A multi-parameter graphical method for comprehensive evaluation of mechanical properties of structural materials

Abstract

The application belongs to the field of structural strength design, and particularly relates to a multi-parameter graphical method for comprehensively evaluating mechanical properties of structural materials. The method comprises the following steps: designing a corresponding test piece according to typical characteristic parts of an aero-engine structure; performing a static tensile test on the test piece to obtain a tensile ultimate strength; respectively performing a fatigue initiation life test, a durability life test and a crack propagation life test on the test piece to obtain a fatigue initiation life test life value, a durability life test life value and a crack propagation life test life value; calculating a net cross-section nominal peak stress value of the test piece according to a test load and a cross-section geometric size of the test piece, and calculating a strength reserve coefficient according to the net cross-section nominal peak stress value and the tensile ultimate strength; and drawing a strength reserve coefficient-life relationship graph with the strength reserve coefficient as the horizontal coordinate and the logarithmic life as the vertical coordinate. The application realizes comprehensive representation of the relationship among the fatigue initiation life, the durability life and the crack propagation life.

Description

Technical Field

[0001] This application belongs to the field of structural strength design, and specifically relates to a multi-parameter graphical method for comprehensively evaluating the mechanical properties of structural materials. Background Technology

[0002] The development of civilian and military needs has increasingly demanded higher performance, durability, reliability, and maintainability of aero-engines, promoting continuous progress and improvement in aero-engine structural strength design technology and the materials and their performance data. In the preliminary design phase of aero-engines, only simple static strength estimations are typically performed on components. Once the structure meets the static strength reserve requirements, further technical and detailed structural design can proceed. In the technical and detailed design phases, life calculations are required for components, including fatigue crack initiation life, rupture life, and fatigue crack propagation life calculations. When calculations show that the design scheme does not meet certain life performance requirements, such as fatigue initiation life, rupture life, or fatigue crack life, it is often necessary to return to the preliminary design phase and make significant adjustments, thus affecting the design cycle. This also illustrates that for a selected material scheme, meeting the static strength reserve requirements does not necessarily guarantee meeting the life performance design requirements; adjustments to the static strength reserve are needed to ensure that all life performance indicators meet the design requirements.

[0003] When designing structural lifespan, material life curves are often used. These curves typically describe single failure modes, such as low-cycle fatigue life curves, rupture life curves, or crack propagation rate curves. These curves often use stress or stress intensity factor as independent variables, characterizing the material's fatigue performance, rupture performance, and crack propagation performance through stress-fatigue life curves, stress-rupture life curves, and crack propagation rate curves, respectively. This representation method largely corresponds to experimental conditions, reflecting the relationship between stress experienced by the material under given conditions and fatigue life, rupture life, and crack propagation life. However, this method cannot effectively represent the relationship between lifespan under different parameter and stress combinations. It cannot intuitively express situations where low-temperature high stress and high-temperature low stress may have the same fatigue life, or where low stress concentration and high average stress and high stress concentration and low average stress may have the same rupture life. Furthermore, current methods fail to establish a correlation between the most basic static strength reserve factor used in structural strength design and fatigue life, rupture life, and crack propagation life. This can lead to situations where, when an inappropriate static strength reserve factor is selected, one life metric meets the requirements while others do not.

[0004] Therefore, it is desirable to have a technical solution to overcome or at least mitigate one of the aforementioned defects of the prior art. Summary of the Invention

[0005] The purpose of this application is to provide a multi-parameter graphical method for comprehensively evaluating the mechanical properties of structural materials, in order to solve at least one problem existing in the prior art.

[0006] The technical solution of this application is:

[0007] A multi-parameter graphical method for comprehensively evaluating the mechanical properties of structural materials includes:

[0008] Step 1: Design corresponding test pieces based on the typical characteristic parts of the aero-engine structure;

[0009] Step 2: Under typical temperature conditions, a static tensile test is performed on the test specimen to obtain the tensile ultimate strength of the test specimen at the corresponding test temperature;

[0010] Step 3: Under typical load conditions, the test specimen is subjected to fatigue initiation life test, rupture life test and crack propagation life test respectively, and the fatigue initiation life test life value, rupture life test life value and crack propagation life test life value of the test specimen under the corresponding test load are obtained.

