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Artificial-neural-network-based storage method for three-dimensional temperature field data during friction stir welding
Ce Han, , Qingyu Shi, Tianxiang Tang, Xin Liu, Gong Zhang, Gaoqiang Chen
, Available online  
[Abstract](3) [FullText HTML] (1) [PDF 2252KB](0)
In this paper, a new storage method for the three-dimensional temperature field data based on artificial neural network (ANN)was proposed. A multilayer perceptron that takes the coordinate \begin{document}$ (x,y,z) $\end{document} as inputs and temperature \begin{document}$ T $\end{document} as output, is used to fit the three-dimensional welding temperature field. Effect of number of ANN layers and number of neurons on the fitting errors is investigated. It is found that the errors decrease with the number of hidden layers and neural numbers per layers generally. When the number of hidden layers increases from 1 to 6, the maximum temperature error decreases from 74.74℃ to less than 2℃. The three-dimensional temperature field data is obtained by finite element simulation, and the experimental verification is completed by comparing the simulation peak temperatures with the measured results. As an example, an ANN with 4 hidden layers and 12 neurons in each layer were applied to test the performance of the proposed method in storage of the three-dimensional temperature field data during friction stir welding. It is found that the average error between the temperature data stored in ANN and the original simulation data that stored point-by-point is 0.517 ℃, and the error on the maximum temperature is 0.193℃, while the occupied disk space is only 0.27% of that is required in the conventional point-by-point storage.
Geometric effects on competing failure modes in lap shear testing of spot joints
Telmasre Tushar, Abdelmotagaly Abdelrahman, Gao Yanfei, Yu Zhenzhen
, Available online  
[Abstract](10) [FullText HTML] (4) [PDF 2366KB](0)
When subjected to the lap shear testing, spot welds created by brazing, resistance welding, or other techniques may fail either by a plug failure mode (also called pull-out mode) or an interfacial shear failure mode. In the past, plug failure mode was thought to be dependent on base metal ultimate tensile strength, spot diameter and plate thickness, while interfacial failure be determined by interface shear strength and spot area. No fracture mechanics model or failure process is invoked in such an approach, and its predictive capability is often doubted compared to realistic experiments. This work conducts a parametric study to assess the failure behavior as a function of dominant three-dimensional geometric parameters based on the Gurson-Tvergaard-Needleman (GTN) damage mechanics model and no-damage model respectively. Different necking conditions are considered as precursors to the two failure modes in the no-damage model. It is found out that a small ratio of spot diameter to plate thickness promotes interfacial shear failure while a large ratio favors plug failure. Other geometric parameters such as the filler interlayer thickness, if used, play a secondary role. The calculated peak force \begin{document}$ {F_{wt}} $\end{document} is not much different between the GTN and no-damage analyses, and better agreement is shown in the small nugget region. Normalized peak force calculated from the GTN model with the porosity \begin{document}$ {f_0} $\end{document} set to 0.01 showed the best agreement with pervious tensile shear tests on spot-welded DP980 lap joints in comparison to that calculated from the GTN model with \begin{document}$ {f_0} $\end{document} at 0.02 and the no-damage model. Note that heterogeneous distribution of material strength across the joint region was considered in the GTN model, which was estimated based on the hardness map measured across the joint cross section.
Approximate entropy analysis of arc stability in VPPA-GMAW hybrid welding
Haitao Hong, Yongquan Han, Yin Lu, Lu Wang, Yifan Wang
, Available online  
[Abstract](6) [FullText HTML] (2) [PDF 807KB](0)
Variable polarity plasma arc-gas metal arc welding (VPPA-GMAW) integrates the advantages of VPPA and GMAW, and it is particularly applied to weld thick-plates aluminum alloys. High-speed camera and data acquisition system were used to analyze the arc shape and the welding process electrical signal. According to the analysis of arc swing amplitude and the approximate entropy of arc voltage signal denoised by wavelet threshold method, the influence of VPPA frequency on the arc stability was studied. The results show that the approximate entropy of GMAW arc voltage decreases with the increase of VPPA frequency in a certain range, and the stability of the hybrid arc is significantly improved. The spectral analysis shows that the arc stability is reduced due to the resonance effect between the VPPA and the GMAW arc when the VPPA frequency closes to the GMAW arc pulse frequency. The results are helpful to understand hybrid welding mechanism and the selection of welding process parameters.
Investigation on automated loading of dynamic 3D heat source model for welding simulation
Guangxu Hu, xingya Yang, Xingbin Yu, Yanhong Wei
, Available online  , doi: 10.12073/ doi: 10.12073/
[Abstract](186) [FullText HTML] (63) [PDF 1700KB](11)
Since programing complex and dynamic heat source model for welding simulation is a complex job, the parametric methods are studied in this paper. Firstly, an overall flow to achieve automatically modeling welding was introduced. Secondly, an expert module rules for selecting welding heat source model was founded, which is based on simulation knowledge and experiences. Thirdly, a modularity routine method was investigated using writing with C++ programing, which automatically creates subroutines of 3D dynamic heat source model for user. To realize the dynamic weld path, the local weld path coordinate system was moved in the global coordinate system and it is used to model direction of weld gun, welding path and welding pose. The weld path data file was prepared by the automatic tool for the welding heat source subroutines. All above functions were integrated in the user interface and the connection with architecture was introduced. At last, a laser beam welding heat source modeling was automatically modeled and the weld pool geometry was compared with the reported literature. It demonstrated that the automated tool is valid for welding simulation. Since modeling became convenient for welding simulation using the tool proposed, it could be easily and useful for welding engineers to acquire the needed information.