A fatigue testing method for structural parts made of polymer materials

Abstract

The present invention discloses a fatigue testing method for a structural part made of a polymer material, which belongs to the field of material testing and comprises the following steps: S1, heating a thermoplastic polymer raw material for preparing the structural part to a molten state to form a first intermediate; S2, using polylactic acid, Y-type polyethylene glycol succinic acid, acetylsalicylic acid, and a DCP catalyst as raw materials to prepare a shell layer, and using a high-temperature resistant liquid fluorescent color developer as a core material to prepare fluorescent color developer microspheres; S3, adding the fluorescent color developer microspheres to the first intermediate, stirring evenly, and then heating and continuing to stir. After the color developer is released, it is mixed evenly with the first intermediate to obtain a second intermediate, and the second intermediate is injection molded, formed, cured, and cooled to obtain a structural part sample; S4, using a fatigue testing machine to perform fatigue testing on the structural part sample. The present invention solves the current problem that it is difficult to directly identify closed cracks or internal defects from the inside, and it is impossible to capture the initiation and expansion process of cracks inside the component.

Description

Technical Field

[0001] The invention belongs to the field of material detection and relates to an anti-fatigue detection method for a structural part made of a polymer material. Background Art

[0002] In the automotive field, polymer materials are widely used in many 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, the finished products need to be subjected to fatigue resistance testing to avoid sudden structural defects in the components.

[0003] When performing fatigue testing on polymer components, color-developing penetrants are currently generally used for flaw detection. Defect identification is achieved through surface penetration, making it easier to observe 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 difficult to directly identify closed cracks or internal defects from the inside, and it is impossible to capture the initiation and expansion process of cracks inside the component. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for fatigue testing of structural parts made of polymer materials, which solves the problem that when performing fatigue testing on polymer components, a 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 difficult to directly identify closed cracks or internal defects from the inside, and it is impossible to capture the initiation and expansion process of cracks inside the component.

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

[0006] A method for detecting fatigue resistance of a structural part made of a polymer material comprises the following steps:

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

[0008] S2. Preparation of fluorescent developer microspheres: using polylactic acid, Y-type polyethylene glycol succinate, acetylsalicylic acid, and DCP catalyst as raw materials to prepare a shell layer, and using a high-temperature resistant liquid fluorescent developer as a core material to prepare fluorescent developer microspheres;

[0009] S3. Add fluorescent developer microspheres to the first intermediate at 65-70° C., stir evenly, and then heat to 130-140° C., continue stirring, and release the developer and mix evenly with the first intermediate to obtain a second intermediate. Injection mold, form, cure, and cool the second intermediate to obtain a structural component sample; wherein the amount of fluorescent developer microspheres added is within 0.5% of the mass of the first intermediate;

[0010] S4. Use a fatigue testing machine to perform fatigue testing on structural component samples. During the testing process, observe the internal color of the component under the irradiation of excitation light.

[0011] The present invention utilizes the existing fatigue testing machine when performing anti-fatigue testing on polymer components. However, the difference from the existing one is that the present invention mixes a fluorescent color developer into the polymer material in a molten state when preparing the test sample, thereby obtaining a polymer component uniformly mixed with the fluorescent color developer. When defects appear in the internal structure of the polymer component, the color developer will change color under the excitation light, which is convenient for identifying the defects. The present invention replaces the existing color penetrant by developing a fluorescent color developer microsphere that can be uniformly dispersed in the polymer melt without significantly changing the performance of the polymer component, thereby changing the defect display method of the polymer component in anti-fatigue testing. The color penetrant no longer uses the penetration effect from the outside to the inside, and can directly identify defects from the inside. This solves the problem that when performing anti-fatigue testing on polymer components, a color 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 difficult to directly identify closed cracks or internal defects from the inside, and cannot capture the initiation and expansion process of cracks inside the component.

