Quantitative Characterization Method for Ice Impact Damage of Composite Materials Based on In-situ Sampling

Abstract

A method for quantitatively characterizing the ice impact damage of composite materials based on in-situ sampling belongs to the field of composite material performance testing. The method is as follows: Step 1: Fill the water storage area I of the ice-making mold with pure water or distilled water and then freeze it; then take out the ice-making mold; take out the ice projectile from the ice-making mold; Step 2: Use the ice impact experimental device to conduct an ice projectile impact experiment on the composite material target plate; Step 3: Use a mechanical testing machine to carry out an in-plane compression experiment on the specimen, and draw a stress-strain curve based on the load-displacement curve output by the mechanical testing machine; the maximum stress value on the stress-strain curve is the compression strength of the specimen; taking the average compression strength of the control group specimens as a reference, calculate the strength attenuation coefficient of all in-situ specimens; based on the strength attenuation coefficient, draw a damage envelope curve at the corresponding position of the target plate, and quantitatively characterize the damage condition of the composite material target plate after impact based on the area enclosed by the curve. The present invention is applicable to the quantitative characterization of ice impact damage of composite materials.

Description

Technical Field

[0001] The present invention belongs to the field of composite material performance testing, and particularly relates to a method for quantitatively characterizing ice impact damage of composite materials based on in-situ sampling. Background Art

[0002] Composite materials are widely used in aircraft structures (such as wings, fuselage skins, etc.), and they will inevitably bear various impact loads during service. Hail impact is one of the most common and concerned problems. Severe hail impact will cause damage to the aircraft structure and directly threaten flight safety.

[0003] At present, relevant research work is extremely limited. Some scholars use a light gas gun device to eject ice projectiles onto a composite material target plate, and use strain gauges / displacement sensors to record the local strain / displacement conditions on the back surface of the composite material target plate. The impact damage mode and damage conditions of the composite material target plate are identified and evaluated by detection means such as optical microscopy / C-scan / CT. However, the above solutions also have obvious limitations: (1) The production process of ice projectiles (ice balls) is not standardized, resulting in bubbles or other insoluble impurities inside the ice projectiles, and the ice projectiles are prone to spontaneous ice cracking; (2) Strain gauges / displacement sensors can only measure the point strain at key positions of the composite material target plate and cannot reflect the full-field strain. Moreover, the high-speed impact of the ice projectiles may cause the premature detachment of the strain gauges / sensors, resulting in the inability to obtain effective data; (3) Using optical microscopy / C-scan / CT to detect the impact damage of the composite material target plate can only judge whether the composite material target plate is damaged, and it is difficult to quantitatively characterize the degree of damage.

[0004] Therefore, providing a practical technical solution to achieve quantitative evaluation of the damage of composite materials after being impacted by ice projectiles is of great significance for the wide and in-depth application of composite materials in the engineering field. Summary of the Invention

[0005] The purpose of the present invention is to solve the above problems existing in the prior art, and provide a method for quantitatively characterizing ice impact damage of composite materials based on in-situ sampling. The method of the present invention can quantitatively characterize the damage degree / remaining mechanical properties of composite materials under ice impact.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0007] A method for quantitatively characterizing ice impact damage of composite materials based on in-situ sampling, the method comprising the following steps:

[0008] Step 1: Ice projectile preparation;

[0009] Step 2: Ice impact experiment, the specific steps are as follows:

[0010] Step 2-1: Spray speckles on the back impact surface of the composite material target plate, and assemble the composite material target plate onto the fixture of the ice impact experiment device;

[0011] Step 2-2: Place the fixture equipped with the composite material target plate at the set position in the target chamber of the ice impact experiment device, and detachably and fixedly connect the fixture to the target chamber;

[0012] Step 2-3: Install the separator of the ice impact experiment device into the round hole on the front panel of the target chamber;

[0013] Step 2-4: Adjust the position of the target chamber so that the central axis of the light gas gun of the ice impact experiment device coincides with the central axis of the separator and intersects the center of the composite material target plate;

[0014] Step 2-5: Align the three lenses of the high-speed camera of the ice impact experiment device with the center of the front impact surface of the composite material target plate to record the situation of the front impact surface of the composite material target plate;

[0015] Step 2-6: Align the lenses of the first high-speed camera and the second high-speed camera of the ice impact experiment device with the center of the back impact surface of the composite material target plate to form a DIC test system for measuring the full-field strain and displacement of the back impact surface of the composite material target plate;

[0016] Step 2-7: Take out the ice projectile from the freezing environment, place it into the composite projectile holder of the ice impact experiment device, and quickly load the composite projectile holder with the ice projectile into the light gas gun of the ice impact experiment device;

[0017] Step 2-8: Inject nitrogen with a predetermined pressure into the gas chamber of the light gas gun to launch the ice projectile, and the ice projectile impacts the composite material target plate;

[0018] Step 3: Damage quantification and characterization;

[0019] Step 3-1: Use a mechanical testing machine to conduct in-plane compression experiments on the control group specimens and in-situ specimens respectively. According to the load-displacement curves output by the mechanical testing machine, draw the stress-strain curves of the control group specimens and in-situ specimens respectively; among them, the maximum stress value on the stress-strain curve is the compression strength of the specimen; the control group specimens should be taken from the same composite material plate as the composite material target plate to be tested;

[0020] Step 3-2: Taking the average compression strength of the control group specimens as a reference, calculate the strength attenuation coefficient S of all in-situ specimens, and use the strength attenuation coefficient S to characterize the damage degree of the composite material, and then draw a damage envelope curve, as shown in formula (1);

[0021]

[0022] Among them, σ uis the in-plane compressive strength of the control group specimen, and σ is the in-plane compressive strength of the in-situ specimen;

[0023] Step 3: Use the linear interpolation algorithm to draw multiple damage envelope curves in the damaged area of the composite target plate after being impacted. Finally, quantitatively characterize the damage condition of the composite target plate after impact based on the area enclosed by the damage envelope curves.

