Constitutive equations for use in prediction of flow stress during extrusion of aluminium alloys

Sheppard, T.; Jackson, A. G.

doi:10.1179/026708397790302476

Cited by 45 publications

(48 citation statements)

References 5 publications

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“…As the value of the dynamic viscosity of the material is not constant and is a function of the temperature and strain rate, this property has been specified using a UDF. Friction stir welding can be considered a hot deformation process and the interaction between the flow stress and material strain rate is important; to account for this, a constitutive equation initially proposed by Zener and Selloors and then modified by Sheppard et al [29] has been used to represent the material. The UDF includes the formulations, presented in Equations 7, 8 and 9; to calculate the flow stress, the Zener-Hollomon parameter and subsequently material viscosity [30], the material constants and further relevant properties are shown in Table 2 for both materials.…”

Section: Materials Modelmentioning

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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Section: Materials Modelmentioning

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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“…Upper and lower bound flow stress values were calculated from the constitutive equation constants supplied by Sheppard and Jackson. [25] Data for 7050, 7150 and 7075 was used. Data for 7010 is not available but this alloys has very similar chemistry to 7050 and 7150.…”

Section: Stress-displacement Analysismentioning

confidence: 99%

The influence of quench sensitivity on residual stresses in the aluminium alloys 7010 and 7075

Robinson

Tanner

Truman

et al. 2012

Materials Characterization

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The most critical stage in the heat treatment of high strength aluminium alloys is the rapid cooling necessary to form a supersaturated solid solution. A disadvantage of quenching is that the thermal gradients can be sufficient to cause inhomogeneous plastic deformation which in turn leads to the development of large residual stresses. Two 215 mm thick rectilinear forgings have been made from 7000 series alloys with widely different quench sensitivity to determine if solute loss in the form of precipitation during quenching can significantly affect residual stress magnitudes. The forgings were heat treated and immersion quenched using cold water to produce large magnitude residual stresses. The through thickness residual stresses were measured by neutron diffraction and incremental deep hole drilling. The distribution of residual stresses was found to be similar for both alloys varying from highly triaxial and tensile in the interior, to a state of biaxial compression in the surface. The 7010 forging exhibited larger tensile stresses in the interior. The microstructural variation from surface to centre for both forgings was determined using optical and transmission electron microscopy. These observations were used to confirm the origin of the hardness variation measured through the forging thickness. When the microstructural changes were accounted for in the through thickness lattice parameter, the residual stresses in the two forgings were found to be very similar. Solute loss in the 7075 forging appeared to have no significant effect on the residual stress magnitudes when compared to 7010.

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“…Unlike the elastic behaviour, the flow stress of 7010 is strain rate dependent. Knowledge of the deformation behaviour of 7010 at varying strain rates and temperatures up to 475°C is not widespread, and thus a compromise was reached in this model by using flow stress values obtained from torsion tests on 7150 10 . Using other available plasticity data for similar alloys had very little effect on the displacement predicted during quenching or on the final predicted stress distribution.…”

Section: Materials Datamentioning

confidence: 99%

Time transient validation of residual stress prediction models for aluminium alloy quenching

Tanner

Robinson

2016

Materials Science and Technology

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Finite element models that predict residual stress states in relatively large quenched aluminium alloy products tend to give reliable results. However, even though there is confidence that the predicted stress state is correct, there is no validation indicating that the stress / displacement development during the quench is comparable to the experimental case. Combined with this, finite element predictions for small samples tend to underestimate surface stress. This paper uses a "Navy C-ring" benchmark design to monitor displacement during quenching. The heat transfer coefficient is found to be the most dominant boundary condition and is critical to ensuring displacement and residual stress predictions that match the experimental case.

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Constitutive equations for use in prediction of flow stress during extrusion of aluminium alloys

Cited by 45 publications

References 5 publications

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

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

The influence of quench sensitivity on residual stresses in the aluminium alloys 7010 and 7075

Time transient validation of residual stress prediction models for aluminium alloy quenching

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