Research On Evaluation Method Of Thermal Fatigue Crack Propagation Life Of Brake Disc Of Offshore Drilling Drawworks

Disc brake is one core component of brake system of offshore drilling winch. It is turnto crack and even break due to thermal fatigue when it works, therefore，to carry out theresearch of crack propagation life of disc brake of brake system of offshore drilling winchunder thermal fatigue has a very important significance in safeguarding the safety of thedrilling person and equipments. In this article, the research object is the water-cooled discbrakes. Finite element method and test methods will be used to analysis the crackpropagation of water-cooled disc brakes and as the basis the life of crack propagation of discbrakes under thermal fatigue. The main research and innovation work include:(1) Related basic theory of this thesis is elaborated, including the theory of stress andstrain fields of Crack-tip, the theory of the stress intensity factor and extend finite elementmethod;the solution methods of stress and strain fields and stress intensity factors are givenand the extended finite element method which is used to simulate the crack propagation isdescribed.(2) The toughness of35CrMo materials is studied by the test of plane strain fracturetoughness. The relationship (a~da/dN) between crack growth rate and crack length isdecided by the test of self-constrained thermal fatigue of35CrMo Materials notchedspecimens under the cyclic temperature with20C~290C.(3) By the extended finite element method, stress intensity factors under the differentlength of crack are studied and therefore the relationship between the range of stressintensity factors and crack length（a~K）is built; the curve of expansion rate of thethermal fatigue (da/dN~K)is built under the combination of the relationship betweenthe crack growth rate and the crack length(a~da/dN), eventually the formula-Parisformula which is used to calculate the life of crack propagation is established.(4) The Actual crack size of disc is measured by the rule processing on cracks andintensity factor of radial stress and intensity factor of axial stress are calculated respectivelyand by combining Paris formula, the life evaluation system of brake disc crack propagationin matlab is designed to calculate the life of crack propagation of the brake disc.The study showed that: during braking，the surface of brake disc has the thermalfatigue crack due to brake disc being affected by cyclic thermal stress, the crack continues to expand under thermal stress; stress intensity factor of crack tip and growth rate of crack isincreasing with the growth of the crack; the study of the life of crack propagation shows thataxial extension of crack is failure firstly which resulting in water leakage of the brake discwhen there is no defect on the water-cooled disc.