Optimum seeking of spot weld model on numerical simulation of stress and modal analysis for corn combine harvester frame

Abstract: More and more spot weld have been used extensively to joint different components in industry, thus many finite element models of spot weld have been developed for various types of analysis, for example, static analysis, modal analysis, fatigue analysis and optimization analysis. Currently, there are already plenty spot weld models, but few comprehensive study and guidance are available for how to evaluate performance of different kinds of spot weld models, such as, which model with a proper mesh refinement can represent adequately behavior of spot weld joint and perform properly in the process of structural analysis. For frame structure of corn combine harvester, which can be considered as a typical thin-wall structure and its components are mainly connected by welding, spot weld model are always neglected and replaced by treating frame structure as a whole unit or considering the connection as contact relation. However, spot weld connection model will affect accuracy of finite element model and numerical simulation, especially when there are a lot of welding relationships in the frame structure of corn combine harvester machine. At present, finite element modeling and seeking optimization of different spot weld models are seldom considered and no guideline exists in static analysis and model analysis. The purpose of this paper is to seek optimal spot weld model on numerical simulation of static analysis and modal analysis for combine harvester frame. Influence of different welding spot models on the accuracy of the finite element calculation of the harvesting machine frame was investigated, and accuracy of finite element modeling and precision of numerical simulation was improved. Firstly, schematic mechanism and mathematical descriptions of four different kinds of spot weld models, including Rbe2 (rigid bar element 2), RBAR (rigid-bar), CWELD and ACM2 (area contact model 2) models were studied and corresponding finite element models were established to conduct two kinds of numerical simulation mode including static analysis and modal analysis. Then, strain test and signal collection system of the frame were designed. The distribution of strains at different measuring points were analyzed by comparing with results from numerical simulation by finite element method. It is shown that the RBAR spot weld model is more suitable for static analysis, because numerical results based on RBAR spot weld model is the closest to that from strain experiment，and its correlation coefficient is 0.993 2, but there are larger errors when other spot weld models are applied. In addition, Block Lanczos algorithm was used to calculate the modal vibration frequency and mode shape of the frame model when four kinds of different spot weld finite element models were considered respectively, and effects of spot weld model type on modal results are investigated. It is found that correlation coefficients of modal vibration frequencies with spot weld models of ACM2 and Rbe2 is better than that with spot weld models of RBAR and CWELD. Finally, it is concluded that RBAR is more suitable for the static analysis and ACM2 model is more suitable for the analysis of vibration mode and dynamic stiffness of the frame when both applicability of different spot weld model and modeling efficiency are considered. These conclusions are able to provide significant reference and useful guidelines for establishment of proper finite element model, selection of spot weld connection model and improvement of accuracy and efficiency of numerical simulation for welding structure of harvesting machinery.