Designing Accelerated Creep Buckling Test Protocols for Downgauged Boxboard
Accelerated creep buckling protocols require cyclic humidity chambers and parallel platens to predict thin boxboard stacking failure under dead loads.
Platen Parallelism
Alignment Accuracy
Uniform pressure distribution during testing requires that the upper and lower compression surfaces remain perfectly aligned. For crushing tests on paperboard, platen parallelism describes the angular alignment between the two plates that squeeze the sample. If these surfaces are even slightly out of line, the specimen experiences uneven stress and fails prematurely.
Mechanical Influence
Test results for box compression suffer from high variability when the faces of the testing machine are misaligned. A slight tilt means one side of the paperboard carton receives the load before the other. This concentrated pressure causes early crease failures.
In labs, maintaining platen parallelism is a standard requirement for generating reproducible crush data.
Verification Process
Calibration of laboratory equipment utilizes dial indicators or electronic load cells to measure deviation across the plate surface. These measurements are taken at multiple points to ensure the tilt remains below the threshold defined by ISO or TAPPI standards. Adjusting the spherical seat of the upper platen allows technicians to lock the plates into a true parallel position before starting a test series.
Because routine operations involve high force, platen parallelism requires frequent checking to prevent wear from introducing measurement errors. Ensuring this alignment protects the validity of structural calculations for shipping containers.