CN114912211A - Cylinder cover fatigue life prediction method based on energy method and equivalent component model - Google Patents
Cylinder cover fatigue life prediction method based on energy method and equivalent component model Download PDFInfo
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Abstract
The invention discloses a cylinder cover fatigue life prediction method based on an energy method and an equivalent component model, and belongs to the technical field of material science and engineering application. Firstly, establishing a cylinder cover equivalent component model according to the structural characteristics of a fire surface, and then defining corresponding material parameters and unit types by using a finite element software pretreatment module to finish the application of boundary conditions and loads; further carrying out thermal-mechanical coupling dynamics simulation, and extracting a load spectrum curve under a service working condition based on a post-processing module; and finally, introducing a thermal-mechanical load spectrum obtained by finite element simulation by means of an energy method fatigue life prediction module, completing thermal-mechanical fatigue life analysis based on an energy method theory, and further obtaining damage distribution and life values of key components such as a cylinder cover under the service working condition by a linear accumulation method. The method is easy to realize, has low cost, can effectively solve the problems of high cost, low efficiency and the like of the traditional thermal-mechanical fatigue test, and can provide an effective tool for the design and optimization of complex components such as a cylinder cover and the like.
Description
Technical Field
The invention relates to the technical field of thermal-mechanical fatigue life prediction of components such as a cylinder cover, in particular to a cylinder cover fatigue life prediction method based on an energy method and an equivalent component model.
Background
The cylinder cover and other key components of the internal combustion engine bear the coupling effect of the heat-engine complex load under the service working condition, and the problem of heat-engine fatigue failure is easily induced. The development trend of high load, high efficiency, compactness, lightness and thinness of the internal combustion engine makes the service performance of key components such as a cylinder cover face new challenges. Therefore, the fatigue life prediction of key component key parts under the service working condition is very necessary to ensure the service safety and reliability.
The thermal-mechanical fatigue test of the key components has the problems of high cost, low efficiency and the like, and is difficult to realize for complex service working conditions. The numerical simulation means can realize the visual solution of the heat-machine problem of the complex component, and meanwhile, the energy law theory provides a better way for predicting the fatigue life of the heat-machine, but the energy law theory is not developed and utilized in related engineering software. The method for predicting the fatigue life of the cylinder cover based on the energy method and the equivalent component model is easy to implement, low in cost, accurate and efficient, and can provide an effective means for predicting the fatigue life of key components such as the cylinder cover and the like.
Disclosure of Invention
The invention provides a cylinder cover fatigue life prediction method based on an energy method and an equivalent component model, which aims to solve the problem of fatigue life prediction of key components of internal combustion engines such as a cylinder cover under the service working condition. The method is based on equivalent components and finite element simulation, is easy to implement, low in cost, accurate and efficient, can obtain damage distribution and service life values of key components, and can effectively solve the fatigue life prediction problem of the key components of the internal combustion engine such as a cylinder cover under the service working condition.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
a cylinder cover fatigue life prediction method based on an energy method and an equivalent component model comprises the steps of firstly establishing a cylinder cover equivalent component model according to structural characteristics of a fire face part, and then obtaining a thermal-airborne charge spectrum curve of a key region under a service working condition by utilizing finite element simulation; and further completing thermal-mechanical fatigue life prediction by means of an energy method fatigue life prediction module based on an energy method theory, and further obtaining damage distribution and a life value of the cylinder cover under the service working condition. The method specifically comprises the following steps:
(1) establishing a cylinder cover equivalent component model according to the structural characteristics of the fire surface, importing finite element software for grid division, defining corresponding material parameters and unit types, and arranging a grounding spring to finish the application of boundary conditions and loads;
(2) completing thermal-mechanical coupling dynamics simulation based on a heat transfer analysis and dynamics analysis module, and extracting a load spectrum curve under a service working condition;
(3) defining a material cyclic stress-strain curve, and inputting the curve into the step (2) for simulation to obtain fatigue load spectrums under different working conditions;
(4) an energy method fatigue life prediction module is established based on an energy method theory, thermal-mechanical fatigue life analysis is completed, and then damage distribution and a life value of a cylinder cover under a service working condition are obtained through a linear accumulation method.
