A simple method to judge the failure of boron fiber

Abstract

The present invention relates to the field of ceramic fibers and non-metallic elements, and specifically to a simple method for judging the failure of boron fibers. Boron fibers are prepared into a sample to be tested with a length of 20 cm and a test area of ​​25 mm. The boron fiber tensile specimen is stretched at a tensile speed of 1 mm / min using a universal mechanical testing machine to obtain stress-strain data. A corresponding differential curve is made according to the stress-strain data. By comparing the initial stable ordinate value (elastic modulus value) of the stress-strain differential curve with the initial stable ordinate value of the stress-strain differential curve of a boron fiber with good mechanical properties and no defects, it is determined whether the fiber has defects before stretching. The strain value at which the boron fiber undergoes major failure is determined based on the position of the ordinate mutation of the stress-strain differential curve, and the strength of the fiber is predicted based on the degree of ordinate fluctuation and the frequency of fluctuation in the equal deformation area in the stable stage of the stress-strain differential curve.

Description

Technical Field

[0001] The invention relates to the field of ceramic fibers and non-metallic elements, and in particular to a simple method for determining the failure of boron fibers. Background Art

[0002] Boron (B) fiber has a high elastic modulus (approximately 400 GPa), low average density, high strength, high temperature resistance, corrosion resistance, and excellent insulation properties. When prepared into composite materials, it exhibits good wettability with metals and low reactivity. Consequently, continuous B fiber-reinforced metal-matrix composites exhibit excellent performance, particularly with aluminum and magnesium alloys. Currently, boron fiber has been prepared into composite materials with metals, plastics, and ceramics for applications in aerospace, chemical, and military industries.

[0003] The axial tensile properties of boron fibers play an important role in the mechanical properties of composite materials. Examining the fracture morphology of boron fibers helps to understand the failure location and mode of boron fibers, and thus, it is possible to propose methods for optimizing and improving the preparation of boron fibers. There are two main types of boron fiber tensile fractures: splashing type and retention type. Among them: splashing type fractures usually correspond to boron fibers with medium to high tensile strength, but splashing fractures are difficult to provide failure characteristics of boron fibers. Retention type fractures usually correspond to fibers with extremely low strength, and most of these fibers have obvious defects on the surface and inside. Therefore, if you want to understand the fracture characteristics of medium to high strength fibers, and whether there are subtle defects in medium to high strength fibers, it is impossible to analyze them through the fracture of boron fibers.

[0004] Therefore, how to analyze the fracture failure mode of boron fiber through other methods will help to understand the failure process of boron fiber and improve the preparation process of boron fiber. Summary of the Invention

[0005] The purpose of the present invention is to provide a simple method for judging the failure of boron fibers, and to improve the preparation method of boron fibers by analyzing the fracture modes and failure causes of boron fibers and other brittle fibers.

[0006] The technical solution of the present invention is:

[0007] A simple method for judging the failure of boron fiber, the specific steps are as follows:

[0008] Step 1: Use acrylic adhesive to bond the boron fibers onto clean white paper at equal intervals and cut them into single fiber tensile specimens with a gauge length of 25 mm.

[0009] Step 2: Measure the gauge diameter of the single fiber tensile specimen and stretch the boron fiber using a high-precision universal mechanical testing machine with an accuracy level greater than 0.5. The tensile rate of the universal mechanical testing machine is 0.5 to 1.5 mm / min to obtain stress-strain tensile test data.

[0010] Step 3: Differentiate the obtained tensile test data and make a corresponding differential curve, and smooth the obtained differential curve to obtain a smooth curve of the differential curve;

[0011] Step 4: Determine the elastic modulus based on the differential smooth curve and compare it with the elastic modulus of a standard boron fiber with excellent performance to determine whether the boron fiber is damaged before stretching;

[0012] Step 5: Determine the deformation at which the main failure of the boron fiber occurs based on the tensile differential curve of the boron fiber;

[0013] Step 6: Predict whether the fiber has good tensile strength based on the peak fluctuation degree of the boron fiber tensile differential curve after stabilization.