[0012] In the prior art, fluorescent developers are generally not directly mixed into polymer melts to participate in sample preparation, mainly because fluorescent developers are difficult to disperse evenly in high-viscosity polymer melts, and the effect of defect color development cannot be achieved. Based on this, the present application converts the liquid developer into a microsphere structure, and utilizes the microsphere structure to achieve uniform dispersion of the fluorescent developer in high-viscosity polymer melts. The principle is as follows: the shell surface of the fluorescent developer microspheres in the present invention is smooth and has a uniform spherical structure, low flow resistance, and good fluidity. The microsphere structure used in the present invention utilizes the good properties of the microspheres. The shell of the microspheres of the present invention is mainly composed of polylactic acid (PLA), Y-type polyethylene glycol succinic acid (YPEG-SA), acetylsalicylic acid (ASA) and DCP catalyst, wherein polylactic acid is the main substance. When heated to a certain temperature, polylactic acid will decompose into carbon dioxide and water. The carbon dioxide will volatilize, and the water will evaporate during the polymer injection molding and curing process, thereby reducing the residual amount of the shell in the polymer (solid matter content) after the liquid developer is released, and avoiding obvious filling of the polymer after the shell is broken, thereby avoiding affecting the mechanical properties of the polymer component sample.

[0013] At present, the thermal decomposition temperature of polylactic acid is generally above 150°C, basically around 170-210°C, and it is difficult to maintain at around 150°C. The temperature around 170-210°C will affect the properties of the polymer and the fluorescent developer. Therefore, during the research and development process, the applicant added Y-type polyethylene glycol succinic acid (YPEG-SA), acetylsalicylic acid (ASA) and DCP catalyst to the shell in order to lower the thermal decomposition temperature of the shell. While ensuring the dispersibility of the microspheres in the polymer melt, the thermal decomposition temperature of the shell is lowered. The shell will break and partially decompose at around 130-140°C, and the products include carbon dioxide and water, which can significantly reduce the residual amount of shell solid matter in the polymer after the microsphere shell breaks, thereby reducing the impact of the shell on the polymer component and ensuring the validity of the anti-fatigue test results.

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

[0015] Furthermore, the method for preparing the fluorescent developer microspheres in step S2 comprises the following steps:

[0016] S2.1, adding Y-type polyethylene glycol succinic acid and DCP catalyst to the polylactic acid solution, mixing evenly, and then performing a three-stage temperature-elevated reaction to obtain an intermediate, wherein the three-stage temperature-elevated reaction includes the following three stages:

[0017] Stage 1: Heat to 160±5℃ and react for 30±5 minutes;

[0018] Stage 2: After the first stage reaction, continue to heat up to 170±5℃ and react for 20-25 minutes;

[0019] Stage 3: After the reaction in stage 2, continue heating to 180±5℃ and react for 10 minutes;

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

[0021] S2.3, using a high temperature resistant liquid fluorescent developer as the core material;

[0022] S2.4. Using 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 it at 40-60°C for 6-8 hours to obtain fluorescent developer microspheres.

[0023] Furthermore, the surface roughness of the fluorescent developer microspheres is Ra≤0.2 μm, and the compressive strength is ≥8 MPa.

[0024] Furthermore, in step S2, the mass ratio of polylactic acid, Y-type polyethylene glycol succinic acid, and acetylsalicylic acid is 9:1:2, and the amount of DCP catalyst added is 1% of the amount of polylactic acid added.

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

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

[0027] Furthermore, the thermoplastic polymer raw material for preparing the structural component includes polycarbonate or a polycarbonate copolymer.

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

[0029] 1. The present invention provides a fatigue testing method for structural components made of polymer materials. Liquid fluorescent colorants are delivered to various locations within the polymer material using microspheres. The microspheres are evenly distributed within the polymer material. Heating ruptures the microsphere shells, causing them to decompose and release the liquid fluorescent colorants. Under stirring, the liquid fluorescent colorants diffuse over a small area to form a continuous and uniform fluorescent display layer within the polymer material. During fatigue testing of polymer components, as internal defects emerge, the fluorescent display layer can identify closed cracks or internal defects.

