Fatigue Performance Analysis of Automobile Engine Crankshaft

Crankshaft is an important part of the car engine, both in the car crankshaft R & D or actual production stage, need to test the fatigue performance of the car crankshaft. In the actual operation of the car engine, the crankshaft to bear the form of the load for the bending and torsional load, so the actual case shows that the main form of failure of the car crankshaft fatigue damage. In addition, if the engine crankshaft output power is large, the greater the torque generated, will produce a certain degree of torsional fatigue damage. Early automotive engine crankshaft used by the material for the 40Cr and 42CrMo and other carbon quenched and tempered steel. However, since the late 1990s, a large number of automotive crankshaft began to widely use non-quenched and tempered steel, especially for heavy-duty engine crankshaft production, the materials used mainly include 48MnV and C38N2, these two materials and medium carbon Compared with the quenched and tempered steel, in the case of ensuring the same strength, a lot of conditioning process is omitted. In recent years, the use of ductile iron production of china crankshaft has better mechanical processing performance and bending fatigue strength, especially in the use of heavy-duty engine to show a good application prospects.

Automotive crankshaft in the design, the choice of raw materials, forging, machining and heat treatment and surface strengthening of all aspects, if any one part of the mistakes will cause the china crankshaft failure. A company combined with the actual bearing production case, introduced and analyzed the car engine crankshaft common failure form and internal reasons.

The factors that affect the fatigue strength of the crankshaft of the vehicle mainly include the stress concentration, the size, the surface condition and the environment medium at the journal. In these factors, stress concentration and size and surface state are most important. The factors that affect the stress distribution of the crankshaft mainly include the design shape of the crankshaft and the basic properties of the material. The bending fatigue strength of the crankshaft can be improved by changing the kind and size of the material, but this will greatly increase the manufacturing cost of the material. In the actual application process, the surface strengthening process is usually used to improve the fatigue strength of china crankshaft. Under the effect of variable load, the maximum stress should appear in a range near the rounded corners of the crankshaft due to the abrupt change in the shape of the crankshaft journal Inside. Research indicates:

(1) Fatigue test of automobile crankshaft The fatigue limit of crank moment is 96.7MPa, the crankshaft stress concentration coefficient is 6.72, and the fatigue test process is in the middle of crankshaft journal. The safety factor at 99% was 1.31.

(2) SEM microstructure analysis of the microstructure and crack fracture of the 40Cr crankshaft journal shows that the microstructure after 40Cr quenching and tempering is tempered sorbite + ferrite + few bainite, conforms to the relevant standard The Fracture analysis shows that the 40Cr crankshaft fracture is a typical dimple and step mixed fracture, and no obvious inclusions.

(3) From the chemical composition and tensile properties of the material and the hardened layer of the journal surface, it can be seen that the reason of the fatigue failure of the crankshaft can exclude the influence of the above factors.

(4) crankshaft drilling hole in the journal internal wall caused by stress concentration, more prone to defects; crankshaft journal under the action of alternating stress is prone to fatigue cracks and expansion, resulting in early fracture of the crankshaft.

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