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The present work addresses the microstructure and mechanical properties of similar and dissimilar resistance spot welds of low carbon steel (LCS) and dual phase steel (DP600). Correlations between the critical fusion zone size required to ensure pullout failure mode, the weld microstructure and the weld hardness characteristics were developed. Dissimilar DP600/LCS spot welds exhibit the lowest tendency to fail in interfacial failure mode. Effects of weld physical attributes and weld microstructure on the peak load and energy absorption of similar and dissimilar DP600/LCS resistance spot welds are analysed.

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The aim of this work is to investigate and analyse the microstructure and mechanical properties of dissimilar low carbon steel/dual phase steel (DP600) resistance spot welds. The failure modes of spot welds during the tensile-shear test were detailed by examination of the weld fracture surfaces. Relationships between the fracture path and the mechanical properties (peak load and energy absorption) were developed using the observed microstructures in the fusion and heat affected zones. It was found that the failure of DP600/low carbon steel is initiated from the stronger side (i.e. DP600 side). This was explained in terms of hardness profile, difference in tensile strength and workhardening behaviour of the base metals. A transition in the failure mode from interfacial failure mode to pullout failure mode was observed with increasing the fusion zone size caused by increasing the welding current. However, when expulsion occurred, the spot welds failed in the partial thickness-partial pullout mode, with reduced energy absorption and peak load, compared to those spot welds with the same or smaller nugget size, which failed in the pullout mode. This can be related to the low ductility of the location of the failure initiation (i.e. heat affected zone of DP600 side) in this mode.

Summary Utilization of AC/DC distribution networks has become more reasonable because of the recent developments in power electronic devices and increasing employment of DC electronic loads. In this paper, load flow calculation problem in AC/DC distribution networks is addressed. Because a large number of load buses in both AC and DC parts and high R/X ratios in the AC part of these networks can lead to the divergence of recent Jacobian matrix based methods, in this paper, a new direct approach based on backward forward sweep algorithm is presented. Comprehensive investigation considering weakly meshed and different types of converters and their control strategies is also carried out. The presented algorithm is applied to the test systems equipped with different types of converters. The results demonstrate the validity and capability of the proposed method. Copyright © 2016 John Wiley & Sons, Ltd.