[0024] Furthermore, in Step 1, the specific steps for preparing the ice projectile are as follows:

[0025] Step 1-1: Inject pure water or distilled water into the water storage area 1 of the silicone mold of the ice-making mold along the water injection hole until the water storage area 1 is full;

[0026] Step 1-2: Move the ice-making mold into the freezer for freezing;

[0027] Step 1-3: After freezing is completed, take out the ice-making mold and let it stand at room temperature for 5 - 10 minutes;

[0028] Step 1-4: Take out the silicone mold from the ice-making mold, unfold the silicone mold along the demolding cut, and take out the frozen ice ball inside, which is the ice projectile.

[0029] Furthermore, in Step 1-2, move the ice-making mold into the freezer for freezing for at least 36 hours, and set the temperature to -18°.

[0030] Furthermore, the ice-making mold includes a cup body and a silicone mold. The outer wall of the silicone mold is closely attached to the inner wall of the cup body. The cup body is made of heat-insulating material; the silicone mold is internally provided with a water storage area 1, and the upper and lower ends of the silicone mold are respectively provided with a water injection hole and a drain hole communicating with the water storage area 1. The silicone mold is axially provided with a demolding cut communicating with the water storage area 1. The area between the bottom of the cup body and the bottom of the silicone mold is the water storage area 2.

[0031] Furthermore, in Step 2, the ice impact experimental device includes a light gas gun, an experimental table, a composite sabot, a separator, a target chamber, a fixture, and three high-speed cameras; the light gas gun includes a gas chamber, a gun barrel, a gas chamber support, and a gun barrel support; the fixture includes a fixture front panel and a fixture rear panel; the three high-speed cameras are respectively a high-speed camera 1, a high-speed camera 2, and a high-speed camera 3;

[0032] The gas chamber and the gun barrel are respectively detachably fixed on the horizontally arranged experimental table through the gas chamber support and the gun barrel support. The gas chamber inlet is connected to an external nitrogen cylinder, and the gas chamber outlet is connected to the gun barrel inlet;

[0033] The target chamber is fixed on the experimental table and located directly in front of the light gas gun. There is a round hole on the front panel of the target chamber, and the separator is installed in the round hole. The front panel and the rear panel of the fixture are both arranged inside the target chamber. The upper and lower ends of the rear panel of the fixture are detachably and fixedly connected to the upper cover plate and the bottom cover plate of the target chamber through two limit chucks respectively. The front panel and the rear panel of the fixture are detachably and fixedly connected. Through holes with the same size are correspondingly arranged in the middle of the front panel and the rear panel of the fixture. The composite material target plate is fitted and installed in the through hole of the front panel of the fixture. The centers of the gas chamber, the gun barrel, the separator and the composite material target plate are collinear. When conducting the ice projectile impact experiment, the composite projectile holder loaded with ice projectiles is loaded into the gun barrel. One of the side panels and the rear panel of the target chamber are made of high-definition transparent acrylic glass. Three high-speed cameras are arranged outside the target chamber. The three lenses of the high-speed camera are aligned with the center of the impact surface of the composite material target plate. The lenses of the first high-speed camera and the second high-speed camera are aligned with the center of the back surface of the composite material target plate and form an angle of 30° - 45° with each other. The lens heights of the three high-speed cameras are flush with the center of the composite material target plate.

[0034] Furthermore, the composite projectile holder consists of a plastic shell and a foam lining. The foam lining fits against the inner wall of the plastic shell. There is a convex platform at the front end of the foam lining. The convex platform is arranged outside the plastic shell and abuts against the front end of the plastic shell. There is a concave pit matching the ice projectile at the front end of the foam lining.

[0035] Furthermore, the separator consists of an inner ring and an outer ring. One end of the outer ring surface of the inner ring is fixedly sleeved with the outer ring. The inner ring is fixedly installed in the round hole on the front panel of the target chamber. The end face of the outer ring abuts against the rear panel of the target chamber. The inner diameter of the inner ring is smaller than the outer diameter of the foam lining. When firing the ice projectile, the ice projectile passes through the inner ring with a gap, and the composite projectile holder is blocked outside the target chamber.

[0036] Furthermore, the target chamber includes a front panel of the target chamber, a rear panel of the target chamber, an upper cover plate of the target chamber, a bottom cover plate of the target chamber and two side panels of the target chamber. The front panel of the target chamber, the rear panel of the target chamber and the two side panels of the target chamber are respectively detachably and fixedly connected to the upper cover plate of the target chamber and the bottom cover plate of the target chamber.

[0037] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0038] 1. The present invention designs a mold for producing pure ice projectiles (ice balls) based on the constant temperature unidirectional freezing technology, which has many advantages such as simple structure, convenient use and the ability to quickly produce pure ice projectiles.

[0039] 2. The ice-making process is standardized, solving the problem that initial defects such as air bubbles and cracks are likely to exist inside the ice bullets during the preparation process. Since the ice bullets are made of pure water, the internal material of the ice bullets is more uniform, the mechanical properties are more stable, ensuring the reliability and effectiveness of mechanical experiments; and they have a higher density, melt more slowly, are more likely to maintain integrity in appearance, and are convenient for storage and transportation.

[0040] 3. A new type of composite sabot and separator is designed, which can not only ensure the integrity of the appearance of the ice bullet during the launching process of the ice impact experiment, but also achieve the effective separation of the ice bullet from the sabot, avoiding the interference with the quantitative characterization of damage caused by the collision between the sabot and the composite material target plate.

[0041] 4. The DIC technology is introduced in the ice impact experiment. This is an advanced non-contact measurement technology with advantages such as high measurement accuracy and low measurement risk, and can realize the real-time measurement of the full-field strain / displacement of the composite material target plate.

