Based on the concept of local thermal inconsistency, a constitutive model was developed for the description of the behaviors of metallic materials subjected to thermomechanical loading with fast heating, with reference to heating-assisted forming applications. The model considers effect of plastic deformation, of temperature as well as heating-rate and of recrystallization, on the mechanical property, hardening and damage of the materials. It can account for the reduction of the rupture strength of metallic materials subjected to high heating-rates or heating-rate histories, and the reduction of failure temperature of pre-stressed metallic materials heated at high heating-rates. The constitutive behavior of brass H62 subjected to uniaxial thermomechanical loading with fast heating is described and compared with experimental results. The satisfactory agreement between the computed and the experimental results shows the validity of the proposed model.

The effect of heating-rate and its history on the thermomechanical behavior of aluminum alloy LY12 is investigated with a Gleeble 1500 thermal–mechanical material testing system. It was found that the material experiencing higher heating-rate histories possesses lower rupture strength, and the pre-stressed material fails at a lower temperature when it is heated at a higher heating-rate. The SEM observation shows that, in general, there are more defects in the material subjected to higher heating-rates or higher heating-rate histories. The concept of local thermal inconsistency is introduced to account for the effect of heating-rate on mechanical properties, such as hardening and damage. A constitutive model is proposed for the description of the behavior of the materials subjected to thermomechanical loading incorporating fast heating, which can take into account the effect of plastic deformation, temperature and its rate, and recrystallization on the mechanical property, hardening and damage of the material. The constitutive behavior of LY12 subjected to uniaxial thermomechanical loading incorporating fast heating is described, and the comparison with the experimental results demonstrates the validity of the proposed model.

A 3D constitutive equation for large elastoplastic deformation is derived by taking into account the energy stored in the residual microstress fields in plastically deformed material and its effect on subsequent plastic deformation: this model may be used to describe the non-linear behaviour of material at the onset of loading and unloading. Non-linear mixed isotropic and kinematic hardening, and the effects of temperature and strain rate on material properties, are also considered. Expressions with and without a yield surface are provided. A numerical algorithm which corresponds to the constitutive equation without a yield surface is proposed and the material-user-subroutine UMAT is programmed and embedded in the commercial software ABAQUS. The analyses of necking, upsetting and extrusion were used to validate the proposed constitutive model and the corresponding numerical approach in metal forming analysis.

Laser-aided stamping of copper work-material was simulated using the FE code ABAQUS, by which temperature distributions and the stamping forces under different heating conditions were investigated. The simulation results showed that laser-heating can provide a satisfactory distribution of temperature at the shear-zone of the work-material, which will substantially reduce the maximum stamping force and enable stamping with larger aspect ratios. A high heating rate may also be achievable so that the desired stamping-temperature can be reached within a heating period that can match the requirement of industrial applications.

Two classes of experiments were conducted with a Gleeble 1500 thermal–mechanical testing system to investigate the effect of heating-rate and its history on the mechanical behavior of aluminum alloy LY12. In the first class of experiment, specimens were heated at different heating-rates to prescribed temperatures and then stretched until fracture. It was found that the specimen heated with higher heating-rate possesses lower rupture strength. In the second class of experiment, the specimens were preloaded and then heated at different rates until fracture. It was found that the higher the heating-rate was, the lower the failure temperature would be. Metallographical analysis showed that there are more defects in the specimens undergoing higher heating-rate. It was conjectured that higher heating-rate may cause stronger local thermal inconsistency due to the heterogeneous nature of the material. It may then cause local residual microstress fields, which, together with external thermal-mechanical load, may result in the changes in the microstructure of the material, such as recovery, recrystallization, nucleation and growth of microdefects, accounting for the changes in the macroscopic mechanical properties including hardening/softening, damage and failure, etc. A numerical simulation was performed, in which the mechanisms of local thermal inconsistency and the effect of the influencing factors were investigated.