[0030] 2. The present invention adds Y-type polyethylene glycol succinate, acetylsalicylic acid and DCP catalyst to the shell layer, which ensures the dispersibility of the microspheres in the polymer melt and reduces the thermal decomposition temperature of the shell layer. The shell layer will break and partially decompose at around 130-140°C, and the products include carbon dioxide and water. It can significantly reduce the residual amount of the microsphere shell layer in the polymer material after the shell layer breaks, thereby reducing the impact of the shell layer on the polymer component and ensuring the validity of the anti-fatigue test results. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and should not be considered as limiting the scope. A person of ordinary skill in the art can also derive other relevant drawings based on these drawings without inventive effort, among which:

[0032] Figure 1 This is a physical picture of the second intermediate of Example 2. DETAILED DESCRIPTION

[0033] In order to make the objectives, technical solutions, and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only intended to explain the present invention and are not intended to limit the present invention. That is, the embodiments described herein are only some embodiments of the present invention, not all embodiments. Generally, the components of the embodiments of the present invention described and illustrated in the drawings herein may 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 invention as claimed, but is merely intended to represent selected embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative work are within the scope of protection of the present invention.

[0035] It should be noted that relational terms such as "first" and "second" are used only 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 "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of additional identical elements in the process, method, article, or apparatus comprising the element.

[0036] The features and performance of the present invention are further described in detail below with reference to the embodiments.

[0037] Example 1

[0038] A preferred embodiment of the present invention provides a method for detecting fatigue resistance of a structural part made of a polymer material, comprising the following steps:

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

[0040] S2. Preparation of fluorescent developer microspheres: using polylactic acid, Y-type polyethylene glycol succinate, acetylsalicylic acid, and DCP catalyst as raw materials to prepare a shell layer, and using a high-temperature resistant liquid fluorescent developer as a core material to prepare fluorescent developer microspheres;

[0041] S3. Add fluorescent developer microspheres to the first intermediate at 65°C, stir evenly, and then heat to 140°C. Continue stirring to release the developer and mix evenly with the first intermediate to obtain a second intermediate. Injection mold, form, cure, and cool the second intermediate to obtain a structural component sample. The amount of fluorescent developer microspheres added is 0.5% of the mass of the first intermediate.

[0042] S4. Use a fatigue testing machine to perform fatigue testing on structural component samples. During the testing process, observe the internal color of the component under the irradiation of excitation light.

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

[0044] The method for preparing fluorescent developer microspheres in step S2 comprises the following steps:

[0045] S2.1, adding Y-type polyethylene glycol succinic acid and DCP catalyst to the polylactic acid solution, mixing evenly, and then performing a three-stage temperature-elevated reaction to obtain an intermediate, wherein the three-stage temperature-elevated reaction includes the following three stages:

[0046] Stage 1: Heat to 160±5℃ and react for 30±5 minutes;

[0047] Stage 2: After the first stage reaction, continue to heat up to 170±5℃ and react for 20-25 minutes;

[0048] Stage 3: After the reaction in stage 2, continue heating to 180±5℃ 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, then cool to obtain a shell intermediate;

[0050] S2.3, using a high temperature resistant liquid fluorescent developer as the core material;

[0051] S2.4. Using 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 to form an emulsion, and vacuum dry it at 40-60°C for 6-8 hours to obtain fluorescent developer microspheres.

[0052] The surface roughness of the fluorescent developer microspheres Ra is less than or equal to 0.2 μm, and the compressive strength is greater than or equal to 8 MPa.

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

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

[0055] Example 2

[0056] This embodiment is based on the embodiment 1, and the difference from the embodiment 1 is that in step S2, the mass ratio of polylactic acid, Y-type polyethylene glycol succinic acid, and acetylsalicylic acid is 9:1:2, the amount of DCP catalyst added is 1% of the amount of polylactic acid added, and the amount of fluorescent developer microspheres added is 0.3% of the mass of the first intermediate. The second intermediate obtained within the scope of this embodiment is as follows Figure 1 As shown, the developer is uniformly mixed in the polymer melt.

