CN114250356B - Method for improving fatigue performance of fiber metal laminate mechanical connector - Google Patents
Method for improving fatigue performance of fiber metal laminate mechanical connector Download PDFInfo
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- CN114250356B CN114250356B CN202111546171.0A CN202111546171A CN114250356B CN 114250356 B CN114250356 B CN 114250356B CN 202111546171 A CN202111546171 A CN 202111546171A CN 114250356 B CN114250356 B CN 114250356B
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D10/00—Modifying the physical properties by methods other than heat treatment or deformation
- C21D10/005—Modifying the physical properties by methods other than heat treatment or deformation by laser shock processing
Abstract
The invention provides a method for improving fatigue performance of a fiber metal laminate mechanical connector, which comprises the following steps: determining the number of laser impact turns, the first reinforced edge diameter and the second reinforced edge diameter according to the nominal diameter, the light spot diameter and the gasket diameter or the nut diameter of the mechanical connecting piece; respectively carrying out laser shock reinforcement on the two metal surfaces of the fiber metal layer, and sweeping the center of a laser spot along the second reinforcement edge towards the first reinforcement edge in a concentric circle mode until the outer edge of the last circle of light spot coincides with the first reinforcement edge; and then respectively carrying out laser shock reinforcement on the two metal surfaces of the fiber metal layer, and sweeping the laser spot center along the first reinforcement edge towards the fastening hole edge in a concentric circle mode until the outer edge of the last circle of light spots coincides with the fastening hole edge. The invention can improve the fatigue performance of the fiber metal laminate mechanical connecting piece on the premise of avoiding layering damage and bending deformation.
Description
Technical Field
The invention relates to the field of material surface reinforcement, in particular to a method for improving fatigue performance of a fiber metal laminate mechanical connector.
Background
The fiber metal laminate is an interlayer super-hybrid composite material formed by alternately paving metal sheets and fiber composite materials and solidifying the same under certain temperature and pressure, combines the performance advantages of the metal and fiber composite materials, has the characteristics of high specific strength, high specific modulus, excellent fatigue resistance, high damage tolerance and the like, and is particularly suitable for manufacturing aircraft parts such as skins, fairings, wing panels and the like. Residual tensile stress can be generated on the metal layer of the fiber metal laminate after curing and forming, so that the fatigue performance of the fiber metal laminate is reduced, and the service life of the structure is greatly reduced due to micro-contact in mechanical connection of the fiber metal laminate.
The surface plastic deformation method can effectively improve the fretting fatigue life of the metal material under the condition of not introducing other elements. Conventional surface plastic deformation methods, including shot blasting, surface mechanical milling, etc., typically use large-size particles to hammer the surface of the material, which can cause delamination damage to the fiber metal laminate, and are not suitable for surface strengthening of the fiber metal laminate. However, the conventional laser shock reinforcement process uses a larger light spot size, and shock waves induced by the light spot with the larger size are transmitted in the form of plane waves, so that the shock waves are not easy to dissipate and can cause layering damage.
Disclosure of Invention
Aiming at the defects existing in the prior art, the invention provides a method for improving the fatigue performance of the fiber metal laminate mechanical connector, which utilizes high-frequency and small-facula nanosecond pulse laser-induced shock waves to act on the surface of the fiber metal laminate, and can improve the fatigue performance of the fiber metal laminate mechanical connector on the premise of avoiding layering damage and bending deformation by planning an impact area and a laser facula walking path.
The present invention achieves the above technical object by the following means.
A method of improving fatigue performance of a fiber metal laminate mechanical joint comprising the steps of:
determining the number of laser impact turns according to the nominal diameter, the light spot diameter and the gasket diameter or the nut diameter of the mechanical connecting piece;
determining a first reinforced edge diameter and a second reinforced edge diameter according to the number of laser impact turns, the diameter of the light spot and the nominal diameter of the mechanical connecting piece;
respectively carrying out laser shock reinforcement on the two metal surfaces of the fiber metal layer, and sweeping the center of a laser spot along the second reinforcement edge towards the first reinforcement edge in a concentric circle mode until the outer edge of the last circle of light spot coincides with the first reinforcement edge;
and then respectively carrying out laser shock reinforcement on the two metal surfaces of the fiber metal layer, and sweeping the laser spot center along the first reinforcement edge towards the fastening hole edge in a concentric circle mode until the outer edge of the last circle of light spots coincides with the fastening hole edge.
