Method for calculating wear depth of rough joint surface of combined piston top skirt bolt

Abstract

The invention provides a method for calculating the wear depth of a rough joint surface of a combined piston top skirt bolt, and relates to the technical field of health state evaluation of the rough joint surface of the combined piston top skirt bolt of a diesel engine. The method comprises the following steps: obtaining basic parameters of a rough joint surface of the combined piston top skirt bolt and an alternating load borne by the joint surface of the piston top skirt bolt; constructing a piston top skirt bolt rough joint surface contact non-uniform pressure distribution model; according to the piston top skirt bolt rough junction surface contact non-uniform pressure distribution model, the tangential micro-slip length of the piston top skirt bolt rough junction surface is deduced; and according to the contact non-uniform pressure distribution model of the rough joint surface of the piston top skirt bolt and the tangential micro-slip length of the rough joint surface of the piston top skirt bolt, predicting the fretting wear depth of the rough joint surface of the combined piston top skirt bolt under the action of the alternating load so as to accurately predict the fretting wear depth of the joint surface of the bolt. The method is good in universality in an application scene of piston top skirt bolt joint surface health state evaluation.

Description

Technical Field

[0001] The invention relates to the technical field of health status assessment of rough joint surfaces of combined piston top skirt bolts of diesel engines, in particular to a method for calculating the wear depth of rough joint surfaces of combined piston top skirt bolts. Background Art

[0002] During the operation of a diesel engine, the piston top skirt bolt joint surface not only bears assembly loads such as bolt preload generated during the assembly process, but also bears alternating loads such as periodic gas explosion pressure, inertial restoring force, and rotational restoring force formed by the combustion pressure in the cylinder. Under the action of these periodic composite alternating loads, the bolt connection joint surface produces high-frequency micro-relative sliding locally. Since the micro-relative sliding between the joint surfaces is in a friction state, micro-motion wear occurs on the joint surface. Accurately predicting the micro-motion wear depth of the rough joint surface of the piston top skirt bolt helps to evaluate the health status of the rough joint surface of the combined piston top skirt bolt of a diesel engine.

[0003] For wear simulation prediction methods, the existing patents are as follows: Taking the Chinese invention patent CN106844912A as an example, a wear simulation method for a kinematic pair of a mechanism using mesh deformation technology is disclosed. By dividing the contact surface into meshes, the ADAMS software command stream is written using matlab and combined with ADAMS dynamics simulation to calculate the wear depth of the kinematic pair. Taking the Chinese invention patent CN114218815A as an example, a wear simulation method based on ABAQUS is disclosed. The interface model is solved by ABAQUS software and the odb file of the variables required by the wear formula is obtained. Then the data in the file is extracted using Python language and substituted into the wear formula to realize wear simulation prediction. Taking the Chinese invention patent CN117874995A as an example, a wear simulation prediction model for a kinematic mechanism based on dynamic characteristics is disclosed. A geometric model of the ball pair of a vector nozzle is established. Two subroutines of the wear factor and friction coefficient in the ABAQUS software are developed using Fortran language. At the same time, the parametric modeling of the ball pair is realized using Python language. The above method is based on the solution of the contact surface setting by finite element software, and the wear depth of the contact surface is predicted by secondary development. However, these methods ignore the rough morphology between the contact surfaces during modeling. At the same time, the finite element simulation-based methods can only obtain the contact surface wear characteristics under specific structural parameter conditions. Replacing the structural parameters requires re-modeling, which lacks versatility and takes a long time to calculate.

[0004] However, the technical solution disclosed in the above patent document cannot be fully applied to the special conditions of the bolt joint surface of the combined piston top skirt of a diesel engine. The alternating load of the pressure inside the diesel engine's gas cylinder on the bolt joint surface of the combined piston top skirt and the surface roughness morphology characteristics of the bolt joint surface have not been considered, and the wear depth measurement experiment on the bolt joint surface of the piston top skirt is relatively complicated. Summary of the invention

[0005] In order to solve a technical problem existing in the prior art, an embodiment of the present invention provides a method for calculating the wear depth of the rough joint surface of the combined piston top skirt bolt, so as to solve the problems of the existing finite element simulation method being insufficient in versatility and being unable to consider the rough morphology, as well as the limitation of the experimental method being complex in measurement, and can accurately predict the fretting wear depth of the rough joint surface of the combined piston top skirt bolt. The technical solution is as follows:

