THE SHAPE OF THE RING CRUSH CURVE

Two experimental rigs have been developed for attachment to a universa l tester for quick and accurate measurement of tensile and ring crush load displacement curves at various environmental conditions. The full load displacement curve of the ring crush test is available to examin e the effect of testing conditions. Handsheets were formed from a rand omized stock of never dried NSCC pulp. The ring crush load displacemen t curve exhibited an initial take up response then an almost linear re gion before a peak load at which the sample was not crushed and was vi sually undamaged. This contradicts traditional ideas that the ring cru sh failure mechanism is the crushing of the ring corresponding to the recorded peak load. The general shape of the ring crush curve was inde pendent of loading rate and moisture content. The peak load was more s ensitive to moisture than the stiffness of the specimen. The modulus o f the ring crush sample was significantly lower than the modulus in te nsion with the shape of the stress strain ring crush curve significant ly different from that of the tension curve.