阅读说明：本技术 一种特征结构模拟件疲劳极限的测试方法 (Method for testing fatigue limit of feature structure simulation piece ) 是由 陈柳 李真成 张聪凯 李兴无 沙爱学 于 2021-08-24 设计创作，主要内容包括：本发明涉及一种特征结构模拟件疲劳极限的测试方法,包括步骤在疲劳加载测试,以满足名义循环周次N-(life)且未发生断裂为达成条件,每达成条件一次,则初始应力增加5％作为最大应力S-(MAX),并通过上述的关系得到对应的施加载荷Fi(i＝2,3,…,n),以施加载荷Fi对特征结构模拟件继续进行疲劳加载测试,直至发生断裂,结束疲劳加载测试。本发明提供的特征结构模拟件疲劳极限的测试方法,适用于几乎所有几何结构复杂的模拟件；同时,对没有或轻微疲劳Coaxing效应的材料均适用,典型如钛铝、钛合金等,适用范围广,且适用的限制条件少。(The invention relates to a method for testing fatigue limit of a feature structure simulation piece, which comprises the step of testing fatigue loading to meet N nominal cycle times life And no fracture is taken as an achievement condition, and the initial stress is increased by 5% as the maximum stress S every time the achievement condition is met MAX And obtaining a corresponding applied load Fi (i is 2,3, …, n) according to the relation, and continuing the fatigue loading test on the characteristic structure simulation piece by using the applied load Fi until the fracture occurs, and ending the fatigue loading test. The method for testing the fatigue limit of the characteristic structure simulation piece is suitable for almost all simulation pieces with complicated geometric structures; meanwhile, the method is suitable for materials without or with slight fatigue Coaxing effect, such as titanium aluminum, titanium alloy and the like, and has wide application range and few applicable limiting conditions.)

1. A method for testing the fatigue limit of a feature structure simulation piece is characterized by comprising the following steps:

step 1, installing a characteristic structure simulation piece with a preset geometric characteristic design, and obtaining an applied load F and a corresponding maximum stress S of the characteristic structure simulation piece by utilizing a finite element simulation calculation mode_MAXThe relationship between;

obtaining nominal fatigue of a material used for said feature simulationLimit S_lifeAnd nominal cycle number N_life；

Step 2, from the nominal fatigue limit S_lifeAnd obtaining an initial stress by a predetermined proportionality coefficient, and taking the initial stress as a maximum stress S_MAXObtaining a corresponding applied load F1 through the relationship, and carrying out fatigue loading test on the characteristic structure simulation piece by using the applied load F1;

in fatigue loading test, to meet the nominal cycle number N_lifeAnd no fracture is taken as an achievement condition, and the initial stress is increased by 5% as the maximum stress S every time the achievement condition is met_MAXObtaining a corresponding applied load Fi (i is 2,3,., n) through the relationship, and continuing to perform a fatigue loading test on the characteristic structure simulation piece by using the applied load Fi until the characteristic structure simulation piece is broken, and ending the fatigue loading test;

step 3, by applying a load F at the time of fracture_nAnd said relation yields the applied load F_nCorresponding maximum stress S_fail(ii) a Obtaining an applied load F at which a fracture occurs_nCorresponding fatigue cycle number N_n；

Step 4, according to the fatigue cycle number N_nAnd fatigue load F_nCalculating to obtain the fatigue limit S 'of the characteristic structure simulation piece'_eThe formula is as follows:wherein the content of the first and second substances,

2. a method of testing the fatigue limit of a feature simulation according to claim 1, wherein: fatigue cycle number N_n< nominal cycle number N_life。

3. A method of testing the fatigue limit of a feature simulation according to claim 1, wherein: the geometric features of the feature simulator comprise one or more combinations of holes, rounded corners, thin sections, profiled sections, non-integral surfaces.

4. A method of testing the fatigue limit of a feature simulation according to claim 1, wherein: the material of the characteristic structure simulator is one of metal or alloy with unobvious Coaxing effect.

5. A method of testing the fatigue limit of a feature simulation according to claim 1, wherein: the fatigue loading test is at a nominal fatigue limit S of 80%_lifeThe corresponding fatigue test load is carried out.

