**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)

• porosity (when stir to fast, bubble will form)
• fiber misalignment (material properties will become weaker -> it will not able to withstand load that will be applied)
• crack delamination (thermal stress)
• wavy fiber (fibers not align)

• impact
• debonding (did not put adhesive / not cure at the proper temperature)
• Bolt hole damage (residual & thermal stresses -> cause crack)
• moisture ingression (moisture absorb -> can cause corrosion)

** 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

Determine microstructural parameters:

1. voids
2. fiber orientation
3. spatial distribution of fiber
4. ply count
5. delamination
   

Sample preparation is very important before sample can be viewed under microscope:

1. sectioning
2. mounting
3. grinding and polishing
   

• 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:

1. Specimen shape and size
2. Precaution to be taken test set up and apparatus
3. Specimen conditioning
4. Acceptable failure mode
5. Calculation and report

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

Testing Condition:

• Machining effects
• Alignment of specimen
• Conditioning and environmental test chamber

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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

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.
• 
• transverse / shear waves
  

• 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

• detect deep defects
• determine size and shape
• safe method

• 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

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.

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