Anti-fatigue detection method for structural member made of high polymer material

Abstract

The invention discloses an anti-fatigue detection method for a structural member made of a high polymer material, and belongs to the field of material detection.The anti-fatigue detection method comprises the following steps that S1, a thermoplastic high polymer raw material for preparing the structural member is heated to be in a molten state, and a first intermediate is formed; s2, preparing a shell layer by taking polylactic acid, Y-type polyethylene glycol succinic acid, acetylsalicylic acid and a DCP catalyst as raw materials, and preparing fluorescent color developing agent microspheres by taking a high-temperature-resistant liquid fluorescent color developing agent as a core material; s3, adding fluorescent color developing agent microspheres into the first intermediate, uniformly stirring, heating, continuously stirring, uniformly mixing the color developing agent with the first intermediate after the color developing agent is released to obtain a second intermediate, and performing injection molding, molding, curing and cooling on the second intermediate to obtain a structural part sample; and S4, carrying out fatigue detection on the structural member sample by adopting a fatigue testing machine. The method solves the problems that closed cracks or internal defects are difficult to directly recognize from the inside and the initiation and expansion process of the internal cracks of the component cannot be captured at present.

Description

Technical Field

[0001] The present invention belongs to the field of material testing and relates to a method for anti-fatigue testing of structural components made of polymer materials. Background Art

[0002] In the automotive field, polymer materials are widely used in multiple key components due to their advantages such as lightweight, corrosion resistance, and easy processing. In order to ensure driving safety, when using polymers to prepare components, it is necessary to conduct anti-fatigue testing on the finished products to avoid sudden structural defects in the components.

[0003] When conducting anti-fatigue testing on polymer components, currently, color-developing penetrant is generally used for flaw detection. Defect identification is achieved through surface penetration, which is convenient for observing defects. However, this method relies on the penetration of the penetrant from the outside to the inside and can only detect cracks connected to the surface. It is very difficult to directly identify closed cracks or internal defects from the inside and cannot capture the process of crack initiation and propagation inside the component. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for anti-fatigue testing of structural components made of polymer materials, which solves the problem that when conducting anti-fatigue testing on polymer components currently, color-developing penetrant is used for flaw detection. This method relies on the penetration of the penetrant from the outside to the inside and can only detect cracks connected to the surface. It is very difficult to directly identify closed cracks or internal defects from the inside and cannot capture the process of crack initiation and propagation inside the component.

[0005] The technical solution adopted by the present invention is as follows:

[0006] A method for anti-fatigue testing of structural components made of polymer materials, comprising the following steps:

[0007] S1. Heat the thermoplastic polymer raw material for preparing the structural component to a molten state to form a first intermediate;

[0008] S2. Prepare fluorescent color-developing agent microspheres: Use polylactic acid, Y-shaped polyethylene glycol succinate, acetylsalicylic acid, and DCP catalyst as raw materials to prepare a shell layer, and use a high-temperature resistant liquid fluorescent color-developing agent as the core material to prepare fluorescent color-developing agent microspheres;

[0009] S3. At 65 - 70 °C, add the fluorescent color-developing agent microspheres to the first intermediate, stir evenly, then raise the temperature to 130 - 140 °C, continue stirring. After the color-developing agent is released, it is mixed evenly with the first intermediate to obtain a second intermediate. The second intermediate is injection-molded, formed, cured, and cooled to obtain a structural component sample; wherein, the addition amount of the fluorescent color-developing agent microspheres is within 0.5% of the mass of the first intermediate;

[0010] S4. Use a fatigue testing machine to conduct fatigue detection on the structural member sample, and observe the color development inside the member under the irradiation of the excitation light during the detection process.

[0011] When the present invention conducts anti-fatigue detection on polymer members, it utilizes an existing fatigue testing machine. However, different from the prior art, when preparing the detection sample in the present invention, a fluorescent color developer is mixed into the molten polymer material to obtain a polymer member uniformly mixed with the fluorescent color developer. When there are defects in the internal structure of the polymer member, the color developer will exhibit a color change under the excitation light, facilitating the identification of defects. The present invention develops a fluorescent color developer microsphere that can be uniformly dispersed in the polymer melt and does not significantly change the performance of the polymer member, replacing the existing color penetration agent, changing the defect display method in the anti-fatigue detection of polymer members, no longer relying on the penetration of the color penetration agent from the outside to the inside, and being able to directly identify defects from the inside, solving the problem that when conducting anti-fatigue detection on polymer members currently, using a color penetration liquid for flaw detection, this method relies on the penetration of the penetration agent from the outside to the inside, and can only detect cracks communicating with the surface, and it is difficult to directly identify closed cracks or internal defects from the inside, and unable to capture the process of crack initiation and propagation inside the member.

