A composite material component level hot force test method for a holed web in tension shear composite

Abstract

This invention discloses a composite material component-level tensile-shear combined thermodynamic testing method for perforated web plates, belonging to the technical field of aircraft structural thermal strength testing. The method comprises two parts: Part 1: calculating the number of connecting bolts and their clearances; Part 2: conducting tests under non-uniform temperature fields and a method for arranging strain measurement points considering temperature effects. The invention proposes a method for determining the number of connecting bolts under thermal loads, calculated based on material properties considering temperature reduction and an uncertainty factor of not less than 3. It also proposes a method for setting bolt clearances without connection-matching thermal stress, eliminating the additional thermal expansion load caused by thermal matching and achieving accurate loading. Furthermore, it proposes a combined heating method using a high-temperature environmental chamber and a localized flexible electric heater to apply non-uniform temperature loads to the test piece.

Description

Technical Field

[0001] This invention relates to a method for testing the thermal strength of composite wing components taking temperature into account, and belongs to the technical field of thermal strength testing of aircraft structures. Background Technology

[0002] The stringent lightweight requirements of high-speed aerospace vehicles have led to the extensive use of lightweight resin-based composite materials in the main load-bearing components of wings, such as beams, ribs, and skins. Under thermal load conditions, the material structure will undergo changes in material properties and failure modes different from those at room temperature. Therefore, complex composite material components need to be verified through thermal testing.

[0003] Composite perforated web tensile-shear combined tests, which typically consider the temperature effect, are conducted in a heated ground environment. The force load application method is the same as that for the room temperature test. The test system is described below. Figure 1 1 is a composite perforated web, used as the test specimen; 2 is a metal clamp, used as the test fixture; 3 is a connecting bolt. Under the uniform temperature of the environmental chamber, the four metal clamps are connected to the four sides of the web by the connecting bolt. After the four metal clamps are connected end to end in sequence, diagonal tension is applied to the metal clamps to simulate the combined tensile and shear load of the web.

[0004] This experimental method has the following two problems:

[0005] 1) During the heating process, there is a large difference in the coefficient of thermal expansion between the metal clamp and the composite perforated web specimen. After the connecting bolts are tightened, the composite perforated web is subjected to the expansion and tension of the metal clamp, which generates additional shear load and will produce a large test loading error. If the thermal deformation matching load is not considered, the strength of the metal clamp and bolt connection will also be at risk of exceeding the limit.

[0006] 2) Ground heating environment is difficult to accurately simulate the temperature distribution of the edge and middle of the perforated web of composite material in actual use, while slow heating in high temperature environment chamber will keep the test fixture and test piece at the same temperature. Summary of the Invention

[0007] The purpose of this invention is to provide a component-level composite material perforated web tensile-shear composite thermodynamic test method that takes temperature into account. This method can accurately apply thermal loads by modifying the test connection and heat transfer boundary conditions, precisely simulate the actual temperature distribution, accurately capture high stress and fracture initiation location, and support accurate and sufficient verification of the thermal strength test of composite material perforated web structure for aerospace vehicle wing ribs.

[0008] The technical solution of this invention:

[0009] A composite component-level tensile-shear combined thermodynamic testing method for perforated webs comprises two parts:

[0010] Part 1: Calculating the number of connecting bolts and the clearance, the steps are as follows:

[0011] Step 1: Determine the number of connecting bolts under thermal load

[0012] The composite perforated web is used as the test specimen. The test system includes the composite perforated web 1, metal clamps 2, and connecting bolts 3. There are eight metal clamps in total, four short sides and four long sides. They are connected end to end to form a square frame. Two square frames are put together to hold the composite perforated web 1. Connecting bolts 3 are evenly arranged on each metal clamp 2.

