Analyzing microforming by developing a crystal plasticity-based constitutive model

Date

2025-9-01

Author

Dal, Saniye Rabia

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The deformation behavior of materials changes significantly when their size is reduced to the micro-scale. Therefore, the traditional knowledge obtained from macroscale forming may no longer be sufficient for accurate analysis of microforming processes. To address this, a dislocation density based crystal plasticity constitutive model is proposed to investigate size effects on micro-scale deformation. The proposed model can also predict the effects of slip-rate gradients using a simplified approach that does not require higher-order stresses or additional balance equations, unlike conventional gradient theories. To incorporate the slip-rate gradient effect, the minimal gradient-enhanced hardening law is employed. A distinct approach for calculating geometrically necessary dislocation (GND) and statistically stored dislocation (SSD) densities is developed and incorporated into the hardening law. The constitutive model is implemented into a commercial finite element code through user subroutines. Electron Backscatter Diffraction (EBSD) data is obtained before and after the tensile test of a copper sample. In this way, it is possible to identify the grain orientations before and after experiments in terms of Euler angles. Furthermore, GND density analysis is conducted based on the EBSD data. The copper sample is analyzed using the developed constitutive model and the predictions are found to be in good agreement with the experimental data. Moreover, the developed approach is applied to investigate the effects of the thickness-to-grain diameter ratio (t/d) and grain orientation on deformation behavior by using two copper foils with different t/d ratios. Consequently, the proposed size-dependent model accurately captures the effect of microstructural characteristics.

Subject Keywords

Crystal plasticity theory, Geometrically necessary dislocation, Statistically stored dislocation, Size effect, Electron backscatter diffraction

URI

https://hdl.handle.net/11511/116110

Collections

Graduate School of Natural and Applied Sciences, Thesis