A launch tube frangible front cover, a method of making, and a test system including the frangible front cover

Abstract

The application discloses a fragile front cover of a launching tube, a preparation method and a test system comprising the same, which comprises a cover body and a flange part arranged around the periphery of the cover body, the front surface of the cover body is provided with at least three radial weakening grooves, and the back surface of the cover body is provided with a circumferential weakening groove near the edge, the cross section of the circumferential weakening groove is a single inclined wedge shape, which comprises a vertical side wall and an inclined side wall, the vertical side wall is vertically connected with the end surface of the flange part, the inclined side wall forms an angle a with the end surface of the flange part, the inclined side wall extends from the groove bottom of the circumferential weakening groove to the surface of the cover body and meets the vertical side wall to form a directional crack propagation area, so that the crack under the action of the load preferentially extends along the angle a. Through the design of the integrated polyurethane foam body combined with the directional crack propagation area, the actual peak breaking force is less than or equal to 7kN, which meets the low impact requirement of the missile fairing. The radial weakening grooves on the front surface and the wedge-shaped circumferential weakening groove on the back surface work together, so that the maximum size of the fragments is much smaller than the safety threshold.

Description

Technical Field

[0001] This invention relates to the field of missile launch canister cover technology, and in particular to a fragile front cover for a launch tube, a method for manufacturing the cover, and a testing system including the fragile front cover. Background Technology

[0002] The fragile front cover of the missile launch tube must meet multiple contradictory requirements under extreme working conditions. It must withstand the pressure of the harsh storage and transportation environment, and be instantly shattered by the missile fairing with a breaking force of ≤7kN during launch. Moreover, the residue after breakage must not obstruct the missile channel, and the fragments must be strictly confined within the inner diameter of the launch tube.

[0003] Chinese patent CN110806151A discloses a fragile front cover for a missile, comprising a front cover body with weakening grooves and a tethering mechanism for restraining the splashing of the front cover body. The weakening grooves are arranged radially and / or latitudinally along the front cover body, dividing the front cover body into multiple fracture zones. The tethering mechanism is a rope with fixed ends at both ends. One end of the tethering mechanism is fixedly connected to the wall of the missile launch tube, and the other end is fixedly connected to the upper surface of the fracture zone. While the radial and / or latitudinal weakening grooves on the front of the front cover body allow it to fracture upon impact, the weakening grooves are only located on the front of the front cover body, resulting in a relatively uniform distribution area and failing to produce a satisfactory fracture effect. The application uses a rigid polyurethane foam reinforced with fiberglass or nylon fiber cloth to improve the pressure resistance of the front cover, but this also leads to a significant increase in the actual bursting force, which fails to meet the low bursting force requirement for missile launches. In addition, the multi-layer material scheme causes the weak interlayer bonding force during machining of the weakened groove, resulting in fiber peeling at the groove edge and damaging the structural integrity. In actual use, the lack of crack guidance leads to random deviation of the fracture trajectory, making it difficult to meet the safety threshold for the maximum residual fragment inner diameter of the missile launch channel. Summary of the Invention

[0004] To address the shortcomings of the existing technology, this invention proposes a launch tube fragility front cover with a crack-guided fracture trajectory, a wider distribution of weakening grooves, and a better fragility effect, where the residue after breakage does not obstruct the missile channel.

[0005] The technical solution of the present invention: A fragile front cover for a launch tube includes a cover body and a flange portion circumferentially disposed around the outer periphery of the cover body. The front side of the cover body is provided with at least three radial weakening grooves, and the back side of the cover body is provided with a circumferential weakening groove near the edge. The cross-section of the circumferential weakening groove is a single-sloping wedge shape, including a vertical sidewall and an inclined sidewall. The vertical sidewall is perpendicularly connected to the end face of the flange portion, and the inclined sidewall forms an angle α with the end face of the flange portion. The angle α ranges from 100° < α < 150°. The inclined sidewall extends from the bottom of the circumferential weakening groove to the surface of the cover body and converges with the vertical sidewall to form a directional crack propagation zone, so that under the action of impact load, the crack preferentially extends along the angle α.

