If a sheet of material of limited width is buckled, it will be found that in the outer arc of the fold the material tends to contract along the direction of the fold hinge, while in the inner arc of the fold the material tends to expand along the fold hinge. This gives rise to an additional curvature of the sheet in a direction perpendicular to the main fold axial direction. This curvature is a well-known phenomenon studied by engineers investigating the stability of buckled plates and beams and is termed anticlastic bending. This process could be important in producing some of the variations in axial plunge seen in fold systems, but it should be remembered that although the strains set up in this way look impressive at the edges of a narrow sheet of folded material, they have less structural significance when the sheet is a competent layer of wide lateral extent.

Ramsay J G 1967, McGraw Hill, N.Y.