A method for determining the loading frequency range of magnesium alloy components in engineering

Abstract

The present invention provides a method for determining the loading frequency range of a magnesium alloy component in an engineering project, and relates to the technical field of magnesium alloy plastic deformation. The present invention finds the relationship between frequency and ratchet strain by determining the ratchet strain under different cyclic frequencies, and finds the frequency value corresponding to the minimum ratchet strain. Then, the maximum strain value of the material during engineering use and the frequency corresponding to the above maximum strain are determined according to the technical documents of the industry standard. Therefore, this method can be used to determine the cyclic loading range of magnesium alloy components applied to engineering environments, which is of great significance for studying the ratchet strain and fatigue life of magnesium alloys and their components under cyclic loading conditions, and has important practical significance for the reliability and failure analysis of the system.

Description

Technical Field

[0001] The present invention relates to the technical field of magnesium alloy plastic deformation, and in particular to a method for determining a loading frequency range of a magnesium alloy component in engineering. Background Art

[0002] Lightweighting has become an important strategy in modern manufacturing. Extruded magnesium alloys are widely used in transportation fields such as railway transportation and aerospace due to their high specific strength, high specific stiffness and ideal toughness. The dynamic behavior of magnesium alloys under cyclic loads has received widespread attention. As metal structural parts, they will undergo plastic deformation and ratchet effect due to fatigue when used under complex working conditions. Therefore, it is necessary to clarify their fatigue performance and durability. Due to their anisotropy, magnesium alloys usually have more complex cyclic stress-strain responses than other metals.

[0003] During the cyclic loading process under stress control, the accumulated plastic deformation has a significant effect on the damage of the material. Generally speaking, increasing the loading frequency or reducing the average stress will reduce the ratchet strain and extend the fatigue life of the magnesium alloy. So far, the method used to analyze whether magnesium alloy components can be applied to fatigue load environments is still to determine the relationship between the fatigue limit stress of the component and the use environment (the fatigue limit stress is less than the maximum stress in the fatigue environment). In the above judgment process, the ratchet strain during stress loading and the influence of the loading frequency that is closely related to the ratchet strain size are not considered. Therefore, it is necessary to establish a method to determine the possible ratchet strain extreme value by adjusting the frequency of the stress control cycle process under given load conditions. Summary of the invention

[0004] In view of the shortcomings of the prior art, the present invention provides a method for determining the loading frequency range of magnesium alloy components in engineering, which can solve the related problems of the influence of frequency on ratchet strain during the application of components, and find a more reasonable and accurate method for the extreme value of ratchet strain under stress control, thereby determining the frequency range of safe application of components under given loading conditions.

[0005] A method for determining the loading frequency range of a magnesium alloy component in engineering comprises the following steps:

[0006] Step 1: Determine the texture and stress loading mode of magnesium alloy components and materials, and produce samples that meet fatigue test standards;

[0007] The fatigue test standard is the fatigue test standard in GB / T15248 Axial Constant Amplitude Low Cycle Fatigue Test Method for Metal Materials;

[0008] Step 2: Perform a monotonic tensile or compression test at 18°C ​​to 25°C to obtain basic mechanical properties of the material, including tensile yield strength, compressive yield strength, tensile strength and compressive strength;

[0009] Step 3, determine the loading stress, select different loading frequencies under a given stress level, first select a frequency below 0.5 Hz for cyclic loading experiments, and compare the strain values ​​under different loading frequencies: when the strain value decreases with increasing frequency, continue to increase the frequency for experiments; when the strain value begins to increase, it means that under the above stress loading conditions, the last selected loading frequency makes the strain value reach an extreme point, select a larger loading frequency for cyclic loading experiments, and the strain extreme value continues to increase, indicating that the above strain extreme point is the minimum point under the current loading stress level.

