How to analyze the crankshaft fracture and the cause of the crankshaft fracture?

The question is too general. If I want to complete your question, I'll have to write a book.

Crankshafts are generally designed with a high safety factor and do not break under normal circumstances. However, the crankshaft is one of the parts with the most complex shape, the most complex processing technology and the most complex force in the engine.

A common fracture of a crankshaft is a combined fatigue fracture of bending-torsion that occurs at the fillet. The reason is that this is where the crankshaft is most stressed, and at the same time, it is also the most difficult to work hot and cold, so any defect in the fillet can lead to fatigue fracture of the crankshaft. Secondly, since the crankshaft is a typical part subject to bending and torsional compound fatigue stress, the stress concentration factors in any part of the crankshaft (machining knife marks, microcracks, etc.) will cause fatigue cracking of the crankshaft.

To analyze the fracture of the crankshaft, in addition to the manufacturing and service of the crankshaft, it is necessary to have the corresponding fracture analysis knowledge. First of all, it is necessary to find the crack source area of the fracture, and judge the force of the source area, the surface (side of the fracture) of the source area, whether it is a point source or a line source, and so on. Secondly, the fatigue propagation of cracks (mostly fatigue in general), the distribution, shape and size of the fatigue arc are observed.

Thirdly, observe the crack propagation path to determine whether it conforms to the force judgment, and thirdly, observe the area of the static fault zone to judge the force at the moment of crankshaft fracture.

In this way, combined with the analysis of the crankshaft material, the state of related parts, etc., the failure analysis of the crankshaft should be completed.

First of all, the macroscopic fracture observation is carried out, the fracture nature is preliminarily judged, and then the sampling location and testing items are determined, and the material problem, processing technology problem, or use problem is analyzed according to the inspection data. The analysis of macro fractures must be careful, the analysis of macro fractures is very important, if the macro is not clear, it is of no practical significance to do micro fractures.

1) The size of the crankshaft journal exceeds the repair size limit.

2) There are annular cracks at the crankshaft crank and oil holes.

3) After the crankshaft is polished, the transition fillet at the crank turn is too small, resulting in excessive stress concentration.

4) The gap between the journal and the bearing is too large, resulting in additional dynamic load.

5) The dynamic imbalance of the crank connecting rod mechanism makes the stress of each journal uneven.

6) The deformation of the cylinder block leads to the coaxiality of the main bearing bore exceeding the standard, and the bending and torsional deformation of the crankshaft exceeding the standard.

7) The piston jams the cylinder, causing the crankshaft to be seriously bent and torsionally deformed.

8) Improper operation of the driver, such as using the inertia of the bend to start, lifting the clutch pedal with a large throttle of a heavy vehicle, and sudden explosion of large load.

It is necessary to open the engine disassembly analysis, it is possible to judge or approximate the cause;

If there is no biting phenomenon of crankshaft bearing and connecting rod bearing, it is mainly the quality of the crankshaft itself, you can check whether the crystal particles of the crankshaft section are delicate and uniform, whether the fracture has penetrating wounds, etc., and analyze whether it is the cause of material, processing, heat treatment, etc. (you can even do metallographic analysis);

If the size tile has bite, combined with the cross-sectional situation, is it because of the oil quality, water ingress, foreign matter, oil channel blockage, and the spalling of the tile surface caused by biting and crankshaft;

In addition, it is necessary to check whether the gap between the crankshaft and the large tile is too large or the tile is cut off and the tile is loose, resulting in the crankshaft shaking and force impact breakage;

However, under normal circumstances, the crankshaft of a small gasoline engine of a small car is rarely broken, while the large engine of diesel engine and truck, especially the large engine with large bearings or crankshaft due to bite and wear, will have a certain proportion of broken shafts.

1. It is generally caused by the ablation of the bearing.

2. The working conditions are not good for a long time, and the crankshaft fatigue causes cracks to break after extension.

3. Accessories quality problems. The main reason is that the R angle at the root of the journal is too small, the stress is concentrated, and the material is not good.

4. The assembly quality is not good. The main thing is that the dynamic balance exceeds the standard.

The crankshaft is also divided into left-handed crankshaft and right-handed crankshaft, and if you make a mistake, it will also be a section, and there is a crankshaft quality problem.

What kind of car will the crankshaft break, the truck is that you are overweight, and the car is a quality problem.