[0014] In the simple method for determining boron fiber failure, in step 1, the length of each section of boron fiber is 20 cm ± 2 cm, and the clamping ends are symmetrical about the middle position of the boron fiber test portion.

[0015] The simple method for judging the failure of the boron fiber is as follows: in step 1, an acrylic adhesive is evenly applied on a paper sheet, and the paper sheet is compacted so that the paper sheet and the adhesive can fully wrap the clamping end of the boron fiber. After the clamping end of the boron fiber is wrapped, it is placed in an oven for curing at a temperature of 60 to 80° C. and a curing time of 10 to 20 minutes.

[0016] The simple method for determining whether the boron fiber has failed is as follows: in step 2, when performing the tensile test, the tensile direction is as parallel as possible to the axial direction of the boron fiber, ensuring that the angle is less than 1°.

[0017] The simple method for judging the failure of the boron fiber is as follows: in step 2, the fiber is surrounded by a sample bag during the stretching process, and after the fiber breaks, the splashed fiber is collected to judge whether the boron fiber has an initial fracture.

[0018] In the simple method for determining the failure of boron fiber, in step 3, the differential curve is smoothed by the adjacent average method, and the window points of the adjacent average method are 10 to 15; if the curve fluctuates greatly, the number of points can be increased as appropriate.

[0019] The simple method for judging the failure of the boron fiber is as follows: in step 3, a stress-strain differential curve is drawn using a differential formula according to the stress-strain tensile test data. The differential formula is:

[0020] Δy=F′(X)ΔX

[0021] In the formula, Δy represents a small variable of stress, with the unit of MPa; Δx represents a small variable of strain, with the unit of 100%.

[0022] In the simple method for determining the failure of boron fiber, in step 3, ensure that the X value variable of the tensile data is not equal to 0 before performing differentiation.

[0023] The simple method for judging the failure of the boron fiber is as follows: in step 3, the obtained boron fiber differential curve is compared with the standard boron fiber differential curve:

[0024] (1) Compare the F′(X) value of the differential curve after stabilization with the F′(X) value of the intact boron fiber to determine whether the boron fiber has damage or defects before stretching;

[0025] (2) The strength of the fiber is predicted based on the fluctuation degree and frequency of F′(X) per unit deformation after stabilization. The greater the fluctuation frequency of F′(X), the greater the fluctuation degree and the higher the strength.

[0026] (3) According to the decrease of F′(X) value in the differential curve, it is determined at what deformation amount the boron fiber will fail.

[0027] The design concept of the present invention is:

[0028] The present invention obtains the instantaneous rate of change of stress of the boron fiber at a certain strain position by differential processing of the boron fiber tensile curve, so that the details of stress changes that cannot be observed on the stress-strain curve can be observed. The numerical value of F'(X) reflects the elastic modulus of the boron fiber at a specific strain position. The degree of fluctuation of F'(X) reflects the strain resistance of the boron fiber, and the performance of the boron fiber can be roughly predicted. The initial stable value of F'(X) (i.e., the elastic modulus) can be used to determine whether the fiber is damaged. According to the decrease of F'(X) in the later stage of stretching, it can be determined how much deformation of the fiber will cause irreversible failure.

[0029] The advantages and beneficial effects obtained by the present invention are as follows:

[0030] 1. The present invention can determine whether the boron fiber is damaged or defective during the manufacturing process through the stress-strain differential curve of the boron fiber.

[0031] 2. The present invention can determine the deformation amount at which serious failure of the boron fiber occurs during the stretching process through the stress-strain curve of the boron fiber.

[0032] 3. If the stretching is interrupted due to loose fiber support or instrument failure during the stretching process, the present invention can predict the strength of the fiber by comparing the fluctuation degree and fluctuation frequency of the local F′(X) of the differential curve of other boron fibers. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 .Schematic diagram of the preparation process of boron fiber tensile specimens.

[0034] Figure 2 Differential curve of high-strength boron fiber. In the figure, the horizontal axis X represents the strain (unit: 100%), and the vertical axis F'(X) represents the stress derivative (i.e., elastic modulus).

[0035] Figure 3 Differential curve of medium-strength boron fiber. In the figure, the horizontal axis X represents the strain (unit: 100%), and the vertical axis F'(X) represents the stress derivative (i.e., elastic modulus).

