Matching Items (17)

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Evaluation of Current Helmet Technologies for Redesign of Cycling Helmets

Description

Traumatic brain injuries and the effects they can bring are becoming the main focus among researchers and physicians. Cycling is the leading sport with the most traumatic brain injuries, but

Traumatic brain injuries and the effects they can bring are becoming the main focus among researchers and physicians. Cycling is the leading sport with the most traumatic brain injuries, but the design of the cycling helmet has stayed the same for decades now. The technology of a bike is constantly getting developed and testing but the helmet is lagging behind. This project consists of designing and testing different cycling helmets through ANSYS simulations to determine the ideal geometry and features a cycling helmet must include, reducing the stress that the head experiences upon impact during a fall.

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Created

Date Created
  • 2020-05

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Finite Element Analysis of Microstructural Weak and Strong Links for Shock-Induced Damage in Metallic Materials

Description

Understanding damage evolution, particularly as it relates to local nucleation and growth kinetics of spall failure in metallic materials subjected to shock loading, is critical to national security. This work

Understanding damage evolution, particularly as it relates to local nucleation and growth kinetics of spall failure in metallic materials subjected to shock loading, is critical to national security. This work uses computational modeling to elucidate what characteristics have the highest impact on damage localization at the microstructural level in metallic materials, since knowledge of these characteristics is critical to improve these materials. The numerical framework consists of a user-defined material model implemented in a user subroutine run in ABAQUS/Explicit that takes into account crystal plasticity, grain boundary effects, void nucleation and initial growth, and both isotropic and kinematic hardening to model incipient spall. Finite element simulations were performed on copper bicrystal models to isolate the boundary effects between two grains. Two types of simulations were performed in this work: experimentally verified cases in order to validate the constitutive model as well as idealized cases in an attempt to determine the microstructural characteristic that define weakest links in terms of spall damage. Grain boundary effects on damage localization were studied by varying grain boundary orientation in respect to the shock direction and the crystallographic properties of each grain in the bicrystal. Varying these parameters resulted in a mismatch in Taylor factor across the grain boundary and along the shock direction. The experimentally verified cases are models of specific damage sites found from flyer plate impact tests on copper multicrystals in which the Taylor factor mismatch across the grain boundary and along the shock direction are both high or both low. For the idealized cases, grain boundary orientation and crystallography of the grains are chosen such that the Taylor factor mismatch in the grain boundary normal and along the shock direction are maximized or minimized. A perpendicular grain boundary orientation in respect to the shock direction maximizes Taylor factor mismatch, while a parallel grain boundary minimizes the mismatch. Furthermore, it is known that <1 1 1> crystals have the highest Taylor factor, while <0 0 1> has nearly the lowest Taylor factor. The permutation of these extremes for mismatch in the grain boundary normal and along the shock direction results in four idealized cases that were studied for this work. Results of the simulations demonstrate that the material model is capable of predicting damage localization, as it has been able to reproduce damage sites found experimentally. However, these results are qualitative since further calibration is still required to produce quantitatively accurate results. Moreover, comparisons of results for void nucleation rate and void growth rate suggests that void nucleation is more influential in the total void volume fraction for bicrystals with high property mismatch across the interface, suggesting that nucleation is the dominant characteristic in the propagation of damage in the material. Further work in recalibrating the simulation parameters and modeling different bicrystal orientations must be done to verify these results.

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Created

Date Created
  • 2014-12

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Explicit Dynamics Analysis of Collapsible Polymer-Carbon Lightweight Ammunition Package

Description

Structural assemblies for military applications must be guaranteed to withstand normal operating environments. Traditionally, experimental testing is performed on a prototype of the object to understand how it will behave

Structural assemblies for military applications must be guaranteed to withstand normal operating environments. Traditionally, experimental testing is performed on a prototype of the object to understand how it will behave under potential failure conditions. However, this process can be time-consuming and expensive, and it is often desired to have preliminary information to guide the design of the components. Consequently, a finite element analysis (FEA) can be performed using computational tools to approximate the failure behavior of the object before experiments are performed. This can provide information for a faster preliminary evaluation of the design, which very useful when implementing new technologies in the defense sector.
Currently, a new design for collapsible, lightweight ammunition package (LAP) has been proposed for military applications. The design employs rubber gaskets which enable the LAP to fold when it is empty, in addition to carbon fiber walls which decrease weight while increasing strength. To evaluate the new design, it is desired to perform a finite element analysis to simulate the behavior of the can under various drop impact conditions. Because the design includes complex joinery, which is often difficult to model, the purpose of this thesis project is to determine the most effective methodology to define the physical system using finite elements for impact simulations, and consequently perform the desired analysis for the LAP.

