CN103808806A - Ultrasonic non-destructive testing method for measuring circumference residual stress at gear root - Google Patents

Abstract

The invention provides an ultrasonic non-destructive testing method for measuring circumference residual stress at root, the method is suitable for the non-destructive measurement of residual stress at the gear root. An LCR (critically refracted longitudinal) wave which is most sensitive to the stress is motivated through the combination of an ultrasonic stress measurement system, an ultrasonic transducer and a wedge block, and the residue stress at the region is precisely computed by using acoustic time difference of the LCR wave for detecting whether the stress is near to the root. The method is capable of accurately, fast and non-destructively detecting the residue stress value.

Description

A kind of supersonic damage-free detection method for the circumferential unrelieved stress of prototype gear tooth root

One, technical field

The present invention proposes a kind of supersonic damage-free detection method for prototype gear tooth root unrelieved stress, the method is applicable to the nondestructive measurement of Gear Root unrelieved stress.

Two, background technology

Gear is the strength member in the machines such as automobile, tractor, lathe, the vital task that it is being undertaken and transmitting motion, is changing movement velocity and direction of motion.Therefore, no matter be the situation that produces stress in the manufacture process of gear, still stress situation in the time of work, is all the important topic that people study.

Literature search is found, paper: (Zhao Xiyong. the mensuration of wearing and tearing traction gear root stress) in mentioned the stress of measuring tooth root by the method for subsides foil gauge, but this method is only confined to the stressing conditions of prototype gear in motion process, the unrelieved stress that tooth root produces due to factors such as processing cannot be detected.Paper: (wear into. Gear Root Dynamic Stress Analysis and Optimal Structure Designing thereof [D]. Changsha: Central South University, 2008.) in a literary composition, mentioned the calculating of carrying out root stress by the method for finite element analysis, this is a kind of computer based analogy method, human factor is very large, and the difference that grid is divided can have influence on the final detection result of stress to a great extent.Patent: (Jiang Chuanhai, Deng. the detection method [P] of little curved surface gear root shot-peening layer unrelieved stress. the patent No.: CN102628815A, 2012) a kind of rectangle diffraction baffle plate of preparing different size according to gear radius-of-curvature is disclosed, measure under different size baffle plate condition, curved surface gear root residual-stress value, obtain the relation between rectangle barrier width and residual-stress value, this is a kind of stress detection method based on X ray, requirement Gear Root surface is substantially smooth and will pass through suitable chemical treatment, expose lattice, and to repeatedly adjust the incident angle of X ray, in suitable angle of diffraction, there is certain intensity to can obtain, trivial operations, influence factor is many, accuracy is not high, practical application is very limited.

In this paper is a kind of method of utilizing ultrasonic technology to carry out detection of gear tooth root unrelieved stress, the method is high to unrelieved stress susceptibility, measure easy to operate, speed is fast, axial unrelieved stress that not only can prototype gear root, can also measure the axial unrelieved stress of tooth root, be applicable to very much on-the-spot use.

Three, summary of the invention

The object of this invention is to provide a kind of supersonic damage-free detection method for Gear Root residual stress measurement, be used for carrying out quickly and accurately the detection of gear root unrelieved stress.Reach accurately, harmless, object fast.

Concrete technical scheme of the present invention is as follows:

(1) work out two voussoirs and be placed in respectively two flank of tooth and measure the method for tooth root unrelieved stress according to the special size of gear and curved-surface structure.

(2) having designed according to the special size of gear and curved-surface structure can be for the sound voussoir of tooth root residual stress measurement, and the sound voussoir material velocity of sound of this particular design is lower than the velocity of sound of tested gear material.

(3) according to Snell law, when ultrasonic longitudinal wave from velocity of wave slower medium propagate into velocity of wave faster in the middle of medium time (as, incide the flank of tooth from this sound voussoir) can there is refraction effect, when compressional wave refraction angle equals 90 ^°time corresponding incident angle be called first critical angle, refracted longitudinal wave is propagated surface along gear, i.e. critical refraction longitudinal wave (English: Longitudinal critically refracted wave-English abbreviation L _cRripple).According to L _cRthe theoretical feature of ripple, has verified L by experiment _cRat the propagation law of this special surface of gear.

Four, accompanying drawing explanation

Fig. 1 Gear Root Stress instrumentation plan;

Fig. 2 tensile sample figure;

Fig. 3 compresses assay maps;

Fig. 4 red copper voussoir figure.

Five, embodiment

Below the specific embodiment of the present invention is elaborated:

1, L _cRexciting of ripple

According to Snell law, when propagating into velocity of wave, the ultrasonic longitudinal wave sound voussoir slower from velocity of wave can there is refraction effect faster in the middle of gear material time, and incident angle corresponding in the time that compressional wave refraction angle equals 90 ° is called first critical angle, and computing formula is as follows.

${\mathrm{\θ}}_{\mathrm{cr}}={\sin }^{-1}(V/V_2)$

In formula:

V ₁ultrasonic longitudinal wave velocity of propagation (m/s) in the slower medium of-velocity of wave;

V ₂-velocity of wave is ultrasonic longitudinal wave velocity of propagation (m/s) in medium faster.