[0042] 5. A method for quantitatively characterizing the ice impact damage of composite materials based on in-situ sampling is proposed. This method defines the strength attenuation coefficient at local positions of the composite material target plate, thus solving the difficult problem of quantitatively characterizing the damage of composite materials under ice impact. Description of the Drawings

[0043] Figure 1 is a schematic structural diagram of the ice-making mold of the present invention;

[0044] Figure 2 is a schematic diagram of the traditional ice-making technology principle;

[0045] Figure 3 is a schematic diagram of the ice-making principle of the present invention using the constant-temperature unidirectional freezing technology;

[0046] Figure 4 is a schematic structural diagram of the ice impact experiment device of the present invention;

[0047] Figure 5 is a schematic diagram of the assembly of the ice bullet and the composite sabot;

[0048] Figure 6 is a schematic diagram of the separator of the present invention;

[0049] Figure 7 is an external view of the assembly of the ice bullet and the composite sabot;

[0050] Figure 8 is a sectional view of the assembly of the ice bullet and the composite sabot;

[0051] Figure 9 is a schematic diagram of the target chamber assembly;

[0052] Figure 10It is a flow chart of the method for quantitatively characterizing the ice impact damage of composite materials based on in-situ sampling according to the present invention;

[0053] Figure 11 It is a schematic diagram of the present angle interlock woven structure in Embodiment 1;

[0054] Figure 12 It is a schematic diagram of taking an in-situ sample in the area where the composite material target plate does not show obvious deformation after being impacted;

[0055] Figure 13 It is a schematic diagram of using a linear interpolation algorithm to draw a damage envelope curve of 70% remaining performance in the damaged area of the composite material target plate after being impacted in the damage quantification and characterization step of the present invention;

[0056] Figure 14 It is a schematic diagram of the linear interpolation algorithm;

[0057] Figure 15 It is a partial cross-sectional view of the ice-making mold of the present invention;

[0058] Figure 16 It is an external view of the ice-making mold of the present invention.

[0059] The names of the components and the reference numerals involved in the above drawings are as follows:

[0060] Water injection hole 1, cup body 2, silicone mold 3, demolding cut 4, ice projectile 5, composite material target plate 6, fixture 7, target chamber 8, separator 9, front panel of the target chamber 10, composite projectile holder 12, air chamber 13, drain hole 14, experimental bench 15, gun barrel 16, air chamber support 17, gun barrel support 18, front panel of the fixture 19, rear panel of the fixture 20, limit chuck 21, upper cover plate of the target chamber 22, rear panel of the target chamber 24, plastic shell 26, foam lining 27, limit hole 28, water storage area M, water storage area N, high-speed camera B1, high-speed camera B2, high-speed camera A1. Detailed implementation manners

[0061] Next, the technical solutions in the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0062] Detailed implementation manner one: As Figure 1 , Figures 4 - 10 , Figure 15 , Figure 16 shown, this implementation manner discloses a method for quantitatively characterizing the ice impact damage of composite materials based on in-situ sampling, and the method includes the following steps:

[0063] Step 1: Preparation of ice bullets; the specific steps are as follows:

[0064] Step 1-1: Inject pure water (in order to reduce the dissolved air and impurities in the water, preferably use pure water that has been boiled and naturally cooled to room temperature (25°)) or distilled water into the water storage area M of the silicone mold 3 of the ice-making mold through the water injection hole 1 of the silicone mold 3 until the water storage area M is full (the water flow rate should be kept slow and stable during the water injection process);

[0065] Step 1-2: Move the ice-making mold into the freezer and freeze it (the environment should be kept stable during the process, and do not shake or move the ice-making mold) for at least 36 hours, with the temperature set at -18°;

[0066] Step 1-3: After freezing is completed, take out the ice-making mold and let it stand at room temperature for 5 - 10 minutes;

[0067] Step 1-4: Take out the silicone mold 3 from the ice-making mold (cup body 2), unfold the silicone mold 3 along the demolding cut 4 of the silicone mold 3, and take out the internally frozen ice ball, that is, the ice bullet 5 (and immediately place the ice bullet 5 into a sealed bag, and then put it back into the freezer for storage for subsequent experiments);

[0068] Step 2: Ice impact experiment, the specific steps are as follows:

[0069] Step 2-1: Spray speckles on the back bullet surface of the composite material target plate 6, and assemble the composite material target plate 6 onto the fixture 7 of the ice impact experiment device;

[0070] Step 2-2: Place the fixture 7 equipped with the composite material target plate 6 at the set position in the target chamber 8 of the ice impact experiment device, and detachably and fixedly connect the fixture 7 with the target chamber 8; the target chamber 8 includes a target chamber front panel 10, a target chamber rear panel 24, a target chamber upper cover plate 22, a target chamber bottom cover plate, and two target chamber side panels; the target chamber front panel 10, the target chamber rear panel 24, and the two target chamber side panels are respectively detachably and fixedly connected with the target chamber upper cover plate 22 and the target chamber bottom cover plate (the two target chamber side panels are arranged on the left and right sides of the target chamber 8);

[0071] Step 2-3: Install the separator 9 of the ice impact experiment device into the round hole of the target chamber front panel 10;

[0072] Step 2-4: Adjust the position of the target chamber 8 so that the central axis of the light gas gun of the ice impact experiment device coincides with the central axis of the separator 9 and intersects the center of the composite material target plate 6;

[0073] Step 2-5: Align the high-speed camera three A1 lens of the ice impact experiment device with the center of the front bullet surface of the composite material target plate 6 to record the situation of the front bullet surface of the composite material target plate 6;

[0074] Step 26: Align the lenses of high-speed camera 1 B1 and high-speed camera 2 B2 of the ice impact experimental device with the center of the back surface of the composite material target plate 6 to form a DIC test system for measuring the full-field strain and displacement of the back surface of the composite material target plate 6;

[0075] Step 27: Take out the ice projectile 5 from the freezing environment, place it into the composite projectile holder 12 of the ice impact experimental device, and quickly load the composite projectile holder 12 containing the ice projectile 5 into the light gas gun of the ice impact experimental device;

[0076] Step 28: Inject nitrogen with a predetermined pressure (0.5 - 2.0 MPa) into the gas chamber 13 of the light gas gun, launch the ice projectile 5, and the ice projectile 5 impacts the composite material target plate 6;

[0077] Step 3: Damage quantification and characterization;

