Tensile strength and strain at rupture are determined as values characteristic of paper strength (ISO 1924, 1992). The tensile strength together with the sample width gives the tensile strength per unit width, measured in N m–1. Together with the sample thickness the tensile strength can be expressed in kPa. The tensile index results from tensile strength per unit width (expressed in N m–1 divided by grammage).

In paper technology, the breaking length is also of some importance as a calcu¬lated value. It is the length of a freely suspended paper strip of any constant width and thickness that just breaks at the point of suspension due to its own weight.

The breaking length L is calculated from the tensile strength force FB of the paper measured in N, the basis weight mA, the width of the strip w, and the gravita¬tional constant g = 9.81 m s–2.

B

L =

A • w • g