CN105424243A - Torsion residual stress ultrasonic nondestructive test method - Google Patents

Abstract

The invention relates to an ultrasonic non-destructive testing method for torsional residual stress. The ultrasonic longitudinal wave forms a critical refraction longitudinal wave on the torsion surface of the shaft through a waveform conversion, and measures the propagation time of the critical refraction longitudinal wave in the shaft, which can be calculated by the acoustic elasticity theory. The corresponding torsional residual stress. Moreover, the torsional residual stress at different depths on the same torsion surface can also be measured by changing the frequency of the ultrasonic longitudinal wave. This technical invention can effectively solve the problem of the size distribution of torsional residual stress on the torsion surface at different angles, find the direction of the main stress, and analyze the fatigue strength. It is very suitable for wide use in the production site and maintenance site. The new method of stress distribution has very bright application prospects.

Description

A method for ultrasonic non-destructive testing of torsional residual stress

1. Technical field

The invention relates to an ultrasonic non-destructive testing method for torsional residual stress. The method utilizes ultrasonic critical refraction longitudinal waves to detect the residual stress generated in different directions during the torsion process of a shaft member.

2. Background technology

Torsional residual stress exists in transmission components such as cylindrical components and shaft components, and has an important impact on transmission strength. Transmission components are subjected to large stress random torsional loads during service, and are mostly fractured due to cracks, surface scratches and internal defects. This kind of fatigue fracture is an extremely common and serious failure mode. Torsional fracture belongs to low stress torsional fatigue fracture. According to the macroscopic and microscopic analysis of the fracture and the measured hardness distribution curve, the cause is generally due to the long-term shock and vibration during the service process, which has been subjected to alternating stress. Under the combined action of shear stress and shear stress, the crack rapidly and gradually expands and breaks.

The existing residual stress detection methods are mainly small hole method, X-ray diffraction method, electromagnetic method, neutron diffraction method and ultrasonic non-destructive testing method. Among them, the small hole method has a destructive effect on the surface of parts and can only be used for random inspection and cannot Batch inspection, and cannot detect components in service; X-rays are harmful to the human body and their penetration depth is small, neutron diffraction method is also very harmful to the human body, not only requires a special protection environment, but also the detection equipment is complicated and cannot be used for transmission Detection of components; electromagnetic methods are currently unable to quantitatively detect residual stress, and are affected by the degree of residual magnetism of the components to be tested.

Ultrasonic non-destructive testing method has received extensive attention because of its flexible and convenient use, suitable for on-site use, harmless to the human body, and quantitative detection of residual stress. The invention adopts ultrasonic critical refraction longitudinal wave to detect the torsional residual stress of the transmission component, and can detect the torsional residual stress of the transmission component non-destructively. Practical significance.

Searching the patent and service system and related public documents from 1997 to 2015 on CNKI, no similar public papers, invention patents or proprietary technologies on the detection of torsional residual stress of transmission components have been found so far.

3. Contents of the invention

The object of the present invention is to provide an ultrasonic non-destructive testing method for torsional residual stress, which solves the problem of rapid non-destructive testing of torsional residual stress of transmission components, and the method is repeatable.

The invention detects torsional residual stress by exciting critical refraction longitudinal waves on the shaft surface according to Snell's law. Acoustic wedges with different sound beam angles are designed according to the diameter and material of the workpiece. At the same time, the acoustic wedges can be designed as torsion wedges with different angles to the axial direction according to the direction to be detected. For an ultrasonic transducer of one frequency, the critical refraction longitudinal wave propagation time of the shaft can be obtained through the time difference between two ultrasonic transducers exciting and receiving ultrasonic waves, and the torsional residual stress in the measured direction of the shaft can be obtained by the theory of acoustoelasticity. By changing the ultrasonic frequency, the average torsional residual stress at different depths on the torsional surface of the workpiece can be detected.

4. Description of drawings

Fig. 1 is the front view of the principle schematic diagram of torsional residual stress detection;

Fig. 2 is a schematic top view of the principle of torsional residual stress detection;

Figure 3 is a schematic cross-sectional view of the principle of torsional residual stress detection;

5. Specific implementation

The specific embodiment of the present invention is described in detail below:

Torsional residual stress refers to the residual internal stress of transmission components such as shafts and cylinders during processing and service, which has an important impact on the life and safety of transmission components. Here, the drive shaft is taken as an example to detect the torsional residual stress in the 30° torsional direction.

1. Shaft torsion residual stress detection principle

According to the theory of acoustoelasticity, when ultrasonic waves propagate in isotropic elastic media, when the polarization direction of wave particles is consistent with or opposite to the direction of residual stress, the change of ultrasonic wave velocity is linearly related to the change of residual stress. Therefore, the torsional residual stress of the shaft can be detected by ultrasonic critically refracted longitudinal waves.

$\mathrm{<span\; class="notranslate">\; \&sigma;</span>}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}}{{\mathrm{<span\; class="notranslate">\; kV</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span>$

Among them, σ is the torsional residual stress value to be detected; V ₀ is the propagation velocity of longitudinal wave in the material under zero stress state, unit: m/s; k is the acoustic elastic coefficient; s is the critical refraction longitudinal wave propagation on the torsional surface of the measured shaft The arc length (m); t is the time used by the detection member to excite and receive the ultrasonic signal; t ₀ is the time used by the zero stress sample to excite and receive the ultrasonic signal.

Through the zero stress calibration of the shaft, k and t ₀ are determined, and then according to the installation method shown in Figure 1, Figure 2, and Figure 3, the sound time t is calculated by the ultrasonic testing system, and the torsional residual stress can be calculated according to the above formula value. During the detection process, temperature compensation is performed in real time to eliminate the influence of temperature changes on stress detection.