[0078] Step 31: Use a mechanical testing machine to conduct in-plane compression experiments on the control group specimens (i.e., specimens taken from the composite material plate) and in-situ specimens (i.e., specimens taken from the area where the composite material target plate 6 after impact has not undergone obvious deformation), and respectively plot the stress-strain curves of the control group specimens and in-situ specimens based on the load-displacement curves output by the mechanical testing machine; among them, the maximum stress value on the stress-strain curve is the compression strength of the specimen; the control group specimens should be taken from the same composite material plate as the composite material target plate 6 to be tested;

[0079] Step 32: Taking the average compression strength of the control group specimens as a reference, calculate the strength attenuation coefficient S of all in-situ specimens, and use the strength attenuation coefficient S to characterize the damage degree of the composite material, and then plot the damage envelope curve, as shown in formula (1);

[0080]

[0081] where, σ u is the in-plane compression strength of the control group specimens, and σ is the in-plane compression strength of the in-situ specimens;

[0082] Step 33: Use the linear interpolation algorithm to plot multiple damage envelope curves (such as plotting 50%, 70%, and 90% remaining performance damage envelope curves) in the damaged area of the composite material target plate 6 after impact. Finally, quantitatively characterize the damage condition of the composite material target plate 6 after impact based on the area enclosed by the damage envelope curve.

[0083] Specific implementation method 2: As Figure 1As shown in the figure, this embodiment is a further illustration of the first specific embodiment. The ice-making mold includes a cup body 2 (with a frustum shape) and a silicone mold 3 (a frustum-shaped silicone block). The outer wall of the silicone mold 3 is closely attached to the inner wall of the cup body 2 (but without any mechanical connection and can be freely taken out). The cup body 2 is made of heat-insulating materials (such as vacuum glass, vacuum insulation board or polystyrene) (the purpose is to isolate the external air, avoid heat transfer, and make the direction of the cold air intrusion process and the water condensation into ice process the same, only from top to bottom); a water storage area M (the water storage area M is a reserved cavity for freezing ice bullets 5) is provided inside the silicone mold 3. Water injection holes 1 and drainage holes 14 that communicate with the water storage area M are respectively provided at the upper and lower ends of the silicone mold 3 (the water injection holes 1 and drainage holes 14 are for facilitating the injection and drainage of water on the one hand, and also for restricting the intrusion direction and speed of cold air to delay the freezing progress of the internal ice bullets 5). A demolding cut 4 that communicates with the water storage area M is provided along the axial direction of the silicone mold 3 (the purpose is to facilitate the quick removal of the ice bullets 5). The area between the inner bottom of the cup body 2 and the bottom of the silicone mold 3 is the water storage area N (which can store the excess water, air bubbles and other impurities discharged during the freezing process).

[0084] Specific embodiment three: As Figures 4 - 9 shown in the figure, this embodiment is a further illustration of the first specific embodiment. In step two, the ice impact experimental device includes a light gas gun, an experimental table 15, a composite sabot 12 (which can prevent the ice bullet 5 from breaking during the launch), a separator 9, a target chamber 8, a fixture 7 and three high-speed cameras; the light gas gun includes a gas chamber 13, a gun barrel 16, a gas chamber support 17 and a gun barrel support 18; the fixture 7 includes a fixture front panel 19 and a fixture rear panel 20; the three high-speed cameras are respectively a high-speed camera one B1, a high-speed camera two B2 and a high-speed camera three A1;

[0085] The gas chamber 13 and the gun barrel 16 are respectively detachably fixed on the horizontally arranged experimental table 15 through the gas chamber support 17 and the gun barrel support 18 (with the help of bolts). The inlet of the gas chamber 13 is connected to an external nitrogen cylinder (the launch speed of the ice bullet 5 can be controlled by adjusting the pressure in the gas chamber 13), and the outlet of the gas chamber 13 is connected to the inlet of the gun barrel 16;

[0086] The target chamber 8 is fixed on the test bench 15 and located directly in front of the light gas gun. There is a round hole on the front panel 10 of the target chamber. The separator 9 is installed in the round hole. Both the front panel 19 of the fixture and the rear panel 20 of the fixture are arranged in the target chamber 8. The upper and lower ends of the rear panel 20 of the fixture are respectively detachably and fixedly connected to the upper cover plate 22 of the target chamber and the bottom cover plate of the target chamber through two limit chucks 21 (there are multiple columns of limit holes 28 provided on the upper cover plate 22 of the target chamber and the bottom cover plate of the target chamber in one-to-one correspondence. The upper and lower ends of the rear panel 20 of the fixture are respectively detachably and fixedly connected to the corresponding limit holes 28 of the upper cover plate 22 of the target chamber and the bottom cover plate of the target chamber through two limit chucks 21). The front panel 19 of the fixture and the rear panel 20 of the fixture are detachably and fixedly connected (by bolts). Through holes of the same size are correspondingly provided in the middle of the front panel 19 of the fixture and the rear panel 20 of the fixture (for the convenience of DIC observation). The composite target plate 6 is fitted and installed in the through hole of the front panel 19 of the fixture (so as to fix the composite target plate 6 at the central position of the fixture 7. An appropriate space should be left between the fixture 7 and the front panel 10 of the target chamber and the rear panel 24 of the target chamber. The fixture 7 can be placed at a position 1 / 3 to 1 / 2 away from the front panel 10 of the target chamber in the target chamber 8). The centers of the gas chamber 13, the gun barrel 16, the separator 9 and the composite target plate 6 are collinear (which can ensure the alignment of the impact experiment). When conducting the impact experiment of the ice projectile 5, the composite projectile holder 12 loaded with the ice projectile 5 is loaded into the gun barrel 16. One of the side panels of the target chamber 8 and the rear panel 24 of the target chamber are both made of high-definition transparent acrylic glass (for using a high-speed camera to record the process of the ice projectile 5 impact experiment). Three high-speed cameras are arranged outside the target chamber 8. The lens of the high-speed camera three A1 is aligned with the center of the front impact surface of the composite target plate 6. The lenses of the high-speed camera one B1 and the high-speed camera two B2 are aligned with the center of the rear impact surface of the composite target plate 6 and form an angle of 30° to 45° with each other. The lens heights of the three high-speed cameras are flush with the center of the composite target plate 6. (The high-speed camera three A1 can, on the one hand, measure the incident velocity of the ice projectile 5 through the pixel calibration method, and on the other hand, record the impact process of the ice projectile 5. The high-speed camera one B1 and the high-speed camera two B2 form a DIC (Digital Image Correlation) test system to measure the full-field displacement / strain of the rear impact surface of the composite target plate 6).

