| As a new manufacturing technology,Laser melting deposition(LMD)technology is expected to become one of the core technology to promote the innovation of the existing manufacturing industry due to its unlimited size and high efficiency.Because of the complex structure and high performance requirements of nuclear power emergency diesel engine camshaft,the traditional manufacturing technology has been unable to meet the demand due to the disadvantages of cumbersome process and long time consuming.The LMD technology with its advantages makes the manufacturing of the parts have great engineering significance.However,the research on the fatigue performance of industrial components formed by LMD is not yet perfect.Therefore,this paper mainly studies the fatigue crack growth of LMD nuclear power emergency diesel engine camshaft,and analyzes the stress field and fatigue crack growth law of camshaft in the service process.The main research contents and conclusions of this paper are as follows:(1)The suitable process route and post-treatment scheme of LMD forming 12CrNi2 high performance alloy steel were selected,and the corresponding samples were prepared.The fatigue crack growth test of compact tensile shear specimens(CTS)was carried out.The a-N curve of fatigue crack growth under different loading conditions was obtained;The inner part of the formed part and the fracture of the sample are analyzed.It is found that the plasticity of the material is good,and the micro defects such as lack of fusion,inclusion and porosity formed in the forming process are the main causes of crack initiation.There are fatigue striations and secondary cracks in the fatigue fracture surface.The formation of secondary cracks reduces the crack growth rate to a certain extent.(2)The fatigue crack growth path and residual life of LMD samples were analyzed by using the simulation method of extended finite element method(XFEM)and direct cyclic.The simulation results show that the crack growth path of the center crack tension specimen(CCT)obtained by the finite element simulation is almost the same as the test results,and the fatigue life error is about 0.44%;The error of fatigue crack growth path of CTS sample is within 16.54%,and the error of crack growth times is within 3.05%.It shows that this method can accurately predict the fatigue crack growth behavior of LMD formed 12CrNi2 high performance alloy steel.(3)Based on the actual working load condition of camshaft,a set of user subroutines of DLOAD are compiled.The fatigue crack growth path and remaining life of LMD nuclear power emergency diesel engine camshaft are predicted by the validated numerical simulation method.The results show that the position where the maximum stress occurs during the service of the camshaft is the root of the middle cam,and here the crack will expand in the direction of about 45°with the camshaft axis until the boss with a larger shaft diameter,and the corresponding number of fatigue is about 2,170,000.In addition,the effects of initial crack length,direction and location on the fatigue crack growth behavior of camshaft are analyzed.It is found that with the increase of initial crack,the life of camshaft decreases.The closer the initial crack is to the middle,the faster the fatigue crack growth rate of cam is.The danger of transverse crack is much greater than that of longitudinal crack. |
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