Firas Akasheh

Multiscale Modeling of Dislocation Mechanisms in Nanoscale Multilayered Composites

It is well known that the mechanical behavior of nanoscale multilayered composites is strongly governed by single dislocation mechanisms and dislocation-interface interactions. Such interactions are complex and multiscale in nature. In this work, two such significant effects are modeled within the dislocation dynamics-continuum plasticity framework: elastic properties mismatch (Koehler image forces) and interface shearing in the case of weak interfaces. The superposition principle is used to introduce the stress fields due to both effects solved for by finite elements. The validation of both methodologies is presented. Furthermore, it was found that the layer-confined threading stress of a dislocation in hair-pin configuration increases if the layer is surrounded by layers made of a stiffer material and that this strengthening effect grows more significant as the layer thickness decreases. The observation made through molecular dynamics, that weak interfaces act as dislocation sinks, was also captured with our approach. A dislocation is attracted to the interface independent of its sign or character. Also the force increases sharply as the dislocation approaches the interface. These findings agree with published molecular dynamics simulations and dislocation-based equilibrium models of this type of interaction.

Bridging Learning Gap Through Peer-to-Peer Information Exchange in a Flat Environment

In this paper, we present a technology assisted flat learning environment, Teaching to Learn (TeatoL), where all participants have dual roles as students and instructors. The main objective of this work is to investigate how peer-to-peer information exchange aids in bridging knowledge gap in a flat-learning environment. We present our TeatoL implementation that was developed to enhance ill-structured problem solving skill along with its assessment. The participants in the learning environment were given an open design problem related to sheet metal forming. A short lecture about 35 minutes (Phase 0) was given and then student teams were asked to make an instructional video (Phase I) describing their approach for solving the open-ended problem. The videos were viewed by peers, using their computers and mobile devices. The students then critiqued and provided feedback on the posted videos (Phase II). The final step of the process had students write short reports on their problem solving approach (Phase III) that was modified based on peer-to-peer interactions. Student learning in all three phases was assessed to understand the effects of different modes of learning in TeatoL. Our findings indicate that TeatoL is an effective flat online learning environment. Correlation analysis suggests that learning gains are dependent on the level of knowledge on the topic for the learning community (class) and the number of meaningful comments provided by peers. The findings from this work can be utilized to develop technology based online peer learning environments to improve learning outcomes through active collaborative learning. Such an environment can be particularly useful for open course delivery.Copyright

Dislocation Structure of Cu/Nu (100) Semi‐Coherent Interface and Its Role in Lattice Dislocation Nucleation

Using molecular dynamics simulations and dislocation theory, we studied dislocation structure of Cu/Ni (100) semi-coherent interface and its role in nucleating lattice dislocation under mechanical loading. We found that misfit dislocation pattern is dependent on layer thickness. On each interface, there are two sets of edge-type misfit dislocation with the Burgers vector of 1/2 and the line sense along . The relative position of misfit dislocations at the adjacent interfaces is related to the layer thickness. This is ascribed to two factors, interaction energy among misfit dislocations and the core dissociation of misfit dislocations. Both of them show layer thickness dependence. Under mechanical loading, lattice dislocations nucleate from misfit dislocation lines. Thus, the incipient of plastic deformation of layered Cu/Ni composites in terms of initial yielding stress is dependent on the layer thickness.

Modeling a Flat Learning Environment as a Social Network to Understand Effects of Peer-to-Peer Information Exchange on Learning

In this paper we present a technology assisted flat learning environment, Teaching to Learn (TeatoL), that capitalizes on the research findings on linkages between higher-order thinking and peer-learning. Within TeatoL students are introduced to a “flatter” instructional environment; all participants have dual roles as students and instructors who are embedded in a collaborative environment where all learn collectively from each other’s experiences, even the instructor. The main objective of this paper is to understand flat learning environment as a social network. The focus is on peer learning mode, where students are instructors to share their experience and then learn from fellow student instructors. In this paper, we present our initial analysis of a flat learning environment, implemented at the University of Oklahoma, as a network. The participants in the learning environment were given an open design problem related to sheet metal forming. We close the paper with observations from our initial implementations on peer-learning as a network.Copyright

Scenario-Based Learning Environment to Support Peer-Learning

It is well documented that students learn more effectively when they are actively involved in the learning process, and interacting with peers. Interactive scenario-based education is a novel concept expected to stimulate active learning and provide a peer-learning experience. In this paper we present Create your Scenario Interactively (CSI) module, which is an interactive storybook-like learning tool composed of interactive storyline, 2D/3D visualization, simulation, and state-of-the-art interaction technology. The CSI method allows peer-interactions and prepares students to solve open-ended problems.The CSI module has been developed for metal casting and implemented in manufacturing engineering courses at the University of Oklahoma and Tuskegee University. In this paper, we discuss the impact of the CSI on students’ learning in manufacturing engineering education. Our preliminary results suggest that a majority of the students feels that the CSI module is very effective in keeping them engaged. We also analyze the effect of peer-learning to develop critical thinking and solve design problems. The details of the CSI module, implementation details, and assessment results are discussed in the paper.Copyright

Interactive Scenario-Based Teaching of Metal Casting Processes

It is well documented that students learn more effectively when they are actively involved in the learning process. Interactive scenario-based education is a novel concept expected to stimulate active learning and provide an engaging learning experience. Recently we have developed a Create your Scenario Interactively (CSI) module to teach metal casting and have implemented it in manufacturing engineering courses at the University of Oklahoma. In this paper, we discuss the impact of the CSI on students’ learning in manufacturing engineering education. The pedagogical effectiveness of the CSI instruction has been evaluated in several areas such as students’ engaging and active learning through pre-test and post-test format and survey questionnaires. Our preliminary results suggest that a majority of the students feels that the CSI module is very effective in keeping them engaged. Results also indicate that the CSI instructions help improve their understanding of the metal casting process. The details of the CSI module, implementation details, and assessment results are discussed.Copyright

Treating internal surfaces and interfaces in discrete dislocation dynamics

Abstract The treatment of coherent interfaces and cracks is discussed in the framework of dislocation dynamics (DD). In the case of interfaces, we use DD to study dislocation interactions in nanoscale bimetallic laminates, and to predict their structure after relaxation and during loading. In agreement with experimental observations, our discrete dynamics simulations show that dislocation structure develops only at the interface between coherent layers leaving layers’ interior dislocation-free. The main dislocation mechanism at this length scale is Oworan bowing of threading dislocations confined to their respective layers by the sign-alternating coherency stress field in the layers. Slip transmission across the interfaces marks the end of the confined slip regime, hence, the breakdown of the interfaces and macroscopic yielding of these structures. In the case of crack, its long-range and singular stress field is determined by modeling the crack as continuous distribution of dislocation loops. The traction boundary condition to be satisfied at the crack surface, results into a singular integral equation of the first kind that is solved numerically. The model is integrated with the DD technique to investigate the behavior of a specimen containing cracks of different shapes under fatigue. The results are compared with the behavior of an uncracked specimen and conclusions are extracted. Extension of this crack treatment methodology to account for their presence at interfaces, all within the frame dislocations dynamics, opens the door for a more realistic approach to a wide range of interfaces-related problems.