A DOUBLE-SIDE SYNCHRONOUS LASER SHOCK PEENING METHOD FOR LEADING EDGE OF TURBINE BLADE

Abstract

A double-side synchronous laser shock peening (LSP) method for leading edges of turbine blades employs two laser beams with the same diameter and different pulse energy to synchronously shock the front and back sides of each point within 8-10 mm range of the leading edge of the blade, wherein the laser pulse energy on the front side is greater than the laser pulse energy on the back side, and wherein, the laser power density on the front side is used to generate dynamic plastic deformation on the entire laser-shock spot area, while the laser power density on the back side is used to balance off excessive shock-wave pressure in the central area of laser-shock spot on the front side and avoid macroscopic deformation of the blade in the central area of laser-shock spot on the front side, and an optimal strengthening effect is achieved finally.

Claims

1-10. (canceled)

11: A double-side synchronous laser shock peening (LSP) method for strengthening a leading edge of turbine blade, comprising simultaneously using two laser beams with a same diameter and different pulse energy to shock front and back sides of each point within 8-10 mm range of the leading edge of the blade, wherein the laser pulse energy on the front side is greater than the laser pulse energy on the back side, and wherein, the laser power density on the front side is used to generate dynamic plastic deformation on the entire laser-shock spot area, while the laser power density on the back side is used to balance off excessive shock-wave pressure in the central area of laser-shock spot on front side and avoid macroscopic deformation of the blade in the central area of laser-shock spot on the front side, whereupon an optimal strengthening effect is achieved.

12: The double-side synchronous LSP method according to claim 11, comprising the following specific steps: (1) the turbine blade is fixed with fixtures; (2) flowing water is used as a confinement layer, wherein, the spot of laser at each shock point on the front side of the blade and the corresponding spot of laser at each shock point on the back side of the blade are in a straight line perpendicular to the surface of the blade by a positioning device; (3) the front and back sides are shocked synchronously by two laser beams by a laser control system; and (4) the leading edge of the turbine blade is shocked on two sides synchronously by two pulse lasers with different laser power density I.sub.1 and I.sub.2.

13: The double-side synchronous LSP method of claim 11, wherein: peak pressures on the front and the back sides are P.sub.1 and P.sub.3 respectively; pressures in the edge area of spot on the front and the back sides are P.sub.2 and P.sub.4 respectively; and, in order to generate dynamic plastic deformation in the entire laser-shock spot area while preventing macroscopic deformation of the blade in the central area of the spot, the following conditions are met: P.sub.1>2.5.sub.H, 2.sub.HP.sub.1P.sub.32.5.sub.H and P.sub.2P.sub.4.sub.H, where, .sub.H is Hugoniot elastic limit of the material of the turbine blade.

14: The double-side synchronous LSP method of claim 12, wherein: peak pressures on the front and the back sides are P.sub.1 and P.sub.3 respectively; pressures in the edge area of spot on the front and the back sides are P.sub.2 and P.sub.4 respectively; and, in order to generate dynamic plastic deformation in the entire laser-shock spot area while preventing macroscopic deformation of the blade in the central area of the spot, the following conditions are met: P.sub.1>2.5.sub.H, 2.sub.HP.sub.1P.sub.32.5.sub.H and P.sub.2P.sub.4.sub.H, where, .sub.H is Hugoniot elastic limit of the material of the turbine blade.

15: The double-side synchronous LSP method according to claim 11, wherein the turbine blade is formed of an aluminum alloy, stainless steel, a titanium alloy or a nickel-based alloy; and the Hugoniot elastic limit of the material of the turbine blade is defined as ${}_H={}_Y^{\mathrm{dyn}}.Math.\frac{\left(1-v\right)}{\left(1-2.Math.v\right)},$ where, is the Poisson's ratio of the material, and .sub.Y.sup.dyn is dynamic yield strength.

