CN111199115A - Method for determining deformation curvature radius of multipoint laser shock peening thin-walled part - Google Patents
Method for determining deformation curvature radius of multipoint laser shock peening thin-walled part Download PDFInfo
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- CN111199115A CN111199115A CN201811291528.3A CN201811291528A CN111199115A CN 111199115 A CN111199115 A CN 111199115A CN 201811291528 A CN201811291528 A CN 201811291528A CN 111199115 A CN111199115 A CN 111199115A
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Abstract
The invention provides a method for determining the deformation curvature radius of a multipoint laser shock peening thin-walled piece, which comprises the following steps: finite element software ABAQUS is adopted to firstly simulate the laser shock strengthening process of a characteristic unit body (a part with a smaller geometric dimension) with a certain size, and the distribution of plastic strain after laser shock strengthening in the thickness directions of different positions is obtained; leading the obtained data into Matlab for averaging, and then fitting the data in the Matlab to obtain a fitting function of the distribution of the plastic strain in the thickness direction; and (4) introducing the fitting function into a curvature radius theoretical formula, and finally obtaining the deformation curvature radius of the laser shock peening thin-walled part. The method considers the complexity of the deformation mechanism of the multipoint laser shock peening thin-walled part and the influence of a plurality of variable factors in the deformation, adopts a method combining theory and simulation to determine the deformation curvature radius of the multipoint laser shock peening thin-walled part, and has the characteristics of low cost, short time consumption, simplicity, convenience, practicability and the like.
Description
One, the technical field
The invention relates to the field of laser shock peening, in particular to a method for determining deformation curvature radius of a multipoint laser shock peening thin-walled part.
Second, background Art
By utilizing the plasma shock wave effect generated by nanosecond pulse laser induction, residual compressive stress with a certain depth is introduced into the surface metal material, so that the fatigue resistance of the metal part is improved, the fatigue life is further prolonged, meanwhile, the hardness, the strength and other properties of the surface of the material are also improved, and the laser shock strengthening technology is widely applied to the fields of aviation, aerospace and the like. However, the laser shock peening technology brings the above benefits and also causes deformation of the part, especially of the metal thin-wall part, and the deformation of the part caused by laser shock peening affects the use performance and subsequent assembly of the part. The laser shock strengthening deformation of the metal thin-wall part is one of the problems to be solved urgently at present.
In order to achieve a better laser shock peening effect, reasonable shock peening process parameters need to be adopted, but due to the complexity of a deformation mechanism of the laser shock peening thin-walled part and the influence of a plurality of variable factors in deformation, great difficulty exists in optimizing the process parameters. It is time and cost consuming if only experimental data and operating experience are relied upon to determine the process parameters. Therefore, a finite element is introduced into the laser shock strengthening thin-wall part to optimize shock strengthening process parameters, but in actual operation, because the size of a light spot is small relative to a workpiece, the number of the light spots in the shock strengthening process is thousands of light spots, and meanwhile, grid refinement is needed to be carried out along the thickness direction of the part for obtaining stress and strain distribution along the thickness direction, so that the calculation amount of finite element simulation is huge and is limited by the calculation cost, and a calculation method for establishing association between the laser shock strengthening process parameters and the part deformation curvature radius is needed at present.
Third, the invention
In order to overcome the defects in the prior art for optimizing the technological parameters of the laser shock peening thin-walled part, the invention provides a method for determining the deformation curvature radius of the multipoint laser shock peening thin-walled part. The method adopts a method of combining theory and finite element simulation, and utilizes the idea of intrinsic strain to determine the deformation curvature radius of the laser shock peening thin-wall part in less time, thereby establishing the relationship between the laser shock peening process parameters and the deformation of the thin-wall part with less cost.
The invention is realized by adopting the following technical scheme:
(1) in ABAQUS, performing multi-point laser shock peening simulation on a characteristic unit body with the same thickness as an actual thin-wall part to obtain plastic strain distribution in the thickness direction of the part under specific process parameters;
(2) importing the plastic strain thickness direction distribution data obtained by finite element simulation into Matlab, averaging the simulation data, and fitting the average plastic strain data to obtain a distribution function of the plastic strain in the thickness direction;
(3) and substituting the plastic strain distribution function into a theoretical formula of the deformation radius of curvature of the laser shock-strengthened thin-wall part to obtain the size of the radius of curvature.
The invention provides a method for determining the deformation curvature radius of a multipoint laser shock peening thin-walled part. According to the method, according to the idea of intrinsic strain, only the characteristic unit bodies need to be simulated and analyzed in finite element simulation, the plastic strain distribution in the actual part thickness direction can be obtained, meanwhile, the numerical simulation in the laser shock peening process only needs to be explicitly analyzed, and for the laser shock peening load application process of multiple light spots, the subprogram edited by Fortran language is adopted to realize the loading at different positions and different moments, so that the efficiency is improved, and the calculation cost is greatly reduced; meanwhile, Matlab is adopted to carry out averaging processing on the plastic strain thickness direction distribution data obtained by simulation, data fitting processing is further carried out, the efficiency and accuracy of data analysis are improved, finally, the thickness direction plastic strain distribution data obtained by different process parameters (laser power density, spot radius, impact strengthening route, strengthening times, lap joint rate and pulse width) are brought into the proposed deformation curvature radius theoretical formula, and the numerical value of the deformation curvature radius is determined.
Description of the drawings
FIG. 1 is a flow chart of a method for determining a radius of curvature of deformation of a multi-point laser shock peening thin wall part.
Fig. 2 is a diagram of a plastic strain distribution obtained by numerical simulation.
Fig. 3 is a distribution graph of the fitting of the thickness direction plastic strain averaged data in Matlab.
