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Material Testing

Material Testing. Material Testing. Reproducible evaluation of material properties . Static Testing. Material response to constant loading. Dynamic Testing. Material response to varying loading conditions, including magnitude, cycling, and mode. Static Material Testing.

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Material Testing

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  1. Material Testing

  2. Material Testing Reproducible evaluation of material properties Static Testing Material response to constant loading Dynamic Testing Material response to varying loading conditions, including magnitude, cycling, and mode

  3. Static Material Testing Evaluation of Material StrengthDeformationFractureDesign requirement compliance Standardized Tests Tensile testCompression testHardness test

  4. Tensile Test Uniaxial A straight line axial force is applied to a test sample(typically in the y axis) Hounsfield Tensometer Image courtesy of NSW Department of Education and Training Destructive Force is applied until sample fails

  5. Tensile Test Standard Test Sample (dog bone) • Ensures meaningful and reproducible results • Uniform cross section

  6. Tensile Test Procedure Dog bone is created to test specifications Dog bone is secured in tester

  7. Tensile Test Procedure A tension force (F) is applied to the dog bone until failure occurs Simultaneously the applied tension force (F) and dog bone elongation (d)are recorded F d A plot is created from the stored load elongation data

  8. Tensile Test Data F d A B Test sample A and B are 230 red brass. Test sample A has a diameter of 0.125 in. Test sample B has a diameter of 0.375 in. If both samples are tested to failure, will the applied tension force and elongation be the same for both tests? NO – Why?

  9. Tensile Test Data Load-elongation results are dependent upon sample size Larger sample indicates larger load-elongation How can test data be manipulated to represent a material and not an individual test sample?

  10. Tensile Test Data To eliminate test results based on sample size, calculate sample stress Stress is load per unit area Divide load (F) by the original test sample cross-sectional area (A0)

  11. Tensile Test Data Calculate the stress in the dog bone with a 430 lb applied force.

  12. Tensile Test Data Manipulating Elongation Results To eliminate test results based on sample size, calculate sample strain • Strain (e) - the amount of stretch per unit length • Elongation (d) under load divided by the original Length (L0)

  13. Tensile Test Data Calculate the strain in the dog bone with an elongation of 0.0625in.

  14. Tensile Test – Stress-Strain Curve

  15. Tensile Test – Stress-Strain Curve Initial response is linear Stress and strain are proportional to one another Elastic Range Proportional Limit (The stress at which proportionality ceases)

  16. Tensile Test – Stress-Strain Curve Modulus of Elasticity (E)The proportional constant (ratio of stress and strain) A measure of stiffness – The ability of a material to resist stretching when loaded An inherent property of a given material

  17. Tensile Test – Stress-Strain Curve If the load is removed, the test sample will return to its original length The response is elastic or recoverable Exaggerated stretch to illustrate principle

  18. Tensile Test – Stress-Strain Curve Elastic LimitUppermost stress of elastic behavior Elastic and proportional limit are almost identical, with the elastic limit being slightly higher

  19. Tensile Test – Stress-Strain Curve ResilienceThe amount of energy per unit volume that a material can absorb while in the elastic range Area under the stress-strain curve Why would this be important to designers? Hint: car bumper

  20. Tensile Test – Stress-Strain Curve Yield PointWhen the elastic limit is exceeded A very small increase in stress produces a much greater strain Most materials do not have a well-defined yield point

  21. Tensile Test – Stress-Strain Curve Offset Yield Strength • Defines the stress required to produce a tolerable amount of permanent strain • Common value is 0.2%

  22. Tensile Test – Stress-Strain Curve Plastic DeformationUnrecoverable elongation beyond the elastic limit When the load is removed, only the elastic deformation will be recovered

  23. Tensile Test – Strength Properties • Stress Strain Curve Plastic deformation represents failure Part dimensions will now be outside of allowable tolerances

  24. Tensile Test – Stress-Strain Curve Deformation • Test sample elongation • Cross-sectional area decreases • Load bearing ability increases – Why? • The material is getting stronger – How?

  25. Tensile Test – Stress-Strain Curve • Weakest point is stretched and becomes stronger • New weakest point is stretched and becomes stronger, and so on • This keeps occurring until the decrease in area overcomes the increase in strength

  26. Tensile Test – Stress-Strain Curve • Tensile StrengthLoad bearing ability peaks • Force required to continue straining the test sample decreases • Weakest location at the peak continues to decrease in area – Necking

  27. Tensile Test – Stress-Strain Curve FailureIf continued force is applied, necking will continue until fracture occurs DuctilityAmount of plasticity before fracture The greater the ductility, the more a material can be deformed

  28. Tensile Test – Samples Compare the material properties of these three metal samples

  29. Tensile Test – Stress-Strain Curve • Brittleness • Material failure with little or no ductility • Lack of ductility, not lack of strength

  30. Tensile Test – Stress-Strain Curve • Toughness • Work per unit volume required to fracture a material • Total area under the stress-strain curve from test initiation to fracture (both strength and ductility)

  31. Compression Test • Stress and strain relationships are similar to tension tests – elastic and plastic behavior • Test samples must have large cross-sectional area to resist bending and buckling • Material strengthens by stretching laterally and increasing its cross-sectional area

  32. Hardness Testing • Resistance to permanent deformation • Resistance to scratching, wear, cutting or drilling, and elastic rebound • Brinell Hardness TestA tungsten carbide ball is held with a 500lb force for 15 sec into the material • The resulting crater is measured and compared

  33. Hardness Testing • Rockwell TestA small diamond-tipped cone is forced into the test sample by a predetermined load • Depth of penetration is measured and compared

  34. Image Resources NSW Department of Education and Training (2011). Retrieved from http://lrrpublic.cli.det.nsw.edu.au/lrrSecure/Sites/Web/tensile_testing/index.htm?Signature=%287e02281c-318a-461b-a8ed-3394db0c4fe6%29

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