[0087] Specific implementation method four: As Figure 4 , Figure 5 , Figure 7 and Figure 8As shown in the figure, this embodiment is a further illustration of the third specific embodiment. The composite sabot 12 is composed of a plastic outer shell 26 and a foam inner lining 27; the foam inner lining 27 fits against the inner wall of the plastic outer shell 26. A boss is provided at the front end of the foam inner lining 27. The boss is arranged outside the plastic outer shell 26 and abuts against the front end of the plastic outer shell 26. A concave pit matching the ice bullet 5 is provided at the front end of the foam inner lining 27. (The wall surface of the plastic outer shell 26 is smooth and has a certain structural strength, which can reduce friction and prevent large deformation of the ice bullet 5. The foam inner lining 27 can further play a role in buffering and energy absorption, protecting the ice bullet 5 so that it will not be prematurely broken due to internal collision).

[0088] Specific Embodiment Five: As Figures 4 - 6 shown in the figure, this embodiment is a further illustration of the third specific embodiment. The separator 9 is composed of an inner ring and an outer ring. One end of the outer ring surface of the inner ring is fixedly sleeved with the outer ring. The inner ring is fixedly installed in a circular hole on the front panel 10 of the target chamber. The end face of the outer ring abuts against the rear panel 24 of the target chamber. The inner diameter of the inner ring is smaller than the outer diameter of the foam inner lining 27 of the composite sabot 12; when the ice bullet 5 is launched, the ice bullet 5 passes through the inner ring with a gap, and the composite sabot 12 is blocked outside the target chamber 8.

[0089] Another difficulty in this experiment is to achieve the separation of the ice bullet 5, that is, to make the ice bullet 5 separate from the composite sabot 12 before hitting the composite material target plate 6, and in this experiment, only the ice bullet 5 is allowed to enter the target chamber 8. The purpose is to avoid the secondary impact of the composite sabot 12 on the composite material target plate 6 from interfering with the experimental results. The separator 9 is as Figure 6 shown in the figure. The aperture of the separator 9 (i.e., the inner diameter of the inner ring) is slightly larger than the diameter of the ice bullet 5 and slightly smaller than the outer diameter (diameter) of the foam inner lining 27 of the composite sabot 12. Therefore, this experimental device only allows the ice bullet 5 to pass through and can well play the role of separating the ice bullet 5 and the composite sabot 12.

[0090] Example 1:

[0091] This example discloses a method for quantitatively characterizing the ice impact damage of composite materials based on in-situ sampling. The method includes the following steps:

[0092] Step One: Ice bullet preparation;

[0093] Step 1.1: As Figure 1 shown in the figure, pour purified water / distilled water that has been boiled and naturally cooled to room temperature (25°) (to reduce the air and impurities dissolved in the water) into the water injection hole 1 of the silicone mold 3 of the ice-making mold along the water injection hole 1 of the silicone mold 3 of the ice-making mold until the cavity of the cup body 2 is completely submerged. The water flow rate should be kept slow and stable during the water injection process.

[0094] The ice-making mold consists of a cup body 2 and a silicone mold 3. The cup body 2 is made of heat-insulating materials (such as vacuum glass, vacuum insulation panel or polystyrene). Inside the silicone mold 3, there is a first water storage area M. At the upper and lower ends of the silicone mold 3, there are respectively a water injection hole 1 and a drainage hole 14 that communicate with the first water storage area M. The silicone mold 3 is placed into the cup body 2. The upper surface of the silicone mold 3 is flush with the top of the cup body 2, and the outer wall of the silicone mold 3 fits perfectly with the inner wall of the cup body 2. Axially, the silicone mold 3 is provided with a demolding cut 4 that communicates with the first water storage area M. The area between the bottom of the cup body 2 and the bottom of the silicone mold 3 is the second water storage area N.

[0095] Taking the example of freezing an ice ball with a diameter of 50 mm, the first water storage area M is a spherical cavity with a diameter of 50 mm, and the diameters of both the drainage hole 14 and the water injection hole 1 are 8 mm.

[0096] Steps 1-2: Move the ice-making mold into the freezer and freeze for at least 36 hours at a temperature of -18°. During this period, the environment should be kept stable, and the ice-making mold should not be shaken or moved.

[0097] Steps 1-3: After freezing is completed, take out the ice-making mold and let it stand at room temperature for 5 minutes.

[0098] Steps 1-4: Take out the silicone mold 3 from the cup body 2 of the ice-making mold. Unfold the silicone mold 3 along the demolding cut 4 of the silicone mold 3, and take out the frozen ice ball inside, which is the ice bullet 5. Then immediately place it into a sealed bag and put it back into the freezer for storage for subsequent experiments.

[0099] The traditional ice-making process is as Figure 2 shown ( Figure 2 In the figure, W1 represents pure water; W2 represents ice; W3 represents ice cracks; W4 represents air bubbles). Cold air continuously cools the water in the ice tray from all directions. Therefore, the temperature of the water in contact with the inner wall surface of the ice tray reaches below zero first and begins to freeze into ice. This freezing process is from the outside to the inside. When the outside has completely frozen into ice, there is still unfrozen water and gas inside. The generation of these gases is due to the decrease in the dissolved oxygen content of water when the temperature drops, and they will diffuse to the outside in the form of small bubbles. In addition, the volume of water expands during the freezing process, but the space in the central area is limited and cannot continue to expand outward, which will cause excessive internal stress in the ice block and result in the ice block being cracked.

[0100] As Figure 3 shown ( Figure 3Among them, W1 represents pure water; W2 represents ice; W4 represents bubbles; W5 represents thermal insulation material). The present invention adopts the constant-temperature unidirectional freezing technology, which can solve the above problems existing in traditional ice making. The ice making principle is as follows. The cup body 2 made of thermal insulation material can effectively isolate the intrusion of external cold air, making the ice formation process of water unidirectionally controllable. Therefore, the water in the upper part starts to freeze when it encounters cold first, and the dissolved oxygen and impurities in the water are discharged downward. In this case, the ice in the upper part is always pure and bubble-free, and there will be no excessive internal stress in the ice due to inability to expand. In addition, in order to further reduce the dissolved air and impurities in the water, ice bullets 5 can be frozen using pure water / distilled water that has been boiled and then naturally cooled.

