Ultrasonic measurement of residual stress in steels using critically refracted longitudinal waves (L(CR))

The problem of measuring residual stress in steel welded plates by applying the acoustoelasticity of the critically refracted longitudinal waves (L{dollar}sb{lcub}rm CR{rcub}{dollar} waves) was approached. Residual stresses are self-equilibrating and exist in a material that is deformed in a non-homogeneous manner. When high residual stress is present in a structure, the working stress is added to the residual stress producing an unknown stress field. In a corrosive environment, highly stressed areas in a material (i.e., those found near welds that have not been properly stress relieved) are prone to stress corrosion cracking.; Two welded plates were investigated: one hot-rolled and one cold-rolled. It is known from other studies that longitudinal residual stress (i.e., stress parallel to the weld bead) has the largest residual stress gradient after welding, and the acoustoelastic behavior of L{dollar}sb{lcub}rm CR{rcub}{dollar} waves is largest when a uniaxial stress is applied parallel to its propagation direction. Thus, the L{dollar}sb{lcub}rm CR{rcub}{dollar} waves technique was used and found capable of measuring stress changes after welding and after stress relieving of the plates. Two differential probes of 1 MHz and 2.25 MHz transducers were used and effectively measured longitudinal residual stress.; The hole drilling technique (HDT), a semidestructive surface stress measurement technique, was used to verify the results from the ultrasonic technique. The HDT showed about the same stress level, but with an opposite orientation at the weld, which was caused by the grinding process used to flatten the weld bead. The HDT verified the stress relief process by showing a decrease in stress after the stress relief.; The (001)(110) texture also was investigated by using a neutron diffraction technique. The technique yields an average of the orientation distribution of the (110) planes since it is a through-the-thickness transmission technique. At locations in the parent material and in the weld, the distribution was found to be very similar in the angular region near the rolling direction which is parallel to the propagation direction of the L{dollar}sb{lcub}rm CR{rcub}{dollar} waves. Thus, no significant changes should be expected in the travel-time of the L{dollar}sb{lcub}rm CR{rcub}{dollar} waves.