[0006] By setting a wedge-shaped circumferential weakening groove near the edge on the back side, the circumferential weakening groove provides guidance for the crack, causing the fracture trajectory to extend preferentially along the angle. After the launch tube fragility cover is impacted, the circumferential weakening groove on the back side, together with the radial weakening groove on the front side, can cause the fragility cover to break off at the root, and the residue after breakage will not obstruct the missile passage.

[0007] In one embodiment, the cover has a crack initiation hole at its center, and the radial weakening grooves are distributed radially with the crack initiation hole as the origin, with the ends of the radial weakening grooves extending to the edge of the cover.

[0008] The crack initiation hole depth is equal to the radial groove depth, and the crack initiation hole diameter should be 4 times the radial groove width.

[0009] In one embodiment, the number of radial weakening grooves is 6 to 12 and they are distributed at equal angles. The width of the radial weakening grooves is 1 / 10 to 2 / 15 of the thickness of the cover, and the depth of the radial weakening grooves is 2 / 3 to 3 / 4 of the thickness of the cover.

[0010] In one embodiment, the depth of the circumferential weakening groove is 2 / 5 to 3 / 5 of the thickness of the cover, and the thickness of the directional crack propagation zone is 2 / 5 to 3 / 5 of the thickness of the cover.

[0011] In one embodiment, the cover is integrally molded from polyurethane cavity foam, and the density of the polyurethane foam material is controlled at 580~620kg / m³.

[0012] Based on the same inventive concept, this invention provides a method for preparing a fragile front cover for a launch tube, comprising the following steps:

[0013] S1. Polyurethane cavity foaming molding to produce the cover body, including mold pretreatment, raw material injection and foaming, and density control;

[0014] S2. The radial weakening groove, circumferential weakening groove, crack initiation hole, and flange part are machined using machining processes;

[0015] S3. Product surface processing, including initial surface sanding, initial application of primer, application of putty, surface repair and sanding, secondary application of primer, and application of topcoat;

[0016] S4. Conduct forward pressure test, reverse pressure test and bursting force test. If the pressure applied in the two pressure tests exceeds 0.1MPa, it indicates that the product meets the pressure performance requirements. If the peak value of the transient bursting force of the product is less than 7kN, it indicates that the product is qualified.

[0017] In step S1,

[0018] Mold pretreatment: First, spray the mold release agent evenly into the inner cavity of the mold. Use water-based mold release agent and spray with a thickness of 5~10μm to ensure no missed spraying or accumulation. Preheat the mold to 60-70℃ to eliminate internal stress.

[0019] Raw material injection and foaming: Prepare 100 parts isocyanate and 105 parts polyol + foaming agent (98~102 parts polyol, 3~7 parts foaming agent). Mix the above-mentioned weight parts of isocyanate and polyol + foaming agent, and control the stirring speed at 2000rpm±5%. Inject polyurethane raw material with a material temperature of 20℃~22℃ into the mold, with an injection pressure of 0.2~0.3MPa and an injection time of no more than 8s. The foaming time is 90~120s, and the pressure is maintained for 5min to obtain a polyurethane cavity.

[0020] Density control: The density is stabilized at 600±10 kg / m³ by adjusting the foaming pressure through real-time monitoring with an ultrasonic density meter.

[0021] Demolding: Demolding time is 10~15 minutes. Place at room temperature for more than 24 hours to release internal stress.

[0022] In step S3,

[0023] First surface polishing: Use sandpaper to smooth and roughen the product surface, and remove the release wax;

[0024] First coat of primer: The product is sprayed in the spray booth, with two even coats, and the paint film thickness reaches 30~50μm. Ensure that the paint surface is free of particles and drips. The product is allowed to air dry at room temperature for 12 hours and then dried in the drying room.

[0025] Applying putty: When the product is laid flat, do not apply putty to the rubber area. Apply a thin layer of putty to the curved joints, less than 200μm. Apply a thin layer of putty to the flat front, less than 300μm. The surface should be flat and free of defects.

[0026] Surface repair and polishing: Use putty to repair surface defects of the product. After the putty dries, polish the entire product. After polishing, blow away all the dust.

[0027] Secondary primer spraying: The product is sprayed in the spray booth, with two even coats, and the paint film thickness reaches 30~50μm. Ensure that the paint surface is free of particles and drips, achieves the set fullness, and does not show sandpaper marks after the film dries.

