Numerical and experimental investigation of mechanical strength of spot welded joints
In this work, an inverse FE modelling indentation method to predict the plastic ies of materials has been systematically studied and used to characterise detailed properties of spot welded joints in steel. An inverse program based on a dual indenter approach and continuous indentation curves has been established and validated, which provided the framework for an improved method based on static indentation. The method was successfully used to study two typical auto steels and simulate the tensile shear deformation of the spot welded joints and to investigate the effect of dimensional parameters on the strength of welded joints. Systematic studies of inverse FE modelling approaches with different indenter types showed that there are a variety of materials with different stress-strain relationships but identical indentation curves for Vickers, Knoop or spherical indenters and dual sharp indenters. This suggests that these methods can not be used to predict material plastic properties unless the range of material properties is pre-known. Dual spherical indenters showed significant improvement of the prediction accuracy, but showed strong sensitivity to experimental error. The combination of sharp (Vickers or Knoop) and spherical indenters is proven to be the best approach over a wide range of material properties and showed a clear improvement over other methods. Based on the framework established, a new method using static indentation data rather than continuous indentation data has been developed. Experimental work on two steels show the stress-strain curves inversely predicted are comparable to standard tensile tests and notched specimen. The method was applied to extract the detailed material properties in spot welded joints and the results were applied to extract the detailed material properties in spot welded joints and the results were applied to simulate the tensile shear deformation.
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