Railway axle critical load calculation method considering surface residual stress

Abstract

The invention discloses a railway axle critical load calculation method considering surface residual stress, and relates to the field of mechanical engineering. The method comprises the following steps: correcting a stress intensity factor at a surface defect of a railway axle by considering a residual stress field generated by the railway axle under the dual action of rolling and foreign matter impact, so as to obtain a corrected effective stress intensity factor amplitude delta Keff; the corrected stress intensity factor amplitude is compared with a defect expansion threshold value delta Kth, and when delta Koff is equal to delta Kth, the loaded load is the critical load. According to the scheme, the stress intensity factor and the defect expansion threshold value at the defect are analyzed, so that the critical loading load of the axle steel in a corrosion environment under the dual effects of rolling strengthening and foreign matter impact is explored; the critical load of the railway axle can be effectively improved by introducing a residual stress field to a certain depth of the surface of the reinforced component, and data support is provided for ensuring the safety and reliability of railway transportation.

Description

Technical Field

[0001] The invention relates to the field of mechanical engineering, and in particular to a method for calculating critical load of a railway axle taking into account surface residual stress. Background Art

[0002] China's high-speed rail has developed rapidly and achieved remarkable results. With the increase in train speed, the axle surface is easily hit by foreign objects such as ballast and ice slag rolled up due to aerodynamic effects, causing foreign object damage, destroying its structural integrity, and exposing the material interior to the service environment. In addition, my country has a vast territory and a complex climate environment, which places higher requirements on the adaptability of various vehicle components in complex environments. Under the coupling of alternating loads, surface damage and corrosive environment, the service life of the axle is greatly reduced, which seriously threatens the safety of train operation. In the process of structural design, processing and manufacturing and service of the axle, residual stress is an important factor affecting its service behavior and life cycle. Residual tensile stress increases the local force of the axle by superimposing with the external load, promotes crack initiation, and reduces fatigue performance. Residual compressive stress can offset part of the external load, inhibit crack initiation and propagation to a certain extent, thereby improving fatigue performance. Therefore, it is necessary to conduct in-depth research on the residual stress field at the notch under the dual effects of foreign object impact and rolling strengthening, so as to accurately grasp the critical load of the axle under the influence of the two mechanisms. Summary of the invention

[0003] The object of the present invention is to overcome one or more deficiencies of the prior art and to provide a method for calculating the critical load of a railway axle taking into account surface residual stress.

[0004] The objective of the present invention is achieved through the following technical solutions:

[0005] A method for calculating the critical load of a railway axle considering surface residual stress, the calculation method is an analysis of the stress intensity factor at the defect, and the specific steps are:

[0006] Step S1. By considering the residual stress field generated by rolling and foreign body impact on the railway axle, the stress intensity factor at the surface defect (according to the theory proposed by Murakami, the defect is equivalent to a semi-elliptical surface crack with the same projected area in the loading direction) is analyzed and corrected, so as to obtain the corrected effective stress intensity factor amplitude ΔK eff ;

[0007] Step S2: The corrected stress intensity factor amplitude ΔK eff and the defect extension threshold ΔK th For comparison, when ΔK eff =ΔK th When , the applied load is the critical load;

[0008] In the step S1, when analyzing the stress intensity factor at the defect, the stress intensity factor amplitude ΔK eff The calculation formula of (EffectiveΔK) is:

[0009] ΔK eff =K eff,max -K eff，min ;

[0010] Where K eff,max , K eff,min They are:

[0011] K eff,max =K max +K r ;

[0012] K eff,min =K min +K r ;

[0013] Among them, K max With K min is the maximum and minimum value of the stress intensity factor applied by the load, K r is the stress intensity factor generated by the residual stress field;

[0014] In step S2, the defect extension threshold ΔK th The calculation formula is:

[0015]

[0016] Where, α = 0.226 + Hv × 10 -4 , R is the real stress ratio at the defect, Hv is the hardness value of the strengthening layer; through ΔK eff With ΔK th The size between them is used to obtain the critical loading load value of the railway axle under different defect sizes, that is, the critical load.

[0017] Furthermore, in step S1, if there is residual compressive stress at the defect, then K r The value may be negative, so K r There are two situations:

[0018] 1) When:

[0019]

[0020] at this time:

[0021] ΔK eff =(K max +K r )-(Kmin +K r )=K max -K min =ΔK;

[0022] 2) When:

[0023]

[0024] at this time:

[0025] ΔK eff =(K max +K r )-(K min +K r )=K max +K r -0=K max +K r ;

[0026] Among them, R eff is the effective stress ratio.

