PRISM - Materials Simulation Tool

MEMS (Micro-electromechanical System) is a combined electrical and mechanical nano-scaled device with rapidly growing applications. We have developed a contacting radio frequency capacitive MEMS that is commonly used as capacitive switches and contact actuators in PRISM (Prediction of Reliability, Integrity and Survivability of Microsystems) lab at Purdue University. Our research team has focused on creating a simulation of MEMS’s survivability towards crazing and cracking. Our particular objective in this project is to create a tool that can help users perform complex quantitative calculations regarding the properties of different materials. This tool will generate various plots visualizing the properties, such as stress and strain analysis, deviatoric and volumetric graphs, etc. Currently, a MATLAB based interfaced tool has been created by utilizing Rapture, Rapid Application Infrastructure, designed by the nanoHUB team at Purdue University. This tool has embedded user-friendly documentations for users. In summary, we found that changing the fracture energy density per length ‘Gc/l’ ratio can affect both volumetric stress and strain, as well as deviatoric stress and strain. Also, we discovered that when the loading condition is anywhere between 1 and -0.5 exclusive, there exists more than one phase of ‘gamma’ value, usually up to three phases. These understandings allow us to develop an improved material that can withstand cracks and be used by micro-electromechanical systems industries

Micro-Mechanics Simulation Tool Optimization

Crystalline films grown epitaxially on substrates consisting of a different crystalline material are of considerable interest in optoelectronic devices and the semiconductor industry. One way to progress in this field is to develop simulation tools based on specially designed numerical method. A nanoHUB simulation tool was developed based on the phase field theory, which considers the propagation of dislocations inside the crystalline film. However, the current tool needs several improvements to be more realistic and user-friendly. First, the inputs of the simulation tool are adjusted so that the user can use this tool directly without any additional calculation. The output graphs of this tool are also edited in order to show the dislocation propagation more clearly. Finally, an algorithm was developed to initialize several dislocations in the crystalline film according to the input dislocation density. The new version is much more user-friendly and it considers a more realistic setting with multiple dislocations propagating in the film simultaneously (the current version only considers a single dislocation line). The new tool would serve as a verification of numerical methods and help the understanding of this process

Phase-field Dislocation Dynamics Code Optimization

The importance of the study of nanocrystalline materials has gained a huge amount of attention these years due to its extraordinary mechanical, electrical and chemical properties. One significant way to progress in this field is by simulating the behavior of the particles in nano scale, which is not only a need but a challenge due to massive interactions that occur there. The phase-field dislocation dynamics (PFDD) method has been successfully employed in the modeling of plastic deformation, creep and grain boundary sliding. In PFDD, the plastic strain and the energy are functions of phase fields that obey a set of complex equations. In the algorithm approach this complexity increases depending on different factors that, in the end, increase the time and computational resource used, which this research pretend optimize. Even though Fast Fourier Transformation and MPI have been utilized in the PFDD code due to his optimal approach and matricial representation which makes the algorithms more understandable the efficiency is still a major concern in matters of computational time and resource consumption. This research intends to give an improvement to the programs that simulates the nanocrystalline materials and the models that follows the dynamics locations so outgoing researchers can use it in a more efficient way. The result will be a improved program that follows the PFDD models and simulates the nanocrystalline behavior with different materials and different constraints in the environment as in the materials itselfs with a more friendly and intelligent input for the user

Code Optimization for Phase Field Method

The Phase field model method for studying grain dislocation at atomic level after applying an external force to the materials being tested, enables simulate the behavior of different materials after applying stress. With the appropriate numerical method the simulation could change drastically the complexity of the algorithm. Finding the most accurate and stable numerical method for the phase field model give us a considerable improving in the performance of the code used to simulate the phase field dynamic dislocation in larger and more complex simulations can be performed. We made an statistic comparison between the different methods, comparing stability and convergence, testing the most optimal configuration for the best performance achievable with our particular conditions of the problem. The Multi Step Numerical method algorithm seems to be the most promising method in our particular conditions, the fast convergence and big stability. Currently a big challenge is the development new models and computer algorithms with better overall performance allowing to efficiently use multiple processors, with the help of improvement for large data simulations

Applications of a (k–ϵ) model for the analysis of continuous casting processes

The finite element solution of the turbulent Navier–Stokes equations developed via (k–ϵ) turbulence models was addressed in previous publications [1–4], where a (k–L)‐predictor/(ϵ)‐corrector iterative algorithm was developed. It was shown that the developed algorithm is robust and converges for the analyses of different flows without requiring the implementation of ad hoc numerical procedures. The turbulent convection–diffusion transport equations are solved by using the velocity distributions determined from the solution of the turbulent Navier–Stokes equations. The dispersion of a die in a turbulent flow can therefore be modelled and the obtained dispersion patterns are validated via flow visualizations in water models. In the present paper, the developed analysis capability is applied to the analysis of continuous casting processes

