Page 108 - Manufacturing Engineering and Technology - Kalpakjian, Serope : Schmid, Steven R.

Synthesis, Design, and Projects 87

2.67. Using a large rubber band and a set of weights, obtain |]2.72. By pushing a small ball bearing against the top sur-
the force-displacement curve for the rubber band. Is the re- faces of various materials, such as clay and dough, observe
sult different from the stress-strain curves shown in Figure the shape of the indentation with a magnifier, referring to
2.5? Comment. those shapes shown in Fig. 2.14a and b.
2.68. Figure 2.4 shows the ductility of only four metals. 2.73. Describe your observations regarding Fig. 2.14c.
Search the technical literature, and add other metals and al- 2.74. Embed a small steel ball in a soft block of material
loys to this chart, including their different conditions, such as
such as clay, and compress the clay as shown in Fig. 2.24a.
hot Worked, cold Worked, annealed, etc.
Then cut the clay carefully along the center plane and observe
2.69. Find or prepare some solid circular pieces of brittle the deformation of the material. Repeat the experiment by
materials, such as chalk, ceramics, etc. and subject them to embedding a small round jelly bean in the clay and deforming
the type of test shown in Fig. 2.9 by using the jaws of a sim- the material. Comment on your observations.
ple vise. Describe your observations as to how the materials 2.75. Devise a simple experiment, and perform tests on ma-
fracture. Repeat the tests, using ductile materials, such as
terials commonly found around the house by bending them at
clay, soft metals, etc., and describe your observations.
different temperatures for a qualitative assessment of their
2.70. Take several rubber bands and pull them at different transition temperature, as shown in Fig. 2.25.
temperatures, including from a frozen state. Comment on
2.76. Obtain some solid and some tubular metal pieces, and
their behavior such as ductile or brittle.
slit them as shown in Fig. 2.31. Comment on Whether there
2.7I. Devise a simple fixture for conducting the bend tests are any residual stresses in the parts prior to slitting them.
shown in Fig. 2.11. Test sticks of various brittle materials by
2.77. Explain how you would obtain an estimate of the
loading them with dead Weights until they break. Verify
hardness for a carbon nanotube. (See Section 8.6.)
the statement in the text that the specimens on the right in the
figure will fracture sooner than the ones on the left.