[0012] In the prior art, generally, the fluorescent color developer is not directly mixed into the polymer melt to participate in the preparation of the sample, mainly because it is difficult for the fluorescent color developer to be uniformly dispersed in the high-viscosity polymer melt, and the effect of defect color development cannot be achieved; based on this, the present application converts the liquid color developer into a microsphere structure, and uses the microsphere structure to achieve the uniform dispersion of the fluorescent color developer in the high-viscosity polymer melt. The principle is as follows: The shell surface of the fluorescent color developer microsphere in the present invention is smooth and has a uniform spherical structure, with low flow resistance and good fluidity. The present invention adopts the microsphere structure to utilize the good fluidity of the microspheres; in addition, the shell layer of the microspheres in the present invention is mainly composed of polylactic acid (PLA), Y-shaped polyethylene glycol succinate (YPEG-SA), acetylsalicylic acid (ASA), and DCP catalyst, where polylactic acid is the main substance. When heated to a certain temperature, polylactic acid will decompose into carbon dioxide and water, the carbon dioxide volatilizes, and the water will evaporate during the polymer injection molding and curing process, reducing the residual amount (solid content) of the shell layer in the polymer after the release of the liquid color developer, and avoiding the obvious filling of the polymer by the shell layer after rupture and affecting the mechanical properties of the polymer member sample, etc.

[0013] At present, the thermal decomposition temperature of polylactic acid is generally above 150°C, basically around 170 - 210°C. It is very difficult to maintain it around 150°C. The temperature around 170 - 210°C will affect the properties of high-molecular substances and fluorescent color-developing agents. Therefore, during the R & D process, in order to reduce the thermal decomposition temperature of the shell, Y-shaped polyethylene glycol succinate (YPEG-SA), acetylsalicylic acid (ASA) and DCP catalyst are added to the shell. While ensuring the dispersion of the microspheres in the high-molecular melt, the thermal decomposition temperature of the shell is reduced. The shell will break and partially decompose around 130 - 140°C, and the products include carbon dioxide and water, which can significantly reduce the residue of the solid matter of the shell in the high-molecular substance after the shell of the microsphere breaks, thereby reducing the influence of the shell on the high-molecular component and ensuring the effectiveness of the anti-fatigue test result.

[0014] Further, in the step S2, the mass ratio of polylactic acid, Y-shaped polyethylene glycol succinate, and acetylsalicylic acid is 8 - 9:1:2 - 3, and the addition amount of the DCP catalyst is 0.5 - 1% of the addition amount of polylactic acid.

[0015] Further, the preparation method of the fluorescent color-developing agent microspheres in the step S2 includes the following steps:

[0016] S2.1. Add Y-shaped polyethylene glycol succinate and DCP catalyst to the polylactic acid solution, mix evenly, and then carry out a three-stage temperature-raising reaction to obtain an intermediate. The three-stage temperature-raising reaction includes the following three stages:

[0017] The first stage: Raise the temperature to 160 ± 5°C and react for 30 ± 5 minutes;

[0018] The second stage: After the reaction in the first stage, continue to raise the temperature to 170 ± 5°C and react for 20 - 25 minutes;

[0019] The third stage: After the reaction in the second stage, continue to raise the temperature to 180 ± 5°C and react for 10 minutes;

[0020] S2.2. Under nitrogen protection, add acetylsalicylic acid to the intermediate and stir and react at 110 - 120°C for 1 hour to obtain a shell intermediate;

[0021] S2.3. Use the high-temperature resistant liquid fluorescent color-developing agent as the core material;

[0022] S2.4. Adopt a microfluidic chip with a channel width of 150 - 200 μm, inject the core material and the shell intermediate at a volume ratio of 1:3 - 5 to form an emulsion, and vacuum dry at 40 - 60°C for 6 - 8 hours to obtain the fluorescent color-developing agent microspheres.

[0023] Further, the surface roughness Ra of the fluorescent color-developing agent microspheres is ≤ 0.2 μm, and the compressive strength is ≥ 8 MPa.

[0024] Further, in the step S2, the mass ratio of polylactic acid, Y-shaped polyethylene glycol succinate, and acetylsalicylic acid is 9:1:2, and the addition amount of the DCP catalyst is 1% of the addition amount of polylactic acid.

[0025] Further, the high-temperature resistant liquid fluorescent color developer includes a dioctyl phthalate solution containing 0.5 - 0.6 wt% rhodamine B and 0.3 - 0.5 wt% coumarin derivative.

[0026] Further, the excitation light in the step S4 is a composite light source formed by 365 nm ultraviolet light and 532 nm green light.

[0027] Further, the thermoplastic polymer raw material for preparing the structural member includes polycarbonate or polycarbonate copolymer.

