- Dr. Iwona Jasiuk is a professor in the Department of Mechanical Science and Engineering at the University of Illinois... moreDr. Iwona Jasiuk is a professor in the Department of Mechanical Science and Engineering at the University of Illinois at Urbana-Champaign. Dr. Jasiuk’s research interests focus on the mechanics of materials for medical, aerospace, energy, and other technological applications. Her projects address the design, manufacture, characterization, and modeling of composite and nanocomposite materials, architectured materials, and studies of biological and bioinspired materials.edit
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It has recently been shown [1] that fracture response of nominally identical elastic-brittle (epoxy) as well as ductile (aluminum) sheets, each containing randomly distributed circular holes, is non-unique. This non-uniqueness pertains,... more
It has recently been shown [1] that fracture response of nominally identical elastic-brittle (epoxy) as well as ductile (aluminum) sheets, each containing randomly distributed circular holes, is non-unique. This non-uniqueness pertains, in particular, to the resulting fracture patterns and effective stress-strain curves, whereby both of these characteristics display considerable scatter. This result points to the significant influence which microscale random noise in material parameters may have on the global, macroscopic behavior. In this paper we formulate, on the basis of a maximum entropy method [2], a stochastic fracture mechanics model for this class of problems. The method is based on the statistics of experimental data, obtained for a number of specimens, involving the inter-hole crack lengths and their angles. It allows prediction of probability distributions of damage responses and patterns of Gibbs ensembles of random hole systems such as, for example, porous materials with millions of voids.
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Spatial randomness, as opposed to periodic geometries, may have a significant effect on damage formation in composite materials. This issue was studied extensively over the last few years [1, 2, 3, 4], and in this paper we report new... more
Spatial randomness, as opposed to periodic geometries, may have a significant effect on damage formation in composite materials. This issue was studied extensively over the last few years [1, 2, 3, 4], and in this paper we report new results on effects of scale and boundary conditions in the determination of meso-scale continuum-type models for elasticity and fracture. These models are formulated on scales larger than the single inclusion, yet smaller than the conventional continuum limit. The latter corresponds to the classical concept of aRepresentative Volume Element (RVE) which presupposes the presence representation of the microstructure with all the typical microheterogeneities, and thus calls for relatively large volumes. Indeed, according to Hill [5], an RVE should be such that the relations between volume average stress and strain should be the same regardless of whether kinematic or stress boundary conditions have been used.
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Nanofillers with highly anisotropic shapes, such as carbon nanotubes, graphene nanoplatelets, carbon black, and metallic nanowires are used as inclusions in polymer matrix materials to generate nanocomposites with superior electrical,... more
Nanofillers with highly anisotropic shapes, such as carbon nanotubes, graphene nanoplatelets, carbon black, and metallic nanowires are used as inclusions in polymer matrix materials to generate nanocomposites with superior electrical, mechanical, and thermal properties. In this paper, we report on our recent and ongoing studies focusing on the enhanced effective electrical conductivity of such composites. First, we report on Monte Carlo simulations of systems of polydisperse prolate and oblate ellipsoids using the critical path-based tunneling-percolation mode. For polydisperse prolate ellipsoids, the critical percolation volume fraction, c , is shown to have a quasi-universal dependence on the weight-averaged aspect ratio. For polydisperse oblate ellipsoids, c is shown to have a quasi-universal dependence on the apparent aspect ratio, which is a function of up to fourth moment of the size distribution, as given by percolation theory. In both cases, the function approaches the theoretical predictions for higher volume fractions and higher aspect ratios. The model predictions are then compared with experimental data to estimate the tunneling length scale which is found to be within the expected range. Next, we examine the effect of filler alignment on percolation behavior of nanocomposites using Monte Carlo simulations of monodisperse prolate and oblate hard-core soft-shell ellipsoids representing carbon nanotubes and graphene nanoplatelets, respectively. As expected, the percolation threshold is observed to increase with increasing extent of alignment. For a highly aligned system of rod-like fillers, the simulation results are shown to be in good agreement with the second virial approximation-based predictions. However, for a highly aligned system of disk-like fillers, the second virial approximation-based results are observed to significantly deviate from the simulations, even for higher aspect ratios. The anisotropy in percolation threshold is found to vanish with increasing system size even for highly aligned systems of fillers.
