A method for predicting the thermal-mechanical coupling fatigue life of a cylinder head simulation component

Abstract

This invention, belonging to the field of internal combustion engines, provides a method for predicting the thermal-mechanical coupling fatigue life of a cylinder head simulation component. The method includes establishing a thermal-mechanical coupling model, acquiring temperature field distribution, acquiring thermal-mechanical coupling stress and strain data, analyzing the data, and finally predicting fatigue life. By covering four different load conditions, the method provides more comprehensive analysis and data support. By combining simulation prediction with experimental verification, the method provides in-depth research and accurate prediction of the thermal-mechanical coupling fatigue life of the cylinder head.

Description

Technical Field

[0001] The present invention relates to the field of internal combustion engines, and in particular to a method for predicting the thermal-mechanical coupling fatigue life of a cylinder head simulation part. Background Art

[0002] The cylinder head is a critical structural component of an internal combustion engine, enclosing the upper portion of the cylinder and, together with the piston crown and cylinder wall, forming the combustion chamber. The cylinder head possesses an extremely complex structure, featuring inboard inlet and exhaust valves, valve guide holes, and internally cast cooling channels, intake and exhaust manifolds, and portions of the combustion chamber. During engine operation, the cylinder head faces a harsh and complex operating environment. It not only withstands mechanical loads such as bolt preload generated during engine assembly, but also thermal loads from combustion and the pressure of the gas explosion. Furthermore, the presence of cooling channels and the uneven distribution of coolant flow paths contribute to complex temperature and stress distributions within the cylinder head. During service, the cylinder head faces complex multi-physics interactions, including thermal, fluid-structure interaction. However, traditional testing methods have inherent limitations in addressing these challenges, including high costs, lengthy testing cycles, complex operational procedures, and limitations in accuracy and precision. Patent CN109598079A discloses a method for zoning fatigue life estimation for cylinder heads. This invention provides a method for zoning fatigue life estimation for cylinder heads. This method addresses the varying material properties and load conditions of different cylinder head components, developing a zoning fatigue analysis method to estimate cylinder head fatigue life. This reduces the deviations caused by varying failure modes in conventional fatigue analysis and provides technical support for using software to complete the entire cylinder head fatigue life estimation in one go. The method includes the following steps: Simulating and analyzing the thermal-mechanical coupling failure mechanism of the cylinder head to determine the criteria for distinguishing between different failure modes; Partitioning the cylinder head based on the failure modes of different regions, and employing different fatigue damage and life prediction models for specific failure modes to estimate the fatigue life of the cylinder head by region.

[0003] Existing methods often fail to comprehensively consider the thermal-mechanical coupled fatigue effects that the cylinder head is subjected to in actual operation. Although separate thermal fatigue areas or mechanical fatigue areas are considered separately, these areas are not truly coupled to simulate the complex conditions of the cylinder head in actual operation. Most studies are only conducted under full-load conditions and fail to cover the actual operation of the engine under different load conditions. This limits the prediction of the fatigue life of the cylinder head under variable operating conditions. Summary of the Invention

[0004] In order to overcome the deficiencies of the prior art, the purpose of the present invention is to provide a method for predicting the thermal-mechanical coupling fatigue life of a cylinder head simulation component, so as to achieve in-depth research and accurate prediction of the thermal-mechanical coupling fatigue life of the cylinder head.

[0005] To achieve the above object, the present invention provides the following solutions:

[0006] A method for predicting the thermal-mechanical coupling fatigue life of a cylinder head simulation component comprises:

[0007] Establishing a thermal-mechanical coupling model of the equivalent model component of the cylinder head nose bridge area; the load conditions of the thermal-mechanical coupling model include: 25% load rate, 50% load rate, 75% load rate and 100% load rate;

[0008] Applying thermal boundary conditions to the thermal-mechanical coupling model to obtain temperature field distribution;

[0009] Under the temperature field distribution, the maximum gas explosion pressure and the bolt preload are superimposed on the thermal-mechanical coupling model to obtain thermal-mechanical coupling stress-strain data;

[0010] Analyzing the thermal engine coupled stress and strain data using a rain flow counting method to obtain a load spectrum;

[0011] Based on the critical plane method, the maximum shear strain criterion and the Brown-Miller criterion are used to analyze the thermo-mechanical coupled stress-strain data to obtain the target critical plane;