[0028] In summary, due to the adoption of the above technical solutions, the beneficial effects of the present invention are as follows:

[0029] 1. In the anti-fatigue detection method of the structural member made of the polymer material of the present invention, the liquid fluorescent color developer inside is sent to each position of the polymer material through microspheres. The microspheres are evenly distributed in the polymer material in the form of dots. After heating, the shell layer of the microspheres ruptures and decomposes, and the microspheres release the internal liquid fluorescent color developer. At this time, under the action of stirring, the liquid fluorescent color developer can form a continuous and uniform fluorescent display layer in the polymer material only through a small range of diffusion. During the anti-fatigue detection of the polymer component, with the appearance of internal defects, the fluorescent display layer can identify closed cracks or internal defects;

[0030] 2. In the present invention, Y-shaped polyethylene glycol succinate, acetylsalicylic acid, and DCP catalyst are added to the shell layer, which ensures the dispersion of the microspheres in the polymer melt and reduces the thermal decomposition temperature of the shell layer. The shell layer will rupture and partially decompose at about 130 - 140 °C, and the products include carbon dioxide and water, which can significantly reduce the residue amount of the shell layer in the polymer substance after the shell layer of the microspheres ruptures, thereby reducing the influence of the shell layer on the polymer component and ensuring the effectiveness of the anti-fatigue detection result. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required to be used in the embodiments. It should be understood that the following drawings only show some embodiments of the present invention, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other related drawings can also be obtained based on these drawings, where:

[0032] Figure 1 is the physical diagram of the second intermediate in Embodiment 2. Detailed implementation manners

[0033] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention, that is, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Usually, the components of the embodiments of the present invention described and shown in the accompanying drawings herein can be arranged and designed in various different configurations.

[0034] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed present invention, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative efforts fall within the scope of protection of the present invention.

[0035] It should be noted that relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variant thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or also includes elements inherent to such process, method, article or device. Without further limitation, the element defined by the phrase "including a..." does not exclude the existence of additional identical elements in the process, method, article or device including the said element.

[0036] The features and performance of the present invention will be further described in detail below in conjunction with the embodiments.

[0037] Embodiment 1

[0038] A method for detecting the fatigue resistance of a structural member made of a polymer material provided by a preferred embodiment of the present invention includes the following steps:

[0039] S1. Heat polycarbonate at 215-225 °C to a molten state to form a first intermediate;

[0040] S2. Prepare fluorescent chromogenic agent microspheres: Use polylactic acid, Y-shaped polyethylene glycol succinate, acetylsalicylic acid, and DCP catalyst as raw materials to prepare a shell layer, and use a high-temperature liquid fluorescent chromogenic agent as the core material to prepare fluorescent chromogenic agent microspheres;

[0041] S3. At 65 °C, add the fluorescent chromogenic agent microspheres to the first intermediate, stir evenly, then raise the temperature to 140 °C, continue stirring. After the chromogenic agent is released, mix evenly with the first intermediate to obtain the second intermediate. Inject, mold, cure, and cool the second intermediate to obtain the structural part sample; wherein, the addition amount of the fluorescent chromogenic agent microspheres is 0.5% of the mass of the first intermediate.

[0042] S4. Use a fatigue testing machine to conduct fatigue detection on the structural part sample, and observe the chromogenic situation inside the component under the irradiation of excitation light during the detection process.

[0043] In the step S2, the mass ratio of polylactic acid, Y-shaped polyethylene glycol succinate, and acetylsalicylic acid is 8:1:2, and the addition amount of the DCP catalyst is 0.5% of the addition amount of polylactic acid.

[0044] The preparation method of the fluorescent chromogenic agent microspheres in the step S2 includes the following steps:

[0045] S2.1. Add Y-shaped polyethylene glycol succinate and the DCP catalyst to the polylactic acid solution, mix evenly, and then conduct a three-stage temperature-raising reaction to obtain an intermediate. The three-stage temperature-raising reaction includes the following three stages:

[0046] The first stage: Raise the temperature to 160 ± 5 °C and react for 30 ± 5 minutes;

[0047] The second stage: After the first stage reaction ends, continue to raise the temperature to 170 ± 5 °C and react for 20 - 25 minutes;

[0048] The third stage: After the second stage reaction ends, continue to raise the temperature to 180 ± 5 °C and react for 10 minutes;

[0049] S2.2. Under nitrogen protection, add acetylsalicylic acid to the intermediate, stir and react at 110 - 120 °C for 1 hour, and then cool down to obtain the shell intermediate;

[0050] S2.3. Use the high-temperature resistant liquid fluorescent chromogenic agent as the core material;

[0051] S2.4. Adopt a microfluidic chip with a channel width of 150 - 200 μm, inject the core material and the shell intermediate in a volume ratio of 1:3 to form an emulsion, and vacuum dry at 40 - 60 °C for 6 - 8 hours to obtain the fluorescent chromogenic agent microspheres.