2. Detection of torsional residual stress at different depths of the shaft

According to the theory of acoustoelasticity, the penetration depth of the critically refracted longitudinal wave in the axial torsion plane is a function of the ultrasonic excitation frequency. The lower the frequency, the deeper the penetration depth, generally about 1 wavelength.

Therefore, the torsional residual stress value of the shaft at different depths can be detected by changing the ultrasonic frequency.

3. Surface acoustic field of critically refracted longitudinal waves

Near the axis of the transducer, the ultrasonic sound pressure is highest. When the incident angle of the ultrasonic waves (the angle between the transducer axis and the normal direction of the surface) is greater than or equal to the first critical angle _θcr and less than the second critical angle, the incident longitudinal wave undergoes waveform conversion at the interface, and a critical refracted longitudinal wave is generated on the workpiece surface . The critically refracted longitudinal wave propagates along the twisted surface of the axis within a certain depth. When the sound wave propagates, the particle vibrates from near to far layer by layer, so that the energy is also propagated layer by layer. The echoes are received at the same angle as the transducer.

4. Data processing and analysis

Measure the torsional stress of the transmission shaft along the direction of 30 degrees, usually 3 to 4 times, and take the average value as the torsional residual stress value in this direction. Check the strength of the transmission shaft according to the following conditions:

1> When the transmission shaft is being processed or statically loaded, compare the measured torsional stress value with the allowable stress value of the shaft. When σ≥[σ], the shaft does not meet the strength requirements, and there is a potential safety hazard. It should be replaced in time or improved in the processing technology;

2> When processing and static loading, σ≤[σ], it is also necessary to consider the strength of the shaft when it is subjected to alternating loads during service, that is, σ+ _σwork≤ [σ].

Among them, σ is the _working stress in this direction when the shaft is subjected to the maximum load during the working process, α is the angle between the torsion direction and the axial direction, where α=30°; for a solid shaft In the formula, D is the diameter of the circular section; the hollow shaft (cylindrical) where D and d are the outer and inner diameters of the circular section, respectively.

Claims (11)

1. one kind is reversed unrelieved stress supersonic damage-free detection method, it is characterized in that: the sound voussoir designing different acoustic beam angle for different-diameter different angles torsional surface, the compressional wave ultrasonic transducer of a certain frequency is arranged on the two ends of sound voussoir, one of them ultrasonic transducer is used for excitation ultrasound compressional wave, another is used for receiving ultrasonic longitudinal wave, drawing the workpiece time that critical refraction longitudinal wave is propagated on torsional direction by launching with acceptance hyperacoustic mistiming, just can calculate torsion unrelieved stress according to Vocal cord injection.

2. one according to claim 1 reverses unrelieved stress supersonic damage-free detection method, its mentality of designing derives from the transmission components such as axle class, cylindrical parts in processing and military service process, because the unrelieved stress of a certain angle direction is excessive, the phenomenon that frequent appearance twists off along a certain angle, therefore need a kind of lossless detection method reversing unrelieved stress.

3. torsion unrelieved stress according to claim 1, refer to that the compressional wave that ultrasound transducer probe is launched produces critical refraction longitudinal wave through first critical angle incidence and can propagate along arc-shaped curved surface, within the scope of the spread angle that receiving transducer is propagated at critical refraction longitudinal wave, and receive critical refraction longitudinal wave with the receiving angle identical with incident angle.

4. the critical refraction longitudinal wave transmitting and receiving process of torsion unrelieved stress according to claim 1 and claim 4, detect the angle that the ultrasonic longitudinal wave critical angle of incidence reversing unrelieved stress refers to the normal of ultrasonic longitudinal wave acoustic beam and circular arc camber point of intersection, meet snell law, the minimum value of this angle is greater than the first critical refraction angle and is less than second critical angle.

5. the critical refraction longitudinal wave transmitting and receiving angle of torsion unrelieved stress according to claim 1 and claim 4, because the different materials velocity of sound is different, different materials has different grazing incidence angles and receiving angle.

6. torsion unrelieved stress according to claim 1, the unrelieved stress of a direction referring to the unrelieved stress that transmission component remains in a direction of inside workpiece in process and produce by alterante stress in process under arms.

7. torsion unrelieved stress according to claim 1, ultrasonic critical refraction longitudinal wave velocity of propagation is subject to the impact of detected component harmony voussoir temperature, in order to compensate with demarcate the difference of temperature and the velocity contrast brought to the metrical error of unrelieved stress, laying temperature sensor in sound voussoir, to obtain the temperature variation of testing environment, sound voussoir and detected component in real time.

8. torsion unrelieved stress according to claim 3, be not only confined to the 30 ° of torsional directions mentioned in instructions, torsional direction can be any direction, as arbitrarily angled in conventional 0 °, 45 °, 60 ° and 90 ° etc.

9. ultrasonic transducer according to claim 1, is characterized in that: can by regulating the frequency of transducer, can the size of the torsion unrelieved stress of different depth and distribution on detection axis torsional surface.

10. torsion unrelieved stress supersonic damage-free detection method according to claim 1, is characterized in that: the direction that can be found principle stress by the unrelieved stress of more different torsional direction, is judged the validity of its intensity in time.

11. torsion unrelieved stress supersonic damage-free detection methods according to claim 1, it is characterized in that: can obtain by reversing unrelieved stress transducer the Changing Pattern dynamically reversing unrelieved stress, in time Fatigue Strength Analysis being carried out to the rotation class A of geometric unitA in twist process.