16: The double-side synchronous LSP method according to claim 11, wherein the LSP path is in a reciprocating linear shape; the spot of laser is in a circular shape, the LSP parameters are as follows: spot diameter is 3 mm; pulse width is 8-30 ns; pulse energy is 2-15 J; and overlapping rate in transverse direction and longitudinal direction is 50%.

17: The double-side synchronous LSP method according to claim 12, wherein the LSP path is in a reciprocating linear shape; the spot of laser is in a circular shape, the LSP parameters are as follows: spot diameter is 3 mm; pulse width is 8-30 ns; pulse energy is 2-15 J; and overlapping rate in transverse direction and longitudinal direction is 50%.

18: The double-side synchronous LSP method according to claim 11, wherein overlapped LSP is applied at laser power density I.sub.1 to the front side of the leading edge of turbine blade, wherein $I_1=\frac{4.Math.E_1}{.Math..Math.d^2},$ where, E.sub.1 is laser pulse energy of LSP on the front side, is laser pulse width, d is spot diameter; a laser power density I.sub.2 on the back side of the leading edge of turbine blade is used to balance off the excessive shock wave pressure in the central area of the laser-shock spot on the front side, wherein, $I_2=\frac{4.Math.E_2}{.Math..Math.d^2},$ and wherein, E.sub.2 is laser pulse energy of LSP on the back side, is laser pulse width, d is spot diameter.

19: The double-side synchronous LSP method according to claim 12, wherein overlapped LSP is applied at laser power density I.sub.1, to the front side of the leading edge of turbine blade, wherein $I_1=\frac{4.Math.E_1}{.Math..Math.d^2},$ where, E.sub.1 is laser pulse energy of LSP on the front side, is laser pulse width, d is spot diameter; a laser power density I.sub.2 on the back side of the leading edge of turbine blade is used to balance off the excessive shock wave pressure in the central area of the laser-shock spot on the front side, wherein, $I_2=\frac{4.Math.E_2}{.Math..Math.d^2},$ and wherein, E.sub.2 is laser pulse energy of LSP on the back side, is laser pulse width, d is spot diameter.

20: The double-side synchronous LSP method according to claim 13, wherein, peak pressure on the front side $P_1=0.01.Math.\sqrt{\frac{.Math..Math.{\mathrm{ZI}}_1}{2.Math.+3}}$ is obtained according to a Gaussian distribution law of circular spot and a peak pressure calculation formula, where, is plasma-material interaction coefficient, Z is equivalent acoustic impedance, I.sub.1 is laser power density; the pressure in the edge area of the spot on the front side is $P_2=P_1\left(t\right).Math.\exp \left(\frac{-R^2}{2.Math.R^2}\right)=P_1\left(t\right).Math.e^{-\frac{1}{2}},$ wherein, P.sub.1(t) is peak pressure on the front side, and R is the spot diameter; peak pressure on the back side $P_3=0.0.Math.1.Math.\sqrt{\frac{.Math..Math.{\mathrm{ZI}}_2}{2.Math.+3}}$ is obtained according to Gaussian distribution law of circular spot and a peak pressure calculation formula, where, is plasma-material interaction coefficient, Z is equivalent acoustic impedance, and I.sub.2 is laser power density; the pressure in the edge area of the spot on the back side is $P_4=P_2\left(t\right).Math.\exp \left(\frac{-R^2}{2.Math.R^2}\right)=P_2\left(t\right).Math.e^{-\frac{1}{2}},$ where, P.sub.2(t) is peak pressure on the back side, and R is spot diameter, wherein, $P_3=\sqrt{\frac{E_2}{E_1}}.Math.P_1,$ and wherein, E.sub.1 is laser pulse energy of LSP on the front side, E.sub.2 is laser pulse energy of LSP on the back side, and P.sub.1 is peak pressure on the front side.

21. The double-side synchronous LSP method according to claim 20, wherein, is the plasma-material interaction coefficient which is an empirical coefficient and is 0.10.25; $Z=\frac{2.Math.Z_1.Math.Z_2}{Z_1+Z_2},$ wherein, Z.sub.1 is acoustic impedance of the target material, and Z.sub.2 is the acoustic impedance of the confinement layer.