[0052] The surface roughness Ra of the fluorescent chromogenic agent microspheres is ≤ 0.2 μm, and the compressive strength is ≥ 8 MPa.

[0053] The high-temperature resistant liquid fluorescent chromogenic agent includes a dioctyl phthalate solution containing 0.5 - 0.6 wt% rhodamine B and 0.3 - 0.5 wt% coumarin derivative.

[0054] The excitation light in step S4 is a composite light source formed by 365 nm ultraviolet light and 532 nm green light.

[0055] Example 2

[0056] Based on Example 1, the differences in this example are as follows: In step S2, the mass ratio of polylactic acid, Y-shaped polyethylene glycol succinate, and acetylsalicylic acid is 9:1:2. The addition amount of the DCP catalyst is 1% of the addition amount of polylactic acid, and the addition amount of the fluorescent colorant microspheres is 0.3% of the mass of the first intermediate. The second intermediate obtained within the scope of this example is as Figure 1 shown, and the colorant is uniformly mixed in the polymer melt.

[0057] Example 3

[0058] Based on Example 1, the differences in this example are as follows: In step S2, the mass ratio of polylactic acid, Y-shaped polyethylene glycol succinate, and acetylsalicylic acid is 9:1:3. The addition amount of the DCP catalyst is 0.7% of the addition amount of polylactic acid, and the addition amount of the fluorescent colorant microspheres is 0.5% of the mass of the first intermediate.

[0059] Example 4

[0060] Based on Example 1, the differences in this example are as follows: In step S2, the mass ratio of polylactic acid, Y-shaped polyethylene glycol succinate, and acetylsalicylic acid is 8:1:3. The addition amount of the DCP catalyst is 0.8% of the addition amount of polylactic acid, and the addition amount of the fluorescent colorant microspheres is 0.5% of the mass of the first intermediate.

[0061] Example 5

[0062] Based on Example 2, the differences in this example are as follows: A fatigue resistance detection method for a structural member made of a polymer material provided in this example includes the following steps:

[0063] S1. Heat polycarbonate to a molten state at 215 - 225 °C to form a first intermediate;

[0064] S2. Prepare fluorescent colorant microspheres: Use polylactic acid, Y-shaped polyethylene glycol succinate, acetylsalicylic acid, and DCP catalyst as raw materials to prepare a shell layer, and use a high-temperature resistant liquid fluorescent colorant as the core material to prepare fluorescent colorant microspheres;

[0065] S3. At 70 °C, add the fluorescent colorant microspheres to the first intermediate, stir evenly, then raise the temperature to 130 °C, continue stirring. After the colorant is released, it is uniformly mixed with the first intermediate to obtain a second intermediate. Inject, mold, cure, and cool the second intermediate to obtain a structural member sample; among them, the addition amount of the fluorescent colorant microspheres is 0.3% of the mass of the first intermediate.

[0066] S4. Use a fatigue testing machine to conduct fatigue testing on the structural component sample, and observe the color development inside the component under the irradiation of the excitation light during the testing process.

[0067] Example 6

[0068] Based on Example 2, the difference from Example 2 in this example is: A method for anti-fatigue detection of a structural component made of a polymer material provided in this example includes the following steps:

[0069] S1. Heat polycarbonate to a molten state at 215 - 225 °C to form a first intermediate.

[0070] S2. Prepare fluorescent color-developing agent microspheres: Use polylactic acid, Y-shaped polyethylene glycol succinate, acetylsalicylic acid, and DCP catalyst as raw materials to prepare the shell layer, and use a high-temperature resistant liquid fluorescent color-developing agent as the core material to prepare fluorescent color-developing agent microspheres.

[0071] S3. At 70 °C, add the fluorescent color-developing agent microspheres to the first intermediate, stir evenly, then raise the temperature to 135 °C, continue stirring. After the color-developing agent is released, mix it evenly with the first intermediate to obtain a second intermediate. Inject, mold, cure, and cool the second intermediate to obtain a structural component sample; among them, the addition amount of the fluorescent color-developing agent microspheres is 0.3% of the mass of the first intermediate.

[0072] S4. Use a fatigue testing machine to conduct fatigue testing on the structural component sample, and observe the color development inside the component under the irradiation of the excitation light during the testing process.

[0073] Example 7

[0074] Based on Example 2, the difference from Example 2 in this example is: In step S2.4 of this example, a microfluidic chip with a channel width of 150 - 200 μm is used, and the core material and the shell intermediate are injected at a volume ratio of 1:4 to form an emulsion, and vacuum-dried at 40 - 60 °C for 6 - 8 hours to obtain fluorescent color-developing agent microspheres.