[0036] Figure 4 Differential curve of low-strength boron fiber. In the figure, the horizontal axis X represents the strain (unit: 100%), and the vertical axis F'(X) represents the stress derivative (i.e., elastic modulus).

[0037] Figure 5 .Fracture morphology of retained boron fiber. DETAILED DESCRIPTION

[0038] In a specific implementation process, the present invention prepares boron fiber into a boron fiber tensile specimen, stretches it at a tensile speed of 1 mm / min using a universal mechanical testing machine, and obtains stress-strain data. A corresponding differential curve is made based on the stress-strain data, and a stress-strain differential curve is compared with the initial stable ordinate value (elastic modulus value) of the stress-strain differential curve and a boron fiber with good mechanical properties and no defects. It is judged whether the fiber has defects before stretching. The strain amount of the boron fiber that has undergone major failure is determined based on the position of the ordinate mutation of the stress-strain differential curve. The strength of the fiber is predicted based on the ordinate fluctuation frequency and degree of fluctuation of the equal deformation amount area in the stable stage of the stress-strain differential curve.

[0039] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are fully described below. If there are any specific conditions not specified in the embodiments, they shall be carried out in accordance with conventional conditions and manufacturer's recommendations.

[0040] Example 1

[0041] In this embodiment, a specific method for determining the failure type and failure mode of boron fiber is as follows:

[0042] like Figure 1 As shown, first, use double-sided tape to secure the ends of the boron fiber to equally spaced clean white paper. Each section of boron fiber is approximately 20 cm long, and the boron fibers are arranged to maintain a gauge length of 25 mm, with the clamping ends symmetrically positioned about the center of the boron fiber test area. Acrylic adhesive is then evenly applied to the paper and compacted to ensure that the paper and adhesive fully encapsulate the clamping ends of the boron fiber. After the wrapped ends are securely attached, they are placed in an oven for curing at 60-80°C for 10-20 minutes to form a boron fiber tensile specimen.

[0043] Take a boron fiber tensile specimen and measure the diameter of the boron fiber at five locations within the gauge length of the boron fiber using a lever micrometer. Take the average value. During the measurement process, avoid damaging the boron fiber surface with the micrometer or scratching it due to external factors.

[0044] After measuring the diameter of the boron fiber tensile specimen, the boron fiber was subjected to tensile testing using a universal mechanical testing machine. During testing, the tensile direction was maintained parallel to the boron fiber axis, with an angle of less than 1°. The universal mechanical testing machine has a maximum test force of 200N, a tensile rate of 1mm / min, and an accuracy level of 0.5. During the tensile process, the fiber was surrounded by a sample bag. After the fiber broke, the fiber splash was collected to determine whether the boron fiber had an initial fracture.

[0045] Before performing differentiation, ensure that the X value variable of the stretching data is not equal to 0, otherwise the calculation cannot be performed (the improvement of the accuracy of the universal mechanical testing machine can avoid this problem). Figure 2 As shown in the figure, a stress-strain differential curve is drawn based on the tensile fracture curve of the boron fiber using the differential formula. The differential formula is:

[0046] Δy=F′(X)ΔX

[0047] In the formula, Δy = 340.339 MPa; Δx = 0.001; fiber elastic modulus E = F′(X) ≈ 340 GPa.

[0048] Comparing the F'(X) value obtained after the fiber differential curve stabilized with the measured elastic modulus of the high-performance fiber (310-340 GPa) confirmed that the fiber was defect-free before stretching. The fluctuations in the F'(X) value indicate that the fiber has high strength. The actual measured tensile strength of the fiber is 3346 MPa, which is a relatively accurate prediction. The F'(X) value in the differential curve remains relatively stable, indicating that the fiber broke directly in the late stage of stretching.

[0049] Example 2

[0050] In this embodiment, a specific method for determining the failure type and failure mode of boron fiber is as follows:

[0051] like Figure 1 As shown, first, use double-sided tape to secure the ends of the boron fiber to equally spaced, clean, white paper. Each section of boron fiber is approximately 20 cm long, arranged to maintain a gauge length of 25 mm, and the clamping ends are symmetrical about the center of the boron fiber test area. Then, apply acrylic adhesive evenly to the paper and compact it until the paper and adhesive fully encapsulate the clamping ends of the boron fiber. After the wrapped ends are securely attached, place them in an oven for curing at 60-80°C for 10-20 minutes.

