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Papers by Mehrdad Negahban

Research paper thumbnail of Improved Methodologies in Modeling and Predicting Failure in AASHTO M-180 Guardrail Steel Using Finite Element Analysis - Phase I

Research paper thumbnail of Negahban Group Report: Saw-tooth shear response of aged poly(methyl methacrylate) (PMMA)

Group Report: Saw-tooth shear response of aged poly(methyl methacrylate) (PMMA)" (2017). Abs... more Group Report: Saw-tooth shear response of aged poly(methyl methacrylate) (PMMA)" (2017). Abstract: Results for isothermal saw-tooth shear loading experiments conducted on annealed and oven-cooled poly(methyl methacrylate) (PMMA) at temperatures between 50 o C and 140 o C. The experiments were conducted 1996.

Research paper thumbnail of Wedges and screws

Research paper thumbnail of The Mechanical and Thermodynamical Theory of Plasticity

The Mechanical and Thermodynamical Theory of Plasticity, 2012

ABSTRACT Born out of 15 years of courses and lectures on continuum mechanics, nonlinear mechanics... more ABSTRACT Born out of 15 years of courses and lectures on continuum mechanics, nonlinear mechanics, continuum thermodynamics, viscoelasticity, plasticity, crystal plasticity, and thermodynamic plasticity, The Mechanical and Thermodynamical Theory of Plasticity represents one of the most extensive and in-depth treatises on the mechanical and thermodynamical aspects of plastic and visicoplastic flow. Suitable for student readers and experts alike, it offers a clear and comprehensive presentation of multi-dimensional continuum thermodynamics to both aid in initial understanding and introduce and explore advanced topics. Covering a wide range of foundational subjects and presenting unique insights into the unification of disparate theories and practices, this book offers an extensive number of problems, figures, and examples to help the reader grasp the subject from many levels. Starting from one-dimensional axial motion in bars, the book builds a clear understanding of mechanics and continuum thermodynamics during plastic flow. This approach makes it accessible and applicable for a varied audience, including students and experts from engineering mechanics, mechanical engineering, civil engineering, and materials science.

Research paper thumbnail of Preliminary results on an effort to characterize thermo-mechanical response of amorphous polymers in the glass-transition range

Research paper thumbnail of Current research in the thermo-mechanics of polymers in the rubbery-glassy range, 1995: presented at the 1995 Joint ASME Applied Mechanics and Materials Summer Meeting, Los Angeles, California, June 28-30, 1995

Research paper thumbnail of Results of implementing a computer-based mechanics readiness program in statics

Research paper thumbnail of Thermodynamic Modeling of Crystallization in Polyethylene for use in the Simulation of Rotational Molding

Research paper thumbnail of Shape Recovery in Glassy Polymers

Research paper thumbnail of A Thermodynamic Theory for Characterizing Thermo-Mechanical Response of Polymers During Crystallization

Research paper thumbnail of A study of statistical mechanics of long-chain molecules and its role in the determination of the characteristics of crystallizing polymers

Research paper thumbnail of Optimization of the distribution of properties: Using acrylate/epoxy mixtures in the extension of an FGM plate with a hole

We looked at optimization of property distribution in parts. As it will be shown, by changing the... more We looked at optimization of property distribution in parts. As it will be shown, by changing the distribution of material properties, one can make an inhomogeneous part that is better than the best uniform part. To demonstrate this, we looked at optimizing the distribution of properties in a plate with a hole that is under uniaxial extension. In this problem, for a uniform plate the hole creates a stress concentration that limits the maximum applied stress on the plate to one third the load carrying capacity of the material. We show that for real materials one can select material distributions that allows applied stresses close to the maximum capacity of the best material (i.e. 3 times the load carrying capacity of the best uniform plate with a hole). An acrylate/epoxy IPN plate with a hole was selected for the investigated. We modeled, as a function of each components concentration, the real characterized values of the Young’s modulus, Poisson’s ratio and fracture strength. A fini...

Research paper thumbnail of Modeling the thermomechanical effects of crystallization in natural rubber: I. The theoretical structure

International Journal of Solids and Structures, 2000

Research paper thumbnail of Single and multiple material constraints in thermoelasticity

Mathematics and Mechanics of Solids, 2006

Constraints on the possible forms of material response, such as incompressibility or inextensibil... more Constraints on the possible forms of material response, such as incompressibility or inextensibility, have long been used to simplify constitutive response models, and have resulted in substantial progress in fields such as fluid mechanics and the mechanics of composite materials. A method of imposing these constraints for thermoelastic materials is considered that follows steps that remove the need for assuming an additive term resulting from the constraint. In the process, three methods are considered for the separation of the constitutively prescribed part of the response from the part that is in reaction to the constraints. Both the case of single and multiple constraints are considered with extensive examples including special considerations for including effects associated with isotropic or anisotropic thermal expansion.

