The third order elastic constants of polycrystalline aluminum (purity of 99.79%) and copper (purity of 99.98%) were determined by measuring their ultrasonic velocities under uniaxialy applied stress and the results were discussed by comparing with the previous data.The travel time of ultrasonic waves (5MHz) in a specimen of 10mm thickness was measured precisely with a singaround system. The longitudinal and shear waves polarized parallel or perpendicular to the uniaxial stress axis were propagated perpendicular to the axis.Since the traveling time under zero stress varied slightly in the experiment, the traveling time was measured before and after periodical stress and no plastic strains were observed.The results are summarized as follows:(1) The traveling time did not change linearly with applied stress. The deviation toward longer travel times was very large for copper both in tension and compression.However, the deviation for aluminum was a little. This is inferred to be the dislocation contribution. (2) To separate the measured traveling time change into two parts, one caused by the lattice anharmonicity and the other by dislocations, the measurements in both tensile and compressive conditions are needed.(3) The values of third order elastic constants measured for aluminum were in good agreement with the previous data, but not for copper.The present values, however, were most close to those calculated from the data of single crystal without containing dislocation contributions.
The variation of mechanical properties due to the mass effect in cast iron was examined on the specimens cut from several parts of a gray cast iron flywheel by subjecting them the repetition of heating and cooling, and of annealing.The conditions of heat treatment were as follows: (1) fromIn the case (1), the change in mechanical properties of each part decreased rapidly in the early stage of heat repetition, and every part yielded almost the same strength after heating cycles of more than 50 times.On the other hand, their microscopic structures showed that the area percentage of graphite and ferrite increased with increasing number of heat repetition, and a good correspondence existed between the changes in the structure and in mechanical properties.In the case (2), the same tendency with the case (1) could be recognized between the changes in mechanical property and microscopic structure, but since these changes were small, a larger number of heat cycles was necessary for the homogenization of mechanical properties of every part.And, in the heat cycles structures were not detected even after 100 cycles. In the case (3), that is, in the repetition of annealing, the changes in mechanical properties and microscopic structures revealed almost the same tendency with those in the case of the heat treatment mentioned above.
In an experimental study of acousto-elastic effect, some anomalous phenomena in ultrasonic velocity, that could not be interpreted by the lattice anharmonicity, have been observed. In this paper, we have observed in detail the behaviors of an ultrasonic velocity propagating in a copper specimen (99.98% of purity) perpendicularly to the stress axis, as the uniaxial tensile and compressive stresses exceeding the range of plastic deformation were applied or released stepwisely.The results obtained are summarized as follows:(1) The decrease of the traveling time (in a traveling path of 10mm) after one minute of pre-existed, they decreased at first depending on the amount of the plastic strain, reached a minimum, and then increased with the stress.
To study a possibility of practical application of this method, the ultrasonic velocities of longitudinal waves propagating perpendicularly to the stress axis of specimens stressed uniaxially were lated from the relation between strains and travelling time deviations was discussed.Using the sing-around method, the ultrasonic velocities were obtained from the travelling time of ultrasonic wave (5MHz) in the 10mm thick specimens. The experimental procedure was as follows:The stress was applied on the specimen and then released abruptly, and the change in travelling time responding to the instantaneous change in stress was measured.The results are summarized as follows:M0 under a given stress are of the same order of the strain caused by the stress.(2) In copper, the relation between the modulus deviation and the strain is representable by a to the density and the pinnig length of dislocation.(3) In annealed aluminum, the modulus deviation measured was in accordance with that expected from the third order elastic constants, but not in steel. The former was explained from that, because of a lot of impurity atoms, the mobility of dislocation would be reduced, and the later seemed to be due to pre-existent structures which would still remain after annealing at a relatively (4) In 6-nylon, the relation between the modulus deviation and the strain shows almost a straigtht line with little scattering.
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