Further, according to the nominal diameter, the spot diameter and the washer diameter or the nut diameter of the mechanical connector, the number of laser impact turns N is determined specifically as:
in the formula, int []Is a rounding function; d is the diameter of the washer or the diameter of the nut; d is the diameter of the fastening hole; d, d 0 Is the diameter of the light spot; η is the spot overlap ratio; n is a non-negative integer.
Further, according to the number of laser shock turns, the spot diameter and the nominal diameter of the mechanical connection, determining a first reinforced edge diameter and a second reinforced edge diameter, specifically:
first reinforced edge diameter D 1 The determining method of (1) comprises the following steps:
second reinforced edge diameter D 2 The determining method of (1) comprises the following steps:
wherein d is the diameter of the fastening hole; d, d 0 Is the diameter of the light spot; η is the spot overlap ratio; n is the number of laser impact turns.
Furthermore, the laser used for laser shock peening is a nanosecond pulse laser with the wavelength of 532nm, the pulse energy of 20-150 mJ and the pulse width of 5-10 ns.
Further, the laser spot diameter d 0 The lap joint rate eta is 50 to 75 percent and is 0.4 to 0.6 mm.
Furthermore, the flowing water with the thickness of 2-3 mm is adopted as the constraint layer in the laser shock peening process, and an absorption protection layer is not used.
The invention has the beneficial effects that:
(1) According to the method for improving the fatigue performance of the fiber metal laminate mechanical connecting piece, the bending deformation of the structure caused by large-range residual stress can be avoided by carrying out laser shock reinforcement in different areas and on two sides.
(2) According to the method for improving the fatigue performance of the fiber metal laminate mechanical connector, the light spots with diameters of less than 0.4-0.6 mm are used, the laser-induced impact is rapidly dissipated in a spherical wave mode, and the layering damage of the fiber metal laminate can be avoided.
(3) According to the method for improving the fatigue performance of the fiber metal laminate mechanical connector, the planned light spot path can introduce a residual compressive stress layer with the depth of about 0.3mm into the inner wall of the fastening hole.
(4) The method for improving the fatigue performance of the fiber metal laminate mechanical connecting piece is applicable to the fatigue resistance reinforcement of other metal material mechanical connecting pieces by the facula walking strategy.
Drawings
FIG. 1 is a cross-sectional view of a fiber metal laminate with 2 layers of metal and 1 layer of fibers cured and formed with fastening holes.
Fig. 2 is a schematic diagram of enhanced edge division and spot coverage in step 3 and step 4.
Fig. 3 is a schematic view of the impact edge division and the light spot coverage in step 5 and step 6.
FIG. 4 is a cross-sectional view of a fiber metal laminate mechanical connector;
FIG. 5 is a graph showing the radial residual stress distribution of the fastening hole surface.
FIG. 6 is a graph showing the residual stress distribution of the inner wall of the fastening hole in the depth direction.
FIG. 7 is a graph showing the residual stress distribution curves of the fastening hole surface in the radial direction and the fastening hole inner wall in the depth direction.
In the figure:
1-A surface; a 100-A face impingement area; 2-B surface; a 200-B face impact area; 3-a first metal layer; 4-fiber layers; 5-a second metal layer; 101-fastening hole edges; 102-a first reinforced edge; 103-second reinforced edge.
Detailed Description
The invention will be further described with reference to the drawings and the specific embodiments, but the scope of the invention is not limited thereto.
Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to like or similar elements or elements having like or similar functions throughout. The embodiments described below by referring to the drawings are illustrative and intended to explain the present invention and should not be construed as limiting the invention.
In the description of the present invention, it should be understood that the terms "center," "longitudinal," "transverse," "length," "width," "thickness," "upper," "lower," "axial," "radial," "vertical," "horizontal," "inner," "outer," and the like indicate orientations or positional relationships based on the orientation or positional relationships shown in the drawings, merely to facilitate describing the present invention and simplify the description, and do not indicate or imply that the devices or elements referred to must have a specific orientation, be configured and operated in a specific orientation, and therefore should not be construed as limiting the present invention. Furthermore, the terms "first," "second," and the like, are used for descriptive purposes only and are not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include one or more such feature. In the description of the present invention, the meaning of "a plurality" is two or more, unless explicitly defined otherwise.
In the present invention, unless explicitly specified and limited otherwise, the terms "mounted," "connected," "secured," and the like are to be construed broadly and may be, for example, fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; can be directly connected or indirectly connected through an intermediate medium, and can be communication between two elements. The specific meaning of the above terms in the present invention can be understood by those of ordinary skill in the art according to the specific circumstances.
