Dissertation > Industrial Technology > Metallurgy and Metal Craft > Metallurgy and Heat Treatment > Metallurgy ( Physical Metallurgy ) > Analytical tests of the metal (Metal Testing and Materials ) > Mechanical properties ( mechanical properties ) test > Fatigue and creep tests , the fracture toughness test

Research on Influence Factors on Metal Fatigue Strength

Author LiangXu
Tutor XieLiYang
School Northeastern University
Course Mechanical Design and Theory
Keywords fatigue strength stress concentration size effect surface condition fatigue life comprehensive coefficient
CLC TG115.57
Type Master's thesis
Year 2009
Downloads 42
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In the fracture accident of equipment, about 80% belongs to the fatigue fracture. This mechanical structure’s failure brings great threat to equipment safety service. The S-N curve and fatigue limit of material, only representative sample of the standard smooth fatigue limit. But the size, shape and surface of actual parts has a big difference between standard specimens. In parts of fatigue strength design must take these factors into account. The problem of fatigue strength’s influence factors is still a meaningful research topic.There are many influence factors of fatigue strength. Stress concentration, size and surface are more important than others. Based on the fatigue strength theory and fatigue test, study the above three factors on the part of fatigue strength and their interaction.35CrMo forging steel is taken as research object. Classify samples according to the different size and number of gap, surface processing condition. Test the fatigue life of specimens respectively to get the corresponding fatigue life data, so the basis of theory analysis is provided.Between stress concentration, size and surface, there is some interaction. Put these three factors together, a coefficient of colligation Kαwhich about affecting parts fatigue strength is defined. Now some different expression of comprehensive coefficient Kαhas been put forward. The fatigue strength of parts can be calculated with that of material and comprehensive coefficient Kα. Specimens’S-N curve can be fixed through material’s S-N curve with different expression of comprehensive coefficient Kα, then compare the fatigue life on specimens’S-N curve and the experimental value under test stress amplitude, to verify which comprehensive coefficient expression is more tally with the actual situation.Fit the test data by three parameters weibull distribution to get statistical distribution of fatigue life. Compare of the fatigue life probability density curves and further analysis stress concentration, size, surface for the fatigue life of specimens. The absolute size effect model which based on the theory of "the weakest link" is verified by test results

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