In the step (1), the thermal face part of the cylinder cover is most seriously loaded and complicated and is one of the most vulnerable parts, so the cylinder cover equivalent component model selects the cylinder cover thermal face part; the finite element mesh needs to be subjected to independence test so as to ensure sufficient calculation precision and efficiency; the material parameters are determined according to the elastic-plastic curves of the actual component material at different temperatures; the boundary conditions and loads applied depend on the constraints and loading of the actual component.
In the step (2), the temperature distribution of the equivalent component under the service working condition is obtained based on heat transfer analysis, the temperature field calculation result is further led into a dynamics analysis module, the thermal-mechanical coupling dynamics simulation is completed, and a load spectrum curve under the service working condition is extracted.
In the step (3), defining a material cyclic stress-strain curve; and (3) importing the finite element simulation result in the step (2), and inputting the heat-machine load spectrum under different working conditions (working conditions such as starting, idling, rated power and stopping).
The energy method fatigue life prediction module in the step (4) is specifically as follows:
the fatigue damage theory based on the energy method can be represented by formula (1):
W s ＝W 0 ·N f -1/β (1)
in the formula (1), N f The cycle of the load is repeated; w is a group of s The area of the hysteresis loop is the area of the circulation stability; w is a group of 0 Fatigue toughness; beta is a material fatigue damage conversion factor;
at different temperatures, W 0 And β can be calculated by the following equations (2) to (3):
W 0 ＝eT+f (2)
β＝mT+n (3)
in formulas (2) to (3), e, f, m and n are material parameters;
an energy accumulated damage model is established based on the fatigue damage theory of an energy method, and the service life is predicted by utilizing the energy accumulated damage model. The energy accumulation damage model is shown in formulas (4) to (5):
in formulae (4) to (5), W i Is the hysteresis energy of week i, W i ＝k·Δε p Δ σ, k is the shape factor, Δ ε p Is the plastic strain variation, and Δ σ is the stress variation; w 0 And β is the material constant; d i Is the damage parameter of the i week; d is the sum of fatigue damage, and when the D value reaches 1, the material fails.
The method is characterized in that the influence of the thermal-mechanical load coupling effect is considered for load spectrums of the internal combustion engine under different working conditions, thermal-mechanical fatigue analysis under the service load condition is completed based on an energy method, and then damage distribution and service life values of a cylinder cover under the service working condition are obtained through a linear accumulation method.
The invention has the following advantages and beneficial effects:
1. the method can realize the visual solution of the fatigue life of the complex component under the service condition, obtain the damage distribution and the life value of the component, and provide an effective means for the design and optimization of key components under the complex service conditions such as heat-machine coupling and the like.
2. The method has good universality and good applicability to fatigue life prediction of internal combustion engine components such as cylinder covers and pistons and aeroengines and gas turbine components such as blades and wheel discs.
3. The method is realized based on equivalent components and finite element simulation, the prediction method is easy to implement, accurate and high in efficiency, and time, labor and money costs are greatly saved. The problems of high cost, low efficiency and the like in the thermal-mechanical fatigue test and numerical simulation of the key component can be effectively solved.
Drawings
FIG. 1 is a cylinder head equivalent member and working load; wherein: (a) a cylinder cover real object; (b) a working load; (c) a finite element model; (d) the fire surface area.
FIG. 2 is a schematic view of a service condition of a cylinder head; wherein: (a) three working conditions of starting and stopping, idling and running; (b) starting and stopping and high-speed operation; (c) simplifying the starting and stopping working conditions; (d) simplifying the high-speed operation condition.
FIG. 3 is a flow chart of energy method based thermo-mechanical coupling fatigue life analysis;
FIG. 4 is a fatigue life result and actual component damage; wherein: (a) and (b) is a fatigue life distribution cloud; (c) is the damage part of the actual service component.
Detailed Description
The invention is further illustrated below with reference to examples and figures.