As shown in fig. 1, the fiber metal laminate comprises a first metal layer 3, a fiber layer 4 and a second metal layer 5; a fiber layer 4 is arranged between the first metal layer 3 and the second metal layer 5. The fiber metal laminate is provided with fastener mounting holes, and the fastener mounting holes penetrate through the first metal layer 3, the fiber layer 4 and the second metal layer 5. The method for improving the fatigue performance of the fiber metal laminate mechanical connector comprises the following steps:
s01: removing burrs around the fiber metal laminate fastening holes by sand paper, and cleaning the surfaces of the first metal layer 3 and the second metal layer 5;
s02: according to the nominal diameter, the spot diameter and the gasket diameter or the nut diameter of the mechanical connecting piece, the laser impact turns N are determined as follows:
in the formula, int []Is a rounding function; d is the diameter of the washer or the diameter of the nut; d is the diameter of the fastening hole; d, d 0 Is the diameter of the light spot; η is the spot overlap ratio; n is a non-negative integer;
the diameter of the first reinforced edge 102 and the diameter of the second reinforced edge 103 are determined according to the number of laser impact turns, the diameter of the light spot and the nominal diameter of the mechanical connecting piece, specifically:
first stiffening edge 102 diameter D 1 The determining method of (1) comprises the following steps:
second strengthening edge 103 diameter D 2 The determining method of (1) comprises the following steps:
wherein d is the diameter of the fastening hole; d, d 0 Is the diameter of the light spot; η is the spot overlap ratio; n is the number of laser impact turns.
S03: carrying out laser shock peening on the surface A of the fiber metal laminate, namely the surface of the first metal layer 3, wherein the center of a laser spot is swept along the second strengthening edge 103 to the first strengthening edge 10) in a concentric circle mode until the outer edge of the last circle of spot coincides with the first strengthening edge 102;
s04: carrying out laser shock peening on the surface of the B surface 2 of the fiber metal laminate, namely the surface of the second metal layer 5, and sweeping the center of a laser spot along the second strengthening edge 103 to the first strengthening edge 10) in a concentric circle mode until the outer edge of the last circle of the laser spot coincides with the first strengthening edge 102; the structure can be prevented from bending deformation caused by large-range residual stress by carrying out laser shock peening in a divided area and on two sides;
s05: the laser shock peening is performed on the surface of the first metal layer 3, and the laser spot center is swept along the first peening edge 102 toward the fastening hole edge 101 in a concentric circle form until the outer edge of the last circle of the laser spot coincides with the fastening hole edge 101.
S06: performing laser shock peening on the surface of the second metal layer 5, and sweeping the laser spot center along the first strengthening edge 102 towards the fastening hole edge 101 in a concentric circle mode until the outer edge of the last circle of light spots coincides with the fastening hole edge 101; the laser shock reinforcement is performed by dividing the area and the two sides, so that the bending deformation of the structure caused by the residual stress in a large range can be avoided.
S07: the reinforced area was lightly sanded with fine sandpaper to remove the remelted layer.
After the step 4 and the step 5 are finished, the light spot edge is attached to the fastening hole edge 101; the laser is a nanosecond pulse laser with the wavelength of 532nm, the pulse energy of 20-150 mJ and the pulse width of 5-10 ns; the nanosecond pulse laser spot is round, and the diameter d of the spot is 0 0.4-0.6 mm, and the lap joint rate eta is 50-75 percent; the flowing water with the thickness of 2-3 mm is used as a constraint layer in the laser shock peening process, and an absorption protection layer is not used.
In this example, the carbon fiber reinforced TA2 titanium alloy laminate is taken as an object, and fig. 1 is a cross-sectional view of the laminate after the fastening holes are machined, wherein the fiber layer is a carbon fiber prepreg designed in a 0 °/90 °/0 °/90 ° orientation:
s01: removing burrs around the fastening holes of the workpiece by using 800# abrasive paper, and cleaning the surface of the workpiece by using alcohol;
s02: determining the diameter d=4mm of the fastening hole, the diameter d=8mm of the gasket, and taking 0 as n; by using the calculation method provided by the invention, the laser impact turns N=10 and the diameter D of the first reinforced edge 102 are calculated 1 =8mm, second strengthening edge 103 diameter D 2 ＝12mm；
S03: laser shock strengthening is carried out on the surface of the first metal layer 3, and the light spot size d 0 The laser pulse energy is 30mJ, and the spot overlap ratio eta is 50 percent, wherein the laser pulse energy is 0.4 mm; the center of the spot walks along the second strengthening edge 103 toward the first strengthening edge 102 in a concentric circle form until the outer edge of the last circle of spot is in contact with the first strengthening edge 102, as shown in fig. 2;
s04: performing laser shock reinforcement on the surface of the second metal layer 5, and adopting the same facula walking strategy as that of S03, as shown in fig. 2;
s05: performing laser shock peening on the surface of the first metal layer 3, wherein the center of the light spot extends to the edge 101 of the fastening hole along the first strengthening edge 102 in a concentric circle mode until the outer edge of the light spot of the last circle contacts with the edge 101 of the fastening hole, as shown in fig. 3;
s06: performing laser shock reinforcement on the surface of the second metal layer 5, and adopting the same facula walking strategy as the step 5, as shown in fig. 3;
s07: the reinforced area was lightly sanded with 1000# sandpaper to remove the remelted layer.
