Numerical study of strengths of spot-welded joints of steel

Kong, Xiangfei; Yang, Qilin; Li, B.; Rothwell, Glynn; English, Russell; Ren, Xuejun

doi:10.1016/j.matdes.2007.12.001

Cited by 56 publications

(22 citation statements)

References 17 publications

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“…In the absence of local heat affected zone (HAZ) constitutive behaviour, most authors would scale the base metal stressstrain curve according to the evolution of a hardness profile for example. [1][2][3][4] The approach developed in this study consists in an experimental-based characterization of the local microstructures and mechanical properties of spot welds. The constitutive behaviours obtained can then be used for an accurate modelling of the weld response under various loading modes.…”

Section: Introductionmentioning

confidence: 99%

HAZ Microstructures and Local Mechanical Properties of High Strength Steels Resistance Spot Welds

et al. 2011

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as in the case of DP450, a decrease of martensite hardness can be observed for 1.0 mm cycles as compared to water quenches. This may be due to an auto-tempering phenomenon, which can be activated by the decreasing cooling rates at the end of the cooling cycles (electrodes removal). Once again, the hardness levels are comparable with the ones obtained after welding, 1 mm He hardness being the closer to the value expected in the weld.As a conclusion for this section, subcritical and coarse grained HAZ weld microstructures could be successfully reproduced experimentally. These simulated specimens are used in the following in order to study their detailed mechanical properties. Local Constitutive BehaviourThe constitutive behaviour in tension of the different SCHAZ and CGHAZ is illustrated in Fig. 14. The true stress vs. true plastic strain is plotted until the onset of plastic localization. As expected from the microstructural observations and micro hardness of DP450, the different subcritical thermal cycles do not alter the base metal constitutive behaviour significantly. Both ultimate tensile strengths and uniform elongations remain in the same order of magnitude ( Fig. 14(a)). On the contrary, the different cooling cycles from 1 200°C result in a strong evolution of strain hardening and ultimate tensile strength. Martensitic microstructures (water quench and 1.0 mm cycle) are characterised by a high strength and low ductility, while the bainitic 3.0 mm microstructure exhibits a lower strength and increased ductility.In the case of DP980, martensite tempering in the SCHAZ highlighted previously allows an increase in ductility and a loss of yield and ultimate tensile strengths ( Fig. 14(b)). This softening is more pronounced for the 3.0 mm thermal cycle than for the 1.0 mm one, in accordance with a longer time in the subcritical temperature range. CGHAZ microstructures present high strengths and low ductilities. However, it can be noticed that the 1.0 mm and 3.0 mm microstructures exhibit lower strength in comparison with the water quench. This may be attributed to the auto-tempering of the martensite in formation at the end of the CGHAZ thermal cycles, where the cooling rates are reduced.Moreover, it is worth to mention that martensitic microstructures present low ductility, but not zero. A few percents uniform elongation can be obtained even with water quenched DP980. This can be related to the relatively low level of carbon content for such automotive steels. ConclusionA Finite element analysis of the resistance spot welding process was conducted in this paper in order to assess the order of magnitude of heating and cooling rates experienced in dual phase steel spot welds. The evolution of thermal cycles when welding sheets with thicknesses in the range [1.0-3.0] mm was highlighted. Spot welding thermal cycles could then be simulated experimentally with a Gleeble and their influences on microstructure and mechanical properties investigated. Gleeble simulations were targeted for the reproduction of the thermal ...

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Section: Introductionmentioning

confidence: 99%

HAZ Microstructures and Local Mechanical Properties of High Strength Steels Resistance Spot Welds

et al. 2011

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“…Penelitian menggunakan software juga pernah dilakukan oleh Kong dkk [3] yang melakukan penelitian tentang numerical untuk kekuatan hasil las titik pada baja karbon rendah. Hasil penelitian menunjukkan bahwa meningkatnya diameter nugget untuk dua plat sejenis berdampak terhadap meningkatnya kekuatan geser sambungan las titik.…”

