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Compressive modulus measurement techniques

Pfeiffer, J. D.
The compression testing of stacks of sheet materials is done to learn the behavior of the group of sheets, a behavior that is quite different from that of a solid, or even one single thick sheet of the same material. Many interfaces are present at the sheet contact, consisting of soft fibers, asperities, or minor surface protrusions, and these cooperate to make the stress-strain relationship of the package nonlinear. Reasons for doing the testing are presented, with models for estimating the pressure versus strain curves, and implications for roll structure prediction based upon these models. The concept of strain loss in compression is reintroduced, and techniques are presented for improving curve-fitting when strain loss exists. A list of alternative ways for evaluating wound roll structure is given, with comments on the relative merits of these methods.