Composite material paddle pull rod and forming mold and forming method thereof

Abstract

The invention relates to the technical field of composite material structures, in particular to a composite material paddle pull rod and a forming die and method thereof, the composite material paddle pull rod comprises a rod body and two metal joints, and the two metal joints are fixedly connected to the two ends of the rod body; the rod body comprises an inner pipe, and the two metal connectors are symmetrically and fixedly connected to the two ends of the inner pipe. The inner pipe is coaxially sleeved with a middle pipe, and the two ends of the middle pipe extend out of the inner pipe and are fixedly connected to the metal connectors in a sleeving mode. The middle pipe is coaxially sleeved with an outer pipe, and the two ends of the outer pipe are flush with the two ends of the middle pipe. The diameter of the blade pull rod is not changed, the existing design is met, the connecting strength of the metal connector and the rod body made of the composite material is high, loosening is avoided in the fatigue test process, and the requirement of the helicopter blade pull rod for the fatigue performance is met.

Description

Technical Field

[0001] This invention relates to the field of composite material structure technology, and in particular to a composite material blade tie rod, its molding die, and molding method. Background Technology

[0002] A rotor blade tie rod is a type of tie rod that controls the angle and position of helicopter rotor blades. Due to space constraints, the diameter of the rotor blade tie rod is relatively small, but it needs to withstand large tensile and compressive loads during use and must withstand high-frequency switching between tensile and compressive loads, thus requiring very high tensile and compressive fatigue performance. Currently tested composite rotor blade tie rods have exhibited issues with metal joint loosening during fatigue testing, failing to meet the fatigue performance requirements of helicopter rotor blade tie rods. Therefore, most helicopters still use metal rotor blade tie rods. However, with the increasing demand for lightweight helicopters, the application of composite rotor blade tie rods is imperative.

[0003] Therefore, this invention discloses a composite material blade tie rod, its molding die, and molding method to solve the above-mentioned technical problems. Summary of the Invention

[0004] The purpose of this invention is to provide a composite material blade tie rod, its molding die, and molding method to solve the problems existing in the prior art.

[0005] To achieve the above objectives, the present invention provides the following solution: The present invention provides a composite material blade tie rod, comprising a rod body and two metal joints, wherein the two metal joints are fixedly connected to both ends of the rod body;

[0006] The rod body includes an inner tube, and the two metal joints are symmetrically fixed to both ends of the inner tube;

[0007] The inner tube is coaxially sleeved with a middle tube, and the two ends of the middle tube extend out of the inner tube and are sleeved and fixed to the metal joint.

[0008] An outer tube is coaxially sleeved around the middle tube, and the two ends of the outer tube are flush with the two ends of the middle tube.

[0009] Preferably, the inner tube includes an inner tube body, and two ends of the inner tube body are respectively fixed with inner tube straight platforms, which are inserted and fixed in the connection holes at the ends of the metal connector.

[0010] Preferably, the metal connector is provided with an annular first groove, and the inner walls of both ends of the inner tube are respectively fixed with a central tube inner boss that corresponds to the first groove, and the central tube inner boss is embedded and fixed in the first groove.

[0011] Preferably, the metal connector is provided with an annular second groove, and the two ends of the middle tube are respectively provided with middle tube grooves corresponding to the second groove, and the middle tube grooves are snapped and fixed in the second groove.

[0012] Preferably, the inner ends of the outer tube are respectively provided with an inner boss corresponding to the groove of the middle tube, and the inner boss of the outer tube is snapped and fixed in the groove of the middle tube.

[0013] The present invention also discloses a molding die for preparing composite material blade tie rods, including a core mold adapted to the inner cavity of the inner tube, an extension shaft detachably connected to both ends of the core mold, a yarn-blocking ring detachably connected to the extension shaft, and the rod body being formed between the two yarn-blocking rings.

[0014] Preferably, the end of the extension shaft is provided with an insertion hole that is adapted to the core mold, and when connected, the end of the core mold is inserted into the insertion hole and detachably connected to the insertion hole.