[0057] Example 3

[0058] This embodiment is based on Example 1, but differs from Example 1 in that in step S2, the mass ratio of polylactic acid, Y-type polyethylene glycol succinic acid, and acetylsalicylic acid is 9:1:3, the amount of DCP catalyst added is 0.7% of the amount of polylactic acid added, and the amount of fluorescent developer microspheres added is 0.5% of the mass of the first intermediate.

[0059] Example 4

[0060] This embodiment is based on Example 1, but differs from Example 1 in that in step S2, the mass ratio of polylactic acid, Y-type polyethylene glycol succinic acid, and acetylsalicylic acid is 8:1:3, the amount of DCP catalyst added is 0.8% of the amount of polylactic acid added, and the amount of fluorescent developer microspheres added is 0.5% of the mass of the first intermediate.

[0061] Example 5

[0062] This embodiment is based on the second embodiment, but differs from the second embodiment in that: this embodiment provides a method for detecting fatigue resistance of a structural part made of a polymer material, including the following steps:

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

[0064] S2. Preparation of fluorescent developer microspheres: using polylactic acid, Y-type polyethylene glycol succinate, acetylsalicylic acid, and DCP catalyst as raw materials to prepare a shell layer, and using a high-temperature resistant liquid fluorescent developer as a core material to prepare fluorescent developer microspheres;

[0065] S3. Add fluorescent developer microspheres to the first intermediate at 70°C, stir evenly, and then heat to 130°C. Continue stirring to release the developer and mix evenly with the first intermediate to obtain a second intermediate. Injection mold, form, cure, and cool the second intermediate to obtain a structural component sample. The amount of fluorescent developer microspheres added is 0.3% of the mass of the first intermediate.

[0066] S4. Use a fatigue testing machine to perform fatigue testing on structural component samples. During the testing process, observe the internal color of the component under the irradiation of excitation light.

[0067] Example 6

[0068] This embodiment is based on Example 2, but differs from Example 2 in that: this embodiment provides a method for detecting fatigue resistance of a structural part made of a polymer material, including the following steps:

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

[0070] S2. Preparation of fluorescent developer microspheres: using polylactic acid, Y-type polyethylene glycol succinate, acetylsalicylic acid, and DCP catalyst as raw materials to prepare a shell layer, and using a high-temperature resistant liquid fluorescent developer as a core material to prepare fluorescent developer microspheres;

[0071] S3. Add fluorescent developer microspheres to the first intermediate at 70°C, stir evenly, and then heat to 135°C. Continue stirring to release the developer and mix evenly with the first intermediate to obtain a second intermediate. Injection mold, form, cure, and cool the second intermediate to obtain a structural component sample. The amount of fluorescent developer microspheres added is 0.3% of the mass of the first intermediate.

[0072] S4. Use a fatigue testing machine to perform fatigue testing on structural component samples. During the testing process, observe the internal color of the component under the irradiation of excitation light.

[0073] Example 7

[0074] This embodiment is based on Example 2, but differs from Example 2 in that: in step S2.4 of this embodiment, 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, which is vacuum dried at 40-60°C for 6-8 hours to obtain fluorescent developer microspheres.

[0075] Example 8

[0076] This embodiment is based on Example 2, but differs from Example 2 in that: in step S2.4 of this embodiment, 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, which is vacuum dried at 40-60°C for 6-8 hours to obtain fluorescent developer microspheres.

[0077] Comparative Example 1

[0078] This comparative example provides a method for detecting fatigue resistance of a structural part made of a polymer material, comprising the following steps:

[0079] Polycarbonate is heated to a molten state at 215-225°C, then injection molded, formed, cured, and cooled to produce structural component samples. A liquid fluorescent developer is sprayed onto the surface of the sample for fatigue testing to observe any structural defects. Fluid replenishment is required throughout the testing process.