6. A method of testing the fatigue limit of a feature simulation according to claim 1, wherein: in step S1, the maximum stress S_maxSelecting the Von Mises equivalent stress or the maximum principal stress according to the material characteristics adopted by the feature structure simulation piece.

7. A method of testing the fatigue limit of a feature simulation according to claim 1, wherein: the specific process of step S1 is: after the characteristic structure simulation piece and the fixture are connected, corresponding materials and contact attributes are set, the fixture adopts a pure elastic structure, the characteristic structure simulation piece utilizes an elastic-plastic structure to calculate the equivalent stress distribution and the maximum stress position of the simulation piece in the process of increasing the load F, and then the maximum stress S of the characteristic structure simulation piece is obtained_maxAnd the applied load F.

8. A method of testing the fatigue limit of a feature simulation according to claim 1, wherein: in step S2, the nominal fatigue limit S of the material used for the feature simulation piece_lifeAnd the fatigue limit S_lifeCorresponding nominal cycle number N_lifeThe acquisition method comprises the following steps: searching a material performance manual or obtaining the material performance manual by using a conventional fatigue performance test method.

9. A method of testing the fatigue limit of a feature simulation according to claim 1, wherein: the characteristic structure simulation piece is made of titanium-aluminum alloy, titanium alloy or titanium-based composite material.

Technical Field

The invention relates to the technical field of material fatigue limit testing, and particularly provides a method for testing fatigue limit of a feature structure simulation piece.

Background

When the material is applied to an actual component, the material often has certain structural characteristics, and a characteristic structure simulation piece designed by utilizing one or more geometric characteristics of the actual component is used for testing in a simulation environment, so that the service performance of the structural characteristics can be truly reflected. However, the feature structure simulation piece has high processing cost and high testing cost, the number of samples is extremely limited during physical sampling, and a large number of samples are needed for the traditional lifting fatigue limit test, so that how to obtain the fatigue limit of the feature part by using the limited simulation piece is very critical.

Meanwhile, for brittle materials such as titanium-aluminum alloy and the like, the brittle materials have strong brittleness tendency, so that the mechanical properties are large in dispersity among different samples, the fatigue strength is extremely sensitive to a load level, and the like, and even if a fatigue limit test of a standard sample is carried out, the number of the samples is more than that of the traditional metal.

The invention patent with the application number of CN201510850219.5 discloses a fatigue limit rapid prediction method based on strain increment. Under gradient stress load, the change rule of the dependent variable is very similar to the change rule of temperature rise, the Luong method can predict the fatigue limit by using the corresponding stable temperature rise value under the gradient load, and the fatigue limit can be rapidly predicted theoretically by using the dependent variable under the gradient load. However, the above prediction method has difficulty in obtaining the fatigue limit of a test piece having a complicated geometric feature structure.

In view of the above, there is a need to design an improved method for testing fatigue limit of a feature simulator to solve the above problems.

Disclosure of Invention

The purpose of the invention is: the method for testing the fatigue limit of the feature structure simulation piece is provided.

The technical scheme of the invention is as follows:

the method for testing the fatigue limit of the feature structure simulation piece is characterized by comprising the following steps of:

step 1, installing a characteristic structure simulation piece with a preset geometric characteristic design, and obtaining an applied load F and a corresponding maximum stress S of the characteristic structure simulation piece by utilizing a finite element simulation calculation mode_MAXThe relationship between;

obtaining a nominal fatigue limit S of a material used for said feature simulation_lifeAnd nominal cycle periodSub N_life；

Step 2, from the nominal fatigue limit S_lifeAnd obtaining an initial stress by a predetermined proportionality coefficient, and taking the initial stress as a maximum stress S_MAXObtaining a corresponding applied load F1 through the relationship, and carrying out fatigue loading test on the characteristic structure simulation piece by using the applied load F1;

in fatigue loading test, to meet the nominal cycle number N_lifeAnd no fracture is taken as an achievement condition, and the initial stress is increased by 5% as the maximum stress S every time the achievement condition is met_MAXObtaining a corresponding applied load Fi (i is 2,3, …, n) through the relationship, continuing the fatigue loading test on the characteristic structure simulation piece by using the applied load Fi until the characteristic structure simulation piece is broken, and ending the fatigue loading test;

step 3, by applying a load F at the time of fracture_nAnd said relation yields the applied load F_nCorresponding maximum stress S_fail(ii) a Obtaining an applied load F at which a fracture occurs_nCorresponding fatigue cycle number N_n；

