جستجوی مقالات مرتبط با کلیدواژه « مود شکست » در نشریات گروه « مواد و متالورژی »

In this paper, resistance spot welding process of AISI 201 stainless steel is studied experimentally. For this purpose, effect of welding current on quality of weld is investigated and relationships between welding current and fusion zone characteristics are examined. For determining mechanical properties such as maximum load and fracture mode, tensile - shear test of spot welds is performed. Hardness and microstructural examinations are performed for study the influence of welding current on characteristics of welded joints. The results show that strength of resistance spot welds of AISI 201 stainless steel is increased with increase in welding current. Transition of fracture mode from interfacial to pullout and then pullout with tearing of sheet mode during tensile-shear tests of AISI 201 spot welds is investigated through experimental and theoretical approaches. It is concluded from results that increasing in welding current leads to change in fracture mode from interfacial to pullout mode due to increase in fusion zone size (weld nugget size). Also, it is observed that increasing in fusion zone size is accompanied by an increase in load carrying capacity of resistance spot welds. The minimum required fusion zone size to ensure pullout fracture mode is estimated using an analytical model.

Weldability of high carbon steels due to the high percentage of carbon and consequently formation of martensitic structure is very poor. In this research, resistance spot welding of eutectoid high carbon steel 1075 is experimentally and numerically investigated from various points of view. The effect of welding current as one of the most effective parameters on failure mode, mechanical properties and nugget size diameter in resistance spot welding is analyzed with experimental tests and numerical simulations. The results show that with increase of welding current, the diameter of nugget size is increased and consequently the failure mode changes from interfacial mode to pull out mode.

This paper aims at investigating the microstructure and failure mode of DP780 ferrite-martensite dual phase steel resistance spot welds between. Microstructural characterization, microhardness tests and the cross-tension shear tests were conducted. Results showed that the fusion zone microstructure exhibited mainly martensite with some Widmanstätten ferrite and bainite. A hardness reduction was observed in heat affected zone in respect to the base metal. Results showed that the mode of failure changed from interfacial fracture to pullout as the welding current was increased. Results indicate that there is a critical weld nugget size to ensure the pullout failure mode. Based on the failure mechanism of the spot welds in the cross-tension test, a simple analytical model is proposed to predict the minimum FZ size (DC) to ensure the pull-out failure mode. According to this mode, the sheet thickness, the hardness ratio of fusion zone to pull-out failure location (i.e. HAZ), the amount of shrinkage voids and porosity in fusion zone and the width of the HAZ are the main controlling factors for interfacial to pullout failure mode transition in cross-tension loading.

In this paper, failure behavior of similar and dissimilar resistance spot welded joints of low carbon steel (CS) and austenitic stainless steel (SS) sheets was studied under tensile-shear test with attention focused on the failure mode transition form interfacial to pullout. Results showed that the microstructure of the fusion zone and the hardness distribution across the weld have a profound effect on the failure behavior. Similar SS/SS resistance spot welds exhibit the highest tendency to fail in interfacial failure mode, compared to CS/ CS similar and dissimilar SS/CS spot welds. This behavior is explained by the consideration of pullout failure location and hardness profile characteristics of each joint. It was shown that the failure mode transition is controlled by the hardness ratio of the fusion zone and the pullout failure location.