[0027] Furthermore, in step S1, the K r The calculation method is:

[0028]

[0029] Among them, σ res (x) is the stress distribution function at the defect, m(x,a) is the weight function, and a is the ordinate of point A, the deepest point of the crack;

[0030] Furthermore, since the rolling process increases the roughness of the sample surface, this surface roughness can be considered as tiny pits to a certain extent. These pits will cause stress concentration on the sample surface and increase the stress intensity factor value borne by the sample. In step S1, the following formula is used to correct the stress intensity factor generated by the load, and K max and K min Perform the calculation:

[0031]

[0032] Among them, K t is the stress concentration factor caused by surface roughness, and σ is the fatigue limit of the smooth specimen.

[0033] in,

[0034]

[0035] R tm is the average peak-to-valley height, S m is the distance between adjacent peaks.

[0036] The beneficial effects of the present invention are:

[0037] (1) The stress intensity factor and defect extension threshold at the defect site were analyzed to explore the critical loading load of the axle in a corrosive environment under the dual effects of rolling hardening and foreign body impact;

[0038] (2) By introducing a residual stress field at a certain depth on the surface of the strengthened component, the corrosion fatigue performance of the component is improved, so that the surface defects have a critical non-extended size, that is, defects smaller than this size can have the same fatigue limit value as smooth specimens;

[0039] (3) By calculating, rationally utilizing and controlling surface residual stress, the critical load of railway axles and bridges can be effectively increased, providing data support for ensuring the safety and reliability of railway transportation. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 For R eff >0 when the stress intensity factor amplitude ΔK eff (EffectiveΔK) schematic diagram;

[0041] Figure 2 For R eff ≤0 when stress intensity factor amplitude ΔK eff (EffectiveΔK) schematic diagram;

[0042] Figure 3 This is the image of the rolling surface roughness;

[0043] Figure 4 Schematic diagram of residual stress field in rolling layer;

[0044] Figure 5 This is the data analysis diagram of a semi-elliptical crack in a finite thickness plate. DETAILED DESCRIPTION

[0045] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0046] This embodiment provides a method for calculating the critical load of a railway axle taking into account the surface residual stress. The calculation method is an analysis of the stress intensity factor at the defect, and the specific steps are:

[0047] Step S1. By considering the residual stress field generated by rolling and foreign body impact on the railway axle, the stress intensity factor at the surface defect (according to the theory proposed by Murakami, the defect is equivalent to a semi-elliptical surface crack with the same projected area in the loading direction) is analyzed and corrected, so as to obtain the corrected effective stress intensity factor amplitude ΔK eff ;

[0048] Step S2: The corrected stress intensity factor amplitude ΔK eff and the defect extension threshold ΔK th For comparison, when ΔK eff =ΔK th When , the applied load is the critical load;

[0049] In the step S1, when analyzing the stress intensity factor at the defect, the stress intensity factor amplitude ΔK eff The calculation formula of (EffectiveΔK) is:

[0050] ΔK eff =K eff,max -K eff，min ;

[0051] Among them, K eff,max , K eff,min They are:

[0052] K eff,max =K max +K r ,

[0053] K eff,min =K min +K r ,

[0054] Among them, K max With K min is the maximum and minimum value of the stress intensity factor applied by the load, K r is the stress intensity factor generated by the residual stress field;

[0055] In step S2, the defect extension threshold ΔK th The calculation formula is:

[0056]

[0057] Where, α = 0.226 + Hv × 10 -4 , R is the real stress ratio at the defect, Hv is the hardness value of the strengthening layer; through ΔK eff With ΔK thThe size between them is used to obtain the critical loading load value in the corrosion environment of railway axles under different defect sizes, that is, the critical load.

[0058] See also Figure 1-Figure 2 , stress intensity factor analysis at the defect, there is residual compressive stress at the defect, then K r The value may be negative, so K r There are two situations:

[0059] 1) If Figure 1 As shown, when:

[0060]

[0061] at this time:

[0062] ΔK eff =(K max +K r )-(K min +K r )=K max -K min =ΔK;

[0063] 2) If Figure 2 As shown, when:

[0064]

[0065] at this time:

[0066] ΔK eff =(K max +K r )-(K min +K r )=K max +K r -0=K max +K r ;

[0067] Among them, R eff is the effective stress ratio.

[0068] See also Figure 3 Since the rolling process increases the roughness of the sample surface, this surface roughness can be considered as tiny pits. These pits will cause stress concentration on the sample surface and increase the stress intensity factor value borne by the sample. The following formula is used to correct the stress intensity factor generated by the load and K max and K min Perform the calculation:

[0069]

[0070] Among them, K tis the stress concentration factor caused by surface roughness:

[0071]

[0072] R tm is the average peak-to-valley height, S m is the distance between adjacent peaks.