[0006] A method for calculating the wear depth of a rough joint surface of a combined piston top skirt bolt includes:

[0007] S1. Obtaining basic parameters of the rough joint surface of the combined piston top skirt bolt and the alternating load on the joint surface of the piston top skirt bolt;

[0008] S2. Based on the basic parameters of the rough joint surface of the combined piston top skirt bolt and the alternating load on the joint surface of the piston top skirt bolt, a contact non-uniform pressure distribution model of the rough joint surface of the piston top skirt bolt is constructed;

[0009] S3, deriving the tangential micro-slip length of the rough joint surface of the piston top skirt bolt according to the non-uniform pressure distribution model of the rough joint surface of the piston top skirt bolt;

[0010] S4. Predict the micro-wear depth of the rough joint surface of the combined piston top skirt bolt under the action of alternating load based on the contact non-uniform pressure distribution model of the rough joint surface of the piston top skirt bolt and the tangential micro-slip length of the rough joint surface of the piston top skirt bolt.

[0011] Optionally, the formula of the non-uniform pressure distribution model of the rough joint surface of the piston top skirt bolt of S2 is formula (1):

[0012] ; (1)

[0013] in, is the obtained alternating load amplitude;

[0014] α is a non-negative coefficient (α≥0) that characterizes different pressure functions, α=0 corresponds to uniform pressure distribution, and α>0 corresponds to non-uniform pressure distribution;

[0015] L bis the length of the equivalent beam of the rough joint surface of the piston top skirt bolt;

[0016] x is the different positions of the equivalent beam on the rough joint surface of the piston top skirt bolt;

[0017] The pressure distribution function p(x) satisfies , N0 is the bolt preload, and S is the contact area.

[0018] Optionally, the step S3 of deriving the tangential micro-slip length of the rough joint surface of the piston top skirt bolt according to the non-uniform pressure distribution model of the rough joint surface of the piston top skirt bolt comprises:

[0019] S301, establishing a shear layer model, wherein the shear layer model is a one-dimensional rectangular beam subjected to a tangential load F t Excitation, the length of the one-dimensional rectangular beam is L b , the cross-sectional area of ​​the one-dimensional rectangular beam is A, and the elastic modulus of the shear layer model is E;

[0020] S302, based on the shear layer model, obtaining the displacement of the overall sliding state corresponding to when the one-dimensional rectangular beam slips, and the displacement of the rough interface when the one-dimensional rectangular beam does not slip;

[0021] S303, obtaining a tangential micro-slip length of the rough joint surface of the piston top skirt bolt according to the displacement of the overall sliding state corresponding to the one-dimensional rectangular beam when the one-dimensional rectangular beam slips and the rough interface displacement when the one-dimensional rectangular beam does not slip.

[0022] Optionally, the formula of the shear layer model is formula (2):

[0023] ; (2)

[0024] Where u is the displacement of a point at a distance x from the left end of the beam;

[0025] μ is the shear layer obeys Coulomb friction law and the friction coefficient;

[0026] K t is the tangential contact stiffness;

[0027] L1 is the length of the slip zone.

[0028] Optionally, when the one-dimensional rectangular beam slips in S302, the corresponding displacement of the overall slip state is The formula is formula (3):

[0029] ; (3)

[0030] The formula for the rough interface displacement when the one-dimensional rectangular beam does not slip in S302 is formula (4):

[0031] ; (4)

[0032] is the dimensionless position coordinate, expressed as , It is defined as the dimensionless stiffness of the left-end spring relative to the compressive stiffness of the beam and is expressed as , Defined as the ratio of the shear layer tangential contact stiffness to the beam compressive stiffness.

[0033] Optionally, the formula for the ratio λ of the shear layer tangential contact stiffness to the beam compressive stiffness is formula (5):

[0034] ; (5)

[0035] Where G is the shear modulus, H is e is the material hardness, β is the dimensionless adhesion zone length, n is the number of asperity contacts, A n is the nominal contact area, σ r is the standard deviation of the asperity height distribution, σ rs is the standard deviation of the surface height, z n is the height of the microconvex body, f s is the asperity contact load.

[0036] Optionally, the tangential micro-slip length of the rough joint surface of the piston top skirt bolt in 303 is:

[0037] ; (6)

[0038] Where u(x) is the displacement when the rough interface has slip, u e (x) is the displacement when there is no slip on the rough interface.

