George Z. Voyiadjis

• D.Eng.Sc. (Engineering Mechanics), May 1973, Columbia University, New York, New York
• Louisiana State University

A mathematical formulation incorporating the relationship between the damage tensor, healing tensor, and fabric tensors is presented. This formulation provides for a direct link between the subjects of Damage and Healing Mechanics using Fabric Tensors. A new damage-healing tensor is introduced that is based on the fabric of the material. This new t...

The areas where the weld line is located are weak areas in terms of impact strength and tensile strength, which negatively affects the overall strength of the final product. It can also cause visual defects on the surface and create an aesthetically undesirable situation. The injection molding process introduces anisotropic behaviors in materials,...

The crashworthiness of electric vehicles depends on the response of lithium-ion cells to significant deformation and high strain rates. This study thoroughly explores the mechanical behavior due to damage of lithium-ion battery (LIB) cells, focusing on Lithium Nickel Manganese Cobalt Oxide (NMC) and Lithium Iron Phosphate (LFP) types during both qu...

The mechanisms of tool‒rock frictional contact are reviewed, with a focus on recent advances in numerical modeling. An idealized problem is defined for tool‒rock frictional contact with a rigid blunt tool sliding on the surface of a half-space. The governing dimensionless parameters are summarized for rocks characterized by various rock material mo...

The mechanism is investigated for frictional contact between a wear flat and rocks. A brief review focuses on the governing parameters of frictional contact on different types of rocks. Anisotropic damage is taken into account using an anisotropic elasto-plastic-damage model, as demonstrated by a single-element test in uniaxial compression. Anisotr...

The mechanism of frictional contact is investigated between a blunt tool and quasi-brittle rocks with anisotropic damage. A recently developed anisotropic elasto-plastic-damage model is further validated using experimental results under monotonic and cyclic loadings for rocks and concrete. A finite element model of tool-rock frictional contact is v...

A constitutive model for C45 steel alloys is proposed in this work by integrating the effect of damage and a specific phenomenon, so-called dynamic strain aging. For damage modeling, an energy-based isotropic damage model is implemented within a frame of continuum damage mechanics. The total stress is decomposed into athermal and thermal elements....

Dynamic Strain Aging (DSA) is a sudden increase in the strength of a material under certain combinations of temperatures and strain rates. Despite the phenomenon being reported in several other studies, the literature still lacks a specific constitutive model that can physically interpret its effect. Therefore, this work proposes a modification ba...

Interferometric Synthetic Aperture Radar (InSAR) techniques can be used to derive spatially dense “relative” measurements of vertical land motion (VLM), whereas Global Navigation Satellite System (GNSS) provides point-based “absolute” measurements of VLM. The combination of GNSS and InSAR observations can yield spatially dense VLM measurements in a...

The paper explores plastic deformation mechanisms in metal–graphene nanocomposites, illustrating their material strengthening effects through a crystal plasticity finite element (CPFE) model. This model is compared with published experimental results, which have previously shown that the two-dimensional shape of graphene effectively controls disloc...

In recent years the design and performance of aerospace vehicles changed due to enhancement and improvement in the design and the materials employed. Special consideration has to be given to the performance of the materials chosen for such vehicles. Titanium matrix composites (TMC) have been identified among the metal matrix composites as candidate...

This study proposes a novel approach to convert the load–depth curve measured in the experimental indentation test into stress–strain curves. Due to the lack of the tensile test results for the cylindrical lithium-ion battery (LIB) cell, a combination of the analytical analysis and the inverse optimization approach is first conducted as a reference...

Damage healing mechanics has been under tremendous development during the past decade in which many constitutive models for different classes of materials have been proposed in the literature. However, to bridge the gap between the physics of healing and the theoretical framework, the statistical nature of the damage healing mechanics must be consi...

Mechanical internal short circuit (ISC) is one of the significant safety issues in lithium-ion battery design. As a result, it is possible to subject LIB cells to thorough mechanical abuse tests to determine when and why failure may occur. The indentation test is a recommended loading condition for evaluating mechanical damage and ISC. In this stud...

Constitutive description of the plastic flow in metallic foams has been rarely explored in the literature. Even though the material is of great interest to researchers, its plasticity remains a topic that has a much room for exploration. With the help of the rich literature that explored the material deformation mechanism, it is possible to introdu...

A comprehensive review of destructive testing techniques to understand concrete behavior is presented in this work. The main objective of this article is to summarize the literature from the last three decades related to the following topics: 1) the size effect in plain and reinforced concrete, 2) the crack estimation and propagation in concrete un...

This work discusses the combined effect of the microstructure and geometry on the deformation modes and energy-absorbing characteristics of laser powder bed fusion (LPBF)-manufactured Inconel 718 (IN718) hexagonal honeycomb structures tested under quasi-static compression. Three different geometries of the hexagonal cells, varying only in the cell...

