Influence of pulsed current pattern on cross tension strength of spot welded joint with nugget diameter variation

Destructive tests are generally applied to evaluate the fixed strength of spot-welding nuggets of zinc-plated steel (which is a widely used primary structural material for automobiles). These destructive tests, however, are expensive and time-consuming. This paper proposes a nondestructive method for evaluating the fixed strength of the welded joints using surface electrical resistance. A direct current nugget-tester and probes have been developed by the authors for this purpose. The proposed nondestructive method uses the relative decrease in surface electrical resistance, α. The proposed method also considers the effect of the corona bond. The nugget diameter is estimated by two factors: RQuota, which is calculated from variation of resistance, and a constant that represents the area of the corona bond. Since the maximum tensile strength is correlated with the nugget diameter, it can be inferred from the estimated nugget diameter. When appropriate measuring conditions for the surface electrical resistance are chosen, the proposed method can effectively evaluate the fixed strength of the spot-welded joints even if the steel sheet is zinc-plated.

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Microstructure and Mechanical Performance of Resistance Spot Welded Martensitic Advanced High Strength Steel

Processes ◽

10.3390/pr9061021 ◽

2021 ◽

Vol 9 (6) ◽

pp. 1021

Author(s):

Yunzhao Li ◽

Huaping Tang ◽

Ruilin Lai

Keyword(s):

Mechanical Properties ◽

Failure Modes ◽

Mechanical Performance ◽

Strong Dependence ◽

High Strength ◽

Weld Nugget ◽

Resistance Spot ◽

Pull Out ◽

Cross Tension ◽

Spot Welded

Resistance spot welded 1.2 mm (t)-thick 1400 MPa martensitic steel (MS1400) samples are fabricated and their microstructure, mechanical properties are investigated thoroughly. The mechanical performance and failure modes exhibit a strong dependence on weld-nugget size. The pull-out failure mode for MS1400 steel resistance spot welds does not follow the conventional weld-nugget size recommendation criteria of 4t0.5. Significant softening was observed due to dual phase microstructure of ferrite and martensite in the inter-critical heat affected zone (HAZ) and tempered martensite (TM) structure in sub-critical HAZ. However, the upper-critical HAZ exhibits obvious higher hardness than the nugget zone (NZ). In addition, the mechanical properties show that the cross-tension strength (CTS) is about one quarter of the tension-shear strength (TSS) of MS1400 weld joints, whilst the absorbed energy of cross-tension and tension-shear are almost identical.

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Influence of electrode tip diameter on metallurgical and mechanical aspects of spot welded duplex stainless steel

High Temperature Materials and Processes ◽

10.1515/htmp-2020-0055 ◽

2020 ◽

Vol 39 (1) ◽

pp. 317-327

Author(s):

Vivek D. Kalyankar ◽

Gautam P. Chudasama

Keyword(s):

Stainless Steel ◽

Duplex Stainless Steel ◽

Mechanical Performance ◽

Welding Current ◽

Thick Sheet ◽

Automotive Body ◽

Nugget Diameter ◽

Feasible Range ◽

Research Outcome ◽

Spot Welded

AbstractIn this article, the influence of electrode tip diameter is investigated for spot welded duplex stainless steel (DSS). Electrode tip diameter and welding current are considered as the major influencing parameters and their values are varied within the feasible range, suitable for 0.8 mm thick sheet, whereas other important parameters such as welding time and electrode force are kept constant. DSS with the chosen thickness range is now becoming a useful material in automotive body-in-white applications and in future it will become one of the key materials replacing the existing materials and hence research outcome of the present work may be beneficial from application view point. In this work, the spot welding quality is inspected through metallurgical aspects (microstructure and microhardness), physical aspects (nugget diameter and electrode indentation), mechanical performance (tensile shear strength [TSS]) and failure mode. The obtained result shows that smaller electrode tip diameter limits nugget diameter due to expulsion phenomena and increases electrode indentation due to higher current intensity. TSS decreases with increase in electrode tip diameter for the same welding current but maximum TSS obtained for particular electrode tip diameter increases with increase in electrode tip diameter up to a specific limit and then it remains constant.

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Rapid fatigue life prediction for spot-welded joint of SUS301 L-DLT stainless steel and Q235B carbon steel based on energy dissipation

Advances in Mechanical Engineering ◽

10.1177/1687814018811013 ◽

2018 ◽

Vol 10 (11) ◽

pp. 168781401881101 ◽

Cited By ~ 1

Author(s):

Yaliang Liu ◽

Yibo Sun ◽

Yang Sun ◽

Hongji Xu ◽

Xinhua Yang

Keyword(s):

Stainless Steel ◽

Fatigue Life ◽

Carbon Steel ◽

Energy Dissipation ◽

Life Prediction ◽

Welded Joint ◽

Fatigue Behavior ◽

Dissimilar Materials ◽

Fatigue Life Prediction ◽

Spot Welded

Spot welding of dissimilar materials can utilize the respective advantage comprehensively, of which reliable prediction of fatigue life is the key issue in the structure design and service process. Taking into account almost all the complex factors that have effects on the fatigue behavior such as load level, thickness, welding nugget diameter, vibrational frequency, and material properties, this article proposed an energy dissipation-based method that is able to predict the fatigue life for spot-welded dissimilar materials rapidly. In order to obtain the temperature gradient, the temperature variations of four-group spot-welded joint of SUS301 L-DLT stainless steel and Q235 carbon steel during high-cycle fatigue tests were monitored by thermal infrared scanner. Specifically, temperature variation disciplines of specimen surface were divided into four stages: temperature increase, temperature decrease, continuous steady increase in temperature, and ultimate drop after the fracture. The material constant C that a spot-welded joint of dissimilar material needs to reach fracture is 0.05425°C·mm3. When the specimen was applied higher than the fatigue limit, the highest error between experimental values and predicted values is 18.90%, and others are lower than 10%. Therefore, a good agreement was achieved in fatigue life prediction between the new method and the validation test results.

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