An original fatigue quality assessment method based on uncertainty analysis

Abstract

The invention provides an original fatigue quality assessment method based on uncertainty analysis. The equivalent initial flaw size of all fracture surfaces obtained from durability test is no longerdivided into different stress levels, but is used as a whole data set for original fatigue quality assessment, which improves the data sample size, ensures the authenticity of the analysis results and simplifies the data processing flow. Via EIFS- TTCI data conversion formula, which converts the EIFS data set into TTCI data set obeying three-parameter Weibull distribution, is convenient for parameter determination and verification; By introducing fuzzy theory, more uncertain information can be mined from the data, which improves the calculation accuracy of cumulative failure probability. Theparameters of TTCI distribution are estimated by grey system theory, which is more suitable for the case of less sub-samples. The invention can improve the sample capacity, fully mine the uncertain information contained in the data, simplify the analysis flow, reduce the calculation workload, is more suitable for the situation of small sample number, and ensures that the evaluation result is moretrue and accurate.

Description

technical field [0001] The invention belongs to the field of aircraft structure durability design, in particular to a method and device for evaluating original fatigue quality based on uncertainty analysis. Background technique [0002] Durability design is one of the important ideas guiding the structural design of aircraft, automobiles, ships, etc. One of the commonly used analysis methods is the probabilistic fracture mechanics analysis (PFMA, Probabilistic Fracture Mechanics Analysis) method. When performing durability analysis, it is necessary to obtain the original fatigue quality (IFQ, Initial FatigueQuality) of materials and structures. As an important part of the original fatigue quality model, the distribution of the equivalent initial flaw size (EIFS) is used to describe the original fatigue quality of the material structure, and it is also the key input data in the probabilistic fracture mechanics analysis method, which directly affects the durability. sex analy...

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Problems solved by technology

However, because the TTCI fitting method considers that the crack growth rate is the same under the same stress level, the randomness of crack growth is ignored, which makes the original fatigue quality evaluation result unreal; at the same time, because the TTCI fitting method needs to divide the fracture data into different stress levels Therefore, the number of fracture data at each stress level is less, and the cumulative failure probability of TTCI obtained by the rank estimation adopted by the TTCI fitting method is not suitable for such a situation with a small sample size, and the calculation accuracy needs to be improved; in addition, Using the fitting method to determine the parameters of the TTCI distribution is not suitable for the case of a small sample size; finally, the fracture data needs to use general conditional assumptions, resulting in complicated data processing and easy to bring cumulative errors

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