A method for determining the tensile fracture type and fracture mode of silicon carbide fiber reinforced titanium matrix composites

Abstract

The present invention relates to the field of silicon carbide fiber reinforced titanium-based composite materials, in particular to a silicon carbide fiber reinforced titanium-based composite material (SiC f / Ti) tensile fracture type and fracture mode judgment method. f The Ti / Ti composite material specimens were machined into standard rod-shaped tensile specimens with an L=21 mm diameter, and the surface of the specimens was ensured to be free of scratches. Stress-strain data were obtained using a universal mechanical testing machine at a tensile rate of 1 mm / min, and the corresponding differential curve was generated using the stress-strain data. Whether the F'(X) value decreased in the later stages of the curve determined whether the composite material fracture model was a full load model (GLS) or a partial load model (LLS). By comparing the F'(X) value with the elastic modulus of the intact specimen, it was determined whether the composite material was uncompacted and had major defects before stretching. The later decrease in the F'(X) value determined the amount of deformation at which fiber fracture would occur in the composite material.

Description

Technical Field

[0001] The present invention relates to the field of silicon carbide fiber reinforced titanium-based composite materials, in particular to a silicon carbide fiber reinforced titanium-based composite material (SiC f / Ti) tensile fracture type and fracture mode determination method. Background Art

[0002] Silicon carbide fiber reinforced titanium matrix composites (SiC f Ti / Ti is a lightweight, high-strength material with excellent fatigue resistance, corrosion resistance, and high-temperature resistance, and holds broad application prospects in the aerospace field. The type and mode of fracture of composite materials during tension significantly impacts their performance. Failure models for materials include the local load model (LLS) and the global load model (GLS). The primary difference between these two models lies in whether fiber fracture affects adjacent fibers. Currently, the most convenient method for determining this model is through SEM morphology of the fracture surface. The failure mode of composite materials is typically predicted by observing the primary fracture surface morphology, but this method cannot determine the strain at which significant failure occurs. Failure analysis, particularly regarding composite material improvement, is hampered by the inability to determine the strain at which primary failure occurs. Furthermore, after tensioning, composite performance can be significantly lower than expected experimentally. To ensure that this is not due to defects in the material during preparation, a common approach is to perform SEM observations of multiple fiber cross sections and morphologies, predicting the presence of voids, surface cracks, and fiber breakage. However, this method is generally time-consuming.

[0003] In summary, SEM observation is generally an effective method for determining the fracture type and mode of a material. However, this method requires rigorous sample pretreatment. Furthermore, the sample preparation process for samples requiring grinding and polishing is more cumbersome, and there is also a risk of failure during sample preparation.

[0004] Therefore, how to conveniently determine the fracture type and fracture mode of composite materials through other means will help to more efficiently guide and improve the design of composite materials. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for determining the tensile fracture type and fracture mode of silicon carbide fiber reinforced titanium-based composite materials, so as to solve the problems in the prior art such as the strict pretreatment requirements and the complicated treatment process during SEM observation, and can be used to realize the improved design of silicon carbide fiber reinforced titanium-based composite materials.

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

[0007] A method for determining the tensile fracture type and fracture mode of a silicon carbide fiber reinforced titanium-based composite material, comprising the following steps:

[0008] Step 1: SiC f / Ti composite materials are processed into Standard rod-shaped tensile specimen with L=21mm and smooth surface;

[0009] Step 2: The prepared tensile specimen is tested for its actual average diameter and actual gauge length using a vernier caliper; the measured corresponding parameters are input into the testing system, and the prepared tensile specimen is tested for tensile properties using a universal mechanical testing machine to obtain a stress-strain curve;

[0010] Step 3: Differentiate the obtained tensile test data and make a corresponding differential curve, and smooth the obtained differential curve to remove the stray peak signal;

[0011] Step 4: Determine whether the F'(X) value of the differential curve decreases in the later stage and whether the SiC f / Ti composite fracture model is full load model (GLS) or local load model (LLS);

[0012] Step 5: According to SiC f The F'(X) value of the differential curve of the / Ti composite material decreases in the later period, which determines the amount of deformation at which the fiber fracture of the composite material begins;

[0013] Step 6: According to SiC f The F'(X) value of the differential curve of the SiC / Ti composite material at the stable position is compared with the F'(X) value of the differential curve of the intact tensile specimen (elastic modulus). f / Ti composites before stretching to determine whether they are uncompacted and have large-size defects.