θ _cr-first critical angle (°);

Refracted longitudinal wave will be propagated in the propagation top layer along gear.

According to the profile geometry of gear, find out the tangent line of involute urve at this point in the position of flank of tooth placement sound voussoir, calculate the first critical angle at this point according to Snell law and the sound velocimeter in sound voussoir material and gear material.

2, ultrasound stress principle

According to acoustic elasticity ultimate principle, when ultrasound wave is propagated in transversely isotropic elastic media, when the polarization direction of fluctuation particle is consistent with unrelieved stress direction or on the contrary when (that is, being that 0 degree or 180 is spent), ultrasonic velocity change amount and unrelieved stress variable quantity are linear.Therefore, can utilize ultrasonic critical refraction longitudinal wave to detect the unrelieved stress of this direction.In the time that critical refraction longitudinal wave speed increases, represent to have compressive residual stress in material, otherwise, there is stretching unrelieved stress, under material behavior is determined condition, the relation between critical refraction longitudinal wave velocity of wave variable quantity dV and unrelieved stress variable quantity d σ is as follows:

$\mathrm{d\σ}=\frac{2}{k{V}_0}\×\mathrm{dV}$

In formula:

The change amount (MPa) of d σ-unrelieved stress;

The change amount (m/s) of dV-critical refraction longitudinal wave velocity of propagation;

V ₀the velocity of propagation (m/s) of-zero stress condition lower critical refracted longitudinal wave;

K-sonoelastic coefficient (ns/m ²);

After critical refraction longitudinal wave propagation distance L determines, the sonic velocity change in measured medium changes equivalent substitute can be with sound time, as shown in the formula:

$\mathrm{d\σ}=-\frac{2}{k\×T_0}\mathrm{dt}$

In formula:

Variable quantity (s) when dt-critical refraction longitudinal wave propagation sound;

T ₀-zero stress condition lower critical refracted longitudinal wave is propagated fixed range L needed time (s);

Make Stress Constants K=2/kt ₀wherein T ₀be longitudinal wave propagation mistake under zero stress condition, be at this moment varied to linear approximate relationship, i.e. Δ σ=K Δ t when STRESS VARIATION and ultrasonic propagation sound.

3, the calculating of Stress Constants K value

Make the stretching identical with gear material and compression sample, use electronics tensile and compression testing machine, ultrasonic pulse transmitting-receiving instrument, oscillograph to carry out the demarcation of K value.Concrete steps are as follows:

In the yield limit of gear material, use cupping machine to carry out tension and compression to tension and compression test specimen, every certain stress value (this method adopts every 30MPa), the mistiming t showing in recording oscillometer _istress value σ with cupping machine demonstration _i.Carry out curve fitting by least square method, calculated stress constant K value.

$\underset{i=0}{\overset{i=n}{\mathrm{\Σ}}}[{\mathrm{\σ}}_i-K\×(t_i-t_0){]}^2={\mathrm{\σ}}_{\min }$

4, the measurement of Gear Root Stress

First the sound path of measuring between two voussoirs is designated as S, and, under zero stress state, the travel-time of ultrasonic longitudinal wave between two voussoirs is

under note stress state, the velocity of sound of ultrasonic longitudinal wave in gear is Vi, and the stress intensity in gear is

Claims (8)

1. the present invention proposes the measuring method of the circumferential unrelieved stress of a kind of tooth root, it is characterized in that it comprises: gear, ultrasonic measurement of stress system, unrelieved stress Ultrasonic Testing Transducer, sound voussoir.

2. the measuring method of the circumferential unrelieved stress of tooth root according to claim 1, first carries out the demarcation of Stress Constants K value.

3. K value according to claim 2 is demarcated, and first formulates, heat treatment mode identical tensile test specimen identical with measured material, stretches and records not stress value σ in the same time with drawing machine _i, measure the sound time difference t of different stress values by ultrasonic measurement of stress system _i, carry out linear fit by least square method, obtain K value.

$\underset{i=0}{\overset{i=n}{\mathrm{\Σ}}}[{\mathrm{\σ}}_i-K\×(t_i-t_0){]}^2={\mathrm{\σ}}_{\min }$

4. the measuring method of the circumferential unrelieved stress of tooth root according to claim 1, carries out special sound voussoir design, makes Ultrasonic Testing Transducer be excited and be received critical refraction longitudinal wave by voussoir.

5. the measuring method of the circumferential unrelieved stress of tooth root according to claim 1 need to have good coupling with gear teeth face, therefore the involute surface matching with gear teeth face will be made in voussoir bottom surface in the time that voussoir designs.

6. the measuring method of the circumferential unrelieved stress of tooth root according to claim 1, the physical dimension special according to gear, selecting the velocity of sound material slower than the gear material velocity of sound is sound voussoir material.

7. the measuring method of the circumferential unrelieved stress of tooth root according to claim 1 is first carried out zero stress demarcation in the time measuring stress, records zero stress waveform.

8. the measuring method of the circumferential unrelieved stress of tooth root according to claim 1, in the time measuring tooth root unrelieved stress, the contrast of waveform and zero stress waveform during by measurement, system-computed is spoken the time difference, by formula σ=K × (t _i-t ₀).

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