GB/T 32073.1-2025Non-destructive testing - Ultrasonic method for measuring residual stress - Part 1: Critically refracted longitudinal wave method (English PDF)

1 Scope

This document describes the ultrasonic testing method for testing residual stress based on critical refraction longitudinal wave, specifies the testing system, testing procedures, temperature compensation and correction, and testing report for the critical refraction longitudinal wave method.

This document applies to the testing of residual stress and load stress in metallic materials with a sound transmission rate of not less than 6 dB/m sound path attenuation.

Other non-metallic materials shall be handled with reference to this method.

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 228.1 Metallic materials - Tensile testing - Part 1: Method of test at room temperature

GB/T 11345-2023 Non-destructive testing of welds - Ultrasonic testing - Techniques, testing levels, and assessment

GB/T 12604.1 Non-destructive testing - Terminology - Ultrasonic testing

GB/T 16923 Normalizing and annealing of steel parts

GB/T 18852 Non-destructive testing - Ultrasonic testing - Reference blocks and test procedures for the characterization of contact probe sound beams

GB/T 25712 Vibratory stress relief technology - Parameter selection and effect evaluation methods

GB/T 38811 Metallic materials - Residual stress - Method of sound beam control

3 Terms and definitions

For the purpose of this document, the terms and definitions defined in GB/T 12604.1 apply.

4 Testing overview

When an ultrasonic longitudinal wave excited by a transmitting transducer is obliquely incident on the surface of the component under test at the first critical angle, according to the law of refraction, an ultrasonic critical refraction longitudinal wave can be generated inside the material of the component under test, and can be received by a receiving transducer. The principle of transmitting and receiving ultrasonic critical refraction longitudinal waves and the residual stress testing area are shown in Figure 1.

According to the principle of acoustoelasticity, residual stress in the material affects the propagation speed of ultrasonic waves. When the direction of residual stress is consistent with the direction of the longitudinal wave, tensile stress slows down the propagation speed of the ultrasonic longitudinal wave or prolongs the propagation time t, while compressive stress speeds up the propagation speed of the ultrasonic longitudinal wave or shortens the propagation time t. Therefore, under the condition that the distance between the transmitting and receiving transducers (probe spacing) remains constant, if the ultrasonic propagation time t0 corresponding to the reference zero stress sigma0 and the ultrasonic propagation time t corresponding to the stress sigma of the component under test are measured, the absolute value of the residual stress sigma in the component under test can be calculated according to formula (1) or formula (2) based on the time difference, i.e.:

where:

deltasigma - the change in residual stress (stress difference), deltasigma = sigma - sigma0;

deltat - the change in propagation time (acoustic time difference), deltat = t - t0;

K - the stress coefficient, which is related to the material of the component under test, the coupling state, and the probe spacing, and can be obtained through tensile test calibration (see 6.3).

The stress measured by the method specified in this document is the average residual stress along the direction of sound wave propagation within a three-dimensional spatial region inside the material beneath the surface of the component under test.

5 Testing system