[0015] Preferably, the core mold has several fixing screw holes at both ends, and the extension shaft has several fixing round holes that are adapted to the fixing screw holes. When the core mold is inserted into the insertion hole, the fixing screw holes are aligned with the fixing round holes and locked in place by fixing bolts.

[0016] Preferably, the yarn-blocking ring includes a connecting cylinder, the connecting cylinder having a through hole adapted to the extension shaft, the extension shaft being inserted into the connecting cylinder through the through hole and locked in place.

[0017] This invention also discloses a molding method for preparing composite material blade tie rods, comprising the following steps:

[0018] The prepreg for preparing the inner tube is wound around the outer wall of the core mold, and then semi-cured to obtain a semi-cured inner tube blank with the core mold.

[0019] The semi-cured inner tube blank is machined to form a semi-cured inner tube;

[0020] The pre-formed metal connector is inserted into both ends of the core mold and fixed with the semi-cured inner tube. Then, extension shafts are installed at both ends of the core mold and the extension shafts are pressed against the ends of the metal connectors.

[0021] Prepreg of the middle tube is placed outside the semi-cured inner tube and metal joint, and then the prepreg of the semi-cured inner tube and middle tube is cured to obtain a fully cured inner tube and middle tube.

[0022] Install the yarn-blocking ring on the extension shaft, then wrap the prepreg required for preparing the outer tube around the surface of the middle tube, and then cure it;

[0023] After curing, demolding and cleaning are performed to obtain the required rod.

[0024] Compared with the prior art, the present invention has the following advantages and technical effects: The present invention discloses a composite material rotor rod with a three-layer structure. The inner tube, middle tube and outer tube are all made of composite carbon fiber composite material, without changing the diameter of the rotor rod, which meets the requirements of helicopter rotor rod diameter due to space constraints; it is made of high-strength carbon fiber composite material, which ensures structural strength and performance, can ensure the dimensional stability of the rod under heavy load, avoid deformation affecting the blade angle control accuracy, and can also effectively reduce weight, meeting the lightweight requirements of helicopters; the three-layer structure of the metal joint and the rod body has a multi-layer connection with high connection strength, and does not loosen during fatigue testing, which can meet the high requirements of helicopter rotor rod for tensile and compressive fatigue performance.

[0025] This invention does not change the diameter of the rotor rod, meets existing design requirements, and provides a high connection strength between the metal joint and the composite material rod, preventing loosening during fatigue testing and meeting the fatigue performance requirements of helicopter rotor rods. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly described below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. In the drawings:

[0027] Figure 1 This is an axial view of the composite material blade tie rod of the present invention;

[0028] Figure 2 This is a schematic diagram of the composite material blade tie rod of the present invention;

[0029] Figure 3 For the present invention Figure 2 A partial view of area A in the middle;

[0030] Figure 4 This is an axial view of the metal connector of the present invention;

[0031] Figure 5 This is a schematic diagram of the metal joint structure of the present invention;

[0032] Figure 6 This is an axial view of the inner rod of the present invention;

[0033] Figure 7 This is a schematic diagram of the inner rod structure of the present invention;

[0034] Figure 8 This is a rod axis view in the present invention;

[0035] Figure 9 This is a schematic diagram of the rod structure in this invention;

[0036] Figure 10 This is a schematic diagram of the outer rod of the present invention;

[0037] Figure 11 This is an axial view of the composite material blade tie rod molding die of the present invention;

[0038] Figure 12 This is a schematic diagram of the composite material blade tie rod molding die structure of the present invention;

[0039] Figure 13 This is an axial view of the mandrel of the present invention;

[0040] Figure 14 This is an axial view of the extended shaft of the present invention;

[0041] Figure 15 This is an axial view of the yarn-blocking ring of the present invention;

[0042] Figure 16 This is an axial view of the semi-cured inner rod of the present invention;

[0043] Figure 17 This is a schematic diagram of the molding die after the inner tube of the present invention has been semi-cured;

[0044] Figure 18 This is a schematic diagram of the molding die after the rod has been cured and formed in this invention;