[0101] Step Two: Ice impact experiment;

[0102] The purpose of this step is to overcome the deficiencies existing in the current experimental scheme: (1) It is difficult for the ice bullet to maintain its complete appearance during the launch process and cannot achieve effective separation from the projectile holder; (2) It can only measure the local strain / displacement field of the target plate, cannot obtain the full-field strain / displacement, and there is a great measurement risk (the strain gauge falls off in advance).

[0103] In this embodiment, taking a composite material target plate with a length × width × thickness = 180 × 180 × 6 mm as an example, it is recommended to use an ice hockey with a diameter of 50 mm as the ice bullet 5, and the diameter of the barrel 16 of the light gas gun is 70 mm. The specific experimental steps are as follows:

[0104] Step Two - One: Spray speckles on the back of the composite material target plate 6, and then install the composite material target plate 6 on the fixture 7;

[0105] Step Two - Two: Fix the fixture 7 with the installed composite material target plate 6 at a suitable position in the target chamber 8;

[0106] Step Two - Three: Install the separator 9 in the round hole on the front panel 10 of the target chamber;

[0107] Step Two - Four: Adjust the position of the target chamber 8 so that the central axes of the barrel 16 and the separator 9 coincide and intersect with the center of the composite material target plate 6;

[0108] Step Two - Five: Set up the high-speed camera Three A1 to record the situation of the front surface of the composite material target plate 6 facing the projectile;

[0109] Step Two - Six: Set up the high-speed camera One B1 and the high-speed camera Two B2 to form a DIC test system to measure the full-field strain and displacement of the back surface of the composite material target plate 6;

[0110] Step Two - Seven: Take out the ice bullet 5 from the freezing environment, place it in the composite projectile holder 12, and quickly load the composite projectile holder 12 with the ice bullet 5 into the light gas gun;

[0111] Step 2-2: Inject nitrogen gas with a pressure of 0.5 - 2.0 MPa into the air chamber 13, launch the ice projectile 5, and let the ice projectile 5 impact the composite material target plate 6;

[0112] Step 3: Damage quantification and characterization;

[0113] A method for quantitatively characterizing ice impact damage of composite materials based on in-situ sampling proposed by the present invention solves the problem of difficultly and accurately evaluating the damage condition of the composite material target plate after impact.

[0114] Traditional post-impact damage detection mostly focuses on qualitative research of the target plate damage, such as: (1) observing the external morphological characteristics of the target plate with the aid of an optical microscope; (2) detecting the internal delamination condition of the target plate with the aid of C-scan; (3) identifying the internal damage mode of the target plate with the aid of CT. There is little quantitative analysis. Some scholars use the remaining compressive strength of the whole target plate as the standard for measuring the damage degree, but this method also has some defects: (1) The size of the target plate used in the impact experiment is generally large, which does not meet the requirements of the standard compression experiment. Therefore, relevant quasi-static compression fixtures need to be designed and manufactured separately; (2) If the impact velocity of the projectile is high, the target plate will be bent, which will affect the measurement accuracy of the compression experiment; (3) There is a lack of a control reference group, and the consistency and repeatability of the compression experiment are poor, and the effective data that can be obtained is extremely limited.

[0115] The specific steps of the damage quantification and characterization are as follows:

[0116] Step 3-1: Use a mechanical testing machine to conduct in-plane compression experiments on the control group specimens (i.e., specimens taken from the composite material plate) and in-situ specimens (i.e., specimens taken from the area where the composite material target plate 6 after impact has not undergone obvious deformation, Figure 12 where the '+' cross in it represents the sampling point of the in-situ specimen), and respectively draw the stress-strain curves of the control group specimens and in-situ specimens according to the load-displacement curves output by the mechanical testing machine; among them, the maximum value of the stress-strain curve is the compressive strength of the specimen; the control group specimens should be taken from the same composite material plate as the composite material target plate 6 to be measured to ensure the consistency and stability of their mechanical properties;

[0117] After the composite material target plate 6 bears the impact load, large deformation is very likely to occur in the central area. If sampling is carried out in this area and further compression experiments are carried out, the specimen is likely to become unstable during the loading process, resulting in invalid experimental data. Therefore, when taking in-situ samples of the composite material target plate 6, the places where obvious deformation has occurred should be discarded.

[0118] For unidirectional composite materials, the size requirements of the specimen are: its length and width should be the same, and the ratio of the length to the thickness should be controlled between 1.6 and 2.5; for composite materials with a woven structure (such asFigure 12 As shown, its length and width should also be at least greater than or equal to 1.5 times the size of the unit cell (representative volume element).

[0119] To ensure the repeatability of the compression experiment, there should be at least 5 control specimens sampled from the composite material plate. And for the in-situ specimens sampled from the impacted composite target plate 6, the more the better under the premise of meeting the size requirements of the compression specimens. In addition, during the sampling process, the processing damage to the specimens caused by the cutting process should be avoided.

[0120] Step 3-2: Taking the average compressive strength of the control specimens as a reference, calculate the strength attenuation coefficient S of all in-situ specimens, and use the strength attenuation coefficient S to characterize the damage degree of the material, as shown in formula (1);

[0121]

[0122] where, σ u is the in-plane compressive strength of the control specimens, and σ is the in-plane compressive strength of the in-situ specimens;

[0123] Step 3-3: Using the linear interpolation algorithm, draw three damage envelope curves (50%, 70%, and 90% remaining performance) in the damaged area after impact of the composite target plate 6. Finally, quantitatively characterize the damage condition of the composite target plate 6 after impact based on the area enclosed by the damage envelope curves. Specifically:

[0124] (1) The research object of this embodiment is a typical three-dimensional woven composite material (angle-interlocked woven structure), and its structure is as Figure 11 shown, including warp yarn F1, weft yarn F2, and stitching warp yarn F3. Among them, warp yarn F1 and weft yarn F2 are perpendicular to each other, and are interlocked in the thickness direction by stitching warp yarn F3. Its in-plane unit cell length × width = 6.6 mm × 6.6 mm;

[0125] (2) Use traditional damage detection methods to conduct qualitative damage analysis on the impacted composite target plate, including using visual observation method to roughly evaluate the overall damage condition of the composite target plate 6; using C-scan to obtain the damaged area of the composite target plate 6; using a microscope to observe local damage characteristics (such as fiber fracture, matrix cracking, interface separation, etc.); using CT to further extract the damage distribution law of the composite target plate 6, etc.