Example 1:
the embodiment is used for predicting the fatigue life of a heat engine of a cylinder cover of a diesel engine, as shown in figure 3. Based on an energy method and an equivalent component model, the fatigue life prediction of the diesel engine cylinder cover is carried out by utilizing finite element simulation, and the prediction result is compared with the damage part of the actual service component for verification. The prediction process is as follows:
(1) according to the service load characteristic of the diesel engine cylinder cover, selecting a cylinder cover fire surface part as a key area, and establishing a cylinder cover equivalent component model as shown in figure 1. Here the equivalent component comprises, in addition to the firepower area, also the bolted area of the cylinder head and the cylinder block. And carrying out mesh division on the established equivalent component model by using finite element software, defining corresponding material parameters and unit types, and arranging a grounding spring to finish the application of boundary conditions and loads.
(2) And (3) setting a time history according to the load condition of the actual service working condition based on a finite element software heat transfer analysis and dynamics analysis module, as shown in a figure 2 (a). And carrying out thermal-mechanical coupling dynamics simulation on the equivalent component of the cylinder cover, and extracting a load spectrum curve of a key part under a service working condition. Wherein, the temperature load obtained by the heat transfer analysis is input into the kinetic analysis module in the form of a predefined field, and the specific flow of the analysis step is shown in the left side of fig. 3.
(3) Defining a material cyclic stress-strain curve, importing a finite element simulation result in the step (2), inputting a simplified load spectrum as shown in a figure 2(b), and selecting a start-stop-high-speed operation working condition with the most serious damage; considering the cooling speed, the initial temperature of the heat load is set at 20 ℃, the maximum temperature is 500 ℃, the temperature is increased and decreased for 60s respectively, and the high-speed stable operation is carried out for 240 s. The cyclic stress-strain curve of the material can be determined by standard experiments, and the load spectrum comprises a temperature spectrum, a stress spectrum, a strain spectrum and a corresponding time history.
(4) Considering the influence of the heat-machine load coupling effect, and combining the load spectrum shown in figure 2(b), the heat-machine fatigue analysis under the service load condition is completed. The method comprises the following specific steps:
calculating the low cycle fatigue life based on an energy law theory as shown in formula (1):
W s ＝W 0 ·N f -1/β (1)
in the formula, N f The cycle of the load is repeated; w s When the circulation is stableThe area of the hysteresis loop; w is a group of 0 Fatigue toughness; beta is a material fatigue damage conversion factor.
Calculating the high cycle fatigue life based on the Basquin formula as shown in formula (6):
σ a ＝σ′ f ·(2N f ) b (6)
wherein σ a Is a stress amplitude of 2N f The number of load reversals; sigma' f The fatigue strength coefficient; b is fatigue strength index.
Finally, the damage distribution and the service life value of the cylinder head under the service working condition are obtained by a linear accumulation method (formulas (4) to (5)), as shown in fig. 4(a) and fig. 4 (b). And further comparing with the actual damage part of the service component (as shown in figure 4(c)), verifying the accuracy of the thermal-mechanical fatigue life prediction method provided by the invention.
Example 2:
the embodiment is used for predicting the fatigue life of other cylinder covers of certain types. Based on an energy method and an equivalent component model, coupled dynamic simulation and fatigue life prediction are carried out by combining load spectrums shown in fig. 2(c) and 2(d), and a simulation result is compared with a fatigue damage part of an actual service component for verification.
The fatigue life prediction method provided by the invention is accurate and feasible.
Claims (7)
1. A cylinder cover fatigue life prediction method based on an energy method and an equivalent component model is characterized in that: firstly, establishing a cylinder cover equivalent component model according to the structural characteristics of a fire surface, and then obtaining a thermal-airborne load spectrum curve of a key part under a service working condition by utilizing finite element simulation; based on the theory of an energy method, the thermal-mechanical fatigue life prediction is completed by means of an energy method fatigue life prediction module, and then the damage distribution and the life value of the cylinder cover under the service working condition are obtained.
2. The cylinder head fatigue life prediction method based on the energy method and the equivalent component model according to claim 1, characterized in that: the method comprises the following steps:
(1) establishing a cylinder cover equivalent component model according to the structural characteristics of the fire surface, importing finite element software for grid division, defining corresponding material parameters and unit types, and arranging a grounding spring to finish the application of boundary conditions and loads;
(2) completing thermal-mechanical coupling dynamics simulation based on a heat transfer analysis and dynamics analysis module, and extracting a load spectrum curve under a service working condition;
(3) defining a material cyclic stress-strain curve, and inputting the curve into the step (2) for simulation to obtain fatigue load spectrums under different working conditions;
(4) an energy method fatigue life prediction module is established based on an energy method theory, thermal-mechanical fatigue life analysis is completed, and then damage distribution and a life value of a cylinder cover under a service working condition are obtained through a linear accumulation method.