[0014] The method for determining the tensile fracture type and fracture mode of the silicon carbide fiber reinforced titanium-based composite material, in step 1, SiC f The / Ti composite material is a SiC fiber reinforced Ti-based alloy or a Ti-Al series intermetallic compound, and the volume fraction of the SiC fiber is 25-80%.

[0015] The method for determining the tensile fracture type and fracture mode of the silicon carbide fiber reinforced titanium-based composite material is as follows: in step 2, when performing the tensile performance test, the stretching direction is as parallel to the fiber axis as possible, ensuring that the angle is less than 1°, and the stretching rate is 0.5-1.5 mm / min.

[0016] In the method for determining the tensile fracture type and fracture mode of the silicon carbide fiber reinforced titanium-based composite material, in step 2, in order to ensure the accuracy of the stress-strain curve tested, a mechanical extensometer is added to the tensile specimen tested at room temperature, and a laser extensometer is added to the tensile specimen tested at high temperature.

[0017] In the method for determining the tensile fracture type and fracture mode of the silicon carbide fiber reinforced titanium-based composite material, in step 3, the obtained stress-strain data is obtained by a differential formula to obtain a corresponding differential curve graph, based on the differential formula: Δy = F'(X)ΔX; in the formula, Δy represents a small stress variable, unit: MPa; Δx represents a small strain variable, unit: 100%.

[0018] The design concept of the present invention is:

[0019] The present invention is to SiC f Differentiation of the tensile curve of the Ti / Ti composite material yields the instantaneous rate of change of stress at a certain strain position, allowing for the observation of stress variation details that are not observable on the stress-strain curve. The F'(X) value reflects the elastic modulus of the composite material at a specific strain position. Whether the composite material's fracture model is a full load (GLS) model or a local load (LLS) model can be quickly determined based on whether F'(X) decreases in the later stages of the differential curve. Whether the composite material is damaged can be determined based on the initial stable value of F'(X) (i.e., the elastic modulus). Based on the decrease in F'(X) in the later stages of tension, it can be determined at what deformation level the composite material will experience fiber fracture.

[0020] The advantages and beneficial effects obtained by the present invention are as follows:

[0021] 1. The present invention can be realized by SiC f The stress-strain differential curve of SiC / Ti composite material is convenient to determine f The fracture types of the Ti / Ti composites are full load model and local load model.

[0022] 2. The present invention can be realized by SiC f The stress-strain differential curve of SiC / Ti composite material is convenient to determine f Whether there are damage and defects in the / Ti composite material during the manufacturing process.

[0023] 3. The present invention uses SiC f The stress-strain differential curve of the SiC / Ti composite material can be used to determine the f At what deformation amount does the fiber breakage of the Ti / Ti composite material begin? BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1Dimensions of rod tensile specimens.

[0025] Figure 2 For the SiC in Example 1 f Room temperature tensile differential curve of Ti2AlNb composite material. 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).

[0026] Figure 3 For the SiC in Example 1 f Room temperature fracture diagram of / Ti2AlNb composite material.

[0027] Figure 4 For the SiC in Example 2 f Room temperature tensile differential curve of Ti2AlNb composite material. 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).

[0028] Figure 5 For the SiC in Example 2 f High temperature fracture diagram of / Ti2AlNb composite material. DETAILED DESCRIPTION

[0029] In the specific implementation process, the present invention will SiC f The Ti / Ti composite material specimens were machined into standard rod-shaped tensile specimens, and the surface of the specimens was ensured to be free of scratches. Stress-strain data were obtained using a universal mechanical testing machine at a tensile rate of 1 mm / min, and the corresponding differential curve was generated using the stress-strain data. Based on whether the F'(X) value decreased before fracture, it was determined whether the composite material fracture model was a full load model (GLS) or a local load model (LLS). Based on the difference between the F'(X) value and the elastic modulus of the intact specimen, it was determined whether the composite material was uncompacted and had large defects before stretching. Based on the decrease in the F'(X) value in the later stage of fracture, it was determined at what deformation the composite material began to break.