[0045] In the diagram: 1. Rod body; 2. Metal joint; 3. Core mold; 4. Extension shaft; 5. String ring; 6. Fixing bolt; 101. Inner tube; 102. Middle tube; 103. Outer tube; 10101. Main body of inner tube; 10102. Straight platform of inner tube; 10103. Semi-cured inner tube; 10104. Fully cured inner tube; 10201. Boss inside the middle tube; 10202. Groove in the middle tube; 10301. Boss inside the outer tube; 201. First groove; 202. Second groove; 203. Inner hole; 204. Connecting hole; 301. Fixing screw hole; 401. Insertion hole; 402. Fixing round hole; 403. Operating groove; 501. Fitting hole; 502. Connecting cylinder; 503. Fastening screw hole. Detailed Implementation

[0046] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0047] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0048] Reference Figures 1 to 10 As shown, this embodiment provides a composite material blade tie rod, including a rod body 1 and two metal joints 2, which are fixed to both ends of the rod body 1;

[0049] The rod body 1 includes an inner tube 101, and two metal joints 2 are symmetrically fixed at both ends of the inner tube 101;

[0050] The inner tube 101 is coaxially sleeved with the middle tube 102, and the two ends of the middle tube 102 extend out of the inner tube 101 and are sleeved and fixed to the metal joint 2.

[0051] An outer tube 103 is coaxially sleeved outside the middle tube 102, and the two ends of the outer tube 103 are flush with the two ends of the middle tube 102.

[0052] This invention discloses a composite material rotor tie rod. The rod body 1 adopts a three-layer structure, with the inner tube 101, middle tube 102, and outer tube 103 all made of composite carbon fiber composite material. This does not change the diameter of the rotor tie rod, adapting to the space constraints of helicopters that limit the diameter of the rotor tie rod. The use of high-strength carbon fiber composite material ensures structural strength and performance, guarantees the dimensional stability of the tie rod under heavy loads, avoids deformation affecting the accuracy of rotor angle control, and effectively reduces weight, meeting the lightweight requirements of helicopters. The metal joint 2 and the three-layer structure of the rod body 1 form a multi-layer connection with high connection strength, preventing loosening during fatigue testing and meeting the high requirements of helicopter rotor tie rod for tensile and compressive fatigue performance.

[0053] Further optimizing the design, the inner tube 101 includes an inner tube main body 10101, with inner tube straight platforms 10102 fixedly connected to both ends of the inner tube main body 10101. The inner tube straight platforms 10102 are inserted and fixed in the connection holes 204 at the ends of the metal connector 2. The material of the inner tube 101 is carbon fiber composite material, with the middle section being the inner tube main body 10101 and the two ends being inner tube straight platforms 10102. The inner tube straight platforms 10102 are inserted into the connection holes 204 and connected by adhesive bonding.

[0054] Further optimizing the design, the metal connector 2 is provided with an annular first groove 201. The inner walls of both ends of the inner tube 101 are respectively fixed with inner tube protrusions 10201 corresponding to the first groove 201, which are embedded and fixed in the first groove 201. The material of the middle tube 102 is carbon fiber composite material. The middle tube 102 is cured integrally with the inner tube main body 10101 and the metal connector 2 through an adhesive film, so that the middle tube 102 is located on the outer surface of the inner tube main body 10101 and the metal connector 2. The inner surfaces of both ends of the middle tube 102 are provided with inner tube protrusions 10201, which engage with the first groove 201 on the metal connector 2 and fill the first groove 201, thus connecting the metal connector 2 and the middle tube 102 together.

[0055] In a further optimized design, the metal connector 2 is provided with an annular second groove 202, and the two ends of the middle tube 102 are respectively provided with middle tube grooves 10202 corresponding to the second groove 202. The middle tube grooves 10202 are snapped and fixed in the second groove 202. The middle tube grooves 10202 are located on the outer walls of the two ends of the middle tube 102, so that the two ends of the middle tube 102 are recessed inward and snapped into the second groove 202 and cover the second groove 202, thereby achieving the connection between the metal connector 2 and the middle tube 102 again. Combined with the connection between the inner boss 10201 of the middle tube and the first groove 201, the connection strength between the middle tube 102 and the metal connector 2 is increased.