[0013] The number of connecting bolts is determined based on the combined tensile-shear thermodynamic test load of the perforated web. Determining the number of connecting bolts requires considering the reduction in composite material properties of the perforated web after temperature application, by introducing an uncertainty factor S. F To achieve this, for thermodynamic tests of composite materials with large dispersion S F The strength should not be less than 3; on the other hand, the shear stress on the bolt itself and the bolt extrusion stress on the bolt hole of the test piece should also meet the strength requirements, by introducing the allowable shear stress τ of the connecting bolt material at the corresponding temperature. T 剪切许用 And the allowable compressive stress σ of the composite material of the test specimen at the corresponding temperature. T 挤压 Therefore, the system of inequalities that determines the number of connecting bolts is as follows:

[0014] n≥ a·F / [ ·S F ·π·r 2 ·τ T 剪切许用 ]

[0015] n≥ a·F / [ ·S F ·2·t·r·σ T 挤压 ]

[0016] Where n is the number of connecting bolts, a is the length of the long side of the composite perforated web, b is the length of the short side of the composite perforated web, r is the radius of the connecting bolts, t is the end thickness of the composite perforated web, F is the experimental diagonal tensile load, and S F τ is the uncertainty coefficient. T 剪切许用 σ is the allowable shear stress of the connecting bolt material at the corresponding temperature. T 挤压 This represents the allowable compressive stress of the composite material at the corresponding temperature.

[0017] Step 2: Determine the gap of the connecting bolts for thermal connection matching.

[0018] The thermal expansion coefficient of the perforated web of the composite material differs from that of the metal clamps, resulting in localized thermal stress at the connection. To ensure sufficient release of this localized thermal stress, the bolt hole clearance needs to be set. For ease of description, the connecting bolts are numbered. Four metal clamps form a rectangular boundary around the perforated web of the composite material. The connecting bolts are distributed in rows and columns on the metal clamps. Let the connecting bolt at the upper left corner of the four metal clamps be the diagonal fixing bolt, numbered 11. Taking the diagonal fixing bolt as the fixing origin, let the connecting bolt in the i-th row and j-th column be numbered ij. When subjected to temperature load, the positions of the remaining connecting bolts deviate outward relative to the diagonal fixing bolt due to the thermal deformation of the perforated web of the composite material and the metal clamps, as shown in the diagram. Figure 2 The deformation matching amount at other connecting bolt connection points is the difference in thermal expansion coefficients between the perforated web of the composite material and the metal clamp multiplied by the distance from the connecting bolt to the diagonally fixed bolt. Therefore, the inequality for determining the fitting clearance of the connecting bolts is:

[0019] The distance between the j-th connecting bolt and the diagonal fixing bolt: L ij =

[0020] Clearance of bolt number ij:

[0021] Where, α 试件 α is the coefficient of thermal expansion of the perforated web of the composite material. 夹具 The coefficient of thermal expansion of the metal clamp is . L represents the temperature change of the perforated web of the composite material. ij Let be the distance between bolt number ij and the diagonal fixing bolt, and n represent the total number of connecting bolts on each metal clamp.

[0022] Part Two: Conducting experiments under non-uniform temperature fields and the method for arranging strain measurement points considering the effect of temperature. The steps are as follows:

[0023] Step 1: Apply a non-uniform temperature field to the test specimen.

[0024] A non-uniform temperature field was created by additionally heating metal clamps to simulate temperature gradient changes within a uniformly heated environmental chamber. Electric heating blankets were added inside the metal clamps at the two short sides of the perforated web of the composite material. By controlling these heating blankets, the temperature gradient between the upper and lower surfaces was simulated, achieving an accurate simulation of the actual temperature field within the environmental chamber. (See...) Figure 3 2 is a metal clamp, and 4 is an electric heating blanket. The clamping position of the electric heating blanket is controlled by the temperature measuring point to control the heating parameters. The temperature measuring points are evenly distributed at the overlap of the metal clamp and the electric heating blanket.

[0025] The ambient temperature chamber is heated until the temperature of the entire perforated web of the composite material reaches T1. Then, electric heating blankets at both ends are used to heat the perimeter of the perforated web of the composite material until the temperature reaches T2. After heat transfer, the temperature reaches equilibrium, forming a temperature gradient and internal thermal stress that simulate the actual situation, and the experiment is carried out.