3. The cylinder head fatigue life prediction method based on the energy method and the equivalent component model according to claim 2, characterized in that: in the step (1), the thermal face part of the cylinder cover is most seriously loaded and complicated and is one of the most vulnerable parts, so the cylinder cover equivalent component model selects the cylinder cover thermal face part; the finite element mesh needs to be subjected to independence test so as to ensure sufficient calculation precision and efficiency; the material parameters are determined according to the elastic-plastic curves of the actual component material at different temperatures; the boundary conditions and loads applied depend on the constraints and loading of the actual component.
4. The cylinder head fatigue life prediction method based on the energy method and the equivalent component model according to claim 2, characterized in that: in the step (2), the temperature distribution of the equivalent component under the service working condition is obtained based on heat transfer analysis, the temperature field calculation result is further led into a dynamics analysis module, the thermal-mechanical coupling dynamics simulation is completed, and a load spectrum curve under the service working condition is extracted.
5. The cylinder head fatigue life prediction method based on the energy method and the equivalent component model according to claim 2, characterized in that: and (3) defining a material cyclic stress-strain curve, and importing the material cyclic stress-strain curve into the finite element simulation result in the step (2) to obtain fatigue load spectrums under different working conditions.
6. The cylinder head fatigue life prediction method based on the energy method and the equivalent component model according to claim 2, characterized in that: the energy method fatigue life prediction module in the step (4) is specifically as follows:
the fatigue damage theory based on the energy method can be represented by formula (1):
W s ＝W 0 ·N f -1/β (1)
in the formula (1), N f The cycle of the load is repeated; w s The area of the hysteresis loop is the area of the circulation stability; w 0 Fatigue toughness; beta is a material fatigue damage conversion factor;
at different temperatures, W 0 And the value of β can be calculated by the following equations (2) to (3):
W 0 ＝eT+f (2)
β＝mT+n (3)
in the formulas (2) to (3), e, f, m and n are material parameters;
establishing an energy accumulation damage model based on the fatigue damage theory of an energy method, and predicting the service life by using the energy accumulation damage model; the energy accumulation damage model is shown in formulas (4) to (5):
in formulae (4) to (5), W i Is the hysteresis energy of week i, W i ＝k·Δε p Δ σ, k is the shape factor, Δ ε p Is the plastic strain variation, and Δ σ is the stress variation; w 0 And β is the material constant; d i Is the loss of week iA damage parameter; d is the sum of fatigue damage, and when the D value reaches 1, the material fails.
7. The method for predicting the fatigue life of the cylinder head based on the energy method and the equivalent component model according to claim 6, wherein: in the step (4), the influence of the thermal-mechanical load coupling effect is considered for the load spectrum of the internal combustion engine under different working conditions, thermal-mechanical fatigue analysis under the service load condition is completed based on an energy method, and then damage distribution and service life values of the cylinder cover under the service working condition are obtained through a linear accumulation method.
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN116384011A (en) * | 2023-06-02 | 2023-07-04 | 山东建筑大学 | Simulation method for rolling deformation correction and fatigue life prediction of aviation structural component |
| CN117350138A (en) * | 2023-12-06 | 2024-01-05 | 西北工业大学 | Modeling method for thermal cycle fatigue failure physical model of chip bonding structure |
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Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN116384011A (en) * | 2023-06-02 | 2023-07-04 | 山东建筑大学 | Simulation method for rolling deformation correction and fatigue life prediction of aviation structural component |
| CN116384011B (en) * | 2023-06-02 | 2023-08-01 | 山东建筑大学 | Simulation method for rolling deformation correction and fatigue life prediction of aviation structural component |
| CN117350138A (en) * | 2023-12-06 | 2024-01-05 | 西北工业大学 | Modeling method for thermal cycle fatigue failure physical model of chip bonding structure |
| CN117350138B (en) * | 2023-12-06 | 2024-02-23 | 西北工业大学 | Modeling method for thermal cycle fatigue failure physical model of chip bonding structure |
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