[0056] In a further optimized design, the inner ends of the outer tube 103 are respectively provided with inner bosses 10301 corresponding to the grooves 10202 of the middle tube. The inner bosses 10301 are snapped and fixed inside the grooves 10202 of the middle tube. The outer tube 103 is made of carbon fiber composite material. The outer tube 103 is cured with the middle tube 102 as a whole by epoxy resin, so that the outer tube 103 is located on the outer surface of the middle tube 102. The inner surfaces of both ends of the outer tube 103 are provided with inner bosses 10301, which fill the grooves 10202 of the middle tube, realizing the fitting of the middle tube 102 and the outer tube 103, and increasing the connection strength.

[0057] See attached document Figures 11 to 15As shown, this invention also discloses a molding die for preparing composite material blade tie rods, including a core mold 3 adapted to the inner cavity of the inner tube 101. Extension shafts 4 are detachably connected to both ends of the core mold 3, and yarn-blocking rings 5 ​​are detachably connected to the extension shafts 4. The rod body 1 is formed between the two yarn-blocking rings 5. Both the core mold 3 and the extension shaft 4 are cylindrical. The core mold 3 is adapted to the through hole of the inner tube 101, facilitating the forming of the inner tube 101. The extension shaft 4 is detachably connected to both ends of the core mold 3, facilitating the positioning and fixing of the metal joint 2 and ensuring the quality of the composite material blade tie rod. The yarn-blocking rings 5 ​​are detachably sleeved on the extension shaft 4, used to catch the carbon fiber during the winding process when the carbon fiber rotates, preventing the carbon fiber from loosening. Finally, the composite material blade tie rod is formed between the two yarn-blocking rings 5.

[0058] Further optimizing the design, the end of the extension shaft 4 is provided with an insertion hole 401 that matches the core mold 3. During connection, the end of the core mold 3 is inserted into the insertion hole 401 and detachably connected to it. Both ends of the core mold 3 are provided with several fixing screw holes 301, and the extension shaft 4 is provided with several fixing round holes 402 that match the fixing screw holes 301. When the core mold 3 is inserted into the insertion hole 401, the fixing screw holes 301 and the fixing round holes 402 are aligned and locked together by fixing bolts 6. One end of the extension shaft 4 is provided with an insertion hole 401 and a fixing round hole 402, with the fixing round hole 402 penetrating the insertion hole 401. During connection, the core mold 3 is inserted into the insertion hole 401 of the extension shaft 4, the fixing screw holes 301 and 402 are aligned, and the fixing bolts 6 pass through the fixing round holes 402 and are tightened in the fixing screw holes 301, thus fixing the core mold 3 and the extension shaft 4 together.

[0059] In one embodiment of the present invention, an annular operating groove 403 is provided at the end of the extension shaft 4 away from the insertion hole 401 for mold hanging and demolding, to avoid slippage.

[0060] Further optimizing the design, the yarn-blocking ring 5 includes a connecting cylinder 502. The connecting cylinder 502 has a through-hole 501 adapted to the extension shaft 4. The extension shaft 4 is inserted into the connecting cylinder 502 through the through-hole 501 and locked in place. The yarn-blocking ring 5 is disc-shaped, with the connecting cylinder 502 having an axially penetrating through-hole 501. The yarn-blocking ring 5 is fitted onto the extension shaft 4 through the through-hole 501 for locking and fixing.

[0061] In one embodiment of the present invention, a fastening screw hole 503 is provided on the connecting cylinder 502. When connecting, the fixing screw passes through the fastening screw hole 503 of the yarn-blocking ring 5 and abuts against the extension shaft 4 to fix the yarn-blocking ring 5 on the extension shaft 4.

