Page 20 - Rotating Machinery Pratical Solutions to Unbalance and Misalignment

Introduction to Vibrations

Figure 1-8. A typical Figure 1-9. Stretching be-
Stress-Strain Curve. yond the Elastic Limit

is where the material changes from elastic to plastic. As the force
is continually increased, the cross-sectional area of the material is
reduced and thus the curve begins to reverse. Eventually, the force
per unit area is too great and the material fails.
Stress is defined as the force per unit area or:

Stress = F/A (1.3)
Strain is defined as the elongation divided by the original
length or:

Strain = dL/L (1.4)
o

Figure 1-10. A Material being Stressed until Failure