After disassembling the double transformer oil filter, it was found that its barrel was intact and the upper cover was damaged. The fracture surface is basically straight and perpendicular to the bolt axis. The fracture has no obvious plastic deformation. The two fractures of the broken bolt can be matched up and down, indicating that the bolt has high hardness.

(1)分析螺栓断口

(1) Analysis of bolt fracture

螺栓正确安装后，其螺纹连接处的1扣大约承受25%的总载荷，第2扣承受19%的总载荷，因此60%~65%螺栓断裂均位于螺纹连接处1扣的根部。该双变滤油器螺栓的断裂就是发生在1扣螺纹根部，由此可知螺栓1扣螺纹位置确实承受了较大的载荷，载荷过大是引起螺栓断裂的主要原因。小型装载机

After the bolt is correctly installed, one buckle at the threaded connection bears about 25% of the total load, and the second buckle bears 19% of the total load. Therefore, 60% ~ 65% of the bolt fractures are located at the root of one buckle at the threaded connection. The fracture of the bolt of the double transformer oil filter occurred at the root of one thread. Therefore, it can be seen that the position of one thread of the bolt does bear a large load, and excessive load is the main reason for the fracture of the bolt. Small loader

(2)分析螺栓断裂面

(2) Analysis of bolt fracture surface

我们从螺栓的断裂面发现，该断裂面形成的区域非常明显，可清楚看到疲劳裂纹源、疲劳扩展区和脆性断裂区。据此分析认为，螺栓长期承受预紧力和双变滤油器内油液脉动冲击的交变载荷，在疲劳裂纹源处产生裂纹，并向疲劳断裂区延伸。当剩余部分不足以承担预紧力及交变载荷时，终会导致螺栓发生断裂。小型装载机

The fatigue crack source and brittle fracture surface can be seen clearly. According to the analysis, the bolt bears the alternating load of preload and oil pulsation impact in the double variable oil filter for a long time, and the crack first occurs at the fatigue crack source and extends to the fatigue fracture zone. When the remaining part is insufficient to bear the preload and alternating load, the bolt will eventually break. Small loader

(3)确定断裂原因

(3) Determine the cause of fracture

以上分析，虽然可以确定螺栓是由于疲劳断裂引起，但是不能确切得出引起疲劳断裂的原因。我们检查了多个螺栓断裂的双变滤油器，对螺栓断裂面研究后发现，不论哪个位置的螺栓断裂，螺栓断裂的疲劳裂纹源总是位于筒体近心端，疲劳扩展区、脆性断裂区总是位于筒体远心端。

Through the above analysis, although it can be determined that the bolt is caused by fatigue fracture, the cause of fatigue fracture cannot be determined. We checked several double variable oil filters with broken bolts. After studying the bolt fracture surface, we found that no matter where the bolt is broken, the fatigue crack source of bolt fracture is always located at the proximal end of the cylinder, and the fatigue growth zone and brittle fracture zone are always located at the distal end of the cylinder.

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