[0126] (3) Conduct in-situ sampling on the impacted composite target plate 6, with its length × width × thickness = 12 × 12 × 6 mm. The sampling points are required to have no obvious visual damage, and the sampling interval is 5 mm. Conduct in-plane compression experiments on all in-situ specimens in turn, and record the experimental results;

[0127] (4) Similarly, for 5 control specimens taken from the same composite material plate with length × width × thickness = 12 × 12 × 6 mm, in-plane compression experiments were carried out, and their average strength was taken as the reference value, and the attenuation coefficient of each compression specimen was calculated;

[0128] (5) Combining the spatial position coordinates of the sampling points on the composite material target plate 6, using the linear interpolation algorithm, the damage envelope curves (50%, 70% and 90% remaining performance) of the composite material target plate were drawn. It can be considered that the area within 50% is severely damaged, the area within 70% is moderately damaged, and the area within 90% is slightly damaged area.

[0129] Taking the example of drawing the damage envelope curve of 70% remaining performance. Usually, due to the discreteness of the sampling positions of the in-situ specimens, the position coordinates of the sampling points with a strength attenuation coefficient of 70% cannot be directly obtained, but this information can be calculated through the linear interpolation algorithm. As Figure 13 shown ( Figure 13 In it, the envelope curve within the range indicated by A represents 61% remaining performance, the envelope curve within the range indicated by B represents 70% remaining performance, and the envelope curve within the range indicated by C represents 83% remaining performance), what is obtained are the position coordinates of multiple sampling points with 70% remaining performance. Connecting these discrete points in sequence, a closed two-dimensional curve can be obtained, and this curve is the required damage envelope curve of 70% remaining performance.

[0130] Regarding the linear interpolation algorithm, linear interpolation refers to the interpolation method where the interpolation function is a first-degree polynomial, and its interpolation error at the interpolation nodes is 0.

[0131] Taking single linear interpolation as an example, assuming that the coordinates (x0, y0) and (x1, y1) are known, and the value of a certain position x within the interval [x0, x1] on the straight line is to be obtained. According to Figure 14 shown in it, it can be obtained that:

[0132]

[0133] Since the value of x is known, the value of y can be obtained from the above formula:

[0134]

[0135] Among them: the value of x corresponds to the position coordinate function of the sampling point, and the value of y corresponds to the strength attenuation coefficient S.

[0136] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above-described exemplary embodiments, and the present invention can be implemented in other forms without departing from the spirit or basic characteristics of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent conditions of the claims are intended to be embraced within the present invention. Any reference signs in the claims should not be construed as limiting the claims involved.

[0137] The composite target plate used in the present invention is made of unidirectional composite materials, woven composite materials or braided composite materials, and the woven composite materials are two-dimensional woven composite materials or three-dimensional woven composite materials.

[0138] In addition, it should be understood that although this specification is described according to embodiments, not every embodiment only contains an independent technical solution. This narrative way of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for quantitatively characterizing ice impact damage of composite materials based on in-situ sampling, characterized in that: The method includes the following steps: Step 1: Ice projectile preparation; Step 2: Ice impact experiment, and the specific steps are as follows: Step 2-1: Spray speckles on the back surface of the composite target plate (6), and assemble the composite target plate (6) onto the fixture (7) of the ice impact experiment device; Step 2-2: Place the fixture (7) equipped with the composite target plate (6) at a set position in the target chamber (8) of the ice impact experiment device, and detachably and fixedly connect the fixture (7) to the target chamber (8); Step 2-3: Install the separator (9) of the ice impact experiment device in the round hole of the front panel (10) of the target chamber; Step 2-4: Adjust the position of the target chamber (8) so that the central axis of the light gas gun of the ice impact experiment device coincides with the central axis of the separator (9) and intersects the center of the composite target plate (6); Step 2-5: Align the lens of the high-speed camera III (A1) of the ice impact experiment device with the center of the front surface of the composite target plate (6) to record the situation of the front surface of the composite target plate (6); Step 2-6: Align the lenses of the high-speed camera I (B1) and the high-speed camera II (B2) of the ice impact experiment device with the center of the back surface of the composite target plate (6) to form a DIC test system for measuring the full-field strain and displacement of the back surface of the composite target plate (6); Step 2-7: Take out the ice projectile (5) from the freezing environment, place it into the composite projectile holder (12) of the ice impact experiment device, and quickly load the composite projectile holder (12) containing the ice projectile (5) into the light gas gun of the ice impact experiment device; Step 2-8: Inject nitrogen gas with a predetermined pressure into the gas chamber (13) of the light gas gun to launch the ice projectile (5), and the ice projectile (5) impacts the composite target plate (6); Step 3: Damage quantification and characterization; Step 3-1: Use a mechanical testing machine to conduct in-plane compression experiments on the control group specimens and the in-situ specimens respectively. According to the load-displacement curves output by the mechanical testing machine, draw the stress-strain curves of the control group specimens and the in-situ specimens respectively; among them, the maximum stress value on the stress-strain curve is the compression strength of the specimen; the control group specimens should be taken from the same composite material plate as the composite target plate (6) to be tested; Step 3-2: Taking the average compression strength of the control group specimens as a reference, calculate the strength attenuation coefficient S of all in-situ specimens, and use the strength attenuation coefficient S to characterize the damage degree of the composite material, and then draw a damage envelope curve, as shown in formula (1); where σ u is the in-plane compressive strength of the control group specimen, and σ is the in-plane compressive strength of the in-situ specimen; Step 3-3: Use the linear interpolation algorithm to draw multiple damage envelope curves in the damaged area of the composite target plate (6) after being impacted. Finally, quantitatively characterize the damage situation of the composite target plate (6) after impact based on the area enclosed by the damage envelope curves.

