An important notation convention will be observed throughout this book: the
Greek letter s denotes normal stress, which is a function of the applied loads; S (with
appropriate subscripts) designates strength properties of the material. For example,
Figure 3.1 shows that when s = 39 ksi,1 the material begins to yield. Hence, Sy = 39
ksi. Similarly, the greatest (ultimate) load that the test specimen can withstand corresponds
to an engineering stress of 66 ksi. Hence, Su = 66 ksi.
Whereas S (with suitable subscripts) is used for all strength values including
those for torsion or shear, the letter s is used for normal stresses only, that is, stresses
caused by tensile, compressive, or bending loads. Shear stresses, caused by torsional
or transverse shear loads, are designated by the Greek letter t.