[0052] Take a boron fiber tensile specimen and measure the diameter of the boron fiber at five locations within the gauge length of the boron fiber using a lever micrometer. Take the average value. During the measurement process, avoid damaging the boron fiber surface with the micrometer or scratching it due to external factors.

[0053] After measuring the diameter of the boron fiber tensile specimen, the boron fiber was subjected to tensile testing using a universal mechanical testing machine. During testing, the tensile direction was maintained parallel to the boron fiber axis, with an angle of less than 1°. The universal mechanical testing machine has a maximum test force of 200N, a tensile rate of 1mm / min, and an accuracy level of 0.5. During the tensile process, the fiber was surrounded by a sample bag. After the fiber broke, the fiber splash was collected to determine whether the boron fiber had an initial fracture.

[0054] Before performing differentiation, ensure that the X value variable of the stretching data is not equal to 0, otherwise the calculation cannot be performed (the accuracy of the universal mechanical testing machine can meet this requirement). Figure 3 As shown in the figure, a stress-strain differential curve is drawn based on the tensile fracture curve of the boron fiber using the differential formula. The differential formula is:

[0055] Δy=F′(X)ΔX

[0056] In the formula, Δy = 334.156 MPa; Δx = 0.001; fiber elastic modulus E = F′(X) ≈ 334 GPa.

[0057] Comparing the F'(X) value of the fiber's stabilized differential curve with the measured elastic modulus of high-performance fibers (310-340 GPa) confirmed that the fiber was defect-free before stretching. The fluctuations in the F'(X) value suggest the fiber may have high strength, with a measured strength of 2477 MPa. The F'(X) value in the differential curve suddenly drops at 0.64% deformation, indicating significant fiber damage at this deformation location and accelerated fiber breakage.

[0058] Example 3

[0059] In this embodiment, a specific method for determining the failure type and failure mode of boron fiber is as follows:

[0060] like Figure 1 As shown, first, use double-sided tape to secure the ends of the boron fiber to equally spaced, clean, white paper. Each section of boron fiber is approximately 20 cm long, arranged to maintain a gauge length of 25 mm, and the clamping ends are symmetrical about the center of the boron fiber test area. Then, apply acrylic adhesive evenly to the paper and compact it until the paper and adhesive fully encapsulate the clamping ends of the boron fiber. After the wrapped ends are securely attached, place them in an oven for curing at 60-80°C for 10-20 minutes.

[0061] Take a boron fiber tensile specimen and measure the diameter of the boron fiber at five locations within the gauge length of the boron fiber using a lever micrometer. Take the average value. During the measurement process, avoid damaging the boron fiber surface with the micrometer or scratching it due to external factors.

[0062] After measuring the diameter of the boron fiber tensile specimen, the boron fiber was subjected to tensile testing using a universal mechanical testing machine. During testing, the tensile direction was maintained parallel to the boron fiber axis, with an angle of less than 1°. The universal mechanical testing machine has a maximum test force of 200N, a tensile rate of 1mm / min, and an accuracy level of 0.5. During the tensile process, the fiber was surrounded by a sample bag. After the fiber broke, the fiber splash was collected to determine whether the boron fiber had an initial fracture.

[0063] Before performing differentiation, ensure that the X value variable of the stretching data is not equal to 0, otherwise the calculation cannot be performed (the accuracy of the universal mechanical testing machine can meet this requirement). Figure 4 As shown in the figure, a stress-strain differential curve is drawn based on the tensile fracture curve of the boron fiber using the differential formula. The differential formula is:

[0064] Δy=F′(X)ΔX

[0065] In the formula, Δy = 286.431 MPa; Δx = 0.001; fiber elastic modulus E = F′(X) ≈ 286 GPa.