[0012] Based on the load spectrum and the critical plane, a fatigue life prediction is performed on the thermal-mechanical coupling model using a fatigue damage model based on FE-SAFE software to obtain a simulated fatigue life of the equivalent model component in the nose bridge area of ​​the cylinder head; the fatigue damage model has embedded stress-life sub-model, normal strain sub-model, maximum shear strain sub-model, and Brown-Miller sub-model;

[0013] Building a thermal-mechanical coupling fatigue test bench for an equivalent model of the cylinder head nose bridge area;

[0014] Using the thermal-mechanical coupling fatigue test bench, fatigue cycling is performed on the equivalent model component of the cylinder head nose bridge area, and the crack length of the equivalent model component of the cylinder head nose bridge area is recorded; the fatigue cycling includes: temperature load cycling and mechanical load cycling;

[0015] When the crack length reaches a preset failure boundary, stopping the fatigue cycle and recording the thermal-mechanical coupling fatigue life;

[0016] When the error ratio between the thermo-mechanical coupled fatigue life and the simulated fatigue life is less than a preset threshold, the simulation state of the simulated fatigue life is determined to be a valid state.

[0017] Preferably, the number of simulations of the simulated fatigue life and the number of experiments of the thermal-mechanical coupling fatigue life are both 2 times.

[0018] Preferably, the temperature load cycle includes a heating stage, a heat preservation stage and a cooling stage.

[0019] Preferably, the crack length is collected once every 100 mechanical load cycles.

[0020] The present invention discloses the following technical effects:

[0021] The present invention provides a method for predicting the thermal-mechanical coupled fatigue life of a cylinder head simulation component. By covering four different load conditions, the present invention solves the problem that existing methods fail to cover the actual operation of the engine under different load conditions, and realizes the acquisition and analysis of multi-condition data. By combining simulation prediction with experimental verification, the present invention solves the defect that conventional methods only consider the thermal fatigue area or the mechanical fatigue area but do not simulate under complex conditions, and realizes in-depth research and accurate prediction of the thermal-mechanical coupled fatigue life of the cylinder head. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in 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 paying any creative work.

[0023] Figure 1 A schematic diagram of a process flow for predicting the thermal-mechanical coupled fatigue life of a cylinder head simulation component provided by an embodiment of the present invention;

[0024] Figure 2 A flow chart for predicting the thermal-mechanical coupled fatigue life of a cylinder head simulation component provided by an embodiment of the present invention;

[0025] Figure 3 The equivalent simulation part model of the nose bridge area of ​​the cylinder head provided in the embodiment of the present invention;

[0026] Figure 4 Schematic diagram of a thermal-mechanical coupling test bench provided in an embodiment of the present invention;

[0027] Figure 5 This is a temperature-mechanical load cycle curve provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0028] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0029] The purpose of the present invention is to provide a method for predicting the thermal-mechanical coupling fatigue life of a cylinder head simulation part, so as to achieve in-depth research and accurate prediction of the thermal-mechanical coupling fatigue life of the cylinder head.

[0030] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0031] Figure 1 The schematic diagram of the thermal-mechanical coupling fatigue life prediction process of the cylinder head simulation part provided by the embodiment of the present invention is as follows: Figure 1 As shown, the present invention provides a method for predicting the thermal-mechanical coupling fatigue life of a cylinder head simulation component, comprising:

[0032] Step 100: Establishing a thermal-mechanical coupling model of the equivalent model component of the cylinder head nose bridge area; the load conditions of the thermal-mechanical coupling model include: 25% load rate, 50% load rate, 75% load rate, and 100% load rate;

[0033] Step 200: Apply thermal boundary conditions to the thermal-mechanical coupling model to obtain temperature field distribution;

[0034] Step 300: Under the temperature field distribution, superimpose the maximum gas explosion pressure and the bolt preload on the thermal-mechanical coupling model to obtain thermal-mechanical coupling stress and strain data;

[0035] Step 400: Analyze the heat-engine coupled stress-strain data using the rain flow counting method to obtain a load spectrum;

[0036] Step 500: Based on the critical plane method, the maximum shear strain criterion and the Brown-Miller criterion are used to analyze the thermo-mechanical coupling stress-strain data to obtain the target critical plane;

[0037] Step 600: Based on the load spectrum and critical plane, the fatigue damage model is used to predict the fatigue life of the thermal-mechanical coupling model using the FE-SAFE software to obtain the simulated fatigue life of the equivalent model component in the nose bridge area of ​​the cylinder head; the fatigue damage model is embedded with a stress-life sub-model, a normal strain sub-model, a maximum shear strain sub-model, and a Brown-Miller sub-model;

