Volume 9, Issue 4, 01 April 1938
Index of content:
9(1938); http://dx.doi.org/10.1063/1.1710415View Description Hide Description
9(1938); http://dx.doi.org/10.1063/1.1710416View Description Hide Description
A wave theory analysis is given for the reflection of wave pulses from plates, which heretofore has been treated by the methods of geometrical optics. The general theorem is proved that if the reflection coefficient for a harmonic wave system is exactly periodic in the frequency of the waves, the reflections from the plate due to an incident pulse will consist of a series of wave trains of exactly the same form as the incident pulse. This theorem may be applied to electromagnetic waves polarized in and normal to the plane of incidence, longitudinal waves in fluid media, and transverse waves polarized normal to the plane of incidence in general elastic media, when absorptive and dispersive effects can be neglected.
The Effect of Pressure Upon the Elastic Parameters of Isotropic Solids, According to Murnaghan's Theory of Finite Strain9(1938); http://dx.doi.org/10.1063/1.1710417View Description Hide Description
Murnaghan's theory of finite deformations is applied to a discussion of the effect of hydrostaticpressure upon the elastic coefficients of an isotropic body, for small strains superposed on the hydrostatic strain. Stress‐strain equations for the small strains, and the equations of small motion, are shown to have the same form as those of the classical theory, with elastic parameters which depend upon the pressure. Using a form of elastic potential identical with that of the classical theory, explicit results are found for the pressure coefficients of compressibility, Young's modulus, rigidity and so on; these are compared with such experimental results as are available, with good agreement. A single‐constant formula is derived which gives the volume change of such compressible materials as sodium and cesium up to the highest experimental pressure, 45,000 kg/cm2, within the experimental error.