GB/T 38811-2020 English PDF (GBT38811-2020)

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GB/T 38811-2020: Metallic materials--Residual stress--Method of sound beam control
GB/T 38811-2020
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 77.040.10
H 22
Metallic materials - Residual stress - Method of sound
beam control
ISSUED ON: JUNE 02, 2020
IMPLEMENTED ON: DECEMBER 01, 2020
Issued by: State Administration for Market Regulation;
Standardization Administration of the People's Republic of
China.
Table of Contents
Foreword ... 3 
Introduction ... 4 
1 Scope ... 5 
2 Normative references ... 5 
3 Terms and definitions ... 5 
4 Principle ... 6 
5 Equipment ... 6 
6 Work process ... 8 
7 Treatment effect comparison ... 13 
8 Control report ... 14 
Metallic materials - Residual stress - Method of sound
beam control
1 Scope
This Standard specifies the principle, equipment, workflow, treatment effect
comparison and control report for using a sound beam with a certain energy
and directionality (elastic beam in a solid) to control the residual stress on the
surface and inside of metal materials.
This Standard is applicable to the on-site in-situ reduction and homogenization
of the assembly and welding of large metal components such as metal
containers, steel structures, pipelines, tracks, car bodies, aerospace cabins.
The control of the surface and internal residual stress of other non-metallic
sound-transmitting materials can also use it as reference.
2 Normative references
The following referenced documents are indispensable for the application of
this document. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any
amendments) applies.
GB/T 12604.1, Non-destructive testing - Terminology - Terms used in
ultrasonic testing
GB/T 20737, Non-destructive testing - General terms and definitions
GB/T 32073, Non-destructive testing - Test method for measuring residual
stress using ultrasonic critical refracted longitudinal wave
3 Terms and definitions
For the purposes of this document, the terms and definitions defined in GB/T
12604.1 and GB/T 20737 as well as the followings apply.
3.1 method of sound beam control
a method that injects a sound wave or elastic wave with a certain energy into
the material in a certain direction along a certain direction, so as to reduce and
coupling. Ensure that sound waves can be effectively and directed into the
interior of the processed material. At the same time, the surface of the exciter
shall not cause any damage to the surface of the material.
6.3 Selection of control part
The control position of the residual stress of the material shall be negotiated by
related parties, in accordance with GB/T 32073. Use non-destructive testing
method to determine the size, direction and gradient distribution or
concentration area of residual stress inside the component.
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 α. 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;
α, β - 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.
7 Treatment effect comparison
7.1 The parameter value and gradient distribution of normal (normal) stress and
cut (shear) stress have an important impact on product quality and performance.
Generally, there shall be clear requirements and clear marks in the stages of
structure design, manufacturing process, combined assembly, inspection and
testing, and safe service.
7.2 If the residual stress changes before and after the control is small, it shall
be considered whether the curvature of the excitation wedge and the
component surface is fit, whether the coupling is good, whether the exciter is
working normally, whether the power supply and the output power of the exciter
are sufficient. Re-control after correction.