arXiv subjects

Amirreza Keyhani

Publications and source records attributed to Amirreza Keyhani.

4 recordsLinked to original sources

arXiv2018

Multi-scale Modeling of Plasticity Nearby Precipitates in Nanostructured Materials

Precipitation strengthening is one of the most effective methods to design alloys with the desired combination of strength and ductility. The main mechanism of strengthening is generally known to be the interaction between dislocations and precipitates. When a dislocation encounters a precipitate, it bends and therefore the level of applied stress to the precipitate increases. Once the applied stress reaches the precipitate resistance, it passes the precipitate. Dislocations can bypass precipitates either by forming the Orowan loops or by cutting them. In this research, the focus is set on a small domain nearby precipitates to investigate their effects on the effective plastic strain. Both penetrable and impenetrable precipitates are considered. Two scales are coupled to model this phenomenon, the nano-micro scale where plasticity is determined by explicit three-dimensional discrete dislocation dynamics analysis and the continuum scale where the finite element method is applied. With this hybrid approach, complex problems in plastic deformation of nanostructured materials can be addressed. Finally, the relation between the precipitate resistance and the effective plastic strain is investigated.

cond-mat.mtrl-sci↗

arXiv2018

Overdriven dislocation-precipitate interactions at elevated temperatures in aluminum

The two-dimensional dislocation dynamics approach has been recently used for analyzing plastic deformation in metals and alloys at elevated temperatures. The two-dimensional approach, however, only accounts for the dislocation climbing process, and it assumes that dislocation bypassing and shearing of precipitates are negligible. To examine the validity of this assumption, this study quantifies dislocation bypassing and shearing of precipitates in terms of critical resolved shear stress, interaction time, and thermal activation energy for various precipitate strength levels, temperatures, and precipitate spacings. This study uses a modified dislocation dynamics approach that accounts for shearable and non-shearable precipitates. Simulations focus on the overdriven dislocation dynamics regime wherein the climbing process is limited by fast interactions between dislocations and precipitates. The results show that even though the resolved shear stress level required for a dislocation to overcome an array of precipitates decreases at higher temperatures, the interaction time between the dislocation and the precipitates increases. In addition, the maximum ratio of thermal activation energy to the precipitate energy barrier is only 0.15.

cond-mat.mtrl-sci↗

arXiv2017

Computational analysis of short-range interactions between an edge dislocation and an array of equally-spaced identical shearable or non-shearable precipitates

The interaction between dislocations and precipitates plays an important role in the mechanical behavior of alloys. To provide more insight into the physics of this interaction, this research analyzes short-range interactions of an edge dislocation with an array of equally-spaced identical precipitates. We use a modified dislocation dynamics approach accounting for penetrable and impenetrable precipitates. This research quantifies the effects of precipitate resistance on the geometry of the dislocation-precipitation interaction and the local distribution of plastic strain near a precipitate. The results show that a precipitate with a higher resistance causes an increase in the maximum value of dislocation curvature during the bypass. In addition, a higher level of precipitate resistance leads to a lower level of plastic deformation. Moreover, we observed a high plastic strain gradient at the interface of non-shearable precipitates.

cond-mat.mtrl-sci↗

arXiv2017

Quantification of Dislocation-Precipitate Interactions

The present research is the first attempt to systematically quantify the dislocation-precipitate interaction in terms of applied shear stress, precipitate resistance, and the required time to reach the critical state of dislocation-precipitate interaction when a dislocation line is about to pass through precipitates. To model the dislocation-precipitate interaction, we adopt a modified three-dimensional dislocation dynamics. Using the present modeling approach, which employs three-dimensional dislocation dynamics simulations, we obtain thousands of data points, accounting for various precipitate resistances, applied shear stresses, and precipitate spacing. The material of reference is Copper (Cu). From the simulations, which quantify the dislocation-precipitate interaction in terms of the applied shear stress, precipitate resistance scale, and dislocation-precipitate interaction time, we found a universal equation. The dislocation-precipitate interaction time versus precipitate resistance and stress, referred to as the "dislocation-precipitate interaction map," determines the "pass" or "no-pass" state of the interaction. Using this map, we incorporate the dislocation-precipitate interaction time in a two-dimensional multiscale framework which adopts the dislocation dynamics approach at the micro-scale and the finite element method at the macro-scale. We use this framework to model the mechanical behavior of free-standing copper thin films. The results show a dual effect of the dislocation-precipitate interaction time on the hardening level.

cond-mat.mtrl-sci↗