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Research Interests: Mechanical Engineering, Biomechanical Engineering, Materials Science, Biomedical Engineering, Finite element method, and 11 moreNanotechnology, Medicine, Finite Element Analysis, Collagen, Stiffness, Mechanical Stress, Rotational Symmetry, Durapatite, Bone and Bones, Collagen Fibril, and Ultimate Tensile Strength
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Research Interests: Plasticity and Biology
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We study the reduced parameter dependence in linear plane Cosserat elasticity with eigenstrains and eigencurvatures. The focus is on singly connected inhomogeneous materials. We find conditions on the eigenstrains and eigencurvatures for... more
We study the reduced parameter dependence in linear plane Cosserat elasticity with eigenstrains and eigencurvatures. The focus is on singly connected inhomogeneous materials. We find conditions on the eigenstrains and eigencurvatures for the planar stress field to be invariant under a shift in area Cosserat compliances. The analysis can be extended to multiply connected inhomogeneous or multiphase materials. The special
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Previous studies show that the properties of parts manufactured via additive manufacturing, such as selective laser melting, depend on local feature sizes like lattice wall thickness and strut diameter. Although size dependence has been... more
Previous studies show that the properties of parts manufactured via additive manufacturing, such as selective laser melting, depend on local feature sizes like lattice wall thickness and strut diameter. Although size dependence has been studied extensively, it was not included in constitutive models for numerical simulations. In this work, flat dog-bone tensile specimens of different thicknesses were manufactured and tested under quasi-static conditions to characterize the size-dependent properties experimentally. It was observed that key mechanical properties decrease with specimen thickness. Through curve-fitting to experimental data, this work provides approximate analytical expressions for the material properties values as a function of specimen thickness, furnishing a phenomenological size-dependent constitutive model. The interpolating capability of the model is cross-validated with existing experimental data. Two numerical examples demonstrate the application of the size-dependent material model. The axial crushing of thin-walled lattices at varying wall thicknesses was simulated by the size-dependent material model and one that ignores size effects. Results show that ignoring size effects leads to overestimated peak crushing force and specific energy absorption. The two material models were also compared in the topology optimization of thin-walled structures. Results show that the size-dependent model leads to a more robust optimized design: having higher energy absorption and sustaining less material fracture.
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Cortical and trabecular bones were modeled as nanocomposite materials with hierarchical structures spanning from collagen-mineral level to cortical and trabecular bone levels. In order to verify theoretical models, compression testing was... more
Cortical and trabecular bones were modeled as nanocomposite materials with hierarchical structures spanning from collagen-mineral level to cortical and trabecular bone levels. In order to verify theoretical models, compression testing was done on cortical and trabecular bovine femur bone samples and the experimental data were compared with the theoretical results. The micro-computed tomography technique was used to characterize the porosities and structures of these bones at different length scales and to provide the inputs needed for the modeling. To obtain more insight on the structure of bone, especially on the interaction of the main constituents (collagen and mineral phases), both cortical and trabecular bone samples were deproteinized and demineralized and, afterwards, tested in compression. This information was used to fine-tune our multi-scale model representing bone as an interpenetrating composite material. Very good agreement was found between the theory and experiments for the elastic moduli of untreated, deproteinized, and demineralized cortical and trabecular bones.
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BACKGROUND AND OBJECTIVE Finite element models built from micro-computed tomography scans have become a powerful tool to investigate the mechanical properties of trabecular bone. There are two types of solving algorithms in the finite... more
BACKGROUND AND OBJECTIVE Finite element models built from micro-computed tomography scans have become a powerful tool to investigate the mechanical properties of trabecular bone. There are two types of solving algorithms in the finite element method: implicit and explicit. Both of these methods have been utilized to study the trabecular bone. However, an investigation comparing the results obtained using the implicit and explicit solvers is lacking. Thus, in this paper, we contrast implicit and explicit procedures by analyzing trabecular bone samples as a case study. METHODS Micro-computed tomography-based finite element analysis of trabecular bone under a direct quasi-static compression was done using implicit and explicit methods. The differences in the predictions of mechanical properties and computational time of the two methods were studied using high-performance computing. RESULTS Our findings indicate that the results using implicit and explicit solvers are well comparable, given that similar problem set up is carefully utilized. Also, the parallel scalability of the two methods was similar, while the explicit solver performed about five times faster than the implicit method. Along with faster performance, the explicit method utilized significantly less memory for the analysis, which shows another benefit of using an explicit solver for this case study. CONCLUSIONS The comparison of the implicit and explicit methods for the simulation of trabecular bone samples should be highly valuable to the bone modeling community and researchers studying complex cellular and architectured materials.