[0073] See also Figure 5 For a semi-elliptical crack, the maximum stress intensity factor is usually located at the deepest part of the crack (point A), and the minimum stress intensity factor is located at the crack surface (point B). The stress intensity factor formed by the residual stress at the deepest point A and the crack surface point B is fitted through the weight function to obtain the values ​​of a and c, which are:

[0074]

[0075] Among them, m A (x,a) is the weight function of the deepest crack (point A), and a is the ordinate of point A;

[0076]

[0077] M 2A =3,

[0078]

[0079] in:

[0080]

[0081] Similarly, the weight function of point B on the crack surface is:

[0082]

[0083] M 3B =-(1+M 1B +M 2B )

[0084] in:

[0085]

[0086] The stress intensity factor generated by the residual stress at the crack points A and B is calculated by the above weight function. Crack extension threshold: According to the Murakami formula:

[0087]

[0088] Where, α = 0.226 + Hv × 10 -4 , R is the true stress ratio at the defect, and Hv is the hardness value of the strengthening layer.

[0089] Conclusion: Through ΔK eff With ΔK th The size between them is calculated to obtain the critical loading load value of railway axle under different defect sizes.

[0090] This embodiment analyzes the stress intensity factor at the defect and the defect extension threshold value to explore the critical loading load of the axle in a corrosive environment under the dual effects of rolling strengthening and foreign body impact; by introducing a residual stress field at a certain depth on the surface of the strengthened component, it helps to improve the fatigue performance of the component, so that the surface defects have a critical non-expanded size, that is, defects smaller than this size can have the same fatigue limit value as the smooth specimen; by calculating and reasonably utilizing and controlling the surface residual stress, the critical load of the railway axle can be effectively improved, providing data support for ensuring the safety and reliability of railway transportation.

[0091] The above is only a preferred embodiment of the present invention. It should be understood that the present invention is not limited to the form disclosed herein, and should not be regarded as excluding other embodiments, but can be used in various other combinations, modifications and environments, and can be modified within the scope of the concept described herein through the above teachings or the technology or knowledge of the relevant field. The changes and modifications made by those skilled in the art shall not deviate from the spirit and scope of the present invention, and shall be within the scope of protection of the claims attached to the present invention.

Claims

1. A method for calculating the critical load of a railway axle considering surface residual stress, characterized in that: The calculation method is an analysis of the stress intensity factor at the defect, and the specific steps are: Step S1. By considering the residual stress field generated by rolling and foreign body impact on the railway axle, the stress intensity factor of the surface defect is analyzed and corrected to obtain the corrected effective stress intensity factor amplitude ΔK eff ; Step S2: The corrected stress intensity factor amplitude ΔK eff and the defect extension threshold ΔK th For comparison, when ΔK eff =ΔK th When , the applied load is the critical load; In the step S1, when analyzing the stress intensity factor at the defect, the stress intensity factor amplitude ΔK eff The calculation formula is: ΔK eff =K eff,max -K eff，min ; Where K eff,max , K eff,min They are: K eff,max =K max +K r ; K eff,min =K min +K r ; Among them, K max With K min is the maximum and minimum value of the stress intensity factor applied by the load, K r is the stress intensity factor generated by the residual stress field; In step S2, the defect extension threshold ΔK th The calculation formula is: Where, α = 0.226 + Hv × 10 -4 , R is the real stress ratio at the defect, Hv is the hardness value of the strengthening layer; through ΔK eff With ΔK th The critical load of railway axle under different defect sizes is obtained by calculating the size between them.

2. A method for calculating critical load of railway axles considering surface residual stress according to claim 1, characterized in that: In step S1, K r There are two situations: 1) When: at this time: ΔK eff =(K max +K r )-(K min +K r )=K max -K min =ΔK; 2) When: at this time: ΔK eff =(K max +K r )-(K min +K r )=K max +K r -0=K max +K r ; Among them, R eff is the effective stress ratio.

3. The method for calculating the critical load of a railway axle considering surface residual stress according to claim 1, characterized in that: In step S1, the K r The calculation method is: Among them, σ res (x) is the stress distribution function at the defect, and m(x,a) is the weight function.

4. The method for calculating the critical load of a railway axle considering surface residual stress according to claim 1, characterized in that: In step S1, the stress intensity factor generated by the applied load is corrected using the following formula, and K max and K min Calculation: Among them, K t is the stress concentration factor caused by surface roughness, and σ is the fatigue limit of the smooth specimen.

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