[0038] Step 700: Build a thermal-mechanical coupling fatigue test bench for an equivalent model of the cylinder head nose bridge area;

[0039] Step 800: Fatigue cycling is performed on an equivalent model component of the cylinder head nose bridge region using a thermal-mechanical coupling fatigue test bench, and the crack length of the equivalent model component of the cylinder head nose bridge region is recorded; the fatigue cycling includes: a temperature load cycle and a mechanical load cycle;

[0040] Step 900: When the crack length reaches the preset failure boundary, the fatigue cycle is stopped and the thermal-mechanical coupling fatigue life is recorded;

[0041] Step 1000: When the error ratio between the thermal-mechanical coupled fatigue life and the simulated fatigue life is less than a preset threshold, the simulation state of the simulated fatigue life is determined to be a valid state.

[0042] Optionally, the number of simulations for the fatigue life simulation and the number of experiments for the thermal-mechanical coupling fatigue life are both 2.

[0043] Specifically, the temperature load cycle includes a heating stage, a heat preservation stage, and a cooling stage.

[0044] Preferably, the crack length is collected once every 100 mechanical load cycles.

[0045] refer to Figure 2 , simulate and calculate the fatigue life of the cylinder head nose bridge area simulation parts, and build Figure 3 The equivalent simulation model of the cylinder head nose bridge area with integrated cooling water channels is shown. Finite element simulation software such as ABAQUS is used to perform thermal-mechanical coupling simulation analysis on the cylinder head nose bridge area simulation under 100% load conditions to obtain the stress-strain response of the equivalent simulation part. The thermal-mechanical coupling simulation process is as follows: First, the corresponding thermal boundary conditions are applied to different areas of the simulation part to obtain the temperature field distribution of the simulation part, and the thermal stress field is further calculated based on this. Then, on the basis of the obtained thermal stress field, mechanical loads such as the maximum gas explosion pressure and bolt preload are superimposed, while maintaining the consistency of the boundary constraints, and finally the thermal-mechanical coupling stress-strain field of the cylinder head is calculated.

[0046] Specifically, this embodiment uses the rain flow counting method and the critical plane method to estimate the fatigue life of the cylinder head nose bridge area simulation parts. This solution uses fatigue analysis software such as FE-SAFE to import the thermal-mechanical coupling stress results of the equivalent cylinder head nose bridge area simulation parts under 100% load conditions calculated by software such as ABAQUS into the FE-SAFE working environment, and uses the rain flow counting method and the critical plane method to perform fatigue life analysis and prediction on the cylinder head nose bridge area simulation parts:

[0047] 1) Rainflow counting method: The measured load-time curve needs to be organized into a frequency distribution curve through a certain method. The load spectrum after counting statistics has statistical characteristics and can reflect the change of load over time on the equivalent simulation parts in the nose bridge area of ​​the cylinder head under different working conditions.

[0048] 2) Critical Plane Method: Cylinder heads are subject to periodic explosive pressure during operation, resulting in high-cycle fatigue. High-cycle fatigue calculations for the cylinder head nose bridge fatigue simulator are performed using the critical plane method. This method, based on fracture models and crack initiation mechanisms, assumes cracks originate in a specific plane, and fatigue damage accumulation and life prediction are performed on that plane. The maximum shear strain criterion and the Brown-Miller criterion are used to determine the critical plane.

[0049] Furthermore, fatigue analysis of the cylinder head nose bridge simulated component was performed using fatigue analysis software such as FE-SAFE. The specific process is as follows: First, the thermomechanical coupled stresses of the equivalent cylinder head nose bridge simulated component under 100% load conditions, calculated using software such as ABAQUS, are read. Then, the results are proportionally iteratively generated to generate an operating stress-time history based on the actual load conditions and alternating load patterns. Fatigue life calculations are then performed based on the fatigue properties of the cylinder head material. FE-SAFE includes the following fatigue damage models:

[0050] 1) Stress-life model: The model assumes that the damage to the material is caused by the maximum normal stress, that is, the plane with the maximum normal stress is the critical plane.

[0051] Δσ=σ f (2N f ) b

[0052] Where Δσ is the maximum stress, σ f is the fatigue strength coefficient, and b is the fatigue strength index.