[0026] The length of the heating zone of the aforementioned electric blanket is the same as the short side length of the perforated web of the composite material, and its size is b; the thickness of the heating zone is the same as the end thickness of the perforated web of the composite material, and its size is t; the width of the heating zone is the width of the overlapping area between the metal clamp, the perforated web of the composite material, and the electric blanket, and its size is d. The density of the perforated web of the composite material is ρ, its specific heat capacity is c, and its heating efficiency coefficient is ξ. Then, in time... Inside, the electric heating blanket located on one short side of the test piece heats the sample from temperature T1 to temperature T2. The calculated heating power P is:

[0027]

[0028] Step 2: Strain Measurement Point Arrangement under the Influence of Temperature Distribution

[0029] Due to the application of thermal stress, the fracture direction of the test specimen will be offset from the diagonal of the perforated web of the composite material. It is necessary to obtain the thermal stress distribution map through simulation, and obtain the location of the maximum principal stress and the crack propagation direction through thermo-mechanical coupling simulation. The angle θ between the crack propagation direction and the horizontal edge of the perforated web of the composite material is obtained. Strain gauges are set along the crack propagation direction and in combination with the location of the maximum principal stress to capture the generation of the maximum strain and the trend of crack propagation.

[0030] The first part of the above steps provides the assembly and connection scheme of the test specimen and the test fixture, and the second part provides the test temperature loading and measurement scheme, which finally forms a composite component-level tensile-shear composite thermodynamic test method.

[0031] Compared with existing technologies, the innovative aspects of this invention are as follows:

[0032] 1) A method for determining the number of connecting bolts considering thermal load is proposed, which should be calculated based on material properties considering temperature reduction and an uncertainty factor of not less than 3;

[0033] 2) A bolt matching gap setting method without connection matching thermal stress is proposed to remove the additional thermal expansion load caused by thermal matching and achieve accurate loading;

[0034] 3) A combined heating method of high-temperature environmental chamber + local flexible electric heater is proposed to apply non-uniform temperature load to the test piece. Attached Figure Description

[0035] Figure 1 Schematic diagram of tensile-shear combined loading on a wall panel at room temperature.

[0036] Figure 2 A schematic diagram showing the positional change of the connecting bolts as the test fixture expands.

[0037] Figure 3 A schematic diagram of the temperature measurement point setup, where (a) is a side view and (b) is a front view.

[0038] Figure 4 The distribution of thermal expansion stress caused by temperature distribution.

[0039] Figure 5 The simulation diagram shows the loading process, where (a) is the thermal stress distribution diagram and (b) is the step angle θ diagram.

[0040] Figure 6 Set the position map for the strain gauges.

[0041] In the figure: 1. Composite material perforated web; 2. Metal clamp; 3. Connecting bolt; 4. Electric heating blanket. Detailed Implementation

[0042] The effectiveness of this method is illustrated by taking a resin-based composite material with a perforated web and a stainless steel metal clamp and connecting bolt as an example.

[0043] The thermal expansion coefficient α of the perforated web of the composite material 试件 For a composite material with a perforated web (model 5e-6), the long side length *a* is 250 mm, and the short side length *b* is 200 mm. What is the allowable compressive stress σ of the composite material with a perforated web at an ambient temperature of 200 degrees Celsius? T 挤压 The maximum strength is 150 MPa; the thickness t of the perforated web end of the composite material is 4 mm. The coefficient of thermal expansion of the metal fixture is 13e-6. The radius r of the connecting bolt is 4 mm, and the allowable shear stress τ of the connecting bolt at an ambient temperature of 200 degrees Celsius is... T 剪切许用 The test load was 100 MPa; the diagonal tensile load F was 160,000 N; the test temperature load was achieved by heating the entire structure to 150 degrees Celsius (T1), and then heating the two short-side fixed areas to 200 degrees Celsius (T2) within 100 s using an electric heating blanket; the heating power efficiency coefficient ξ was 0.65. The uncertainty factor S due to the dispersion of the composite material was considered. F The value is 3.

[0044] First, the experimental connection scheme is given:

[0045] 1) Determine the number of connecting bolts

[0046] The number of connecting bolts n should be greater than 9, as determined by two inequalities. Example: n=9.