[0080] Comparative Example 2

[0081] This comparative example provides a method for detecting fatigue resistance of a structural part made of a polymer material, comprising the following steps:

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

[0083] S2. adding a liquid fluorescent developer to the first intermediate, stirring, and then performing injection molding, molding, curing, and cooling to obtain a structural component sample;

[0084] S4. Use a fatigue testing machine to perform fatigue testing on structural component samples. During the testing process, observe the internal color of the component under the irradiation of excitation light.

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

[0086] Comparative Example 3

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

[0088] If the shell is too thin, it is easy to break prematurely during the stirring process, releasing the fluorescent color developer prematurely, and affecting the dispersion uniformity of the fluorescent color developer.

[0089] Comparative Example 4

[0090] This comparative example is based on Example 2, and differs from Example 2 in that, in step S2.4 of this comparative example, a microfluidic chip is used with a channel width of 150-200 μm, 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 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-type polyethylene glycol succinic acid, and acetylsalicylic acid is 10:1:2, the amount of DCP catalyst added is 1% of the amount of polylactic acid added, and the amount of fluorescent developer microspheres added is 0.3% of the mass of the first intermediate.

[0093] Comparative Example 6

[0094] This comparative example provides a method for preparing fluorescent developer microspheres, comprising the following steps:

[0095] S2.1, using polylactic acid solution as the shell layer;

[0096] S2.2, using a high temperature resistant liquid fluorescent developer as the core material;

[0097] S2.4. Using 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 to form an emulsion, and vacuum dry it at 40-60°C for 6-8 hours to obtain fluorescent developer microspheres.

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

[0099] Comparative Example 7

[0100] This comparative example provides a method for preparing fluorescent developer microspheres, comprising the following steps:

[0101] S2.1, adding Y-type polyethylene glycol succinic acid and DCP catalyst to the polylactic acid solution, mixing evenly, and then performing a three-stage temperature-elevated reaction to obtain an intermediate, wherein the three-stage temperature-elevated reaction includes the following three stages:

[0102] Stage 1: Heat to 160±5℃ and react for 30±5 minutes;

[0103] Stage 2: After the first stage reaction, continue to heat up to 170±5℃ and react for 20-25 minutes;

[0104] Stage 3: After the reaction in stage 2, continue heating to 180±5°C, react for 10 minutes, and then cool down to obtain the shell intermediate;

[0105] S2.2, using a high temperature resistant liquid fluorescent developer as the core material;

[0106] S2.3. 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, which is vacuum-dried at 40-60°C for 6-8 hours to obtain fluorescent developer microspheres.

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

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

[0109] Comparative Example 8

[0110] This comparative example provides a method for preparing fluorescent developer microspheres, comprising the following steps:

[0111] S2.1. Under nitrogen protection, add acetylsalicylic acid to the polylactic acid solution, stir and react at 110-120°C for 1 hour, then cool to obtain a shell intermediate;

[0112] S2.3, using a high temperature resistant liquid fluorescent developer as the core material;

[0113] S2.4. Using 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 to form an emulsion, and vacuum dry it at 40-60°C for 6-8 hours to obtain fluorescent developer microspheres.

[0114] The surface roughness of the fluorescent developer microspheres Ra is less than or equal to 0.2 μm, and the compressive strength is greater than or equal to 8 MPa.

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

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

[0117] Comparative Example 9

[0118] This comparative example is based on Example 1, and differs from Example 1 in that the amount of fluorescent developer microspheres added in this comparative example is 0.6% of the mass of the first intermediate.

[0119] Test Example 1

[0120] The performance of the polymer components obtained in Examples 1-8 and Comparative Example 9 and the blank control group was tested using a structural component sample obtained by heating polycarbonate to a molten state at 215-225°C, injection molding, molding, curing, and cooling as a blank control group. The results are shown in Table 1; the detection method is the existing technology.

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

[0122] Tensile strength test: Test the tensile strength of component samples according to GB / T 1040 standard;

[0123] Bending strength test: Test the bending strength of component samples according to GB / T 9341-2008 standard;

[0124] Impact toughness test: Test the impact toughness of component samples according to GB / T 1043 standard;

[0125] The mean ± deviation value was obtained from 5 parallel samples in each group.

