﻿ 基于应力云图和有限元的柴油机曲轴疲劳强度分析
 舰船科学技术  2019, Vol. 41 Issue (10): 144-147, 158 PDF

Based on the stress cloud map and Ansys fatigue strength analysis diesel engine
CHEN Zuo-tian, GU Han, WANG Xiao-lin, CAI Peng-fei, SU Xian-ming
China Satellite Maritime Tracking and Control Department, Jiangyin 214431, China
Abstract: The diesel engine is subjected to severe vibration during the operation, which will damage the accessories of the shaft, the fuel injection and valve timing, which will seriously affect the balance of diesel engine and aggravate the noise of the diesel engine. The strong vibration will cause the fatigue fracture of the crankshaft. In this paper, by modeling the crankshaft - shaft system of the ship's main engine,by using the three-dimensional integral model of crankshaft and preprocessing in Ansys Workbench, meshing solid model of the crankshaft. The force analysis is carried out with the finite element software Ansys​​​​​​​, obtaining the deformation and stress cloud map of the crankshaft. Finally, the fatigue strength of the crankshaft is carried out. Strength analysis is focused on the crankshaft fatigue strength under the three functions of cylinder force, bearing support force and propulsion shaft load.
Key words: crankshaft     finite element     fatigue strength     torque     thrust
0 引　言

1 曲轴疲劳强度力学计算模型 1.1 受力模型

1）气体作用力

 ${F_g} = \frac{{{\text{π}} {D^2}}}{4}\left( {{P_g}{\rm{ - }}{P^{\rm{'}}}} \right){\text{。}}$ (1)

2）动力机构的惯性力

①往复惯性力

 ${F_j} = {\rm{ - }}{m_j}{V^{\rm{'}}} = {\rm{ - }}{m_j}R{\omega ^2}\left( {\cos \alpha + \lambda \cos 2\alpha } \right){\text{。}}$ (2)

②离心惯性力

 ${F_r} = {m_r}R{\omega ^2}{\text{。}}$ (3)

3）活塞销处的受力[4]

 $F = {F_g} + {F_j}{\text{。}}$ (4)

 ${F_h} = F{\rm{tg}}\beta = F\frac{{\sin \alpha }}{{\sqrt {1/{\lambda ^2}{\rm{ - }}{{\sin }^2}\alpha } }}{\text{，}}$ (5)
 ${F_c} = \frac{F}{{\cos \beta }} = \frac{F}{{\sqrt {1{\rm{ - }}{\lambda ^2}{{\sin }^2}\alpha } }}{\text{。}}$ (6)

4）曲柄销处的受力[57]

 ${F_\tau } = {F_c}\sin \left( {\alpha + \beta } \right) = F\left( {\sin \alpha + \frac{{\lambda \sin 2\alpha }}{{2\sqrt {1{\rm{ - }}{\lambda ^{\rm{2}}}{{\sin }^2}\alpha } }}} \right){\text{，}}$ (7)
 ${F_n} = {F_c}\cos \left( {\alpha + \beta } \right) = F\left( {\cos \alpha + \frac{{\lambda {{\sin }^2}\alpha }}{{\sqrt {1{\rm{ - }}{\lambda ^{\rm{2}}}{{\sin }^2}\alpha } }}} \right){\text{。}}$ (8)

1.2 边界条件

 图 1 轴颈压力分布示意图 Fig. 1 Sketch of axial pressure distribution

1）在轴颈轴向上

 ${q_x} = {q_{\max }}\left( {1{\rm{ - }}\frac{{{x^2}}}{{{L^2}}}} \right){\text{。}}$ (9)

2）在轴颈周向上

 $q\left( {x{\rm{,}}\theta } \right) = \frac{9}{{16}} \times \frac{Z}{{RL}}\left( {1{\rm{ - }}\frac{{{x^2}}}{{{L^2}}}} \right) \times \cos \frac{3}{2}\theta{\text{。}}$ (10)

1.3 有限元网格划分

 图 2 曲轴网格划分图 Fig. 2 Grid diagram of crankshaft

2 曲轴疲劳强度计算结果分析 2.1 轴颈受力分析

 图 3 扭矩切应力分布 Fig. 3 Distribution of torque shear stress

 ${\tau _\rho } = \frac{T}{{{I_p}}} \cdot \rho{\text{，}}$ (11)
 $T = \frac{{9\;550 \cdot P}}{n}{\text{。}}$ (12)

 $F = \frac{T}{R} = \frac{{{\rm{4}}{\rm{.78}} \times {{10}^{\rm{4}}}}}{{{\rm{25}} \times {{10}^{{\rm{ - }}3}}}} = {\rm{1}}{\rm{.91}} \times {\rm{1}}{{\rm{0}}^{\rm{6}}}{\rm{N}}{\text{。}}$ (13)

 图 4 第4缸发火曲轴应力云图 Fig. 4 Stress cloud diagram of firing crankshaft of fourth cylinder
2.2 曲轴变形量分析

 图 5 第5缸发火曲轴变形云图 Fig. 5 Deformation cloud diagram of fifth cylinder crankshaft

2.3 疲劳强度校核

 $n_\sigma = \frac{{{\sigma _{ - 1}}}}{{\frac{{{K_\sigma }{k_\sigma }}}{{{\varepsilon _\sigma }\beta }}{\sigma _\alpha } + {\psi _\alpha }{\sigma _m}}}{\text{。}}$ (14)

 图 6 曲轴的安全系数显示图 Fig. 6 Safety factor display of crankshaft

3 结　语

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