Load Deformation Properties
Not only the strength properties, tensile strength and strain to rupture can be determined in the tensile strength test (ISO 1924, 1992), but also the tensile energy absorption, TEA, which is especially important for bag paper. The TEA value repre¬sents the nonelastic portion of the deformation energy and thus that portion of dissipated energy which should be high in the case of bag paper.
The resistance to flexural stress is measured as the bending stiffness under ap¬proximately pure elastic deformation, as defined in DIN 53 121. This test is usually performed with a two-point beam method. To guarantee elastic deformation, max¬imum bending angles, which depend on the span length and the sample thick¬ness, are specified. This may be circumvented by the resonance length method (ISO 5629, 1983) in which the resonance length of a free sample strip is measured. Resonance is generated via a clamp vibrating at 25 Hz.
Deformations in board and cardboard can also be produced by creasing. Testing the properties of creases requires defined production processes, e. g., DIN 55 437 Part 1. In Parts 2 and 3 of this standard, methods are described for the manual folding of the creases and for the visual evaluation of the folding or the technical evaluation of the creases with a folding-moment tester.