[0053] 2) Normal strain model: The model assumes that material damage is caused by the maximum normal strain, that is, the maximum normal strain plane is the critical plane.

[0054]

[0055] where Δε n is the maximum strain, ε f is the fatigue ductility coefficient, c is the fatigue ductility index, N f is the fatigue life, which is the number of cycles a material can withstand at a specific stress level before it finally breaks. E is the elastic modulus of the material, measured in Pascals (Pa).

[0056] 3) Maximum shear strain model: The model assumes that the damage to the material is caused by the maximum shear strain, and defines the plane that bears the maximum shear strain as the critical plane.

[0057]

[0058] where Δγ max is the maximum shear strain.

[0059] 4) Brown-Miller model: The model considers that the main factor of crack initiation is the maximum shear stress, while the correction factor is the principal strain on the maximum shear plane.

[0060]

[0061] Furthermore, the fatigue prediction method is experimentally verified. A thermal-mechanical coupling fatigue test bench is built, such as Figure 4 As shown, the test piece is securely clamped using a fixture, a mechanical load application device, an electromagnetic induction heating device, and a measurement and control unit. The test piece is securely clamped using bolts and a flat plate, limiting its degrees of freedom during the test.

[0062] Specifically, the temperature load cycle consists of a heating phase, a holding phase, and a cooling phase, forming a complete temperature cycle, with a cycle duration defined as Δt1. Electromagnetic induction heating technology is used, with specially designed coils precisely heating the bottom firing surface of the simulated component. Thermocouples are placed at key observation points to measure temperature changes in the nose bridge area of ​​the cylinder head. To realistically simulate the environmental changes in the cylinder head, air is blown through the water channel during the cooling phase to achieve rapid cooling, and the cooling rate is controlled by adjusting the air speed.

[0063] Furthermore, the duration of a mechanical load cycle, Δt2, is defined as the time interval between two consecutive peak burst pressures (measured in actual machine tests). A hydraulic loading system applies a cyclically loaded, sinusoidal hydraulic pressure curve to the underside of the simulated component, reproducing the gas pressure variations characteristic of an internal combustion engine's operating cycle. Bolt preload is simulated using actual assembly torque, precisely controlled by a torque wrench.

[0064] Specifically, a thermal engine fatigue cycle consists of a temperature load cycle and n gas burst pressure cycles, all accompanied by a constant bolt preload. The relationship between the temperature load cycle duration Δt1 and the mechanical load cycle duration Δt2 is Δt1 = n × Δt2, where n is an integer and n ≥ 1.

[0065] refer to Figure 5 Based on the temperature-mechanical load cycle curve, the thermomechanical coupled load is applied cyclically, including the real-time corresponding application of temperature and mechanical loads. The control unit receives feedback from the sensor and automatically adjusts the operating status of the mechanical and temperature load application devices to ensure that the test is carried out according to the predetermined procedure.

[0066] Preferably, the crack development of the nose bridge simulation component is observed by stopping the machine for crack inspection every 100 cycles. When the crack length reaches 5 mm, it is considered to be the failure boundary, the test is stopped, and the thermal-mechanical coupled fatigue life N (number of cycles) is recorded.

[0067] Furthermore, by comparing the simulation prediction results with the test results, the effectiveness of the simulation model can be evaluated. If the two are basically consistent and the error is within an acceptable range (e.g., less than 10%), the simulation model is considered to meet the engineering needs.

[0068] Preferably, the fatigue life is calculated under different load conditions. This embodiment further deepens the study of the fatigue life of the cylinder head nose bridge area simulation parts under different load conditions. In actual applications, the internal combustion engine is not always in a 100% load working state. Therefore, in order to more realistically reflect the working conditions of the engine, this embodiment comprehensively considers four different load conditions of 25%, 50%, 75% and 100% for in-depth analysis and comparison. Under each working condition, the simulation and test were repeated twice to ensure the accuracy of the results, and the final fatigue life results were based on the average of these tests. The boundary conditions of the simulation and the test are based on the actual machine test data under the corresponding load conditions, which include the explosion pressure change process of the nose bridge area of ​​the cylinder head fire surface and the temperature changes at the key observation points.

