CN104089760A - Fatigue test method of internal combustion engine part - Google Patents
Fatigue test method of internal combustion engine part Download PDFInfo
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- CN104089760A CN104089760A CN201410273023.XA CN201410273023A CN104089760A CN 104089760 A CN104089760 A CN 104089760A CN 201410273023 A CN201410273023 A CN 201410273023A CN 104089760 A CN104089760 A CN 104089760A
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Abstract
The invention discloses a fatigue test method of an internal combustion engine part. The fatigue test method of internal combustion engine part comprises the steps of obtaining load-service life sample data of multiple samples and drawing the data in a load-service life double logarithmic coordinate system; utilizing a least square method to perform linear fitting on the sample data and obtaining a high/low-cycle fatigue demarcation point BLCF; utilizing the high/low-cycle fatigue demarcation point BLCF and a failure point of each sample to obtain a durable fatigue limit estimation value FSi; obtaining middle-position sequences and standard normal deviators Di of all of sample and utilizing the least square method to perform linear fitting to obtain linear relation of a mean value and a standard deviation of fatigue test limit load. Compared with the prior art, the mean values are replaced by the middle-position sequences so as to accumulate the linear relation between the failure probability, average sequence numbers and standard normal deviators and the durable fatigue limit estimation value and obtain a statistical test result of the fatigue test limit load. Therefore, the accurate statistical characteristic of the fatigue test limit load is obtained, the sample amount can be obviously decreased, and a test period is shortened.
Description
Technical field
The present invention relates to internal combustion engine reliability test method, be specifically related to the fatigue test method of gas engine part.
Background technology
Reliability is to weigh the important indicator of internal combustion engine quality, is also one of focus of future market competition.At present, the internal combustion engine output of China accounts for 1/4 of world wide production, and IC Engine Industry is the infrastructural industries of Chinese national economy.As power core, internal combustion engine plays an important role in national economy every field.But in output rapid growth, the reliability of internal combustion engine product becomes the problem can not be ignored.Because the reliability of internal combustion engine directly affects the reliability of supporting machinery, also affect the sustainable development of China's ic engine industry.
As everyone knows, torture test is one of evaluation method of gas engine part reliability.Nowadays, the normal method adopting of the torture test of gas engine part has three kinds:
The first is by method, is issued to test life (number of times) in the load of regulation and is and passes through.This method, only for trial production of new products, cannot be assessed the fatigue strength of batch production product;
It two is one-point testing methods, sets series of experiments load, and the testing site that fatigue failure occurs under this group load is adopted to least square fitting method.In the method, first set up load-life-span log-log coordinate system according to the fatigue test results of gas engine part, then the testing site of finite life region is fitted to least-squares line, again this least-squares line is extended and crossing with low-cycle fatigue circulation critical line (vertical line N=10000 time), thereby obtain the fatigue limit load of gas engine part.Although this method is the method the most extensively adopting at present, but the method is merely able to the average of the fatigue limit load that obtains gas engine part and can not obtains standard deviation, cannot provide the statistical nature of the fatigue limit load of gas engine part, therefore, test findings is comparatively coarse;
It three is lifting and lowering method, the method extensively adopts in fatigue test of materials, test findings also has higher accuracy, but in Parts test due to a large amount of test sample of needs and comparatively permanent test period, this is for expensive test specimen and urgent time cycle, not too applicable.
In view of this, urgently improve for the method for existing gas engine part torture test, to utilizing less sample size to draw the statistical nature of fatigue limit load relatively accurately, and shorten the test period.
Summary of the invention
For above-mentioned defect, the technical matters that the present invention solves is to provide a kind of fatigue test method of gas engine part, effectively to utilize less gas engine part sample data to draw the statistical nature of fatigue limit load relatively accurately, and the test period of this test method is shorter.
The fatigue test method of gas engine part provided by the invention, comprises the following steps:
The sample of multiple gas engine parts is carried out to torture test and obtain load-life-span sample data of multiple samples, and be plotted in load-life-span log log coordinates system, wherein, the torture test of all samples is carried out in high-Cycle Fatigue Life Prediction region;
Utilize least square method to carry out linear fit to described load-life-span sample data, and utilize fit line to carry out the tired separation B of high/low week of regretional analysis acquisition gas engine part
lCF;
Utilize the tired separation B of high/low week of gas engine part
lCFfailpoint B with each sample
iobtain the anti-fatigue LIMIT ESTIMATION value FS of each sample
i;
To the anti-fatigue LIMIT ESTIMATION value FS of each sample
isort, then try to achieve meta order and the standard normal deviator D of all samples
i;
Utilize the standard normal deviator D of least square method to each sample
iwith fatigue limit estimated value FS
icarry out linear fit, and utilize fit line to carry out regretional analysis to obtain the average of torture test ultimate load and the linear relationship of standard deviation of gas engine part.
