Torsion Experiment Essay

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DISCUSSION From the book Mechanics of Materials,3rd Edition by R. C. Hibbeler, Ferdinand P. Beer, E. Russell Johnston Jr. and John T. DeWolf, the value for modulus of rigidity, G of mild steel is 80GPa. The authors also wrote that the value of G is not less than one third and not more than half of modulus of elasticity, E. which E for mild steel is 210GPa. The value of G, for this experiment can be obtained from the slope of the graph shear strees against shear strain. By using simple calculation, the value of G is 54.27 GPa. The differences experimental value and theoretical value is around 32.16%, which the experimental value is smaller than theoretical value. Those value were difference because we are using a manual torsion tester with raising the revolution twist by staged. After one revolution and after the meter tester were stop the reading will be taken, and so on until the specimen fractured. So the graph of this experiment not exactly obeyed Hooke’s Law. We can obey the Hooke’s Law if we are using the automatic torsion tester with smooth load will be apply to the specimen, and much more accurate. We also can get the exact fracture load of the specimen. The graph torque, T against angle θ for the first five reading are plotted obeyed the Hooke’ Law, those graph seem almost a linear line. For the torsion test experiment, there will be 2 type fracture surface; a) Cup-and-cone fracture. b) Brittle fracture. (ductile fracture) i. The ductile fracture may have a gray, fibrous appearance. ii. Ductile fractures are associated with overload of the structure or large discontinuities. The brittle fracture are associated with a smooth and constant load continuities. So our specimen were had a ductile fracture surface, with having a bit necking and cup-and-cone surface. Figure
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