[0039] Optionally, the step S4 predicts the fretting wear depth of the rough joint surface of the combined piston top skirt bolt under the action of the alternating load according to the contact non-uniform pressure distribution model of the rough joint surface of the piston top skirt bolt and the tangential micro-slip length of the rough joint surface of the piston top skirt bolt, including:

[0040] When the peaks of the micro-convex bodies on the rough interface are worn away and the stress reaches the yield limit of the micro-convex body material, n peaks of the contact interface are worn away, and the relationship between the initial preload force W and the yield limit s is expressed as formula (7):

[0041] ; (7)

[0042] in, is the yield limit of the micro-convex material, a c is the radius of the microconvex body, S c is the maximum contact area of ​​the micro-asperity protrusion during the wear process;

[0043] Based on the initial preload, when the contact interface slides for a length of L, the Archard wear calculation model is as follows:

[0044] ; (9)

[0045] Q0 is the wear volume, K is the wear factor, and H is the hardness;

[0046] Based on formula (7) and formula (9), the fretting wear depth of the rough joint surface of the combined piston top skirt bolt under the action of the alternating load is obtained. The prediction formula for the fretting wear depth of the rough joint surface of the combined piston top skirt bolt under the action of the alternating load is formula (12):

[0047] ; (12)

[0048] Among them, d(x) is the relative sliding length of the rough joint surface of the bolt, t is the sliding time, and h is the wear depth.

[0049] Optionally, the yield limit formula of the micro-convex material is formula (8):

[0050] ; (8)

[0051] The incremental mode formula of the Archard wear calculation model is formula (10):

[0052] ; (10)

[0053] in, ; ; ; v is the relative slip velocity of the interface, and p is the non-uniform pressure distribution.

[0054] Based on formula (8) to formula (10), formula (11) includes:

[0055] :(11).

[0056] The beneficial effects brought about by the technical solution provided by the embodiment of the present invention include at least:

[0057] The method for predicting the fretting wear depth of the rough joint surface of the piston top skirt bolt provided by the present invention takes into account the rough morphological characteristics of the piston top skirt bolt joint surface and the non-uniform pressure distribution of the rough joint surface of the piston top skirt bolt under alternating loads, thereby solving the limitations of existing finite element simulations and the complexity of experimental measurement methods.

[0058] The present invention accurately predicts the fretting wear depth of the rough joint surface of the piston top skirt bolt, and provides a basis for the health status evaluation of the rough joint surface of the combined piston top skirt bolt of the diesel engine. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0060] Figure 1 A schematic flow chart of a method for calculating the fretting wear depth of the rough joint surface of the combined piston top skirt bolt under the action of alternating loads provided by an embodiment of the present invention;

[0061] Figure 2 A schematic diagram of the principle of fretting wear of the rough joint surface of the piston top skirt bolt provided by an embodiment of the present invention;

[0062] Figure 3 A schematic diagram of a shear layer micro-slip model of a rough joint surface of a piston top skirt bolt provided in an embodiment of the present invention;

[0063] Figure 4 A schematic diagram for comparing the wear depth predicted by the present invention and the experimental measurement result provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0064] In order to make the purpose, technical solution and advantages of the embodiment of the present invention clearer, the technical solution of the embodiment of the present invention will be clearly and completely described below in conjunction with the drawings of the embodiment of the present invention. Obviously, the described embodiment is a part of the embodiment of the present invention, not all of the embodiments. Based on the described embodiment of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0065] Unless otherwise defined, the technical terms or scientific terms used in the present invention should be understood by people with ordinary skills in the field to which the present invention belongs. The words "first", "second" and similar words used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. Similarly, words such as "one", "one" or "the" do not indicate a quantitative limitation, but indicate the existence of at least one. Words such as "include" or "comprise" mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. Words such as "connect" or "connected" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect.

[0066] It should be noted that the terms "up", "down", "left", "right", "front", "back", etc. used in the present invention are only used to indicate relative position relationships. When the absolute position of the object being described changes, the relative position relationship may also change accordingly.

[0067] Based on the obtained alternating load on the combined piston top skirt bolt joint surface, the present invention considers the influence of the surface roughness morphology and constructs a non-uniform pressure distribution model for the contact of the rough joint surface of the piston top skirt bolt; establishes a shear layer micro-slip model for the rough joint surface of the piston top skirt bolt, and derives the tangential micro-slip length of the rough joint surface according to the pressure distribution; establishes a fretting wear depth prediction model for the rough joint surface of the piston top skirt bolt based on the Archard model, and combines the pressure distribution and the tangential micro-slip length to predict the fretting wear depth of the rough joint surface of the piston top skirt bolt, which specifically includes the following contents:

[0068] like Figures 1 to 4 As shown, a method for calculating the wear depth of the rough joint surface of the combined piston top skirt bolt includes:

[0069] S1. Obtaining basic parameters of the rough joint surface of the combined piston top skirt bolt and the alternating load on the joint surface of the piston top skirt bolt;

[0070] S2. Based on the basic parameters of the rough joint surface of the combined piston top skirt bolt and the alternating load on the joint surface of the piston top skirt bolt, a contact non-uniform pressure distribution model of the rough joint surface of the piston top skirt bolt is constructed;

[0071] S3, deriving the tangential micro-slip length of the rough joint surface of the piston top skirt bolt according to the non-uniform pressure distribution model of the rough joint surface of the piston top skirt bolt;

[0072] S4. Predict the micro-wear depth of the rough joint surface of the combined piston top skirt bolt under the action of alternating load based on the contact non-uniform pressure distribution model of the rough joint surface of the piston top skirt bolt and the tangential micro-slip length of the rough joint surface of the piston top skirt bolt.

[0073] Figure 2 The diesel engine piston top skirt structure is shown, which is connected by multiple bolts to form a rough joint surface of the combined piston top skirt bolts. Due to the alternating load of the combined piston top skirt bolt joint surface caused by the pressure in the diesel engine gas cylinder and the surface roughness morphology of the bolt joint surface, the rough joint surface of the combined piston top skirt bolts will experience micro-motion wear.

[0074] A specific implementation method, S2, based on the basic parameters of the rough joint surface of the combined piston top skirt bolt and the alternating load on the joint surface of the piston top skirt bolt, construct a non-uniform pressure distribution model of the rough joint surface of the piston top skirt bolt, including the following contents:

[0075] According to the basic parameters of the rough joint surface of the piston top skirt bolt, on the basis of the obtained alternating load, considering the uneven force distribution of the piston top skirt bolt joint surface due to the influence of the rough morphology, a non-uniform pressure distribution model of the rough joint surface of the piston top skirt bolt is constructed. The formula of the non-uniform pressure distribution model of the rough joint surface of the piston top skirt bolt is formula (1):

[0076] ; (1)

[0077] in, is the obtained alternating load amplitude;

[0078] α is a non-negative coefficient (α≥0) that characterizes different pressure functions, α=0 corresponds to uniform pressure distribution, and α>0 corresponds to non-uniform pressure distribution;

[0079] L b is the length of the equivalent beam of the rough joint surface of the piston top skirt bolt;

[0080] x is the different positions of the equivalent beam on the rough joint surface of the piston top skirt bolt;

[0081] The pressure distribution function p(x) satisfies , N0 is the bolt preload, and S is the contact area.

[0082] In this embodiment, the alternating load Through Fourier series fitting, Mpa, bolt preload N0 = 50 kN, and pressure distribution index α is set to α = 2. Equivalent beam length L of piston top skirt bolt combined with rough interface b=25 mm, the cross-sectional area of ​​the equivalent beam is A=125 mm 2 The material parameters are elastic modulus E = 114 GPa, shear modulus G = 23 GPa. The roughness of the piston top skirt bolt-to-rough interface is R a =0.4 μm, corresponding to the standard deviation of the asperity distribution σ r =0.501 μm. Yield strength of the material =900Mpa.

[0083] A specific implementation method, S3, deriving the tangential micro-slip length of the rough joint surface of the piston top skirt bolt according to the non-uniform pressure distribution model of the rough joint surface of the piston top skirt bolt;

[0084] The rough joint surface of the piston top skirt bolt is the contact between multiple micro-convex bodies. Under the action of non-uniform pressure distribution, relative motion and micro-slip will occur. The shear layer micro-slip model of the rough joint surface of the piston top skirt bolt is constructed to derive the length of the slip zone at each position of the plane. The shear layer model is a method to simplify the rough contact interface of the bolt connection into a virtual material thin layer, such as Figure 3 As shown. The model is a one-dimensional rectangular beam subjected to a tangential load F t Excitation, the length of the beam is L b , the cross-sectional area of ​​the beam is A, and the elastic modulus is E. The beam and the bottom fixed surface have a tangential contact stiffness of K t The shear layer is connected to describe the elastic deformation of the beam before slip occurs. The shear layer obeys Coulomb's friction law and has a friction coefficient of μ. The beam is subjected to a non-uniformly distributed normal pressure p(x). Assuming that the load is directly transferred to the shear layer, the shear layer will undergo a strain hardening effect after the overall slip. The beam is connected to the shear layer by a stiffness of K. s The spring is connected to the left fixed end to simulate the strain hardening effect.

[0085] This step specifically includes:

[0086] S301, establishing a shear layer model, wherein the shear layer model is a one-dimensional rectangular beam subjected to a tangential load F t Excitation, the length of the one-dimensional rectangular beam is L b , the cross-sectional area of ​​the one-dimensional rectangular beam is A, and the elastic modulus of the shear layer model is E;

[0087] The formula of the shear layer model is formula (2):

[0088] ; (2)

[0089] Where u is the displacement of a point at a distance x from the left end of the beam;

[0090] μ is the shear layer obeys Coulomb friction law and the friction coefficient;

[0091] K t is the tangential contact stiffness;

[0092] L1 is the length of the slip zone.

[0093] S302, based on the shear layer model, obtaining the displacement of the overall sliding state corresponding to when the one-dimensional rectangular beam slips, and the displacement of the rough interface when the one-dimensional rectangular beam does not slip;

[0094] When the one-dimensional rectangular beam slips, the corresponding displacement of the overall sliding state is The formula is formula (3):

[0095] ; (3)

[0096] The formula for the rough interface displacement when the one-dimensional rectangular beam does not slip is formula (4):

[0097] ; (4)

[0098] is the dimensionless position coordinate, expressed as , It is defined as the dimensionless stiffness of the left-end spring relative to the compressive stiffness of the beam and is expressed as , λ is defined as the ratio of the shear layer tangential contact stiffness to the beam compressive stiffness.

[0099] The formula for the ratio λ of the shear layer tangential contact stiffness to the beam compressive stiffness is formula (5):

[0100] ; (5)

[0101] Where G is the shear modulus, H is e is the material hardness, β is the dimensionless adhesion zone length, n is the number of asperity contacts, A n is the nominal contact area, σ r is the standard deviation of the asperity height distribution, σ rs is the standard deviation of the surface height, z n is the height of the microconvex body, f s is the asperity contact load.

[0102] S303, obtaining a tangential micro-slip length of the rough joint surface of the piston top skirt bolt according to the displacement of the overall sliding state corresponding to the one-dimensional rectangular beam when the one-dimensional rectangular beam slips and the rough interface displacement when the one-dimensional rectangular beam does not slip.

[0103] Tangential micro-slip length of the rough joint surface of the piston top skirt bolt:

[0104] ; (6)

[0105] Where u(x) is the displacement when the rough interface has slip, u e (x) is the displacement when there is no slip on the rough interface.

[0106] A specific implementation method, S4, predicting the micro-wear depth of the rough joint surface of the combined piston top skirt bolt under the action of alternating load according to the non-uniform pressure distribution model of the rough joint surface of the piston top skirt bolt and the tangential micro-slip length of the rough joint surface of the piston top skirt bolt;

[0107] Based on the local micro-slip of the rough joint surface of the piston top skirt bolt, the Archard wear model is introduced to construct a calculation model for the fretting wear depth of the piston top skirt bolt joint surface under alternating load considering the rough morphology, including:

[0108] When the peaks of the micro-convex bodies on the rough interface are worn away and the stress reaches the yield limit of the micro-convex body material, n peaks of the contact interface are worn away, and the relationship between the initial preload force W and the yield limit s is expressed as formula (7):

[0109] ; (7)

[0110] in, is the yield limit of the micro-convex material, a c is the radius of the microconvex body, S c is the maximum contact area of ​​the micro-asperity protrusion during the wear process;

[0111] The formula for the yield limit of the micro-convex material is formula (8):

[0112] ; (8)

[0113] Based on the initial preload, when the contact interface slides for a length of L, the Archard wear calculation model is as follows:

[0114] ; (9)

[0115] Q0 is the wear volume, K is the wear factor, and H is the hardness;

[0116] The incremental mode formula of the Archard wear calculation model is formula (10):

[0117] ; (10)

[0118] Based on formula (8) to formula (10), formula (11) includes:

[0119] :(11).

