Tensile Strain Measurement in Recycled Paperboard Grades
Recycled paperboard strain measurement requires direct optical extensometry under ISO 1924-3 to isolate true sheet elongation from clamp slippage.
Jaw Slippage
Test Displacement
Tensile testing error occurs when a paper specimen moves relative to clamping surfaces during physical load application. Jaw slippage alters tensile energy absorption calculations, producing falsely inflated stretch percentage values and inaccurate tensile index readings. Laboratory technicians evaluate paper and paperboard strength using mechanical clamps designed to grip specimen strips without damaging individual cellulose fibers.
Slippage at the clamp interface shifts the force-elongation curve, invalidating standard test results according to international testing standards. The condition affects physical testing procedures across paper grades, folding boxboard and linerboard evaluation.
Measurement Error
Pneumatic and manual clamps utilize serrated or rubber-faced jaw inserts to hold test strips under defined clamping pressure. High-grammage paperboard requires elevated clamping force to overcome smooth surface coatings and friction-reducing sizing agents. When jaw slippage occurs, force readings plateau unexpectedly while crosshead displacement continues to advance, skewing modulus of elasticity determinations.
Adjusting clamping pressure between five hundred and seven hundred kilopascals prevents specimen motion while avoiding fiber crushing at the grip line. Laser extensometers and optical tracking systems eliminate grip motion errors by measuring strain directly on the central specimen span.
Equipment Capacity
Direct strain measurement via video extensometry bypasses clamp boundary movement completely. Test invalidation criteria require immediate recalibration whenever grip failure exceeds two percent of total sample extension.