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Mechanical Engineering

1. Summary (1/12) (The summary should be succinct (limited to one page), but contain the following four pieces of information, namely, the purpose of the experiment; experimental methods; results; and conclusion.) 2. Results (612) Carry out the following steps for A36 steel. a. Tabulate the results according to the following format. T (in-lb) θ (radian) dT/dθ (plastic region only) τr (psi) γr (in/in) b. Plot T vs θ . c. Plot T vs θ in the plastic region leaving out the elastic part of the data, and fit the data by the power law relation, i.e. b T a = θ . Include the determined curve fitting relation in the plot. From the curve fitting relation, dT d/ θ can be determined as 1 / () b dT d ab θ θ − = d. Plot τr vs γr. e. Show some sample calculations. f. Determine the material properties: 1. Shearing proportional limit 2. Yield strength at an offset of 0.2% 3 3. Shearing modulus of rupture 4. Modulus of rigidity 5. Modulus of resilience 3. Question (4/12) a. Let the tensile stress in a tension test be σ and the shear stress in a torsion test be τ. Draw a stress Mohr circle for each test (let the specimen axis, i.e. longitudinal direction, be x-axis and the transverse direction be y-axis) and express both the maximum principal stress (σmax) and the maximum shear stress (τmax) in terms of σ (for tension test) or τ (for torsion test). Mark the x-axis on the Mohr’s circle. Also indicate the directions of σmax and τmax with respect the x-axis for each case. Refer to your CE215 textbook. b. Briefly explain the maximum shear stress theory for ductile failure, e.g. A36 steel; and the maximum normal stress theory for brittle failure, e.g. cast iron. Refer to your CE215 textbook. c. Compare the orientations of the fracture surfaces of A36 steel and cast iron and explain your observations in terms of your answers to questions (a) and (b). d. The (ultimate) tensile strength of a brittle material (has little plastic deformation) is 30,000 psi. A torque is applied to a ¼ inch diameter cylindrical bar made of the same brittle material. Estimate the amount of torque that is needed to fracture this bar. Sketch the orientation of the fracture surface. (Refer to a, b, and c and your CE215 textbook). 4. Conclusion (1/12)