Homework 3 and 4 Contribution - Group 1

Overview

Crystal plasticity models became popular during 1980s as a tool to study deformation and texture behavior of metals during material processing and shear localization. The basic elements of the theory comprise (i) kinetics including self and latent hardening components; (ii) kinematics in which the concept of the plastic spin plays an important role; and (iii) intergranular constraint laws to govern interactions among crystals or grains. The theory is commonly acknowledged for providing realistic prediction/correlation of texture development and stress-strain behavior at large strains as it joins continuum theory with discretized crystal activity.

Crystal Plasticity

The crystal plasticity simulations for the one, twenty, fifty-five grains were successfully ran in the tension, compression, and shear loading conditions. Four hardening cases taken from Groh were studied for each loading condition. For all loading conditions the lowest saturation strength variable, κ_s = 46.75 MPa created the curves with the higher ultimate stress, with κ_s = 47.75, κ_s = 48.84, and κ_s = 49.10 MPa following, respectively. Figure 1 illustrates the stress-strain relationships for the tension loading condition for the various grain numbers and hardening constant cases.

Figure 1: Stress-strain relations from the tension loading condition at grain densities of (a) 1 grain, (b) 20 grains, and (c) 55 grains.

The representation of orientations within the crystal structures are usually given by Euler angles. The angles are based off of an orientation in three-dimensional Euclidean space and represent the rotations from the reference to the current configuration. For this study, the Euler angles were randomly generated and then graphically represented using pole figures. The pole figures (Figures 2) show the crystallographic preferred orientations (texture) on the face centered cubic (111) plane via the stereographic projection method.

Figure 2: Pole figures comparing texture for (a) tension, (b) compression, (c)shear. The difference between the texture developments in the tension, shear, and compression loading conditions can be noticed.

Macroscale Internal State Variable Plasticity

In order to quantify the effects of damage, stress-strain data from the above crystal plasticity investigation was used to fit the constants from the Internal State Variable Plasticity-Damage Model DMG-fit tool. Table 1 shows the non-zero constants used to fit the tension data. Figure 3 shows the fit.

Table 1: Non-zero DMGfit material parameters

Parameter	G	Bulk	Kic	Tint	Tmelt	heat	nv	fn	dcs	dcs0	C1	C3	C5	C9	C13	CAcon
	25563.9	66666.7	1000	297	933.52	0.370521	0.3	0.001	30	30	2.1	10	500	120.339	0.166	0.5

Figure 3: Stress-strain comparison between results gained from crystal plasticity calculations and plasticity-damage calculations.

Following the crystal plasticity simulations and DMGfit routine, a one element finite element simulation in ABAQUS with the ISV-Damage UMAT was ran using the constants in Table 1. Figure 4 serves to validate the plasticity-damage model as the stress-strain response shows good agreement.

Figure 4: Comparison between stress-strain results from crystal plasticity finite element simulations and plasticity damage finite element simulations.