Fig. 4 is a cross-sectional view of a fiber metal laminate after laser shock peening followed by mechanical joining. And (3) carrying out mechanical property analysis on the fiber metal laminate after mechanical connection, and analyzing residual stress distribution, wherein after laser shock reinforcement, as shown in fig. 5, 6 and 7, the surface of the fastening hole of the fiber metal laminate is compressive stress, and the fastening inner wall forms residual compressive stress with a certain depth. The residual compressive stress can effectively inhibit the initiation and the expansion of fretting fatigue cracks, thereby prolonging the fatigue life of the fiber metal laminate.
It should be understood that although the present disclosure has been described in terms of various embodiments, not every embodiment is provided with a separate technical solution, and this description is for clarity only, and those skilled in the art should consider the disclosure as a whole, and the technical solutions in the various embodiments may be combined appropriately to form other embodiments that will be understood by those skilled in the art.
The above list of detailed descriptions is only specific to practical embodiments of the present invention, and they are not intended to limit the scope of the present invention, and all equivalent embodiments or modifications that do not depart from the spirit of the present invention should be included in the scope of the present invention.
Claims (4)
1. A method for improving fatigue performance of a fiber metal laminate mechanical connector, comprising the steps of:
according to the nominal diameter, the spot diameter and the gasket diameter or the nut diameter of the mechanical connecting piece, the laser impact turns are determined, and the laser impact turns are specifically as follows:
in the formula, int []Is a rounding function; d is the diameter of the washer or the diameter of the nut; d is the diameter of the fastening hole; d, d 0 Is the diameter of the light spot; η is the spot overlap ratio; n is a non-negative integer;
determining the diameter of the first strengthening edge (102) and the diameter of the second strengthening edge (103) according to the number of laser impact turns, the diameter of a light spot and the nominal diameter of a mechanical connecting piece, wherein the method specifically comprises the following steps:
diameter D of the first reinforcing edge (102) 1 The determining method of (1) comprises the following steps:
diameter D of the second reinforcing edge (103) 2 The determining method of (1) comprises the following steps:
wherein d is the diameter of the fastening hole; d, d 0 Is the diameter of the light spot; η is the spot overlap ratio; n is the number of laser impact turns;
respectively carrying out laser shock reinforcement on the two metal surfaces of the fiber metal layer, and sweeping the center of a laser spot along a second reinforcement edge (103) towards a first reinforcement edge (102) in a concentric circle mode until the outer edge of the last circle of the laser spot coincides with the first reinforcement edge (102);
and then respectively carrying out laser shock reinforcement on the two metal surfaces of the fiber metal layer, and sweeping the laser spot center along the first reinforcement edge (102) towards the fastening hole edge (101) in a concentric circle mode until the outer edge of the last circle of light spots coincides with the fastening hole edge (101).
2. The method for improving the fatigue performance of the fiber metal laminate mechanical connector according to claim 1, wherein the laser used for laser shock peening is a nanosecond pulse laser with a wavelength of 532nm, a pulse energy of 20-150 mJ and a pulse width of 5-10 ns.
3. The method for improving fatigue performance of a fiber metal laminate mechanical joint according to claim 1, wherein the laser spot diameter d 0 The lap joint rate eta is 50 to 75 percent and is 0.4 to 0.6 mm.
4. The method for improving fatigue performance of a fiber metal laminate mechanical connector according to claim 1, wherein the laser shock peening process uses running water with a thickness of 2-3 mm as a constraining layer without using an absorbing protective layer.
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| CN113088674A (en) * | 2021-03-30 | 2021-07-09 | 武汉大学 | Additive manufacturing metal surface strengthening method based on laser shock strengthening |
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2021
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| WO1995025821A1 (en) * | 1994-03-22 | 1995-09-28 | Battelle Memorial Institute | Reducing edge effects of laser shock peening |
| US6541733B1 (en) * | 2001-01-29 | 2003-04-01 | General Electric Company | Laser shock peening integrally bladed rotor blade edges |
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