Mechanics of Multi-scale Materials

The Mechanics of Multi-scale Materials research group uncovers the relationships of structures across the full range of engineering scales, from the molecular to the macro. In addition to established practices of nano-scale modeling and large-scale structural mechanics, the group is bridging the gap between these scales by developing accurate constitutive modeling and characterization of each intermediate level.

Uncovering how the nano- and micro-level mechanics play into the millimeter- and meter-level structures enables advanced composite materials to be optimized for structural performance. Through advanced multi-scale modeling, simulation, and experimentation, research is focused on developing methods that will inform emerging technologies including nano-, micro-, and biomedical engineering and science. This research group is well positioned to advance the state-of-the-art in this rapidly emerging field.

Research activities include identifying the critical parameters that lead to the success or failure of material for a particular application and working to model structural foam designs for aerospace and automotive products, with the goal of improving thermal insulation, impact absorption, and moment of inertia.

As functions of intermediate scales between the nano and macro are characterized, novel materials and composites can be created and optimized. Researchers are working on novel experiments, MEMS/NEMS, atomistic and continuum modeling, multifunction materials and devices, microfluidic, tissue engineering, nanostructured material, material characterization, biological transport, cell mechanics, and physics-based modeling.

Faculty + Research = Discovery

Our department boasts world-class faculty who have access to numerous innovative research labs and are committed to discovery and learning. This encompasses a range of research areas, experiences, and expertise related to the mechanics of multi-scale materials. Learn more about our faculty and their research interests:

Research Projects

Our faculty engage in a number of research projects, many of which are publicly funded. A sample listing of recent research projects related to the mechanics of multi-scale materials appears below. You can also view a broader list of research projects taking place across the mechanical engineering department.

Recently Funded Projects

Fundamental Understanding on the Role of Structural Defects on Lithiation of Nanoscale Transition Metal Oxides

Investigators
Principal Investigator: Reza Shahbazian-Yassar
College/School: College of Engineering
Department(s): Mechanical Engineering-Engineering Mechanics

Overview:

Nano-sized transition metal oxides (TMO) are promising materials for lithium-ion batteries. These materials operate through conversion reactions and are associated with much higher energy densities than intercalation reactions. Extensive research is ongoing on the electrochemical characterization of TMO-based electrodes; however, many fundamental questions remained to be addressed. For instance, TMOs exhibit a mysterious extra capacity beyond their theoretical capacity through mechanisms that are still poorly understood. In addition, nano-sized TMOs are highly vulnerable to structural defects produced during synthesis that can alter lithium ion pathways by perturbing the local electronic and lattice strains. No experimental work has been reported to reveal the underlying mechanisms that can correlate structural defects to the electrochemical lithiation in TMOs owing to the difficulty in characterizing structure at the nanoscale, particularly at buried interfaces. This research aims to fill this gap.

The objective is to understand the underlying atomistic mechanisms by which structural defects such as hetrointerfaces, heteroatoms, dislocations, twining, and grain boundaries affect the lithiation behavior of TMOs. In order to meet this objective, single TMO nanowires (NWs) will be subjected to in situ electrochemical lithiation inside high-resolution transmission electron microscope (HRTEM) and aberration-corrected scanning transmission electron microscope (CsSTEM). The in situ electrochemical lithiation will be conducted using state-of-the art scanning tunneling microscope (STM-TEM) and conductive atomic force microscope (cAFM-TEM) holders. This unique combination enables the study of evolution of local lattice strains and electronic perturbations at the vicinity of defects with unprecedented spatial resolutions better than 0.7 A and chemical sensitivity down to 0.35eV.

Intellectual Merit: 

The in situ studies will enable research in three poorly understood fields: (I) the effect of structural defects (twins, dislocations, grain boundaries, and hetrointerfaces) on the nucleation of Li20 and TM particles due to conversion reactions in TMOs; (II) the pinning/unpinning effect of impurities or dopants during grain boundary movement associated with the nucleation of Li20 and TM phases; and (III) the evolution of localized strain and electronic structure at the vicinity of structural defects and their effect on Li-ion pathways The new understanding can facilitate the design of structurally-tailored TMOs for Li-ion battery applications. Furthermore, the experimental methodology and protocols to analyze the in situ data can be extended to other nanomaterials to enable high performance batteries.

