Tensile Test Multiple Shapes

Document Sample
Tensile Test Multiple Shapes Powered By Docstoc
					                                          Test of a Bolted Joint

   Determine the optimum size bolt to use to connect two plates to produce the strongest possible joint.


1. Measure samples and calculate the predicted capacity of each joint. The plates are 1020 HRS, and the bolts
   are simple grade 2 bolts.
2. Place the samples in the flat grips of the testing machine.
3. Apply the tensile load slowly and record the maximum load capacity and mode of failure of each joint.
4. Use the information from the multiples shape lab for calculations on the solid bar.


   There are two possible types of failure:

   1. The bolt may shear on the root diameter or the shank of the bolt, whichever is in the hole.

   2. The plate may fail in tension at its weakest point. Be sure to use stress concentration factors in the text
      appendix to calculate this.

Note: The plate may also fail in bearing, on the projected area of the bolt. It will most usually fail in the plate,
but since bearing is a compression failure it is difficult to “see” this failure occur on the testing machine load
gauge (dial), or by visual examination. The plate may also fail in “tear-out” through the end of the plate. Please
read page 613 for this discussion. What did we do on these plates to insure tear out will not occur?
   The maximum load capacity for each type of failure can be calculated since s=F/A or lead F=A*s where s is
   the maximum unit stress for the material and type of loading. The joint will fail when the weakest case is
   reached. Therefore, the predicted load at failure will be the smallest load, either in shear or in tension. The
   joint efficiency is defined as the (percent) ratio of the actual load carrying capacity of the joint as compared
   to the load carrying capacity of a solid (continuous) plate.

   Use the data you collected from previous labs. In the multiple shapes lab you determined an exact ultimate
   tensile stress, and in the shear lab you were able to calculate the ultimate shear stress for 1020 HRS.

           Nominal               Actual Bolt
                                                                              Plate              Diameter
  Assembly    Bolt                Diameter              Plate Width
                                                                            Thickness             of hole
           Diameter            (Root or Shank)
   Joint 1         1/2
   Joint 2         5/8
  Solid Bar     XXXXX              XXXXX                                                         XXXXX

       Maximum Tensile
                                   Maximum Shear             Mode of        Maximum load       Predicted joint
        Load of Plate at
 Joint                            Load of Root/Shank         Failure        of solid plate*      efficiency
        * to be taken from the multiple shapes lab actual results

       Maximum Load of Description of                     Maximum Load of Solid Actual Joint Efficiency
 Joint Joints          fracture                           Plate

1. Did each joint fail as predicted? If not, can you explain why?

2. How accurate were your predicted joint efficiencies? Give the % difference for each.

3. State 2 reasons that could justify % difference (from question 2) in this experiment.

4. Based on your initial data, was edge split a possible mode of failure? Why?

5. Would using higher-grade bolts affect the results for either joint #1 or joint #2? Explain

6. Using the same grade bolts, would you recommend either a 9/16 diameter or 11/16-diameter bolt to increase
   the joint efficiency for either joints #1 or #2? Why?

7. If you could purchase any size bolt for the same price, what would you use as the optimum size bolt?