Therefore, it is necessary to test several samples and calculate an average for each property. Among the more important mechanical properties of polymers are tensile strength, elongation, flexural strength, and impact resistance. A large number of standard tests have been developed. To measure tensile strength, a test specimen of uniform cross-section is clamped at each end and stretched until it breaks. Tensile strength is defined as the stress force necessary to break the sample at a constant rate of stretching.
Elongation is the increase in length of a sample at the breaking point.
Elongation is associated with the uncoiling of polymer molecules and their movement relative to other molecules. Highly crosslinked polymers have a low elongation relative to linear polymers. Elongation can vary widely among polymers and is usually expressed as a percent of the original length of the sample. Flexural strength is measured by supporting a sample test bar of uniform cross-section at each end, in a horizontal position. The sample is then subjected to a vertical stress until it yields or breaks.