CN102419224B - Local thermal disturbance method for residual stress test analysis - Google Patents

Abstract

The invention discloses a local thermal disturbance method for residual stress test analysis. The method comprises the following steps of: 1) heating an area to be tested, of a material, until the local area generates large enough elastic deformation, including elastic deformation contributed by initial residual stress, measuring the temperature of a critical point by means of an infrared temperature measurement unit, and collecting image information of the surface deformation process of the material by means of a camera shooting unit; 2) calculating an apparent strain field epsilon SH of thelocal area after thermal disturbance according to the image information, meanwhile, calculating a temperature field formed by local heating based on a finite element method, and calculating a thermalelastic strain field epsilon TE according to the temperature field T; 3) calculating a strain field increment delta epsilon IN corresponding to contribution of the initial residual stress according to a formula of epsilon SH=epsilon TE+delta epsilon IN; and 4) calculating and acquiring the initial residual stress according to a formula of delta epsilon IN=[K]*epsilon IN. In the local thermal disturbance method, the distribution of local residual stress of the material is detected by adopting a local thermal disturbance manner, so that the material per se is not damaged, and the result of residual stress distribution in the detected area can be acquired.

Description

The localized heat perturbation motion method of unrelieved stress test analysis

Technical field

The present invention relates to a kind of localized heat perturbation motion method of unrelieved stress test analysis.

Background technology

Unrelieved stress is the interactional embodiment of the structure/material internal of self-equilibrating, is the important prerequisite of thoroughly evaluating material mechanical performance and structural reliability to the abundant description of unrelieved stress, also is the important evidence of carrying out the material appropriate design.For the very simple material of preparation process, perhaps can predict its residual stress state more accurately by existing theoretical calculating; But for most material system, its unrelieved stress feature need be carried out test analysis with the test binding isotherm.

Main unrelieved stress test philosophy and technology comprises mechanical method for releasing and physical testing method at present.Wherein mechanical method for releasing such as boring method, plastic deformation method etc. have destruction or half destructiveness mostly, and this is difficult to be suitable in a lot of occasions.Be the physical testing method of representative with X-ray diffraction method etc., mainly the material microstructure that causes by the test unrelieved stress such as the variation of lattice constant come the inverting residual stress level.Regrettably X ray has certain influence to environment and operating personnel, and X-ray diffraction equipment is relatively expensive, test process is relatively complicated, and this just makes this method and can only do more accurate the analysis at finite point at present.

Summary of the invention

Problem at prior art exists the object of the present invention is to provide a kind of localized heat perturbation motion method of measuring accurately and can not destroying the unrelieved stress test analysis of material.

The localized heat perturbation motion method of a kind of unrelieved stress test analysis provided by the invention comprises the steps:

1) regional area to be measured to material is heated to the elastic deformation that this regional area generation comprises the initial residual stress contribution, measure the key point temperature by the infrared measurement of temperature unit simultaneously, and gather the image information of the surface deformation process of described material by image unit;

2) according to described image information by calculating the apparent strain field ε of this regional area after the thermal perturbation _SH, calculate the formed temperature field T of spot heating based on finite element method, and calculate thermoelastic strain field ε according to temperature field T _TE

3) according to ε _SH=ε _TE+ Δ ε _INFormula calculate unrelieved stress strain field increment Delta ε _IN

4) according to formula σ _IN=[K] * Δ ε _INCalculate the initial residual stress field, the low order form of matrix of coefficients wherein [K] is

$\left[K\right]=\frac{-E^3}{(1+v)(1-2v)({\left(\mathrm{\ΔE}\right)}^2+\mathrm{E\ΔE\Δv})}\×\left(\begin{array}{ccc}1-v& v& v\\ v& 1-v& v\\ v& v& 1-v\end{array}\right)$

$\left(\begin{array}{ccc}\frac{\mathrm{\ΔE}}{E}+\mathrm{\Δv}& \mathrm{\Δv}& -\mathrm{\Δv}\\ -\mathrm{\Δv}& \frac{\mathrm{\ΔE}}{E}+\mathrm{\Δv}& \mathrm{\Δv}\\ \mathrm{\Δv}& -\mathrm{\Δv}& \frac{\mathrm{\ΔE}}{E}+\mathrm{\Δv}\end{array}\right)\left(\begin{array}{ccc}1& v& v\\ v& 1& v\\ v& v& 1\end{array}\right)\left(\begin{array}{c}\mathrm{\Δ}{\mathrm{\ϵ}}_{\mathrm{IN}}^i\\ \mathrm{\Δ}{\mathrm{\ϵ}}_{\mathrm{IN}}^i\\ \mathrm{\Δ}{\mathrm{\ϵ}}_{\mathrm{IN}}^i\end{array}\right)$ , at the beginning of E, ν be in this formula

Beginning state elasticity modulus of materials and Poisson ratio, Δ E, Δ ν are the variable quantity of elasticity modulus of materials and Poisson ratio after the thermal perturbation.

Preferably, with the infrared measurement of temperature result thermal boundary condition of FEM (finite element) calculation is revised.

Preferably, described image unit is the high resolution CCD camera.

