Tension and Compression
For simple tension or compression, the stress on an object is defined as , where F is the magnitude of the force applied perpendicularly to the area A on the object. The strain, or unit deformation, is then the dimensionless quantity , the fractional (or sometimes percentage) change in the length of the specimen. If the specimen is a long rod and the stress does not exceed the yield strength.
Although the Young’s modulus for an object may be almost the same for tension and compression, the object’s ultimate strength may well be different for the two types of stress. Concrete, for example, is very strong in compression but is so weak in tension that it is almost never used in that manner.