Awarded Amount: $445,658

I/UCRC: Novel High Voltage/Temperature Materials and Structures

Investigators
Principal Investigator: Gregory Odegard
College/School: College of Engineering
Department(s): Mechanical Engineering-Engineering Mechanics
Awarded Amount: $637,495

Ongoing Projects

Past Projects

Developing and Deploying Thin Wall Ductile Iron Casting for High Volume Production

Investigators
Principal Investigator: Paul Sanders
Co-Investigator: Gregory Odegard
Co-Investigator: Stephen Kampe
College/School: College of Engineering
Department(s): Materials Science & Engineering,  Mechanical Engineering-Engineering Mechanics

Project Executive Summary:

The ability to cast thin wall ductile iron (DI) castings is critical to leveraging the high stiffness and strength of these materials. Current components often have section sizes thicker than dictated by mechanical requirements due to process and material limitations. By implementing improved methods and alloys, there is potential to decrease wall thicknesses by 50%, thus enabling lightweighting of transportation components by 30%-50% depending on component loading. In addition to geometry optimization, some thin wall applications have shown 10% higher strengths and 100% more elongation compared to standard chemistries and wall thicknesses. This project will focus initially on vertical green sand molding, in which wall thicknesses could be reduced from 3 mm to 1.5 mm. Similar reductions are possible with other molding techniques such as horizontal green sand molding from 6 mm to 2 mm, and the lost foam process from 4 mm to 1.5 mm.

High volume production of thin wall DI castings presents challenges in both metallurgy and processing.

  • DI alloys will need better inoculation practice to control graphite morphology and matrix structure
  • Pearlitic and high silicon, ferritic ductile iron alloys (MRL 4) will be used; compositions may need to be optimized to avoid carbides
  • Sand molding dimensional capability and surface finish require improvement; heat transfer may need better control.
  • Given the thinner walls, shakeout, finishing, machining, and heat treatment processes will have to be fine-tuned
  • In addition to the above manufacturing considerations, design engineers will need updated design rule for thin wall DI castings to take advantage of this lightweighting opportunity. A component case study will be used to quantify weight save.

 This project will focus on the manufacturing process development required to bring thin wall, vertical green sand molded DI castings to high volume production. All parts of the process denoted above have been previously developed; this project will integrate these into a capable production system. After successful implementation, this knowledge will be transferred to horizontal and lost foam molding processes.

Awarded Amount: $472,000

Multiscale Modeling of Polymer Nanocomposites

Investigators
Principal Investigator: Gregory Odegard
College/School: College of Engineering
Department(s): Mechanical Engineering-Engineering Mechanics

Introduction/Synopsis

Polymer-matrix nanocomposites have the potential to become one of the primary structural materials used in future aircraft and spacecraft. High specific-stiffness and specific-strength properties of these materials can be established by using the right combination of polymer matrices, nanostructured reinforcement, matrix/reinforcement interfacial conditions, reinforcement weight fraction, and reinforcement orientation.

This large combination of nanostructural/microstructural material parameters renders the experimental development of these materials to be expensive and time consuming if a trial-and-error approach is used. Fortunately, multiscale computational modeling can be used to facilitate material development through the prediction of structure-property relationships that are efficient and accurate.

While a significant effort has been put forth by numerous researchers to predict bulk-level mechanical properties of crystalline materials (e.g. metals, ceramics) and other highly-ordered systems (e.g. carbon nanotubes) based on molecular structure, very little attention has been paid to amorphous polymer systems. However, an equivalent-continuum modeling method has been established to predict the macroscopic Young's modulus of polymers and polymer nanocomposites based on polymer type, reinforcement geometry, and polymer/reinforcement conditions using a simple, efficient, and accurate modeling approach. Recently, this approach was improved by placing it within a thermodynamic framework. As a result, the equivalent-continuum modeling method can now predict bulk mechanical properties, such as strength and Young's modulus, of polymer nanocomposites as a function of molecular structure in a manner that is thermodynamically consistent and accurate.

