Mechanical Evaluation
Bending test configuration using two outer supports and two inner loading points creates a region of uniform bending moment without shear forces between the loading points. This method of four-point bending provides an accurate measure of the pure flexural stiffness of paperboard specimens. The absence of shear strain in the central zone ensures that the test isolates the elastic behavior of the material.
Laboratory Protocol
Laboratory technicians place the specimen across the support span and apply the force through the dual loading noses. Because the bending moment is constant in the middle region, any local defect in the sheet does not disproportionately skew the results. This makes the test highly reliable for assessing thick, corrugated boards where local flute crushing might otherwise affect measurements.
The instrumentation captures the force and deflection data to calculate the bending stiffness with high precision. Advanced systems automate the calculation to increase daily throughput.
Converting Application
Production lines utilize these precise stiffness values to predict how containers will perform under compressive warehouse loads. Using four-point bending data helps converting plants select the optimal linerboard weights for heavy-duty applications. This prevents both the over-packaging of lightweight goods and the failure of protective cartons during transport.
