A New Test Method for the Determination of the Flexural Modulus of Spirally Wound Paper Tubes

A new static test method to determine the flexural modulus of spirally wound paper tubes is described. The experimental method is based on the standard three-point-bend procedure. The method requires testing the tube at multiple (two or more) span lengths. The testing can be performed on either a rigid frame fixture under constant static load or in a universal testing machine under monotonically increasing quasi-static load. The test data are analyzed with a modified form of a classical Euler-Bernoulli beam theory. The modified theory accounts for nonbending deflection components that are obtained with the three-point-bend test. The effect of time-dependent creep deflection on the modulus prediction is also discussed. Extensive testing of a variety of paper tubes was conducted to verify the proposed test method. The accuracy of the method was determined by comparison with dynamic bending modulus predictions obtained from modal tests on the tubes. The dynamic modulus predictions were based on Euler-Bernoulli beam theory. Results of tests performed on a specially designed static frame fixture and tests performed on a universal testing machine are compared. It is found that the bending modulus predictions using the new analysis method are considerably closer to the dynamic bending modulus than those predictions obtained by classical beam theory.