Preferably, adopt laser beam, electron beam or flame gun etc. that described regional area is heated.

Preferably, described enough elastic deformations refer to variation delta E 〉=10% of elastic modulus E.

Preferably, described key point refers to that described regional area central point, distance center point are respectively the point of 2 times, 1 times, 1/2 times, 1/4 times and 1/8 times of central point and edge wire length.

The present invention carries out spot heating and makes the localized heat disturbance by treating geodesic structure, and the material Yin Wendu of heat-affected zone raises and elastic performance takes place changes, causes initial residual stress/strain redistribution; The redistribution of unrelieved stress/strain will produce an increment in the body structure surface apparent strain; By the formation of apparent strain being calculated the contribution that separates initial residual stress, thereby obtain the distribution of initial residual stress.Because the present invention adopts the mode of localized heat disturbance to come the local residual stress distribution of test material, therefore not only need not destroy material itself, and can obtain the residual stress distribution result in tested zone, and the X-ray diffraction method that adopts usually can only obtain the unrelieved stress result of some measuring points usually.In addition, the resolution of the present invention by control Infrared survey precision and CCD shooting can be so that measurement result be more accurate, thereby improves the accuracy of analyzing greatly.

Description of drawings

Fig. 1 is the invention process example sample extended state synoptic diagram.

Embodiment

Come localized heat method of perturbation of the present invention is described below in conjunction with concrete material.

Adopting the dull and stereotyped sample of testing machine elastic stretching titanium alloy (Ti6Al4V) material strip to the strain of effective section is 4e-3, then with laser irradiation spot heating sample and to keep the sample total deformation that stress is taken place under the localized heat disturbance lax, take surface deformation with CCD, obtain the typical position temperature history with the infrared thermometer test, as shown in Figure 1.

The zone of measuring is the laser facula coverage, as shown in Figure 1.

When can determine that according to the heat-mechanical property of material material is heated to 425 ℃ (central temperature, down with), the variation delta E of elastic modulus E can be more than or equal to 10%, but can not surpass 500 ℃ of degree, prevents that material from moulding distortion taking place.

Adopt laser beam (can be electron beam or flame gun etc. also, as long as can produce the instrument of beam of higher energy density or equipment just can) regional area to be measured shown in Figure 1 is heated to 425 ℃.Adopt infrared thermometer to measure the temperature of the key point of this regional area, the key point here refers to that heating region central point, distance center point are respectively the point of 2 times, 1 times, 1/2 times, 1/4 times and 1/8 times of central point and edge wire length.

Simultaneously, the image information by the distortion of this regional area of high resolution CCD camera acquisition and obtain the surface by correlation analysis and look deformation field u _SH, by calculating the apparent strain field ε of this regional area after the thermal perturbation _SH, its component form is

Obtain looking deformation field u by image information _SHCan adopt known computing method, for example, the disclosed computing method of article [Experimental Mechanics 22 (2007) 556 – 567 and International Journal of Impact Engineering31 (2005) 329 – 339].For this example, ε _SH≈ 2.55e-3.

By finite element model for solving structure heat-conduction equation, accounting temperature field T, make comparisons with the result of finite element of aforementioned key point infrared measurement of temperature result and corresponding point simultaneously.If the two difference, is then revised the thermal boundary condition parameter greater than 1% and is found the solution heat-conduction equation again, so repeatedly, until the two difference less than 1% o'clock, can obtain malformation field u based on the fundamental equation that this temperature field T find the solution the structure Thermoelastic Problems _TH, can directly calculate strain field (the containing thermal strain) ε that structure is caused by the material thermal perturbation merely from the malformation field _TE, its method for solving can list of references [Wang Honggang, thermoelasticity outline, Beijing: publishing house of Tsing-Hua University 1989.].For this example, ε _TE≈ 1.71e-3.

Then, because at given temperature levels, superposition principle is satisfied in linear elasticity material deformation and strain.Therefore vector equation ε is arranged _SH=ε _TE+ Δ ε _INSet up, equation can calculate unrelieved stress and partly discharges the strain field increment Delta ε that causes accordingly _IN, Δ ε _IN=ε _SH-ε _TE≈ 0.84e-3.

At last, based on the balance equation of surface residual stress before and after linear elasticity material constitutive system of equations and incremental form thereof and the structure thermal perturbation etc., can derive obtains at tested regional top layer σ _IN=[K] * Δ ε _IN, the low order form of matrix of coefficients wherein [K] is

$\left[K\right]=\frac{-E^3}{(1+v)(1-2v)({\left(\mathrm{\ΔE}\right)}^2+\mathrm{E\ΔE\Δv})}\×\left(\begin{array}{ccc}1-v& v& v\\ v& 1-v& v\\ v& v& 1-v\end{array}\right)$