[0011] Step 4: Calculate the nominal peak stress value of the net cross-section of the test specimen based on the test load and the cross-sectional geometry of the test specimen, and calculate the strength reserve coefficient based on the nominal peak stress value of the net cross-section and the tensile ultimate strength.

[0012] σ max =Fmax / S

[0013] n b =σ b / σ max

[0014] Where, σ max Where is the nominal peak stress value of the net cross-section, Fmax is the peak load of the test, S is the net cross-sectional area of ​​the test specimen, and n b σ is the strength reserve coefficient. b It is the tensile ultimate strength;

[0015] Step 5: Plot a graph showing the relationship between strength reserve coefficient and lifespan, with strength reserve coefficient as the horizontal axis and lifespan as the vertical axis.

[0016] In at least one embodiment of this application, in step one, the test specimen includes:

[0017] The first test piece includes a first test section, a first transition section, and a first loading section. The two ends of the first test section are respectively connected to the first loading section through the first transition section. The first transition section is conical, and the first test section is cylindrical. The radius of the first test section is R1 = 6 mm.

[0018] The second test piece includes a second test section, a second transition section, and a second loading section. The two ends of the second test section are respectively connected to the second loading section through the second transition section. The second transition section includes a cylindrical section connected to the second test section and a conical section connected to the second loading section. The second test section is cylindrical, and the size of the second test section is smaller than the size of the cylindrical section of the second transition section. The radius of the second test section is R2 = 2 mm.

[0019] The third test piece includes a third test section, a third transition section, and a third loading section. The two ends of the third test section are connected to the third loading section through the third transition section. The third transition section includes a cylindrical section connected to the third test section and a conical section connected to the third loading section. The third test section is cylindrical, and the size of the third test section is smaller than the size of the cylindrical section of the third transition section. The radius of the third test section is R3 = 0.5 mm.

[0020] In at least one embodiment of this application, the test piece is made of TC11 or GH4169.

[0021] In at least one embodiment of this application, step five, which involves plotting a graph showing the relationship between the strength reserve coefficient and lifespan with the strength reserve coefficient as the abscissa and lifespan as the ordinate, includes:

[0022] S51. Using the strength reserve coefficient as the abscissa and the life as the ordinate, and the test piece type as the classification condition, plot the relationship between the strength reserve coefficient and the fatigue initiation life and the endurance life corresponding to different test temperatures.

[0023] S52. Using the strength reserve coefficient as the abscissa, the life as the ordinate, and the test temperature as the classification condition, plot the relationship between the strength reserve coefficient, fatigue initiation life, and endurance life for different test pieces.

[0024] In at least one embodiment of this application, step five, which involves plotting the relationship between the strength reserve coefficient and lifespan using the strength reserve coefficient as the abscissa and lifespan as the ordinate, further includes:

[0025] S53. Plot the relationship between the strength reserve coefficient, fatigue initiation life, and crack propagation life with the strength reserve coefficient as the abscissa.

[0026] In at least one embodiment of this application, the strength reserve coefficient versus crack propagation life curve in the strength reserve coefficient versus fatigue initiation life and crack propagation life graph in S53 is obtained as follows:

[0027] Assume the crack propagation rate model satisfies the Paris formula:

[0028]

[0029] Where da / dN is the crack propagation rate, ΔK is the stress intensity factor amplitude, and C and m are material parameters;

[0030] A crack propagation rate model was obtained by fitting crack propagation life test data;

[0031] The stress intensity factor is calculated for an infinitely large plate containing cracks, and the crack propagation life is estimated as follows:

[0032]

[0033] Where f is the geometric correction factor, a0 is the initial crack size, and a c This is the critical crack size;

[0034] The critical crack size is:

[0035]

[0036] Among them, K IC Where F is the fracture toughness of the material, and F is the external load.

[0037] but:

[0038]

[0039] Based on the definition of the strength reserve factor, the expression for the relationship between crack propagation life and the strength reserve factor is obtained:

[0040]

[0041] Based on the expression for the relationship between crack propagation life and strength reserve coefficient, plot the relationship curve between strength reserve coefficient and crack propagation life.