[0126] Table 1 Mechanical properties test:

[0127] .

[0128] The addition of fluorescent microspheres in the present invention has a minimal impact on component performance, resulting in minimal performance fluctuations. As long as the amount of microspheres added is moderate, they will not cause significant performance fluctuations and will have little impact on component fatigue testing results. However, if the amount of microspheres is excessive, the residual amount after decomposition will be large, which will initially improve component performance to a certain extent. As the amount of microspheres added increases, the component performance will show a downward trend. Therefore, the present invention limits the amount of fluorescent developer microspheres added to achieve a low addition amount while ensuring uniform dispersion of the fluorescent developer.

[0129] Test Example 2

[0130] Fatigue resistance tests were conducted on Examples 1-8, Comparative Example 1, and a blank control group. A blank control group was formed by heating polycarbonate to a molten state at 215-225° C., injection molding, forming, curing, and cooling to obtain a structural member sample. The results are shown in Table 2.

[0131] The fatigue test method is as follows: according to GB / T 35465.3, the test stress is 10Mpa, the test frequency is 15Hz, the test temperature is 23℃ and 80℃ respectively, and the number of fatigue cycles after the product breaks is finally counted;

[0132] Crack detection sensitivity test: The crack detection sensitivity of the samples of Examples 1-8 and Comparative Example 1 was tested during the fatigue resistance test at 23° C., and the number of cycles when color development and color change occurred was recorded.

[0133] Table 2 Anti-fatigue test results:

[0134] <![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 .

[0135] The liquid fluorescent developer in the present invention includes a dioctyl phthalate solution containing 0.5-0.6wt% rhodamine B and 0.3-0.5wt% coumarin derivatives, and the excitation light is a composite light source formed by 365nm ultraviolet light and 532nm green light. When there are no structural defects, the component appears light yellow. When microcracks (less than 50μm) appear, the crack area appears spotted orange-red and can be observed with a high-resolution camera or a magnifying glass; when macrocracks (50-100μm) appear, the crack area appears bright yellow or yellow-green banded area, which is visible to the naked eye; when cracks with a width greater than 100μm appear, the crack area appears blue-green and is visible to the naked eye.

[0136] The present invention has a higher sensitivity for detecting cracks in components, and the fatigue detection result of the final fracture of the present invention is within the same detection range as the fatigue detection result of the component without adding fluorescent color-developing microspheres. In actual use, in order to ensure the safe use of the component, a range is generally used to limit the performance of the component, that is, a safe range value for the use of the component is given. Therefore, during the performance detection process of the present invention, the data recorded is the range value.

[0137] Test Example 3

[0138] The dispersion uniformity of the fluorescent color developer in the polymer melt in Examples 1-8 and Comparative Examples 2-5 was tested by judging the color uniformity of the components under the action of excitation light. The results are shown in Table 3.

[0139] Table 3 Dispersion uniformity of fluorescent color development:

[0140] 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 uniformity Uniform Uniform Uniform Uniform Uniform Uniform Uniform Uniform Uneven Uneven Uniform Uniform .

[0141] Test Example 4

[0142] The thermal decomposition temperatures, the residual amount of the microsphere shell after rupture and decomposition in the polymer melt, and the products of the shell thermal decomposition of the fluorescent microspheres prepared in Examples 1-4, 7, and 8, and Comparative Examples 3-8 were measured. The fluorescent microspheres were added in an amount of 0.5% by mass of the polymer melt. The measurement methods were all conventional. The results are shown in Table 4. The residual amount of the microsphere shell after rupture and decomposition in the polymer melt refers to the solid content of the polymer.

[0143] Table 4 Performance test of fluorescent microspheres:

[0144] Thermal decomposition temperature Shell residue Thermal decomposition products 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 .

