Question 3.23:  A 3/4-in diameter steel tension rod is 5 ft long and carrie...

A  \frac{3}{4} -in-diameter steel tension rod is  5 \mathrm{ft} long and carries a load of 15 kip. Find the tensile stress, the total deformation, the unit strains, and the change in the rod diameter.

 

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\sigma=\frac{F}{A}=\frac{15000}{(\pi / 4)\left(0.75^{2}\right)}=33950 \mathrm{psi}=34.0 \mathrm{kpsi} \quad .

 

\delta=\frac{F L}{A E}=\sigma \frac{L}{E}=33950 \frac{60}{30\left(10^{6}\right)}=0.0679 in

 

\epsilon_{1}=\frac{\delta}{L}=\frac{0.0679}{60}=1130\left(10^{-6}\right)=1130 \mu \quad

 

From Table A-5,  v=0.292

 

\epsilon_{2}=-v_{\epsilon_{1}}=-0.292(1130)=-330 \mu \quad .

\Delta d=\epsilon_{2} d=-330\left(10^{-6}\right)(0.75)=-248\left(10^{-6}\right) in .

Table A-5

Material Modulus of Elasticity E Modulus of Elasticity G Poisson’s Ratio Unit Weight w
Mpsi Gpa Mpsi GPa lbf/in^{3} lbf/ft^{3} kN/m^{3}
Aluminum(all alloys) 10.4 71.7 3.9 26.9 0.333 0.098 169 26.6
Beryllium copper 18 124 7 48.3 0.285 0.297 513 80.6
Brass 15.4 106 5.82 40.1 0.324 0.309 534 83.8
Carbon steel 30 207 11.5 79.3 0.292 0.282 487 76.5
Cast iron(gray) 14.5 100 6 41.4 0.211 0.26 450 70.6
Copper 17.2 119 6.49 44.7 0.326 0.322 556 87.3
Douglas fir 1.6 11 0.6 4.1 0.33 0.016 28 4.3
Glass 6.7 46.2 2.7 18.6 0.245 0.094 162 25.4
Inconel 31 214 11 75.8 0.29 0.307 530 83.3
Lead 5.3 36.5 1.9 13.1 0.425 0.411 710 111.5
Magnesium 6.5 44.8 2.4 16.5 0.35 0.065 112 17.6
Molybdenum 48 331 17 117 0.307 0.368 636 100
Monel metal 26 179 9.5 65.5 0.32 0.319 551 86.6
Nickel silver 18.5 127 7 48.3 0.322 0.316 546 85.8
Nickel steel 30 207 11.5 79.3 0.291 0.28 484 76
Phosphor bronze 16.1 111 6 41.4 0.349 0.295 510 80.1
Stainless steel(18-8) 27.6 190 10.6 73.1 0.305 0.28 484 76
Titanium alloys 16.5 114 6.2 42.4 0.34 0.16 276 43.4

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