[0075] Example 8

[0076] Based on Example 2, the difference from Example 2 in this example is: In step S2.4 of this example, a microfluidic chip with a channel width of 150 - 200 μm is used, and the core material and the shell intermediate are injected at a volume ratio of 1:5 to form an emulsion, and vacuum-dried at 40 - 60 °C for 6 - 8 hours to obtain fluorescent color-developing agent microspheres.

[0077] Comparative Example 1

[0078] A method for anti-fatigue detection of a structural component made of a polymer material provided in this comparative example includes the following steps:

[0079] The polycarbonate is heated to a molten state at 215 - 225 °C and then injection - molded, formed, cured, and cooled to obtain a structural part sample; a liquid fluorescent color developer is sprayed on the surface layer of the sample for fatigue detection, and the display situation of the structural defects of the sample is observed. During the detection process, it is necessary to replenish the liquid at any time.

[0080] Comparative Example 2

[0081] A method for detecting the fatigue resistance of a structural part made of a polymer material provided in this comparative example includes the following steps:

[0082] S1. The polycarbonate is heated to a molten state at 215 - 225 °C to form a first intermediate;

[0083] S2. The liquid fluorescent color developer is added to the first intermediate, stirred, and then injection - molded, formed, cured, and cooled to obtain a structural part sample;

[0084] S4. A fatigue testing machine is used to perform fatigue detection on the structural part sample, and the color development situation inside the component is observed under the irradiation of excitation light during the detection process.

[0085] The liquid fluorescent color developer includes a dioctyl phthalate solution containing 0.5 - 0.6 wt% rhodamine B and 0.3 - 0.5 wt% coumarin derivative, and the addition amount of the liquid fluorescent color developer is 0.5% of the mass of the first intermediate.

[0086] Comparative Example 3

[0087] This comparative example is based on Example 2. The difference from Example 2 is that in step S2.4 of this comparative example, a microfluidic chip with a channel width of 150 - 200 μm is used, and the core material and the shell intermediate are injected at a volume ratio of 1:2 to form an emulsion, which is vacuum - dried at 40 - 60 °C for 6 - 8 hours to obtain fluorescent color developer microspheres.

[0088] The shell is too thin and is prone to premature rupture during the stirring process, prematurely releasing the fluorescent color developer and affecting the uniform dispersion of the fluorescent color developer.

[0089] Comparative Example 4

[0090] This comparative example is based on Example 2. The difference from Example 2 is that in step S2.4 of this comparative example, a microfluidic chip with a channel width of 150 - 200 μm is used, and the core material and the shell intermediate are injected at a volume ratio of 1:6 to form an emulsion, which is vacuum - dried at 40 - 60 °C for 6 - 8 hours to obtain fluorescent color developer microspheres.

[0091] Comparative Example 5

[0092] This comparative example is based on Example 2. The difference from Example 2 is that in step S2 of this comparative example, the mass ratio of polylactic acid, Y-shaped polyethylene glycol succinate, and acetylsalicylic acid is 10:1:2, the addition amount of DCP catalyst is 1% of the addition amount of polylactic acid, and the addition amount of fluorescent chromogenic agent microspheres is 0.3% of the mass of the first intermediate.

[0093] Comparative Example 6

[0094] A preparation method of fluorescent chromogenic agent microspheres provided in this comparative example includes the following steps:

[0095] S2.1. Use a polylactic acid solution as the shell layer;

[0096] S2.2. Use a high-temperature resistant liquid fluorescent chromogenic agent as the core material;

[0097] S2.4. Adopt a microfluidic chip with a channel width of 150 - 200 μm, inject the core material and the shell layer intermediate in a volume ratio of 1:3 to form an emulsion, and vacuum dry at 40 - 60 °C for 6 - 8 hours to obtain fluorescent chromogenic agent microspheres.

[0098] The high-temperature resistant liquid fluorescent chromogenic agent includes a dioctyl phthalate solution containing 0.5 - 0.6 wt% rhodamine B and 0.3 - 0.5 wt% coumarin derivative.

