282 Chapter 10 Force and Force-Related Parameters
10.6 Modulus of Elasticity, Modulus of Rigidity, and Bulk Modulus of Compressibility
In this section, we will discuss some important properties of materials. The way an object
responds to an application of a force also depends on its material properties. Engineers, when
designing products and structural members, need to know how a selected material behaves
under applied forces or how well the material conducts thermal energy or electricity. Here we
will look at ways of quantifying ( measuring) the response of solid materials to pulling or push-
ing forces or twisting torques. We will also investigate the behavior of fluids in response to
applied pressures in terms of bulk modulus of compressibility.
Tensile tests are performed to measure the modulus of elasticity and strength of solid mate-
rials. A test specimen with a size in compliance with the American Society for Testing and
Materials (ASTM) standards is made and placed in a tensile testing machine. When a material
specimen is tested for its strength, the applied tensile load is increased slowly. In the very begin-
ning of the test, the material will deform elastically, meaning that if the load is removed, the
material will return to its original size and shape without any permanent deformation. The
point to which the material exhibits this elastic behavior is calledelastic point. As the material
stretches, the normal stress (the normal force divided by the cross-sectional area) is plotted ver-
sus the strain (deformation divided by the original length of the specimen). An example of such
test results for a steel sample is shown in Figure 10.28.62080_10_ch10_p251-302.qxd 5/22/10 12:32 AM Page 282
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