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ABSTRACT High resolution measurements of mechanical properties of the constituent phases of multi-phase materials are of immerse importance in design of new composites. In this study, the nanoindentation, X-ray analysis and... more
ABSTRACT High resolution measurements of mechanical properties of the constituent phases of multi-phase materials are of immerse importance in design of new composites. In this study, the nanoindentation, X-ray analysis and microstructural SEM investigations have been used to reveal the properties and structural features of ceramic – metal composites involving chromium carbide based cermets with different additives (Mo and Cu) in nickel binder. The additives influence microstructural parameters such as grain size and residual stresses; however, nanohardness and Young's moduli of constituent phases remain less affected. Phase – specific mechanical properties are measured and correlated with bulk behaviour. Furthermore, hardness of the binder metal is found to be higher in cermet as compared to the bulk hardness of metal.
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High-resolution measurements of mechanical properties of composites produced by powder metallurgy techniques are of immerse importance for reliable materials production. Measuring the intrinsic properties of each phase separately in... more
High-resolution measurements of mechanical properties of composites produced by powder metallurgy techniques are of immerse importance for reliable materials production. Measuring the intrinsic properties of each phase separately in multiphase composites gives the information on the spatial heterogeneity in local material properties and serves as a guide to process engineering and advanced materials design. In this study, the nanoindentation, X-ray
Research Interests: Materials Science, Powder Metallurgy, Metallurgy, Nanoindentation, Process Engineering, and 13 moreX Rays, Spatial Heterogeneity, Chromium, Composite Material, Materials Design, Ceramic, High Resolution, Phase Separation, Microstructures, Material Properties, Carbide, Modulus of Elasticity, and Mechanical Property
Plastic waste is an outstanding environmental thread. Poly (ethylene terephthalate) (PET) is one of the most abundantly produced single-use plastics worldwide, while its recycling rates are low. In parallel, additive manufacturing is a... more
Plastic waste is an outstanding environmental thread. Poly (ethylene terephthalate) (PET) is one of the most abundantly produced single-use plastics worldwide, while its recycling rates are low. In parallel, additive manufacturing is a rapidly evolving technology with wide-ranging applications. Thus, there is a need for a broad spectrum of polymers to meet the demands of this growing industry and address post-use waste materials. This perspective article highlights the potential of designing microbial cell factories to upcycle PET into functionalized chemical building blocks for additive manufacturing. We present the leveraging of PET hydrolyzing enzymes and rewiring the bacterial C2 and aromatic catabolic pathways to obtain high-value chemicals and polymers. Since PET mechanical recycling back to original materials is cost-prohibitive, the biochemical technology is a viable alternative to upcycle PET into novel 3D printing materials, such as replacements for acrylonitrile butadiene...
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D. Ciprari , I. Jasiuk , R. Tannenbaum, and K. I. Jacob* 1 School of Material Science and Engineering, Georgia Institute of Technology, Atlanta, GA 2 Department of Mechanical Engineering, University of Illinois at Urbana Champaign, IL, 3... more
D. Ciprari , I. Jasiuk , R. Tannenbaum, and K. I. Jacob* 1 School of Material Science and Engineering, Georgia Institute of Technology, Atlanta, GA 2 Department of Mechanical Engineering, University of Illinois at Urbana Champaign, IL, 3 School of Polymer, Textile and Fiber Engineering, and G. W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA, USA karl.jacob@tfe.gatech.edu
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In this study, we examine the effect of filler alignment on percolation behavior of polymer nanocomposites using Monte Carlo simulations of monodisperse prolate and oblate hard-core soft-shell ellipsoids representing carbon nanotubes and... more
In this study, we examine the effect of filler alignment on percolation behavior of polymer nanocomposites using Monte Carlo simulations of monodisperse prolate and oblate hard-core soft-shell ellipsoids representing carbon nanotubes and graphene nanoplatelets, respectively. The percolation threshold is observed to increase with increasing extent of alignment as expected. For a highly aligned system of rod-like fillers, the simulation results are shown to be in good agreement with the second virial approximation based predictions. However, for a highly aligned system of disk-like fillers, the second virial approximation based results are observed to significantly deviate from the simulations, even for higher aspect ratios. The effect of filler alignment on anisotropy in percolation behavior is also studied by predicting the percolation threshold along different directions. The anisotropy in percolation threshold is found to vanish even for highly aligned systems of fillers with incr...
