CN113792414A - Prediction method for fatigue life of ceramic matrix composite under variable amplitude loading - Google Patents
Prediction method for fatigue life of ceramic matrix composite under variable amplitude loading Download PDFInfo
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- CN113792414A CN113792414A CN202110958637.1A CN202110958637A CN113792414A CN 113792414 A CN113792414 A CN 113792414A CN 202110958637 A CN202110958637 A CN 202110958637A CN 113792414 A CN113792414 A CN 113792414A
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- 239000011153 ceramic matrix composite Substances 0.000 title claims abstract description 25
- 238000000034 method Methods 0.000 title claims abstract description 18
- 230000015556 catabolic process Effects 0.000 claims abstract description 21
- 238000006731 degradation reaction Methods 0.000 claims abstract description 21
- 238000001228 spectrum Methods 0.000 claims abstract description 16
- 239000000463 material Substances 0.000 claims abstract description 9
- 238000009661 fatigue test Methods 0.000 claims abstract description 8
- 238000012545 processing Methods 0.000 claims abstract description 7
- 238000009825 accumulation Methods 0.000 claims abstract description 4
- 239000002131 composite material Substances 0.000 claims description 6
- 238000012360 testing method Methods 0.000 abstract description 3
- 238000011160 research Methods 0.000 description 6
- 238000013461 design Methods 0.000 description 2
- 239000000956 alloy Substances 0.000 description 1
- 229910045601 alloy Inorganic materials 0.000 description 1
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Abstract
The invention discloses a method for predicting fatigue life of a ceramic matrix composite under variable amplitude loading, which comprises the following steps: step 1, developing a fatigue test of the ceramic matrix composite material, and establishing an equal service life curve; step 2, fitting a rigidity degradation model and determining parameters in the model; step 3, processing the amplitude-variable load spectrum; and 4, calculating damage accumulation and service life based on the rigidity degradation. The invention predicts the service life under variable amplitude based on the rigidity degradation of the ceramic matrix composite, and the required data can be obtained in the process of carrying out basic fatigue test, thereby saving the test cost.
Description
Technical Field
The invention relates to a method for predicting fatigue life of a ceramic matrix composite under variable amplitude loading, and belongs to the field of fatigue performance of the ceramic matrix composite.
Background
The ceramic matrix composite material not only has the advantages of high modulus, low density and good thermal stability, but also has better high-temperature performance and strength compared with the traditional high-temperature alloy, and is widely applied to the fields of spaceflight, military affairs and the like. The structural member of the ceramic matrix composite is under the action of tensile, compression and alternating stress in the actual working environment, so that the service life of the structural member is far shorter than the design life of the structural member, economic loss is caused, and even serious accidents occur. Therefore, the fatigue performance research of the ceramic matrix composite material is very important, and the ceramic matrix composite material plays a key role in optimizing the design of the composite material.
At present, the research on the ceramic matrix composite material mainly focuses on performance research under static load and fatigue constant amplitude load, most of the fatigue performance research under the amplitude load relates to a service life prediction method under load block loading (high-low loading or low-high loading), and the fatigue performance research of load amplitude change is rarely researched. Therefore, the method for predicting the service life of the ceramic matrix composite under the reasonable and effective amplitude variation is very important.
Disclosure of Invention
The invention aims to provide a method for predicting the fatigue life of a ceramic matrix composite under variable amplitude loading. The method can predict the fatigue life of the composite material by using less test cost, and provides technical support for the research of the ceramic matrix composite material under the variable amplitude load.
In order to achieve the purpose, the invention adopts the following technical scheme:
carrying out fatigue tests of the ceramic matrix composite under the conditions that the stress ratio R is 0.1 and R is-1, obtaining S-N curves of the two stress ratios, drawing an equal life curve of the composite according to the S-N curves under the two stress ratios, obtaining corresponding fatigue life by using the equal life curve according to different stresses and stress ratios, substituting the life data into corresponding rigidity degradation models, and carrying out subsequent calculation.
v1＝p1σmax+p2 v2＝p3σmax+p4
in the formula, E0Is the initial stiffness; e (n) is the residual stiffness; sigmamaxIs the maximum value of the applied stress; n is the cycle number of the current load; n is the life of the current load level; a and b are fitting parameters and are independent of stress; q, v1、v2The average stress establishes a relationship, wherein c1, c2, p1, p2, p3 and p4 are all fitting parameters.