[0145] Combined with the data in Tables 1 to 4, it can be seen that the present invention can improve the detection sensitivity without affecting the results of the anti-fatigue test of the polymer component, and can detect the occurrence and expansion of cracks inside the component; the present invention prepares microspheres with high dispersibility in the polymer melt to achieve uniform dispersion of the liquid fluorescent color developer in the polymer melt. The better the dispersibility of the microspheres, the lower the dosage will be. If the dispersibility of the microspheres is poor, some color blind areas will appear, and the color blind areas will need to be supplemented. The more microspheres are used, the greater the residual amount, which will affect the performance of the polymer component; the present application achieves high dispersion and low dosage in the part of adding the fluorescent color developer, which solves the problems existing in the prior art.

[0146] The above description is only a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions and improvements made by any technician familiar with the field within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for detecting fatigue resistance of a structural part made of a polymer material, characterized by: The following steps are involved: S1. Heating a thermoplastic polymer raw material for preparing a structural part to a molten state to form a first intermediate; S2. Preparation of fluorescent developer microspheres: using polylactic acid, Y-type polyethylene glycol succinate, acetylsalicylic acid, and DCP catalyst as raw materials to prepare a shell layer, and using a high-temperature resistant liquid fluorescent developer as a core material to prepare fluorescent developer microspheres; S3. Add fluorescent developer microspheres to the first intermediate at 65-70° C., stir evenly, and then heat to 130-140° C., continue stirring, and release the developer and mix evenly with the first intermediate to obtain a second intermediate. Injection mold, form, cure, and cool the second intermediate to obtain a structural component sample; wherein the amount of fluorescent developer microspheres added is within 0.5% of the mass of the first intermediate; S4. Use a fatigue testing machine to perform fatigue testing on structural component samples. During the testing process, observe the internal color of the component under the irradiation of excitation light; In step S2, the mass ratio of polylactic acid, Y-type polyethylene glycol succinic acid, and acetylsalicylic acid is 8-9:1:2-3, and the amount of DCP catalyst added is 0.5-1% of the amount of polylactic acid added; The method for preparing fluorescent developer microspheres in step S2 comprises the following steps: S2.1, adding Y-type polyethylene glycol succinic acid and DCP catalyst to the polylactic acid solution, mixing evenly, and then performing a three-stage temperature-elevated reaction to obtain an intermediate, wherein the three-stage temperature-elevated reaction includes the following three stages: Stage 1: Heat to 160±5℃ and react for 30±5 minutes; Stage 2: After the first stage reaction, continue to heat up to 170±5℃ and react for 20-25 minutes; Stage 3: After the reaction in stage 2, continue heating to 180±5℃ and react for 10 minutes; S2.

2. Under nitrogen protection, add acetylsalicylic acid to the intermediate and stir the reaction at 110-120°C for 1 hour to obtain a shell intermediate; S2.3, using a high temperature resistant liquid fluorescent developer as the core material; S2.

4. Using 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 it at 40-60°C for 6-8 hours to obtain fluorescent developer microspheres.

2. The fatigue resistance testing method for a structural part made of a polymer material according to claim 1, characterized in that: The surface roughness of the fluorescent developer microspheres Ra is less than or equal to 0.2 μm, and the compressive strength is greater than or equal to 8 MPa.

3. The fatigue resistance testing method for a structural part made of a polymer material according to claim 1, characterized in that: In step S2, the mass ratio of polylactic acid, Y-type polyethylene glycol succinic acid, and acetylsalicylic acid is 9:1:2, and the amount of DCP catalyst added is 1% of the amount of polylactic acid added.

4. The fatigue resistance testing method for a structural part made of a polymer material according to claim 1, characterized in that: The high-temperature resistant liquid fluorescent developer comprises a dioctyl phthalate solution containing 0.5-0.6 wt % of rhodamine B and 0.3-0.5 wt % of a coumarin derivative.

5. The fatigue resistance testing method for a structural part made of a polymer material according to claim 4, characterized in that: The excitation light in step S4 is a composite light source formed by 365 nm ultraviolet light and 532 nm green light.

6. The fatigue resistance testing method for a structural part made of a polymer material according to claim 1, characterized in that: The thermoplastic polymer raw material for preparing the structural component includes polycarbonate or polycarbonate copolymer.

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