Step 4, according to the fatigue cycle number N_nAnd fatigue load F_nCalculating to obtain the fatigue limit S 'of the characteristic structure simulation piece'_eThe formula is as follows:wherein the content of the first and second substances,

further, fatigue cycle number N_n<Nominal cycle number N_life。

Further, the geometric features of the feature simulator comprise one or more combinations of holes, rounded corners, thin sections, profiled sections, non-integral surfaces.

Further, the material of the feature simulator is one of metal or alloy with insignificant Coaxing effect.

Further, the fatigue loading test is at a nominal fatigue of 80%Labor limit S_lifeThe corresponding fatigue test load is carried out.

Further, in step S1, the maximum stress S_maxSelecting the Von Mises equivalent stress or the maximum principal stress according to the material characteristics adopted by the feature structure simulation piece.

Further, the specific process of step S1 is: after the characteristic structure simulation piece and the fixture are connected, corresponding materials and contact attributes are set, the fixture adopts a pure elastic structure, the characteristic structure simulation piece utilizes an elastic-plastic structure to calculate the equivalent stress distribution and the maximum stress position of the simulation piece in the process of increasing the load F, and then the maximum stress S of the characteristic structure simulation piece is obtained_maxAnd the applied load F.

Further, in step S2, the feature simulator has a nominal fatigue limit S of the material used_lifeAnd the fatigue limit S_lifeCorresponding nominal cycle number N_lifeThe acquisition method comprises the following steps: searching a material performance manual or obtaining the material performance manual by using a conventional fatigue performance test method.

The invention has the advantages that: 1. the method for testing the fatigue limit of the characteristic structure simulation piece is suitable for almost all simulation pieces with complicated geometric structures; meanwhile, the method is suitable for materials without or with slight fatigue Coaxing effect, such as titanium aluminum, titanium alloy and the like, and has wide application range and few applicable limiting conditions.

2. According to the method for testing the fatigue limit of the characteristic structure simulation part, the initial load is set by combining the fatigue limit of the standard sample and the finite element calculation result of the load-maximum stress of the characteristic structure simulation part, and the accuracy of initial load setting and the accuracy of fatigue limit testing can be improved by combining the standard sample fatigue limit and the characteristic structure simulation part; in addition, the fatigue limit of the simulation piece with the preset geometric structure can be obtained by theoretically 1 structural feature simulation piece by using the testing method provided by the invention, and the fatigue limit obtained by the step loading method is very close to the fatigue limit obtained by the traditional method, which indicates that the method has higher testing precision.

3. Compared with the method for measuring the fatigue limit by adopting a lifting method in the prior art, the method for testing the fatigue limit of the characteristic structure simulation piece can obviously save the number of test pieces for testing the structural characteristics, quickly obtain the fatigue limit of the structural characteristic simulation piece at low cost, and is used for verifying the design scheme of the simulation piece or further optimizing the design.

4. According to the method for testing the fatigue limit of the characteristic structure simulation piece, the initial load of the experimental working condition is determined by adopting a finite element method, so that the structural characteristic simulation piece and the structural piece under the real working condition keep the same contact load and fatigue damage form, the initial load of the fatigue test is determined on the basis of keeping the equivalent contact stress, and the method has the advantage of quickly and accurately setting the initial load; and the fatigue limit is determined by utilizing the step loading, the fatigue limit aims at a structural part with a preset geometric shape but not a pure material sample, the fatigue is performed for a certain cycle number under the stable load, the first-stage step stress is increased if no fracture occurs, and the final fatigue limit is determined by the step stress with the fracture, the previous-stage step stress and the cycle number of fatigue before the fracture, so that the method has the advantage of economically and accurately obtaining the fatigue limit of the characteristic structure simulation part.

Drawings

FIG. 1 is a diagram of a finite element solution feature structure simulator maximum stress process and stress distribution.