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Date Created
  • 2020-05

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A generalized orthotropic elasto-plastic material model for impact analysis

Description

Composite materials are now beginning to provide uses hitherto reserved for metals in structural systems such as airframes and engine containment systems, wraps for repair and rehabilitation, and ballistic/blast mitigation

Composite materials are now beginning to provide uses hitherto reserved for metals in structural systems such as airframes and engine containment systems, wraps for repair and rehabilitation, and ballistic/blast mitigation systems. These structural systems are often subjected to impact loads and there is a pressing need for accurate prediction of deformation, damage and failure. There are numerous material models that have been developed to analyze the dynamic impact response of polymer matrix composites. However, there are key features that are missing in those models that prevent them from providing accurate predictive capabilities. In this dissertation, a general purpose orthotropic elasto-plastic computational constitutive material model has been developed to predict the response of composites subjected to high velocity impacts. The constitutive model is divided into three components – deformation model, damage model and failure model, with failure to be added at a later date. The deformation model generalizes the Tsai-Wu failure criteria and extends it using a strain-hardening-based orthotropic yield function with a non-associative flow rule. A strain equivalent formulation is utilized in the damage model that permits plastic and damage calculations to be uncoupled and capture the nonlinear unloading and local softening of the stress-strain response. A diagonal damage tensor is defined to account for the directionally dependent variation of damage. However, in composites it has been found that loading in one direction can lead to damage in multiple coordinate directions. To account for this phenomena, the terms in the damage matrix are semi-coupled such that the damage in a particular coordinate direction is a function of the stresses and plastic strains in all of the coordinate directions. The overall framework is driven by experimental tabulated temperature and rate-dependent stress-strain data as well as data that characterizes the damage matrix and failure. The developed theory has been implemented in a commercial explicit finite element analysis code, LS-DYNA®, as MAT213. Several verification and validation tests using a commonly available carbon-fiber composite, Toyobo’s T800/F3900, have been carried and the results show that the theory and implementation are efficient, robust and accurate.

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Created

Date Created
  • 2016

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A finite element-based framework for understanding the energy performance of concrete elements incorporating phase change materials

Description

Dwindling energy resources and associated environmental costs have resulted in a serious need to design and construct energy efficient buildings. One of the strategies to develop energy efficient structural materials

Dwindling energy resources and associated environmental costs have resulted in a serious need to design and construct energy efficient buildings. One of the strategies to develop energy efficient structural materials is through the incorporation of phase change materials (PCM) in the host matrix. This research work presents details of a finite element-based framework that is used to study the thermal performance of structural precast concrete wall elements with and without a layer of phase change material. The simulation platform developed can be implemented for a wide variety of input parameters. In this study, two different locations in the continental United States, representing different ambient temperature conditions (corresponding to hot, cold and typical days of the year) are studied. Two different types of concrete - normal weight and lightweight, different PCM types, gypsum wallboard's with varying PCM percentages and different PCM layer thicknesses are also considered with an aim of understanding the energy flow across the wall member. Effect of changing PCM location and prolonged thermal loading are also studied. The temperature of the inside face of the wall and energy flow through the inside face of the wall, which determines the indoor HVAC energy consumption are used as the defining parameters. An ad-hoc optimization scheme is also implemented where the PCM thickness is fixed but its location and properties are varied. Numerical results show that energy savings are possible with small changes in baseline values, facilitating appropriate material design for desired characteristics.