[0042] The invention has at least the following beneficial technical effects:

[0043] The multi-parameter graphical method for comprehensively evaluating the mechanical properties of structural materials in this application establishes a comprehensive representation of the relationship between fatigue initiation life, endurance life, and crack propagation life of materials and their components based on the mechanical test data of the materials and using strength reserve as the characterization parameter. Attached Figure Description

[0044] Figure 1 This is a flowchart of a multi-parameter graphical method for comprehensively evaluating the mechanical properties of structural materials according to one embodiment of this application;

[0045] Figure 2 This is a schematic diagram of a test specimen according to one embodiment of this application;

[0046] Figure 3 This is a schematic diagram of a test specimen according to the second embodiment of this application;

[0047] Figure 4 This is a schematic diagram of a test specimen according to the third embodiment of this application;

[0048] Figure 5 This is a graph showing the relationship between the strength reserve coefficient, fatigue initiation life, and endurance life of the first test specimen of one embodiment of this application at different test temperatures;

[0049] Figure 6 This is a graph showing the relationship between the strength reserve coefficient, fatigue initiation life, and endurance life of a second test specimen according to one embodiment of this application at different test temperatures;

[0050] Figure 7 This is a graph showing the relationship between the strength reserve coefficient, fatigue initiation life, and endurance life of a third test specimen according to one embodiment of this application at different test temperatures.

[0051] Figure 8 This is a graph showing the relationship between the strength reserve coefficient, fatigue initiation life, and endurance life of different test specimens at 500°C according to one embodiment of this application.

[0052] Figure 9 This is a graph showing the relationship between the strength reserve coefficient, fatigue initiation life, and endurance life of different test specimens at 450°C according to one embodiment of this application.

[0053] Figure 10 This is a graph showing the relationship between the strength reserve coefficient, fatigue initiation life, and crack propagation life in one embodiment of this application. Detailed Implementation

[0054] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be described in more detail below with reference to the accompanying drawings. In the drawings, the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The described embodiments are some, but not all, embodiments of this application. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application. The embodiments of this application will be described in detail below with reference to the accompanying drawings.

[0055] In the description of this application, it should be understood that the terms "center", "longitudinal", "lateral", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting the scope of protection of this application.

[0056] The following is in conjunction with the appendix Figures 1 to 10 This application will be described in further detail.

[0057] This application provides a multi-parameter graphical method for comprehensively evaluating the mechanical properties of structural materials. (See [link to relevant documentation]) Figure 1 This includes the following steps:

[0058] Step 1: Design corresponding test pieces based on the typical characteristic parts of the aero-engine structure;

[0059] Step 2: Under typical temperature conditions, perform static tensile tests on the test specimen to obtain the tensile ultimate strength of the test specimen at the corresponding test temperature;

[0060] Step 3: Under typical load conditions, conduct fatigue initiation life test, rupture life test and crack propagation life test on the test specimen respectively, and obtain the fatigue initiation life test life value, rupture life test life value and crack propagation life test life value of the test specimen under the corresponding test load.

[0061] Step 4: Calculate the nominal peak stress value of the net cross-section of the test specimen based on the test load and the cross-sectional geometry of the test specimen, and calculate the strength reserve factor based on the nominal peak stress value of the net cross-section and the tensile ultimate strength.

[0062] σ max =Fmax / S

[0063] n b =σ b / σ max

[0064] Where, σ max Where is the nominal peak stress value of the net cross-section, Fmax is the peak load of the test, S is the net cross-sectional area of ​​the test specimen, and n b σ is the strength reserve coefficient. b It is the tensile ultimate strength;

[0065] Step 5: Plot a graph showing the relationship between strength reserve coefficient and lifespan, with strength reserve coefficient as the horizontal axis and lifespan as the vertical axis.