Objectives

The overall goal of the research is to use multiscale modeling to establish structure-property relationships for polyimide nanocomposites. Molecular- and rnicrostructural characteristics of these materials will be related to tl1e predicted mechanical properties. Specifically, the following nanocomposite materials systems will be studied:

• Polymer matrix materials

  1. ULTEM
  2. sp;         LaRC-8515

• Reinforcement materials

  1. SWNTs
  2. Graphene oxide sheets

The structure-property relationships will relate the following structures and mechanical properties:

• Molecular- and micro-structural parameters

  1. Polymer matrix material type
  2. Reinforcement material type
  3. Matrix/reinforcement interface conditions
  4. Reinforcement weight fraction
  5. Reinforcement orientation
  6. Reinforcement size

• Bulk-level mechanical properties

  1. Young's modulus
  2. Strength (onset of microvoid formation)

The overall objective of establishing the structure-property relationships will be achieved with the following series of tasks:

• Task 1: Establish a series of equilibrated molecular structures for different combinations of matrix and polymer materials and a range of interfacial conditions using MD-based techniques

• Task 2: Predict the molecular-level Young's modulus and the onset of mechanical failure for these materials systems using MD-based techniques

• Task 3: Construct a series of micromechanical models that incorporate the results of Task 2 and predicts the bulk-level stiffness and strength for a range of reinforcement weight fractions, orientations (randomly dispersed, aligned), and size (length, diameter)

Awarded Amount: $266,818

New Insights on High Performance Anodes for Lithium-Ion Batteries

Investigators
Principal Investigator: Reza Shahbazian-Yassar
College/School: College of Engineering
Department(s): Mechanical Engineering-Engineering Mechanics

Abstract:

To obtain a noticeable improvement in the specific capacity of current Li-ion batteries (graphite anodes, capacity of 372 mAhg-1), it is essential to increase the capacity of the anodes. The most attractive candidate is silicon which has the highest known capacity, in excess of 4000 mAhg-1. A major drawback with silicon is that upon driving Li into Si, large mechanical stresses develop in Si that lead to fracture and pulverization of Si and, eventually, capacity fade. It appears that the mechanistic and structural details regarding the lithiation/ delithiation degradation of Si nanostructures are not well understood. This research aims to fill this gap.

The objectives are to understand:

    (i) The pulverization mechanics and the correlation with LixSi phase transformations in Si NRs;

    (ii) The role of size-scale and crystallography on Li insertion/ extraction;

    (iii) Degradation of =rent collector-NR interface during lithiation/ delithiation cycles.

The Li insertion/ extraction studies conducted in real time by using a novel in-situ electrochemical setup that operates inside a chamber of a transmission elech•on microscope (TEM). Ionic liquids are used as the Li-enriched media and nanorods are subjected to electrical potential using a scanning probe microscopy (STM and AFM) inside TEM. The mechanics of lithiated/ delithiated NRs and the strength of their interface with current collector is also being studied. The experimental methodology and protocols to analyze the data are not limited to Si nanorods and can be extended to other nanomaterials with potential to be used as anodes in lithium-ion batteries.

Awarded Amount: $154,000

Revealing the Inside of a Nanoscale Na-ion Battery: New Understanding on Sodium Intercalation in Cathodes

Investigators
Principal Investigator: Reza Shahbazian-Yassar
College/School: College of Engineering
Department(s): Mechanical Engineering-Engineering Mechanics

Introduction

While tremendous research is focused on lithium-ion batteries worldwide, scientific challenges associated with room-temperature rechargeable sodium-ion batteries, the next alternative for Li-batteries, have been relatively unexplored. These challenges are much more complicated than the Li-ion case. Na+ is larger than Li+ by 70%, which induces huge mechanical stresses upon driving the Na-ion into the host electrode. Na+ is chemically more reactive than Li, thus, sodium intercalation triggers multiphase reactions that remain to be identified. The sodium intercalation/ deintercalation process, therefore, leads to series of coupled electrochemically-driven mechanical instabilities, electrical conductivity degradation, and complex phase transformations that reduce the battery life drastically. In spite of this scientific complexity, a glance through the list of active awards in NSF website shows that there have been more than 30 recent awards to

Li-ion battery research while this has been almost none for Na-ion batteries. Thus, the field of room-temperature rechargeable Na-ion battery research is thriving for federal support to overcome these obstacles and make a viable alternative technology to Li-ion batteries. This is of prime importance considering that Li resources are very limited and their price has increased continuously during the past 20 years.

