Abstract
Data are presented from additional mechanical tests of specimens taken from the same sheet of cellulose acetate for which tests have been reported in two previous papers by the author. The tests were conducted in a laboratory maintained at a constant temperature of 77 F and a relative humidity of 50 per cent: (1) Repeated bending (fatigue) tests were made at different speeds of testing and different ranges of stress, which demonstrate that both of these variables are important. The effect of different shapes of fatigue specimens (circular, square, and rectangular cross sections) on the endurance limit is also discussed. (2) Static compression tests of preconditioned specimens tested at intervals of time up to 10 months show the effect of initial moisture content and time on the yield point and the weight. (3) Static torsion, tension, and compression tests, conducted at the same rate of strain, indicate the effect of rate of strain and type of loading on the strength properties of the material. (4) Static tension tests of a specimen containing a transverse hole show the effect of a stress concentration on the tensile strength.