[0066] This application presents a multi-parameter graphical method for comprehensively evaluating the mechanical properties of structural materials. First, based on the design characteristics of key aero-engine structures, corresponding test specimens are designed for typical feature areas. These test specimens can be designed with different cross-sectional geometries, and their structural forms can include smooth and notched specimens. The test specimen material can be commonly used aero-engine materials, such as TC11 and GH4169. In a preferred embodiment of this application, taking TC11, a commonly used material in aero-engines, as an example, three different types of test specimens are designed according to the design scheme, and the specific structural forms of the three test specimens are given. For example... Figure 2 As shown, the first test piece includes a first test section, a first transition section, and a first loading section. The two ends of the first test section are connected to the first loading section via the first transition section. The first transition section is conical, and the first test section is cylindrical. The radius of the first test section is R1 = 6 mm. Figure 3 As shown, the second test piece includes a second test section, a second transition section, and a second loading section. Both ends of the second test section are connected to the second loading section via the second transition section. The second transition section includes a cylindrical section connected to the second test section and a conical section connected to the second loading section. The second test section is cylindrical, and its dimensions are smaller than the cylindrical section of the second transition section. The radius of the second test section is R2 = 2 mm. Figure 4 As shown, the third test piece includes a third test section, a third transition section, and a third loading section. The two ends of the third test section are connected to the third loading section via the third transition section. The third transition section includes a cylindrical section connected to the third test section and a conical section connected to the third loading section. The third test section is cylindrical, and its dimensions are smaller than the cylindrical section of the third transition section. The radius of the third test section is R3 = 0.5 mm. In this embodiment, the first test piece is called a smooth specimen, and the second and third test pieces are both called notched specimens.

[0067] This application presents a multi-parameter graphical method for comprehensively evaluating the mechanical properties of structural materials. Multiple specimens of each cross-sectional geometry are fabricated, and static tensile tests, fatigue initiation life tests, endurance life tests, and crack propagation life tests are conducted on each specimen. Specifically, based on the load environment of the structure, a typical temperature level is selected, and static tensile tests are performed on the specimens to obtain the tensile ultimate strength σ of the specimen at a given temperature. b Under typical load conditions, fatigue initiation life tests are conducted on the test specimens to obtain the fatigue initiation life test values ​​of the test specimens under the corresponding test loads; under typical load conditions, rupture life tests are conducted on the test specimens to obtain the rupture life test values ​​of the test specimens under the corresponding test loads; under typical load conditions, crack propagation life tests are conducted on the test specimens to obtain the crack propagation life test values ​​of the test specimens under the corresponding test loads.

[0068] Furthermore, the strength reserve coefficient is calculated based on the nominal peak stress value of the net cross-section and the tensile ultimate strength, and finally, a graph showing the relationship between the strength reserve coefficient and the service life is plotted.

[0069] In a preferred embodiment of this application, the strength reserve coefficient versus lifespan graph includes:

[0070] S51. Using the strength reserve coefficient as the abscissa and the life as the ordinate, and the test piece type as the classification condition, plot the relationship between the strength reserve coefficient and the fatigue initiation life and the endurance life corresponding to different test temperatures.

[0071] In this embodiment, based on the test results, the results are summarized according to different test specimens and expressed as a curve with the strength reserve coefficient as the abscissa and the life as the ordinate, such as... Figure 5-7 As shown in the figure, the fatigue data of smooth and notched specimens at different temperatures, measured by the strength reserve coefficient, all conform to the same pattern. This indicates that the fatigue performance of both smooth and notched specimens depends on the strength reserve of their peak fatigue stress, and is independent of temperature. This provides a basis for converting the fatigue performance of materials at different temperatures. It also explains why low-temperature high-stress and high-temperature low-stress, as long as they have the same strength reserve coefficient, may have the same fatigue life value. However, the current fatigue performance representation method, which only expresses fatigue life in terms of stress-fatigue life, cannot intuitively describe this pattern.

[0072] The multi-parameter graphical method for comprehensively evaluating the mechanical properties of structural materials in this application, based on the aforementioned relationship diagram, can provide a basis for selecting a reasonable strength reserve coefficient during the design phase. Figure 5-7It can be seen that with a strength reserve of 1.5 times (a commonly used reserve factor in engineering), the fatigue life of the material at different temperatures is well over 1000 hours. However, at this strength reserve factor, the fatigue life of smooth specimens and R2=2mm specimens is around 10⁴–10⁵ cycles, while the life of R3=0.5mm specimens is only around 1000 cycles. Therefore, fatigue performance is the main factor limiting lifespan, and stress concentration effects need to be considered in structural design, appropriately increasing the strength reserve to improve fatigue performance.