Step 3, processing the amplitude-variable load spectrum;
and removing the load points which are not peak points or valley points in the variable amplitude load spectrum, so that the processed load spectrum only comprises the peak points and the valley points. Carrying out rain flow counting treatment on the treated load spectrum to obtain the stress amplitude sigma under each cycleaAverage stress σmAnd maximum stress σmaxWill σa、σmAnd σmaxAnd respectively substituting the equivalent life curve and the rigidity degradation model for calculation.
Step 4, calculating damage accumulation and service life based on the rigidity degradation;
the damage caused under the first level of loading is:
D1＝E0-E(n1)/E0-Ef1
in the formula, E1The residual stiffness after the first stage load action; ef1Is the critical stiffness for first stage load failure.
Under the second level load, the equivalent cycle number required for generating the same damage is n21，
D21＝E0-E(n21)/E0-Ef2
According to D1＝D21The equivalent cycle number n can be obtained21And thus the residual stiffness E (n) after the first two stage load cycle1+n2) Comprises the following steps:
by analogy, the residual stiffness after the m-level load action can be obtained, and the total damage after the m-level load action is as follows:
fatigue life is then the reciprocal of total damage:
N＝1/Dm
the method for predicting the fatigue life of the ceramic matrix composite under variable amplitude loading provided by the invention has the following advantages:
1. the rigidity degradation model provided by the invention can fit three stages of rigidity degradation trends under different loads, so that the service life prediction has higher accuracy.
2. The method provided by the invention accumulates the damage based on the rigidity degradation mode, and the stress-strain data required by the rigidity degradation can be completely obtained in the process of making an S-N curve, so that the test cost is saved.
Drawings
FIG. 1 is a flowchart of a fatigue life prediction procedure;
FIG. 2 is a schematic of an equal lifetime curve;
FIG. 3 is a variable amplitude load spectrum;
FIG. 4 is a load spectrum after processing;
FIG. 5 is a schematic representation of stiffness degradation under luffing load.
Detailed Description
The embodiments of the invention will be described with reference to the accompanying drawings
As shown in FIG. 1, the method for predicting the fatigue life of the ceramic matrix composite under variable amplitude loading provided by the invention comprises the following steps:
carrying out fatigue tests of the ceramic matrix composite under the conditions that the stress ratio R is 0.1 and R is-1, obtaining S-N curves of the two stress ratios, drawing equal-life curves of the composite according to the S-N curves of the two stress ratios and the method shown in figure 2, obtaining corresponding fatigue life aiming at different stresses and stress ratios by using the equal-life curves, and substituting the life data into corresponding rigidity degradation models for subsequent calculation.
v1＝p1σmax+p2 v2＝p3σmax+p4
in the formula, E0Is the initial stiffness; e (n) is the residual stiffness; sigmamaxIs the maximum value of the applied stress; n is the cycle number of the current load; n is the life of the current load level; a and b are fitting parameters and are independent of stress; q, v1、v2The average stress establishes a relationship, wherein c1, c2, p1, p2, p3 and p4 are all fitting parameters.
Step 3, processing the amplitude-variable load spectrum;
as shown in fig. 3, an arbitrary amplitude load spectrum is obtained, and load points that are neither peak points nor valley points in the amplitude load spectrum are removed, so that the processed load spectrum only includes peak points and valley points, as shown in fig. 4. Carrying out rain flow counting treatment on the treated load spectrum to obtain the stress amplitude sigma under each cycleaAverage stress σmAnd maximum stress σmaxWill σa、σmAnd σmaxAnd respectively substituting the equivalent life curve and the rigidity degradation model for calculation.
Step 4, calculating damage accumulation and service life based on the rigidity degradation;
as shown in FIG. 5, this figure shows a graph of stiffness degradation for a two-stage loading, assuming cycle n under a first stage load1Second, cycle n under second level load2Second, the damage caused under the first level of loading is:
D1＝E0-E(n1)/E0-Ef1
in the formula, E1The residual stiffness after the first stage load action; ef1Is the critical stiffness for first stage load failure.
