Thus, if, for instance, the object illustrated above contains 4 square inches of cross-sectional area, and the total load it is called upon to endure is 10 tons, the stress would be expressed as 2-1/2 tons.
Strain is the deformation produced by stress.
The Factor of Safety is usually expressed by the result found by dividing the stress at which it is known the body will collapse by the maximum stress it will be called upon to endure. For instance, if a control wire be called upon to endure a maximum stress of 2 cwts., and the known stress at which it will collapse is 10 cwts., the factor of safety is then 5.
Compression.—The simple stress of compression tends to produce a crushing strain. Example: the interplane and fuselage struts.
Tension.—The simple stress of tension tends to produce the strain of elongation. Example: all the wires.
Bending.—The compound stress of bending is a combination of compression and tension.
The above sketch illustrates a straight piece of wood of which the top, centre, and bottom lines are of equal length. We will now imagine it bent to form a circle, thus: