Fang-Jun Zuo

A modified nonlinear fatigue damage accumulation model

This paper presents a modified nonlinear fatigue damage accumulation model accounting for load interaction effects. The original model is based on physical property degradation of materials, from which the load interaction effects are ignored. However, the load interaction effects have a significant influence on the fatigue life. In the study, by analyzing five damage models, a load interaction parameter is obtained and added to the original model. Experimental work is then carried out to verify the modified model of four categories of experimental data from smooth and notch specimens under two-level stress loading. Moreover, comparison is made among the results calculated by the test data, the Miner’s rule, the original model, and the modified model.

Fatigue life prediction under variable amplitude loading using a non-linear damage accumulation model

Most of engineering components in service are usually subjected to variable cyclic loading. It is important to predict fatigue life and deal with the issue about fatigue damage accumulation for these components. One of the largest difficulties in fatigue failure analysis is to find a representative ‘damage criterion’ which can be easily connected with the Wöhler curve taken as the known material data. The most commonly used model is the Miner’s rule which ignores the loading history effect, under the same loading conditions the experimental results are higher than the Miner expectations for low-to-high load sequence and are lower than the Miner expectations for high-to-low load sequence. The fatigue driving stress that causes fatigue damage is presented to predict residual fatigue life under variable amplitude loading. It increases with loading cycles until equals the fatigue strength when fracture occurs. By determining the equivalent number of cycles that yields the same fatigue driving stress as the previous loads, the remaining life can be predicted. The proposed damage criterion is connected cycle by cycle to the Wöhler curve and the experimental results are in a good agreement with the model predictions.

Contact Stress Analysis and Fatigue Life Prediction of a Turbine Fan Disc

Abstract Fan discs are critical components of an aero engine. In this paper, contact stress and life prediction of a turbine fan disc were investigated. A simplified pin/disc model was conducted to simulate the practical working condition under applied loads using finite element (FE) analysis. This study is devoted to examining the effects of interface condition of pin/disc such as gap and coefficient upon the maximum stress. The FE model indicated that the maximum stress occurs at the top right corner in the second pin hole, and larger gap or friction coefficient has a significant effect on the maximum stress. In addition, FE analysis without considering friction is also conducted. The results show that the dangerous point is similar to the result which considers friction and the stress state is relatively larger than that of considering friction. Finally, based on FE analysis result, life prediction for the fan disc is conducted to combine the material S-N curve, mean stress effects and concentration stress factor obtained by means of FE method.

A Practical Method to Predict Total Fatigue Life of Welded Joints Structures

Welded joints are usually the weakest link for welded structures due to the existence of stress concentration caused from welding. Fracture mechanics-based approach is a main method used to predict fatigue life for welded joints structures. In engineering, there are two main problems in fatigue life prediction, one is whether crack initiation life can be ignored or not, and the other one is to determine the crack size starting to propagate. Based on this research, a practical procedure is proposed to predict fatigue life of welded joints structures using an initial crack life model and Paris law. Emphasis is put on the discussion about crack initiation life and how to choose an appropriate method to determine the initial crack size. Noted that the proposed method in this paper does not need any tests to determine crack initiation life when crack size reaches a specified value, which depends on experience and is considered as crack size starting to propagate, thus human factors and uncertainty can be minished. Through comparison analysis, fatigue life predictions based on the proposed method are in a good agreement with experimental data.Copyright

Notice of Retraction A modified non-linear damage accumulation model considering load interaction effects under two-level loading

Many structures are subjected to variable amplitude loading in engineering practice. The foundation of fatigue life prediction under variable amplitude loading is how to deal with the fatigue damage accumulation in the case of two-level loading. A non-linear fatigue damage accumulation model which can explain the influence of loading sequences was proposed in earlier literature, but the model cannot consider the load interaction effect. A modified non-linear damage accumulation model is proposed in this paper to account for the loading interaction effects. Experimental data of two metallic materials are used to validate the proposed model. The agreement between model predictions and experimental data is observed, especially under high-low loading conditions.

Notice of Retraction Fatigue life estimation considering strengthening of low amplitude loads using grey model

For the usual failure mode of structural components under variable loading, fatigue life prediction is very important for the selection, design, and safety assessments of these components. The linear damage model (Miners rule) is used most widely for life prediction in practical engineering application. However, the fatigue damage caused by small loads cannot be ignored, especially when the load is near the constant amplitude of fatigue limit of a component. In the paper we use grey model to predict fatigue Life. The model improves the application of the traditional Miner rule, by considering the damaging and strengthening of low amplitude loads, under low amplitude loading strengthening.

Notice of Retraction A nonlinear fatigue damage accumulation model accounting for load interaction effects

According to the shortcomings of the nonlinear cumulative damage models which are based on material physical properties degradation, these models ignored the effects of load interaction, but the effects of load interaction really play a very important role on fatigue damage by studying the theories accounting for load interaction effects. In this paper, a new model is proposed to consider the effects of load interaction based on the material physical properties degradation. Then two categories of experimental data from smooth specimens are used to verify the proposed model.