GB/T 38811-2020Metallic materials - Residual stress - Method of sound beam control (English PDF)

6.4 Control mode

6.4.1 Overview The control modes are divided into four categories: vertical incident body wave mode, oblique incident guided wave mode, oblique incident surface wave mode, oblique incident array focus mode. When the sound beam is controlled, the control mode can be selected according to the actual situation.

6.4.2 Vertical incident body wave mode Place the sound beam exciter vertically on the surface of the material. The axis of the sound beam is consistent with the surface normal of the material. Longitudinal sound beam is reflected back and forth in the thickness direction with boundary. The acoustic mode converses for multiple times at the interface to form a superposition wave of longitudinal and transverse waves. Material point is in irregular and forced fluctuation. It can reduce and homogenize the residual stress in any direction in the material and in the area near the sound beam incidence. This mode is mainly used for the reduction and homogenization of residual stress on the surface and internal concentrated areas of the material. The schematic diagram of the control mode of the vertical incident body wave is shown in Figure 1.

6.4.3 Oblique incident guided wave mode Place the sound beam exciter on the surface of the waveguide component at a certain angle. The axis of the sound beam and the tangent plane direction of the material surface maintain a certain angle alpha. Meet the conditions of guided wave incidence. The control mode of oblique incident guided wave is shown in Figure 2. The direction of the arrow indicates the main direction of stress in the component. This angle depends on the excitation wedge material, the thickness or diameter of the waveguide component material, and the elastic constant. Usually choose the incident angle and frequency of the low-order symmetric or asymmetric mode of the guided wave. Guided waves propagate in the form of superposed waves of longitudinal and transverse waves in waveguides such as plates, tubes, columns. Material point is in irregular and forced fluctuation. It 4 - Regulated component; alpha, beta - incident angles of sound beam. Figure 4 -- Oblique incident array focus mode

6.5 Control process During the control process, the actuator wedge shall be firmly and tightly attached to the material surface; coupling contact force remains stable during control. The specific operations of the control process are as follows:

a) The electrical connection of the working system is intact and meets the equipment specifications and requirements;

b) Place the exciter on the surface of the material according to the required control mode. Apply couplant evenly on the end face of the exciter. Use vacuum, magnetic or mechanical clamping to clamp the exciter on the surface of the component stably. Ensure that the end surface of the exciter and the surface of the component are closely fit and coupled;

c) After checking the working system connection, turn on the system equipment and start working. Set the exciter to work at the natural frequency. According to tooling compaction state and incentive effect, properly adjust the optimal frequency and working time of the exciter, to make the exciter always keep in the best working condition;

d) After the residual stress control process is over, turn off and organize the control equipment. Remove the clamping fixture. Clean the surface of the component and the couplant on the end face of the acoustic beam exciter;

e) Record process parameters.