midterm-exam by keralaguest

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									                 MECH 101 Midterm Exam March 30, 2010


1. Simple Questions (20pts)

      (1) The stress-strain curve of a material obtained from the standard tensile test
          is plotted in Figure 1. In this figure, nominal stress and nominal strain are
          employed. On the plot, please identify the ultimate stress and the fracture
          stress. Which stress should be higher and why?




                                    Figure 1.

      (2) Thermal stress always occurs when temperature changes. True or False?

      (3) There is no normal stress inside a torsional shaft which is subject to
          torques only. True or False?

      (4) In the two cases illustrated in Figure 2, the only difference is that in case b,
          the bar is heated about T degree after P is applied. Find the reaction
          force in both cases.




                                                        P




                                          (a)
                                                         P




                                          (b)

                                       Figure 2.

2. (40pts) A device illustrated in Figure 3 is made of steel and consists of a solid
   inner shaft CB surrounded by a tube AB which is connected to shaft CB through a
   rigid ring at B. The other end of the tube AB is attached to a fixed ring A. If the
   allowable shear stress for the material is  allow  84 MPa and the angle of twist at
   C is limited to allow  3o , determine the maximum torque T that can be applied at
   the end C. The shear modulus of the material is 80 GPa.




                                       Figure 3.
3. (40 pts) Two rods, one of aluminum and the other of copper, are fixed to the rigid
   walls as shown in Figure 4. The gap between the two rods is 0.2 mm. When the
   temperature increases about 100oC, find the reactions and the location of the
   interface between the two rods? The diameter of each rod is 30 mm. The thermal
   expansion coefficients are copper  17 106 / oC ,  al  24  106 / oC and the
   Young’s modulus are Ecopper  126 GPa , Eal  70 GPa .




                                        Figure 4.

								
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