[0030] 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.

[0031] Example 1

[0032] In this embodiment, a method for determining SiC f The specific methods of tensile fracture types and fracture modes of / Ti composite materials are as follows:

[0033] The SiC fiber volume fraction is 50%. fMachining of Ti2AlNb / Ti2AlNb composite materials Standard rod tensile specimen with L=21mm. Figure 1 As shown, the specific dimensions of the tensile specimen are as follows: total length L1 = 52 mm, gauge length L2 = 21 mm, gauge diameter Nominal diameter of external thread of clamping end Then SiC f The surface of the Ti2AlNb / Ti2AlNb composite material was smoothed and polished using 800#, 1500# and 3000# sandpaper in sequence to ensure that there were no scratches on the surface.

[0034] The prepared SiC f The actual average diameter and actual length of the tensile specimen of the Ti2AlNb composite material were measured by using a vernier caliper at three locations on the gauge length. The measured parameters were input into the test system, and the prepared tensile specimen was subjected to a tensile performance test using a universal mechanical testing machine. During the test, the tensile direction was ensured to be parallel to the fiber axis, with an angle of less than 1° and a tensile rate of 1 mm / min. In order to ensure the accuracy of the room temperature stress-strain curve, the SiC f / Ti2AlNb composite material coupled with a mechanical extensometer.

[0035] like Figure 2 As shown, the obtained room temperature stress-strain data is used to obtain the corresponding differential curve through the differential formula, and the differential formula is:

[0036] Δy=F'(X)ΔX

[0037] In the formula, Δy = 284.863 MPa; Δx = 0.001; and the elastic modulus of the composite material E = F'(X) ≈ 285 GPa.

[0038] SiC f The room temperature tensile differential curve F'(X) value of SiCf / Ti2AlNb composite material has been stable and has no obvious decreasing trend, indicating that the fracture type of SiCf / Ti2AlNb composite material is more inclined to the local load model (LLS model), and the composite material is instantaneous fracture, and no obvious defects are generated in the early stage. The obtained differential curve F'(X) is compared with the elastic modulus (250~290GPa) of the intact SiCf / Ti2AlNb composite material. f / Ti2AlNb composites have no uncompacted and large-sized defects before stretching.

[0039] like Figure 3 As shown, according to the fracture diagram of SiCf / Ti2AlNb composite material, the cross section is relatively smooth, which can be determined that SiC f / Ti2AlNb composites fractured according to the local load (LLS) model, and the fracture process was consistent with the prediction results of the differential curve without any uncompacted or large defects.

[0040] Example 2

[0041] In this embodiment, a method for determining SiC f The specific methods of tensile fracture types and fracture modes of / Ti composite materials are as follows:

[0042] The SiC fiber volume fraction is 50%. f Machining of Ti2AlNb / Ti2AlNb composite materials Standard rod tensile specimen with L=21mm. Figure 1 As shown, the specific dimensions of the tensile specimen are as follows: total length L1 = 52 mm, gauge length L2 = 21 mm, gauge diameter Nominal diameter of external thread of clamping end The surface of the SiCf / Ti2AlNb composite material was then smoothed and polished using 800#, 1500# and 3000# sandpaper in sequence to ensure that there were no scratches on the surface.

[0043] The prepared SiC f The actual average diameter and actual length of the tensile specimen of the Ti2AlNb composite material were tested by using a vernier caliper at three locations on the gauge length. The measured corresponding parameters were input into the test system, and the prepared tensile specimen was subjected to a tensile performance test using a universal mechanical testing machine. During the test, the tensile direction was ensured to be parallel to the fiber axis, the angle was less than 1°, and the tensile rate was 1mm / min. The high-temperature tensile temperature was 450°C. In order to ensure the accuracy of the high-temperature stress-strain curve of the test, the SiC f / Ti2AlNb composite material plus laser extensometer.