FIG. 2 is a diagram of the relationship between the stress level at the maximum stress position and the applied load of the simulation member of the characteristic structure provided by the present invention.

Fig. 3 is a schematic diagram of the selection of the initial fatigue load provided by the present invention.

FIG. 4 is a schematic view of the step loading provided by the present invention.

Fig. 5 is a fatigue limit diagram obtained by the step loading of the feature simulation piece provided by the invention.

Detailed Description

The present invention will be described in detail with reference to specific examples.

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in detail with reference to the accompanying drawings and specific embodiments.

It should be noted that, in order to avoid obscuring the present invention with unnecessary details, only the structures and/or processing steps closely related to the aspects of the present invention are shown in the drawings, and other details not closely related to the present invention are omitted.

In addition, it is also to be noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.

The invention provides a method for testing fatigue limit of a feature structure simulation piece, which comprises the following steps:

s1, installing the feature structure simulation piece with the preset geometric feature design, and obtaining the applied load F and the corresponding maximum stress S of the feature structure simulation piece by utilizing the calculation mode of finite element simulation_MAXThe relationship between;

obtaining a nominal fatigue limit S of a material used for said feature simulation_lifeAnd nominal cycle number N_life；

S2 from nominal fatigue limit S_lifeAnd obtaining an initial stress by a predetermined proportionality coefficient, and taking the initial stress as a maximum stress S_MAXObtaining a corresponding applied load F1 through the relationship, and carrying out fatigue loading test on the characteristic structure simulation piece by using the applied load F1;

in fatigue loading test, to meet the nominal cycle number N_lifeAnd no fracture is taken as an achievement condition, and the initial stress is increased by 5% as the maximum stress S every time the achievement condition is met_MAXObtaining a corresponding applied load Fi (i is 2,3, …, n) through the relationship, continuing the fatigue loading test on the characteristic structure simulation piece by using the applied load Fi until the characteristic structure simulation piece is broken, and ending the fatigue loading test;

s3, under the applied load F at the time of fracture_nAnd said relation is obtainedLoad F_nCorresponding maximum stress S_fail(ii) a Obtaining an applied load F at which a fracture occurs_nCorresponding fatigue cycle number N_n；

S4, according to the fatigue cycle number N_nAnd fatigue load F_nCalculating to obtain the fatigue limit S 'of the characteristic structure simulation piece'_eThe formula is as follows:

wherein the content of the first and second substances,

preferably, the predetermined proportionality coefficient is 70% -80%.

Preferably, the fatigue cycle number N_fail< nominal cycle number N_life。

Preferably, in step S2, the feature simulator has a nominal fatigue limit S of the material used_lifeAnd the fatigue limit S_lifeCorresponding cycle number N_lifeThe acquisition method comprises the following steps: searching a material performance manual or obtaining the material performance manual by using a conventional fatigue performance test method.

Preferably, in step S1, the maximum stress S_maxSelecting the Von Mises equivalent stress or the maximum principal stress according to the material characteristics adopted by the feature structure simulation piece.

Preferably, the specific process of step S1 is: after the characteristic structure simulation piece and the fixture are connected, corresponding materials and contact attributes are set, the fixture adopts a pure elastic structure, the characteristic structure simulation piece utilizes an elastic-plastic structure to calculate the equivalent stress distribution and the maximum stress position of the simulation piece in the process of increasing the load F, and then the maximum stress S of the characteristic structure simulation piece is obtained_maxAnd the applied load F.

Preferably, the geometric feature design of the feature simulator includes, but is not limited to, one or more combinations of structural features such as holes, rounded corners, thin sections, profiled sections, non-integral surfaces, connections, and the like.

Preferably, the material of the feature simulation piece is one of metals or alloys with insignificant Coaxing effect, such as titanium-aluminum alloy, titanium-based composite material, and high-temperature alloy.