One of the most effective ways to increase the longevity of pavement structures is through the integration of geosynthetic reinforcement. Geosynthetics are synthetic materials such as geotextiles, geogrids, or geocomposites that are added to the interface between the subgrade and the base layer of a pavement structure. To evaluate the effect of var...

The development of the theories of undamageable materials and bimodal self-regenerating materials leads directly to four-dimensional materials. Both are types of sought after materials. The authors have established that undamageable materials are the limit of Voyiadjis-Kattan materials of order n as n approaches infinity. Similarly, the authors est...

In this study, a unified p–y curve model is developed for clays in undrained conditions using the results of 3D finite element (FE) modeling. The p–y curves are primarily used in the analysis of laterally loaded piles. Formulas for the ultimate lateral bearing capacity factor (Np), and the reference deflection in the p–y curve (y50), were obtained...

The GTN micromechanical fracture model is frequently used to predict the ductile fracture. This model is based on the microscopic mechanism of void nucleation, growth and coalescence in ductile material. GTN model includes many parameters that need to be precisely calibrated in order to obtain the maximum accuracy. In this study, an indirect approa...

Traditional lithium-ion battery (LIB) research often overlooks a crucial factor - the mechanical stress-induced degradation of LIB components. In this groundbreaking study, we introduce a novel damage model to comprehensively assess the structural wear and tear within LIB cells. Our approach employs an advanced elastoplastic constitutive model with...

This paper investigates experimentally the thermomechanical response of 42CrMo steel under several combinations of temperatures and strain-rate. To characterize the flow stress of this highstrength 42CrMo steel, two distinct test configurations were utilized. The first consisted of conventional uniaxial tensile tests conducted at room and elevated...

In this paper, the effect of Ti-rich areas on the fracture of NiTi alloys has been studied. To carry out this investigation, a series of experimental tests, as well as numerical analyses are conducted. In the experimental plan, NiTi smooth and notched bars with various notch sizes are subjected to tensile load until fracture. Moreover, the correspo...

A new nonlocal crystal plasticity model is developed to study the mechanical behavior of face-centered cubic single crystals under heterogeneous inelastic deformation through a crystal plasticity finite element method. The main feature of this work is generalized constitutive relations that incorporate the thermally activated and drag mechanisms to...

SELECTIVE LASER MELTING OF A HIGH PRECISION TURBOMACHINERY APPLICATION IN IN718 ALLOY

In this study, a 3-D finite element (FE) analysis was used for estimating the lateral capacity of piles driven in sand soils. The effects of different properties of the sand on the p-y curves were studied. Using the results of FE analysis, a model for predicting p-y curves for sandy soils was developed based on the pile shape, which is a combinatio...

Finite element (FE) models were developed to evaluate the benefits of geosynthetic reinforcement in flexible pavements built over weak subgrades. The parametric study was conducted to evaluate the effect of different variables such as base thickness, geosynthetic type, geosynthetic stiffness, and double-geogrid layers. FE analyses were performed fo...

In the past few decades, extensive research on concrete modeling to predict behavior, crack propagation, microcrack coalescence by utilizing different approaches (fracture mechanics, continuum damage mechanics) were investigated theoretically and numerically. The presented paper aims to review the theoretical work of continuum concrete damage and p...

An anisotropic elasto-plastic-damage model is developed for quasi-brittle materials within the thermodynamics framework. The anisotropic damage is characterized by second-order damage tensors that are different under tensile and compressive loadings. The hypothesis of strain energy equivalence is adopted with two components, including the hypothesi...

In this part II, companion article, we present the numerical review of continuum damage mechanics and plasticity in the context of finite element. The numerical advancements in local, nonlocal, and rate-dependent models are presented. The numerical algorithms, type of elements utilized in numerical analysis, the commercial software’s or in-house co...

Grain boundary strengthening effect for polycrystalline copper is studied numerically using crystal plasticity in conjunction with cylindrical indentation simulations under the plane strain condition. In order to compare with an isotropic, heterogeneous continuum model a new constitutive relation is developed. This new nonlocal continuum model that...

In the presented work, a nonlocal gradient enhanced damage model for concrete is proposed with a stress decomposition, to account for shear induced damage. The nonlocal model is an extension of the recently proposed local plasticity damage model by the authors, which can handle directional dependency of damage, pure shear and biaxial damage, damage...

The mechanical behavior of Martensitic Microcomposite Formable Steel alloy for a wide range of temperatures from room temperature to 923 K and strain rates from 0.0015 s⁻¹ to 500 s⁻¹ is investigated focusing on the effect of dynamic strain aging. A new constitutive model including an additional flow stress component due to the dynamic strain aging...

Nanoporous gold (NP-Au) is of great interest to researchers due to its high surface area; and accordingly, the wide range of applications that the material can be utilized for especially those where high temperature is involved. Therefore, the effect of temperature on NP-Au is studied by performing Molecular Dynamics (MD) simulations at temperature...