Section: Gambar 1 Ketidaksimetrisan Nugget Hasil Las [1]unclassified

“…Logam mengalami perubahan struktur mikro untuk daerah FZ (Fusion Zone) dan HAZ (Heat Affected Zone) akibat panas yang ditimbulkan oleh aliran listrik. Penelitian pengaruh las titik terhadap kekuatan tekan telah dilakukan oleh Kong dkk [3] yang melakukan penelitian tentang kekuatan las spot welding pada baja karbon rendah secara numerical. Hasil penelitian menunjukkan kekerasan logam antara daerah FZ (Fusion Zone), HAZ (Heat Affected Zone) dan BM (BaseMetal) berbeda seperti terlihat pada gambar 9.…”

Section: Gambarunclassified

Studi Literatur Pengaruh Parameter Pengelasan Terhadap Sifat Fisik Dan Mekanik Pada Las Titik (Resistance Spot Welding)

Haikal

Triyono

2013

Rot.

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Resistance spot welding (RSW) is the most widely used for joining thin sheet metals in automotive industry. Various applications of dissimilar materials and thicknesses were commonly found in many spot welding processes especially in the manufacture of car body. The resistance spot welding of dissimilar materials are generally more challenge than similar materials due to differences in the physical, chemical, and mechanical properties of the base metals. Differences of materials have an impact on heat input generated at the spot welding. Diameter of the weld nugget size is influenced by several parameters such as electric current, welding time, different types of material, and the thickness of the plate. Nugget diameter will influence on physical and mechanical properties weld such as microstructure, shear strength and hardness. For practical use, various industrial standards have recommended a minimum weld size for a given sheet thickness, mostly in the form of tables. For example the American Welding Society (AWS), Society of Automotive Engineering (SAE) and the American National Standards Institute (ANSI). They were only suitable to be apllied on the similar metal and thickness joint because in this joint, symetrical nugget will be formed. Meanwhile a type of dissimilar metal that joined by spot welding method will result in the asymetrical nugget. This paper aims to review the results of researchs on the similar and dissimilar resistance spot welded joint to evaluate the use of similar metals weld parameters and standards on the dissimilar metals weld. It was determined that parameters welding such as electric current, welding time, and the standard for similar metals weld can not be applied on the dissimilar metals weld. The asymetrical nugget shape decreased shear strength on the weld nugget. The most important factor that was considered on the dissimilar metals weld to make high quality weld joint was nugget diameter. If the nugget diameter weld increased the strength of welding will increase.

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“…Kong et al [34] defined a detailed FE model where the spot weld was divided into sub-zones with different material properties (particularly yield and strain hardening) due to the thermal, metallurgical and mechanical deformation process. A fracture model predicted the deformation of spot-welded slip joints well beyond initial yield under tensile-shear loading and the calculated deformations.…”

Section: Spot Welding Modelizationmentioning

confidence: 99%

Compliant assembly tolerance analysis: guidelines to formalize the resistance spot welding plasticity effects

Moos

Vezzetti

2011

Int J Adv Manuf Technol

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The variational analysis of compliant assemblies is mainly based on linear elastic models. Some guidelines have been defined to integrate material plasticity into a tolerance analysis model in order to improve its results when considering the resistance spot welding (RSW) process. A finite element model that simulates the body-in-white and RSW processes has been applied to butt and slip joints, with parts subjected to dimensional and geometrical tolerances that cause gap mismatching condition and loading interference on fixtures. The dimensional quality of assemblies is affected by plasticization near the welding spot, at the base of welded flanges and near the locators. The springback evidenced relative rotation of parts.

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Numerical study of strengths of spot-welded joints of steel

Cited by 56 publications

References 17 publications

HAZ Microstructures and Local Mechanical Properties of High Strength Steels Resistance Spot Welds

HAZ Microstructures and Local Mechanical Properties of High Strength Steels Resistance Spot Welds

Studi Literatur Pengaruh Parameter Pengelasan Terhadap Sifat Fisik Dan Mekanik Pada Las Titik (Resistance Spot Welding)

Compliant assembly tolerance analysis: guidelines to formalize the resistance spot welding plasticity effects

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