Tear Resistance
Directional mechanical force measurement quantifies the energy required to propagate a previously initiated rupture through paper and board substrates. Mechanical pulp orientation and refining intensity dictate the baseline performance of the ISO 1974 tear index during production on the paper machine. Transverse direction values routinely fall below machine direction figures because fibre alignment during web formation restricts lateral propagation.
Converting machinery demands specific thresholds to prevent web snapping during high speed rotogravure printing and continuous bag manufacturing operations.
Stress Distribution
Force absorption relies heavily on long unbonded fibre lengths that allow local deformation before structural failure occurs. Tensile strength improvements frequently reduce flexibility and compromise tear energy absorption during sudden dynamic loading events. Converters balance burst resistance against tear propagation values when selecting folding boxboard for heavy weight retail packaging lines.
Testing Parameters
Standardized pendulum instruments release a calibrated mass that tears a clamped multi ply specimen across a precisely controlled arc length. Atmospheric conditioning at standard laboratory temperatures and relative humidity levels remains mandatory before testing because moisture content directly alters internal friction between cellulose fibres. Test results emerge as a normalized ratio dividing the total tearing work by the basis weight of the conditioned material sheet.
