| With the rapid development of economy,the space trusses set thesuspension crane, especially heavy crane are applicated gradually, as a result thefatigue problems have to be paied attentions.Bolt ball rack is a kind of spacetrusses.According to the current national standard,the A3suspension crane withabrove50,000cyclic numbers must be tested to determin the fatiguestrength.Based on National Natural Science Foundation of China—The further study on fatigue problem of space grid structure under the action ofthe suspended crane research, the factors of affecting fatigue strength areanalyzed，the test and research of high strength bolt M27are done.A bolt ballrack with suspension crane in service is carried on the static and fatigueanalysis.And the fatigue strength of M27bolt is obtained by experiment, thefurther study on fatigue damage machine is done, the concrete work are asfollows:1. With the aid of finite element software, the influence of stressconcentration is analyzed on the different thread forms, different diameter,exposed grain number and thread angle, root radius, excessive bolt head radiuson. Put forward the effective measures to reduce the stress concentration: choosethe thread, bolt head transition radius not less than0.2times of thread diameter,choose larger root fillet radius ordinary bolt，expose a number of threads.2. The processing technology of bolt on fatigue strength are analyzed: the influence of heat treatment on the fatigue strength is limited, the rolling threadhas higher fatigue strength; at the same time, the corrosion and alternating loadhave larger influence on fatigue strength.3. With the help of MIDAS software, static analysis and mathematicalstatistics of fatigue load of a bolt ball rack in service are done, conclusions areobtained: lifting point, the bolt of bottom chords in the middle of the rack,and the bolt of bottom chords and the ventral rod bolts near the lifting point,have the trends to be fatigue damage; and equivalent stress amplitude of thesebolts are obtained by mathematical statistics.4. Using Amsler fatigue testing machine and loading device, the fatigueexperiment of M27high strength in the bolt ball rack was carried out, eightdates under two kinds of stress amplitude are got.The conclusion is drawn: thefatigue damage of the space truss structure bolt are likely to happen during the50years safety period.5. Through macroscopic and microscopic analysis of the M27high strengthbolt fatigue fracture, the mechanism of fatigue damage is explained furtherly:fatigue source appears at the surface, extension area is formed with crackextension, fracture are is formed with rapid breakage. |
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