Systematic investigation of the fatigue performance of a friction stir welded low alloy steel

Toumpis, Athanasios; Galloway, Alexander; Molter, Lars; Polezhayeva, Helena

doi:10.1016/j.matdes.2015.04.046

Cited by 27 publications

(25 citation statements)

References 15 publications

(54 reference statements)

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“…The formation of bainite raises the yield strength however, ductility is reduced. This type of microstructure lies in between the 'intermediate' and 'fast' welds documented in a previous publication [7]. However no martensite formation was reported as in prior research [8].…”

Section: Weld Microstructuresupporting

confidence: 52%

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Fatigue and bending behaviour of friction stir welded DH36 steel

Fowler

Toumpis

Galloway

2015

Int J Adv Manuf Technol

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Friction stir welding presents many advantages over conventional welding techniques; however, there is limited published data with regards to the fatigue and bending performance of friction stir welded steels. Hence, this investigation aims to evaluate friction stir welded DH36 steel subjected to these loading conditions. A comprehensive fatigue and bending programme has been implemented to assess the impact of process related features, such as weld root flaws, on the welds' performance. Strain gauges located on the top and bottom surfaces of fatigue samples allowed the secondary bending stresses to be quantified when clamped in the fatigue test machine. Bend test samples were completed to a 180° Ubend for as-welded and ground samples. The bend testing programme demonstrated satisfactory performance of friction stir welded DH36 steel. Despite the presence of surface flaws, cracks did not propagate in bending indicating adequate levels of toughness. Fatigue performance was poor in comparison with results from similar welds however, it was found to be acceptable in terms of class recommendations for fusion welding. This lower performance was predominantly attributed to a weld root flaw. Strain gauge measurements indicated that the local stress at the weld root was up to 25% lower than the nominal stress determined prior to testing, thus artificially improving fatigue performance. Welds of good quality and refined microstructure were found, however process related flaws on the top and bottom surface emphasise the need for optimisation of the tool material and welding parameters.

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Section: Weld Microstructuresupporting

confidence: 52%

“…A comprehensive study [7] was undertaken which investigated the effect of welding parameters on the fatigue performance of 6 mm thick FSW DH36 steel. This research determined that fatigue performance improved as the traverse speed decreased.…”

Section: Introductionmentioning

confidence: 99%

Fatigue and bending behaviour of friction stir welded DH36 steel

Fowler

Toumpis

Galloway

2015

Int J Adv Manuf Technol

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“…Defects are found in FSW of DH36 steel especially at high welding speeds [6]. They are also associated with fractures in both tensile [7] and fatigue tests performed on DH36 steel plates [7,8]. These defectrelated failures highlight the need for the ability to predict the formation of sound welds using numerical modelling.…”

Section: Introductionmentioning

confidence: 99%

Modelling of friction stir welding of DH36 steel

Al-moussawi

Smith

Young

et al. 2017

Int J Adv Manuf Technol

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A 3-D computational fluid dynamics (CFD) model was developed to simulate the friction stir welding of 6-mm plates of DH36 steel in an Eulerian steady-state framework. The viscosity of steel plate was represented as a nonNewtonian fluid using a flow stress function. The PCBN-WRe hybrid tool was modelled in a fully sticking condition with the cooling system effectively represented as a negative heat flux. The model predicted the temperature distribution in the stirred zone (SZ) for six welding speeds including low, intermediate and high welding speeds. The results showed higher asymmetry in temperature for high welding speeds. Thermocouple data for the high welding speed sample showed good agreement with the CFD model result. The CFD model results were also validated and compared against previous work carried out on the same steel grade. The CFD model also predicted defects such as wormholes and voids which occurred mainly on the advancing side and are originated due to the local pressure distribution between the advancing and retreating sides. These defects were found to be mainly coming from the lack in material flow which resulted from a stagnant zone formation especially at high traverse speeds. Shear stress on the tool surface was found to increase with increasing tool traverse speed. To produce a "sound" weld, the model showed that the welding speed should remain between 100 and 350 mm/min. Moreover, to prevent local melting, the maximum tool's rotational speed should not exceed 550 RPM.

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“…The FSW technique has many applications in the aeronautical, automotive and shipping industries [2,3] and is considered to be energy efficient and environmentally friendly [4]. In addition, joint strengths that can reach those of the base material can be achieved [5].…”

Section: Introductionmentioning

confidence: 99%

A numerical comparison of the flow behaviour in Friction Stir Welding (FSW) using unworn and worn tool geometries

2015

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The tool is a key component in the friction stir welding (FSW) process, but the tool degrades and changes shape during use, however, only a limited number of experimental studies have been undertaken in order to understand the effect that worn tool geometry has on the material flow and resultant weld quality. In this study, a validated model of the FSW process is generated using the CFD software FLUENT, with this model then being used to assess the detail of the differences in the flow behaviour, mechanically affected zone (MAZ) size and strain rate distribution around the tool for both unworn and worn tool geometries. Comparisons are made at two different tool rotational speeds using a single weld traverse speed. The study shows that there are significant differences in the flow behaviour around and under the tool when the tool is worn. This modelling approach can therefore be used to improve understanding of the effective limits of tool life for welding, with a specific outcome of being able to predict and interpret the behaviour when using specific weld parameters and component geometry without the need for experimental trials.

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Systematic investigation of the fatigue performance of a friction stir welded low alloy steel

Cited by 27 publications

References 15 publications

Fatigue and bending behaviour of friction stir welded DH36 steel

Fatigue and bending behaviour of friction stir welded DH36 steel

Modelling of friction stir welding of DH36 steel

A numerical comparison of the flow behaviour in Friction Stir Welding (FSW) using unworn and worn tool geometries

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