Fracture analysis of valve spring of automobile engine

Failure analysis of automobile engine valve spring fracture analysis Han Yajing. Wang Zheren Wang Huitianyan University 4 Xuegeng Jinyu Village Materials Department, Tianjin Chengbo, to; 1; regional fatigue cracks. In the end, the government led the government;

The valve spring of the automobile engine produced by a spring manufacturing company is made of Dingren 70 steel wire, which is equivalent to domestic 553 steel. Wire diameter, 4 claws. After the steel wire is quenched and tempered at medium temperature, the coil spring peening is subjected to stress tempering and grinding equal process. After the spring was loaded, the car traveled for 200km, and one of the springs broke at the 12th, and the physical photo was 1.

Fracture scanning analysis of the hardness test metallographic observation.

1 Force analysis The automobile valve spring is a cylindrical compression coil spring. Under the action of the axial force, the shear stress of any cross section of the spring is subjected to the maximum force of the inner diameter of the spring. The outer diameter is the least affected. Therefore, the strength of the design material is flat. The valve spring of this structure receives the most torsional and bending stresses at the 13th turn. The k compression spring tends to fail at the 23rd effective circle.

2. This is because the 13th spring coil is first subjected to the impact load, but the load cannot be quickly and efficiently transmitted to the other coil springs. The shock energy absorbed is the most, and these rings are larger than the other rings. In addition, the shape of the end of the bullet is different. The torsional and bending stresses experienced at the 13th lap are also different. The end structure has two ends and is flattened and the end of the spiral type structure, the former is the most stressed, 2 test content and the result of the material chemical composition such as 1. The composition of the measured material is within the scope of the standard requirements.

The metallographic structure intercepts the section near the fracture to prepare a metallographic sample. Observe the inclusions without erosion. According to the 1056989 standard, the inclusion level is 1805, and the inclusion content is within the normal range.

The standard sample to be tested is eroded. The microstructure is a small back-to-three hardness test that maintains the martensitic orientation. The intercepted metallographic specimen is subjected to a Vickers hardness test.

Fire trochanter, 3. Fully tempered. No quenching cracks. No decarburization. No graphitization. However, the tissue is distributed in a strip shape along the direction in which the spring wire is drawn. The analysis of the Aussie 4 fracture is seen from a macro perspective. The surface around the fracture is free of wear. The grain size of the laminated body is rated as 8th grade female according to 563941986, and is from Shandong Dezhou. engineer. Engaged in the teaching of metal materials and heat treatment experiments and the failure analysis of mechanical parts, and the phenomenon of electric layer spot cracks. See clearly from the broken spring. The spring breaks at 12 turns from the end face, and the fracture face intersects the wire axis about 45. The entire fracture consists of three parts of the crack source zone, the crack extension zone and the last instantaneous fracture zone. Its fracture morphology 4. The crack source is on the outer side of the spring, showing a white protruding point. The crack extension area is small. The radiation pattern is presented, and the crack propagation speed is faster. The instantaneous fracture area has rough and uneven surface with obvious tearing edges. The instantaneous break zone has a large surface area. The expansion zone is more brittle than the squeaking material. The break of the 5 spring is a torsional fatigue fracture.

After being cleaned by ultrasonic waves or the like from the micro-view spring fracture, scanning was performed on a 650 electron microscope. It is found that the cracking point of the source area has a distinct protrusion, and the fracture morphology is completely different from the surrounding shape. Similar to the accumulation of rock candy, it can clearly see the polyhedral morphology of each grain, which is a typical intergranular fracture pattern. 5. There are sub-cracks at the junction of the protrusion and the matrix. These strips extend only at high magnification. It is observed that the pattern is the pattern of the fatigue fracture extension zone. The final instantaneous fracture zone of the fracture is rough and has obvious tearing edges, showing a quasi-cleavage fracture pattern. From the pattern of the fracture expansion zone and the final fracture zone, the material is more brittle. After the above-mentioned various tests and the macroscopic microscopic analysis of the fracture, it is found that the 0 spring fracture shows a typical torsional fatigue fracture morphology 2 from the fracture. According to the metallographic structure and hardness test, the metallographic structure and hardness of the inclusions in the spring material are still positive; the fracture is independent of the elasticity of the design material. Under normal stress conditions, the inner side of the spring generates the most stress, and the improper design is broken. The source of the fault is located inside the spring; it can be judged from the location of the crack source, and the source of the crack is in the yellow. 1 storage tube and;! Take the shape and appearance of the crystal break pattern 1 base different. The presence of protrusions in the material. The local fatigue strength is greatly reduced.

This is the source of early fatigue. The protrusions may be surface defects such as dissimilar metal inclusions or slag inclusions in the material. It is stated that the fracture of the spring is a typical torsional fatigue fracture. The cause of the early fatigue fracture is caused by the secondary metallurgical defect of the raw material. Because it is in the second ring of the spring, the end structure is flattened at both ends, which is the maximum force of the spring. The hardness of the material is higher 515210, so the fatigue crack Once formed, the crack growth rate is larger, the fatigue life is shorter, and the 1 medium machine and the 7 materials are divided. Jianxian's 441 juice 1. Beijing Machinery and Metallurgical Industry Ministry of Steel Research Institute. Alloy steel fracture analysis metallographic spectrum Beijing Science Press. 1979, 42.

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