[0099] Comparative Example 7

[0100] A preparation method of fluorescent chromogenic agent microspheres provided in this comparative example includes the following steps:

[0101] S2.1. Add Y-shaped polyethylene glycol succinate and DCP catalyst to the polylactic acid solution, mix evenly, and then carry out a three-stage temperature-raising reaction to obtain an intermediate. The three-stage temperature-raising reaction includes the following three stages:

[0102] The first stage: Raise the temperature to 160 ± 5 °C and react for 30 ± 5 minutes;

[0103] The second stage: After the first stage reaction ends, continue to raise the temperature to 170 ± 5 °C and react for 20 - 25 minutes;

[0104] The third stage: After the second stage reaction ends, continue to raise the temperature to 180 ± 5 °C and react for 10 minutes, and then cool down to obtain the shell layer intermediate;

[0105] S2.2. Use a high-temperature resistant liquid fluorescent chromogenic agent as the core material;

[0106] S2.3. Adopt a microfluidic chip with a channel width of 150 - 200 μm, inject the core material and the shell layer intermediate in a volume ratio of 1:3 to form an emulsion, and vacuum dry at 40 - 60 °C for 6 - 8 hours to obtain fluorescent chromogenic agent microspheres.

[0107] The high-temperature resistant liquid fluorescent color developer includes a dioctyl phthalate solution containing 0.5 - 0.6 wt% rhodamine B and 0.3 - 0.5 wt% coumarin derivative;

[0108] The mass ratio of polylactic acid to Y-shaped polyethylene glycol succinate is 9:1, and the addition amount of DCP catalyst is 1% of the addition amount of polylactic acid.

[0109] Comparative Example 8

[0110] A method for preparing fluorescent color developer microspheres provided in this comparative example includes the following steps:

[0111] S2.1. Under nitrogen protection, acetylsalicylic acid is added to the polylactic acid solution, and after stirring and reacting at 110 - 120 °C for 1 hour, the temperature is lowered to obtain a shell intermediate;

[0112] S2.3. The high-temperature resistant liquid fluorescent color developer is used as the core material;

[0113] S2.4. Using a microfluidic chip with a channel width of 150 - 200 μm, the core material and the shell intermediate are injected at a volume ratio of 1:3 to form an emulsion, and vacuum dried at 40 - 60 °C for 6 - 8 hours to obtain fluorescent color developer microspheres.

[0114] The surface roughness Ra of the fluorescent color developer microspheres is ≤0.2 μm, and the compressive strength is ≥8 MPa.

[0115] The high-temperature resistant liquid fluorescent color developer includes a dioctyl phthalate solution containing 0.5 - 0.6 wt% rhodamine B and 0.3 - 0.5 wt% coumarin derivative;

[0116] The mass ratio of polylactic acid to acetylsalicylic acid is 9:2, and the addition amount of DCP catalyst is 1% of the addition amount of polylactic acid.

[0117] Comparative Example 9

[0118] This comparative example is based on Example 1. Different from Example 1, the addition amount of the fluorescent color developer microspheres in this comparative example is 0.6% of the mass of the first intermediate.

[0119] Test Example 1

[0120] Taking the structural part sample obtained by heating polycarbonate to the molten state at 215 - 225 °C and then injection molding, forming, curing, and cooling as the blank control group, the performances of the polymer components obtained in Examples 1 - 8 and Comparative Example 9 and the blank control group were detected, and the results are shown in Table 1; the detection method is the prior art.

[0121] The shape of the polycarbonate component sample is long strip-shaped, with a width of 25 mm, a length of 100 mm, and a thickness of 4 mm.

[0122] Tensile strength test: The tensile strength of the component sample is tested according to the GB / T 1040 standard;

[0123] Flexural strength test: The flexural strength of the component sample is tested according to the GB / T 9341-2008 standard;

[0124] Impact toughness test: The impact toughness of the component sample is tested according to the GB / T 1043 standard;

[0125] The average value ± deviation value is taken from 5 parallel samples in each group.

[0126] Table 1 Mechanical property test: 。

[0127] The addition of the fluorescent microspheres of the present invention has little effect on the performance of the component, and the performance fluctuation is small. As long as the addition amount of the microspheres is not excessive, it will not cause a large fluctuation in the performance of the component and basically will not affect the fatigue test results of the component; however, once the microspheres are excessive, the residual amount after the decomposition of the microspheres is large, which will first improve the performance of the component to a certain extent. As the addition amount of the microspheres increases, the performance of the component will show a downward trend. Therefore, the present invention limits the addition amount of the fluorescent chromogenic agent microspheres to achieve a low addition amount while ensuring the uniform dispersion of the fluorescent chromogenic agent.

[0128] Test Example 2

[0129] Detect the anti-fatigue test conditions of Test Examples 1-8, Comparative Example 1, and the blank control group. Use the structural component sample obtained by injection molding, forming, curing, and cooling polycarbonate after heating to the molten state at 215-225°C as the blank control group. The results are shown in Table 2;

[0130] The anti-fatigue test method is: According to GB / T 35465.3, the test stress is 10 Mpa, the test frequency is 15 Hz, and the test temperatures are 23°C and 80°C respectively. Finally, count the number of fatigue cycles after the product breaks;

[0131] Crack detection sensitivity test: During the anti-fatigue test at 23°C, detect the crack detection sensitivity of the specimens of Test Examples 1-8 and Comparative Example 1, and record the number of cycles when the color change occurs.