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Created

Date Created
  • 2012

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Probabilistic finite element analysis and design optimization for structural designs

Description

This study focuses on implementing probabilistic nature of material properties (Kevlar® 49) to the existing deterministic finite element analysis (FEA) of fabric based engine containment system through Monte Carlo simulations

This study focuses on implementing probabilistic nature of material properties (Kevlar® 49) to the existing deterministic finite element analysis (FEA) of fabric based engine containment system through Monte Carlo simulations (MCS) and implementation of probabilistic analysis in engineering designs through Reliability Based Design Optimization (RBDO). First, the emphasis is on experimental data analysis focusing on probabilistic distribution models which characterize the randomness associated with the experimental data. The material properties of Kevlar® 49 are modeled using experimental data analysis and implemented along with an existing spiral modeling scheme (SMS) and user defined constitutive model (UMAT) for fabric based engine containment simulations in LS-DYNA. MCS of the model are performed to observe the failure pattern and exit velocities of the models. Then the solutions are compared with NASA experimental tests and deterministic results. MCS with probabilistic material data give a good prospective on results rather than a single deterministic simulation results. The next part of research is to implement the probabilistic material properties in engineering designs. The main aim of structural design is to obtain optimal solutions. In any case, in a deterministic optimization problem even though the structures are cost effective, it becomes highly unreliable if the uncertainty that may be associated with the system (material properties, loading etc.) is not represented or considered in the solution process. Reliable and optimal solution can be obtained by performing reliability optimization along with the deterministic optimization, which is RBDO. In RBDO problem formulation, in addition to structural performance constraints, reliability constraints are also considered. This part of research starts with introduction to reliability analysis such as first order reliability analysis, second order reliability analysis followed by simulation technique that are performed to obtain probability of failure and reliability of structures. Next, decoupled RBDO procedure is proposed with a new reliability analysis formulation with sensitivity analysis, which is performed to remove the highly reliable constraints in the RBDO, thereby reducing the computational time and function evaluations. Followed by implementation of the reliability analysis concepts and RBDO in finite element 2D truss problems and a planar beam problem are presented and discussed.

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Created

Date Created
  • 2012

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Failure Modeling in an Orthotropic Plastic Material Model under Static and Impact Loading

Description

An orthotropic elasto-plastic damage material model (OEPDMM) suitable for impact analysis of composite materials has been developed through a joint research project funded by the Federal Aviation Administration (FAA) and

An orthotropic elasto-plastic damage material model (OEPDMM) suitable for impact analysis of composite materials has been developed through a joint research project funded by the Federal Aviation Administration (FAA) and the National Aeronautics and Space Administration (NASA). The developed material model has been implemented into LS-DYNA®, a commercial finite element program. The material model is modular comprising of deformation, damage and failure sub-models. The deformation sub-model captures the rate and/or temperature dependent elastic and inelastic behavior via a visco-elastic-plastic formulation. The damage sub-model predicts the reduction in the elastic stiffness of the material. The failure sub-model predicts when there is no more load carrying capacity in the finite element and erosion of the element from the finite element model. Most of the input parameters required to drive OEPDMM are in the form of tabulated data. The deformation sub-model is driven by a set of tabulated stress-strain data for a given strain-rate and temperature combination. The damage sub-model is driven by tabulated damage parameter-strain data. Two failure sub-models have been implemented – Puck Failure Model and Generalized Tabulated Failure Model. Puck Failure Model requires scalar parameters as input whereas, the Generalized Tabulated Failure Model is driven by a set of equivalent failure strain tabulated data. The work presented here focuses on the enhancements made to OEPDMM with emphasis on the background, development, and implementation of the failure sub-models. OEPDMM is verified and validated using a carbon/epoxy fiber reinforced composite. Two validation tests are used to evaluate the failure sub-model implementation - a stacked-ply test carried out at room temperature under quasi-static tensile and compressive loadings, and several high-speed impact tests where there is significant damage and material failure of the impacted panel. Results indicate that developed procedures provide the analyst with a reasonable and systematic approach to building predictive impact simulation models.

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Created

Date Created
  • 2020

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Modeling, characterizing and reconstructing mesoscale microstructural evolution in particulate processing and solid-state sintering

Description

In material science, microstructure plays a key role in determining properties, which further determine utility of the material. However, effectively measuring microstructure evolution in real time remains an challenge. To