[0069] Specifically, 25%, 50%, 75%, and 100% refer to the load rate, which is a percentage of the internal combustion engine's maximum effective power output at a constant speed. These ratios correspond to different operating conditions of the internal combustion engine. A 25% load rate represents the internal combustion engine operating at low load or idle, when the throttle opening is small, resulting in a limited amount of mixture entering the cylinder. A 50% load rate simulates the internal combustion engine operating state at medium load, which is a common operating condition in internal combustion engines in daily operation. 75% and 100% represent high load and full load conditions, respectively, when the throttle is nearly or fully open to allow more mixture to enter the cylinder. The whole-engine data collection test follows the following procedure: Start the internal combustion engine and gradually increase the rpm to its rated value to ensure stable operation. After applying a slight load and reaching a stable thermal state, the test begins. The load is gradually increased to various operating conditions, such as 25%, 50%, 75%, and 100% of rated power. Each time the load is adjusted, the throttle position is adjusted accordingly to maintain a constant rpm. Under each operating condition, key parameters are measured two or three times, including the maximum burst pressure and its occurrence time in the cylinder head, as well as the maximum and minimum temperatures in the nose bridge area. As the load increases, the injection volume per cycle increases, resulting in a greater amount of fuel in the combustible mixture formed in the same amount of time. This significantly increases the maximum burst pressure, and the time of peak burst pressure remains relatively constant. Furthermore, the maximum temperature occurs at the rated power point and increases with increasing load, showing a nearly linear relationship.

[0070] The beneficial effects of the present invention are as follows:

[0071] By covering four different load conditions, the present invention provides more comprehensive analysis and data support; by combining simulation prediction with experimental verification, the thermal-mechanical coupled fatigue life of the cylinder head is deeply studied and accurately predicted.

[0072] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0073] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only intended to help understand the method and core concept of the present invention. At the same time, those skilled in the art will find that the specific implementation methods and application scopes may vary based on the concept of the present invention. In summary, the contents of this specification should not be construed as limiting the present invention.

Claims

1. A method for predicting the thermal-mechanical coupling fatigue life of a cylinder head simulation component, characterized in that: include: Establish a thermo-mechanical coupling model of the equivalent model part of the cylinder head nose bridge area; The load conditions of the heat-engine coupling model include: 25% load rate, 50% load rate, 75% load rate and 100% load rate; Applying thermal boundary conditions to the thermal-mechanical coupling model to obtain temperature field distribution; Under the temperature field distribution, the maximum gas explosion pressure and the bolt preload are superimposed on the thermal-mechanical coupling model to obtain thermal-mechanical coupling stress-strain data; Analyzing the thermal engine coupled stress and strain data using a rain flow counting method to obtain a load spectrum; Based on the critical plane method, the maximum shear strain criterion and the Brown-Miller criterion are used to analyze the thermo-mechanical coupled stress-strain data to obtain the target critical plane; Based on the load spectrum and the critical plane, a fatigue life prediction is performed on the thermal-mechanical coupling model using a fatigue damage model based on FE-SAFE software to obtain a simulated fatigue life of the equivalent model component in the nose bridge area of ​​the cylinder head; the fatigue damage model has embedded stress-life sub-model, normal strain sub-model, maximum shear strain sub-model, and Brown-Miller sub-model; Building a thermal-mechanical coupling fatigue test bench for an equivalent model of the cylinder head nose bridge area; Using the thermal-mechanical coupling fatigue test bench, fatigue cycling is performed on the equivalent model component of the cylinder head nose bridge area, and the crack length of the equivalent model component of the cylinder head nose bridge area is recorded; the fatigue cycling includes: temperature load cycling and mechanical load cycling; When the crack length reaches a preset failure boundary, stopping the fatigue cycle and recording the thermal-mechanical coupling fatigue life; When the error ratio between the thermo-mechanical coupled fatigue life and the simulated fatigue life is less than a preset threshold, the simulation state of the simulated fatigue life is determined to be a valid state.

2. The method for predicting the thermal-mechanical coupled fatigue life of a cylinder head simulation component according to claim 1, characterized in that: The number of simulations of the simulated fatigue life and the number of experiments of the thermal-mechanical coupling fatigue life are both 2 times.

3. The method for predicting the thermal-mechanical coupling fatigue life of a cylinder head simulation component according to claim 1, characterized in that: The temperature load cycle includes a heating stage, a heat preservation stage and a cooling stage.

4. The method for predicting the thermal-mechanical coupling fatigue life of a cylinder head simulation component according to claim 1, characterized in that: The crack length is collected once every 100 mechanical load cycles.

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