Multi-scale Simulation Study On Propagation Of Connecting Rod Crack By Wire Cut Electrical Discharge Machining

Connecting rod splitting technology has been researched later in the domestic, there are a lot of technical problems and breaking defects in the practical production. Although the influence mechanisms of various factors on breaking have been discussed, but the splitting parameters can not be determined accurately, especially the researches that have not been reported on microcosmic factors. This is because the connecting rod splitting process occurs in an flash, with a very short time, so there is a big technical obstacle for the analyses in the actual process, especially for the analyses of micro factors, experimental methods are unable to be achieve, unless use the simulation technology.In this paper, the simulation of the splitting process of the connecting rod is studied by using the multi-scale simulation method, including the macro scale finite element method and the micro scale molecular dynamics method.The main study of the Finite Element Analysis is the relationship between the crack groove depth and the splitting force. Firstly, it is the derivation of the expression that describes the relationship between the crack groove depth and the splitting force. Secondly, it is the numerical simulation analysis, the simulation results show that the relationship of different groove depths and splitting forces conforms to the theoretical analysis basically, and meets to the relationship expression. The third part is experimental verification, the small errors verify that the simulation results have a high credibility. Using this simulation method can provide a theoretical basis for the design of the hydraulic system that applies tensile force to the rod.In the molecular dynamics simulation, the atomic model of the crack is established by LAMMPS software, only two kinds of atoms, Fe and C, are included in the model because of the limit of the range of the potential functions. In the early stage of the material analysis experiment, the micro cracks and holes and other defects can be observed in the connecting rod material. Therefore, the molecular dynamics models were established, not only simulated the different crack lengths, different loading speeds and different model volumes, but also simulated the pore sizes and the pore different positions, to research their influences on the crack propagation behavior. In all models, the velocity loading mode are used in the research of crack propagation behavior, and the results are analyzed in detail based on the total energy evolution of the system. The analyses of the simulation results show that:(1) The initial crack length more conducive to the crack propagation, and the splitting time is shorter; (2) Within a certain range, the greater the loading speed, the speed of crack propagation is faster, but the surface after the split became more complex; (3) In the smaller model, crack propagation speed is faster, but it is easily to lost the details of the crack propagation, and can not show the complexity of the crack propagation, in the larger model, crack propagation is more complex, the more time consuming. (4) The size and position of the holes have influences on the crack propagation, when the hole is large, and in the direction of crack propagation, it plays a promoting role in crack propagation, the presence of holes can cause crack propagation direction changed obviously.In the molecular dynamics simulation analysis, it is possible to observe the significant plastic deformation in the crack propagation process of the Fe-C model.