IT 111 Materials Testing

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IT 111 Materials Testing

• Lecture 7
• Thomas E. Scott

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Materials Testing

• Finding new information about a material
• Discovering specific properties
• Developing standard methods for testing
• Testing
• To provide quantitative data
• Inspection
• Confirm properties

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Materials Testing

• Precision
• Repeatability
• Acquire a quantity of data to assure precision
• Accuracy
• Closeness to the real value
• Compare result with test results from others
• Precision and accuracy
• The ultimate goal of testing

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Materials Testing

• Tensile
• Creep
• Compression
• Bend or Flexure
• Hardness

• Impact
• Fatigue
• Non-destructive
• Magnetic
• Dyes
• Ultrasound

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Tensile Testing

• Loading a sample
• Recording the stretch vs load
• From small loads to fracture
• Produce a stress-strain curve
• Stress Load divided by cross sectional area
• Strain Sample stretch as a elongation

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Tensile Testing

• Elastic Range
• Proportional Limit Modulus of Elasticity
• Yield Strength
• Proof stress - 0.2 offset
• Plastic Range
• Ultimate Strength
• Elongation
• Reduction in cross sectional area

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Creep Testing

• LONG TERM effect of load application
• Below the elastic limit
• Creep is plastic deformation
• Deformation over long periods
• Elevated temperature accelerates creep
• Influences
• Safety factor
• Life

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Creep

• Measured by applying a constant load
• Measure strain (elongation)
• Measure at various temperatures

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Compression Testing

• Opposite of tensile test (Plot stress vs strain)
• Brittle materials are low in tensile compared to
  compression (Concrete, ceramics)
• Column action is important
• Bending as in buckling
• Bulging, as in increase in girth
• Length to diameter ratio is important
• 21 length to diameter ratio

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Shear Testing

• Very important to cutting material
• Resistance to separation
• Direct shear (linear)
• Torsional shear (twist)
• Shear stress
• Load divided by area resisting the separation

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Shear Testing

• Energy absorption
• Charpy or Izod tester
• Pendulum principle

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Bend or Flexure Testing

• Loading of a beam across centers
• Compression on top (wrinkles)
• Tension below (tears)
• Neutral axis
• Measure deflection for a given support spacing vs
  load

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Hardness

• Resistance to surface penetration
• Indentation hardness
• Rebound hardness
• Indentation ball or truncated cone

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Hardness Tests

• Brinell
• Pressing a 10 mm hardened steel ball into a
  specimen
• Hard metal - 3000kg (approx 6000 lbs)
• Intermediate hardness metal 1500kg
• Soft metal 500kg
• Measure diameter of ball indentation
• Brinell number is the pressure per area
• Kg per mm

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Hardness Test

• Rockwell
• Various indenters
• Therefore, different scales
• Minor load applied first, then larger load
• Hardness is measure of depth of penetration
• Associated with a letter (indenter and load
  designator)

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Hardness Test

• Others
• Vickers
• Durometer
• Measures indentation depth
• Scratch hardness
• Abrasion testing
• tumbling

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Impact Testing

• Smaller failure load due to sudden impact
• Brittleness
• Toughness resistance to shock loading
• Generally, strength quoted in foot-lbs
• Greater area, then more strength
• Perhaps should normalize by cross sectional area

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Fatigue Testing

• Failure due to repeated cyclic loading
• Data accumulated as load vs cycles to failure
• If indefinite period to failure (long time), then
  stress is referred to the endurance limit
• Critical stress is the endurance limit
• Higher temperature, curve shifts down
• Curve is called SN curve

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Non-Destructive Tests

• Radiography and Diffraction
• Gamma Rays and measure reflection
• Magnetic and Electromagnetic
• Ferro-magnetic materials
• Measure permeability of magnetic flux
• Identifies voids or occulsions
• Magnaflux
• Ultrasound
• Hollow parts (e.g.,pipes) and non metals
• Gives image

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Non-Destructive Tests

• Visual and holographic
• Video imaging, electron microscope
• Photo elasticity
• Light fringe interference due to flexure
• Liquid Penetrants
• Dyes to bring out cracks