[0028] Topcoat application: The product is sprayed in a spray booth, with three even coats applied to achieve a film thickness of 40-60μm and a gloss level of 40-70, ensuring that the paint surface is free of particles and runs.

[0029] Based on the same inventive concept, this invention provides a test system for a fragile front cover of a launch tube, including a control unit, a gas source, an air inlet pipe, an air inlet valve, a gas cylinder, and a pressure vessel. The gas cylinder is installed below the pressure vessel. The gas source is connected to the gas cylinder through the air inlet pipe. The air inlet valve is installed on the air inlet pipe and is electrically connected to the control unit. The fragile front cover of the launch tube is installed on the upper end face of the pressure vessel, and the inner bottom of the pressure vessel has a through hole.

[0030] In one embodiment, a rupture rod is also included, which passes through the through hole and moves vertically along the gas cylinder, and a push plate is provided at the bottom of the rupture rod.

[0031] The beneficial effects of this invention are:

[0032] 1. By combining an integrated polyurethane foam (580-620kg / m³) with a directional crack propagation zone design, the measured peak burst force is ≤7kN, meeting the low impact requirements of the missile fairing.

[0033] 2. No auxiliary mechanism is required to achieve fragment orientation control. The radial weakening groove on the front and the wedge-shaped circumferential weakening groove on the back work together to make the maximum size of the fragment much smaller than the safety threshold.

[0034] 3. Compared with existing glass fiber reinforced caps, the pressure-bearing capacity is improved while the weight is reduced, and there is no reinforcement layer laying process, and there is no fiber peeling phenomenon in the weakening groove. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the fragile cap structure in an embodiment of the present invention;

[0036] Figure 2 This is a top view of the fragile cover body in an embodiment of the present invention;

[0037] Figure 3 for Figure 2 Sectional view of AA;

[0038] Figure 4 for Figure 3 Enlarged schematic diagram of the structure at point A in the middle;

[0039] Figure 5 This is a diagram of the positive pressure test of the fragile cover body in an embodiment of the present invention;

[0040] Figure 6 This is a diagram of the back-facing pressure test of the fragile cover body in an embodiment of the present invention;

[0041] Figure 7 This is a diagram of the test result of the fragile cap breaking through the rim in an embodiment of the present invention;

[0042] In the diagram, 1. Cover, 2. Flange, 3. Radial weakening groove, 4. Circumferential weakening groove, 5. Crack initiation hole, 6. Control unit, 7. Gas source, 8. Inlet pipe, 9. Inlet valve, 10. Gas cylinder, 11. Pressure vessel, 12. Piston rod, 13. Base, 14. Pressure gauge, 15. Push plate, 1301. Upper plate of base, 1302. Base support rod, 1303. Lower plate of base, 401. Vertical side wall, 402. Inclined side wall. Detailed Implementation

[0043] 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.

[0044] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "or / and" as used herein includes any and all combinations of one or more of the associated listed items.

[0045] like Figures 1 to 4 As shown, this embodiment discloses a fragile front cover for a launch tube, including a cover body 1 and a flange portion 2 circumferentially disposed around the outer periphery of the cover body. The front of the cover body 1 is provided with 6 radial weakening grooves 3 distributed at equal angles. The back of the cover body 1 is provided with a circumferential weakening groove 4 near the edge. The cross-section of the circumferential weakening groove 4 is a single-sloping wedge shape, including a vertical sidewall 401 and an inclined sidewall 402. The vertical sidewall 401 is perpendicularly connected to the end face of the flange portion 2. The inclined sidewall 402 forms an angle α with the end face of the flange portion 2. The angle α is 120°. The inclined sidewall 402 extends from the bottom of the circumferential weakening groove 4 to the surface of the cover body 1 and converges with the vertical sidewall to form a directional crack propagation zone, so that the crack preferentially extends along the angle α under the action of impact load.

[0046] In this embodiment, the thickness of the cover 1 is 15mm, the width of the radial weakening groove 3 is ≤ 20% of the radial groove depth, and the width of the circumferential weakening groove 4 is ≤ 15% of the circumferential weakening groove 4 depth; the width of the radial weakening groove 3 is in the range of 1 / 10 to 2 / 15 of the thickness of the cover 1; and the depth of the radial weakening groove 3 is in the range of 2 / 3 to 3 / 4 of the thickness of the cover 1.