The objective of this research is to understand the underlying mechanisms behind the Na intercalation/ deintercalation in cathode electrodes and tailoring the electro-mechanical degradation of cathodes in nanoscale rechargeable Na-ion battery cell. The nano-battery is composed of ionic liquids as electrolyte, anode (Na metal), and cathode (manganese oxide nanowires). The manganese oxide electrode will be subjected to electrochemical probing using a conductive atomic force (AFM) and scanning tunneling microscopy (STM) that operate inside transmission electron microscope (TEM). The proposed research project aims to bring new ideas and momentum to the field of Na-ion battery research.

Intellectual Merit: 

The in-situ studies will enable research in four relatively unexplored fields: (i) The correlation of failure instabilities and loss of electrical conductivity with multi-phase transformations induced by sodiation/ desodiation; (ii) The role of diameter (surface effect) and crystallography of host electrodes on Na-ion intercalation/ deintercalation mechanisms; and (iv) Investigating the Na-dendrite fiber formation and possible safety concerns. The new understanding can facilitate the design of safer and higher capacity cathode electrodes in future rechargeable Na-ion batteries.

The experimental methodology and protocols to analyze the data are not limited to manganese oxide nanowires and can be extended to other nanomaterials (both for anodes and cathodes) to enable new technologies in rechargeable Na-ion batteries.

MRI: Acquisition of a High Resolution Transmission Electron Microscope for In Situ Microscopy Research and Education

Investigators
Principal Investigator: Reza Shahbazian Yassar
Co-PI: Stephen Hackney
Co-PI: Claudio Mazzoleni
Co-PI: Tolou Shokuhfar
Co-PI: Yoke Khin Yap
College/School: College of Engineering
Department(s): Mechanical Engineering-Engineering Mechanics
Awarded Amount: $1,736,592

Microsensor for Intramuscular Pressure Measurement

Investigators
Principal Investigator: Gregory Odegard
College/School: College of Engineering
Department(s): Mechanical Engineering-Engineering Mechanics

Interpretation of data that is computationally-generated at Colorado State University (CSU) and Mayo Clinic as part of the newly-funded NIH program for the development and testing of the intramuscular pressure sensor. Consultation and direct interaction with researchers participating in the computational simulation of skeletal muscle. Dr. Odegard has a unique set of skills in continuum mechanics modeling of materials that will be useful for the successful completion of the overall project.

Awarded Amount: $50,314

Multiscale Model Development and Validation of Graphene/ULTEM Composites for Structural and Noise Reduction Applications

Investigators
Principal Investigator: Gregory Odegard
Co-Investigator: Julia King
Co-Investigator: Warren Perger
College/School: College of Engineering
Department(s): Chemical Engineering,  Electrical & Computer Engineering,  Mechanical Engineering-Engineering Mechanics

Polymer composite materials have become a staple in the design, development, and manufacturing of commercial, military, and research aircraft. Because of their relatively high mechanical properties {per unit mass) they are used as the main structural components in fuselages and control surfaces in many subsonic fixed-wing aircraft. In order to continue to make improvements in aircraft safety, efficiency, and comfort; composites with increased functionality must be developed. Traditionally, a time-consuming trial-and-error approach has been employed 'with the development of polymer composite materials until an acceptable material that meets the design requirements has been found. The development process is further complicated 'with the inclusion of nanoparticles into traditional composite materials {either as a matrix-doping agent or as the primary reinforcement). Because of the small size of nano-reinforcements, the physical basis for observed material behavior cannot always be ascertained through experimental means. Multiscale modeling approaches, which have gained considerable interest in the last decade, can be used to facilitate traditional research by removing these barriers. Thus, coupling multiscale modeling and experiments can increase the rate of materials development and provide physical insight into observed material behavior.

