequence is a common manufacturing error
        
        Stacking sequence can be determined by materialography
        
        Fibers perpendicular to the cutting direction will appear circular while fibers parallel to the cutting direction will appear as lines
        
        Angled cutting allows angled plies to be differentiated
        
        Other methods
        
        FTIR
        
        Type of matrix can be characterized
        
        Identify chemical species
        
        DSC
        
        Matrix degree of cure can be analyzed
        
        Measurement of glass transition temperature (Tg) and residual heat of reaction
        
        Matrix digestion / Matrix ignition
        
        Determine fiber volume content
        
        Remove matrix material in composite
      - Microscopy
        
        Optical microscopy (light) or scanning electron microscopy (electron) can be used
        
        Scanning electron microscopy (SEM) have higher magnification (down to nanometer) and greater depth of field
        
        SEM limitations
        
        Large fracture surface viewing is very tedious
        
        Size of specimen must fit into SEM chamber
        
        Inspection of specimen via SEM must be done in high vacuum
        
        Wet or contaminated samples with volatile material are difficult to be examined
        
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        Non-conductive sample must be coated with conductive film
    - - NDT is used to identify internal and hidden fractures
- - - - Morphology of racks that occurs first is continuous when viewed on a cross-section of a fractured laminate
      - Cracks that are arrested or deflected by a crack did not occur first.
- - - - Types of failure mode
        
        Tension
        
        Fibers failed via tension are characterized by radial lines
        
        Radial lines are formed due to the propagation of cracks from the initiation site, producing rougher fracture topography
        
        Radial lines can be used to infer the crack propagation direction
        
        Inspecting and tracking the fracture morphology of the individual fibers, allows the local crack propagation direction to be tracked
        
        Fiber/matrix interface strength
        
        Can be deduced by fracture morphology
        
        Weak fiber/matrix interface strength, the degree of debonding is high and results in broom-like failure
        
        Strong fiber/matrix interface strength, the degree of debonding will be low and result is a relatively smooth fracture surface
        
        Compression
        
        Fibers failed via compression are characterized by microbuckling of fibers
        
        Materialography done on the cross-section of the sample can help to confirm microbuckling occurred
        
        Fibers that undergone microbuckling are bent
        
        Surface of individual fibers reveal chop marks when inspected
        
        Chop marks represents axis of bending and distinguish the portion of fiber that undergone compression from the portion of the fiber that undergone tension
        
        Flexural failuer
        
        Characterize by the presence of both tensile and compressive failure
        
        Both radial lines, microbuckling and chopmarks will be found on the surface of the fiber that underwent tension and compression failure respectively