[0073] In a preferred embodiment of this application, the strength reserve coefficient versus lifespan graph includes:

[0074] S52. Using the strength reserve coefficient as the abscissa, the life as the ordinate, and the test temperature as the classification condition, plot the relationship between the strength reserve coefficient, fatigue initiation life, and endurance life for different test pieces.

[0075] In this embodiment, based on the test results, the test results are summarized according to different test temperatures, resulting in a curve expression with the strength reserve coefficient as the abscissa and the life as the ordinate, as shown below. Figure 8-9 As shown in the figure, the creep life of smooth and notched specimens at various temperatures, measured by the strength reserve coefficient, follows the same pattern: the creep life of the material at the same temperature is independent of the stress concentration at the notch (the notch is insensitive) and mainly depends on the strength reserve of the working stress. This provides a basis for converting the creep performance of materials under different notches. It also explains why small stress concentration with large average stress and large stress concentration with small average stress may have the same creep life value as long as they have the same strength reserve coefficient. However, the current creep performance representation method in the prior art, which only expresses creep performance in terms of stress-creep life, cannot intuitively describe this pattern.

[0076] In a preferred embodiment of this application, the strength reserve coefficient versus lifespan graph further includes:

[0077] S53. Plot the relationship between the strength reserve coefficient, fatigue initiation life, and crack propagation life with the strength reserve coefficient as the abscissa.

[0078] Among them, in the relationship diagrams between the strength reserve coefficient and fatigue initiation life and crack propagation life, the curve of the strength reserve coefficient and fatigue initiation life can be directly plotted based on fatigue initiation life test data, but the curve of the strength reserve coefficient and crack propagation life needs to be calculated using analytical methods, specifically including:

[0079] Assuming the crack propagation rate model satisfies the Paris formula, we have:

[0080]

[0081] Where da / dN is the crack propagation rate, ΔK is the stress intensity factor amplitude, and C and m are material parameters;

[0082] A crack propagation rate model was obtained by fitting crack propagation life test data;

[0083] The stress intensity factor is calculated for an infinitely large plate containing cracks, and the crack propagation life is estimated as follows:

[0084]

[0085] Where f is the geometric correction factor, a0 is the initial crack size, and a c This is the critical crack size;

[0086] The critical crack size is:

[0087]

[0088] Among them, K IC Where F is the fracture toughness of the material, and F is the external load.

[0089] but:

[0090]

[0091] Based on the definition of the strength reserve factor, the expression for the relationship between crack propagation life and the strength reserve factor is obtained:

[0092]

[0093] Based on the expression for the relationship between crack propagation life and strength reserve coefficient, plot the relationship curve between strength reserve coefficient and crack propagation life.

[0094] In one embodiment of this application, such as Figure 10 The figure shows the variation of crack initiation life and crack propagation life of GH4169 material at 500℃ with the strength reserve coefficient. As can be seen from the figure, when the strength reserve coefficient changes from 1.1 to 1.6, the increase in crack propagation life is limited, remaining basically on the order of 10⁴ cycles, with no significant improvement. However, the initiation life increases significantly from the order of 10⁴ cycles to the order of 10⁷ cycles. Therefore, if a high requirement for propagation life is required, simply increasing the strength reserve coefficient will not significantly improve the propagation life. This provides directional guidance for initial scheme design and material selection.

[0095] This application presents a multi-parameter graphical method for comprehensively evaluating the mechanical properties of structural materials. From the perspective of structural strength design, based on experimental data and using strength reserve as a characterizing parameter, it comprehensively describes the relationship between fatigue initiation life, fatigue life, and crack propagation life of materials and their components. This application can more clearly express the key factors affecting material life from the perspective of structural strength, provide a basis for selecting a reasonable strength reserve coefficient in the design phase, and allow for a more intuitive comparison of the ratio of crack initiation life to crack propagation life under a certain reserve coefficient.

