Diesel engine structural member probabilistic fatigue safety coefficient evaluation method considering load dispersity

Abstract

The invention provides a diesel engine structural member probabilistic fatigue safety coefficient evaluation method considering load dispersibility, and the method comprises the following steps: S1, carrying out the load characteristic analysis of a diesel engine structural member, and obtaining the feasible region boundary of each load parameter; s2, based on the load boundary and distribution, generating a plurality of random load parameter groups by using a modern sampling method; s3, simulating a finite element stress field of the diesel engine structural member by taking the random load parameter group as input; s4, material parameters are set based on a stress field calculation result, and fatigue safety coefficient field calculation is carried out; s5, according to the calculation result of the fatigue safety coefficient field, a plurality of attention nodes are determined in combination with the failure dangerous parts, and fatigue safety coefficient macro calculation is carried out on the attention nodes; and S6, drawing a fatigue safety coefficient cumulative distribution function curve of the concerned node, and carrying out probability fatigue safety coefficient evaluation according to the curve. The method has the beneficial effects that based on the stress-strength interference model, the dispersity of the load is considered, the probability fatigue safety coefficient distribution rule of the diesel engine structural component is obtained, and efficient and accurate evaluation of the fatigue reliability of the diesel engine structural component is facilitated.

Description

Technical Field

[0001] The invention belongs to the field related to structural fatigue reliability, and in particular relates to a method for evaluating the probabilistic fatigue safety factor of a diesel engine structural component taking load dispersion into consideration. Background Art

[0002] Diesel engine structural parts include fixed parts and moving parts, among which the fixed parts are mainly the engine body, cylinder head, etc., and the moving parts include crankshafts, connecting rods, pistons, etc. Diesel engine structural parts usually have complex shapes, a wide range of materials, multiple manufacturing processes, and are subject to complex alternating loads. As the degree of diesel engine strengthening increases, higher requirements are placed on the load-bearing capacity of structural components. Diesel engines expose typical failure locations and failure modes of structural parts in bench tests and actual service. The cause of cracking is mostly cracking at stress concentration locations such as defects caused by alternating loads.

[0003] my country has always been far behind the international advanced technology level in the reliability evaluation of internal combustion engines. The traditional evaluation methods for internal combustion engine structural parts often rely on the analysis of specific load conditions, especially rated conditions or extreme conditions. Although these load conditions can represent the performance of structural parts under extreme conditions, they ignore the complex and variable loads and the wide distribution characteristics of safety factors in actual working processes. Although such point condition evaluation methods are simple and easy to implement, they are difficult to fully reflect the real state and potential risks of structural parts in actual applications, which may lead to overly optimistic or conservative evaluation results, which is not conducive to effectively guiding structural design and optimization. With the gradual deepening of engineering practice needs, higher requirements are placed on the accuracy and comprehensiveness of evaluation methods. Considering the influence of load dispersion, that is, recognizing that the actual load is not constant, but has a certain fluctuation range and distribution law, the evaluation of the safety factor is no longer limited to a single value, but an in-depth analysis of its distribution characteristics. In this way, the evaluation and design of structural parts can be closer to the actual situation, thereby better ensuring the durability and reliability of structural parts.

[0004] The random / probabilistic finite element method formed by combining modern sampling methods with the finite element method can take into account the uncertainty caused by random variables such as geometric dimensions and loads, and can simulate and analyze the actual behavior of the structure, and more accurately reflect the performance of the structure under complex working conditions. In addition, there are few methods that introduce probabilistic thinking into the fatigue safety factor evaluation system in the current fatigue assessment of diesel engine structural parts. The diesel engine structural part probabilistic fatigue safety factor evaluation method proposed in the present invention can reflect the load dispersion on the cumulative distribution curve of the probabilistic fatigue safety factor, and obtain the safety margin of the structural reliability design under a certain reliability. Summary of the invention

[0005] In view of this, the present invention aims to propose a probabilistic fatigue safety factor evaluation method for diesel engine structural parts taking into account load dispersion, in order to address the problems that the existing deterministic fatigue safety factor evaluation method fails to reflect the load dispersion of operating conditions and often suffers from conservative evaluation and accidental evaluation. The present invention aims to propose a probabilistic fatigue safety factor evaluation method for diesel engine structural parts taking into account load dispersion, obtain the boundaries of the feasible domain of each load parameter through structural load characteristic analysis; obtain the cumulative distribution law of the fatigue safety factor of the node of interest through random sampling of load parameters and probabilistic finite element calculation of the stress field, and use fatigue safety factor calculation software, and propose the allowable limit of the safety factor under reliability conditions.

[0006] To achieve the above object, the technical solution of the present invention is achieved as follows:

[0007] A method for evaluating the probabilistic fatigue safety factor of a diesel engine structural component considering load dispersion comprises the following steps:

[0008] S1. Analysis of load characteristics of diesel engine structural parts, including bearing load analysis and stiffness calculation, to obtain the feasible domain boundaries of each load parameter;

[0009] S2. Based on the feasible domain boundary and distribution law of each load parameter, a number of random load parameter groups are generated using modern sampling methods;

[0010] S3, constructing a calculation model of diesel engine structural parts, taking each load parameter group as input conditions, and performing finite element stress field simulation of diesel engine structural parts;

[0011] S4, select the stress field calculation results under the typical working conditions in step S3, substitute them into the fatigue safety factor calculation software, set the material parameters, and perform fatigue safety factor field calculation;

[0012] S5. According to the calculation results of the fatigue safety factor field and in combination with the failure risk position, several nodes of interest are determined, and the fatigue safety factor of the nodes of interest is calculated using the calculation results of all stress fields calculated in step S3 as input;

[0013] S6. According to the fatigue safety factor distribution law, the fatigue safety factor cumulative distribution function curve of the node of interest under random load conditions is obtained, and the probabilistic fatigue safety factor of the diesel engine structural parts is evaluated based on the curve.

[0014] Furthermore, in step S1, the load characteristic analysis of the diesel engine structure, including the bearing load analysis and the stiffness calculation, obtains the feasible region boundary of each load parameter, including the following steps:

[0015] S11, dynamically calculating the mechanical load characteristics according to the explosion pressure of the diesel engine to obtain the gas pressure in the cylinder and the bearing load;

[0016] S12. Determine the key areas of concern based on structural functions and load-bearing status factors; clarify the feasible domain boundaries of each load parameter.

[0017] Further, in step S2, modern sampling methods include uniform stratified sampling or Monte Carlo sampling or Latin hypercube sampling.

[0018] Furthermore, in step S3, the finite element simulation software is Abaqus, and the output stress field result file format is odb format.

[0019] Furthermore, in step S4, the fatigue safety factor calculation software is Femfat.

[0020] Furthermore, in step S5, the method for determining the focus node is:

[0021] In the determined key focus areas, combined with the locations where failures frequently occur in the project, the nodes with the minimum calculated fatigue safety factor are selected as focus nodes.

[0022] Furthermore, in step S6, the method for drawing the cumulative distribution function curve of fatigue safety factor of the node of interest is:

[0023] The macro calculation results of fatigue safety factor are statistically analyzed, and the probability density distribution function is integrated to obtain the cumulative distribution function.

[0024] Compared with the prior art, the probabilistic fatigue safety factor evaluation method for diesel engine structural parts considering load dispersion described in the present invention has the following advantages:

[0025] (1) The present invention discloses a method for evaluating the probabilistic fatigue safety factor of diesel engine structural parts taking into account load dispersion. It proposes to use modern sampling methods to randomly sample various load parameters within the feasible domain, fully considering the load dispersion; by calculating the random / probabilistic finite element stress field with each group of load parameters as input, the uncertainty results of the stress at the nodes of the structural parts are quantified, thereby compensating for the limitations of deterministic finite element calculations and avoiding the problems of conservative evaluation and accidental evaluation.

[0026] (2) The method for evaluating the probabilistic fatigue safety factor of diesel engine structural parts considering load dispersion described in the present invention takes the stress field result file under various load conditions as input, calculates the cumulative distribution curve of the fatigue safety factor of the node of interest, and reflects the statistical characteristics of the probabilistic fatigue safety factor. The present invention provides an efficient and practical method for the reliability evaluation of diesel engine structural parts, which has great guiding significance for the reliability design and evaluation of diesel engine structural parts. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings:

[0028] Figure 1 It is a flow chart of a method for evaluating the probabilistic fatigue safety factor of a diesel engine structural component considering load dispersion disclosed in the present invention;

[0029] Figure 2 This is a schematic diagram of the preload of each bolt obtained by using different sampling methods for the diesel engine body of this embodiment;

[0030] Figure 3 It is a schematic diagram of the probabilistic fatigue safety factor distribution curve of the key focus area of ​​the diesel engine body in this embodiment. DETAILED DESCRIPTION

[0031] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0032] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and the like are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, features defined as "first", "second", and the like may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0033] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood by specific circumstances.

[0034] The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments.

[0035] like Figures 1 to 3As shown, a probabilistic fatigue safety factor evaluation method for diesel engine structural parts considering load dispersion is based on the stress-strength interference model, coupled with random sampling method and probabilistic finite element calculation, to obtain the probabilistic fatigue safety factor distribution of diesel engine structural parts under random load conditions, so as to evaluate the fatigue reliability of diesel engine structural parts. It includes the following steps:

[0036] Step 1: Determine the feasible region boundary and key focus areas of the load parameters of diesel engine structural parts; the specific steps are:

[0037] Step 1.1: Perform dynamic calculation on the mechanical load characteristics according to the explosion pressure of the diesel engine to obtain the feasible domain boundary of load parameters such as the gas pressure in the cylinder and the bearing load;

[0038] Step 1.2: Determine the key areas of concern based on factors such as structural function and load-bearing status;

[0039] Step 2: Based on the feasible domain boundaries and distribution laws of each load parameter, use modern sampling methods (uniform sampling, Monte Carlo sampling, Latin hypercube sampling, etc.) to generate several random load parameter groups.

[0040] Step 3: Construct a calculation model for diesel engine structural parts, use each load parameter group as input conditions, use Abaqus software to perform finite element stress field simulation of diesel engine structural parts, and output the stress field result file in odb format.

[0041] Step 4: Select the stress field calculation results under the typical working conditions in step 3, substitute them into the Femfat software used for fatigue safety factor calculation, set the material parameters, and perform fatigue safety factor field calculation.

[0042] Step 5: Based on the calculation results of the fatigue safety factor field and in combination with the failure risk location, select the focus node with the minimum calculated value of the fatigue safety factor in the key focus area determined in step 1.2; use the calculation results of all stress fields calculated in step 3 as input to calculate the fatigue safety factor of the focus node.

[0043] Step 6: According to the fatigue safety factor distribution law, the fatigue safety factor cumulative distribution function curve of the node of interest under random load conditions is obtained, and the probabilistic fatigue safety factor of the diesel engine structural parts is evaluated according to the curve.

[0044] Example 1

[0045] The method for evaluating the probabilistic fatigue safety factor of a diesel engine structural component considering load dispersion disclosed in this embodiment evaluates the probabilistic fatigue safety factor of a diesel engine body, and the specific implementation steps are as follows:

[0046] Step 1: Perform dynamic calculations under typical working conditions based on the explosion pressure of 22-23 MPa, select the single-diaphragm area of ​​the body where the diaphragm bearing load is relatively large and the resultant force of the diaphragm bearing load and the Z-direction load reach the extreme value synchronously as the research object, and obtain the feasible domain boundary of the cylinder pressure and bearing load parameters;

[0047] Step 1.1: Determine the value ranges of all load parameters of the engine body (including cylinder pressure, bearing load, cylinder head bolt preload, main bearing bolt preload and transverse bolt preload, etc.). Typically, the main bearing bolt preload and cylinder head bolt preload are in the range of 102-138 kN, and the transverse bolt preload is in the range of 45-75 kN.

[0048] Step 1.2: Based on factors such as structural function and load-bearing status, the main bearing partition, cylinder head bolt hole, the space between the two cylinder holes on the top plane, and the bottom fillet of the V-shaped angle water cavity are regarded as key areas of concern.

[0049] Step 2: Based on the feasible domain boundary and distribution law of each load parameter, a number of random load parameter groups are generated using modern sampling methods (Uniform sampling, Monte Carlo sampling, Latin hypercube sampling, etc.). Figure 2 Shown are the individual bolt preloads obtained on a diesel engine block using different sampling methods.

[0050] Step 3: Construct a calculation model of the diesel engine body composite structure (engine body, cylinder head, cylinder head bolts, cylinder liner, bearing cover, cross-tension bolts, main bearing bolts), use each load parameter group as input conditions, use Abaqus software to perform finite element stress field simulation of the diesel engine body, and output the stress field result file in odb format.

[0051] Step 4: Select the stress field calculation results under the typical working conditions in step 3, substitute them into the Femfat software used for fatigue safety factor calculation, set the material parameters, and perform fatigue safety factor field calculation.

[0052] Step 5: Based on the calculation results of the fatigue safety factor field and in combination with the failure risk location, select the focus node with the minimum calculated value of the fatigue safety factor in the key focus area determined in step 1.2; use the calculation results of all stress fields calculated in step 3 as input to calculate the fatigue safety factor of the focus node.

[0053] Step 6: According to the fatigue safety factor distribution law, obtain the fatigue safety factor cumulative distribution function curve of the focus node under random load conditions, and evaluate the probabilistic fatigue safety factor of the focus nodes in each partition of the diesel engine body according to the curve.

[0054] The flow chart of the probabilistic fatigue safety factor evaluation method for diesel engine structural parts considering load dispersion is as follows: Figure 1 shown.

[0055] According to the cumulative distribution function curve of fatigue safety factor obtained in step 6, the critical value of fatigue safety factor of the investigated area is set. If more than 95% of the sample values ​​in the fatigue safety factor distribution of the investigated area are not less than the set critical value (such as 1.3), it can be considered that the reliability of the fatigue safety factor of the structural part not less than the critical value is 95%. Similarly, the reliability of the fatigue safety factor of each partition of the body not less than a given value can be obtained, such as Figure 3 shown.

[0056] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for evaluating the probabilistic fatigue safety factor of diesel engine structural parts considering load dispersion, characterized in that: The following steps are included: S1. Analysis of load characteristics of diesel engine structural parts, including bearing load analysis and stiffness calculation, to obtain the feasible domain boundaries of each load parameter; S2. Based on the feasible domain boundary and distribution law of each load parameter, a number of random load parameter groups are generated using modern sampling methods; S3, constructing a calculation model of diesel engine structural parts, taking each load parameter group as input conditions, and performing finite element stress field simulation of diesel engine structural parts; S4, select the stress field calculation results under the typical working conditions in step S3, substitute them into the fatigue safety factor calculation software, set the material parameters, and perform fatigue safety factor field calculation; S5. According to the calculation results of the fatigue safety factor field and in combination with the failure risk position, several nodes of interest are determined, and the fatigue safety factor of the nodes of interest is calculated using the calculation results of all stress fields calculated in step S3 as input; S6. According to the fatigue safety factor distribution law, the fatigue safety factor cumulative distribution function curve of the node of interest under random load conditions is obtained, and the probabilistic fatigue safety factor of the diesel engine structural parts is evaluated based on the curve.

2. A method for evaluating the probabilistic fatigue safety factor of diesel engine structural parts considering load dispersion according to claim 1, characterized in that: In step S1, the load characteristic analysis of the diesel engine structure includes bearing load analysis and stiffness calculation to obtain the feasible region boundary of each load parameter, including the following steps: S11, dynamically calculating the mechanical load characteristics according to the explosion pressure of the diesel engine to obtain the gas pressure in the cylinder and the bearing load; S12. Determine the key areas of concern based on structural functions and load-bearing status factors; clarify the feasible domain boundaries of each load parameter.

3. The method for evaluating the probabilistic fatigue safety factor of diesel engine structural parts considering load dispersion according to claim 1, characterized in that: In step S2, modern sampling methods include uniform stratified sampling or Monte Carlo sampling or Latin hypercube sampling.

4. The method for evaluating the probabilistic fatigue safety factor of diesel engine structural parts considering load dispersion according to claim 1, characterized in that: In step S3, the finite element simulation software is Abaqus, and the output stress field result file format is odb format.

5. The method for evaluating the probabilistic fatigue safety factor of diesel engine structural parts considering load dispersion according to claim 1, characterized in that: In step S4, the fatigue safety factor calculation software is Femfat.

6. The method for evaluating the probabilistic fatigue safety factor of diesel engine structural parts considering load dispersion according to claim 1, characterized in that: In step S5, the method for determining the focus node is: In the determined key focus areas, combined with the locations where failures frequently occur in the project, the nodes with the minimum calculated fatigue safety factor are selected as focus nodes.

7. A method for evaluating the probabilistic fatigue safety factor of diesel engine structural parts considering load dispersion according to claim 1, characterized in that: In step S6, the method for drawing the cumulative distribution function curve of fatigue safety factor of the node of interest is: The macro calculation results of fatigue safety factor are statistically analyzed, and the probability density distribution function is integrated to obtain the cumulative distribution function.

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