[0047] In this embodiment, the depth of the circumferential weakening groove 4 is 3 / 5 of the thickness of the cover 1, and the thickness of the directional crack propagation zone should be 2 / 5 of the thickness of the cover 1. The sum of the depth of the circumferential weakening groove 4 and the thickness of the directional crack propagation zone is the thickness of the cover 1.

[0048] In this embodiment, the depth of the crack initiation hole 5 is equal to the depth of the radial weakening groove 3, and the diameter of the crack initiation hole 5 is 4 times the width of the radial weakening groove 3.

[0049] The center of mass of the cover 1 is located within 35-40mm above the bottom plane of the rotation axis.

[0050] In this embodiment, the cover 1 is integrally molded from polyurethane cavity foam. To control the strength of the cover, the density of the polyurethane foam material is controlled at 600 kg / m³.

[0051] Based on the same inventive concept, this embodiment provides a method for preparing a fragile front cover for a launch tube, including the following steps:

[0052] Step 1: Polyurethane cavity foaming molding to produce the cover body; Step 1 includes mold pretreatment, raw material injection and foaming, density control and demolding aging.

[0053] Mold pretreatment: First, spray the mold release agent evenly into the inner cavity of the mold. Use water-based mold release agent (such as AXEL 3210) with a spray thickness of 10μm to ensure no missed spraying or accumulation. Preheat the mold to 70℃ to eliminate internal stress.

[0054] Raw material injection and foaming: 100 parts isocyanate, 105 parts polyol + foaming agent (100 parts polyol, 5 parts foaming agent); mix the above-mentioned isocyanate and polyol + foaming agent, and control the stirring speed at 2000 rpm ± 5%; inject polyurethane raw material at a material temperature of 20℃ into the mold, with an injection pressure of 0.2 MPa and an injection time of no more than 8 seconds; foaming time of 100 seconds, holding pressure for 5 minutes to obtain a polyurethane cavity;

[0055] Density control: The density is stabilized at 600±10 kg / m³ by adjusting the foaming pressure through real-time monitoring with an ultrasonic density meter.

[0056] Demolding time: Demolding time is 15 minutes, and the product should be left at room temperature for more than 24 hours to release internal stress.

[0057] Step 2: Machining radial weakening grooves, circumferential weakening grooves, crack initiation holes, and bolt mounting holes on the flange part using machining processes; and treating the sealing surface of the flange part.

[0058] Radial weakening groove machining: Radial grooves are machined using a diamond-coated end mill with a diameter equal to the groove width. A laser rangefinder monitors the groove depth in real time. Six radial weakening grooves are provided on the front of the cover, with an angle of 60° between each pair of grooves. The groove width is 1.5mm and the groove depth is 10mm. A continuous circumferential weakening groove is provided on the back of the cover near the edge, forming a 120° angle with the horizontal plane.

[0059] Crack initiation hole machining: Carbide drill bit diameter is 4 times the flute width, pecking drill method (removing chips once every 0.5mm of drilling) to avoid thermal damage to the hole wall;

[0060] Flange sealing surface treatment: surface roughness less than 3.2μm, using a fine grinding process.

[0061] Step 3: Product surface processing; Step 3 includes initial surface sanding, initial application of primer, application of putty, surface repair and sanding, secondary application of primer, and application of topcoat;

[0062] First surface polishing: Use sandpaper to smooth out any unevenness on the product surface, remove any roughness, and clean off the release wax.

[0063] First coat of primer: The product is sprayed in the spray booth, with two even coats, and the paint film thickness reaches 30-50μm, ensuring that the paint surface is free of particles and drips; the product is air-dried at room temperature for 12 hours, and then dried in an oven at 55°C for 1 hour.

[0064] Applying putty: When the product is laid flat, do not apply putty to the rubber area; apply a thin layer to the curved joints, less than 200μm; apply a thin layer to the flat front, less than 300μm, with a smooth and defect-free surface.

[0065] Surface repair and polishing: Use putty to repair pinholes, unevenness and other defects on the product surface. After the putty dries, polish the entire product. After polishing, blow away all the dust.