Research paper thumbnail of Theoretical Simulation of an Anomalous Response in a Torsional Oscillator

Journal of Applied Mechanics, 1994

In a torsional oscillator, constructed by stretching a hollow cylindrical natural rubber member a... more In a torsional oscillator, constructed by stretching a hollow cylindrical natural rubber member and connecting one end to a fly wheel and the other end to a fixed support, an anomalous behavior has been experimentally observed which is attributed to crystallization in the rubber. The anomalous behavior is observed when the rubber is stretched to more than 3.5 times its initial length and is characterized by a reduction in the period of the oscillator during stress relaxation. This indicates a gradual increase in the torsional rigidity of the rubber which can be explained by crystallization. Analyzing the response of the oscillator based on modeling the rubber as an incompressible isotropic elastic or viscoelastic material predicts a behavior opposite to that observed in the experiments. Using a model developed for characterizing mechanical response during crystallization in polymers, the anomalous behavior of the oscillator is reproduced.

Research paper thumbnail of A study of thermodynamic restrictions, constraint conditions, and material symmetry in fully strain-space theories of plasticity

International Journal of Plasticity, 1995

Research paper thumbnail of Thermodynamic modeling of the thermomechanical effects of polymer crystallization: A general theoretical structure

International Journal of Engineering Science, 1997

A general theoretical structure is developed based on continuum thermodynamics to model the therm... more A general theoretical structure is developed based on continuum thermodynamics to model the thermomechanical effects of polymer crystallization. This phase transition, seen in many polymers, involves the gradual transformation of the polymer's microstructure from an unorganized amorphous structure to that of a much more rigid semi-crystalline structure. This smooth transition is captured by a set of integral models which obtain the response by averaging the apparent response of the amorphous portion and a continuum of different crystals. A commonly used empirical relation between the extent of crystallization and volume change is imposed as a restriction on the material, and the implication of the entropy production inequality in the presence of this constraint is evaluated. General representations are provided.

Research paper thumbnail of Structural periodicity dependent scattering behavior in parity-time symmetric elastic metamaterials

Research paper thumbnail of Asymmetric viscoelastic metamaterials for broad bandgap design and unidirectional zero reflection

Mechanical Systems and Signal Processing

Research paper thumbnail of Extremely thin reflective metasurface for low-frequency underwater acoustic waves: Sharp focusing, self-bending, and carpet cloaking

Journal of Applied Physics, 2021

Research paper thumbnail of Improved Methodologies in Modeling and Predicting Failure in AASHTO M-180 Guardrail Steel Using Finite Element Analysis - Phase I

Research paper thumbnail of Negahban Group Report: Saw-tooth shear response of aged poly(methyl methacrylate) (PMMA)

Group Report: Saw-tooth shear response of aged poly(methyl methacrylate) (PMMA)" (2017). Abs... more Group Report: Saw-tooth shear response of aged poly(methyl methacrylate) (PMMA)" (2017). Abstract: Results for isothermal saw-tooth shear loading experiments conducted on annealed and oven-cooled poly(methyl methacrylate) (PMMA) at temperatures between 50 o C and 140 o C. The experiments were conducted 1996.

Research paper thumbnail of Wedges and screws

Research paper thumbnail of The Mechanical and Thermodynamical Theory of Plasticity

The Mechanical and Thermodynamical Theory of Plasticity, 2012

ABSTRACT Born out of 15 years of courses and lectures on continuum mechanics, nonlinear mechanics... more ABSTRACT Born out of 15 years of courses and lectures on continuum mechanics, nonlinear mechanics, continuum thermodynamics, viscoelasticity, plasticity, crystal plasticity, and thermodynamic plasticity, The Mechanical and Thermodynamical Theory of Plasticity represents one of the most extensive and in-depth treatises on the mechanical and thermodynamical aspects of plastic and visicoplastic flow. Suitable for student readers and experts alike, it offers a clear and comprehensive presentation of multi-dimensional continuum thermodynamics to both aid in initial understanding and introduce and explore advanced topics. Covering a wide range of foundational subjects and presenting unique insights into the unification of disparate theories and practices, this book offers an extensive number of problems, figures, and examples to help the reader grasp the subject from many levels. Starting from one-dimensional axial motion in bars, the book builds a clear understanding of mechanics and continuum thermodynamics during plastic flow. This approach makes it accessible and applicable for a varied audience, including students and experts from engineering mechanics, mechanical engineering, civil engineering, and materials science.