The microstructure and mechanical hardness of Inconel 718 (INC718) hexagonal honeycomb cellular structure manufactured by Selective Laser Melting (SLM) was studied in this work. Non-heat-treated SLM-produced samples with cell wall thicknesses of 0.4, 0.6 and 0.8 mm were studied. The hardness was measured using MTS Nanoindenter. For room temperature...

In this study, the effect of the macro-scale mechanical deformation on the nanostructure of glassy polymers is investigated by scrutinizing the alteration of their nanoscale mechanical response. Nanoindentation technique was used to measure the mechanical properties of the polycarbonate and poly(methyl methacrylate) specimens which were subjected t...

Slip and extension twinning are the dominant deformation mechanisms in Magnesium (Mg) and its alloys. Crystal plasticity is a powerful tool to study these deformation mechanisms. Different schemes have incorporated crystal plasticity models to capture different properties, which vary from the simple homogenization Taylor model to the full-scale cry...

Rock cutting with a blunt cutter includes a cutting process and a frictional contact process. The understanding is still fragmentary for the frictional contact process, with a gap between experimental tests conducted on quasi-brittle rocks and previous numerical and analytical analyses on elastoplastic rocks. This study aims to reduce the gap using...

While several studies assessed the behavior of nanoporous gold (NP-Au) under different loading conditions for various material characteristics and loading scenarios, very limited attention was given to the effect of strain rate on material response. In this study, the effect of strain rate is investigated by performing novel atomistic simulations o...

Significant attention in the literature is directed towards the development of scaling relations that relate the properties of nanoporous metals to bulk materials in order to help in their design. Although nanoporous gold has been under extensive study to develop the proper scaling relations, the literature still lacks a specific model that predict...

In this work, a new damage model for concrete is proposed with an extension of the stress decomposition (limited to biaxial cases), to capture shear damage due to the opposite signed principal stresses. To extract the pure shear stress, the assumption is made that one component of the shear stress is a minimum absolute of the two principal stresses...

The rate-dependent mechanism is analyzed for frictional contact between a blunt tool and a fluid-infiltrated porous rock under pressurized condition. The dimensional analysis is adopted to derive a dimensionless number \(\lambda\) that predominantly governs the rate-dependent mechanism from pore pressure diffusion. The governing nature of \(\lambda...

A 2-D finite flement model was developed in this study to conduct a FE parametric study on the effects of some variables in the performance of geosynthetic reinforced soil integrated bridge system (GRS-IBS). The variables investigated in this study include the effect of internal friction angle of backfill material, width of reinforced soil foundati...

A robust mathematical method for the characterization of damage in carbon nanotubes is presented the presentation here is limited to elasticity. In this regard, the second and third order elastic stiffnesses are employed. All this is based on damage mechanics. The hypotheses of elastic strain equivalence and elastic energy equivalence are utilized....

Nanoporous (NP) metals with ligament sizes up to a few tens of nm show exceptional mechanical properties such as high strength and stiffness per weight. While their elasticity and yield strength have been the subject of numerous studies, less is known about the plastic deformability of these materials under large compressive and tensile strains. In...

In this work a considerable development of the time-fractional damage model for hyperelastic body is presented. The novel model is implemented for full spatial configuration (AceFEM software). A patient-specific 3D computational model is elaborated to mimic the abdominal aortic aneurysm (AAA) phenomena. The considerations include the initial spatia...

In this paper the homogeneity and isotropy of the mechanical hardness of thin-walled Inconel 718 (IN718) alloy samples manufactured by Selective Laser Melting (SLM) were examined using nanoindentation testing. SLM-produced honeycombed samples with wall thicknesses of 0.8, 0.6 and 0.4 mm respectively were studied by measuring the hardness across the...

Cylindrical indentation into polycrystalline copper is studied experimentally using a split-specimen configuration that induces plane strain deformation to a very good approximation. The displacement field is determined by comparing a 5μm pitch grid in the deformed and reference configurations. The deformation gradient tensor is calculated along wi...

In this work, a thermodynamically consistent constitutive formulation for the coupled thermomechanical strain gradient plasticity theory is developed in the context of the finite deformation framework. A corresponding finite element solution is presented to investigate the microstructural features of metallic volumes. The developed model is establi...

Dynamic strain aging hugely affects the microstructural mechanical behavior of metallic materials when activated. It has been extensively reported in the literature that the dynamic strain aging causes significant gaps between model predictions and experimental measurements. Without considering this phenomenon, a constitutive model is unable to acc...

This paper presents an analytical prediction coupled with numerical simulations of a split Hopkinson pressure bar (SHPB) that could be used during further experiments to measure the dynamic compression strength of concrete. The current study combines experimental, modeling and numerical results, permitting an inverse method by which to validate mea...

Molecular dynamics simulations and first-principles calculations are carried out on first order pyramidal plane (π1) of magnesium to study both compression twinning (CTW) and dislocation slip. To this end, a generalized stacking fault energy analysis is employed on dense (π1D) and loose spaced (π1L) π1 planes. The crystal shearing resistance is ext...