A cylindrical metal specimen 12.7 mm (0.5 in.) in diameter and 250 mm (10 in.) long is to be subjected to a tensile stress of 28 MPa (4000 psi); at this stress level the resulting deformation will be totally elastic.
(a) If the elongation must be less than 0.080 mm (3.2 × 10−3 in.), which of the metals in Table 7.1 are suitable candidates? Why?
(b) If, in addition, the maximum permissible diameter decrease is 1.2 × 10−3 mm (4.7 × 10−5 in.) when the tensile stress of 28 MPa is applied, which of the metals that satisfy the criterion in part (a) are suitable candidates? Why?
Table 7.1Room-Temperature Elastic and Shear Moduli and Poisson’s Ratio for Various Materials
| Modulus of Elasticity | Shear Modulus |
| ||
Material | GPa | 106 psi | GPa | 106 psi | Poisson’s Ratio |
Metal Alloys | |||||
Tungsten | 407 | 59 | 160 | 23.2 | 0.28 |
Steel | 207 | 30 | 83 | 12.0 | 0.30 |
Nickel | 207 | 30 | 76 | 11.0 | 0.31 |
Titanium | 107 | 15.5 | 45 | 6.5 | 0.34 |
Copper | 110 | 16 | 46 | 6.7 | 0.34 |
Brass | 97 | 14 | 37 | 5.4 | 0.34 |
Aluminum | 69 | 10 | 25 | 3.6 | 0.33 |
Magnesium | 45 | 6.5 | 17 | 2.5 | 0.35 |
Ceramic Materials | |||||
Aluminum oxide (Al2O3) | 393 | 57 | — | — | 0.22 |
Silicon carbide (SiC) | 345 | 50 | — | — | 0.17 |
Silicon nitride (Si3N4) | 304 | 44 | — | — | 0.30 |
Spinel (MgAl2O4) | 260 | 38 | — | — | — |
Magnesium oxide (MgO) | 225 | 33 | — | — | 0.18 |
Zirconia (ZrO2)a | 205 | 30 | — | — | 0.31 |
Mullite (3Al2O3-2SiO2) | 145 | 21 | — | — | 0.24 |
Glass–ceramic (Pyroceram) | 120 | 17 | — | — | 0.25 |
Fused silica (SiO2) | 73 | 11 | — | — | 0.17 |
Soda–lime glass | 69 | 10 | — | — | 0.23 |
Polymersb | |||||
Phenol-formaldehyde | 2.76–4.83 | 0.40–0.70 | — | — | — |
Poly(vinyl chloride) (PVC) | 2.41–4.14 | 0.35–0.60 | — | — | 0.38 |
Poly(ethylene terephthalate) (PET) | 2.76–4.14 | 0.40–0.60 | — | — | 0.33 |
Polystyrene (PS) | 2.28–3.28 | 0.33–0.48 | — | — | 0.33 |
Poly(methyl methacrylate) (PMMA) | 2.24–3.24 | 0.33–0.47 | — | — | 0.37–0.44 |
Polycarbonate (PC) | 2.38 | 0.35 | — | — | 0.36 |
Nylon 6,6 | 1.59–3.79 | 0.23–0.55 | — | — | 0.39 |
Polypropylene (PP) | 1.14–1.55 | 0.17–0.23 | — | — | 0.40 |
Polyethylene—high density (HDPE) | 1.08 | 0.16 | — | — | 0.46 |
Polytetrafluoroethylene (PTFE) | 0.40–0.55 | 0.058–0.080 | — | — | 0.46 |
Polyethylene—low density (LDPE) | 0.17–0.28 | 0.025–0.041 | — | — | 0.33–0.40 |
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