Preferably, 1/3 of the torture test sample data of all samples should lose efficacy in high life district.
Preferably, tired separation B of the high/low week of described gas engine part
lCFobtain by the following method:
By load-life-span, the fit line of sample data extends to lgN
lCFobtain lgB
lCF, then try to achieve B
lCF, N
1for the test life of gas engine part of setting.
Preferably, carrying out load-life-span when sample data linear fit, if can not reach the significance of setting, needing to supplement increases sample data, until meet the significance of setting.
Preferably, the anti-fatigue LIMIT ESTIMATION value FS of described sample
iemploying following methods obtains:
In fatigue limit statistics, by low-cycle fatigue critical cycle point B
lCFwith failpoint B
ibe connected and form a ray, this ray and the intersection point in fundamental test life-span are the test estimated value FS of this sample anti-fatigue ultimate strength
i.
Preferably, trying to achieve in the process of described meta order, if some meta orders have comprised stop in a test, need according to formula
obtain average sequence number i
k, and with i
kreplace the i in formula P (i)=(i-0.3)/(n+0.4) to calculate meta order P (i), in formula: j is total sequence number, k is inefficacy sequence number, and n is sample size.
Preferably, while utilizing least square method to carry out linear fit to the estimated value of standard normal deviator and fatigue limit, significance should be less than or equal to 0.05.
Preferably, described gas engine part is specially bent axle, connecting rod or cylinder body.
Compared with prior art, the fatigue test method of gas engine part provided by the invention, mathematical statistics knowledge is applied to the fatigue data processing of the gas engine part of small sample, with meta order instead of flat average, obtain the statistical results of fatigue limit load with the linear relationship of cumulative failure probability, average sequence number and standard normal deviator and fatigue limit estimated value, draw thus the statistical nature of fatigue limit load (average of fatigue limit load and standard deviation) relatively accurately.Therefore, the torture test sample size of gas engine part can obviously reduce, and has shortened the test period.
In preferred version of the present invention, 1/3 of the torture test sample data of all samples should lose efficacy in high life district, was guaranteed with the correlativity of guaranteeing the sample data that dispersion degree is larger.
Brief description of the drawings
Fig. 1 is the process flow diagram of the fatigue test method of gas engine part described in embodiment;
Fig. 2 is that load-life-span double-log of drawing in the fatigue test method of gas engine part described in embodiment is counted coordinate system schematic diagram;
Fig. 3 is the fatigue limit statistics schematic diagram of gas engine part in the fatigue test method of gas engine part described in embodiment;
Fig. 4 is the fatigue test method Plays normal state deviator of gas engine part described in embodiment and the linear regression analysis schematic diagram of fatigue limit estimated value.
Embodiment
Core of the present invention is to provide a kind of fatigue test method of gas engine part, can use less sample data to draw the statistical nature of fatigue limit load relatively accurately, and the test period is shorter.Be elaborated for present embodiment below.
First as follows to some explanation of technical terms involved in the present invention for the ease of it will be appreciated by those skilled in the art that:
(1) small sample: the sample that sample size is less than 20.
(2) high/low week tired separation: according to the characteristic of metal fatigue, in the low load high life, the dispersion degree of sample data in district is larger, and the low life-span of top load district the dispersion degree of sample data reduce gradually, consider extreme case: high/low week, tired separation (was set as 10000 circulations in present embodiment, can change according to actual needs) (life-span of locating, load) some dispersiveness very low, thereby can be assumed to and focus on a unique point, therefore, this is called tired separation of high/low week as the point that in test, some load-life estimation curves must pass through.
(3) fatigue limit load estimated value: under life-span-load log-log coordinate system, tired high/low week separation and sample data (testing site) are connected into straight line, and this straight line is extended to basic cycle life (N=N
0, N
0set according to actual needs) load value located is fatigue limit load estimated value.
(4) meta order: arrange by ascending order ascending fatigue limit load estimated value, utilize afterwards formula P (i)=(i-0.3)/(n+0.4) the calculate meta order P (i) of each sample data, in formula: n is sample number, i is sequence number.
(5) cumulative failure probability: in load zones institute likely value probability with, be approximately equal to meta order.
(6) average sequence number:
be used for calculating meta order, in formula:
The total sequence number of j--,
K--inefficacy sequence number,
N--sample size.
(7) standard normal deviator: average is 0, the probability quantile of the normal distribution that variance is 1.
Illustrate present embodiment below in conjunction with Figure of description.
Refer to Fig. 1, this figure is the process flow diagram of the fatigue test method of gas engine part described in present embodiment.