[0096] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A multi-parameter graphical method for comprehensive evaluation of the mechanical properties of structural materials, characterized in that, The method comprises the following steps: Step 1: design corresponding test pieces according to typical characteristic parts of an aero-engine structure; Step 2: perform static tensile tests on the test pieces under a typical temperature environment to obtain tensile ultimate strengths of the test pieces under corresponding test temperatures; Step 3: perform fatigue initiation life tests, endurance life tests and crack propagation life tests on the test pieces under a typical load environment to obtain fatigue initiation life test life values, endurance life test life values and crack propagation life test life values of the test pieces under corresponding test loads; Step 4: calculate a net cross-sectional nominal peak stress value of the test pieces according to the test load and the cross-sectional geometric dimensions of the test pieces, and calculate a strength reserve coefficient according to the net cross-sectional nominal peak stress value and the tensile ultimate strength; σ max = Fmax / S n b = σ b / σ max where σ max is the net section nominal peak stress value, Fmax is the test peak load, S is the net cross-sectional area of the test piece, n b is the strength reserve factor, σ b is the tensile ultimate strength; Step 5: plot a strength reserve coefficient and life relationship graph with the strength reserve coefficient as the horizontal coordinate and the life as the vertical coordinate, comprising: S51: plot a strength reserve coefficient and fatigue initiation life and endurance life relationship graph corresponding to different test temperatures with the strength reserve coefficient as the horizontal coordinate, the life as the vertical coordinate and the test piece type as the classification condition; S52: plot a strength reserve coefficient and fatigue initiation life and endurance life relationship graph corresponding to different test pieces with the strength reserve coefficient as the horizontal coordinate, the life as the vertical coordinate and the test temperature as the classification condition; S53: plot a strength reserve coefficient and fatigue initiation life and crack propagation life relationship graph with the strength reserve coefficient as the horizontal coordinate; In S53, the strength reserve coefficient and crack propagation life relationship curve in the strength reserve coefficient and fatigue initiation life and crack propagation life relationship graph is obtained according to the following manner: Assume that a crack propagation rate model satisfies the Paris formula: Where da / dN is the crack propagation rate, ΔK is the stress intensity factor amplitude, and C and m are material parameters; The crack propagation rate model is obtained by fitting crack propagation life test data; The stress intensity factor is calculated for an infinite plate containing a crack, and the crack propagation life is estimated as: where f is a geometry correction factor, a0is the initial crack size, a c is the critical crack size; The critical crack size is: Among them, K IC Where F is the fracture toughness of the material, and F is the external load. Then: According to the definition of the strength reserve coefficient, the expression of the crack propagation life and the strength reserve coefficient relationship curve is obtained: According to the expression of the crack propagation life and the strength reserve coefficient relationship curve, the strength reserve coefficient and crack propagation life relationship curve is plotted.

2. The multi-parameter graphical method for comprehensive evaluation of mechanical properties of structural materials according to claim 1, characterized in that, In Step 1, the test pieces comprise: The first test piece comprises a first test section, a first transition section and a first loading section, both ends of the first test section are connected to the first loading section through the first transition section, the first transition section is conical, the first test section is cylindrical, and the radius of the first test section is R1=6mm; The second test piece comprises a second test section, a second transition section and a second loading section, two ends of the second test section are connected with the second loading section through the second transition section respectively, the second transition section comprises a cylindrical section connected with the second test section and a conical section connected with the second loading section, the second test section is in a cylindrical shape, and a size of the second test section is smaller than a size of the cylindrical section of the second transition section, a radius of the second test section is R2=2mm; The third test piece comprises a third test section, a third transition section and a third loading section, two ends of the third test section are connected with the third loading section through the third transition section respectively, the third transition section comprises a cylindrical section connected with the third test section and a conical section connected with the third loading section, the third test section is in a cylindrical shape, and a size of the third test section is smaller than a size of the cylindrical section of the third transition section, a radius of the third test section is R3=0.5mm.

3. The multi-parameter graphical method for comprehensive evaluation of mechanical properties of structural materials according to claim 2, characterized in that, The test piece is made of TC11 or GH4169.

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