A constitutive description is proposed for a single pearlitic colony based on its composition of lamellas of ferrite and cementite with a very thin interlamellar spacing. Both phases are assumed to be elastoplastic. The relationship between the increments of overall stress and strain is derived and the corresponding numerical algorithm is developed. The mechanical behavior of the colony subjected to proportional or non-proportional loading is investigated, and it shows that the overall response is anisotropic. Finite element analysis is conducted to analyze the influence of the interlamellar spacing on the mechanical response of the colony. It shows that the proposed model can not only describe the behavior of the pearlitic colony with extremely small interlamellar spacing, but also work with sufficient accuracy in the case of moderate interlamellar spacing. The constitutive response of each phase in a colony can be obtained simultaneously, which is an important step towards developing theories of microstructure-based damage and failure analysis.

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.

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.

The response of the work-material during forward extrusion and the subsequent unloading process was analysed with a view to examining differences in prediction of component-form errors, when different constitutive models are used. Two types of constitutive models were adopted for the analysis-classical theory of plasticity (CP) with isotropic hardening and non-classical theory of plasticity (NCP). When compared the results of the CP model with the NCP model, the latter shows a slightly smaller maximum punch-force requirement, smaller diameter of the extrudate and larger contraction of the die during unloading. The significant difference in the predicted final dimensions of the extrudate with different constitutive models suggests that more accurate constitutive descriptions on the work-material have to be used for the analysis of component-form errors in precision forming, if more accurate results are to be achieved.

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.