Speaker
Description
A good understanding of time-dependant (viscous) phenomena in materials is important for the modelling of transient and long-term behaviours of components, especially at high temperatures. Viscosity has usually been assumed to occur solely after yielding, and most high temperature constitutive models for metals are therefore designed to model elasto-viscoplastic materials. Recent work however suggests the existence in some metals such as aluminium alloy 7175 of viscous behaviour at stress levels that would typically be considered fully elastic.
To investigate the causes of viscoelastic phenomena at the microstructural level, an experimental program of tensile tests was conducted on small specimens of aluminium 7175. Specimens were heated up to 160 °C, a temperature at which creep phenomena have been observed in the literature. They were then loaded up to stress levels around what would be considered initial yield in a viscoelastic material model, held at constant displacement, and allowed to relax for extended times of the scale of several hours. They were then quickly unloaded and cooled using forced convection at zero load to freeze the microstructural changes in place before microscopic observation. Small specimens of two different geometries were tested: small rings and two-bar specimens, the first allowing multiple stress states within a single specimen for a given applied load and the second allowing for straightforward interpretation of stress and strain states within the specimen from measured force and displacement values.
Microstructural changes were then linked to the visco-elastic behaviour through an internal variable and an evolution law was developed that captures the evolution of the microstructure of aluminium alloy 7175 under arbitrary viscoelastic loading.
| Speaker Country | United Kingdom |
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