[0120] Based on formula (7) and formula (9), the fretting wear depth of the rough joint surface of the combined piston top skirt bolt under the action of the alternating load is obtained. The prediction formula for the fretting wear depth of the rough joint surface of the combined piston top skirt bolt under the action of the alternating load is formula (12):

[0121] ; (12)

[0122] Among them, d(x) is the relative sliding length of the rough joint surface of the bolt, t is the sliding time, and h is the wear depth.

[0123] in, ; ; ; v is the relative slip velocity of the interface, and p is the non-uniform pressure distribution.

[0124] Figure 4 The prediction results of the fretting wear depth of the piston top skirt bolt rough joint surface and the experimental results are compared. In the slip zone, the wear depth of the theoretical prediction is basically consistent with the experimental test, with an error of about 7.9%.

[0125] The method for predicting the fretting wear depth of the rough joint surface of the piston top skirt bolt provided by the present invention takes into account the rough morphological characteristics of the piston top skirt bolt joint surface and the non-uniform pressure distribution of the rough joint surface of the piston top skirt bolt under alternating loads, thereby solving the limitations of existing finite element simulations and the complexity of experimental measurement methods.

[0126] The present invention accurately predicts the fretting wear depth of the rough joint surface of the piston top skirt bolt, and provides a basis for the health status evaluation of the rough joint surface of the combined piston top skirt bolt of the diesel engine.

[0127] The following points need to be explained:

[0128] (1) The drawings of the embodiments of the present invention only involve structures related to the embodiments of the present invention. Other structures may refer to conventional designs.

[0129] (2) For the sake of clarity, in the drawings used to describe the embodiments of the present invention, the thickness of layers or regions is exaggerated or reduced, that is, these drawings are not drawn according to the actual scale. It is understood that when an element such as a layer, film, region or substrate is referred to as being "on" or "under" another element, the element may be "directly" "on" or "under" the other element or there may be intermediate elements.

[0130] (3) In the absence of conflict, the embodiments of the present invention and the features therein may be combined with each other to obtain new embodiments.

[0131] The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. The protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A method for calculating the wear depth of the rough joint surface of the combined piston top skirt bolt, characterized in that: include: S1. Obtaining basic parameters of the rough joint surface of the combined piston top skirt bolt and the alternating load on the joint surface of the piston top skirt bolt; S2. Based on the basic parameters of the rough joint surface of the combined piston top skirt bolt and the alternating load on the joint surface of the piston top skirt bolt, a contact non-uniform pressure distribution model of the rough joint surface of the piston top skirt bolt is constructed; S3, deriving the tangential micro-slip length of the rough joint surface of the piston top skirt bolt according to the non-uniform pressure distribution model of the rough joint surface of the piston top skirt bolt; S4. Predict the micro-wear depth of the rough joint surface of the combined piston top skirt bolt under the action of alternating load based on the contact non-uniform pressure distribution model of the rough joint surface of the piston top skirt bolt and the tangential micro-slip length of the rough joint surface of the piston top skirt bolt.

2. The method for calculating the wear depth of the rough joint surface of the combined piston top skirt bolt according to claim 1, characterized in that: The formula of the non-uniform pressure distribution model of the rough contact surface of the piston top skirt bolt of S2 is formula (1): ； （1） in, is the obtained alternating load amplitude; α is a non-negative coefficient (α≥0) that characterizes different pressure functions, α=0 corresponds to uniform pressure distribution, and α>0 corresponds to non-uniform pressure distribution; L b is the length of the equivalent beam of the rough joint surface of the piston top skirt bolt; x is the different positions of the equivalent beam on the rough joint surface of the piston top skirt bolt; The pressure distribution function p(x) satisfies , N0 is the bolt preload, and S is the contact area.