[0047] Number of bolts n ≥ a·F / [ ·S F ·π·r 2 ·τ T 剪切许用 ]

[0048] =250×160000 / (320×3×3.14×16×100) =8.3

[0049] Number of bolts: n ≥ a·F / [ ·S F ·2·t·r·σ T 挤压 ]

[0050] =250×160000 / (320×3×2×4×4×150) =8.7

[0051] 2) Determine the gap between the connecting bolts

[0052] Temperature change of test specimen At a temperature of 200 degrees Celsius, based on the previous steps, each metal clamp should have 9 connecting bolts. Following the bolt numbering rules, taking bolts #19 (row 1, column 9) and #99 (row 9, column 9) as examples, the clearance for bolt #19 is 0.4mm, and the clearance for bolt #99 is 0.5mm.

[0053] The distance between connecting bolts No. 19 and No. 99 and the fixing bolt:

[0054] L 19 =

[0055] L 99 =

[0056] Clearance of bolt number ij:

[0057] δ 19 = (13-5) × 10 -6 ×200×L 19 =0.4 mm

[0058] δ 99 = (13-5) × 10 -6 ×200×L 99 =0.5 mm

[0059] Next, the experimental temperature loading and measurement scheme is given:

[0060] 1) Applying a non-uniform temperature field

[0061] A flexible electric heating device is wrapped around the clamping area. The length b of the heating area of ​​the electric blanket is 200mm, the width d of the heating area is 30mm, and the thickness t of the heating area is 4mm. When the composite material web with holes is uniformly heated to 150 degrees Celsius in the environmental chamber, the electric heating device is started for 100s.

[0062] The density ρ of the perforated web of the composite material is 4000 kg / m³. 3 Given a specific heat capacity c of 5000 J / kg / K and a heating efficiency coefficient ξ = 0.65 (including heat transfer to the center), the heating power on one side is 369 watts when heating from temperature T1 = 150 degrees Celsius to temperature T2 = 200 degrees Celsius in 100 seconds. The total heating power on both sides is 738 watts. The calculation method for the heating power on one side is as follows:

[0063]

[0064] =200e-3×4e-3×30e-3×4000×5000×50 / (0.65×100) =369 watts

[0065] 2) Strain measurement point arrangement

[0066] The thermal stress distribution obtained through simulation is shown below. Figure 4 The maximum thermal stress was found to be 12 MPa. The locations and directions of the two maximum principal stresses were determined through thermo-mechanical coupling simulation, and strain gauges were used for monitoring and measurement. (See...) Figure 5 and Figure 6 strain gauge arrangement angle The angle is 50°, and strain gauges are placed at the corresponding positions.

[0067] The above steps ultimately yield the composite material perforated web tensile-shear composite thermodynamic test scheme.

Claims

1. A composite component-level tensile-shear combined thermodynamic test method for perforated webs, characterized in that, It contains two parts: Part 1: Calculation of the number of connecting bolts and the clearance between them; The number of connecting bolts is calculated using the number of connecting bolts, the length of the long side of the perforated web of the composite material, the length of the short side of the perforated web of the composite material, the radius of the connecting bolts, the end thickness of the perforated web of the composite material, the diagonal tensile load of the test, the uncertainty factor, the allowable shear stress of the connecting bolt material at the corresponding temperature, and the allowable compressive stress of the composite material of the test piece at the corresponding temperature. The connecting bolts are numbered, and the mating clearance of the connecting bolts is calculated by multiplying the difference in thermal expansion coefficients between the perforated web of the composite material and the metal clamp by the distance from the connecting bolt to the diagonal fixing bolt. Part Two: Conducting experiments on the application of non-uniform temperature fields and methods for arranging strain measurement points considering the influence of temperature.

2. The composite component-level tensile-shear combined thermodynamic test method for perforated webs according to claim 1, characterized in that, In the first part, the test system includes a composite material perforated web, metal clamps, and connecting bolts; there are eight metal clamps in total, four short sides and four long sides; they are connected end to end to form a square frame, and two square frames are joined together to hold the composite material perforated web; connecting bolts are evenly arranged on each metal clamp.

3. The composite component-level tensile-shear combined thermodynamic test method for perforated webs according to claim 2, characterized in that, In the first part, the composite material perforated web is used as the test piece, and the set of inequalities determining the number of connecting bolts is as follows: n≥ a·F / [ ·S F ·p·r 2 ·t T 剪切许用 ] n≥ a·F / [ ·S F ·2·t·r·σ T 挤压 ] Where n is the number of connecting bolts, a is the length of the long side of the composite perforated web, b is the length of the short side of the composite perforated web, r is the radius of the connecting bolts, t is the end thickness of the composite perforated web, F is the experimental diagonal tensile load, and S F τ is the uncertainty coefficient. T 剪切许用 σ is the allowable shear stress of the connecting bolt material at the corresponding temperature. T 挤压 This represents the allowable compressive stress of the composite material at the corresponding temperature.

