Ultrasonic elastic properties of steel under tensile stress

Longitudinal and transverse wave velocities, eight kinds of elastic paramet ers and dilational and shear dampings of chromium-molybdenum steel have bee n simultaneously measured at room temperature in terms of acoustoelasticity , by an ultrasonic guise method. Young, sheer and bulk moduli and Lame para meter apparently decrease with increasing tensile stress, suggesting decrem ent of rigidity. However, decease in Poisson's ratio shows actual enhanceme nt of rigidity due to lattice dilation, accompanied by decrease in longitud inal wave frequency, Debye temperature and Gruneisen parameter As the stres s increases, the dilational damping increases and then saturates over 600 M Pa, while the shear one increases abruptly from 600 MPa. This abrupt increa se 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.