The objective of this research is to develop a multiscale modeling approach to predict the mechanical and acoustic absorption properties of nanocomposite materials as a function of material structure. The model will be validated using experimental tests on the modeled material. The modeled material will be a hybrid composite composed of graphene nanoplatelets, traditional carbon fibers, and a Polyetherimide polymer (ULTEM). The graphene nanoplatelets will be dispersed into the ULTEM polymer to form a nanocomposite material. This nanocomposite will be used as the matrix component of a traditional 'woven fabric composite with curb on fiber. Because graphene has been shown to exhibit sound-absorbing capabilities and improved mechanical properties when used in composite materials, it is anticipated that the hybrid composite will have good overall mechanical and acoustic damping properties. This material could potentially be used in aircraft structures, included the fuselage, for mechanical durability and reduced cabin noise.

The research is broken up into three specific tasks. For the first task, a multiscale modeling technique will be established to predict the bulk-level 1nechanical and acoustic absorption properties of carbon fiber/graphene/ULTEM composites. This modeling strategy will incorporate molecular dynamics simulation, micromechanics analysis, and the Fiber Undulation Model to relate molecular structure to bulk-level properties of the composite. For the second task, composite test specimens will be fabricated and tested to determine the elastic and acoustic absorption properties of the material. This data will be used to validate the modeling strategy. The third task will focus on the development of simple structure-property relationships using the validated modeling approach. The resulting structure-property maps will serve as design guides materials researchers and engineers involved in materials selection.

As a result of this study, an efficient and accurate multiscale modeling approach will be developed 'which can be easily adapted by other researchers to continue the development of materials used for aerospace structures. Also, the model \Viii be experimentally validated and used to establish structure-property relationships for a hybrid carbon fiber/graphene/UL TEM composite which have the potential to improve mechanical properties and noise-reduction capabilities for aerospace structures.

Awarded Amount: $354,693

Multiscale Modeling of Grahite/CNT/Epoxy Hybrid Composites

Investigators
Principal Investigator: Gregory Odegard
College/School: College of Engineering
Department(s): Mechanical Engineering-Engineering Mechanics
Awarded Amount: $252,555

New Sulfur-Carbon Cathode Material with Improved Electrochemical Performance

Investigators
Principal Investigator: Reza Shahbazian-Yassar
College/School: College of Engineering
Department(s): Mechanical Engineering-Engineering Mechanics

Abstract

The goal of this research is to improve the current Lithium-Sulfur Batteries. Li-ion batteries have improved in performance, reliability and safety. Lithium-sulfur batteries have a high theoretical capacity (1672 mAh/g) and energy density (2500 Wh/kg), which, along with low cost and toxicity, makes them an excellent candidate for applications ranging from consumer electronics to electric vehicles. This has created opportunities for new applications such as in electric and hybrid vehicles. These applications to such a large-sized device require larger capacity and better durability, and an increase in the capacity of the anode material could be very effective in raising the specific energy of Li-ion batteries. Thereafter, improving the lithium sulfur battery cycling performance could double the current LIB technology.

In order to understand the causes of Lithium-Sulfur Batteries failure when it is cycled for hundreds of cycles, investigation will focus on lithium insertion in sulfur with in situ transmission electron microscopy (TEM). This will help identify small modification in a local area of the cathode before its generation. To date no in situ (TEM) or in situ atomic force microscopy (AFM) studies on Li-S batteries have been reported in the literature. The only in situ structural characterization experiments on Li-S batteries that are reported are based on X-ray experiments.

Objective and Method: The objective of this research is to understand the electrochemically induced polysulfide phase formations and degradation mechanisms in cathode electrodes for  Li-S batteries. In order to meet this objective, novel cathode materials (carbon fibers with encapsulated sulfur) subjected to in situ electrochemical testing inside high-resolution TEM (HRTEM), aberration-corrected scanning transmission electron microscope (Cs-STEM), and AFM. This unique combination enables the study of evolution of local lattice strains and electronic perturbations in the cathode materials with sensitivity to single atoms. This fundamental research yield new understandings on the electrochemical performance of cathode materials in Li-S batteries and will pave the roadmap for developing batteries that surpass current Li-ion batteries.

Awarded Amount: $42,367
Keywords: Lithium-Sulfur Batteries, Electrochemical,