[0010] Step 4: According to the maximum strain and minimum strain of the material in each cycle in the asymmetric cyclic experiment obtained in the experiment, the ratchet strain formula is as follows: ε r =(ε max +ε min ) / 2 to calculate the ratchet strain at different cyclic frequencies, where ε min and ε max They represent the maximum and minimum points respectively, and the curves of ratchet strain variation with period at different frequencies are plotted;

[0011] Step 5: Determine the frequency corresponding to the minimum point of the ratchet strain according to the relationship between the ratchet strain and the loading frequency. That is, when the applied loading frequency is less than the frequency corresponding to the minimum point of the ratchet strain, the ratchet strain decreases with the increase of the loading frequency. When the applied loading frequency is greater than the frequency corresponding to the minimum point of the ratchet strain, the ratchet strain increases with the increase of the loading frequency.

[0012] Step 6: According to the provisions of the ratchet strain extreme value corresponding to the loading condition of the metal material, the ratchet strain is within the maximum value and the minimum value range, and the corresponding loading frequency range is selected;

[0013] Step 7: Determine the safety reliability and life of the component based on the frequency of the loading environment and the ratchet strain. When the loading frequency is less than the frequency corresponding to the minimum value of the ratchet strain, the greater the frequency, the smaller the ratchet strain, the longer the life, and the higher the reliability; when the loading frequency is greater than the frequency corresponding to the minimum value of the ratchet strain, the smaller the frequency, the smaller the ratchet strain, the longer the life, and the higher the reliability.

[0014] The beneficial effects of adopting the above technical solution are:

[0015] The present invention provides a method for determining the loading frequency range of a magnesium alloy component in an engineering project. The method provides a method for quickly judging the loading frequency range of a magnesium alloy applicable to a load environment according to the size of a ratchet strain under stress-controlled cyclic loading conditions. The loading frequency is adjusted according to a critical value to control the size of the plastic deformation and the ratchet strain generated during the cyclic loading process, so that the magnesium alloy component meets the engineering application environment.

[0016] The present invention can determine the loading frequency range of structural parts in the cyclic process according to the ratchet strain, provide a theoretical basis for determining the service safety frequency range of extruded magnesium alloys, and has important practical significance for analyzing the reliability and safety of components under cyclic loads and predicting the fatigue life of materials.

[0017] The present invention realizes comprehensive sharing of data information for the public, improves the method of judging the reliability of magnesium alloy components, and has important theoretical and practical significance for related research on ratchet strain. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The relationship between ratchet strain and cyclic loading times at different loading frequencies in the embodiment of the present invention;

[0019] Figure 2 The relationship between the ratchet strain and the number of loading times when the ratchet strain increases with the increase of the loading frequency in the embodiment of the present invention;

[0020] Figure 3 The relationship between the ratchet strain and the number of loading times when the ratchet strain decreases with the increase of the loading frequency in the embodiment of the present invention;

[0021] Figure 4 Evolution curve of the relationship between ratchet strain and loading frequency according to an embodiment of the present invention. DETAILED DESCRIPTION

[0022] The specific implementation of the present invention is further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0023] A method for determining the loading frequency range of a magnesium alloy component in engineering comprises the following steps:

[0024] Step 1: Determine the texture and stress loading mode of magnesium alloy components and materials, and produce samples that meet fatigue test standards;

[0025] The fatigue test standard is the fatigue test standard in GB / T15248 Axial Constant Amplitude Low Cycle Fatigue Test Method for Metal Materials;

[0026] In this embodiment, the material used in the experiment is an extruded magnesium alloy rod, and the texture form is a fiber texture. In order to eliminate the internal stress of the material and obtain an equiaxed recrystallized structure, the original rod is subjected to an annealing heat treatment at 520°C / 80min, and a round rod with a diameter of 16mm is cut along the axial direction of the rod, and further processed into fatigue test samples with a gauge length of 20mm and a diameter of 10mm, and the samples are polished to meet the experimental requirements.

