Experimental Study of Dilatational‐ versus Distortional‐Straining Action in Material‐Damping Production

It has been conjectured that damping effects due to dilatational straining, small enough to be masked by experimental scatter in the usual test setups, might be significant under conditions of pronounced dilatational straining such as can occur in plate vibrations. For this purpose, a special machine was constructed to measure material damping in thin‐walled, cylindrical specimens subject to combined internal pressure and and axial cyclic loading. Tests were carried out on a number of manganese‐copper alloy specimens for which the usual uniaxial, cyclic‐stress, damping properties had already been established (and published). The new tests extended the ratio of dilatational‐ to distortional‐strain energies from the fraction that occurs under uniaxial stress up to the maximum factor of about 2/3, which is possible under biaxial stress. The results display a small but definite contribution to the material damping by the dilatational‐straining action. As a consequence, a modified formula is suggested for the specification of material damping in plate vibrations.