Marine Main Engine Crankshaft Failure Analysis A Case Study
Study on Crankshaft Design Based on CAD/CAE
Authors: Chang Gao Xia, Jian Kuan Su, Mao Hui Pan
Abstract: This paper presents an integrated method, which is based on the CAD/CAE, for engine crankshaft design. A parametric modeling system of engine crankshaft is established with the CATIA secondary development tools. Taking advantage of the finite element analysis procedure of engine crankshaft strength which is programmed with ANSYS APDL programming language, the parametric loading, automatic solution and result analysis of the crankshaft strength can be realized. Integrating the parametric modeling system of engine crankshaft and the special finite element analysis procedure of the engine crankshaft strength, the three-dimensional digital model of the crankshaft can be generated rapidly. By changing the structure dimension, the crankshaft series design is achieved and the design and analysis can be improved. Therefore, it is helpful to improve the design quality and efficiency of crankshaft and shorten the design cycle.
Investigation on Surface Crack of C38N2 Automobile Engine Crankshaft
Authors: Zhong Yang, Ya Zheng Liu, Le Yu Zhou, Guo Wei Li, Dan Zhang
Abstract: Defect in surface induction hardening layer at the eccentric axle neck of C38N2 automobile engine crankshaft was investigated. Fracture morphology and microstructure of the defect were analyzed by optical microscope and scanning electron microscope, and compared with the microstructure characteristics in defect-free locations. And the reasons and the technical procedures of the defects were discussed. The results indicated that the surface defect is a quenching crack caused by induction hardening process. The crack propagation is along prior-austenite grain boundaries and is affected by MnS inclusions. Martensite lath in surface hardening layer at position having 45° or 90° with mouldjoint is shorter than that at the defect position. Distribution characteristics of inclusions at different positions have significant difference. Inclusions in the defect position are slender spindle and are distributed nearly vertical the crankshaft surface. Distribution of the inclusions in the 45° position is approximately parallel to the crankshaft surface. And the inclusions in the 90° position are mostly graininess. Distributional difference of the inclusions at the different positions is related to uneven flowing of metal during stamp forging process.
The Research on Fatigue of Crankshaft with the Method of Explicit Dynamic
Authors: Chen Hai Guo, Yong Zhang, Xiao Hui Cao
Abstract: The crankshaft fillet rolling process is one of the commonly adopted methods in engineering to improve fatigue life of the crankshaft. The crankshaft fillet rolling process was simulated based on the explicit dynamic calculation in this paper. After the data acquisition program was compiled, the distribution of the crankshaft surface stress could be obtained. Coupling calculation between the operating stress at different bending moments and the rolling residual stress was based on the Smith-Watson-Topper (SWT) modle. After the simulation on the crankshaft fillet rolling process was carried out, which was based on optimization rolling parameters, the crankshaft fatigue strength was improved by 8.6%.
Study on the Stress Distribution of the Piston Rod Fillet Based on the Nonlinear Finite Element Method
Abstract: Because of discontinuity of the shape, the piston rod of rapping device is liable to occur stress concentration phenomenon, leading to fracture of the piston rod. At work, the maximum stress of piston rod which took place in the cross section of the geometric mutations varied with the change of the fillet radius, under the same load, it analyzed the influence of different fillet radius on fracture of the piston rod via ANSYS/LS-DYNA finite element. The results showed that it can meet the requirements when the fillet radius was 5 mm.
A case study of a catastrophic failure of a web marine crankshaft and a failure analysis under bending and torsion applied to crankshafts are presented. A microscopy (eye seen) observation showed that the crack initiation started on the fillet of the crankpin by rotary bending and the propagation was a combination of cyclic bending and steady torsion. The crack front profile approximately adopts a semi-elliptical shape with some distortion due to torsion and this study is supported by a previous research work already published by the authors. The number of cycles from crack initiation to final failure of this crankshaft was achieved by recording of the main engine operation on board, taking into account the beachmarks left on the fatigue crack surface. The cycles calculated by the linear elastic fracture mechanics approaches showed that the propagation was fast which means that the level of bending stress was relatively high when compared with total cycles of main engine in service. Microstructure defects or inclusion were not observed which can conclude that the failure was probably originated by an external cause and not due to an intrinsic latent defect. Possible effects of added torsional vibrations which induce stresses are also discussed. Some causes are analyzed and reported here but the origin of the fatigue fracture was not clearly determined.