Panel in-Plane Stiffness from Vertical Strain Analysis in Box Compression Test

This work is aimed at examining the overall contributions to displacement of a compressed box panel, such as panel compression strain and flap and crease displacements. 3D Digital Image Correlation (DIC) was used to analyse motion of a side panel of a corrugated fibreboard regular slotted container (RSC). The vertical displacement and the vertical component of strain of the panel face during box compression test are examined. Measuring displacements of the whole compressed box with DIC enables measurement of the in-plane compression of a panel in isolation from the horizontal fold or crease zone displacement, without having to test tube sections of the box to infer or extract the in-plane panel compression behaviour. Detailed study of one box design is presented, which in future could be extended to other box designs. Although the crosshead displacement during box compression testing was 10.6 mm at peak load, the in-plane compression of the panel, calculated from the average vertical component of the strain along the right edge of the long panel of the box, was 0.68 mm. At peak load, the portion of the box compression associated with bottom box flaps or crease zone crushing was 6.25 mm. The analysis shows that the majority of the vertical displacement of the box occurred in the top and bottom creased folds and that these folds are responsible for the low apparent in-plane stiffness of the box. The implications of these findings for box design are discussed.