CN104359977A - Acoustic surface wave high-order nonlinear parameter representation method for bending fatigue state of metal plate - Google Patents

Abstract

The invention aims to provide an acoustic surface wave high-order nonlinear parameter representation method for a bending fatigue state of a metal plate, and the method is used for detecting the bending fatigue state of the metal plate in real time and predicting the bending fatigue life of the metal plate and is widely applied to the fields of aerospace, machinery, traffic, chemical engineering, water conservancy and the like. The method comprises the following steps: determining parameters of an excitation signal according to the surface wave transmission distance and the acoustic velocity of a detected material; emitting a pulse string signal by a high-power ultrasonic transceiver, enabling ultrasonic wave beam to be obliquely incident to the material to generate surface waves, and interacting the surface waves with fatigue defects such as microdefects, micro-plastic deformation or microcracks generated in a bending fatigue process to generate a higher harmonic signal; recording the change of nonlinear parameters every a fixed cycle in a bending fatigue test process, comparing with a standard curve, judging whether a test piece has defects or not, emitting an early warning signal, and predicting the residual bending fatigue life of the metal plate.

Description

Sheet metal bending fatigue state surface acoustic wave high-order nonlinear parameter characterization method

One, technical field

The invention belongs to Dynamic Non-Destruction Measurement and metal fatigue field, being specifically related to the surface acoustic wave lossless detection method of sheet metal bending fatigue state, is a kind of method utilizing multiple nonlinear parameter real-time high-precision to detect hardware fatigue damage, prediction To Predict Fatigue Life of Components.

Two, background technology

Sheet metal bending fatigue state surface acoustic wave high-order nonlinear parameter characterization method be a kind of can real-tirne metal sheet material bending fatigue state, prediction sheet metal flexible life Dynamic Non-Destruction Measurement.Utilize in ultrasonic propagation process, sound wave and sheet metal bending fatigue state (microdefect, micro-plastic deformation or micro-crack) interact, and cause the phenomenons such as the scattering of sound wave or reflection, create harmonic signal, sound wave are occurred non-linear.The method is all widely used in field in many ways in Aero-Space, industrial machinery, communications and transportation, building etc., fatigue damage as aircraft engine turbine or blade detects, the detection of the fatigue damages such as automobile or train wheel hub, concrete fatigue damage, and detect common mechanical component (as axle, web member etc.) fatigue crack detection etc., therefore detect fatigue state, predicted fatigue life has important practical significance.

The surface acoustic wave lossless detection method of sheet metal bending fatigue state uses the ultrasound wave that frequency range is 1MHz-20MHz, detects the variation tendency with the sheet metal bending fatigue cycle such as Received signal strength fundamental voltage amplitude and higher hamonic wave amplitude, second order nonlinear coefficient and third-order nonlinear optical coefficient.Non-linear ultrasonic parameter is different to the sensitivity of different materials fatigue damage, therefore needs to demarcate different materials fatigue process.

S.I.Rokhlin etc. carry out the tensile fatigue test of different loads to titanium alloy sample, use the micro-crack in Lamb wave monitoring and quantitative test samples.Laurence J.Jacobs, Jin-Yeon Kim, Jianmin Qu etc. have studied second order nonlinear coefficient to corrosion cracking and sensitivity of stress state degree.Korea S Younho Cho have studied the susceptibility etc. of non-linear ultrasonic to Thermal Fatigue Damage.The distinct grade of domestic Deng uses sound in Lamb wave test material non-linear; In the use such as Wu Bin compressional wave detection tension test, nonlinear factor is with STRESS VARIATION trend.Researchers concentrate on the relation in second order nonlinear coefficient and fatigue damage or life-span.Not yet find at present to use the fatigue state of third-order non-linear ultrasound examination and characterizing metal material, predict the fatigue lifetime of hardware.

Three, summary of the invention

The object of the invention is to provide a kind of sheet metal bending fatigue state surface acoustic wave high-order nonlinear parameter characterization method, for high-order nonlinear ultrasound parameter variation tendency in on-line checkingi sheet metal crooked fatigue experiment process.

