A Fast Prediction Method of Fatigue Limit Based on Strain Increment
A technology of fatigue limit and strain increment, which is applied in the direction of applying repeated force/pulsation force to test the strength of materials, etc., which can solve the problems of narrow application range and poor accuracy
Active Publication Date: 2018-04-17
ACADEMY OF ARMORED FORCES ENG PLA
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[0017] Since the fatigue limit and static parameters have different physical meanings, these empirical prediction formulas are all based on statistical analysis of a large number of fatigue data for a specific material system, so the scope of application is narrow and the accuracy is poor
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[0064] In order to verify the feasibility and accuracy of the strain-based rapid prediction fatigue limit theory, we carried out strain and infrared experiments on two different common materials for blower impellers (precipitation hardening martensitic stainless steel FV520B and KMN-I) under an average stress of 700MPa. Synchronous online monitoring of thermal signals, comparing and verifying the prediction results of strain-based fatigue limit with the prediction results of Luong method in the currently recognized infrared thermal imaging method. The test results are described in detail below.
[0065] Two common compressor impeller materials, FV520B and KMN-I, were selected as raw materials and their simulated overspeed preloading process (test average stress σ’ mean Set to 900MPa to simulate ultra-speed centrifugal force, stress amplitude Δσ' to 10MPa to simulate airflow forced vibration, test frequency to 30HZ, and fatigue loading 5000 times) to prepare samples from pre-st...
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Abstract
A fast prediction method of fatigue limit based on strain increment belongs to the field of fast prediction of material fatigue limit. The present invention finds that under the gradient stress load, the change law of the strain variable is indeed very similar to the change law of the temperature rise. Since the Luong method can predict the fatigue limit with the corresponding stable temperature rise value under the gradient load, the strain variable under the gradient load can also be used theoretically. Rapidly predict fatigue limits. The present invention utilizes the fatigue testing machine and its built-in extensometer (without relying on an expensive high-precision infrared thermal imager), theoretically at least one sample is used, and the strain amount can be loaded by gradient within one day. The change law is fast and low-cost to predict the fatigue limit of more reliable materials or simple components, while the traditional lifting method and group method often take several months and consume a lot of manpower and financial resources. Therefore, the present invention has high engineering practicality value and significant economic benefits.
Description
Technical field: [0001] The invention belongs to the field of rapid prediction of material fatigue limit. Background technique: [0002] At present, there is no mature theoretical model that can reveal the physical nature of the fatigue limit of materials, so it is difficult to obtain it through theoretical calculations. For strain-age hardening materials, under constant amplitude loading conditions, it is found from their S-N curves that usually more than about 10 6 A "plateau" occurs after the fatigue cycle. When the stress amplitude is lower than the platform stress, the sample can withstand infinite fatigue cycles without failure, and the platform stress is called the fatigue limit σ e (or endurance limit). However, for some materials such as high-strength steel and aluminum alloys that do not have strain age hardening, there may be no fatigue limit. With the increase of cycle times, the stress range they can withstand continues to decrease. At this time, the sample c...
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IPC IPC(8): G01N3/32
Inventor 王海斗张玉波徐滨士王桂阳范博楠邢志国
Owner ACADEMY OF ARMORED FORCES ENG PLA