[0132] Table 2 Anti-fatigue test results: <![CDATA[23°C fatigue life (×10 4 times)]]> <![CDATA[80 °C fatigue life (×10 4 times)]]> <![CDATA[Crack detection sensitivity (×10 4 times) <!-- 8 -->]]> Blank control group 120-121 45-45.5 - Example 1 120-121 45-45.5 50.5-51 Example 2 120-121 45-45.5 50.5-51 Example 3 120-121 45-45.5 50.5-51 Example 4 120-121 45-45.5 50.5-51 Example 5 120-121 45-45.5 50.5-51 Example 6 120-121 45-45.5 50.5-51 Example 7 120-121 45-45.5 50.5-51 Example 8 120-121 45-45.5 50.5-51 Comparative example 1 122.0 ± 8.5 47.5 ± 4.3 100-101 。

[0133] In the present invention, the liquid fluorescent colorant comprises a dioctyl phthalate solution containing 0.5 - 0.6 wt% rhodamine B and 0.3 - 0.5 wt% coumarin derivative. The excitation light is a composite light source formed by 365 nm ultraviolet light and 532 nm green light. When there are no structural defects, the component shows a pale yellow color. When microcracks (less than 50 μm) appear, the crack area shows a spotted orange - red color, which can be observed by borrowing a high - resolution camera or a magnifying glass. When macroscopic cracks (50 - 100 μm) appear, a bright yellow or yellow - green banded area appears in the crack area and is visible to the naked eye. When cracks with a width greater than 100 μm appear, the crack area shows a blue - green color and is visible to the naked eye.

[0134] The present invention has higher sensitivity for detecting component cracks. Moreover, the fatigue detection results of the final fracture of the present invention are within the same detection range as those of components without adding fluorescent color - developing microspheres. In actual use, in order to ensure the safe use of components, generally, the performance of components is limited by a range, that is, a safety range value for component use is given. Therefore, during the performance detection process of the present invention, the recorded data are range values.

[0135] Test Example 3

[0136] Detect the dispersion uniformity of the fluorescent colorant in the polymer melt in Detection Examples 1 - 8 and Comparative Examples 2 - 5, and judge by the color - developing uniformity of the component under the action of the excitation light. The results are shown in Table 3.

[0137] Table 3 Dispersion uniformity of fluorescent color development: Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 Comparative example 2 Comparative example 3 Comparative example 4 Comparative example 5 Color rendering uniformity Uniform Uniform Uniform Uniform Uniform Uniform Uniform Uniform Non-uniform Non-uniform Uniform Uniform 。

[0138] Test Example 4

[0139] Detect the thermal decomposition temperature of the fluorescent microspheres prepared in Detection Examples 1 - 4, 7, 8 and Comparative Examples 3 - 8, the residue amount of the microsphere shell layer after rupture and decomposition in the polymer melt, and the products after the thermal decomposition of the shell layer. The addition amount of the fluorescent microspheres is 0.5% of the mass of the polymer melt. The detection methods are all existing conventional technologies. The results are shown in Table 4. The residue amount of the microsphere shell layer after rupture and decomposition in the polymer melt in the present invention refers to the solid content in the polymer substance here.

[0140] Table 4 Performance detection of fluorescent color - developing microspheres: Thermal decomposition temperature Shell residue Thermal decomposition product Example 1 130-140℃ <0.15 wt% Including carbon dioxide, water Example 2 130-140℃ <0.15 wt% Including carbon dioxide, water Example 3 130-140℃ <0.15 wt% Including carbon dioxide, water Example 4 130-140℃ <0.15 wt% Including carbon dioxide, water Example 7 130-140℃ <0.15 wt% Including carbon dioxide, water Example 8 130-140℃ <0.15 wt% Including carbon dioxide, water Comparative example 3 130-140℃ <0.15 wt% Including carbon dioxide, water Comparative example 4 130-140℃ 0.3 - 0.4wt% Including carbon dioxide, water Comparative example 5 ＞150℃ <0.15 wt% Including carbon dioxide, water Comparative example 6 ≥170℃ <0.15 wt% Including carbon dioxide, water Comparative example 7 ＞150℃ 0.3 - 0.4wt% Including carbon dioxide, water Comparative example 8 ＞150℃ 0.3 - 0.4wt% Including carbon dioxide, water 。

[0141] Combined with the data in Table 1 - Table 4, it can be seen that the present invention can improve the detection sensitivity without affecting the results of the fatigue resistance detection of polymer components, and can detect the occurrence and expansion of cracks inside the components; the present invention realizes the uniform dispersion of the liquid fluorescence colorant in the polymer melt by preparing microspheres with high dispersibility in the polymer melt. The better the dispersibility of the microspheres, the relatively lower the dosage. If the dispersibility of the microspheres is poor, there will be partial color development blind spots, and it is necessary to replenish the material in the part of the color development blind spot. The more the microspheres are used, the greater the residual amount, which will affect the performance of the polymer component; the present application realizes high dispersion and low dosage in the part of adding the fluorescence colorant, and solves the problems existing in the prior art.

