﻿ 基于故障树最小割集的解脱器活塞断裂分析
 舰船科学技术  2019, Vol. 41 Issue (1): 133-137, 151 PDF

Fracture analysis of piston of a certain reliever based on the minimum cut set of fault tree
YANG Hong-liang, HUANG Guan-ming
Zhengzhou Electromechanical Engineering Research Institute, Zhengzhou 450015, China
Abstract: Aiming at the phenomenon of fracture in the process of stopping shooting of a reliever piston, the analytical method of the fault tree is used to establish the minimum cut set fault tree of the reliever piston fracture based on the minimum cut set. The fault types in the minimum cut set are verified by the finite element analysis method, the material microanalysis method and the impact power test.The experimental results show that the high hardness of the piston and the short time of hydrogen removal in the secondary chromium plating causing the high hydrogen content of the piston are the main causes of the piston fracture.The research method of this paper has the value of theory and engineering application, and provides the reference for other engineering fault analysis and solution and the formulation of production technology.
Key words: reliever piston fracture     fault tree     minimum cut set     physical and chemical inspection     finite element analysis     hydrogen embrittlement
0 引　言

1 基于故障树的某解脱器活塞断裂分析 1.1 故障树分析法简介

 图 1 解脱器活塞断裂故障树 Fig. 1 Fault tree of the fractured reliever piston

1.2 故障树最小割集的数学描述

 $y = f\left( {{X_1},{X_2}, \cdots ,{X_i}} \right) = \mathop \cup \limits_{j = 1}^{{N_k}} {K_j}\text{。}$

 ${K_j} = \mathop \cap \limits_{i \in {K_j}} {X_i} = \prod\limits_{i \in {K_j}} {{X_i}} \text{。}$

 $y = f\left( {{X_1},{X_2}, \cdots ,{X_i}} \right) = \mathop \cup \limits_{j = 1}^{{N_k}} \prod\limits_{i \in {K_j}} {{X_i}} \text{。}$

 $y = f\left( {{X_1},{X_2}, \cdots ,{X_i}} \right) = \mathop \cup \limits_{j = 1}^{{N_k}} \prod\limits_{i \in {K_j}} {{X_i}} \text{，}$

$ST = S_1 \cup S_2 \cup S_3 \cup S_4 \cup S_5 = X_1 \cup X_6 \cup X_7 \cup X_8 \cup$ $X_9 \cup X_{10} \cup X_2X_3\cup X_2X_4 \cup X_2X_5 \cup X_1X_3 \cup X_1X_4 \cup X_1X_5$

 图 2 解脱器活塞断裂最小割集故障树 Fig. 2 The minimum cut set of fault tree of the fractured reliever piston

2 主要影响因素分析

2.1 解脱器活塞刚强度分析

 图 3 有无圆角应力云图 Fig. 3 With or without a fillet stress cloud

 图 4 有无圆角位移云图 Fig. 4 With or without a fillet displacement cloud

40Cr的抗拉强度为980 MPa以上，其屈服强度为785 MPa，由静力学计算结果可以看出，活塞有圆角最大应力为514 MPa，最大变形为0.169 mm，无圆角最大应力为363 MPa，最大变形为0.171 mm，因此解脱器活塞在强度上还有较大余量。活塞断裂处增加圆角并不能明显降低应力，增加圆角后应力还会增加，这是由于活塞头部在力作用下变形直到接触到气缸壁后停止变形，因此不管活塞有无圆角，其变形量基本一致，而有圆角时的应变更大，因此应力值反而会增加。因此，由上述分析基本上可以排除活塞刚强度不足和活塞断裂处应力集中造成的活塞断裂。

2.2 设计装配问题分析

2.3 理化检验分析 2.3.1 断口分析

 图 5 断裂活塞宏观形貌 Fig. 5 Macrascopical morphology of the fractured piston

 图 6 活塞断口微观形貌 Fig. 6 Microstructure of piston fracture surface
2.3.2 氢含量测定

2.3.3 硬度检测

 图 7 40Cr材料不同温度回火后的机械性能 Fig. 7 Mechanical properties of 40Cr materials after tempering at different temperatures

2.3.4 金相分析

 图 8 金相组织 500× Fig. 8 Metallurgical structure 500×

 图 9 表面镀层500× Fig. 9 Surface finishes500 ×
3 综合分析

4 对比试验验证

1）由1，2和3组试验对比可知，不除氢氢含量最高，冲击功值最低，且除氢时间越久，氢含量越低，冲击功值越大；

2）由2和5组，4和6组，7和10组，9和12组试验对比可知，在相同除氢时间，二次镀铬氢含量比一次镀铬氢含量高，冲击功值低，说明了二次镀铬会造成氢含量偏高；

3）由1～6和7～12组不同硬度对比可知，硬度越高，冲击功值越小，活塞在冲击载荷抵抗变形和断裂的能力越差，活塞越容易断裂。

5 结　语

1）镀铬工艺除氢不彻底，或者在镀铬过程中，镀铬不合格再进行第二次镀铬，造成氢含量高，使得冲击功值低，导致活塞氢脆断裂；

2）活塞热处理硬度偏高，导致材料冲击功值降低，使材料的氢脆敏感性提高，导致活塞氢脆断裂。

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