Research paper thumbnail of Preliminary results on an effort to characterize thermo-mechanical response of amorphous polymers in the glass-transition range

Research paper thumbnail of Current research in the thermo-mechanics of polymers in the rubbery-glassy range, 1995: presented at the 1995 Joint ASME Applied Mechanics and Materials Summer Meeting, Los Angeles, California, June 28-30, 1995

Research paper thumbnail of Results of implementing a computer-based mechanics readiness program in statics

Research paper thumbnail of Thermodynamic Modeling of Crystallization in Polyethylene for use in the Simulation of Rotational Molding

Research paper thumbnail of Shape Recovery in Glassy Polymers

Research paper thumbnail of A Thermodynamic Theory for Characterizing Thermo-Mechanical Response of Polymers During Crystallization

Research paper thumbnail of A study of statistical mechanics of long-chain molecules and its role in the determination of the characteristics of crystallizing polymers

Research paper thumbnail of Optimization of the distribution of properties: Using acrylate/epoxy mixtures in the extension of an FGM plate with a hole

We looked at optimization of property distribution in parts. As it will be shown, by changing the... more We looked at optimization of property distribution in parts. As it will be shown, by changing the distribution of material properties, one can make an inhomogeneous part that is better than the best uniform part. To demonstrate this, we looked at optimizing the distribution of properties in a plate with a hole that is under uniaxial extension. In this problem, for a uniform plate the hole creates a stress concentration that limits the maximum applied stress on the plate to one third the load carrying capacity of the material. We show that for real materials one can select material distributions that allows applied stresses close to the maximum capacity of the best material (i.e. 3 times the load carrying capacity of the best uniform plate with a hole). An acrylate/epoxy IPN plate with a hole was selected for the investigated. We modeled, as a function of each components concentration, the real characterized values of the Young’s modulus, Poisson’s ratio and fracture strength. A fini...

Research paper thumbnail of Modeling the thermomechanical effects of crystallization in natural rubber: I. The theoretical structure

International Journal of Solids and Structures, 2000

Research paper thumbnail of Single and multiple material constraints in thermoelasticity

Mathematics and Mechanics of Solids, 2006

Constraints on the possible forms of material response, such as incompressibility or inextensibil... more Constraints on the possible forms of material response, such as incompressibility or inextensibility, have long been used to simplify constitutive response models, and have resulted in substantial progress in fields such as fluid mechanics and the mechanics of composite materials. A method of imposing these constraints for thermoelastic materials is considered that follows steps that remove the need for assuming an additive term resulting from the constraint. In the process, three methods are considered for the separation of the constitutively prescribed part of the response from the part that is in reaction to the constraints. Both the case of single and multiple constraints are considered with extensive examples including special considerations for including effects associated with isotropic or anisotropic thermal expansion.

Research paper thumbnail of Theoretical Simulation of an Anomalous Response in a Torsional Oscillator

Journal of Applied Mechanics, 1994

In a torsional oscillator, constructed by stretching a hollow cylindrical natural rubber member a... more In a torsional oscillator, constructed by stretching a hollow cylindrical natural rubber member and connecting one end to a fly wheel and the other end to a fixed support, an anomalous behavior has been experimentally observed which is attributed to crystallization in the rubber. The anomalous behavior is observed when the rubber is stretched to more than 3.5 times its initial length and is characterized by a reduction in the period of the oscillator during stress relaxation. This indicates a gradual increase in the torsional rigidity of the rubber which can be explained by crystallization. Analyzing the response of the oscillator based on modeling the rubber as an incompressible isotropic elastic or viscoelastic material predicts a behavior opposite to that observed in the experiments. Using a model developed for characterizing mechanical response during crystallization in polymers, the anomalous behavior of the oscillator is reproduced.

Research paper thumbnail of A study of thermodynamic restrictions, constraint conditions, and material symmetry in fully strain-space theories of plasticity

International Journal of Plasticity, 1995

Research paper thumbnail of Thermodynamic modeling of the thermomechanical effects of polymer crystallization: A general theoretical structure

International Journal of Engineering Science, 1997

A general theoretical structure is developed based on continuum thermodynamics to model the therm... more A general theoretical structure is developed based on continuum thermodynamics to model the thermomechanical effects of polymer crystallization. This phase transition, seen in many polymers, involves the gradual transformation of the polymer's microstructure from an unorganized amorphous structure to that of a much more rigid semi-crystalline structure. This smooth transition is captured by a set of integral models which obtain the response by averaging the apparent response of the amorphous portion and a continuum of different crystals. A commonly used empirical relation between the extent of crystallization and volume change is imposed as a restriction on the material, and the implication of the entropy production inequality in the presence of this constraint is evaluated. General representations are provided.

Research paper thumbnail of Structural periodicity dependent scattering behavior in parity-time symmetric elastic metamaterials

Research paper thumbnail of Asymmetric viscoelastic metamaterials for broad bandgap design and unidirectional zero reflection

Mechanical Systems and Signal Processing

Research paper thumbnail of Extremely thin reflective metasurface for low-frequency underwater acoustic waves: Sharp focusing, self-bending, and carpet cloaking

Journal of Applied Physics, 2021