Fatigue Life Analyses And The Combined Theory Of Strength And Stability

In this dissertation, the fact that the concepts of tangent modulus factor (φ₁,), proportional limit law (PLL) and strength utilization ratio function (SURF) in the combined theory of strength and stability (CTSS) are the extension of concerned concepts in elastic mechanics is illustrated. These concepts can be applied not only in strength theory but also in stability theory.By using strain energy theory, tangent modulus theory is farther discussed and applied, and the combined theory of strength and stability is improved.The approach to apply the combined theory of strength and stability into fatigue analysis is discussed. According to the relationship between material fatigue performance curve and concerned parameters in fracture mechanics, the relationship between fatigue life and crack half length is obtained, that is equivalent crack length of fatigue life. The function relationships between these two aspects are constructed. The experiment data show that this method can express the same character of fatigue life of all kinds of materials and experiment data acquired from different materials can be used each other. That is meaningful.The existed material fatigue performance test curves are dealt with and analyzed, and the non-dimensional stress-strain curve, tangent modulus factor curve and fatigue life curve are drawn based on the experiment data, and these three non-dimensional parameter curves are used to find the inherent rules that the test curves can be replaced each other to some extent. It can be concluded that if the common character and system error of these materials are found, the test curve of a certain material can be used for reference by another material. This is a simple approach about fatigue life estimate and is engineering practical.At the same time, the approach proposed in this thesis is compared withexisted approaches to estimate fatigue life, and the result shows its unique advantages.