Ultrasonic elastic properties of steel under tensile stress

Longitudinal and transverse wave velocities, eight kinds of elastic parameters and dilational and shear dampings of chromium-molybdenum steel have been simultaneously measured at room temperature in terms of acoustoelasticity, by an ultrasonic pulse method. Young, shear and bulk moduli and Lamé parameter apparently decrease with increasing tensile stress, suggesting decrement of rigidity. However, decease in Poisson's ratio shows actual enhancement of rigidity due to lattice dilation, accompanied by decrease in longitudinal wave frequency, Debye temperature and Grüneisen parameter. As the stress increases, the dilational damping increases and then saturates over 600 MPa, while the shear one increases abruptly from 600 MPa. This abrupt increase indicates an increase in motion of dislocation for plastic deformation. The atomic dilation enthalpy shows the endothermal process in elastic field up to 750 MPa.