[0066] Second coat of primer: The product is sprayed in the spray booth. Two coats are applied evenly, achieving a film thickness of 50μm. Ensure the paint surface is free of particles and runs, and achieves a certain degree of fullness, so that no sandpaper marks are visible after the film dries.

[0067] Topcoat application: The product is sprayed in a spray booth, with three even coats applied. The paint film thickness reaches 60μm, with a gloss level of 70, ensuring a smooth surface free of particles and runs.

[0068] Step 4, pressure test and bursting force test; Step 4 includes front cover structure design and calculation verification, positive pressure test, and positive pressure test.

[0069] The fragile front cover of the launch tube undergoes three main processes during rupture: top punching failure, radial expansion of the crack along the weakening groove, and fracture of the front cover fragment at the root after crack expansion. Punching failure determines whether the front cover ruptures normally, while the radial expansion of the crack along the weakening groove and the fracture at the root are controlled by the groove width and depth. The calculation formulas for the groove width and depth, under the condition of meeting structural design requirements, are shown in equations (1)-(5):

[0070] (1)

[0071] (2)

[0072] (3)

[0073] (4)

[0074] (5)

[0075] Where T is the thickness in mm; It is the groove depth in mm; It is the remaining thickness in mm; It is the bursting force in N; It is the groove width in mm;

[0076] In this embodiment, the cover thickness T = 15 mm. Substituting the thickness T = 15 mm into equations (3)-(5) yields...

[0077] (6)

[0078] (7)

[0079] (8)

[0080] Determined according to the formula , , Substitute it into equations (1) and (2) for verification, and it meets the design conditions.

[0081] The calculated structural design parameters are then substituted into the punching shear failure formula for strength verification:

[0082] (9)

[0083] Based on the punching failure formula, the breaking force capable of successfully breaking through the front cover is derived. The calculation formula is as follows: (10)

[0084] Will =10mm, 2mm, =9mm, =1mm, n=6, Substituting 20MPa into equation (10) yields:

[0085] Where n is the number of radial weakening grooves, The diameter of the crack initiation hole.

[0086] because During operation, the warhead can successfully penetrate the front cover, meeting the design requirements.

[0087] Based on the same inventive concept, this invention provides a test system for a fragile front cover of a launch tube, including a control unit 6, a gas source 7, an air inlet pipe 8, an air inlet valve 9, a gas cylinder 10, a pressure vessel 11, and a rupture rod 12. The gas cylinder 10 is installed below the pressure vessel 11. The gas source 7 is connected to the gas cylinder 10 through the air inlet pipe 8. The air inlet valve 9 is installed on the air inlet pipe 8 and is electrically connected to the control unit 6. The fragile front cover 1 of the launch tube is installed on the upper end face of the pressure vessel 11 through a flange 2. The inner bottom of the pressure vessel 11 is provided with a through hole. The rupture rod 12 is installed through the through hole and moves vertically along the gas cylinder 10. A push plate 15 is provided at the bottom of the rupture rod 12.

[0088] like Figure 5 As shown, positive pressure test:

[0089] The pressure vessel 11 and the cover 1 have 12 bolt mounting holes arranged circumferentially on the flange portion 2. The pressure vessel 11 and the cover 1 are connected by bolts.

[0090] The top of the gas cylinder 10 is provided with an outlet, and the bottom of the pressure vessel 11 is provided with a through hole for the outlet of the gas cylinder 10 to pass through. The bottom of the side wall of the gas cylinder 10 is provided with an inlet, which is connected to the gas source 7 through an inlet pipe 8. An inlet valve 9 is installed on the inlet pipe 8. The gas cylinder 10 is fixed below the pressure vessel 11 by the base 13. The base 13 consists of an upper base plate 1301, a base support rod 1302, and a lower base plate 1303. An opening is provided in the middle of the upper base plate 1301 to allow the gas outlet of the gas cylinder 10 to extend from the upper base plate 1301 into the pressure vessel 11. The gas cylinder 10 is installed between the upper base plate 1301 and the lower base plate 1303. The upper base plate 1301 has four bolt mounting holes arranged in a circumferential direction. The bottom of the pressure vessel 11 has four bolt mounting holes arranged in a circumferential direction for bolt connection with the upper base plate 1301. The lower base plate 1303 has four bolt mounting holes arranged in a circumferential direction and is fixed to the ground by bolts.