[0027] Step 2: Perform the test at a strain rate of 10 at 18°C ​​to 25°C. -3 / s monotonic tension or compression test to obtain the basic mechanical properties of the material, including tensile yield strength, compressive yield strength, tensile strength and compressive strength;

[0028] Step 3, determine the loading stress, select different loading frequencies under a given stress level, first select a frequency below 0.5 Hz for cyclic loading experiments, and compare the strain values ​​under different loading frequencies: when the strain value decreases with increasing frequency, continue to increase the frequency for experiments; when the strain value begins to increase, it means that under the above stress loading conditions, the last selected loading frequency makes the strain value reach an extreme point, select a larger loading frequency for cyclic loading experiments, and the strain extreme value continues to increase, indicating that the above strain extreme point is the minimum point under the current loading stress level.

[0029] In this embodiment, the stress level with an average stress of -75Mpa and a stress amplitude of 105Mpa is taken as an example to determine the influence of the loading frequency on the ratchet strain value. The stress cycle experiment is carried out in a compression-compression form, and the loading waveform is a triangular wave along the axial direction of the sample.

[0030] Step 4: According to the maximum strain and minimum strain of the material in each cycle in the asymmetric cyclic experiment obtained in the experiment, the ratchet strain formula is as follows: ε r =(ε max +ε min ) / 2 to calculate the ratchet strain at different cyclic frequencies, where ε min and ε max They represent the maximum and minimum points respectively, and the curves of ratchet strain variation with period at different frequencies are plotted;

[0031] In this embodiment, the preferred frequencies are 0.02 Hz, 0.1 Hz, 0.2 Hz and 0.4 Hz. A cyclic loading experiment with asymmetric stress control is carried out on the magnesium alloy material, and fatigue tests with different loading frequencies are carried out under the above stress level. The relationship between ratchet strain and cyclic loading times at different loading frequencies is shown in Figure 1 shown.

[0032] Step 5: Determine the frequency corresponding to the minimum point of the ratchet strain according to the relationship between the ratchet strain and the loading frequency. That is, when the applied loading frequency is less than the frequency corresponding to the minimum point of the ratchet strain, the ratchet strain decreases with the increase of the loading frequency. When the applied loading frequency is greater than the frequency corresponding to the minimum point of the ratchet strain, the ratchet strain increases with the increase of the loading frequency.

[0033] In this embodiment, the ratchet strain magnitude relationship is 0.02Hz>0.1Hz>0.2Hz>0.4Hz, and the cycle life magnitude relationship is 0.02Hz<0.1Hz<0.2Hz<0.4Hz. The ratchet strain increases with the increase of frequency, and the fatigue life decreases. When the ratchet strain increases with the increase of loading frequency, the relationship between the ratchet strain and the number of loading times is as follows: Figure 2 As shown in the figure, the relationship between the ratchet strain and the number of loading times is as follows: Figure 3 As shown;

[0034] Step 6: According to the provisions of the ratchet strain extreme value corresponding to the loading condition of the metal material, the ratchet strain is within the maximum value and the minimum value range, and the corresponding loading frequency range is selected;

[0035] In this embodiment, a loading frequency greater than 0.4 Hz (0.6 Hz, 1.0 Hz and 2.0 Hz) is selected to continue the cyclic loading experiment to determine the relationship between the above frequency and the ratchet strain. The experimental results show that the ratchet strain size relationship is 2.0 Hz > 1.0 Hz > 0.6 Hz > 0.4 Hz, and the cycle life size relationship is 2.0 Hz < 1.0 Hz < 0.6 Hz < 0.4 Hz. This indicates that the corresponding ratchet strain is the minimum point when the loading frequency is 0.4 Hz.

[0036] Step 7: Determine the safety reliability and life of the component based on the frequency of the loading environment and the ratchet strain. The relationship evolution curve between the ratchet strain and the loading frequency is as follows: Figure 4 When the loading frequency is less than the frequency corresponding to the minimum ratchet strain point, the greater the frequency, the smaller the ratchet strain, the longer the life, and the higher the reliability; when the loading frequency is greater than the frequency corresponding to the minimum ratchet strain point, the smaller the frequency, the smaller the ratchet strain, the longer the life, and the higher the reliability.