22: The double-side synchronous LSP method according to claim 11, wherein a relation between the pressure required for macroscopic deformation of the material and the thickness t.sub.0 and dynamic yield strength .sub.Y.sup.dyn of the material is $P=K_F.Math.\frac{2.Math.t_0}{d}.Math.{}_Y^{\mathrm{dyn}},$ where, K.sub.F is a coefficient and is 1.1, t.sub.0 is thickness of the material (mm), .sub.Y.sup.dyn is dynamic yield strength of the material (GPa), and d is spot diameter.

23: The double-side synchronous LSP method according to claim 11, wherein the intensity of laser is in Gaussian distribution, the space-time distribution of the pressure pulse is expressed with the following quasi-Gaussian formula: $P\left(x,y,t\right)=P\left(t\right).Math.\exp \left[\frac{-\left(x^2+y^2\right)}{2.Math.R^2}\right],$ where, x and y are surface coordinates, and R is spot diameter.

Description

IV. DESCRIPTION OF DRAWINGS

[0011] To describe the technical schemes in the examples of the present application or the prior art, hereunder the accompanying drawings necessary for describing the examples or the prior art will be introduced briefly.

[0012] FIG. 1 is a schematic diagram of overall laser shock peening (LSP) on a turbine blade;

[0013] FIG. 2 is a schematic diagram of LSP on the leading edge of turbine blade;

[0014] FIG. 3 is a schematic diagram of double-side LSP;

[0015] FIG. 4 is a distribution diagram of shock wave at the center of the sample;

[0016] Table 1 compares the results of vibration fatigue tests of turbine blade in different states.

[0017] In the figures: 1, 2, 5laser beam; 3turbine blade; 4spray tube

V. EMBODIMENTS

[0018] Hereunder the embodiments of the present invention will be described in detail with reference to the accompanying drawings and examples, but the present invention should not be limited to those examples.

[0019] In the present invention, a TC4 titanium alloy turbine blade is utilized. The major mechanical properties of the material include: density: 4.5 g.Math.cm.sup.3; dynamic yield strength: 1.43 GPa; Poisson's ratio: 0.3; water resistance: 1.1410.sup.6 g.Math.cm.sup.2.Math.s.sup.1; acoustic impedance: 2.7510.sup.6 g.Math.cm.sup.2.Math.s.sup.1.

[00011]${}_H=0_Y^{\mathrm{dyn}}.Math.\frac{1-v}{1-2.Math.v}=1430\frac{1-0.3}{1-20.3}=2502.5.Math..Math.\mathrm{MPa}$

Example 1

[0020] One side of the leading edge of a turbine blade is shocked with pulse laser which has laser pulse width =10 ns, laser pulse energy E=12 J, and spot diameter d=3 mm, and vibration fatigue test is carried out for the blade after laser shock peening (LSP).

Example 2

[0021] The front and back sides of each point of the leading edge of a turbine blade are shocked synchronously with two laser beams in the same diameter and same pulse energy, wherein, the laser pulse width is =10 ns, the laser pulse energy is E=12 J, the spot diameter is d=3 mm, and vibration fatigue test is carried out for the blade after LSP.

Example 3

[0022] According to the technical scheme described in the present invention, the front and back sides of each point of the leading edge of a turbine blade are shocked with two laser beams having the same diameter but different pulse energy. FIGS. 1 and 2 are schematic diagrams of overall LSP on the turbine blade and LSP on the leading edge of the turbine blade respectively. By means of a positioning device, the spot of laser at each shock point on the front side of the blade and the spot of laser at each corresponding shock point on the back side of the blade are in a straight line perpendicular to the surface of the blade. The front and back sides are shocked synchronously by two laser beams by means of a laser control system. On the front side of the leading edge of the turbine blade, the laser pulse width is =10 ns, the laser pulse energy is E.sub.1=12 J, and the spot diameter is d=3 mm; on the back side of the leading edge of the turbine blade, the laser pulse width is =10 ns, the laser pulse energy is E.sub.2=2 J, and the spot diameter is d=3 mm.