[0066] The F'(X) value after the fiber differential curve is stabilized is compared with the elastic modulus of the high-performance fiber (310-340 GPa) that has been measured to confirm that the fiber has obvious failure before stretching. Figure 5 As shown, the retained tensile fracture of this fiber demonstrates that the fiber splits before stretching, indicating that the differential curve accurately predicts this. The minimal fluctuation in the F′(X) value indicates low fiber strength, with the measured strength being 1511 MPa, demonstrating a relatively accurate prediction. The relatively stable F′(X) value in the differential curve indicates that the fiber breaks directly in the later stages of stretching.

Claims

1. A simple method for judging the failure of boron fiber, characterized in that: The specific steps are: Step 1: Use acrylic adhesive to bond the boron fibers onto clean white paper at equal intervals and cut them into single fiber tensile specimens with a gauge length of 25 mm. Step 2: Measure the gauge diameter of the single fiber tensile specimen and stretch the boron fiber using a high-precision universal mechanical testing machine with an accuracy level greater than 0.

5. The tensile rate of the universal mechanical testing machine is 0.5 to 1.5 mm / min to obtain stress-strain tensile test data. Step 3: Differentiate the obtained tensile test data and make a corresponding differential curve, and smooth the obtained differential curve to obtain a smooth curve of the differential curve; the abscissa X in the differential curve represents strain, and the ordinate F'(X) represents stress derivative; Step 4: Determine the elastic modulus based on the differential smooth curve and compare it with the elastic modulus of a standard boron fiber with excellent performance to determine whether the boron fiber is damaged before stretching; Step 5: Determine the deformation at which the main failure of the boron fiber occurs based on the tensile differential curve of the boron fiber; Step 6: Predict whether the fiber has good tensile strength based on the peak fluctuation degree of the boron fiber tensile differential curve after stabilization.

2. The simple method for determining boron fiber failure according to claim 1, characterized in that: In step 1, the length of each section of boron fiber is 20 cm ± 2 cm, and the clamping ends are symmetrical about the middle position of the boron fiber test part.

3. The simple method for determining boron fiber failure according to claim 1, wherein: In step 1, the acrylic adhesive is evenly applied on the paper sheet, and the paper sheet is compacted so that the paper sheet and the adhesive can fully wrap the boron fiber clamping end. After the boron fiber clamping end is wrapped, it is placed in an oven for curing at a curing temperature of 60 to 80° C. and a time of 10 to 20 minutes.

4. The simple method for determining boron fiber failure according to claim 1, wherein: In step 2, when performing the tensile test, the tensile direction is as parallel to the axial direction of the boron fiber as possible, ensuring that the angle is less than 1°.

5. The simple method for determining boron fiber failure according to claim 1, wherein: In step 2, the fiber is surrounded by a sample bag during the stretching process, and the splashed fiber is collected after the fiber breaks to determine whether the boron fiber is the initial fracture.

6. The simple method for determining boron fiber failure according to claim 1, wherein: In step 3, the differential curve is smoothed by the adjacent averaging method, and the window points of the adjacent averaging method are 10 to 15. If the curve fluctuates greatly, the number of points can be increased as appropriate.

7. The simple method for determining boron fiber failure according to claim 1, characterized in that: In step 3, a stress-strain differential curve is drawn based on the stress-strain tensile test data using the differential formula. The differential formula is: Δy=F'(X)ΔX In the formula, Δy represents a small variable of stress, with the unit of MPa; Δx represents a small variable of strain, with the unit of 100%.

8. The simple method for determining boron fiber failure according to claim 7, characterized in that: In step 3, make sure the X-value variable of the stretched data is not equal to 0 before performing differentiation.

9. The simple method for determining boron fiber failure according to claim 7, wherein: In step 4, the obtained boron fiber differential curve is compared with the standard boron fiber differential curve: (1) Compare the F'(X) value of the differential curve after stabilization with the F'(X) value of the intact boron fiber to determine whether the boron fiber has damage or defects before stretching; (2) The strength of the fiber is predicted based on the fluctuation degree and frequency of F'(X) per unit deformation after stabilization. The greater the fluctuation frequency of F'(X), the greater the fluctuation degree and the higher the strength; (3) According to the decrease of F'(X) value in the differential curve, it is determined at what deformation amount the boron fiber will fail.

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