Sheet metal bending fatigue state surface acoustic wave high-order nonlinear parameter characterization method of the present invention comprises: utilize high-power ultrasonic to receive and dispatch instrument launching and receiving ultrasonic signal, ultrasonic beam is oblique to be mapped in sheet metal, surface wave is produced in sheet metal, the defect (microdefect, micro-plastic deformation or micro-crack) of surface wave and sheet metal interacts, sound wave is reflected, reflects or the phenomenon such as scattering, create higher harmonic component, utilize higher hamonic wave amplitude and second order, the ultrasonic coefficient of third-order non-linear to detect and characterizing metal sheet material bending fatigue state.

Four, accompanying drawing explanation

Fig. 1 sheet metal bending fatigue non-linear ultrasonic detection system schematic diagram.

Five, embodiment

Fig. 1 is sheet metal bending fatigue non-linear ultrasonic detection system test unit schematic diagram, and each several part is: the transmitting-receiving of sheet metal fatigue experimental device, sheet metal, ultrasonic transducer, high-power ultrasonic instrument, computing machine, industrial computer, data collecting card, motion control card etc.According to thickness determination excitation signal cycle number, the frequency and amplitude etc. of tested sheet metal.Sheet metal is arranged on the tired crooked experiment device of Fig. 1 sheet metal, transducer is arranged on Fig. 1 transducer position, connected nonlinearity ultrasonic testing system.

When considering one dimension longitudinal wave propagation by a nonlinear medium, in small strain situation, its equation of motion can be written as:

$\mathrm{\ρ}\frac{{\∂}^{2}u}{\∂t^2}=\frac{\∂\mathrm{\σ}}{\∂x}---\left(1\right)$

In formula, u is the displacement on x direction, and ρ is the density of medium, and σ (x, t) is the normal stress on x direction.When considering small strain situation, normal strain can be defined as (i.e. geometric relationship):

$\mathrm{\ϵ}=\frac{\∂u}{\∂x}---\left(2\right)$

Suppose that the nonlinear constitutive relation of medium can be described by following formula:

σ＝E·f(ε) (3)

In formula: E is elastic modulus.Consider velocity of sound c, between elastic modulus E and density p, pass is formula (2), (3) are substituted into formula (1) and can obtain:

$\frac{{\∂}^{2}u}{{\∂t}^2}=c^2{f}^{\′}\left(\mathrm{\ϵ}\right)\frac{{\∂}^{2}u}{{\∂x}^2}---\left(4\right)$

If f'(is ε) known, above-mentioned nonlinear equation can be solved by numerical value or progressive method.For understanding the characteristic of the party's journey solution, by f'(ε) do power series expansion, can be written as according to its constitutive relation (Van Den Abeele1996):

$f\left(\mathrm{\ϵ}\right)=\mathrm{\ϵ}+\frac{1}{2}{\mathrm{\β\ϵ}}^2+\frac{1}{6}{\mathrm{\δ\ϵ}}^3+\mathrm{\Δ}\left({\mathrm{\ϵ}}^4\right)---\left(5\right)$

In formula: β, δ are respectively the classical nonlinear factor of second order and three rank, relevant with the higher order elastic constant of material; Δ (ε ⁴) be ε higher-order shear deformation item.Again (5) formula is substituted into (4) formula, omits high-order event, can obtain:

$\frac{{\∂}^{2}u}{{\∂t}^2}=c^2\·\frac{{\∂}^{2}u}{{\∂x}^2}[1+\mathrm{\β}\frac{\∂u}{\∂x}+\frac{\mathrm{\δ}}{2}{\left(\frac{\∂u}{\∂x}\right)}^2]---\left(6\right)$

U (x, t) is launched by the square power of x:

u(x,t)＝u ₀(x,t)+xu ₁(x,t)+…+x ⁿu _n(x,t) (7)

Solve after finally merging arrangement by x with power power abbreviation:

$\begin{array}{c}u(x,t)=A_1\cos (\mathrm{kx}-\mathrm{\ωt})-\frac{\mathrm{\β}}{8}{k}^2{A}_1^{2}x\cos 2(\mathrm{kx}-\mathrm{\ωt})\\ +\frac{\mathrm{\δ}}{24}{k}^3{A}_1^{3}x[\cos 3(\mathrm{kx}-\mathrm{\ωt})+3\cos (\mathrm{kx}-\mathrm{\ωt})]\end{array}---\left(8\right)$

In formula, ω is circular frequency, and k is wave number.If the amplitude of the cos2 (kx-ω t) in above formula and cos3 (kx-ω t) item is set to A ₂and A ₃(i.e. second harmonic and third harmonic amplitude), then can obtain following formula:

$\mathrm{\β}=\frac{8A_2}{k^{2}x{A}_1^2}=\frac{2c^2{A}_2}{{\mathrm{\π}}^2{f}^{2}x{A}_1^2};\mathrm{\δ}=\frac{24A_3}{k^{3}x{A}_1^3}=\frac{3c^2{A}_3}{{\mathrm{\π}}^3{f}^{3}x{A}_1^3}---\left(9\right)$

When in sound wave incident to bending fatigue test specimen, microdefect, micro-plastic deformation or micro-crack make sound wave reflect, reflect or scattering, create higher harmonic component.Therefore along with the change of sheet metal bending fatigue state, non-linear ultrasonic parameter there occurs change.The secondary harmonic amplitude A of the method research Received signal strength ₂, third harmonic amplitude A ₃, second order nonlinear coefficient β and third-order nonlinear optical coefficient δ is with the variation tendency in sheet metal bending fatigue cycle.Utilize the evolution of non-linear sound parameter monitoring fatigue state, detect the fatigue state (microdefect, micro-plastic deformation or micro-crack) in sheet metal, the flexible life of prediction sheet metal.

Claims (5)

1. a sheet metal bending fatigue state surface acoustic wave high-order nonlinear parameter characterization method, it is characterized in that: use high-power ultrasonic transmitting-receiving instrument to produce Tone burst burst signal, excitation centre frequency is the ultrasonic surface wave transducer of f, use the ultrasonic surface wave receive MUT acoustic signals that centre frequency is 2f, draw the nonlinear parameter of different metal sheet material and the relation curve of flexible life, for detecting sheet metal bending fatigue state and prediction flexible life.

2. sheet metal bending fatigue state surface acoustic wave high-order nonlinear parameter characterization method according to claim 1, is characterized in that: metal material non-linear main from two aspects: the microdefects such as lattice anharmonicity, micro-plastic deformation and micro-crack.When ultrasound wave is propagated in bending fatigue sheet metal, the change of fatigue state (microdefect, micro-plastic deformation or micro-crack etc.) causes sound wave non-linear, namely there is higher harmonic component in Received signal strength, therefore can utilize the bending fatigue state of non-linear ultrasonic parameter characterization sheet metal.

3. sheet metal bending fatigue state surface acoustic wave high-order nonlinear parameter characterization method according to claim 1, it is characterized in that: utilize high-power ultrasonic to receive and dispatch instrument launching and receiving signal, take train of impulses as pumping signal, the quantity of train of impulses is relevant with speed with sound wave propagation distance in measured material, and receiving transducer centre frequency is at least 2 times of excitation transducer centre frequency.

4. sheet metal bending fatigue state surface acoustic wave high-order nonlinear parameter characterization method according to claim 1, it is characterized in that: docking is received acoustic signals and carried out spectrum analysis, obtain first-harmonic and the high-order harmonic wave amplitude of Received signal strength, calculate Amplitude Ration and second order, the third-order nonlinear optical coefficient of higher hamonic wave and first-harmonic.

5. sheet metal bending fatigue state surface acoustic wave high-order nonlinear parameter characterization method according to claim 1, it is characterized in that: utilize fatigue bending machine to carry out repeated bend test to test specimen, the fatigue state of every minor tick fixed cycle use non-linear ultrasonic systems axiol-ogy sheet metal, obtains higher hamonic wave and fundamental voltage amplitude ratio, second order nonlinear coefficient and the third-order nonlinear optical coefficient variation tendency with fatigue period.