As shown in Figure 1, the fatigue test method of gas engine part provided by the invention, comprises the following steps:
Step 1: the sample of multiple gas engine parts is carried out to torture test and obtain load-life-span sample data of multiple samples, and be plotted in load-life-span log log coordinates system, wherein, the torture test of all samples should be carried out in high-Cycle Fatigue Life Prediction region.
What the torture test of gas engine part adopted is conventional test equipment and test method, test should be carried out in the high-Cycle Fatigue Life Prediction region of gas engine part, and 1/3 should the losing efficacy in high life region of torture test sample data that requires all samples, is guaranteed with the correlativity of guaranteeing the sample data that dispersion degree is larger.
The test life N (cycle index) that supposes sample meets 2 × 10
5<N<5 × 10
6, in this test life, as sample generation failure damage, claim this sample data (testing site) for inefficacy sample point; If the life-span of test specimen is greater than the cycle index upper limit (fundamental test life-span N
0) and failure damage does not occur, claim this sample data (testing site) for ending sample point.
After the torture test of all samples completes, respectively its load-life-span sample data is plotted in load-life-span log log coordinates system, specifically please also refer to Fig. 2.Fig. 2 is that load-life-span double-log of drawing in the fatigue test method of gas engine part described in embodiment is counted coordinate system schematic diagram, and in Fig. 2, abscissa is the logarithm value lgN in sample life-span, the logarithm value lgS that ordinate is load.
Step 2: utilize least square method to carry out linear fit to described load-life-span sample data, and utilize fit line to carry out the tired separation B of high/low week of regretional analysis acquisition gas engine part
lCF.
Known according to the summary of the fatigue test results of gas engine part, the dispersiveness of the sample data in low load/high life region is larger, and the low life-span of top load district less, the data of the dispersiveness of sample data distribute relatively concentrated, therefore can think at low-cycle fatigue critical cycle life-span N
lCF(in the present embodiment, arrange N
lCF=10000) some place, load does not have dispersiveness and only has unique numerical value.For sake of convenience, this point is designated as to (N
lCF, B
lCF).
Refer to again Fig. 2, first by least square method, load-life-span sample data of all samples is carried out to linear fit and form straight line, then the fit line of load-life-span sample data is extended to lgN
lCFobtain lgB
lCF(linear regression), and then try to achieve B
lCF.
In above-mentioned linear regression analysis process, must ensure the correlativity of sample data, need to supplement increase sample data if can not reach the significance (General Requirements significance α is less than or equal to 0.05 in the industry) of setting, until significance meets the demands.For example former sample data is 5, and significance is 0.08, does not meet the demands, and needs to continue to increase 1-2 sample and does experiment, and is less than or equal to 0.05 until reach significance.
Step 3: the tired separation B of high/low week that utilizes gas engine part
lCFfailpoint B with each sample
iobtain the anti-fatigue LIMIT ESTIMATION value FS of each sample
i.
Shown in Fig. 3, Fig. 3 is the fatigue limit statistics schematic diagram of gas engine part in the fatigue test method of gas engine part described in embodiment.
As shown in Figure 3, by tired high/low week separation B
lCFfailpoint B with some samples
ibe connected and form a ray, this ray and fundamental test life-span (circulation radix line N
0) intersection point be exactly the anti-fatigue LIMIT ESTIMATION value FS of this sample
i.
Step 4: to the anti-fatigue LIMIT ESTIMATION value FS of each sample
isort, then try to achieve meta order and the standard normal deviator D of all samples
i.
If some meta orders have comprised stop in a test, need according to formula
obtain average sequence number i
k, with i
kreplace the i in formula P (i)=(i-0.3)/(n+0.4) to calculate meta order P (i), in formula: j is total sequence number, k is inefficacy sequence number, and n is sample size.
Step 5: utilize the standard normal deviator D of least square method to each sample
ifSi carries out linear fit with fatigue limit estimated value, and obtains the average of torture test ultimate load and the linear relationship of standard deviation of gas engine part by linear regression analysis, and then can utilize the linear relationship of average and standard deviation to carry out fail-safe analysis.
Please also refer to Fig. 4, Fig. 4 is the fatigue test method Plays normal state deviator of gas engine part described in embodiment and the linear regression analysis schematic diagram of fatigue limit estimated value.
As shown in Figure 4, first according to formula P (i)=(i-0.3)/(n+0.4) calculate the cumulative failure probability (meta order) of each sample data, and obtain standard normal deviator D
i, then utilize the standard normal deviator D of least square method to each sample
ifSi carries out linear fit with fatigue limit estimated value, under the requirement that meets significance, utilizes linear regression analysis to obtain the average of torture test ultimate load and the linear relationship of standard deviation.In Fig. 4, the intercept of fit line (straight line) is the average of torture test ultimate load, and slope is the standard deviation of torture test ultimate load.
