Prediction And Evaluation Of Ship Shaft Crack Propagation

The ship plays an vital role in international commercial intercourse,the exploration and development of marine resource,the ocean sovereignty of the country.Marine dynamic system provides power and secondary energy for the ship.As the key components of marine power system,the transmission system aims to output and transfer power.After the ship sails on the sea for a long time,the working environment will be very bad.When the transmission system operates,it suffers alternating stress for a longtime.The alternating stress is the result of incentive coming from diesel engine and propeller.There are more or less flaws in the shaft in the forging process.Under alternating stress,the shaft will initiate some cracks,extension and these phenomenon will lead to fracture,which is a disaster to the ship.As a result,it is very essential to study the crack extension of marine shaft and evaluate the lifetime of crack on the shaft.This paper utilizes Mechanical APDL and Workbench modules of software ANSYS to simulate and calculate internal and external cracks of the shaft on the ship.Main work content is as follow:(1)Based on the knowledge of mechanics of materials,the force condition at any point on the shaft is analyzed,which is under torsion and bending.Under torsion,the multi-diameter shaft appears stress concentration phenomenon in the simulation and calculation.The change rule of stress intensity factor under torsion in the stress concentration part is studied.(2)Stress intensity factor of 3-d penny-shaped crack in the shaft is calculated in the software ANSYS.Quadratic interpolation is compared with the interaction integral method.With control variable method,the effects of torque,bending moment,tension to stress intensity factor of elliptical surface crack on the shaft is studied.(3)Based on Paris’ s formula about propagation life of fatigue,the relationship between the speed of crack propagation and ship kinetic parameter(marine main engine running power,velocity of the shafting)is discussed.The crack propagation of the shaft is simulated with ANSYS.Under torsion,the fatigue life of elliptical crack is evaluated and calculated.The relationship between the depth of crack and fatigue life is researched.(4)In order to relief crack failure of the shafting crack and ensure the navigation safety of ship,the flow chart is built to forecast and evaluate crack propagation which is on the transmission in the ship.It laid a foundation to the system establishment.