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Summary Keratin is a highly multifunctional biopolymer serving various roles in nature due to its diverse material properties, wide spectrum of structural designs, and impressive performance. Keratin-based materials are mechanically... more
Summary Keratin is a highly multifunctional biopolymer serving various roles in nature due to its diverse material properties, wide spectrum of structural designs, and impressive performance. Keratin-based materials are mechanically robust, thermally insulating, lightweight, capable of undergoing reversible adhesion through van der Waals forces, and exhibit structural coloration and hydrophobic surfaces. Thus, they have become templates for bioinspired designs and have even been applied as a functional material for biomedical applications and environmentally sustainable fiber-reinforced composites. This review aims to highlight keratin's remarkable capabilities as a biological component, a source of design inspiration, and an engineering material. We conclude with future directions for the exploration of keratinous materials.
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We study crack patterns and effective stress-strain response in unidirectional fiber-matrix composites subjected to out-of-plane and in-plane loading. The fibers are aligned in the longitudinal direction and arranged randomly, with no... more
We study crack patterns and effective stress-strain response in unidirectional fiber-matrix composites subjected to out-of-plane and in-plane loading. The fibers are aligned in the longitudinal direction and arranged randomly, with no overlap, in the transverse plane. The fibers and the matrix are isotropic and elastic-brittle, which allows a parametrization of a wide range of composites in terms of a stiffness ratio and a strain-to-failure ratio. The analysis is carried out numerically using very fine two-dimensional spring networks permitting simulation of the crack initiation and propagation by sequentially removing bonds which exceed a local fracture criterion. Particular attention is given to the effects of scale and geometric randomness in these composites. We consider several “windows of observation” (scales) and study crack patterns, types of constitutive responses, and statistics of the corresponding scale dependent effective elastic stiffness and strength of such composites.
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BACKGROUND AND OBJECTIVE Finite element models built from micro-computed tomography scans have become a powerful tool to investigate the mechanical properties of trabecular bone. There are two types of solving algorithms in the finite... more
BACKGROUND AND OBJECTIVE Finite element models built from micro-computed tomography scans have become a powerful tool to investigate the mechanical properties of trabecular bone. There are two types of solving algorithms in the finite element method: implicit and explicit. Both of these methods have been utilized to study the trabecular bone. However, an investigation comparing the results obtained using the implicit and explicit solvers is lacking. Thus, in this paper, we contrast implicit and explicit procedures by analyzing trabecular bone samples as a case study. METHODS Micro-computed tomography-based finite element analysis of trabecular bone under a direct quasi-static compression was done using implicit and explicit methods. The differences in the predictions of mechanical properties and computational time of the two methods were studied using high-performance computing. RESULTS Our findings indicate that the results using implicit and explicit solvers are well comparable, given that similar problem set up is carefully utilized. Also, the parallel scalability of the two methods was similar, while the explicit solver performed about five times faster than the implicit method. Along with faster performance, the explicit method utilized significantly less memory for the analysis, which shows another benefit of using an explicit solver for this case study. CONCLUSIONS The comparison of the implicit and explicit methods for the simulation of trabecular bone samples should be highly valuable to the bone modeling community and researchers studying complex cellular and architectured materials.
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Research Interests: Materials Engineering, Mechanical Engineering, Materials Science, Biomedical Engineering, Viscoelasticity, and 12 moreFinite element method, Medicine, Finite Element Analysis, Humans, Composite Material, Mechanical Stress, Indentation, Elastic Modulus, Cortical Bone, Modulus, Biomechanical Phenomena, and Isotropy
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Of concern is mechanical breakdown, due to spatially evolving microcracking, of two- dimensional composite materials with randomly distributed circular inclusions. While both the matrix and the inclusion materials are described by two... more
Of concern is mechanical breakdown, due to spatially evolving microcracking, of two- dimensional composite materials with randomly distributed circular inclusions. While both the matrix and the inclusion materials are described by two elastic-brittle stress-strain laws, the question is: {open_quotes}what is the effective response law of the composite as a function of the stiffness ratios and strength ratios of both phases as well as of their volume fractions?{close_quotes} Our answers are based on extensive computer simulations of spring networks, see e.g.. Thus, crack formation and propagation is simulated by progressive breaking of bonds, due to stress concentrations, in the large spring network mesh modelling the entire composite system; meshes having tens of thousands of degrees of freedom are being used. Following issues are addressed: (1) strain-dependent patterns of damage evolution; (2) specification of brittle-type, tough-type, and strain-softening response; (3) effective stress-strain curves of random versus hypothetically periodic composites; and (4) statistical scatter of stress-strain curves, and their scale-dependence.