[0062] See attached document Figures 16 to 18 As shown, the present invention also discloses a molding method for preparing composite material blade tie rods, comprising the following steps:

[0063] The prepreg material for preparing the inner tube 101 is wound around the outer wall of the core mold 3 and then semi-cured to obtain a semi-cured inner tube 10103 blank with the core mold 3; the prepreg material of the inner tube 101 is rolled onto the outer surface of the core mold 3, and BOPP tape is wrapped around the outer surface of the prepreg material of the inner tube 101. It is placed in a curing equipment for semi-curing, and then the BOPP tape is cleaned without demolding to obtain a semi-cured inner tube 10103 blank with the core mold 3.

[0064] The semi-cured inner tube 10103 blank is machined to form the semi-cured inner tube 10103; the semi-cured inner tube 10103 blank is processed with processing equipment to obtain the semi-cured inner tube 10103 with the core mold 3. The middle section of the semi-cured inner tube 10103 is the inner tube main body 10101, and the two ends are the inner tube straight platform 10102.

[0065] The pre-formed metal connector 2 is fitted into both ends of the core mold 3 and fixed to the semi-cured inner tube 10103. Then, extension shafts 4 are installed at both ends of the core mold 3 and the extension shafts 4 are pressed against the ends of the metal connector 2. The metal connector 2 is glued to the inner tube straight platform 10102 using structural adhesive, and the extension shafts 4 are installed on the core mold 3 using fixing screws to hold the metal connector 2 in place.

[0066] Prepreg of the middle tube 102 is placed outside the semi-cured inner tube 10103 and the metal joint 2. Then, the prepreg of the semi-cured inner tube 10103 and the middle tube 102 are cured to obtain the fully cured inner tube 10104 and the middle tube 102. The adhesive film and the prepreg of the middle tube 102 are laid on the outer surface of the inner tube main body 10101 and the metal joint 2. BOPP tape is wrapped around the outer surface of the prepreg of the middle tube 102. The middle tube 102 prepreg and the semi-cured inner tube 10103 are fully cured in a curing device. After curing, the BOPP tape is cleaned, but the tube is not demolded to obtain the fully cured middle tube 102 with the core mold 3 and the extension shaft 4. The fully cured middle tube 102 contains the fully cured inner tube 10104.

[0067] Install the yarn-blocking ring 5 on the extension shaft 4, then wrap the prepreg required for preparing the outer tube 103 around the surface of the middle tube 102, and then cure it; roughen the outer surface of the middle tube 102, install the yarn-blocking ring 5 on the extension shaft 4 using fixing screws, apply adhesive to the outer surface of the middle tube 102, use a winding device to wind carbon fiber and resin onto the outer surface of the middle tube 102, after winding, wrap the outer surface with release cloth and BOPP tape, and put it into the curing device for curing;

[0068] After curing, demolding and cleaning are performed to obtain the required rod body 1; after curing, demolding is performed, and the BOPP tape and release cloth are removed to obtain the composite material blade tie rod.

[0069] In one embodiment of the present invention, semi-curing refers to the inner tube 101 prepreg not being fully cured, resulting in a semi-cured inner tube 10103; in subsequent steps, the inner tube 101 and the middle tube 102 prepreg are fully cured simultaneously, which can make the connection strength between the fully cured inner tube 10104 and the middle tube 102 higher.

[0070] In one embodiment of the present invention, the outer surface of the metal connector 2 is subjected to sandblasting or electron beam texturing.

[0071] In one embodiment of the present invention, after the adhesive film and the prepreg of the middle tube 102 are laid, the first groove 201 of the metal joint 2 is filled, and after the adhesive film and the prepreg of the middle tube 102 are laid, the second groove 202 of the metal joint 2 is covered and the middle tube groove 10202 is formed.

[0072] In one embodiment of the present invention, the adhesive is cured together with the resin, and the central tube groove 10202 is filled after the carbon fiber and resin are wound.

[0073] In the description of this invention, it should be understood that the terms "longitudinal", "lateral", "up", "down", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this invention, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0074] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A composite material blade tie rod, characterized in that: It includes a rod (1) and two metal joints (2), the two metal joints (2) being fixed to both ends of the rod (1); The rod (1) includes an inner tube (101), and two metal joints (2) are symmetrically fixed to both ends of the inner tube (101); The inner tube (101) is coaxially sleeved with a middle tube (102), and the two ends of the middle tube (102) extend out of the inner tube (101) and are sleeved and fixed on the metal joint (2); An outer tube (103) is coaxially sleeved outside the middle tube (102), and the two ends of the outer tube (103) are flush with the two ends of the middle tube (102).