[0091] Install the cover 1 onto the pressure vessel 11 with the convex side facing up. The end faces of the cover 1 and the pressure vessel 11 are provided with sealing gaskets. After aligning the sealing gaskets, cover 1, and pressure vessel 11, the flange 2 of the cover 1 is connected and fixed to the pressure vessel 11 with bolts.

[0092] The gas cylinder 10 is pressurized using the gas source 7, and the internal pressure is controlled by the control unit 6 and the pressure gauge 14 installed on the pressure vessel 11. Compressed air is introduced into the pressure vessel 11 until the specified pressure (0.1 MPa) is reached, and the inlet valve 9 is closed to stop pressurization. If the cover 1 is not damaged during the process, depressurization begins after 10 seconds. After depressurization, the cover 1 is removed, and the condition of the inner and outer surfaces of the cover 1 is checked. If the final pressurization pressure exceeds 0.1 MPa and the specimen is still intact and undamaged, it indicates that the front cover meets the positive pressure bearing performance requirements.

[0093] like Figure 6 As shown, back-facing pressure test:

[0094] Install the cover 1 onto the pressure vessel 11 with the concave side facing up, following the same installation process as the positive pressure test described above. Pressurize the gas cylinder 10 using the air source 7, and control the internal pressure using the control unit 6 and the pressure gauge 14 installed on the pressure vessel 11. Fill the pressure vessel 11 with compressed air until the specified pressure (0.05 MPa), then close the inlet valve 9 to stop pressurizing. If the cover 1 remains intact during the process, begin depressurization after 10 seconds. After depressurization, remove the cover 1 and inspect the inner and outer surfaces of the front cover 1. If the final pressurization pressure exceeds 0.1 MPa and the specimen remains intact, it indicates that the cover meets the negative pressure bearing performance requirements.

[0095] like Figure 7 As shown, bursting force test:

[0096] Install the cover 1 onto the pressure vessel 11 with the convex side facing up, following the same installation process as the positive pressure test described above. The rupture rod 12 passes through the through hole of the pressure vessel 11, enters the pressure vessel 11 from the gas outlet of the gas cylinder 10, and moves vertically along the gas cylinder 10. A through-shaft sensor is installed at the upper end of the rupture rod 12, and a push plate 15 is provided at the bottom of the rupture rod 12. The push plate 15 is located inside the gas cylinder 10 and is used to withstand the gas thrust at the bottom of the gas cylinder 10, pushing the rupture rod 12 to move along the gas cylinder 10 and finally rupture the cover 1.

[0097] Open the air inlet valve 9, and the gas enters the gas cylinder 10, pushing the push plate 15 upwards rapidly. During this rapid movement, the rupture rod 12 ruptures the front cover 1, and the through-shaft sensor records the real-time rupture load. If the peak transient rupture force of the product is less than 7kN, it indicates that the product is qualified in this aspect.

[0098] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a fragile front cover for a launch tube, characterized in that, Includes the following steps: S1. Polyurethane cavity foaming molding for the cover body, including mold pretreatment, raw material injection and foaming, and density control; among which, Mold pretreatment: First, spray the mold release agent evenly into the inner cavity of the mold. Use water-based mold release agent and spray with a thickness of 5~10μm to ensure no missed spraying or accumulation. Preheat the mold to 60-70℃ to eliminate internal stress. Raw material injection and foaming: Prepare 100 parts isocyanate and 105 parts polyol + foaming agent. Mix 100 parts isocyanate and 105 parts polyol + foaming agent, and control the stirring speed at 2000rpm±5%. Inject polyurethane raw material with a material temperature of 20℃~22℃ into the mold at an injection pressure of 0.2~0.3MPa and an injection time of no more than 8s. The foaming time is 90~120s, and the pressure is maintained for 5min to obtain a polyurethane cavity. Density control: The density is stabilized at 600±10 kg / m³ by adjusting the foaming pressure through real-time monitoring with an ultrasonic density meter. Demolding: Demolding time is 10-15 minutes. Place at room temperature for more than 24 hours to release internal stress. S2. The radial weakening groove, circumferential weakening groove, crack initiation hole, and flange part are machined using machining processes; S3. Product surface processing, including initial surface sanding, initial application of primer, application of putty, surface repair and sanding, secondary application of primer, and application of topcoat; S4. Conduct forward pressure test, reverse pressure test and bursting force test. If the pressure applied in the two pressure tests exceeds 0.1MPa, it indicates that the product meets the pressure performance requirements. If the peak value of the transient bursting force of the product is less than 7kN, it indicates that the product is qualified.

