2. Hardness

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2. Hardness

  1. 1. HARDNESS TESTING
  2. 2. Hardness is the resistance of a material to abrasion or localized plastic deformation
  3. 3. Hardness is not necessarily an indication of strength , although for some materials such as steel, a harder steel is a stronger steel.
  4. 4. A.) Brinell Hardness Test (BHN)
  5. 5. 1.) Brinell Test Method <ul><ul><li>a.) Press a 10mm (3/8&quot;) diameter ball into material with a known amount of load. </li></ul></ul><ul><ul><li>b.) Measure diameter of the indentation. </li></ul></ul><ul><ul><li>c.) BHN = Load = 2L Surface Area  D[D-(D 2 -d 2 ) 1/2 ] </li></ul></ul>
  6. 6. <ul><ul><ul><li>L = Load placed on ball, usually 3000 kg , but 1500 kg, and 500 kg can also be used. </li></ul></ul></ul><ul><ul><ul><li>D = Diameter of steel ball ( = 10 mm) </li></ul></ul></ul><ul><ul><ul><li>d = diameter of dent, measured by looking thru a Brinell microscope. </li></ul></ul></ul>
  7. 7. 2.) Limitations of the Brinell Hardness Test <ul><ul><li>a.) Sample must be ten times thicker than the indentation depth (sample usually should be at least 3/8&quot; thick). </li></ul></ul><ul><ul><li>b.) Test is most accurate if the indentation depth is 2.5 - 5.0 mm. Adjust load to achieve this. </li></ul></ul><ul><ul><li>c.) Test is no good if BHN > 650 </li></ul></ul>
  8. 8. 3.) Advantages of the Brinell Test <ul><ul><li>a.) Widely used and well accepted </li></ul></ul><ul><ul><li>b.) Large ball gives good average reading with a single test. </li></ul></ul><ul><ul><li>c.) Accurate </li></ul></ul><ul><ul><li>d.) Easy to learn and use </li></ul></ul>
  9. 9. 4.) Disadvantages of the Brinell Test <ul><ul><li>a.) Destructive </li></ul></ul><ul><ul><li>b.) Non-portable </li></ul></ul><ul><ul><li>c.) High initial cost ($5,000) </li></ul></ul><ul><ul><li>Error due to operator reading Brinell Microscope (10%max) </li></ul></ul>
  10. 10. B.) Rockwell Hardness Test (Hrb,HRc,etc.)
  11. 11. 1.) Method
  12. 12. 1.) Method <ul><li>a.) Select Scale - load and indentor depending on the scale </li></ul><ul><li>b.) Press a point into material </li></ul><ul><ul><li>- Diamond Point (Brale) </li></ul></ul><ul><ul><li>- 1/16&quot; ball </li></ul></ul><ul><ul><li>- 1/8&quot; ball </li></ul></ul><ul><ul><li>- ¼” ball </li></ul></ul>
  13. 13. 1.) Method <ul><li>a.) Select Scale - load and indentor depending on the scale </li></ul><ul><li>b.) Press a point into material </li></ul><ul><ul><li>- Diamond Point (Brale) </li></ul></ul><ul><ul><li>- 1/16&quot; ball </li></ul></ul><ul><ul><li>- 1/8&quot; ball </li></ul></ul>
  14. 14. 1.) Method C.) Machine measures depth of penetration and computes hardness
  15. 15. 2.) Limitations of the Rockwell Test <ul><ul><li>a.) Sample must be ten times thicker than the indentation </li></ul></ul><ul><ul><ul><li>depth (sample usually should be at least 1/8&quot; thick). </li></ul></ul></ul><ul><ul><li>b.) Test is most accurate if the Rockwell Hardness is </li></ul></ul><ul><ul><li> between 0 and 100. Adjust scale to achieve this. </li></ul></ul><ul><li>For Steel: </li></ul><ul><li> If Hra > 60, use Hrc scale </li></ul><ul><li> If Hra < 60, use Hrb scale </li></ul>
  16. 16. <ul><li>c.) Need 3 tests (minimum) to avoid inaccuracies due to impurities, hard spots. </li></ul>
  17. 17. 3.) Advantages of the Rockwell Test <ul><ul><li>a.) Widely used and well accepted </li></ul></ul><ul><ul><li>b.) Little operator subjectivity </li></ul></ul><ul><ul><li>c.) Accurate </li></ul></ul><ul><ul><li>d.) Fast </li></ul></ul><ul><ul><li>e.) Large range of hardnesses (plastics to steels) </li></ul></ul>
  18. 18. 4.) Disadvantages of the Rockwell Test <ul><li>a.) Destructive </li></ul><ul><li>b.) Non-Portable </li></ul><ul><li>c.) Initial cost ($5,000) </li></ul>
  19. 19. C.) Converting Rockwell Readings to Brinell
  20. 21. 1.) If -20 < Hrc < 40 <ul><li>BHN = 1,420,000 </li></ul><ul><li> (100 – HRc) 2 </li></ul>
  21. 22. 2.) If 40 < Hrc < 100 <ul><li>BHN = 25,000__ </li></ul><ul><li> (100 - Hrc) </li></ul>