$\left(\begin{array}{ccc}\frac{\mathrm{\ΔE}}{E}+\mathrm{\Δv}& \mathrm{\Δv}& -\mathrm{\Δv}\\ -\mathrm{\Δv}& \frac{\mathrm{\ΔE}}{E}+\mathrm{\Δv}& \mathrm{\Δv}\\ \mathrm{\Δv}& -\mathrm{\Δv}& \frac{\mathrm{\ΔE}}{E}+\mathrm{\Δv}\end{array}\right)\left(\begin{array}{ccc}1& v& v\\ v& 1& v\\ v& v& 1\end{array}\right)\left(\begin{array}{c}\mathrm{\Δ}{\mathrm{\ϵ}}_{\mathrm{IN}}^i\\ \mathrm{\Δ}{\mathrm{\ϵ}}_{\mathrm{IN}}^i\\ \mathrm{\Δ}{\mathrm{\ϵ}}_{\mathrm{IN}}^i\end{array}\right)$ , E, ν are original state elasticity modulus of materials and Poisson ratio in this formula, Δ E, Δ ν are the variable quantity of elasticity modulus of materials and Poisson ratio after the thermal perturbation.For this example, [K] desirable its simplest one dimension form, i.e. [K]=-E ²/ Δ E ≈-526GPa.Therefore, for this example, σ _IN≈ 441.91MPa.Relative error＜1% of this and the actual primary stress 440MPa that applies.

The surface residual stress that the present invention obtains will be the residual stress field in the scope of heat-affected zone, by the space distribution of control heating region, can obtain the residual stress distribution state of all region-of-interests; And because heating beam, infrared measurement of temperature and CCD deformation test involved in the present invention all be contactless means, so the present invention can realize the non-contact testing analysis of residual stress field, and the error level of analysis can be controlled in 1% magnitude.

In addition, the present invention also is fit to various material and carries out local residual pressure test analysis, thereby the foundation of primary stress condition is provided for material mechanical performance evaluation and structural strength analysis.

Claims (6)

1. the localized heat perturbation motion method of a unrelieved stress test analysis comprises the steps:

1) regional area to be measured to material is heated to the enough temperature rises of this regional area generation, the initial residual stress/strain of this regional area is redistributed by disturbance, generation comprises enough elastic deformations of initial residual stress contribution, measure the key point temperature by the infrared measurement of temperature unit simultaneously, and gather the image information of the surface deformation process of described material by image unit;

2) according to described image information by calculating the apparent strain field ε of this regional area after the thermal perturbation _SH, calculate the formed temperature field T of spot heating based on finite element method, and calculate thermoelastic strain field ε according to temperature field T _TE

3) according to ε _SH=ε _TE+ Δ ε _INFormula calculate the strain field increment Delta ε that the redistribution of unrelieved stress/strain causes _IN

4) according to formula σ _IN=[K] * Δ ε _INCalculate the initial residual stress field, the low order form of matrix of coefficients wherein [K] is

$\left[K\right]=\frac{-E^3}{(1+v)(1-2v)({\left(\mathrm{\ΔE}\right)}^2+\mathrm{E\ΔE\Δv})}\×\left(\begin{array}{ccc}1-v& v& v\\ v& 1-v& v\\ v& v& 1-v\end{array}\right)$

$\left(\begin{array}{ccc}\frac{\mathrm{\ΔE}}{E}+\mathrm{\Δv}& \mathrm{\Δv}& -\mathrm{\Δv}\\ -\mathrm{\Δv}& \frac{\mathrm{\ΔE}}{E}+\mathrm{\Δv}& \mathrm{\Δv}\\ \mathrm{\Δv}& -\mathrm{\Δv}& \frac{\mathrm{\ΔE}}{E}+\mathrm{\Δv}\end{array}\right)\left(\begin{array}{ccc}1& v& v\\ v& 1& v\\ v& v& 1\end{array}\right)\left(\begin{array}{c}\mathrm{\Δ}{\mathrm{\ϵ}}_{\mathrm{IN}}^i\\ \mathrm{\Δ}{\mathrm{\ϵ}}_{\mathrm{IN}}^i\\ \mathrm{\Δ}{\mathrm{\ϵ}}_{\mathrm{IN}}^i\end{array}\right)$ , E, ν are original state elasticity modulus of materials and Poisson ratio in this formula, Δ E, Δ ν are the variable quantity of elasticity modulus of materials and Poisson ratio after the thermal perturbation.

2. the localized heat perturbation motion method of unrelieved stress test analysis as claimed in claim 1 is characterized in that, with the infrared measurement of temperature result thermal boundary condition correction is improved the temperature field computational accuracy.

3. the localized heat perturbation motion method of unrelieved stress test analysis as claimed in claim 1 is characterized in that, described image unit is the high resolution CCD camera.

4. the localized heat perturbation motion method of unrelieved stress test analysis as claimed in claim 1 is characterized in that, adopts laser beam, electron beam or flame gun that described regional area is heated.

5. the localized heat perturbation motion method of unrelieved stress test analysis as claimed in claim 1 is characterized in that, described enough elastic deformations refer to variation delta E 〉=10% of elastic modulus E.

6. the localized heat perturbation motion method of unrelieved stress test analysis as claimed in claim 1, it is characterized in that described key point refers to that described regional area central point, distance center point are respectively the point of 2 times, 1 times, 1/2 times, 1/4 times and 1/8 times of central point and edge wire length.

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