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Adaptive multiscale analyses on structural failure considering localized damage evolution on vulnerable joints

Zheng Z. Y., Li Z. X., Chen Z. W.

Archives of Civil and Mechanical Engineering

2014

Vol. 14, no. 2

304--316

Deterioration in structures starts from meso-scale defects on vulnerable joints where damage evolution becomes main reason of fatigue accumulation. Therefore analyses on structural failure induced by fatigue accumulation must be carried out in multi-scale. This paper is aimed to provide a multi-scale computational approach for structural failure analyses. Scale coupling method based on numerical integrated constraint equations is developed. This scale coupling method can guarantee sufficient computing precision when material at the trans-scale boundary keep elastic. However in structural deterioration process, material nonlinearities can evolve to the trans-scale boundary, thus make this scale coupling method invalid. A methodological strategy considering adaptive trans-scale boundary is proposed to deal with the extension of local nonlinear response during analyses. With application of the multi-scale modeling and computation strategy developed in this paper, failure processes of a beam component with defect and a longitudinal stiffening truss are analyzed. Results show that, damage evolution has acceleration effect on macroscopic deterioration of structure property, and localization phenomenon of damage evolution is obvious. Comparison of failure route of upper and bottom joints of the truss shows different deterioration process.

Friction Stir Lap Welding: material flow, joint structure and strength

Chen Z. W., Yazdanian S

Journal of Achievements in Materials and Manufacturing Engineering

2012

Vol. 55, nr 2

629--637

Friction stir welding has been studied intensively in recent years due to its importance in industrial applications. The majority of these studies have been based on butt joint configuration and friction stir lap welding (FSLW) has received considerably less attention. Joining with lap joint configuration is also widely used in automotive and aerospace industries and thus FSLW has increasingly been the focus of FS research effort recently. number of thermomechancal and metallurgical aspects of FSLW have been studied in our laboratory. In this paper, features of hooking formed during FSLW of Al-to-Al and Mg-to-Mg will first be quantified. Not only the size measured in the vertical direction but hook continuity and hooking direction have been found highly FS condition dependent. These features will be explained taking into account the effects of the two material flows which are speed dependent and alloy deformation behaviour dependent. Strength values of the welds will be presented and how strength is affected by hook features and by alloy dependent local deformation behaviours will be explained. In the last part of the paper, experimental results of FSLW of Al-to-steel will be presented to briefly explain how joint interface microstructures affect the fracturing process during mechanical testing and thus the strength. From the results, tool positioning as a mean for achieving maximum weld strength can be suggested.