Example 1

The embodiment 1 of the invention provides a method for testing fatigue limit of a feature structure simulation piece, which comprises the following steps:

s1, installing the feature structure simulation piece with the preset geometric feature design, and obtaining the maximum stress S of the feature structure simulation piece by utilizing a finite element simulation calculation mode_maxAnd the relation between the applied load F, the specific process is as follows:

as shown in fig. 1, a feature structure simulation piece with geometric features designed to be in tenon-tooth connection is used as a test object, after the feature structure simulation piece is connected with a fixture, a corresponding material (titanium-aluminum alloy) and contact attributes are set, the fixture adopts a pure elastic constitutive structure, the feature structure simulation piece calculates equivalent stress distribution and a maximum stress position of the simulation piece in a load F increasing process by using the elastic-plastic constitutive structure, and then the maximum stress S of the feature structure simulation piece is obtained_maxAnd the applied load F, as shown in fig. 2;

s2, obtaining the nominal fatigue limit S of the titanium-aluminum alloy material adopted by the characteristic structure simulation piece by using a conventional fatigue performance test method_lifeAnd said nominal fatigue limit S_lifeCorresponding nominal cycle number N_life(ii) a Wherein the nominal fatigue limit S_lifeIs 460 MPa; nominal cycle number N_life-10⁷。

S3, at 80% nominal fatigue limit S_life(i.e., 0.8 XS)_life) Carrying out fatigue loading test under corresponding fatigue load, wherein the fatigue load is the maximum stress S in the step S1_maxAnd the applied load F is obtained by calculation; as shown in FIG. 3, in the present example, the specific value of the fatigue load was 368MPa, which corresponds to a tensile load of 31.5kN, by calculation.

S4, performing nominal circulation N times_lifeAfter the cycle of (4), if the feature structure simulation piece is not broken, according to the operation process of step S3, increasing the amplitude of the fatigue load by 5% to obtain the next fatigue load, continuing the fatigue loading test, and so on, performing the step-type fatigue loading test in this cycle until the feature structure simulation piece is broken, as shown in fig. 4.

S5, recording the fatigue cycle number N corresponding to the characteristic structure simulation piece when the last stage of the step type fatigue loading test approaches to fracture_failAnd fatigue load S_failCalculating to obtain the fatigue limit S 'of the characteristic structure simulation piece'_eThe specific calculation formula is as follows:

wherein the content of the first and second substances,for the last experience N_lifeThe stress corresponding to the fracture stage does not occur in the cycle;the last fatigue load increment; one of the samples N_fail＝5×10⁴；S_fail＝425MPa；

As shown in FIG. 5, the average fatigue limit S 'of the feature structure simulation piece provided in example 1 was calculated according to the above formula'_e446 MPa.

It should be noted that, as will be understood by those skilled in the art, the geometric feature design of the feature simulator may also be one or more combinations of structural features such as holes, rounded corners, thin sections, profiled sections, non-integral surfaces, etc.; the material of the characteristic structure simulation piece can also be one of metals or alloys with unobvious Coaxing effect, such as titanium alloy, titanium-based composite material, high-temperature alloy and the like, the fatigue limit of the structural characteristic simulation piece can be quickly obtained at low cost by the testing method provided by the invention, and meanwhile, the fatigue limit obtained by the step loading method is very close to the fatigue limit obtained by the traditional method, which indicates that the method has higher testing precision.

In summary, the present invention provides a method for testing fatigue limit of a feature structure simulation piece. The testing method comprises the steps of firstly, obtaining the relationship between the maximum stress and the applied load of a characteristic structure simulation piece by utilizing a finite element simulation calculation mode; then, acquiring a nominal fatigue limit of a material adopted by the feature structure simulation piece and a nominal cycle frequency corresponding to the nominal fatigue limit; then, carrying out a step type fatigue loading test until the characteristic structure simulation piece is broken; and recording the fatigue cycle and the fatigue load corresponding to the characteristic structure simulation piece approaching to the fracture in the last stage of the stepped fatigue loading test, and calculating to obtain the fatigue limit of the characteristic structure simulation piece. Compared with the method for measuring the fatigue limit by adopting a lifting method in the prior art, the method for measuring the fatigue limit of each structural feature simulation piece can obviously save the number of test pieces for measuring the structural features, and can quickly obtain the fatigue limit of the structural feature simulation piece at low cost for verifying the design scheme of the simulation piece or further optimizing the design.

Although the present invention has been described in detail with reference to the preferred embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the spirit and scope of the present invention.