2. The method for preparing the fragile front cover of the launch tube according to claim 1, characterized in that: In step S3, First surface polishing: Use sandpaper to smooth and roughen the product surface, and remove the release wax; First coat of primer: The product is sprayed in the spray booth, with two even coats, and the paint film thickness reaches 30~50μm. Ensure that the paint surface is free of particles and drips. The product is allowed to air dry at room temperature for 12 hours and then dried in the drying room. Applying putty: When the product is laid flat, do not apply putty to the rubber area. Apply a thin layer of putty to the curved joints, less than 200μm. Apply a thin layer of putty to the flat front, less than 300μm. The surface should be flat and free of defects. Surface repair and polishing: Use putty to repair surface defects of the product. After the putty dries, polish the entire product. After polishing, blow away all the dust. Secondary primer spraying: The product is sprayed in the spray booth, with two even coats, and the paint film thickness reaches 30~50μm. Ensure that the paint surface is free of particles and drips, achieves the set fullness, and does not show sandpaper marks after the film dries. Topcoat application: The product is sprayed in a spray booth, with three even coats applied to achieve a film thickness of 40-60μm and a gloss level of 40-70, ensuring that the paint surface is free of particles and runs.

3. A fragile front cover for a launch tube, manufactured using the preparation method described in claim 1 or 2, characterized in that: The device includes a cover and a flange circumferentially disposed around the cover. The front of the cover has at least three radial weakening grooves, and the back of the cover near the edge has a circumferential weakening groove. The circumferential weakening groove has a single-sloping wedge-shaped cross-section and includes a vertical sidewall and an inclined sidewall. The vertical sidewall is perpendicularly connected to the end face of the flange, and the inclined sidewall forms an angle α with the end face of the flange. The angle α ranges from 100° to 150°. The inclined sidewall extends from the bottom of the circumferential weakening groove to the surface of the cover and converges with the vertical sidewall to form a directional crack propagation zone, so that the crack preferentially extends along angle α under impact load.

4. The fragile front cover of the launch tube according to claim 3, characterized in that: The cover has a crack initiation hole at its center, and the radial weakening grooves are distributed radially with the crack initiation hole as the origin, with the ends of the radial weakening grooves extending to the edge of the cover.

5. The fragile front cover of the launch tube according to claim 3, characterized in that: The number of radial weakening grooves is 6 to 12 and they are distributed at equal angles. The width of the radial weakening groove is 1 / 10 to 2 / 15 of the thickness of the cover, and the depth of the radial weakening groove is 2 / 3 to 3 / 4 of the thickness of the cover.

6. The fragile front cover of the launch tube according to claim 3, characterized in that: The depth of the circumferential weakening groove is 2 / 5 to 3 / 5 of the thickness of the cover, and the thickness of the directional crack propagation zone is 2 / 5 to 3 / 5 of the thickness of the cover.

7. The fragile front cover of the launch tube according to claim 3, characterized in that: The cover is integrally molded from polyurethane cavity foam, and the density of the polyurethane foam material is controlled at 580~620kg / m³.

8. A test system for a fragile front cover of a launch tube, using the fragile front cover of a launch tube as described in any one of claims 3-7, characterized in that: It includes a control unit, a gas source, an air inlet pipe, an air inlet valve, a gas cylinder, and a pressure vessel. The gas cylinder is installed below the pressure vessel. The gas source is connected to the gas cylinder through the air inlet pipe. The air inlet valve is installed on the air inlet pipe and is electrically connected to the control unit. The fragile front cover of the launch tube is installed on the upper end face of the pressure vessel. The inner bottom of the pressure vessel has a through hole.

9. The launch tube fragile front cover testing system according to claim 8, characterized in that: It also includes a rupture rod, which passes through the through hole and moves vertically along the gas cylinder, and a push plate is provided at the bottom of the rupture rod.

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