Under the second level load, the equivalent cycle number required for generating the same damage is n21，
D21＝E0-E(n21)/E0-Ef2
According to D1＝D21The equivalent cycle number n can be obtained21And thus the residual stiffness E (n) after the first two stage load cycle1+n2) Comprises the following steps:
by analogy, the residual stiffness after the m-level load action can be obtained, and the total damage after the m-level load action is as follows:
fatigue life is then the reciprocal of total damage:
N＝1/Dm。
Claims (2)
1. a prediction method of fatigue life of ceramic matrix composite under variable amplitude loading is characterized in that:
step 1, carrying out a fatigue test of the ceramic matrix composite material, and establishing an equal service life curve;
carrying out fatigue tests of the ceramic matrix composite under the conditions that the stress ratio R is 0.1 and R is-1, so as to obtain S-N curves of two stress ratios, and drawing an equal service life curve of the composite according to the S-N curves of the two stress ratios;
step 2, fitting a rigidity degradation model and determining parameters in the model;
v1＝p1σmax+p2 v2＝p3σmax+p4
in the formula, E0Is the initial stiffness; e (n) is the residual stiffness; sigmamaxIs the maximum value of the applied stress; n is the cycle number of the current load; n is the life of the current load level; a and b are fitting parameters and are independent of stress; q, v1、v2The average stress establishes a relation with the stress, wherein c1, c2, p1, p2, p3 and p4 are all fitting parameters;
step 3, processing the amplitude-variable load spectrum;
removing load points which are not peak points or valley points in the variable amplitude load spectrum, so that the processed load spectrum only comprises the peak points and the valley points, and performing rain flow counting processing on the processed load spectrum;
step 4. damage accumulation based on rigidity degradation;
calculating the residual rigidity after the m-level load action, and calculating the total damage D after the m-level load actionm：
i is the serial number of the multilevel load; the fatigue life N is the total damage DmReciprocal of (d):
N＝1/Dm。
2. the method for predicting the fatigue life of the ceramic matrix composite under variable amplitude loading according to claim 1, characterized by comprising the following steps: the rigidity degradation model established by the method can fit three stages of rigidity degradation of the composite material, and can be used for processing the problem of variable amplitude loading by establishing a relation with stress.
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Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2013105995A2 (en) * | 2011-02-25 | 2013-07-18 | Board Of Supervisors Of Louisiana State University And Agricultural And Mechanical College | Fatigue monitoring for composite materials |
| US20140336954A1 (en) * | 2013-05-13 | 2014-11-13 | Michael Bruyneel | Calculating Fatigue and Fatigue Failure of Structures |
| US20150170022A1 (en) * | 2013-12-13 | 2015-06-18 | King Fahd University Of Petroleum And Minerals | Method and apparatus for characterizing composite materials using an artificial neural network |
| CN108693054A (en) * | 2018-05-18 | 2018-10-23 | 北京航空航天大学 | A kind of composite structure spectrum carries the progressive damage algorithm of fatigue life |
| CN111368473A (en) * | 2020-03-04 | 2020-07-03 | 北京航空航天大学 | CFRP-metal hybrid bolt connection structure fatigue life prediction method under competitive failure |
| CN112051146A (en) * | 2020-08-31 | 2020-12-08 | 沈阳建筑大学 | Fatigue life prediction method for fiber metal laminate under complex load |
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|---|---|---|---|---|
| WO2013105995A2 (en) * | 2011-02-25 | 2013-07-18 | Board Of Supervisors Of Louisiana State University And Agricultural And Mechanical College | Fatigue monitoring for composite materials |
| US20140336954A1 (en) * | 2013-05-13 | 2014-11-13 | Michael Bruyneel | Calculating Fatigue and Fatigue Failure of Structures |
| US20150170022A1 (en) * | 2013-12-13 | 2015-06-18 | King Fahd University Of Petroleum And Minerals | Method and apparatus for characterizing composite materials using an artificial neural network |
| CN108693054A (en) * | 2018-05-18 | 2018-10-23 | 北京航空航天大学 | A kind of composite structure spectrum carries the progressive damage algorithm of fatigue life |
| CN111368473A (en) * | 2020-03-04 | 2020-07-03 | 北京航空航天大学 | CFRP-metal hybrid bolt connection structure fatigue life prediction method under competitive failure |
| CN112051146A (en) * | 2020-08-31 | 2020-12-08 | 沈阳建筑大学 | Fatigue life prediction method for fiber metal laminate under complex load |
Non-Patent Citations (4)
| Title |
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| X.H. ZHANGA等: "Tension-tension fatigue behaviour of 3D braided SiCf/SiC composite with film cooling holes at 1350 °C in air", CERAMICS INTERNATIONAL, vol. 46, pages 7703 - 7710, XP086054694, DOI: 10.1016/j.ceramint.2019.11.273 * |
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