3. The method for calculating the wear depth of the rough joint surface of the combined piston top skirt bolt according to claim 2, characterized in that: The step S3 of deducing the tangential micro-slip length of the rough joint surface of the piston top skirt bolt according to the non-uniform pressure distribution model of the rough joint surface of the piston top skirt bolt comprises: S301, establishing a shear layer model, wherein the shear layer model is a one-dimensional rectangular beam subjected to a tangential load F t Excitation, the length of the one-dimensional rectangular beam is L b , the cross-sectional area of ​​the one-dimensional rectangular beam is A, and the elastic modulus of the shear layer model is E; S302, based on the shear layer model, obtaining the displacement of the overall sliding state corresponding to when the one-dimensional rectangular beam slips, and the displacement of the rough interface when the one-dimensional rectangular beam does not slip; S303, obtaining a tangential micro-slip length of the rough joint surface of the piston top skirt bolt according to the displacement of the overall sliding state corresponding to the one-dimensional rectangular beam when the one-dimensional rectangular beam slips and the rough interface displacement when the one-dimensional rectangular beam does not slip.

4. The method for calculating the wear depth of the rough joint surface of the combined piston top skirt bolt according to claim 3 is characterized in that: The formula of the shear layer model is formula (2): ；（2） Where u is the displacement of a point at a distance x from the left end of the beam; μ is the shear layer obeys Coulomb friction law and the friction coefficient; K t is the tangential contact stiffness; L1 is the length of the slip zone.

5. The method for calculating the wear depth of the rough joint surface of the combined piston top skirt bolt according to claim 4, characterized in that: The displacement of the overall sliding state corresponding to the one-dimensional rectangular beam when it slips in S302 The formula is formula (3): ；（3） The formula for the rough interface displacement when the one-dimensional rectangular beam does not slip in S302 is formula (4): ；（4） is the dimensionless position coordinate, expressed as , Defined as the dimensionless stiffness of the left-end spring relative to the compressive stiffness of the beam, expressed as , Defined as the ratio of the shear layer tangential contact stiffness to the beam compressive stiffness.

6. The method for calculating the wear depth of the rough joint surface of the combined piston top skirt bolt according to claim 5, characterized in that: The formula for the ratio λ of the shear layer tangential contact stiffness to the beam compressive stiffness is formula (5): ；（5） Where G is the shear modulus, H is e is the material hardness, β is the dimensionless adhesion zone length, n is the number of asperity contacts, A n is the nominal contact area, σ r is the standard deviation of the asperity height distribution, σ rs is the standard deviation of the surface height, z n is the height of the microconvex body, f s is the asperity contact load.

7. The method for calculating the wear depth of the rough joint surface of the combined piston top skirt bolt according to claim 6, characterized in that: The tangential micro-slip length of the rough joint surface of the piston top skirt bolt in the 303: ；（6） Where u(x) is the displacement when the rough interface has slip, u e (x) is the displacement when there is no slip on the rough interface.

8. The method for calculating the wear depth of the rough joint surface of the combined piston top skirt bolt according to claim 7, characterized in that: The step S4 predicts the fretting wear depth of the rough joint surface of the piston top skirt bolt under the action of the alternating load according to the contact non-uniform pressure distribution model of the rough joint surface of the piston top skirt bolt and the tangential micro-slip length of the rough joint surface of the piston top skirt bolt, including: When the peaks of the micro-convex bodies on the rough interface are worn away and the stress reaches the yield limit of the micro-convex body material, n peaks of the contact interface are worn away, and the relationship between the initial preload force W and the yield limit s is expressed as formula (7): ；（7） in, is the yield limit of the micro-convex material, a c is the radius of the microconvex body, S c is the maximum contact area of ​​the micro-asperity protrusion during the wear process; Based on the initial preload, when the contact interface slides for a length of L, the Archard wear calculation model is as follows: ；（9） Q0 is the wear volume, K is the wear factor, and H is the hardness; Based on formula (7) and formula (9), the fretting wear depth of the rough joint surface of the combined piston top skirt bolt under the action of the alternating load is obtained. The prediction formula for the fretting wear depth of the rough joint surface of the combined piston top skirt bolt under the action of the alternating load is formula (12): ；（12） Among them, d(x) is the relative sliding length of the rough joint surface of the bolt, t is the sliding time, and h is the wear depth.

9. The method for calculating the wear depth of the rough joint surface of the combined piston top skirt bolt according to claim 8, characterized in that: The formula for the yield limit of the micro-convex material is formula (8): ；（8） The incremental mode formula of the Archard wear calculation model is formula (10): ； （10） in, ; ; ; v is the relative slip velocity of the interface, and p is the non-uniform pressure distribution.

10. The method for calculating the wear depth of the rough joint surface of the combined piston top skirt bolt according to claim 9, characterized in that: Based on formula (8) to formula (10), formula (11) includes: ；（11）。

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