Zhengxing Zuo

Effect of Fatigue Behavior on Microstructural Features in a Cast Al-12Si-CuNiMg Alloy Under High Cycle Fatigue Loading

High cycle fatigue tests of a cast Al-12Si-CuNiMg alloy are carried out under different stress amplitudes at room temperature. The scanning and transmission electron microscopy observations are used to examine the fracture surfaces and dislocation structures of the tested material, respectively. The results show that the fatigue damage originates from the microstructural defects, and the fracture surface morphology is typical quasi-cleavage fracture. With the increasing strain amplitude, the material fatigue life obviously decreases; however, the dislocation density increases significantly, which leads to the formation of the dislocation walls and cells. Under the cycle loading, the eutectic Si phase and the secondary particles undergo fracture. The pinning effect of the precipitates on the dislocations becomes obvious, indicating that the Al-12Si-CuNiMg alloy has the cyclic hardening characteristic.

Fretting fatigue mechanism of bearing cap bolted joints

Fretting fatigue is a common type of failure of the bearing cap bolted joints. This paper proposes a methodology to analyze the fretting fatigue mechanism of the bearing cap bolted joint. A biaxially loading system was designed to simulate fretting fatigue failure under typical engine working condition. Meanwhile, a submodel was developed in the finite element calculation to analyze the contact status and stress distribution of the structural models. The test result shows that long inclined cracks (about 650 μm long, orientation at 17°-34°) initiate at the middle region of the contact interface. As the increase of the bolt pretension load (from 6000 N to 10,000 N), the crack initial location is getting away from the bolt screw, and the fretting fatigue lives is increasing (from 7.8 × 10(5) to 6.0 × 10(6)). With the fatigue phenomenon and the stress field analysis result, it concludes that the crack initiation is governed by the maximum shear stress; the bolt pretension load and the additional rotate torque caused by the bearing load are the two main factors which affect the fretting fatigue mechanism of the bearing cap bolted joints. It is beneficial to fretting fatigue lives of the bearing cap joints by increasing the bolt pretension load and restraining the oscillation of the bearing cap.

Experimental and Numerical Study on the Fretting Fatigue Mechanism of the V Type Engine

Fretting fatigue is one of the typical failure forms of engine block. The aim of this study is to investigate the fretting fatigue mechanism of the V type engine and guide engine design. An experiential system was developed to simulate fretting fatigue failure under typical engine working condition. And a submodel was used in the finite element calculation to analyze contact status and stress distribution of the structural model. Through the fretting fatigue experimental observations and finite element analysis, it can be concluded that the additional rotate torque caused by bearing load and the bolt pretension load are the two main factors which affect the fretting fatigue mechanism of the V type engine. Appropriate increasing of the bolt pretension load and using extended skirt block with cross-bolted main bearings design will restrain the oscillation of the main bearing cap can be beneficial to fretting fatigue lives of the engine block.Copyright