  22. 23. 3.) If 35 < Hrb < 100 <ul><li>BHN = 7,300____ </li></ul><ul><li> (130 - Hrb) </li></ul>
  23. 24. Hardness Conversion
  24. 25. Hardness of Plastics From Matweb: Shore (Durometer) Hardness Testing of Plastics The hardness testing of plastics is most commonly measured by the Shore (Durometer) test or Rockwell hardness test. Both methods measure the resistance of the plastic toward indentation. Both scales provide an empirical hardness value that doesn't correlate to other properties or fundamental characteristics. Shore Hardness, using either the Shore A or Shore D scale, is the preferred method for rubbers/elastomers and is also commonly used for 'softer' plastics such as polyolefins, fluoropolymers, and vinyls. The Shore A scale is used for 'softer' rubbers while the Shore D scale is used for 'harder' ones.
  25. 26. Hardness of Plastics
  26. 27. The Shore hardness is measured with an apparatus known as a Durometer and consequently also known as 'Durometer hardness'. The hardness value is determined by the penetration of the Durometer indenter foot into the sample. Because of the resilience of rubbers and plastics, the hardness reading my change over time - so the indentation time is sometimes reported along with the hardness number. The ASTM test number is ASTM D2240 while the analogous ISO test method is ISO 868.
  27. 28. Shore (Durometer) Hardness Testing of Plastics The hardness testing of plastics is most commonly measured by the Shore (Durometer) test or Rockwell hardness test. Both methods measure the resistance of the plastic toward indentation. Both scales provide an empirical hardness value that doesn't correlate to other properties or fundamental characteristics. Shore Hardness, using either the Shore A or Shore D scale, is the preferred method for rubbers/elastomers and is also commonly used for 'softer' plastics such as polyolefins, fluoropolymers, and vinyls. The Shore A scale is used for 'softer' rubbers while the Shore D scale is used for 'harder' ones. The Shore hardness is measured with an apparatus known as a Durometer and consequently also known as 'Durometer hardness'. The hardness value is determined by the penetration of the Durometer indenter foot into the sample. Because of the resilience of rubbers and plastics, the hardness reading my change over time - so the indentation time is sometimes reported along with the hardness number. The ASTM test number is ASTM D2240 while the analogous ISO test method is ISO 868. The results obtained from this test are a useful measure of relative resistance to indentation of various grades of polymers. However, the Shore Durometer hardness test does not serve well as a predictor of other properties such as strength or resistance to scratches, abrasion, or wear, and should not be used alone for product design specifications. As seen in the charts below, the correlation between the two Shore Durometer hardness scales is weak; attempts at conversion between the scales are therefore discouraged. The correlation is higher for materials with similar resiliency properties, but is still too low for reliable conversions. Likewise, conversion between Shore Hardness and Rockwell hardness is discouraged. The results obtained from this test are a useful measure of relative resistance to indentation of various grades of polymers. However, the Shore Durometer hardness test does not serve well as a predictor of other properties such as strength or resistance to scratches, abrasion, or wear, and should not be used alone for product design specifications. As seen in the charts below, the correlation between the two Shore Durometer hardness scales is weak; attempts at conversion between the scales are therefore discouraged. The correlation is higher for materials with similar resiliency properties, but is still too low for reliable conversions. Likewise, conversion between Shore Hardness and Rockwell hardness is discouraged.

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