[0044] like Figure 4 As shown, the high temperature stress-strain data is obtained by differential formula to obtain the corresponding differential curve, and the differential formula is:

[0045] Δy=F'(X)ΔX

[0046] In the formula, Δy = 285.323 MPa; Δx = 0.001; and the elastic modulus of the composite material E = F'(X) ≈ 285 GPa.

[0047] SiC f The F'(X) value of the high temperature tensile differential curve of the SiC / Ti2AlNb composite material is stable in the early stage, and when the deformation is 0.45%, the F'(X) value decreases. fThe fracture type of the SiC / Ti2AlNb composite material is more inclined to the full load model (GLS model), and the composite material is not instantaneous fracture, and partial fiber fracture occurs when the deformation is about 0.45%. The obtained differential curve F'(X) is compared with the intact SiC f / Ti2AlNb composite material elastic modulus (250 ~ 290GPa) comparison, showing that SiC f / Ti2AlNb composites have no uncompacted and large-sized defects before stretching.

[0048] like Figure 5 As shown, according to SiC f / Ti2AlNb composite material fracture diagram, the cross section fluctuates greatly, it can be roughly determined that SiC f / Ti2AlNb composite material fractures in the full load (GLS) model, and the fracture process is consistent with the prediction results of the differential curve without any uncompacted or large defects.

Claims

1. A method for determining the tensile fracture type and fracture mode of a silicon carbide fiber reinforced titanium-based composite material, characterized in that: The specific steps are: Step 1: SiC f / Ti composite materials are processed into Standard rod-shaped tensile specimen with L=21mm and smooth surface; Step 2: The prepared tensile specimen is tested for its actual average diameter and actual gauge length using a vernier caliper; the measured corresponding parameters are input into the testing system, and the prepared tensile specimen is tested for tensile properties using a universal mechanical testing machine to obtain a stress-strain curve; Step 3: Differentiate the obtained tensile test data and make a corresponding differential curve. Smooth the obtained differential curve to remove the noise peak signal. The horizontal axis X in the differential curve represents the strain, and the vertical axis F'(X) represents the stress derivative. Step 4: Determine whether the F'(X) value of the differential curve decreases in the later stage and whether the SiC f / Ti composite fracture model is full load model (GLS) or local load model (LLS); Step 5: According to SiC f The F'(X) value of the differential curve of the / Ti composite material decreases in the later period, which determines the amount of deformation at which the fiber fracture of the composite material begins; Step 6: According to SiC f The F'(X) value of the differential curve of the SiC / Ti composite material at the stable position is compared with the F'(X) value of the differential curve of the intact tensile specimen to determine the f / Ti composites before stretching to determine whether they are uncompacted and have large-size defects.

2. The method for determining the tensile fracture type and fracture mode of a silicon carbide fiber reinforced titanium-based composite material according to claim 1, characterized in that: In step 1, SiC f The / Ti composite material is a SiC fiber reinforced Ti-based alloy or a Ti-Al series intermetallic compound, and the volume fraction of the SiC fiber is 25-80%.

3. The method for determining the tensile fracture type and fracture mode of a silicon carbide fiber reinforced titanium-based composite material according to claim 1, characterized in that: In step 2, when performing the tensile performance test, the stretching direction is as parallel to the fiber axis as possible, ensuring that the angle is less than 1°, and the stretching rate is 0.5-1.5 mm / min.

4. The method for determining the tensile fracture type and fracture mode of a silicon carbide fiber reinforced titanium-based composite material according to claim 1, wherein: In step 2, in order to ensure the accuracy of the stress-strain curve of the test, a mechanical extensometer is added to the tensile specimen tested at room temperature, and a laser extensometer is added to the tensile specimen tested at high temperature.

5. The method for determining the tensile fracture type and fracture mode of a silicon carbide fiber reinforced titanium-based composite material according to claim 1, wherein: In step 3, the obtained stress-strain data is used to obtain the corresponding differential curve graph through the differential formula, based on the differential formula: Δy = F'(X)ΔX; in the formula, Δy represents the stress small variable, unit MPa; Δx represents the strain small variable, unit 100%.

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