Fifth, detailed description of the invention
The following specific examples are combined to calculate the deformation curvature radius R of the multipoint laser shock peening thin-wall part
The technical scheme of the invention is described in detail as follows:
1. firstly, numerical simulation is carried out on the process of multipoint laser shock peening of the thin-wall part, and only an Explicit solver is needed in the process.
The numerical simulation of the multipoint laser shock peening process comprises the following steps:
1.1. establishing a geometric model and defining material properties: the actual size of the laser shock strengthening thin-wall part is
500mm 50mm 3mm, according to the intrinsic strain idea, the geometric dimension of the characteristic unit cell body of the simulation analysis is
22mm 3mm, material density 4500kg/m3Poisson's ratio of 0.34, and elastic modulus of 110 GPa. A Johnson-Cook model is adopted to describe the dynamic constitutive relation of the TC4 titanium alloy, and formula 1 is an expression of the model.
In the formula: a is yield strength, B and n reflect the strain hardening characteristics of the material, C reflects the influence of strain rate on the material properties, epsilonpWhich represents the equivalent plastic strain of the plastic material,
represents a reference strain rate at which the strain is measured,
represents the dynamic strain rate;
1.2. setting an explicit analysis step: the time of the analysis steps should be such that the kinetic energy finally approaches 0 in each analysis step, which in the present example is set to 2 × 10-5s；
1.3. Load application and meshing: the laser power density is 6.42GW/cm2The method adopts a flat-top light beam and a circular light beam, the size of a light spot is 3mm, the pulse width is set to be 10ns, the lap joint rate is 50%, and a Fortran editing subprogram is used for applying loads at different positions and different moments of multiple light spots; carrying out grid refinement in a laser shock strengthening area, wherein the grid size is 150 mu mx75 mu m;
1.4. submitting analysis operation and post-processing: finite element calculation is completed, and numerical simulation results of laser shock peening including stress, strain, displacement and plastic strain distribution are obtained and are shown in figure 2.
2. The thickness direction plastic strain distribution data is averaged and then fitted to obtain a strain distribution function f (x), and the fitting distribution is shown in fig. 3.
f(x)＝0.01241*exp[-((x-3.93)/1.111)2](2)
Wherein x is the position of the part in the thickness direction.
3. Substituting the plastic strain distribution function into a theoretical formula of the deformation radius of curvature of the laser shock-strengthened thin-wall part to obtain the size of the radius of curvature, wherein the radius of curvature is as follows:
where Γ is referred to as the depth-averaged intrinsic strain, Γ1Called intrinsic torque moment, xRIs the part upper surface coordinate, xLIs the part lower surface coordinate, k is the curvature, where xR＝3；xL0; h is the thickness of the part, where h is 3, and finally the radius of curvature R is 206 mm.
Claims (4)
1. A method for determining the deformation curvature radius of a multipoint laser shock peening thin-walled piece is characterized by comprising the following steps:
(1) simulating the laser shock peening process of the characteristic unit body by using finite element software ABAQUS to obtain the distribution of plastic strain after laser shock peening in different positions and thickness directions;
(2) carrying out averaging processing on data of plastic strain distribution in the thickness direction obtained by numerical simulation in Matlab, and then carrying out fitting processing on the data in Matlab to obtain a fitting function of the plastic strain distribution in the thickness direction;
(3) and (4) introducing the fitting function into a curvature radius theoretical formula, and finally obtaining the deformation curvature radius of the laser shock peening thin-walled part.
2. The method for determining the deformation radius of curvature of the multipoint laser shock peening thin walled member according to claim 1,
the numerical simulation of the laser shock peening process in the step (1) comprises the following steps:
2.1. establishing a geometric model and defining material properties:
acquiring the actual size of the laser shock strengthening thin-wall part, setting the geometric size of a characteristic unit body for simulation analysis, and then acquiring the material density, Poisson's ratio and elastic modulus;
a Johnson-Cook model is adopted to describe the dynamic constitutive relation of the Johnson-Cook model:
in the formula: a is yield strength, B and n reflect the strain hardening characteristics of the material, C reflects the influence of strain rate on the material properties, epsilonpWhich represents the equivalent plastic strain of the plastic material,
represents a reference strain rate at which the strain is measured,
representing the dynamic strain rate.
2.2. Setting an explicit analysis step length;
2.3. applying a load and meshing;
2.4. submitting analysis operation and post-processing: completing finite element calculation to obtain the numerical simulation result of laser shock peening,
including stress, strain, and displacement.
3. The method for determining the deformation curvature radius of the multipoint laser shock peening thin-walled member according to claim 2, wherein the step (2) specifically comprises:
carrying out averaging treatment on the plastic strain distribution data in the thickness direction, and then fitting the data to obtain a strain distribution function f (x):
f(x)＝a*exp[-((x-b)/c)2](2)
wherein x is the position of the part in the thickness direction, a, b and c are design variable parameters to be determined, and the specific numerical values can be obtained by data fitting in Matlab.
4. The method for determining the deformation curvature radius of the multipoint laser shock peening thin-walled member according to claim 3, wherein the step (3) of obtaining the size of the curvature radius specifically comprises:
wherein Γ is referred to as depth-averaged intrinsic strain, Γ1Called intrinsic torque moment, xRIs the part upper surface coordinate, xLAnd (5) calculating the curvature radius R by taking the coordinates of the lower surface of the part and k as the curvature.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN111931408A (en) * | 2020-08-13 | 2020-11-13 | 广东工业大学 | Finite element simulation method for laser spalling process |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN111931408A (en) * | 2020-08-13 | 2020-11-13 | 广东工业大学 | Finite element simulation method for laser spalling process |
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