Grain Boundary Motion Analysis

Grain growth is a mechanism to relax residual stresses in thin films. These grains grow out of the thin film surface and are known as whiskers. These whiskers can cause short circuits, so developing scalable and cost effective solutions would increase the reliability and utility of tin electronics. A popular of method of examining tin whiskering is microscopic simulation, as it provides an accurate and cost effective way to predict the consequences of proposed models. Specifically examining the evolution of grain boundaries, this paper aims to present the results of grain boundary motion simulations through a generalized program that streamlines and optimizes the analysis process. Various simulations examining the effects of grain boundary energy and mobility were run through Idaho National Laboratory\u27s Multiphysics Object Oriented Simulation Environment (MOOSE), with processing, analysis, and presentation provided by a Jupyter Notebook program that is available online. The Notebook program was found to graph effectively and flexibly, creating results which provide quantitative data and clear visualizations of the MOOSE simulations, providing examples of how the mobility and energy values of grain boundaries of Tin significantly affect grain migration. The Jupyter notebook will be deployed as a tool in nanohub.org

Simulating Dynamic Failure of Polymer-Bonded Explosives under Periodic Excitation

Accidental mishandling of explosive materials leads to thousands of injuries in the US every year. Understanding the mechanisms behind the detonation process is crucial to prevent such accidents. In polymer-bonded explosives (PBX), high-frequency mechanical excitation generates thermal energy and can lead to an increase in temperature and vapor pressure, and potentially the initiation of the detonation process. However, the mechanisms behind this energy release, such as the effects of dynamic fracture and friction, are not well understood. Experimental data is difficult to collect due to the different time scales of reactions and vibrations, so research is aided by running simulations to computationally understand experimental results. Using phase-field model of fracture, we simulate the behaviors of various crack orientations in single particles of HMX bonded in a polymer matrix. Larger amplitudes induce higher rates of energy buildup which lead to quicker crack propagation, while higher frequencies generate higher spikes in temperature. However, crack location and orientation with respect to loading also significantly affect damage rates and temperature fluctuations. Cracks perpendicular to the loading vibration wave propagate most readily and appear to generate the most frictional energy, especially along the crystal-polymer interface

Dislocation Avalanche Polycrystalline Nickel

Self-organized criticality (SOC) is widely observed in systems ranging from creep deformation of single crystal ice to the movement of glacier. -The behavior of these SOC systems follows a power law distribution, which is time- and space-scale invariant. Previous phase field simulation of single crystal nickel has shown that plastic flow is characterized by intermittent dislocation avalanches, which can be characterized by a power law distribution. Does this scale invariance also exist in polycrystalline material, in which dislocation avalanches may be hindered by grain boundaries? In this study, we characterize the dislocation loops using homogenous region division algorithm and investigate the statistics of dislocation loops in polycrystalline nickel with various average grain sizes. We find that plastic flow in polycrystalline nickel consists of dislocation avalanches with sizes over three orders of magnitude. Sudden dislocation bursts are separated by a large amount of small avalanches. This intermittency may bring into question the traditional treatment of plasticity as homogenous process

Cloud computing in nanoHUB powering education and research

We present a tool that uses a phase field approach to simulate plastic deformation in nanocrystalline materials. It captures the competing grain-boundary and dislocation-mediated deformation mechanisms that govern plastic deformation in these materials. The model is based on a multiphase field approach in which dislocations and grain boundary sliding are represented by means of scalar phase fields described in “The role of grain boundary energetics on the maximum strength of nanocrystalline Ni”, Koslowski, Lee and Lei, Journal of the Mechanics and Physics of Solids, 59 1427–1436, 2011. The tool enables users to quantify how uncertainties in the input parameters (materials properties such as elastic constants, Peierls energy barrier for dislocation glide, and activation barrier for grain boundary sliding) affect the prediction of the yield stress. In addition, it provides a sensitivity analysis that quantifies the relative importance of each input variable. In order to achieve this, the phase field simulation code is orchestrated by the PRISM Uncertainty Quantification tool that enables users to select various state-of-the-art methods for uncertainty propagation

Phase field modeling of crack propagation in double cantilever beam under Mode I

A smeared crack approach using a phase-field approach to fracture with unilateral contact condition was used to study the stress distribution and crack propagation in a double cantilever beam (DCB) specimen. The parameters in the numerical model were informed from atomistic simulations and validated with experimental data for poly(methyl methacrylate) that included data for damage initiation under different levels of volumetric and deviatoric stress components and fracture toughness measurements obtained under Mode I conditions. The phase field model includes two quantities, a length scale that controls the width of the crack and the critical fracture energy density. The study considered a sensitivity analysis of the influence of these two parameters to obtain optimal values. Experiments and simulations of DCB are shown to study the toughness of polymer and polymer composite specimens that include residual stresses developed in the specimen during cure