In material science, microstructure plays a key role in determining properties, which further determine utility of the material. However, effectively measuring microstructure evolution in real time remains an challenge. To date, a wide range of advanced experimental techniques have been developed and applied to characterize material microstructure and structural evolution on different length and time scales. Most of these methods can only resolve 2D structural features within a narrow range of length scale and for a single or a series of snapshots. The currently available 3D microstructure characterization techniques are usually destructive and require slicing and polishing the samples each time a picture is taken. Simulation methods, on the other hand, are cheap, sample-free and versatile without the special necessity of taking care of the physical limitations, such as extreme temperature or pressure, which are prominent

issues for experimental methods. Yet the majority of simulation methods are limited to specific circumstances, for example, first principle computation can only handle several thousands of atoms, molecular dynamics can only efficiently simulate a few seconds of evolution of a system with several millions particles, and finite element method can only be used in continuous medium, etc. Such limitations make these individual methods far from satisfaction to simulate macroscopic processes that a material sample undergoes up to experimental level accuracy. Therefore, it is highly desirable to develop a framework that integrate different simulation schemes from various scales

to model complicated microstructure evolution and corresponding properties. Guided by such an objective, we have made our efforts towards incorporating a collection of simulation methods, including finite element method (FEM), cellular automata (CA), kinetic Monte Carlo (kMC), stochastic reconstruction method, Discrete Element Method (DEM), etc, to generate an integrated computational material engineering platform (ICMEP), which could enable us to effectively model microstructure evolution and use the simulated microstructure to do subsequent performance analysis. In this thesis, we will introduce some cases of building coupled modeling schemes and present

the preliminary results in solid-state sintering. For example, we use coupled DEM and kinetic Monte Carlo method to simulate solid state sintering, and use coupled FEM and cellular automata method to model microstrucutre evolution during selective laser sintering of titanium alloy. Current results indicate that joining models from different length and time scales is fruitful in terms of understanding and describing microstructure evolution of a macroscopic physical process from various perspectives.

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Created

Date Created
  • 2018

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Accurate Estimation of Core Losses for PFC Inductors

Description

As the world becomes more electronic, power electronics designers have continuously designed more efficient converters. However, with the rising number of nonlinear loads (i.e. electronics) attached to the grid, power

As the world becomes more electronic, power electronics designers have continuously designed more efficient converters. However, with the rising number of nonlinear loads (i.e. electronics) attached to the grid, power quality concerns, and emerging legislation, converters that intake alternating current (AC) and output direct current (DC) known as rectifiers are increasingly implementing power factor correction (PFC) by controlling the input current. For a properly designed PFC-stage inductor, the major design goals include exceeding minimum inductance, remaining below the saturation flux density, high power density, and high efficiency. In meeting these goals, loss calculation is critical in evaluating designs. This input current from PFC circuitry leads to a DC bias through the filter inductor that makes accurate core loss estimation exceedingly difficult as most modern loss estimation techniques neglect the effects of a DC bias. This thesis explores prior loss estimation and design methods, investigates finite element analysis (FEA) design tools, and builds a magnetics test bed setup to empirically determine a magnetic core’s loss under any electrical excitation. In the end, the magnetics test bed hardware results are compared and future work needed to improve the test bed is outlined.

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Created

Date Created
  • 2019

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Finite element modeling of human brain response to football helmet impacts

Description

The football helmet is a device used to help mitigate the occurrence of impact-related traumatic (TBI) and minor traumatic brain injuries (mTBI) in the game of American football. The current

The football helmet is a device used to help mitigate the occurrence of impact-related traumatic (TBI) and minor traumatic brain injuries (mTBI) in the game of American football. The current design methodology of using a hard shell with an energy absorbing liner may be adequate for minimizing TBI, however it has had less effect in minimizing mTBI. The latest research in brain injury mechanisms has established that the current design methodology has produced a helmet to reduce linear acceleration of the head. However, angular accelerations also have an adverse effect on the brain response, and must be investigated as a contributor of brain injury.

To help better understand how the football helmet design features effect the brain response during impact, this research develops a validated football helmet model and couples it with a full LS-DYNA human body model developed by the Global Human Body Modeling Consortium (v4.1.1). The human body model is a conglomeration of several validated models of different sections of the body. Of particular interest for this research is the Wayne State University Head Injury Model for modeling the brain. These human body models were validated using a combination of cadaveric and animal studies. In this study, the football helmet was validated by laboratory testing using drop tests on the crown of the helmet. By coupling the two models into one finite element model, the brain response to impact loads caused by helmet design features can be investigated. In the present research, LS-DYNA is used to study a helmet crown impact with a rigid steel plate so as to obtain the strain-rate, strain, and stress experienced in the corpus callosum, midbrain, and brain stem as these anatomical regions are areas of concern with respect to mTBI.

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Agent

Created

Date Created
  • 2014