[0037] In this example, the influence of different frequencies on the ratchet strain and its evolution trend are observed, and the variation of the ratchet strain with frequency is analyzed. The cyclic experiments under all frequency conditions in this example show that the ratchet strain decreases with the increase of frequency and the lifespan increases in the range of 0.02Hz to 0.4Hz. In the range of 0.4Hz to 2.0Hz, the ratchet strain increases with the increase of frequency and the lifespan decreases.

[0038] The above description is only a preferred embodiment of the present disclosure and an explanation of the technical principles used. Those skilled in the art should understand that the scope of the invention involved in the embodiments of the present disclosure is not limited to the technical solutions formed by a specific combination of the above-mentioned technical features, but should also cover other technical solutions formed by any combination of the above-mentioned technical features or their equivalent features without departing from the above-mentioned inventive concept. For example, the above-mentioned features are replaced with the technical features with similar functions disclosed in the embodiments of the present disclosure (but not limited to) to form a technical solution.

Claims

1. A method for determining the loading frequency range of a magnesium alloy component in an engineering project, characterized in that: The following steps are involved: Step 1: Determine the texture and stress loading mode of magnesium alloy components and materials, and produce samples that meet fatigue test standards; Step 2: Perform a monotonic tensile or compression test at 18°C ​​to 25°C to obtain basic mechanical properties of the material; Step 3, determine the loading stress, select different loading frequencies under a given stress level, first select a frequency below 0.5 Hz for cyclic loading experiments, and compare the strain values ​​under different loading frequencies: when the strain value decreases with increasing frequency, continue to increase the frequency for experiments; when the strain value begins to increase, it means that under the above stress loading conditions, the last selected loading frequency makes the strain value reach an extreme point, select a larger loading frequency for cyclic loading experiments, and the strain extreme value continues to increase, indicating that the above strain extreme point is the minimum point under the current loading stress level; Step 4: According to the maximum strain and minimum strain of the material in each cycle in the asymmetric cyclic experiment obtained in the experiment, the ratchet strain formula is as follows: ε r =( ε max + ε min ) / 2, calculate the ratchet strain at different cycle frequencies, where ε min and ε max They represent the maximum and minimum points respectively, and the curves of ratchet strain variation with period at different frequencies are plotted; Step 5, judging the frequency corresponding to the minimum point of the ratchet strain according to the relationship between the ratchet strain and the loading frequency, that is, when the applied loading frequency is less than the frequency corresponding to the minimum point of the ratchet strain, the ratchet strain decreases with the increase of the loading frequency, and when the applied loading frequency is greater than the frequency corresponding to the minimum point of the ratchet strain, the ratchet strain increases with the increase of the loading frequency; Step 6: According to the provisions of the ratchet strain extreme value corresponding to the loading condition of the metal material, the ratchet strain is within the maximum value and the minimum value range, and the corresponding loading frequency range is selected; Step 7, determining the safety reliability and life of the component according to the frequency of the loading environment and the ratchet strain; As described in step 7, the safety reliability and life of the component are determined according to the frequency of the loading environment and the ratchet strain. When the loading frequency is less than the frequency corresponding to the minimum point of the ratchet strain, the larger the frequency, the smaller the ratchet strain, the longer the life and the higher the reliability; when the loading frequency is greater than the frequency corresponding to the minimum point of the ratchet strain, the smaller the frequency, the smaller the ratchet strain, the longer the life and the higher the reliability.

2. A method for determining the loading frequency range of a magnesium alloy component in engineering according to claim 1, characterized in that: The fatigue test standard described in step 1 is the fatigue test standard in GB / T15248 Axial Constant Amplitude Low Cycle Fatigue Test Method for Metal Materials.

3. A method for determining the loading frequency range of a magnesium alloy component in engineering according to claim 1, characterized in that: The basic mechanical performance parameters described in step 2 include: tensile yield strength, compressive yield strength, tensile strength and compressive strength.

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