4. The composite component-level tensile-shear combined thermodynamic test method for perforated webs according to claim 3, characterized in that, In the first part, the calculation process for the mating clearance of the connecting bolts is as follows: The connecting bolts are numbered. Four metal clamps form a rectangular boundary around the perforated web of the composite material. The connecting bolts are distributed in rows and columns on the metal clamps. Let the connecting bolt at the upper left corner of the four metal clamps be the diagonal fixing bolt, numbered 11. Taking the diagonal fixing bolt as the origin, let the connecting bolt in the i-th row and j-th column be numbered ij. When subjected to temperature load, the positions of the remaining connecting bolts deviate outward relative to the diagonal fixing bolt due to the thermal deformation of the perforated web of the composite material and the metal clamps. The deformation matching amount of the connection points of other connecting bolts is the difference in thermal expansion coefficients between the perforated web of the composite material and the metal clamps multiplied by the distance from the connecting bolt to the diagonal fixing bolt. Therefore, the inequality for determining the fitting clearance of the connecting bolts is: The distance between the j-th connecting bolt and the diagonal fixing bolt: L ij = Clearance of bolt number ij: Where, α 试件 α is the coefficient of thermal expansion of the perforated web of the composite material. 夹具 The coefficient of thermal expansion of the metal clamp is given. L represents the temperature change of the perforated web of the composite material. ij Let be the distance between bolt number ij and the diagonal fixing bolt, and n represent the total number of connecting bolts on each metal clamp.

5. The composite component-level tensile-shear combined thermodynamic test method for perforated webs according to claim 4, characterized in that, The second part is as follows: Step 1: Apply a non-uniform temperature field to the test specimen. A non-uniform temperature field is constructed by additionally heating the metal clamps to simulate the change of temperature gradient under the uniform temperature of the environmental chamber. Electric heating blankets are added inside the metal clamps at the two short sides of the perforated web of the composite material. By controlling the electric heating blankets, the change of temperature gradient between the upper and lower surfaces is simulated, so as to achieve the effect of accurately simulating the actual temperature field in the environmental chamber. The clamping position of the electric heating blankets is controlled by the temperature measurement points to control the heating parameters. The temperature measurement points are evenly distributed at the overlap of the metal clamps and the electric heating blankets. The temperature of the environmental chamber is heated so that the temperature of the entire perforated web of the composite material reaches T1. Then, the electric heating blankets at both ends start heating until the temperature of the edge of the perforated web of the composite material reaches T2. After heat transfer, equilibrium is reached, forming a temperature gradient and internal thermal stress that simulate the actual situation, and the experiment is carried out. The length of the heating area of ​​the electric blanket is the same as the short side length of the perforated web of the composite material, and its size is b; the thickness of the heating area is the same as the end thickness of the perforated web of the composite material, and its size is t; the width of the heating area is the width of the overlapping area between the metal clamp, the perforated web of the composite material, and the electric blanket, and its size is d; the density of the perforated web of the composite material is ρ, its specific heat capacity is c, and its heating efficiency coefficient is ξ. Therefore, in time... Inside, the electric heating blanket located on one short side of the test piece heats the sample from temperature T1 to temperature T2. The calculated heating power P is: Step 2: Strain Measurement Point Arrangement under the Influence of Temperature Distribution Due to the application of thermal stress, the fracture direction of the test specimen will be offset from the diagonal of the perforated web of the composite material. It is necessary to obtain the thermal stress distribution map through simulation, and obtain the location of the maximum principal stress and the crack propagation direction through thermo-mechanical coupling simulation. The angle θ between the crack propagation direction and the horizontal edge of the perforated web of the composite material is obtained. Strain gauges are set along the crack propagation direction and in combination with the location of the maximum principal stress to capture the generation of the maximum strain and the trend of crack propagation.

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