[00012]$P_1=0.0.Math.1.Math.\sqrt{\frac{.Math..Math.{\mathrm{ZI}}_1}{2.Math.+3}}=0.01\sqrt{\frac{0.1}{20.1+3}}\sqrt{1.611.Math.0^6}.Math.\sqrt{\frac{41.Math.2}{\left(1.Math.01.Math.0^{-9}\right){0.3}^2}1.Math.0^{-9}}=9.2.Math.4.Math..Math.\mathrm{GPa}$$\mathrm{Where},P_1=K_F.Math.\frac{2.Math.t_1}{d}.Math.{}_Y^{\mathrm{dyn}},i.e.,.Math.9.24=1.1\frac{2.Math.t_1}{3}1.4.Math.3,\mathrm{then}.Math..Math.t_1=8.8.Math..Math.\mathrm{mm},i.e.,0<t_{0}8.8.Math..Math.\mathrm{mm}$$P_2=P_1\left(t\right).Math.\exp \left(\frac{-R^2}{2.Math.R^2}\right)=9.2.Math.4e^{\frac{1}{2}}=5.60.Math..Math.\mathrm{GPa}$$P_3=0.01.Math.\sqrt{\frac{.Math..Math.{\mathrm{ZI}}_2}{2.Math.+3}}=0.01\sqrt{\frac{0.1}{20.1+3}}\sqrt{1.611.Math.0^6}\sqrt{\frac{42}{\left(1.Math.01.Math.0^{-9}\right){0.3}^2}1.Math.0^{-9}}=3.7.Math.7.Math..Math.\mathrm{GPa}$$P_4=P_3\left(t\right).Math.\exp \left(\frac{-R^2}{2.Math.R^2}\right)=3.7.Math.7e^{-\frac{1}{2}}=2.29.Math..Math.\mathrm{GPa}$

[0023] FIGS. 3 and 4 are a schematic diagram of double-side LSP and a distribution diagram of shock wave at the center of the sample, respectively. In order to generate dynamic plastic deformation in the entire laser-shock spot area while preventing macroscopic deformation of the blade in the central area of the spot, the following conditions must be met: P.sub.1>2.5.sub.H, 2.sub.HP.sub.1P.sub.32.5.sub.H and P.sub.2P.sub.4.sub.H. Then, a vibration fatigue test is carried out for the blade after LSP.

[0024] It is seen from Table 1 that: through vibration fatigue life tests in four different states, i.e., as-machined (1-1, 1-2), single-side LSP(2-1, 2-2), double-side synchronous LSP with two laser beams having the same diameter and same pulse energy (3-1, 3-2), and double-side synchronous LSP with two laser beams having the same diameter and different pulse energy (4-1, 4-2), under different stress conditions (430 MPa and 560 MPa), the result indicates that the fatigue life of the turbine blade shocked on both sides with two laser beams having the same diameter and different pulse energy is obviously improved and meets the conditions P.sub.1>2.5.sub.H, 2.sub.HP.sub.1P.sub.32.5.sub.H and P.sub.2P.sub.4.sub.H, and finally an optimal strengthening effect is achieved while no macroscopic deformation or damage of the blade is produced in the central area of the spot.

TABLE-US-00001 TABLE 1 State Stress/MPa Fatigue life 1-1 (as-machined) 430 2.49 10.sup.7 1-2 (as-machined) 560 1.23 10.sup.7 2-1 (example 1) 430 3 10.sup.7 2-2 (example 1) 560 2.49 10.sup.7 3-1 example 2) 430 3.26 10.sup.7 3-2 (example 2) 560 2.86 10.sup.7 4-1 (example 3) 430 3.51 10.sup.7 4-2 (example 3) 560 3.05 10.sup.7