[0142] The above are only the preferred embodiments of the present invention and are not intended to limit the protection scope of the present invention. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for detecting the fatigue resistance of a structural member made of a polymer material, characterized in that: It includes the following steps: S1. Heat the thermoplastic polymer raw material for preparing the structural member to a molten state to form a first intermediate; S2. Prepare fluorescent color-developing agent microspheres: Use polylactic acid, Y-shaped polyethylene glycol succinate, acetylsalicylic acid, and DCP catalyst as raw materials to prepare a shell layer, and use a high-temperature resistant liquid fluorescent color-developing agent as the core material to prepare fluorescent color-developing agent microspheres; S3. At 65 - 70 °C, add the fluorescent color-developing agent microspheres to the first intermediate, stir evenly, then raise the temperature to 130 - 140 °C, continue stirring. After the color-developing agent is released, mix it evenly with the first intermediate to obtain a second intermediate. Inject, mold, cure, and cool the second intermediate to obtain a structural member sample; wherein, the addition amount of the fluorescent color-developing agent microspheres is within 0.5% of the mass of the first intermediate; S4. Use a fatigue testing machine to conduct fatigue testing on the structural member sample, and observe the color development inside the member under the irradiation of excitation light during the testing process.

2. The anti-fatigue detection method of a structural member made of a polymer material according to claim 1, characterized in that: In the step S2, the mass ratio of polylactic acid, Y-shaped polyethylene glycol succinate, and acetylsalicylic acid is 8 - 9:1:2 - 3, and the addition amount of the DCP catalyst is 0.5 - 1% of the addition amount of polylactic acid.

3. The anti-fatigue detection method of a structural member made of a polymer material according to claim 2, characterized in that: The preparation method of the fluorescent color-developing agent microspheres in the step S2 includes the following steps: S2.

1. Add Y-shaped polyethylene glycol succinate and DCP catalyst to the polylactic acid solution, mix evenly, and then carry out a three-stage temperature-raising reaction to obtain an intermediate. The three-stage temperature-raising reaction includes the following three stages: The first stage: Raise the temperature to 160 ± 5 °C and react for 30 ± 5 minutes; The second stage: After the first stage reaction ends, continue to raise the temperature to 170 ± 5 °C and react for 20 - 25 minutes; The third stage: After the second stage reaction ends, continue to raise the temperature to 180 ± 5 °C and react for 10 minutes; S2.

2. Under nitrogen protection, add acetylsalicylic acid to the intermediate, and stir and react at 110 - 120 °C for 1 hour to obtain a shell layer intermediate; S2.

3. Use the high-temperature resistant liquid fluorescent color-developing agent as the core material; S2.

4. Use a microfluidic chip with a channel width of 150 - 200 μm, inject the core material and the shell layer intermediate at a volume ratio of 1:3 - 5 to form an emulsion, and vacuum dry it at 40 - 60 °C for 6 - 8 hours to obtain fluorescent color-developing agent microspheres.

4. The anti-fatigue detection method of a structural member made of a polymer material according to claim 3, characterized in that: The surface roughness Ra of the fluorescent color-developing agent microspheres is ≤ 0.2 μm, and the compressive strength is ≥ 8 MPa.

5. The anti-fatigue detection method for a structural member made of a polymer material according to claim 2, characterized in that: In the step S2, the mass ratio of polylactic acid, Y-shaped polyethylene glycol succinate, and acetylsalicylic acid is 9:1:2, and the addition amount of the DCP catalyst is 1% of the addition amount of polylactic acid.

6. The anti-fatigue detection method for a structural member made of a polymer material according to claim 1, characterized in that: The high-temperature resistant liquid fluorescent color-developing agent includes a dioctyl phthalate solution containing 0.5 - 0.6 wt% rhodamine B and 0.3 - 0.5 wt% coumarin derivative.

7. The anti-fatigue detection method for a structural member made of a polymer material according to claim 6, wherein: The excitation light in the step S4 is a composite light source formed by 365 nm ultraviolet light and 532 nm green light.

8. The anti-fatigue detection method for a structural member made of a polymer material according to claim 1, characterized in that: The thermoplastic polymer raw material for preparing the structural member includes polycarbonate or polycarbonate copolymer.

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