| The frequent fracture accidents of bolts, which connected hydrogen compressor crankshaft box with middle body, have caused enormous danger to normal production and safety. Looking for the reason of the faults, finding effective method to avoid failure is not only positive to production and safety, but also meaningful to decision of inspection period.In this paper, the problems were concerned with thermal and dynamical calculation of compressor, mechanics analysis of bolt joint structure, contact finite element calculation, fatigue life prediction and reliability study of bolt, bolt structure optimization and investigation of extending life technology and so on. The main contents and results were as follows:(1) By means of compressor thermal and dynamical calculation, bolt structure joint load condition was analyzed in detail. Gas force, general piston force and slider vertical force were calculated, and also friction and moment spectrum on bolt structure were given. Analysis results indicated that friction and moment have hardly an effect on stress of bolts, and load led by gas force and vibration of the compressor were the main reasons of fatigue fracture.(2) 3-dimension contact finite element calculation of bolt joint structure demonstrated that the effect of friction on bolt stress can be neglected. By means of axi-symmetrical contact FEA method, the exactly maximal stress and strain of the first root in bolt screw could be acquired.(3) Temperature method was used to simulate pre-tension load of the bolt, and the result were more applicable to practical condition.(4) In axi-symmetrical FEA method, the influence of mesh density on stress and strain and the results by axi-symmetrical FEA method were compared with that by 3-dimension FEA were also discussed.(5) The strain-life curve of bolt material based on the fatigue test was gained. The local stress-strain method was applied to calculate the fatigue life of the bolt. Theprediction results showed that gas force was not alone reason to lead the fatigue fracture of bolt. By the data in practice, the calculation results demonstrated that the life prediction was coincident with the practical life. The fatigue life of tested bolts also indicated that the prediction method was effective and more precise.(6) The influence of the scatter of pre-tension stress and fatigue intensity exponent on the bolt fatigue life was analyzed in detail. The results by the finite element method and local stress-strain method were well explained by bolt deformation plot in theory. The results also pointed that bolt fatigue life could be extended by increasing pre-tension stress .(7) According to S - N curve of bolt material and experiment results, P -S -N curves were plotted and bolt fatigue life under different failure probability was also acquired.(8) The fatigue life of bolt could be extended by optimization of bolt structure or appending of dish spring.
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