2. The method for quantitatively characterizing ice impact damage of composite materials based on in-situ sampling according to claim 1, characterized in that: In Step 1, the specific steps of ice projectile preparation are as follows: Step 1-1: Inject pure water or distilled water into the water storage area I (M) of the silicone mold (3) of the ice-making mold along the water injection hole (1) until the water storage area I (M) is full; Step 1-2: Move the ice-making mold into the freezer for freezing; Step 1-3: After freezing is completed, take out the ice-making mold and let it stand at room temperature for 5 - 10 minutes; Step 14: Take out the silicone mold (3) from the ice-making mold, unfold the silicone mold (3) along the demolding cut (4) of the silicone mold (3), and take out the ice ball frozen inside, that is, the ice bullet (5).

3. The method for quantitatively characterizing ice impact damage of composite materials based on in-situ sampling according to claim 2, characterized in that: In Step 12, move the ice-making mold into the freezer and freeze it for at least 36 hours, with the temperature set at -18°C.

4. The method for quantitatively characterizing ice impact damage of composite materials based on in-situ sampling according to claim 2, characterized in that: The ice-making mold includes a cup body (2) and a silicone mold (3). The outer wall of the silicone mold (3) is closely attached to the inner wall of the cup body (2). The cup body (2) is made of heat-insulating material. The silicone mold (3) is internally provided with a first water storage area (M). The upper and lower ends of the silicone mold (3) are respectively provided with a water injection hole (1) and a drain hole (14) communicating with the first water storage area (M). The silicone mold (3) is axially provided with a demolding cut (4) communicating with the first water storage area (M). The area between the inner bottom of the cup body (2) and the bottom of the silicone mold (3) is the second water storage area (N).

5. The method for quantitatively characterizing ice impact damage of composite materials based on in-situ sampling according to claim 1, characterized in that: In Step 2, the ice impact test device includes a light gas gun, a test bench (15), a composite sabot (12), a separator (9), a target chamber (8), a fixture (7), and three high-speed cameras. The light gas gun includes a gas chamber (13), a gun barrel (16), a gas chamber support (17), and a gun barrel support (18). The fixture (7) includes a fixture front panel (19) and a fixture rear panel (20). The three high-speed cameras are respectively a first high-speed camera (B1), a second high-speed camera (B2), and a third high-speed camera (A1). The gas chamber (13) and the gun barrel (16) are respectively detachably fixed on the horizontally arranged test bench (15) through the gas chamber support (17) and the gun barrel support (18). The inlet of the gas chamber (13) is connected to an external nitrogen cylinder, and the outlet of the gas chamber (13) is connected to the inlet of the gun barrel (16). The target chamber (8) is fixed on the test bench (15) and located directly in front of the light gas gun. There is a round hole on the front panel (10) of the target chamber. The separator (9) is installed in the round hole. The front panel (19) and the rear panel (20) of the fixture are both arranged in the target chamber (8). The upper and lower ends of the rear panel (20) of the fixture are respectively detachably and fixedly connected to the upper cover plate (22) and the bottom cover plate of the target chamber through two limit chucks (21). The front panel (19) and the rear panel (20) of the fixture are detachably and fixedly connected. Through holes of the same size are correspondingly arranged in the middle of the front panel (19) and the rear panel (20) of the fixture. The composite target plate (6) is fitted and installed in the through hole of the front panel (19) of the fixture. The centers of the air chamber (13), the gun barrel (16), the separator (9), and the composite target plate (6) are collinear. When conducting the ice projectile (5) impact experiment, the composite projectile holder (12) loaded with the ice projectile (5) is loaded into the gun barrel (16). One of the side panels of the target chamber (8) and the rear panel (24) of the target chamber are both made of high-definition transparent acrylic glass. Three high-speed cameras are arranged outside the target chamber (8). The lens of the third high-speed camera (A1) is aligned with the center of the impact surface of the composite target plate (6). The lenses of the first high-speed camera (B1) and the second high-speed camera (B2) are aligned with the center of the back surface of the composite target plate (6), and the angle between them is 30° - 45°. The lens heights of the three high-speed cameras are flush with the center of the composite target plate (6).

6. The method for quantitatively characterizing ice impact damage of composite materials based on in-situ sampling according to claim 5, characterized in that: The composite projectile holder (12) consists of a plastic shell (26) and a foam lining (27). The foam lining (27) is fitted to the inner wall of the plastic shell (26). There is a boss at the front end of the foam lining (27). The boss is arranged outside the plastic shell (26) and abuts against the front end of the plastic shell (26). There is a pit matching the ice projectile (5) at the front end of the foam lining (27).

7. The method for quantitatively characterizing the ice impact damage of a composite material based on in-situ sampling according to claim 5, characterized in that: The separator (9) consists of an inner ring and an outer ring. One end of the outer ring surface of the inner ring is fixedly sleeved with the outer ring. The inner ring is fixedly installed in the round hole on the front panel (10) of the target chamber. The end face of the outer ring abuts against the rear panel (24) of the target chamber. The inner diameter of the inner ring is smaller than the outer diameter of the foam lining (27). When the ice projectile (5) is launched, the ice projectile (5) passes through the inner ring at intervals, and the composite projectile holder (12) is blocked outside the target chamber (8).

8. The method for quantitatively characterizing the ice impact damage of a composite material based on in-situ sampling according to claim 1 or 5, characterized in that: The target chamber (8) includes a front panel (10) of the target chamber, a rear panel (24) of the target chamber, an upper cover plate (22) of the target chamber, a bottom cover plate of the target chamber, and two side panels of the target chamber. The front panel (10) of the target chamber, the rear panel (24) of the target chamber, and the two side panels of the target chamber are respectively detachably and fixedly connected to the upper cover plate (22) and the bottom cover plate of the target chamber.

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