Compared with prior art, the fatigue test method of gas engine part provided by the invention, can be applicable to the torture test of the gas engine parts such as bent axle, connecting rod or cylinder body, and the method has following significant advantage:
(1) based on reliability engineering and mathematical statistics method, take full advantage of means and the knowledge of mathematical statistics method, can effectively implement small sample test, and the levels of precision of its result is for relatively maximum; , meeting under the condition of degree of confidence, relative error restriction, it is relatively minimum that the sample number of test also can reach meanwhile.
(2) with meta order instead of flat average, obtain the statistics of fatigue limit load with the linear relationship of cumulative failure probability, average sequence number and standard normal deviator and fatigue limit estimated value, draw thus the statistical nature of fatigue limit load (average of fatigue limit load and standard deviation) relatively accurately, sample size can obviously reduce.
(3), owing to testing, therefore shortened the test period in finite life region.
(4) according to the S-N of metal fatigue (load-life-span) rule, adopt accelerated test method, obtain most of sample data in finite life region, further shorten the test period.
The above is only the preferred embodiment of the present invention; it should be pointed out that for those skilled in the art, under the premise without departing from the principles of the invention; can also make some improvements and modifications, these improvements and modifications also should be considered as protection scope of the present invention.
Claims (8)
1. the fatigue test method of gas engine part, is characterized in that, comprises the following steps:
The sample of multiple gas engine parts is carried out to torture test and obtain load-life-span sample data of multiple samples, and be plotted in load-life-span log log coordinates system, wherein, the torture test of all samples is carried out in high-Cycle Fatigue Life Prediction region;
Utilize least square method to carry out linear fit to described load-life-span sample data, and utilize fit line to carry out the tired separation B of high/low week of regretional analysis acquisition gas engine part
lCF;
Utilize the tired separation B of high/low week of gas engine part
lCFfailpoint B with each sample
iobtain the anti-fatigue LIMIT ESTIMATION value FS of each sample
i;
Anti-fatigue LIMIT ESTIMATION value FSi to each sample sorts, and then tries to achieve meta order and the standard normal deviator D of all samples
i;
Utilize the standard normal deviator D of least square method to each sample
iwith fatigue limit estimated value FS
icarry out linear fit, and utilize fit line to carry out regretional analysis to obtain the average of torture test ultimate load and the linear relationship of standard deviation of gas engine part.
2. the fatigue test method of gas engine part according to claim 1, is characterized in that, 1/3 of the torture test sample data of all samples should lose efficacy in high life district.
3. the fatigue test method of gas engine part according to claim 1, is characterized in that, the tired separation B of high/low week of described gas engine part
lCFobtain by the following method:
By load-life-span, the fit line of sample data extends to lgN
lCFobtain lgB
lCF, then try to achieve B
lCF, N
lCFfor the test life of gas engine part of setting.
4. the fatigue test method of gas engine part according to claim 3, it is characterized in that, carrying out load-life-span when sample data linear fit, if can not reach the significance of setting, needing to supplement increases sample data, until meet the significance of setting.
5. the fatigue test method of gas engine part according to claim 1, is characterized in that, the anti-fatigue LIMIT ESTIMATION value FS of described sample
iemploying following methods obtains:
In fatigue limit statistics, by low-cycle fatigue critical cycle point B
lCFwith failpoint B
ibe connected and form a ray, this ray and the intersection point in fundamental test life-span are the test estimated value FS of this sample anti-fatigue ultimate strength
i.
6. the fatigue test method of gas engine part according to claim 1, is characterized in that, trying to achieve in the process of described meta order, if some meta orders have comprised stop in a test, needs according to formula
obtain average sequence number i
k, and with i
kreplace the i in formula P (i)=(i-0.3)/(n+0.4) to calculate meta order P (i), in formula: j is total sequence number, k is inefficacy sequence number, and n is sample size.
7. the fatigue test method of gas engine part according to claim 1, is characterized in that, while utilizing least square method to carry out linear fit to the estimated value of standard normal deviator and fatigue limit, significance should be less than or equal to 0.05.
8. the fatigue test method of gas engine part according to claim 1, is characterized in that, described gas engine part is specially bent axle, connecting rod or cylinder body.
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| CN108562504A (en) * | 2015-05-21 | 2018-09-21 | 江苏理工学院 | The test method of test material fatigue strength |
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| CN111734585A (en) * | 2020-06-18 | 2020-10-02 | 上海电气风电集团股份有限公司 | Method and device for determining limit load of wind driven generator and readable storage medium |
| CN112067287A (en) * | 2020-09-17 | 2020-12-11 | 中国第一汽车股份有限公司 | Odd-gear input shaft torque fatigue test method and test system |
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