Finite Element Analysis On Dynamic Fracture Of Connecting Rod Fracture Splitting

Compared with the traditional processing method, connecting rod fracture splitting technology has many advantages such as fewer procedures, inexpensive equipment investment, saving machining time, save processing equipment, material and energy, processing quality, the assembly of high precision, high efficiency, low production cost, easy-entry, etc. In a sense, connecting rod fracture splitting technology has become an important indicator for a countries' new engine connecting rod manufacturing level. The research and development of con/rod processing technology and equipment, is of great significance to raise product quality and production efficiency, reduce costs, enhance economic efficiency for China's automobile industry and engine industry.However, there are some problems needed in-depth study and technical difficulties existing in the current con/rod splitting processing. The geometry parameter of cracking groove, reasonable backpressure, loading speed on the quality of cracking, as well as the parameters on the quality and profile accuracy of assembly and so on, and these issues constrained the further development of con/rod splitting technology. It is very urgent to resolve the difficulties. The settlement of these issues will link research and development of materials, con/rod equipment designing, process designing and provide a reliable basis for improving the quality of cracking, which will have a far-reaching impact. In response, this paper makes research from the following aspects.1. Starting notch of connecting rod is processed by broaching, laser and wire cutting. Results show that the fracture surface of laser processing is brittle, almost no plastic deformation. But broaching processing has local plastic deformation. Wire processing is in the middle. So laser processing has unique advantage in notch processing. 2. Software ANSYS is employed to establish finite element model of BYD car connecting rod, to analyze the factors that influent crack tip plastic zone, as well as the stress and strain state of crack tip. And through a large amount of computation and data fitting that cracking groove geometry parameters on the effects of plastic zone. The results show that notch depth is the largest factor of plastic zone, following by the crack tip curvature radius. To car connecting rods, curvature radius r is suitable for 0.1 mm, and notch depth h is suitable for 0.6mm.3. In order to determine the appropriate backpressure and guarantee the cracking quality, ANSYS is employed to establish finite element model of connecting rod. Study the relationship between the load and backpressure and the influence on plastic zone and deformation. The results show that with the increase in back pressure, cracking load decreased, appropriately with linear relationship. Fracture deformation decrease as the back pressure increasing. When back pressure is less than 10 MPa, the value of the equivalent plastic strain decreased rapidly. When the back pressure of greater than 10 MPa,the largest equivalent plastic strain tends to linear. At this time, back pressure hardly influents the plastic strain. Considering the plastic zone and cracking load, the back pressure is from 10 to 15 MPa, which could meet quality requirements.4. The finite element software LS-DYNA is employed to analyze the initial cracking point and crack growth path, comparing different splitting speed on the impact of crack. The results show that the first failed node is not appeared on the free surface, but in the vicinity of the free surface. And the crack propagation in the thickness direction is not at the same time, upward from the surface of the surface layer expansion. With the increasing of load displacement, the unit in the crack tip failed one by one, until the fracture completed. In addition, the greater the speed of loading, the easier of crack expanding, but do not have much impact on the initiation. With the increase in loading rate, plastic zone width decreased. When the loading rate is greater than 100 mm / s, plastic zone width of the area tends to slow decline. In order to reduce the plastic zone width of the area and enhance the quality of cracking process, the proposed loading rate is greater than 100 mm/s.