t0706 - 182 ● Chapter 7 / Mechanical Properties Rockwell...

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Unformatted text preview: 182 ● Chapter 7 / Mechanical Properties Rockwell hardness 60 70 80 90 100 HRB 20 30 40 50 HRC 250 1500 200 1000 150 100 500 Brass Cast iron (nodular) 50 0 0 100 200 300 400 0 500 Brinell hardness number is the energy required to tear apart a cut specimen that has a standard geometry. The magnitude of tensile and tear strengths are related. Polymers are softer than metals and ceramics, and most hardness tests are conducted by penetration techniques similar to those described for metals in the previous section. Rockwell tests are frequently used for polymers.19 Other indentation techniques employed are the Durometer and Barcol.20 Table 7.6 Approximate Knoop Hardness (100 g load) for Seven Ceramic Materials Material Diamond (carbon) Boron carbide (B4C) Silicon carbide (SiC) Tungsten carbide (WC) Aluminum oxide (Al2O3) Quartz (SiO2) Glass Approximate Knoop Hardness 7000 2800 2500 2100 2100 800 550 19 ASTM Standard D 785, ‘‘Rockwell Hardness of Plastics and Electrical Insulating Materials.’’ 20 ASTM Standard D 2240, ‘‘Standard Test Method for Rubber Property—Durometer Hardness;’’ and ASTM Standard D 2583, ‘‘Standard Test Method for Indentation of Rigid Plastics by Means of a Barcol Impressor.’’ Tensile strength (103 psi) Tensile strength (MPa) Steels FIGURE 7.31 Relationships between hardness and tensile strength for steel, brass, and cast iron. (Data taken from Metals Handbook: Properties and Selection: Irons and Steels, Vol. 1, 9th edition, B. Bardes, Editor, American Society for Metals, 1978, pp. 36 and 461; and Metals Handbook: Properties and Selection: Nonferrous Alloys and Pure Metals, Vol. 2, 9th edition, H. Baker, Managing Editor, American Society for Metals, 1979, p. 327.) ...
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