Method for Quantitatively Evaluating Whole-field Lightweight Level of Structure Based on Fatigue Strength

A method for quantitatively evaluating a whole-field lightweight level of a structure based on fatigue strength, characterized by matching a stress field of a structure with a fatigue strength field of the structure to quantitatively evaluate the whole-field lightweight level, comprising the steps of:

• step 1, determining a structural dangerous position to be subjected to a quantitative evaluation of the whole-field lightweight level under a given maximum fatigue load amplitude value, to obtain a maximum stress amplitude value and a gradient distribution of stress amplitude values of a dangerous cross-section at the structural dangerous position;
• step 2, determining an ideal fatigue strength field distribution of the structure according to the maximum stress amplitude and the gradient distribution of the stress amplitudes, wherein:
• the ideal fatigue strength distribution requires no strength surplus at any point and demand for strength is met;
• according to a stress-strength interference theory, an ideal strength at any point of the dangerous cross-section of the structure is designed as the fatigue stress amplitude at the point multiplied by a safety coefficient;
• step 3, determining a microstructural fatigue strength distribution of the dangerous cross-section of the structure according to a static strength distribution requirement of the dangerous cross-section;
• step 4, determining an actual fatigue strength distribution of the dangerous cross-section of the structure finally according to a residual stress distribution requirement of the dangerous cross-section of the structure, wherein:
• the residual stress distribution along a depth is contemplated quantitatively, the residual stress comprises residual compressive stress from cold strengthening, a residual tensile or compressive stress from heat treatment and processing, and the residual stress in structural stress fatigue is treated as average, with the residual compressive stress being negative, and the residual tensile stress being positive;
• and
• step 5, applying a whole-field stress-strength interference model to ensure that the strength at any point of the structure is greater than or equal to a maximum stress amplitude at the point, and carrying out the quantitative evaluation of the whole-field lightweight at the structural dangerous position through the actual fatigue strength distribution at the structural dangerous position determined in step 4 and the maximum fatigue stress amplitude distribution determined in step 1, namely, the quantitative evaluation of the lightweight level of surface and depth distributions thereof, to obtain a ratio of the actual fatigue strength at any point to the maximum stress amplitude at the point;
• finding that the actual fatigue strength is not enough and the fatigue strength design is unreasonable if the ratio of the actual fatigue strength at any point to the stress amplitude at the point is less than the safety coefficient;
• and finding that the strength at the point is surplus if the ratio of the actual fatigue strength at any point to the stress amplitude at the point is greater than the safety coefficient, a greater surplus corresponding to a greater ratio.