2. The composite material blade tie rod according to claim 1, characterized in that: The inner tube (101) includes an inner tube main body (10101), and an inner tube straight platform (10102) is fixedly connected to both ends of the inner tube main body (10101). The inner tube straight platform (10102) is inserted into the connection hole (204) at the end of the metal connector (2).

3. The composite material blade tie rod according to claim 1, characterized in that: The metal connector (2) is provided with an annular first groove (201), and the inner walls of both ends of the inner tube (101) are respectively fixed with a middle tube inner boss (10201) corresponding to the first groove (201), and the middle tube inner boss (10201) is embedded and fixed in the first groove (201).

4. The composite material blade tie rod according to claim 1, characterized in that: The metal connector (2) is provided with an annular second groove (202), and the two ends of the middle tube (102) are respectively provided with middle tube grooves (10202) corresponding to the second groove (202), and the middle tube grooves (10202) are snapped and fixed in the second groove (202).

5. The composite material blade tie rod according to claim 4, characterized in that: The inner ends of the outer tube (103) are respectively provided with an inner boss (10301) corresponding to the groove (10202) of the middle tube, and the inner boss (10301) of the outer tube is snapped and fixed in the groove (10202) of the middle tube.

6. A molding die for a composite material blade tie rod, used to manufacture the composite material blade tie rod according to any one of claims 1-5, characterized in that: Includes a core mold (3) adapted to the inner cavity of the inner tube (101), with extension shafts (4) detachably connected to both ends of the core mold (3), and yarn-blocking rings (5) detachably connected to the extension shafts (4), and the rod body (1) is formed between the two yarn-blocking rings (5).

7. The molding die for the composite material blade tie rod according to claim 6, characterized in that: The end of the extension shaft (4) is provided with an insertion hole (401) that is compatible with the core mold (3). When connected, the end of the core mold (3) is inserted into the insertion hole (401) and is detachably connected to the insertion hole (401).

8. The molding die for the composite material blade tie rod according to claim 7, characterized in that: The core mold (3) has several fixing screw holes (301) at both ends, and the extension shaft (4) has several fixing round holes (402) that are adapted to the fixing screw holes (301). When the core mold (3) is inserted into the insertion hole (401), the fixing screw holes (301) and the fixing round holes (402) are aligned and locked by fixing bolts (6).

9. The molding die for the composite material blade tie rod according to claim 6, characterized in that: The yarn-blocking ring (5) includes a connecting cylinder (502), which has a through hole (501) adapted to the extension shaft (4). The extension shaft (4) is inserted into the connecting cylinder (502) through the through hole (501) and locked in place.

10. A method for molding a composite material blade tie rod, based on the molding die for the composite material blade tie rod according to any one of claims 6-9, characterized in that, Includes the following steps: The prepreg for preparing the inner tube (101) is wound around the outer wall of the core mold (3) and then semi-cured to obtain a semi-cured inner tube (10103) blank with the core mold (3); The semi-cured inner tube (10103) blank is machined to form the semi-cured inner tube (10103); The pre-formed metal connector (2) is fitted into both ends of the core mold (3) and fixed with the semi-cured inner tube (10103). Then, extension shafts (4) are installed at both ends of the core mold (3) and the extension shafts (4) are pressed against the ends of the metal connector (2). Prepreg of the middle tube (102) is placed outside the semi-cured inner tube (10103) and the metal joint (2), and then the prepreg of the semi-cured inner tube (10103) and the middle tube (102) is cured to obtain the fully cured inner tube (10104) and the middle tube (102). Install the yarn-blocking ring (5) on the extension shaft (4), then wrap the prepreg required to prepare the outer tube (103) around the surface of the middle tube (102), and then cure it; After curing, demolding and cleaning are performed to obtain the required rod (1).

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